MeiraGTx

Multiple Poster Presentations Highlight Versatility and Novelty of MeiraGTxs Technology Platforms for Gene and Cell Therapy

LONDONandNEW YORK, Oct. 04, 2022 (GLOBE NEWSWIRE) -- MeiraGTx Holdings plc(Nasdaq: MGTX), a vertically integrated, clinical stage gene therapy company, today announced the Company will exhibit 15 poster presentations at the European Society of Gene and Cell Therapy (ESGCT) 2022 Annual Congress, which will be held from October 11-14, 2022, in Edinburgh, Scotland.

The posters will include data from MeiraGTxs novel gene regulation platform, including the first data demonstrating the potential to regulate CAR-T, as well as data from the Companys promoter platforms and several new, optimized pre-clinical programs addressing severe unmet needs for indications such as amyotrophic lateral sclerosis (ALS) and Wilsons disease. In addition, the Company will have presentations on its proprietary viral vector manufacturing technology and potency assay development.

Were pleased to present data illustrating the depth and versatility of MeiraGTxs scientific platforms, said Alexandria Forbes, Ph.D., president and chief executive officer of MeiraGTx. The 15 published abstracts at this years ESGCT Congress reflect the extraordinary productivity of our research efforts in developing new technologies and applying them to the design of optimized genetic medicines, as well as innovation in manufacturing and process development technology. I am particularly excited for us to present our riboswitch gene regulation technology applied to cell therapy for the first time, in this case the regulation of CAR-Ts, which is a huge area of scientific and clinical interest, continued Dr. Forbes. We look forward to presenting these data highlighting our innovative platform technologies and broad R&D capabilities.

Abstract Title (P101): AI-driven promoter optimization at MeiraGTxSession Title: Advances in viral and non-viral vector designDate: October 12, 2022

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Abstract Title (P124): Promoter Engineering Platform at MeiraGTxSession Title: Advances in viral and non-viral vector designDate: October 13, 2022

Abstract Title (P243): UPF1 delivered by novel expression-enhanced promoters protects cultured neurons in a genetic ALS modelSession Title: CNS and sensoryDate: October 12, 2022

Abstract Title (P254): Optimization and scale-up of AAV2-AQP1 production using a novel transient transfection agentSession Title: Developments in manufacturing and scale upDate: October 13, 2022

Abstract Title (P264): Designing and screening formulations to improve manufacturability and distribution of AAV gene therapiesSession Title: Developments in manufacturing and scale upDate: October 13, 2022

Abstract Title (P270): Use of anion exchange chromatography to provide high empty AAV capsid removal and product yieldsSession Title: Developments in manufacturing and scale upDate: October 13, 2022

Abstract Title (P320): Multivariate analysis for increased understanding of MeiraGTx upstream processSession Title: Developments in manufacturing and scale upDate: October 13, 2022

Abstract Title (P362): Development of AAV-UPF1 gene therapy to rescue ALS pathophysiology using microfluidic platformsSession Title: Disease models (iPS derived and organoids)Date: October 13, 2022

Abstract Title (P399): Titratable and reversible control of CAR-T cell receptor and activity by riboswitch via oral small moleculeSession Title: Engineered T and NK CARs and beyondDate: October 12, 2022

Abstract Title (P436): Novel riboswitches regulate AAV-delivered transgene expression in mammals via oral small molecule inducersSession Title: Gene and epigenetic editingDate: October 13, 2022

Abstract Title (P553): Development of optimized ATP7B gene therapy vectors for the treatment of Wilsons Disease with increased potencySession Title: Metabolic diseasesDate: October 12, 2022

Abstract Title (P554): A CNS-targeted gene therapy for the treatment of obesitySession Title: Metabolic diseasesDate: October 13, 2022

Abstract Title (561): Riboswitch-controlled delivery of therapeutic hormones for gene therapySession Title: Metabolic diseasesDate: October 12, 2022

Abstract Title (P622): Riboswitch-controlled delivery of therapeutic antibodies for gene therapySession Title: OtherDate: October 13, 2022

Abstract Title (P630): Improving AAV in vitro transducibility for cell-based potency assay developmentSession Title: OtherDate: October 13, 2022

About MeiraGTxMeiraGTx (Nasdaq: MGTX) is a vertically integrated, clinical stage gene therapy company with six programs in clinical development and a broad pipeline of preclinical and research programs. MeiraGTx has core capabilities in viral vector design and optimization and gene therapy manufacturing, and a transformative gene regulation platform technology which allows tight, dose responsive control of gene expression by oral small molecules with dynamic range that can exceed 5000-fold. Led by an experienced management team, MeiraGTx has taken a portfolio approach by licensing, acquiring, and developing technologies that give depth across both product candidates and indications. MeiraGTxs initial focus is on three distinct areas of unmet medical need: ocular, including inherited retinal diseases and large degenerative ocular diseases, neurodegenerative diseases, and severe forms of xerostomia. Though initially focusing on the eye, central nervous system, and salivary gland, MeiraGTx plans to expand its focus to develop additional gene therapy treatments for patients suffering from a range of serious diseases.

For more information, please visit http://www.meiragtx.com.

Forward Looking StatementThis press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including, without limitation, statements regarding our product candidate development and our pre-clinical data and reporting of such data and the timing of results of data, including in light of the COVID-19 pandemic, as well as statements that include the words expect, will, intend, plan, believe, project, forecast, estimate, may, could, should, would, continue, anticipate and similar statements of a future or forward-looking nature. These forward-looking statements are based on managements current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including, but not limited to, our incurrence of significant losses; any inability to achieve or maintain profitability, raise additional capital, repay our debt obligations, identify additional and develop existing product candidates, successfully execute strategic priorities, bring product candidates to market, expansion of our manufacturing facilities and processes, successfully enroll patients in and complete clinical trials, accurately predict growth assumptions, recognize benefits of any orphan drug designations, retain key personnel or attract qualified employees, or incur expected levels of operating expenses; the impact of the COVID-19 pandemic on the status, enrollment, timing and results of our clinical trials and on our business, results of operations and financial condition; failure of early data to predict eventual outcomes; failure to obtain FDA or other regulatory approval for product candidates within expected time frames or at all; the novel nature and impact of negative public opinion of gene therapy; failure to comply with ongoing regulatory obligations; contamination or shortage of raw materials or other manufacturing issues; changes in healthcare laws; risks associated with our international operations; significant competition in the pharmaceutical and biotechnology industries; dependence on third parties; risks related to intellectual property; changes in tax policy or treatment; our ability to utilize our loss and tax credit carryforwards; litigation risks; and the other important factors discussed under the caption Risk Factors in our Quarterly Report on Form 10-Q for the quarter ended June 30, 2022, as such factors may be updated from time to time in our other filings with the SEC, which are accessible on the SECs website at http://www.sec.gov. These and other important factors could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent managements estimates as of the date of this press release. While we may elect to update such forward-looking statements at some point in the future, unless required by law, we disclaim any obligation to do so, even if subsequent events cause our views to change. Thus, one should not assume that our silence over time means that actual events are bearing out as expressed or implied in such forward-looking statements. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release.

Contacts

Investors:MeiraGTxInvestors@meiragtx.com

Media:Jason Braco, Ph.D.LifeSci Communicationsjbraco@lifescicomms.com

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MeiraGTx Announces the Upcoming Presentation of 15 Abstracts at the European Society of Gene and Cell Therapy (ESGCT) 2022 Annual Congress - Yahoo...

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A wound is any injury that disrupts the structure of healthy skin tissue caused by chemical, mechanical, biological or thermal trauma. Wounds can be classified as acute or chronic, depending on their period of healing[1]. Acute wounds usually heal without complication within ten days; however, chronic wounds do not undergo normal healing processes, commonly have exaggerated inflammation, persistent infections or microbial biofilm formation and persist longer than six weeks[24]. The most frequent causes of chronic wounds are pressure, diabetes and vascular diseases[5].

Chronic wounds are a global problem, with annual cases rising dramatically owing to the ageing population and increased prevalence of diabetes and obesity[6]. It is estimated that up to 7% of the UK adult population has a chronic wound, costing the NHS 8.3bn each year in staff costs, wound dressings and medication[7]. Individual costs for wound management have been reported to vary, from 358 to 4,684 per patient for a wound that follows the normal healing trajectory, increasing to 831 to 7,886 per patient for a chronic, non-healing wound[7]. The majority of the costs account for GP and nursing time, with infected wounds costing an additional 1.39bn on antibiotics[7].

Results from one study, published in 2020, found that 59% of chronic wounds healed if there was no evidence of infection, compared with 45% if infection was present or suspected[7].Health conditions, such as diabetes mellitus and vascular disease, can predispose people to wounds that are difficult to heal, which can become chronic unless the underlying causes are addressed. For example, people with diabetes are prone to have a high incidence of wounds on their feet, which are slow to heal because of the impact of diabetes on the immune system, circulation and diabetic neuropathy. Complex chronic wounds, such as venous leg ulcers and diabetic ulcers, can significantly impact quality of life, morbidity and mortality[7].

Wound healing is a complex series of physiological reactions and interactions between numerous cell types and chemical mediators[8,9]. It comprises four coordinated and overlapping phases: haemostasis, inflammation, proliferation and remodelling[10].

The Figure below shows the phases of wound healing[11].

The first stage, haemostasis, is instantly activated after injury to stop bleeding at the site and prevent the entry of pathogens. In primary haemostasis, within seconds of an injury occurring, damaged blood vessels vasoconstrict to reduce blood flow through the wound area and diminish blood loss. Platelets adhere to the sub-endothelium of the impaired vessels, initiated by the presence of von Willebrand factor. This binds to glycoprotein Ib receptors on the surface of platelets, causing a conformational change on the platelet surface, activating platelets. These activated platelets release chemicals, such as adenosine diphosphate,serotonin andthromboxane A2, from their dense granules to stimulate platelet recruitment and adhesion to form a platelet plug[12,13]. Secondary haemostasis is a sequence of events, described as a coagulation cascade, that consequently converts soluble fibrinogen into insoluble fibrin. A fibrin mesh sticks to the platelet plug producing a haemostatic plug to seal the inside of wound[12,14].

At the beginning of the inflammatory phase, activated platelets also release pro-inflammatory cytokines and growth factors to stimulate the recruitment of immune cells to clean the wound area, initially involving infiltration of neutrophils and monocytes[15]. Monocytes undergo a phenotypic change to become macrophages. The previously constricted blood vessels also vasodilate because of increased prostaglandins, facilitating the chemotaxis of inflammatory cells[16,17]. The proliferation phase is charactered by re-epithelialization, capillary regeneration and the formation of granulation tissue(18). Fibroblasts and endothelial cells proliferate during this phase, stimulated by the numerous cytokines and growth factors released by the platelets and macrophages. This leads to the formation of new blood vessels in a process called angiogenesis[18].

After migration to the wound site, fibroblasts begin to proliferate and synthesize collagen and extracellular matrix components, such as proteoglycans, hyaluronic acid, glycosaminoglycans, and fibronectin, to form granulation tissue[1618]. The final stage is remodelling, which can last for several years. The formation of new capillaries slows, facilitating maturation of blood vessels in the wound. Type III collagen is replaced by type I collagen in the extracellular matrix to create a denser matrix with a higher tensile strength. The differentiation of fibroblasts into myofibroblasts causes the wound to physically contract. However, owing to differences in collagen type, new tissue after healing does not fully regain its original strength[1618].

Delayed wound healing can be caused by local and/or systemic factors. Local factors in the wound site include oxygen deficiency (causing chronic hypoxia), excessive exudate (causing maceration) or insufficient exudate (leading to desiccation), local infection, foreign bodies intensifying the inflammatory response, repetitive trauma, pressure/shear, and impaired vascular supply to the injury area[16,19].

Systemic factors that delay the healing process include the following[16,19]:

Oestrogen insufficiency, for instance in postmenopausal women, is known to impair all stages of wound repair process, especially inflammation and regranulation, with improved wound healing being a potential benefit of hormone replacement therapy. Androgens can repress cutaneous repair in both acute and chronic wounds, retarding the healing process and increasing inflammation[20].

The process can also be delayed in people with immunocompromised conditions, such as acquired immunodeficiency syndrome, cancer and malnutrition, with deficiencies in protein, carbohydrates, amino acids, vitamins A, C and E, zinc, iron, magnesium all having an effect[16,19,21]. Certain medicines can also delay the process, such as glucocorticoid steroids, chemotherapeutic drugs and non-steroidal anti-inflammatory drugs[19,21].

The most common causes of delayed chronic wound healing are infection and biofilm formation: biofilms are microscopically identifiable in up to 60% of chronic and recurrent wounds,leading to significant morbidity and mortality and an escalated healthcare cost[5,22,23].

A wound is considered infected when there are sufficiently large numbers of microbes presenting in wound environment or sufficient virulence to raise either a local or systemic immune response.

The wound-infection continuum has three stages: contamination, colonisation and infection. In the contamination phase, micro-organisms are unlikely to replicate because of an unfavourable environment. Colonisation happens when microbes successfully multiply, but not in sufficient levels to destroy host defences. However, the accelerated loads and persistence of microbes in wound environments may prolong the inflammatory phase and delay wound healing. When bacteria invade deeper into the wound bed and proliferate speedily, they can provoke an immune reaction and initiate local infection. As pathogens proliferate beyond the boundaries of the wound, infection may spread into deeper tissues, adjacent tissues, fascia, muscle or local organs. Eventually, systemic infection, such as sepsis, can occur when microbes invade into the body via vascular vessels or lymphatic systems, affecting the entirety of the body[24,25].

Biofilm is an extracellular polymeric substance produced by bacteria that acts as a physical barrier, enveloping bacteria and protecting them from host defences and antimicrobial agents. Several pathogens isolated from chronic wounds are typically capable of forming biofilms, such asStaphylococcus aureusandPseudomonas spp[5,23,24,26]. Biofilms persisting within chronic wounds can continuously stimulate host immunity, resulting in the prolonged release of nitric oxide, pro-inflammatory cytokines such as interleukin-1 and TNF-, and free radicals, and activation of immune complexes and complement, causing the healing process to fail and convert to a chronic state[23,27]. Sustained inflammatory reactions also trigger an escalated level of matrix metalloproteases, which can disrupt the extracellular matrix[16].

Most of the time, wound infection is diagnosed via visual inspection based on clinical signs and symptoms, including the classic signs of heat, pain, swelling, suppuration, erythema and fever. Typical characteristics of an acute infected wound are pain, erythema, swelling, purulent drainage, heat and malodour. In addition, a chronic wound may display signs of delayed healing, wound breakdown, friable granulation, epithelial bridging and pocketing in granulation tissue, increasing pain and serious odour.

Microbiological analysis of a specimen from wound cultures (using tissue biopsy or wound swab, pus collection or debrided viable tissue) is performed to identify causative microorganisms and guide the choice of antimicrobial therapy. Traditional diagnostics can be time consuming, and some organisms can be difficult to culture, so molecular techniques including DNA sequencing may help with characterising genetic markers[25]. Other laboratory markers, such as C-reactive protein, have also been used as markers and imaging techniques, such as CT scanning and autofluorescence imaging, may help with real-time diagnosis[25,28].

In clinical practice, the evaluation and identification of underlying conditions that affect wound healing are vital to optimising wound care. Accurate assessment of causes and comorbidities will inform the best course of treatment, such as compression therapy for venous leg ulcers or offloading (relief of pressure points) for people with diabetic foot ulcers[29]. The underlying pathologies of wounds are numerous and failure to address them can lead to a failure in healing[2,29].

Once any underlying conditions are identified, the wound bed should be prepared to optimise the chance of healing. A wound hygiene approach should be considered; its core principle is to remove or minimise unwanted materials, such as biofilm, devitalised tissue and foreign debris, from the wound bed to kickstart the healing process[30]. A holistic patient and wound assessment will ensure wound pathology and wound biofilm are managed simultaneously[30]. The TIME framework (tissue, infection/inflammation, moisture balance, edges) is a systematic approach to wound management[31]. Wound-bed preparation and the TIME approach should be used alongside a holistic assessment of other patient factors such as pain, nutrition and hydration[2].

Effective management of infection in chronic wounds involves the removal of necrotic tissue, debris and biofilms using debridement plus the appropriate use of antimicrobials (including topical antiseptics and systemic antibiotics)[1,32].

Antiseptics have a broad spectrum of bactericidal activity and are used externally for the purposes of eliminating bacterial colonisation, preventing infection, and potentially stimulating wound healing. They are less likely to cause antimicrobial resistance (AMR) than antibioticsand inhibit the development of microbes by disrupting cell walls and cytoplasmic membranes, denaturing proteins, and damaging bacterial DNA and RNA[5,23,33,34]. An ideal antiseptic agent should have broad-spectrum activity, a fast onset of action, long-lasting activity, be safe for healthy surrounding tissue, possess minimal allergenicity, be stable in blood and tissue protein, persistently remain within the wound bed, and potentially be active against biofilms[23,35]. Antiseptics, antimicrobial washes or surfactants can be used to clean the wound and peri-wound skin and prepare the wound bed for debridement[30].

A variety of antiseptic agents are used in clinical practice[23,34]:

Antiseptics can also be used as an adjunct to other therapies (e.g. negative pressure therapies) in treating complicated wound types(e.g.diabetic foot ulcers,venous leg ulcers and sternal wounds)[36].

All open wounds will be colonised with bacteria, but antibiotic therapy is only required for those that are clinically infected[37]. Systemic antibiotic therapy should only be considered for the treatment of cellulitis, osteomyelitis, sepsis, lymphangitis, abscess, and invasive tissue infection. Inappropriate use of systemic antibiotics may increase the risk of side effects and contributes to emergence of AMR[5]. The choice of initial therapy and the duration is frequently empirical and should take into account the type of wound, severity of infection, suspected pathogens and local AMR[38]. With severe infections, broad-spectrum antibiotics should be used against both gram-positive and gram-negative organisms, while a relatively narrow spectrum agent is enough for most mild and many moderate infections[5].

A systematic review assessed the clinical and cost-effective efficacy of systemic and topical antibiotic agents in the treatment of chronic skin wounds. The authors of the review suggested that there was insufficient evidence to support any routine use of systemic antibiotics in specific chronic wounds[39].

Appropriate and judicious use of antimicrobials must be considered when managing wounds. The use of topical antibiotics is not recommended for eliminating bacterial colonisation or wound infections because of their limited effectiveness, high risk of resistance and potential to cause contact allergy[5,35].

AMR occurs when microorganisms naturally evolve in ways that cause medicines used to treat infections to become ineffective, and these micro-organisms become resistant to most[40,41]. The misuse and overuse of antibiotics is a major cause of the emergence of AMR, via four main mechanisms[42]:

Moreover, the multicellular nature of biofilm matrix is likely to give extra protection to bacteria communities, makes them resistant to antibiotics. There are several proposed mechanisms for AMR related to biofilm: the alteration of chemical environment within biofilm, slow or inadequate diffusion of the antibiotics into the biofilm, and a differentiated biofilm subpopulation[43].

Topical antimicrobial use plays an important role when the wound is clinically infected or there is a suspected biofilm. The British Society for Antimicrobial Chemotherapy and European Wound Management Association position paper highlighted antimicrobial stewardship (AMS) a set of strategies to improve the appropriateness and minimise the adverse effects of antibiotic use as being central to wound care treatment to improving patient outcomes, reducing microbial resistance and decreasing the spread of infections caused by multidrug-resistant organisms[37]. Effective AMS avoids the use of antimicrobial therapy when not indicated while enabling the prescribing of appropriate antimicrobial interventions when they are indicated to treat infection.

The UK government has outlined a 20-year vision for reducing AMR, proposing a lower burden of infection through better treatment of resistant infections[44]. This includes the optimal use of antimicrobials and good stewardship across all sectors and appropriate use of new diagnostics, therapies, vaccines and interventions in use, combined with a full AMR research and development pipeline for antimicrobials, alternatives, diagnostics, vaccines and infection prevention across all sectors.

The use of alternatives to traditional antibiotic therapy is of huge interest for combating increasing AMR, including bacteriophage therapy, phage-encoded products, monoclonal antibodies and immunotherapy[45]. Among these, endolysins phage-encoded peptidoglycan hydrolases selectively targeting bacterial taxa have been identified as promising antimicrobial agents because of their ability to kill antimicrobial-resistant bacteria and lack of reported resistance However, challenges restrict the widespread use of endolysin therapy, such as limited drug-delivery methods, their specificity to particular bacteria types, and bioavailability via IV administration[46,47].

Debridement is the physical removal of biofilm, devitalisedtissue, debris and organic matter and is a crucial component of wound care. The presence of non-viable tissue in the wound bed prevents the formation of granulation tissue and delays the wound healing process. The removal of non-viable tissue encourages wound healing. The type of tissue found in the wound bed (e.g. whether necrotic or sloughy) will determine whether debridement is required. Factors such as bioburden, wound edges and the condition of peri-wound skin can also influence whether debridement is required[48]. A range of techniques can be used, dependent on the clinicians ability level: these include autolytic, larval, mechanical, sharp and surgical methods[49,50].

The concept of moist wound healing is not newand can lead to healing up to 23 times quicker than that of dry wound healing[51,52].Wound dressings such as cotton wool, gauze, plasters, bandages, tulle or lint should not be used, as they do not promote a moist wound healing environment, require excessive changes, and can cause skin damage and pain during dressing changes. They have therefore been replaced by newer types of wound dressingsthat can play a role in autolysis and debridement, maintain a relatively stable local temperature, keep the wound hydrated, promote wound repair and prevent bacterial infection[14,53,54].

Wound dressings should keep the wound free from infections, excessive slough, contaminants and poisons, keep the wound at the ideal temperature and optimum pH for healing, be permeable to water, but not microbes, come away from wound trauma during dressing changes, not be painful and be comfortable[55]. There are a variety of dressings available for managing chronic wounds, such as hydrogels, hydrocolloids, alginates, foams, and film dressings[56]. Dressings can also be used carriers for active agents including growth factors, antimicrobial agents, anti-inflammatory agents, monoterpenes, silver sulfadiazine or silver nanoparticles[57].

Potential factors that may influence dressing selection include:

Antimicrobial dressings impregnated with iodine, silver and honey are available[58]. They can be divided into two categories: those that release an antimicrobial into the wound and those that bind bacteria and remove them from the wound into the dressing. A more detailed overview can be found in a recent consensus document on wound care and dressing selection for pharmacists[57].

It is essential wound dressings do not inadvertently lead to moisture-associated skin damage an umbrella term encapsulating incontinence-associated dermatitis, intertriginous dermatitis (or intertrigo), peri-wound maceration and peristomal dermatitis. Practitioners should ensure the dressing can manage any exudate and protects the peri-wound area. Skin barriers can be used to protect the peri-wound area and prevent skin damage[59].

Widely used to aid the healing of acute, chronic and traumatic wounds, negative-pressure wound therapy (NPWT) removes interstitial fluid/oedema and excessive exudate, provides a moist environment, improves blood flow and tissue perfusion, and stimulates angiogenesis and granulation tissue formation[4,60]. Results from several studies have demonstrated the selective effect of NPWT in eliminating non-fermentative gram-negative bacilli in wounds[36]. Additionally, NPWT can be combined with additional topical antimicrobial solutions, reducing bacteria load, stimulating wound closure and decreasing wound size faster than conventional NPWT[36,61,62].

Hyperbaric oxygen therapy wasfirst proposed as an additional treatment for chronic wounds in the mid-1960s. Treatment involves the intermittent exposure of the body within a large chamber to 100% oxygen at a pressure between 2.0 and 2.5 atmosphere absolute, leading to an increase in oxygen levels within haemoglobin and elevating oxygen tissue tension at the wound site[63].A Cochrane reviewpublished in 2015 reported a significant improvement in the healing of diabetes ulcers in the short term when treated with hyperbaric oxygen therapy. However, further high-quality studies are needed before clinical benefits can be proven[64].

For chronic wound healing, electrical stimulation is the most frequently studied biophysical therapy[4]. It uses direct current, alternative current, and pulsed current. Electrical stimulation has been shown to benefit every stage of the wound-healing process, both at cellular and systemic levels. During the inflammation phase, electrical stimulation promotes vasodilation and increases the permeability of blood vessels, thereby facilitating cellular movement to the wound site and so promoting a shorter inflammatory response.

Studies have reported an inhibition in bacterial proliferation after electric stimulation. In the proliferation phase, electrical stimulation raises the migration, proliferation and differentiation of endothelial cells, keratinocytes, myofibroblasts and fibroblasts. At the systemic level, it promotes revascularisation, angiogenesis, collagen matrix organisation, wound contraction, and re-epithelialisation. Ultimately,electrical stimulation promotes the contractility of myofibroblast and converts type III collagen into type I, along with rearranging collagen fibres to optimise the scars tensile strength[8,65,66].

A prospective clinical study conducted across the UK suggested that using an externally applied electroceutical device, combined with compression bandaging and dressings, was a cost-effective treatment for venous leg ulcers, compared with conventional treatments[67].

Low-frequency ultrasound has been used as an adjunct treatment for chronic wounds. It has a debriding effect, removing debris and necrotic tissue (primarily via cavitational and acoustic streaming phenomena). Ultrasound is also reported to disrupt biofilmin vitro, thus increasing the sensitivity of bacteria to antimicrobials[68]. It is proposed to be effective instimulating collagen synthesis, increasing angiogenesis,diminishing the inflammatory phase as well as promoting cellular proliferation[69].Several clinical studies have shown a reduction in wound size when wounds are treated with low-frequency ultrasound therapy[7072].

Extracorporeal shock wave therapy (ESWT) has been proposed to aid wound healing by transmitting acoustic pulsed energy to tissues. ESWT seems to promote angiogenesis, stimulate circulation, reduce anti-inflammatory response, and upregulate cytokine and growth-factor reactions[4]. A clinical trial demonstrated the feasibility and tolerability of ESWT in wounds with different aetiologies[73]. Furthermore, a review concluded that ESWT brings more benefits for patients with diabetic foot ulcers than hyperbaric oxygen therapy, based on increased angiogenesis, tissue perfusion and cellular reactions with reduced cell apoptosis, as well as a higher ulcer healing rate[74].

More recent developments include introducing nanomedicine to wound-healing approaches. It has been used to achieve controlled delivery, stimulate chronic wound healing and control microbial infections[14,75]. Nanotechnology-based wound dressings like nanogels and nanofibers offer a larger surface area and greater porosity, potentially enhancing absorption of wound exudate. They can also facilitate collagen synthesis and ultimately re-epithelisation through supporting the migration and proliferation of fibroblasts and keratinocytes.

Nanomedicines also seem to aid healing through molecular and cellular pathways[75]. For example, a methacrylated gelatin (MeGel)/poly(L-lactic acid) hybrid nanofiber synthesised has been reported to stimulate the recruitment and proliferation of human dermal fibroblasts, thereby promoting wound healing[76]. Nanoparticles can not only act as carriers of antimicrobial agents, they can also have an intrinsic antimicrobial effect[75,77,78]. In 2021, Qiu et al. successfully developed an antibacterial photodynamic gold nanoparticle (AP-AuNPs) that demonstrated antibacterial effects on both Gram-negativeEscherichia coliand Gram-positiveStaphylococcus aureus,as well as potentially inhibiting biofilm formationin vitro[79].

Growth factors such as vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), and fibroblast growth factor (FGF) are down-regulated in chronic wounds, suggesting that topical administration of growth factors and cytokines could improve wound healing[80].

Growth factors can improve wound repair through several mechanisms[81]:

Growth factors that have been studied in wound healing are EGF, VEGF, FGF, PDGF, transforming growth factor-beta 1 (TGF-1) and granulocyte-macrophage colony stimulating factor[82]. Becaplermin (rhPDGF-BB) was the first growth-factor therapy approved by the US Food and Drug Administration, after it demonstrated effectiveness in treating complex wounds when combined with standard wound care[80]. A systematic review and meta-analysis indicated that growth factors were effective in healing venous stasis ulcers, increasing wound healing by 48.8% compared with placebo and showing no difference in adverse effects compared with controls[83].

Stem cells may have certain advantages in wound healing because of their ability to differentiate into specialised cells and secrete numerous mediators including cytokines, chemokines, and growth factors[84,85]. This makes them a promising approach for treating chronic wounds.

Mesenchymal stem cells can be extracted from bone marrow, adipose tissue, umbilical cord blood, nerve tissue, or dermis and used both systemically and locally[86]. They release growth factors that stimulate blood-vessel and granulation tissue formation, fibroblast and keratinocyte migration, collagen synthesis, and fibroblast activation, increase re-epithelialisation, exert immunomodulatory properties, regulate inflammatory responses, and display antibacterial activities[85,8789].

Many studies have investigated the efficacy of stem-cell therapies for a variety of wounds, including burns, non-healing ulcers, and critical limb ischemia[9096]. A systematic review published in 2020 that investigated the clinical application of stem-cell therapy for the treatment of chronic wounds showed the potential of a variety of stem cells in the restoration of impaired wound healing, bothin vitroandin vivo, despite the clinical evidence being very limited. As the recorded studies were on case-by-case basis, there is a lack of comprehensive guidelines for the use of stem cells in different wounds[97].

Auto-transplantationof adipose tissue-derived mesenchymal stromal cells has been proposed as a safe, alternative method to treat chronic venous ulcers[96]. Bioscaffold matrices comprising hyaluronic acid, collagen or other bio-polymeric materials have increasingly been applied for stem-cell transplantation. These matrices not only provide wound coverage, but also offer protection for stem cells and controlled delivery[86].

Skin equivalents are polymeric biomaterials increasingly adopted for both acute and non-healing ulcers, such as venous ulcers, diabetic foot ulcers or pressure ulcers, to temporarily or permanently substitute the structure and function of human skin. Skin substitutes are designed to increase wound healing, provide a physical barrier that protects the wound from trauma or bacteria, provide a moist environment for the repair process, replace impaired skin components and decrease morbidity from more invasive treatments like skin grafting[98,99].

They can usually be classified as one of three major types: dermal replacement, epidermal replacement, and dermal/epidermal replacement[98]. Epidermal replacements (substitutes) comprising isolated autogeneous keratinocytes cultured on top of fibroblasts include Myskin (Regenerys), Laserskin(Fidia Advanced Biopolymers) and Epicel(Genzyme Tissue Repair Corporation). Dermal replacements include Dermagraft (Smith and Nephew) and Transcyte(Shire Regenerative Medicine)[98].

Epidermal/dermal skin replacements (also called composite skin substitutes) contain both epidermal and dermal layers that mimic the histological structure of original skin. The bi-layered bioengineering skin Apligraf (Organogenesis) was the first living skin equivalent for the management of complex chronic wounds like diabetic foot ulcers and venous leg ulcers. It is made up of a dermal layer of human fibroblasts embedded in a bovine type I collagen matrix and an epidermal layer generated by human keratinocytes[100]. Some other commercial products of composite substitutes are OrCel(Forticell Bioscience) andPermaDerm(Regenicin)[98]. In general, the current high cost of such dressings and limited evidence on effectiveness restricts them from being widely adopted[101]. Recently, technologies such as electrospinning or 3D-printing have been used to fabricate skin substitutes. Electrospinning can create nanofibers with high oxygen permeability, variable porosity, a large, exposed surface area and a morphology similar to the extracellular matrix, making them interesting candidates for skin substitutes[102,103].

TheNational Wound Care Strategy Programme, which was implemented by NHS England in 2018, has made progress in reducing unwanted variation in care and addressing suboptimal wound care.

Through its workstreams, the involvement of stakeholders, patients and carers, and the publication of the core capabilities for educating a multi-professional workforce, wound care has become a national priority. There are still many challenges in the management of chronic wounds the complexity of wound environment, limited knowledge of the biological, biochemical, and immunological healing processes, and the increasing complexity of disease pathophysiology that comes with ageing populations.

The development of standardised and clinically relevant testing for wound dressings, along with high-quality clinical trials, would enable useful comparisons of treatments. The whole episode of care should be considered in assessments of the cost-effectiveness of different dressings and devices, rather the simple cost of the individual entity. All these complex concerns restrict success in wound management, which in turn negatively impacts the quality of life of the patients and places a burden on global healthcare systems[75,104]. Organisations and healthcare providers should share best practice and education of healthcare professionals is needed to get the best outcomes for patients with preventable chronic wounds.

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Current and advanced therapies for chronic wound infection - The Pharmaceutical Journal

Introduction

Stem cells are highly specialized cell types with an impressive ability to self-renew, able to transform into one or even more specific cell types that play a significant role in the regulation and tissue healing process.17 To self-renew, a stem divides into two identical daughter stem cells and a progenitor cell and the embryonic and adult cells contain stem cells.1,2,8

Curing patients with serious medical conditions has been the focus of all disciplines of medical research for many years. Stem cell treatment has evolved into a highly exciting and progressed field of scientific research. Major advances have recently been introduced in fundamental and translational stem-cell-based treatment studies. As stem cell research progressed, many therapeutic options were investigated. The development of therapeutic procedures has sparked a great deal of interest.1,9 Humanity has known for many years that it is possible to regenerate lost tissue. Recently, the regenerative medicine research has taken hold, defying the tremendous scientific advances in the molecular biology sciences only. Technological advances provide limitless opportunities for transformational and potentially restorative therapies for many of humanitys most illnesses. A variety of human organs have successfully yielded stem cells. Besides this, the cell therapy is rapidly bringing good advancements in the healthcare system, intending to restore and possibly replace injured tissue, as well as organs, and ultimately restore the functional capacity of the body.2,10,11

The stem cells can be obtained from various sources of Adult (Adult body tissues), Embryonic (Embryos), Mesenchyma (Connective tissue or stroma), and Induced pluripotent stem [ips] cells (Skin cells or tissue-specific cells).3,68,1215

Due to various stem cells cellular characteristics, the therapeutic clinical possibilities of stem-cell-based treatment are considered promising. These cells can regrow and restore various types of body tissues, for this reason, they are recognized as precursor cells to all kinds of cells.15 The following are the distinguishing features: 1. Self-renewal- Divide without distinction to generate an infinite supply, 2. Multi-potency- One mature cell may distinguish more than one, 3. Pluripotency- Create all sorts of cells except for embryonic membrane cells, 4. Toti- potency- Produce various sorts of cells, including embryonic stem cells.1,2,6,7,16

Stem cells are essential human cells that really can self-renew and make a distinction into particular mature cell types.3,6 The different types of stem cells are embryonic, induced pluripotent, and adult kind of cell types. They all share the important feature of self-renewal, and the ability to discern themselves. It should be mentioned that, the stem cells are not homogeneous, but instead appear in a progressive order. Totipotent stem cells are the most basic and immature stem cells. The above cells can form a complete embryo and also extra-embryonic tissue. This one-of-a-kind efficiency is only present for a short period, starting with ovum development and completing whenever the embryo achieves the 4 to 8 cell phases. Having followed that, cells that divide until they approach the blastocyst, about which point they end up losing their totipotency and acquire a pluripotent character trait, at which cells can only distinguish through each embryonic germ stack. After a few divisions, the pluripotency character trait starts to fade and the distinguishing ability has become more lineage constrained, where its cells are becoming multipotent, indicating they could only transform into the cells connected to a cell or tissue of origin.10 Many researchers believe that adult stem cells should be used in stem cell therapies.6,17

The stem cells can be transformed into a wide range of specialized functional cell types.3,18 In response to injury or maturation, those same stem cells can propagate in massive quantities.19 Adult, embryonic, and induced pluripotent stem cells are examples of stem cell-based therapies.14,15,1921 The stem cells, due to their capability to distinguish the specific cell types requisite for a diseased tissue regeneration, can provide an effective solution, while tissue and organ transplantation are considered necessary.10 The sophistication of stem cell-based treatment interventions, on the other hand, probably leads researchers to seek stable, credible, and readily available stem cell sources capable of converting into numerous lineages. As an outcome, it is critical to exercise caution when selecting the type of stem cells to be used in therapeutic trials.12,14,22

Only with the explosive growth of basic stem cell research in recent years, the comparatively recent study sector of Translational Research had also grown exponentially, starting to build on major research knowledge and insight to advance new therapies. Once the necessary regulatory clearances have been obtained, the clinical translation process can start. Translational research is important because it acts as a filtration system, ensuring that only safe and effective therapeutic approaches start making it to the clinic.23 Recent research illustrating, the successful application of stem cell transplantation to patient populations suggests that, such restorative approaches have been used to address a wide variety of complicated ailments of future concerns.19,24

Currently, clinical trials are available for a variety of stem cell-based treatments based on adult stem cells. To date, the WHO International Clinical Experiments Registration process has recorded more than 3000 experiments involved based on adult stem cells. Furthermore, preliminary trials involving novel and intriguing pluripotent stem cell therapies have been registered. These studies findings will assist the ability to comprehend and the timeframes required to obtain effective treatments and it will contribute to a better knowledge of the different disorders or abnormalities.10

The role of stem cells in modern medicine is vital, both for their widespread application in basic research and for the opportunities they provide for developing new therapeutic strategies in clinical practice.6,16 In recent times, the number of studies involving stem cells has expanded tremendously. Globally, thousands of studies claiming to use stem cells in experimental therapies have now been in the investigation field. This may give the impression that such treatments have already been shown to be extremely effective in the context of healthcare. Despite some promising results, the vast majority of stem cell-based therapeutic applications are still in the experimental stage itself.6,25

The stem cells are a valuable resource for understanding organogenesis as well as the bodys continual regenerative capacity. These cells have brought up enormous anticipations among doctors, investigators, patients, and the public at large because of their ability to distinguish into a variety of cell types.25 These cells are necessary for living beings for a variety of reasons and can play a distinguishable role. Several stem cells can play all cell types roles, and when stimulated effectively, they can also repair damaged tissue. This capability has the potential to save lives as well as treat human injuries and tissue destruction. Moreover, different kinds of stem cells could be used for several purposes, including tissue formation, cell deficiency therapeutic interventions, and stem cell donation or retrieval.3,6,26

New research demonstrating that the successful application of stem cell treatments to patients has expressed hope that such regenerative strategies might very well one day is being used to address a wide variety of problematic ailments. Furthermore, clinical trials incorporating stem cell-based therapeutics have advanced at an alarming rate in recent years. Some of these studies had a significant impact on a wide range of medical conditions.10 As a regenerative medicine strategy, cell-based treatment is widely regarded as the most fascinating field of study in advanced science and medicine. Such technological innovation paves the way for an infinite number of transformational and potentially curable solutions to some of humanitys most pressing survival issues. Moreover, it is gradually becoming the next major concern in medical services.11

Modern data, which shows that the successful stem cell transplantation in beneficiaries has raised hopes on the certain rejuvenating approaches, will one day be used to treat many different types of challenging chronic conditions.24 Preliminary data from highly innovative investigations have documented that the prospective advancement of stem cells provides a wide range of life-threatening ailments that have so far eluded current medical therapy.2,10,11 Furthermore, clinical trials involving stem cell-based therapies have advanced at an unprecedented rate. Many of these studies had a significant impact on various disorders.19 Despite the increasing significance of articles concerning viable stem cell-based treatments, the vast majority of clinical experiments have still yet to receive full authorization for stem cell treatments confirmation.11,12,27

Even though the first case of AIDS were noted nearly 27 years ago, and the etiologic agent was noticed 25 years ago, still for the effective control of the AIDS pandemic continues to remain elusive.28 The HIV epidemic started in 1981 when a new virus syndrome defined by a weakened immune system was revealed in human populations across the globe. AIDS showed up to have a substantial reduction in CD4+ cell counts and also elevated B-cell multiplication.15,2831

The agent that causes AIDS, later named HIV, is a retroviral disease with a genomic structural system made up of 2 identical single-stranded RNA particles.3234 According to the Centres for Disease Control and Prevention, with over 1.1 million Americans are presently infected with the virus.31 Compromised immune processes in HIV and AIDS, as well as partial immune restoration, barriers are confirmed for HIV disease eradication. Innovative developmental strategies are essential to maximizing virus protection and enabling the host immune response to eliminate the virus.35

The progression of HIV infection in humans is divided into the following stages of acute infection, chronic infection, and AIDS.15,36 During the acute infection phase, the circulation has a high viral replication, is extremely infectious, that may or may not demonstrate flu-like clinical signs. In the chronic stage, the viral load is lesser than in the acute stage, and individuals are still infectious but may be symptomless. The patient has come to the end stage of AIDS whenever the CD4+ cell count begins to fall below 200 cells/mm or even when opportunistic infections are advanced.15,36

There are currently two types of HIV isolated HIV-1 and HIV-2.15,37,38 However, HIV-1 is the most common cause of AIDS throughout the world, while HIV-2 is only found in a few areas of an African country. Although both virions can cause AIDS, HIV-2 infection is much more likely to occur in central nervous system disorder.15 Besides this, HIV-2 seems to be less infectious than HIV-1, and HIV-2 infection induces AIDS to develop more slowly. Even though both HIV-1 and HIV-2 have a comparable genetic structure comprised of group-specific antigen, polymerase, and envelope genes, their genome organizational structures are differed.15,3739

HIV infiltrates immune cell types, CD4+ T cell types, and monocytes, resulting in a drop in T-cell counts below a critical level and the failure of cell-mediated immune function.15,40 The glycoprotein (gp120) observed in the virion envelope comes into contact with the CD4 particle with high affinity, allowing HIV to infect T cells. By interacting with their co-receptors, CXCR4 and CCR5, the virus infiltrates T cells and monocytes. The retrovirus uses reverse transcriptase to convert its RNA into DNA after attaching it to and entering the host cell. These newly replicated DNA copies then exit the host cell and infect other cells.15,40,41

HIV-1 is a retrovirus and belongs to a subset of retroviruses known as lentiviruses.38,42 Infection is the most common global health concern around the world.15 It has destroyed the millions of peoples health and continues to wreak havoc on the individual health of millions more. The pandemic of HIV-1 is the most devastating plague in the history of humans, as well as a significant challenge in the areas of medicine, public health, and biological science of research activities.34,43 Antiretroviral therapy is the only treatment that is commonly used. This is not a curative treatment; it must be used for the rest of ones life.15 Although antiretroviral therapy has reduced significantly HIV intensity and transmission, the virus has not been eradicated, and its continued presence can lead to additional health issues.44

Infection with the human immunodeficiency virus necessitates entry into target cells, such as through adhesion of the viral envelope to CD4 receptor sites.43 Cellular antiviral responses fail to eliminate the virus, resulting in a gradual depletion of CD4+ T cells and, finally, a severely compromised immune functioning system. Unfortunately, there is no cure for the virus that destroys immunity.4447 In advanced HIV infection, memory T-cell depletion primarily affects cellular and adaptive immune responses, with a minor impact on innate immune responses.48 Globally, 37.7 million people were living with HIV in 2020, and with 1.5 million individuals are infected with the virus.49 The advancement of stem cell therapy and the conduct of implemented clinical trials have revealed that stem cell treatment has high hopes for a range of medical conditions and implementations.15

Stem cell treatment has shown impressive outcomes in HIV management and has the potential to have significant implications for HIV treatment and prevention in the future. In HIV patients, stem cell therapy helps to suppress the viral load even while enabling antiretroviral regimens to be tapered. Interestingly, this practice led to a significant improvement in procedure outcomes soon after starting antiretroviral treatment.15 Stem cell transplantation can alleviate a wide variety of diseases that are currently incurable. They could also be used to create a novel anti-infection therapy strategic plan and to enhance the treatment of immunologic conditions such as HIV infection. HIV wreaks havoc on immune system cells.30,50

The virus infects and replicates within T-helper cells (T-cells), which are white immune system cells. T-cells are also referred to as CD4 cells. HIV weakens a persons immune system over time by pulverizing more CD4 cells and multiplying itself. More pertinently, if the individual has been unable to obtain anti-retroviral medicine, he will progressively fail to control the infectious disease and illnesses.3,15,42

Despite 36 years of scientific research, investigators are still trying to cure human HIV and its potential problem, AIDS.3,5153 HIV continues to face unconquerable dangers to human survival. This virus has developed the potential to avoid anti-retroviral therapy and tends to result in victim death.52 Investigators are still looking for effective and all-encompassing treatment for HIV and its complexity, AIDS.54 This massive amount of data revealed potential AIDS treatment targets.55 Thousands of research projects have yielded a great deal of information on the elusive AIDS life cycle to date.5456 These massive amounts of data supplied possible targets for AIDS treatment.33,55,56 In HIV-infected patients, using stem cell therapy can augment the process of keeping the viral load stagnant by permitting antiretroviral regimens to be tapered.15

Overall, stem cell-based strategies for HIV and AIDS treatment have recently emerged and have become a key area of research. Ideally, effective stem cell-based therapeutic approaches might have several benefits.30 Clinical studies encompassing stem cell therapy have shown substantial therapeutic effects in the treatment of various autoimmune, degenerative, and genetic problems.15,25 Substantial progress has been developed in the treatment of HIV infection using stem cell-based techniques.30

Successfully treated, clinical studies have shown that total tissue recovery is feasible.15,57 In the early 1980s, the first stem cell transplants were accomplished on HIV-positive patients who were unsure of their viral disease. Following the above preliminary aspects, many HIV-positive patients with concurrent malignant tumours or other hematologic disorders underwent allogeneic stem cell transplantation around the world.42 After ART became a common treatment option for patients,58,59 the procedures prognosis improved dramatically. In addition, a retrospective study of 111 HIV+ transplant patients demonstrated a mildly lower overall survivorship performance in comparison to an HIV-uninfected comparison group.60

Earlier, the primary problem for people living with HIV and AIDS was immunodeficiency caused by a loss of productive T-cells. Some clinicians intended to replenish lost lymphocytes through adoptive cell transplants in the initial days before efficacious antiretroviral therapy options were available. Immunologically, it is relatively simple in an isogeneic condition, as illustrated on HIV-positive individuals with just a correlating identical twin who received T-lymphocytes and stem cell transfusions to rebuild the weak immune status of the patient.60 Cell therapy transfusion may be used to remove resting virion genomes from CD4+ immune cells and macrophages mostly through genome-editing or cytotoxic anti-viral cells.15,60 Cell technology and stem cell biological reprogramming developments have made a significant contribution to novel strategies that may give confidence to HIV healing process.3 However, human embryonic stem cells can be distinguished into significant HIV target cells, according to several research findings.30,61,62

Initially, stem cell transplantation was believed to influence the clinical significance of HIV infection, but viral regulation was not accomplished in the discipline. Moreover, improvements in stem cell transplants utilizing synthetic or natural resistant cell resources, in combination with novel genetic manipulative tactics or the advancement of cytotoxic anti-HIV effector cells, have significantly accelerated this sector of HIV cell management.60 Multiple techniques are being introduced to overcome HIV, either through protecting cells from infectious disease or by continuing to increase immune responses to the viral infection.30 The various methods are as follows: Bone marrow stem cells Therapies, Autologous stem cell transplantations, Hematopoietic stem cell transplantation, Genetical modifications of Hematopoietic stem cells (HSCT), HSCT and HAART therapeutic approach, Human umbilical cord mesenchymal stem cell transplantation, Mesenchymal stem/stromal cells (MSCs) applications, CCR5 Delta32/Delta32 Stem-Cell Transplantation, CRISPR and stem cell applications, Induced Pluripotent Stem Cells applications.

According to the findings, circulating replicative HIV remains the most significant threat to effective AIDS therapy. As a result, a method for conferring resistance to circulating HIV particles is required. The effective viral burden in the human body would be significantly reduced if it were possible to defeat reproducing HIV particles.43,44 For the treatment of AIDS, a restorative approach that relies on bone marrow stem cells has been suggested.52 The proposed treatment method captures and eventually destroys circulating HIVs using receptor-integrated red blood cells. Red blood cell membranes can be equipped with the CD4 receptor and the C-C chemokine receptor type 5 and C-X-C chemokine receptor type 4 co-receptors, which will selectively bind circulating HIV particles.15,30,32,33,43,44,46,6365

The term autologous pertains to blood-forming stem cells obtained from the patient for use as a source of fresh blood cells followed by high-dose chemotherapeutic agents.66 Lymphoma is still the biggest cause of mortality in HIV patients. Autologous stem cell recovery or transplantation with high-dose treatments has long been supported as a treatment for certain types of cancer in HIV-negative patients, including leukaemia and lymphoma. Individuals over the age of 65, as well as those with health problems such as HIV, were excluded from initial transfusion experiments. Moreover, the treatment regimen mortality of transplantation has also been reduced significantly due to its use of peripheral blood stem cells rather than bone marrow and the use of newer marginal conditioning therapeutic strategies. HIV-infected clients may be able to utilize enough stem cells for an autologous transplant advancement in HIV management. High-dose Autologous stem cell transplant (ASCT) treatments are better than conventional treatment in people with relapsed non-Hodgkin lymphoma, according to randomized trial evidence. Similarly, studies on HIV-negative people with Hodgkin Lymphoma have shown that ASCT would provide patients with repetitive illness with long-term progression-free survival.66,67 Even so, the clinical trial on Allogeneic Hematopoietic Cell Transplant for HIV Patients with Hematologic Malignancies report was explained as, the cell-associated HIV DNA and inducible infectious virus were not detectable in the blood of patients who attained complete chimerism.68

The study on long-term multilineage engraftment of autologous genome-edited hematopoietic stem cells in nonhuman primates report findings was Genome editing in hematopoietic stem and progenitor cells (HSPCs) is a potential innovative approach for the treatment of numerous human disorders. This report shows that genome-edited HSPCs engraft and contribute to multilineage repopulation following autologous transplantation in a clinically relevant large animal model, which is an important step toward developing stem cell-based genome-editing therapeutics for HIV and possibly other illnesses.69

Research on comprehensive virologic and immune interpretation in an HIV-infected participant again just after allogeneic transfusion and analytical interruption of antiretroviral treatment findings are the instance of HIV-1 cure having followed allogeneic stem cell transplantation (allo-SCT), resulting allo-SCTs in HIV-1 positive participants have failed to cure the disease. It describes adjustments in the HIV reservoir in a single chronically HIV-infected client who had undergone allo-SCT for acute lymphoblastic leukaemia treatment and was obtaining suppressive antiretroviral treatment.

To estimate the size of the HIV-1 reservoir and describe viral phylogenetic and phenotypic modifications in immune cells, the investigators just used leukapheresis to obtain peripheral blood mononuclear cells (PBMCs) from a 55-year-old man with chronic HIV infection prior and after allo-SCT. Once HIV-1 was found to be unrecognizable by numerous tests, including the PCR measurement techniques both of overall and fully integrated HIV-1 DNA, recompilation virus precise measurement by significant cell input quantifiable viral outgrowth assay, and in situ hybridization of intestine tissue, the client accepted to an analytic treatment interruption (ATI) with recurrent clinical observing on day 784 post-transplantation. He continued to remain aviremic off ART until ATI day 288, once a reduced virus rebound of 60 HIV-1 copies/mL resulted, which expanded to 1640 HIV-1 copies/mL five days later, urging ART reinitiation. Rebounding serum HIV-1 action sequences were phylogenetically distinguishable from pro-viral HIV-1 DNA discovered in circulating PBMCs before transplantation. It was indicated that allo-SCT tends to result in significant reductions in the magnitude of the HIV-1 reservoir and a >9-month ART-free cessation from HIV-1 multiplication.34

The Impact of HIV Infection on Transplant Outcomes after Autologous Peripheral Blood Stem Cell Transplantation: A Retrospective Study of Japanese Registry Data reported as ASCT is a successful treatment option for HIV-positive patients with non-Hodgkin lymphoma and multiple myeloma (MM). HIV infection was associated with an increased risk of overall mortality and relapse after ASCT for NHL in a study population.70

The procedure of delivering hematopoietic stem cells mostly through intravenous infusion to restore normal haematopoiesis or treat cancer is known as hematopoietic stem cell transplantation.71 There has recently been a rise in the desire to develop strategies for treating HIV/AIDS diseases employing human hematopoietic stem cells,30 along with this Hutter and Zaia were evaluated the background of Haematopoietic stem cell transplantation (HSCT) in HIV-infected individuals.42

Attempts to use HSCT as a technique for immunologic restoration in AIDS patients or as a therapeutic intervention for malignant tumours were initially insufficient. Regretfully, in the absence of sufficient ART, HSCT seemed to have no impact on the evolution of HIV infection, and the majority of the patients ended up dead of rapidly deteriorating immunosuppression or reoccurring lymphoma or leukaemia. A specific instance report described how an un-associated, matched donor supplied allogeneic HSCT to a patient with refractory lymphoma. The virus was unrecognizable by isolating or PCR of peripheral blood mononuclear cells commencing on day 32 after transplantation. Although HIV-1 was unrecognizable by cultural environment or PCR of several tissues examined at mortem, the patient died of recurring lymphoma on day 47. Another client who obtained both allogeneic HSCT and zidovudine had similar results, with HIV-1 becoming unnoticeable in the blood by PCR analysis. In some other particular instances, a 25-year-old woman with AIDS who obtained an allogeneic HSCT from a corresponding, unfamiliar donor after controlling with busulfan and cyclophosphamide and ART with zidovudine and IFN-2 regimen continued to live for 10 months before falling victim to adult respiratory distress. However, PCR testing of autopsy tissues revealed that they were HIV-1 negative.72

Recent research discovered significant progress towards the clinical application of stem cell-based HIV therapeutic interventions, principally illustrating the opportunity to effectively undertake a large-scale phase two HSC-based gene therapy experiment. In this investigation, the research team used autologous adult HSCs that had been transduced to a retroviral vector that usually contains a tat-vpr-specific anti-HIV ribozyme to develop cells that were less vulnerable to productive infection,73 whereas vector-containing cells have been discovered for extended periods (more than 100 weeks in most people) and CD4+ T cell gets counted were significantly high within anti-HIV ribozyme treating people group compared with the placebo group, the impacts on viral loads were minimal. The studys success, even so, is based on the realization that a stem cell-based strategy like this is being used as a more conventional and efficacious therapeutic approach.30 Some other latest clinical studies used a multi-pronged RNA-based strategic plan which included a CCR5-targeted ribozyme, an shRNA targeting tat/rev transcripts, and a TAR segment decoy.74

These crucial research findings are explained on lentiviral-based gene therapy vectors that can genetically manipulate both dividing and non-dividing HSCs and are less likely to cause cellular changes than murine retro-viral-based vectors. Long-term engraftment and multipotential haematopoiesis have been demonstrated in vector-containing and expressing cells, according to the researchers. Whereas the antiviral effectiveness was not reviewed, the results demonstrate the strategys protection, which helps to expand well for the possibility of a lentiviral-based approach in the upcoming years.30

A further approach, with a different emphasis, has been started up in the hopes of trying to direct immune function to target specific HIV to overcome barriers to attempting to clear the virus from the patient's body. These strategies use gene treatment innovations on peripheral blood cells to biologically modify cells so that they assert a receptor or chimeric particle that enables them to especially target a specific viral antigen,75 deception of HIV-infected peoples peripheral blood T cells raises issues to be addressed, such as the effects of ongoing HIV infection and ex vivo modification on the capabilities and lifetime of peripheral blood cells. Further to that, the above genetically manipulated cells would demonstrate their endogenous T cell receptors, and the representation of the newly introduced receptor could outcome in cross-receptor pairing, resulting in self-reactive T cells. Most of these deficiencies could be countered by enabling specific developmental strategies to take place that can start generating huge numbers of HIV-specific cells in a renewable, consistent way that can restore defective natural immune activity against HIV.30

One strategy being recognized is the application of B cells obtained from HSCs to demonstrate anti-HIV neutralizing specific antibodies. While animal studies have shown that neutralizing antibodies could protect against infection, and extensively neutralizing antibodies have been noticed in some HIV-infected persons, safety from a single engineered antibody might be exceptional.76,77 Realizing antibody binding and virus neutralization may assist in the development of chimeric receptors or single-chain therapeutic antibodies with recognition domains for other techniques that identify cellular immunity against HIV-infected cells.78,79 Thereby, genetically modifying HSCs to generate B cells that produce neutralizing anti-HIV specific antibodies, or engineering HSCs to enable multipotential haematopoiesis of cells that express a chimeric cellular receptor usually contains an antibody recognition domain, indicate one arm of an HSC-based engineered immunity process.30

A further technique of using HSCs that were genetically altered with molecularly cloned T-cell receptors or chimeric molecules particular to HIV to yield antigen-specific T cells. The basic difference in this strategy is that the cells produced from HSCs after standard advancement in the bone marrow and thymus are made subject to normal central tolerance modalities and are antigen-specific naive cells, and therefore do not have the ex-vivo manipulation and impaired functioning or exhaustion problems that other external cell modification methods would have. In this context, the latest actual evidence research using a molecularly cloned T cell receptor particular to an HIV-1 Gag epitope in the aspect of HLA-A*0201 revealed that HSC altered in this ability can progress into fully functioning, mature HIV specialized CD8+ T cells in human thymic tissue that conveys the acceptable constrained HLA-A*0201 particles.80 This explores the possibility of genetically engineering HSCs with a molecularly cloned receptor and signifies a step toward a better understanding and application of initiated T cell responses, which would probably result in the eradication of HIV infection from the body, similar to the natural immune function of other virus infections and pathogenic organisms.30

In an allogeneic transplantation, donor stem cells replace the patients cells.66 Allogeneic hematopoietic stem cell transplantation (HSCT) has appeared as one of the most potent treatment possibilities for many people who suffer from hemopoietic system carcinomas and non-malignant ailments.81 Both HIV-cured people have received HSCT utilizing CCR5 132 donor cells.82,83 This implies that HIV eradication necessitates a decrease in the viral reservoir through the myeloablative procedures,8486 Having followed that, immune rebuilding with HIV-resistant cells was carried out to prevent re-infection.45 The possibility of adoptive transfer of ex vivo-grown, virus-specific T-cells to prevent and control infectious diseases (eg, Cytomegalovirus and EBV) in immunocompromised patients helps to make adoptive T-cell treatment a feasible strategy to inhibit HIV rebound having followed HSCT.81,87,88

The Engineered Zinc Finger Protein Targeting 2LTR Inhibits HIV Integration in Hematopoietic Stem and Progenitor Cell-Derived Macrophages: In Vitro Study, the researchers investigated the efficacy and safety of 2LTRZFP in human CD34+ HSPCs. Researchers used a lentiviral vector to transduce 2LTRZFP with the mCherry tag (2LTRZFPmCherry) into human CD34+ HSPCs. The study findings suggest that the anti-HIV-1 integrase scaffold is an enticing antiviral molecule that could be utilised in human CD34+ HSPC-based gene therapy for AIDS patients.89

The fundamental element of HIV management is stem cell genetic modification, which involves genetically enhanced patient-derived stem cells to overcome HIV infection. In this sector, numerous experimental studies, in vitro as well as in vivo examinations, and positive outcomes for AIDS patients have been conducted.65,74 Genetic engineering for HIV-infected individuals can provide a once-only intervention that minimizes viral load, restores the immune system, and minimizes the accumulated toxicities concerned with highly active antiretroviral therapy (HAART).73 HSCs can be genetically altered, permitting for the addition of exogenous components to the progeny that protects them from direct infectious disease and/or enables them to target a specific antigen. Besides that, HSC-based strategies can enhance multilineage hemopoietic advancement by re-establishing several arms of the immune function. Eventually, as HSCs can be produced autologously, immunologic tolerance is typically high, enabling effective engraftment and subsequent distinction into the fully functioning mature hematopoietic cells.30

The utilization of human HSCs to rebuild the immune function in HIV disease is one application that tries to preserve newly formed cells from HIV infection, while another attempts to develop immune cells that attack HIV infected cells. While each initiative has many different aspects at the moment, they represent huge attention to HIV/AIDS therapies that, most likely when integrated with the other therapeutic approaches, would result in the body trying to overcome the obstacles needed for the virus to be effectively cleaned up.30

While HSC transplantation technique and processes are not accurately novel, as they are commonly and effectively used to address a wide variety of haematological diseases and malignant neoplasms,90 trying to combine them with a gene therapeutic strategy represents a unique and possibly potent therapeutic approach for HIV and AIDS-related ailments. As the results of HIV-infected patients who obtained autologous HSCT continued to improve, there was growing interest in genetically altered stem cells that were tolerant to HIV disease. Multiple logistical challenges have impeded the advancement of genetically modified hematopoietic stem cells as a conceivable therapeutic option for HIV/AIDS.72,73

UCLAs Eli and Edythe Broad Center for Restorative Medicine and Stem Cell Studies is one bit closer to constructing an instrument to arm the bodys immune system to attack and defeat HIV. Dr. Kitchen et al are the first ones to disclose the use of a chimeric antigen receptor (CAR), a genetically manipulated molecule, in blood-forming stem cells. In the experiment, the research team introduced a CAR gene into blood-forming stem cells, which were then moved into HIV-infected mice that had been genetically programmed. The scientists found that CAR-carrying blood stem cells efficiently transformed into fully functioning T cells that have the ability to kill HIV-infected cells in mice. The outcome was an 80-to-95 percentage reduction in HIV levels, suggesting that stem-cell-based genetic engineering with a CAR might be a viable and effective approach for treating HIV infection among humans. The CAR initiative, according to Dr. Kitchen, is much more able to adapt and ultimately more efficient, which can conceivably be used by others. If any further experiment showcases keep promising, the scientists expect that a practice based on their strategy will be accessible for clinical development within the next 510 years.91

HSCT and HAART therapeutic approaches in treating HIV/AIDS as the emergence of highly active antiretroviral therapy (HAART) in the 1990s improved survival rates of HIV infection, leading to a major dramatic drop in the occurrence of AIDS and AIDS-related mortalities. As an outcome, there is much less involvement with using HSCT as a therapy for HIV infection.28,33,43,67,86

A randomized clinical trial of human umbilical cord mesenchymal stem cell transplant among HIV/AIDS immunological non responders investigation, the researchers examined the clinical efficacy of transfusion of human umbilical cord mesenchymal stem cells (hUC-MSC) for immunological non-responder clients with long-term HIV disease who have an unmet medical need in the aspect of effective antiretroviral therapy. From May 2013 to March 2016, 72 HIV-infected participants were admitted in this stage of the randomized, double-blind, multi-center, placebo-controlled dose-determination investigation. They were either given a high dose of hUC-MSC of 1.5106/kg body weight as well as small doses of hUC-MSC of 0.5106/kg body weight, or a placebo application. During the 96-week follow-up experiment, interventional and immunological character traits were analysed. They found that hUC-MSC therapy was both safe and efficacious among humans. There was a significant rise in CD4+ T counts after 48 weeks of treatment in both the high-dose (P 0.001) and low-dose (P 0.001) groups, but no changes in the comparison group.92

One interesting invention made by a team of UC Davis investigators is the recognition of a particular form of stem cell that can minimize the quantity of the virus that tends to cause AIDS, thus dramatically increasing the bodys antiviral immune activity. Mesenchymal stem/stromal cells (MSCs) furnish an incredible opportunity for a creative and innovative, multi-pronged HIV cure strategic plan by augmenting prevailing HIV potential treatments. Even while no antivirals have been used, MSCs have been able to increase the hosts antiviral responses. MSC therapeutic approaches require specialized delivery systems and good cell quality regulation. The studys findings lay the proper scientific foundation for future research into MSC in the ongoing treatment of HIV and other contagious diseases in the clinical organization.35

Infection with HIV-1 necessitates the existence of both specific receptors and a chemokine receptor, particularly chemokine receptor 5 (CCR5).46 Resistance to HIV-1 infection is attained by homozygozygozity for a 32-bp removal in the CCR5 allele.93 In this investigation, stem cells were transplanted in a patient with severe myeloid leukaemia and HIV-1 infection from a donor who was homozygous to Chemokine receptor 5 delta 32. The client seemed to have no viral relapses after 20 months of transplantation and attempting to stop antiretroviral medicine. This finding highlights the essential role that CCR5 tries to play in HIV-1 infection maintenance.86

In comparison, additional HIV-1-infected people who have received allogeneic stem cell transplants with cells from CCR5 truly wild donors did not have long-term relapses from HIV-1 rebound, with 2 of these patients trying to report viral reoccurrence 12 as well as 32 weeks after analytic treatment interruption, respectively. Among these 2 patients, allogeneic stem cell transplantation probably reduced but did not eliminate latently HIV-infected cells, enabling persistent viral reservoirs to activate viral rebound. This viewpoint may not rule out the potential that allogeneic hematopoietic stem cell transplantation might result in a much more comprehensive or near-complete elimination of viral reservoirs, enabling long-term drug-free relapse of HIV-1 infection in some contexts.84 As just one report demonstrated a decade earlier, a curative treatment for HIV-1 remained elusive. The Berlin Patient has undergone 2 allogeneic hematopoietic stem cell transplantations to cure his acute myeloid leukaemia utilizing a potential donor with a homozygous genetic mutation in HIV coreceptor CCR5 (CCR532/32).15,34,46,64,65,72,82,84,86,9496 Other similar studies with CCR5 receptor targets are as follows: Automated production of CCR5-negative CD4+-T cells in a GMP compatible, clinical scale for treatment of HIV-positive patients,97 Mechanistic Models Predict Efficacy of CCR5-Deficient Stem Cell Transplants in HIV Patient Populations,98 Conditional suicidal gene with CCR5 knockout.99

Clustered regularly interspaced short palindromic repeats CRISPR/Cas9 is a promising gene editing approach that can edit genes for gain-of-function or loss-of-function mutations in order to address genetic abnormalities. Despite the fact that other gene editing techniques exist, CRISPR/Cas9 is the most reliable and efficient proven method for gene rectification.100103

Genome engineering employing CRISPR/Cas has proven to be a strong method for quickly and accurately changing specific genomic sequences. The rise of innovative haematopoiesis research tools to examine the complexity of hematopoietic stem cell (HSC) biology has been fuelled by considerable advancements in CRISPR technology over the last five years. High-throughput CRISPR screenings using many new flavours of Cas and sequential and/or functional outcomes, in specific, have become more effective and practical.104,105

The power of the CRISPR/Cas system is that it can specifically and efficiently target sequences in the genome with just a single synthetic guide RNA (sgRNA) and a single protein. Cas9 is directed to the specific DNA sequence by the sgRNA, which causes double stranded breaks and activates the cells DNA repair processes. Non-homologous end joining can cause insertiondeletion (indel) substitutions at the target location, whereas homology-directed repair can use a template DNA to insert new genetic material.104,106

The possibility for CRISPR/Cas9 to be used in the hematopoietic system was emphasised as pretty shortly after it was initiated as a new genome editing method.106,107 The efficiency with which CRISPR-mediated alteration can be used to evaluate hematopoietic stem/progenitor and mature cell function via transplantation. As a result, hematopoietic research has significantly advanced with the implementation of these technologies. Whilst single-gene CRISPR/Cas9 programming is a significant tool for testing gene function in primary hematopoietic cells, high-throughput screenings potentially offer CRISPR/Cas9 an even greater advantage in hematopoietic research.104

While understanding human haematological disorders requires the ability to mimic diseases, the ultimate goal is to transfer this innovation into therapies. Despite significant advancements in CRISPR technology, there are still barriers to overcome before CRISPR/Cas9 can be used effectively and safely in humans. CRISPR has also been used to target CCR5 in CD34+ HSPCs in an effort to make immune cells resistant to HIV infection, as CCR5 is an important coreceptor for HIV infection.104

CRISPR is a modern genome editing technique that could be used to treat immunological illnesses including HIV. The utilization of CRISPR in stem cells for HIV-related investigation, on the other end, was ineffective, and much of the experiment was done in vivo. The new research idea is about increasing CRISPR-editing efficiencies in stem cell transplantation for HIV treatment, as well as its future perspective. The possible genes that enhance HIV resistance and stem cell engraftment should be explored more in the future studies. To strengthen HIV therapy or resistance, double knockout and knock-in approaches must be used to build a positive engraftment. In the future, CRISPR/SaCas9 and Ribonucleoprotein (RNP) administration should be explored in the further investigations.108 As well as some different title studies were explained the effectiveness of the CRISPR gene editing technology on the management of HIV/AIDS including: CRISPR view of hematopoietic stem cells: Moving innovative bioengineering into the clinic,104 CRISPR-Edited Stem Cells in a Patient with HIV and Acute Lymphocytic Leukaemia,109 Sequential LASER ART and CRISPR Treatments Eliminate HIV-1 in a Subset of Infected Humanized Mice,110 Extinction of all infectious HIV in cell culture by the CRISPR-Cas12a system with only a single crRNA,111 HIV-specific humoral immune responses by CRISPR/Cas9-edited B cells,112 CRISPR-Cas9 Mediated Exonic Disruption for HIV-1 Elimination,113 RNA-directed gene editing specifically eradicates latent and prevents new HIV-1 infection,114 CRISPR/Cas9 Ablation of Integrated HIV-1 Accumulates Pro viral DNA Circles with Reformed Long Terminal Repeats,115 CRISPR-Cas9-mediated gene disruption of HIV-1 co-receptors confers broad resistance to infection in human T cells and humanized mice,116 Inhibition of HIV-1 infection of primary CD4+ T-cells by gene editing of CCR5 using adenovirus-delivered CRISPR/Cas9,117 Transient CRISPR-Cas Treatment Can Prevent Reactivation of HIV-1 Replication in a Latently Infected T-Cell Line,118 CCR5 Gene Disruption via Lentiviral Vectors Expressing Cas9 and Single Guided RNA Renders Cells Resistant to HIV-1 Infection,119 CRISPR/Cas9-Mediated CCR5 Ablation in Human Hematopoietic Stem/Progenitor Cells Confers HIV-1 Resistance In Vivo.109

Induced pluripotent stem cells (iPSCs) have significantly advanced the field of regenerative medicine by allowing the generation of patient-specific pluripotent stem cells from adult individuals. The progress of iPSCs for HIV treatment has the potential to generate a continuous supply of therapeutic cells for transplantation into HIV-infected patients. The title of the study is reported on Generation of HIV-1 Resistant and Functional Macrophages from Hematopoietic Stem Cellderived Induced Pluripotent Stem Cells. In this investigation, researchers used human hematopoietic stem cells (HSCs) to produce anti-HIV gene expressing iPSCs for HIV gene therapy. HSCs were dedifferentiated into constantly growing iPSC lines using 4 reprogramming factors and a combination anti-HIV lentiviral vector comprising a CCR5 shRNA and a human/rhesus chimeric TRIM5 gene. After directing the anti-HIV iPSCs toward the hematopoietic lineage, a large number of colony-forming CD133+ HSCs were acquired. These cells were distinguished further into functional end-stage macrophages with a normal phenotypic profile. Upon viral challenge, the anti-HIV iPSC-derived macrophages displayed good protection against HIV-1 infection. Researchers have clearly shown how iPSCs can establish into HIV-1 resistant immune cells and explain their prospective use in HIV gene and cellular therapies.120

Some other similar titles of the studies reported on the effectiveness of IPSCs on HIV/AIDS managements are as follows: Generation of HIV-Resistant Macrophages from IPSCs by Using Transcriptional Gene Silencing and Promoter-Targeted RNA,121 Generation of HIV-1-infected patients gene-edited induced pluripotent stem cells using feeder-free culture conditions,122 A High-Throughput Method as a Diagnostic Tool for HIV Detection in Patient-Specific Induced Pluripotent Stem Cells Generated by Different Reprogramming Methods,123 Genetically edited CD34+ cells derived from human iPS cells in vivo but not in vitro engraft and differentiate into HIV-resistant cells,124 Engineered induced-pluripotent stem cell-derived monocyte extracellular vesicles alter inflammation in HIV humanized mice,125 Sustainable Antiviral Efficacy of Rejuvenated HIV-Specific Cytotoxic T Lymphocytes Generated from Induced Pluripotent Stem Cells.126

Recently, one HIV patient appeared to be virus-free after having undergone a stem-cell transfusion in which their WBCs were changed with HIV-resistant variations.84 Timothy Ray Brown also noted as the Berlin patient, who is still virus-free, was the first individual to undertake stem-cell transplantation a decade earlier. The most recent patient, like Brown, had a type of leukaemia that was vulnerable to chemo treatments. They required a bone marrow transplantation, which involved removing their blood cells and replacing them with stem cells from a donor cell.5,31,34,41,127130 Rather than simply choosing a suitable donor, Ravindra Gupta et al chose one who already had 2 copies of a mutant within the CCR5 gene,128,131 which provides resistance to HIV infection.3

Additionally, this gene encodes for a specific receptor of white blood cells that are assisted in the bodys immunological responses. The transplant, according to Guptas team, completely replaced the clients White cells with HIV-resistant forms.41,83 Cells in the patients blood disrupted expressing the CCR5 receptor, making it unfeasible for the clients form of HIV to infect the above cells again. The scientists determined that the virus had been cleared from the patients blood after the transplantation. Besides that, after 16 months, the client has withdrawn antiretroviral treatment. The infection was not detected in the most recent follow-up, which occurred 18 months after the treatment was discontinued. Adam, also known as the London patient, was the second person to be cured of HIV as a result of a stem cell transfusion. This discovery is an important step forward in HIV research because it may aid in the detection of potential future therapeutic interventions. It must be noted, but even so, that this is not an extensively used HIV treatment. For HIV-infected patients, antiretroviral drugs have been the foremost therapeutic option.3,31,41,94,129,130 It also encourages many investigators and clinicians to look at the use of stem cells in the treatment of a wide range of serious medical conditions. The reprogramming abilities of stem cells, as well as their accessibility, have created a window of opportunity in medical research. The clinical utility of stem cells is forecast to expand rapidly in the coming years.

On Feb 15, 2022, scientific researchers confirmed that a woman had become the 3rd person in history to be successfully treated for HIV, the virus that causes AIDS, after just receiving a stem-cell transfusion that has used cells from cord blood. Within those transplant recipients, adult hematopoietic stem cells have been used; these are stem cells that eventually develop into all blood cell types, which include white blood cells, these are a vital component of the immune framework. Even so, the woman who had fairly recently been completely cured of HIV infection had a more unique experience than that of the 2 men who were actually cured before her.132

The clients physician, Dr. JingMei Hsu of Weill Cornell Medicine in New York, informed them that, she had been discharged from the hospital just 17 days after her procedure was performed, even with no indications of graft vs host ailment. The woman was HIV-positive but also had acute myeloid leukaemia, a blood cancer of the bone marrow that affects blood-forming cells. She had likely received cord blood as a successful treatment for both her cancer and HIV once her doctors decided on a potential donor well with HIV-blocking gene mutation. Cord blood comprises a high accumulation of hematopoietic stem cells; the blood is obtained during a childs birth and donated by the parents.132

The patients donor was partly nearly matched, and she received stem cells from a close family member to enhance her immune function after the transfusion. The procedure was performed on the woman in August of 2017. She chose to discontinue taking antiretroviral drugs, the standardized HIV intervention, 37 months upon her transfusion. After more than 14 months, there is no evidence of the viral infection or antibodies against it in her blood. Umbilical cord blood, in reality, is much more commonly accessible and simpler to try to match to beneficiaries than bone marrow. Perhaps, some research suggests that the method could be more available to HIV patients than bone marrow transplantation. Nearly 38 million people worldwide are infected with HIV. The potential for using partly matched umbilical cord blood transplantation increases the chances of choosing appropriate suitable donors for these clients considerably.132

It is really exciting to see the earlier terminally ill diseases of being effectively treated. In recent times, there has been a surge of focus on stem cell research.3 Stem cell therapy advancements in inpatient care are receiving a growing amount of attention.20 HIV/AIDS has been and remains a significant health concern around the world. Effective control of the HIV pandemic will necessitate a thorough understanding of the viruss transmission.32

Despite concerns about full compliance and adverse reactions, HAART has demonstrated to be able to succeed and is a sign specifically targeted form of treatment against HIV advancement. As illustrated by the first case of HIV infection relapse attained by bone marrow transplant, anti-HIV HPSC-based stem cell treatment and genotype technology have established a possible future upcoming technique to try to combat HIV/AIDS.

Investigators have conducted experiments with engineering distinct anti-HIV genetic traits trying to target different phases of HIV infection utilizing advanced scientific modalities. In numerous in vivo and in vitro animal studies, HSPCs and successive mature cells were secured from HIV infection by trying to target genetic factors in the infection. Anti-HIV gene engineering of HSPCs is safe and efficacious.15

The number of stem-cell-based research trials has risen in recent years. Thousands of studies claiming to use stem cells in experimental therapies have been registered worldwide. Despite some promising results, the majority of clinical stem cell technologies are still in their early life. These achievements have drawn attention to the possibility of the potential and advancement of various promising stem cell treatments currently in development.11

HIV remains a major danger to humanity. This virus has developed the ability to evade antiretroviral medication, resulting in the death of individuals. Scientists are constantly looking for a treatment for HIV/AIDS that is both effective and efficient.52 The 1st treatments in HIV+ clients were conducted in the early 1980s, even though they were cognizant of their viral disease. Following these early cases, allogeneic SCT was used to treat HIV+ patients with associated cancer or other haematological disorders all over the world. Stem cell transplantation developments have also stimulated the improvement of innovative HIV therapeutic approaches, especially for large goals like eradication and relapse.60

Numerous stem cell therapy progressions have been recognized with autologous and allogeneic hematopoietic stem cell transplantation, as well as umbilical cord blood mesenchymal stem cell transplant in AIDS immunologic non-responders. Whereas this sector continues to advance and distinguishing directives for these cells become much more effective, totipotent stem cells such as hESC and the recently reported induced pluripotent stem cells (iPSC) could be very useful for genetic engineering methods to counter hematopoietic abnormalities such as HIV disease.133135

Immunocompromised people are at a higher risk of catching life-threatening diseases. The perseverance of latently infected cells, which is formed by viral genome inclusion into host cell chromosomes, is a significant challenge in HIV-1 elimination. Stem cell therapy is producing impressive patient outcomes, illustrating not only the broad relevance of these strategies but also the huge potential of cell and gene treatment using adult stem cells and somatic derivative products of pluripotent stem cells (PSCs).

Stem cells have enormous regeneration capacity, and a plethora of interesting therapeutic uses are on the frontier. This is a highly interdisciplinary scientific field. Evolutionary biologists, biological technicians, mechanical engineers, and others that have evolved novel concepts and decided to bring them to medical applications are required to make important contributions. Further to that, recent advancements in several different research areas may contribute to stem cell application forms that are novel. Several hurdles must be conquered, however, in the advancement of stem cells. On the other hand, this discipline appears to be a promising and rapidly expanding research area.

Stem cell-based approaches to HIV treatment resemble an innovative approach to trying to rebuild the ravaged bodys immune system with the utmost goal of eliminating the virus from the body. We will probably see effective experiments from the next new generation of stem cell-based strategies shortly, which will start serving as a base for the further development and use of these techniques in a range of treatment application areas for other chronic diseases.

My immense pleasure was mentioned to family members and friends, who supported and encouraged me in every activity.

There was no funding for this work.

The authors declare that they have no conflicts of interest in relation to this work.

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Originally posted here:
PROMISING STEM CELL THERAPY IN THE MANAGEMENT OF HIV & AIDS | BTT - Dove Medical Press

Stem Cells. Author manuscript; available in PMC 2020 Jul 1.

Published in final edited form as:

PMCID: PMC6658105

NIHMSID: NIHMS1024291

1NeuroRepair Department, Mossakowski Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland

1NeuroRepair Department, Mossakowski Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland

1NeuroRepair Department, Mossakowski Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland

2Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA

3Cellular Imaging Section and Vascular Biology Program, Institute for Cell Engineering, Johns Hopkins University, Baltimore, MD, USA

1NeuroRepair Department, Mossakowski Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland

2Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA

3Cellular Imaging Section and Vascular Biology Program, Institute for Cell Engineering, Johns Hopkins University, Baltimore, MD, USA

Author contributions:

Barbara Lukomska: Conception and design, financial support, collection and/or assembly of data, final approval of manuscript

Miroslaw Janowski: Conception and design, financial support, collection and/or assembly of data, manuscript writing, final approval of manuscript

It was shown as long as half a century ago that bone marrow is a source of not only hematopoietic stem cells, but also stem cells of mesenchymal tissues. Then the term of mesenchymal stem cells (MSCs) has been coined in early 1990s and over a decade later the criteria for defining MSCs have been released by International Society for Cellular Therapy. The easy derivation from a variety of fetal and adult tissues and not demanding cell culture conditions made MSCs an attractive research object. It was followed by the avalanche of reports from preclinical studies on potentially therapeutic properties of MSCs such as immunomodulation, trophic support and capability for a spontaneous differentiation into connective tissue cells, and differentiation into majority of cell types upon specific inductive conditions. While ontogenesis, niche and heterogeneity of MSCs are still under investigation, there is a rapid boost of attempts in clinical applications of MSCs, especially for a flood of civilization-driven conditions in so quickly aging societies in not only developed countries, but also very populous developing world. The fields of regenerative medicine and oncology are particularly extensively addressed by MSC applications, in part due to paucity of traditional therapeutic options for these highly demanding and costly conditions. There are currently almost 1000 clinical trials from entire world registered at clinicaltrials.gov and it seems that we are starting to witness the snowball effect with MSCs becoming a powerful global industry, however spectacular effects of MSCs in clinic still need to be shown.

Keywords: Mesenchymal stem cells, clinical, differentiation, immunomodulation, paracrine activity, history

Friedenstein was one of the pioneers of the theory that bone marrow is a reservoir of stem cells of mesenchymal tissues in adult organisms. It was based on his observation at the turn of the 1960s and 1970s., that ectopic transplantation of bone marrow into the kidney capsule, results not only the proliferation of bone marrow cells, but also the formation of bone [1] (). This indicated the existence in the bone marrow of a second, in addition to hematopoietic cells, stem cell population giving rise to bone precursors. Due to the ability of these cells to create osteoblasts, Friedenstein gave them the name of osteogenic stem cells. Friedenstein was also the first to isolate from bone marrow adherent fibroblast-like cells with the ability to grow rapidly in vitro in the form of clonogenic colonies (CFU-F; colony forming unit-fibroblast). These cells derived from CFU-F colonies were characterized by the ability to differentiate in vitro not only to osteocytes, but also to chondrocytes and adipocytes. After transplantation of CFU-F colonies into the recipient, they were capable of co-formation of the bone marrow micro-environment [2,3]. The term mesenchymal stem cells has been proposed by Caplan in 1991 because of their ability to differentiate into more than one type of cells that form connective tissue in many organs [4]. This name has become very popular and is currently the most commonly used, even though it raised doubts about the degree of their stemness [5]. Today, there are many substitutes in the literature for the abbreviation of MSCs, including Multipotent Stromal Cells, Marrow Stromal Cells, Mesodermal Stem Cells, Mesenchymal Stromal Cells and many more. In its latest work, Caplan recommends renaming these cells to Medicinal Signaling Cells due to the emphasis on the mechanism of their therapeutic effects after transplantation, which is believed to be based mainly on the secretion of factors facilitating regenerative processes [6].

The roots of research on bone marrow-derived stem cells of connective tissue, which has been then named: mesenchymal stem cells

Due to the growing controversy regarding the nomenclature, the degree of stemness and the characteristics of the cells discovered by Friedenstein, the International Society for Cellular Therapy (ISCT) in 2006 published its position specifying the criteria defining the population of MSCs, which was accepted by the global scientific community. These guidelines recommend the use of the name multipotent mesenchymal stromal cells, however, the name mesenchymal stem cells still remains the most-used. The condition for the identification of MSCs is the growth of cells in vitro as a population adhering to the substrate, as well as in the case of cells of human origin, a phenotype characterized by the presence of CD73, CD90, CD105 surface antigens and the lack of expression of proteins such as: CD45, CD34, CD14, CD11b, CD79a or CD19 or class II histocompatibility complex antigens (HLA II, human leukocyte antigens class II). Moreover, these cells must have the ability to differentiate towards osteoblasts, adipocytes and chondroblasts [7,8]. In addition to the markers mentioned in the ISCT guidelines, the following antigens turned out to be useful in isolating the human MSCs from the bone marrow: STRO-1 (antigen of the bone marrow stromal-1 antigen, cell surface antigen expressed by stromal elements in human bone marrow-1), VCAM / CD106 (vascular cell adhesion molecule 1) and MCAM / CD146 (melanoma cell adhesion molecule), which characterizes cells growing in vitro in a adherent form, with a high degree of clonogenicity and multidirectional differentiation ability [911].

The common mesenchymal core in both versions of MSC abbreviation comes from the term mesenchyme, which is synonymous with mesenchymal tissue or embryonic connective tissue. It is used to refer to a group of cells present only in the developing embryo derived mainly from the third germ layer - mesoderm. During the development these cells migrate and diffuse throughout the body of the embryo. They give rise to cells that build connective tissue in adult organisms, such as bones, cartilage, tendons, ligaments, muscles and bone marrow. The view about the differentiation of MSCs during embryonic development from mesenchymal cells is widely spread [4]. This is due, inter alia, to the observed convergence in the expression of markers such as: vimentin, laminin 1, fibronectin and osteopontin, which are typical for mesoderm cells during embryonic development, as well as characteristic for in vitro adherent bone marrow stroma cells [12]. However, the true origin of MSCs is unknown. In the literature, we can find also reports indicating that they are ontogenetically associated with a group of cells derived from ectoderm, which originate from Sox1 + cells (SRY - sex determining region Y) that appear during the development of embryonic neuroectoderm and neural crest. These cells inhabit newborn bone marrow and meet the criteria corresponding to their designation as MSCs. However, with the development of animals, the population of these cells disappears and is replaced by cells with a different, unidentified origin [13]. It has also been shown that in the bone marrow of the developing mouse embryo, at least two MSCs populations with distinct expression of the nestin protein and the intensity of cell divisions can be distinguished. The former one originates from mesoderm that does not express nestin, and is characterized by intense proliferation and is involved in the process of creating the embryo skeleton. The latter one is derived from the cells of the neural crest, which expresses nestin and is non-dividing and remains passive during bone formation while in the adult organism contributes to a niche of hematopoietic cells [14]. It seems, therefore, that the ontogenesis of MSCs is associated with cells belonging to different germ layers and their original source determines the role and functions that they play in the adult body.

In 1978, the concept of a niche was defined as a place in the body that is settled by stem cells and whose environment allows them to be maintained in an undifferentiated state [15]. MSCs were first obtained from the bone marrow stroma where they constitute an element of stromal cells, participating in the production of signals modulating the maturation of hematopoietic cells. However, the precise location of the niche for MSCs has not been known so far. In the context of research results indicating that MSCs can be isolated from many mesoderm-derived tissues during embryonic development, a common element was sought for all sources from which MSCs can be isolated and a theory was proposed about the existence of their niche within the blood vessels that are present in all structures from which these cells were isolated.

Crisan and colleagues have shown that cells inhabiting the perivascular space of blood vessels, isolated from human tissues such as skeletal muscle, pancreas, adipose tissue and placenta, with the phenotype CD146 +, NG2 + (neuroglycan-2), PDGF-R + (-type platelet-derived growth factor receptor), ALP + expressing endothelial, hematopoietic and muscle cell markers described as pericytes were precursors for cells that after in vitro expansion meet the criteria for determining them as MSCs [16]. Analogously to the described by Friedenstein MSCs, CD146 + cells colonizing the perivascular space of sinusoidal sinus vessels, are responsible for the production of signals allowing the reconstruction of the bone marrow microenvironment after transplantation to heterotopic location [11]. Whats more, tracing the fate of pericytes in the process of rebuilding a damaged tooth in rodents has shown that they are transforming into odontoblasts, which arise from MSCs found in the pulp. However, the same studies showed that in the process of reconstruction of incisors in mice, a different population of odontoblasts, which is not formed from pericytes, but from MSCs of different origin migrating to the area of damage, prevailed quantitatively [17]. The second cell population associated with blood vessels, proposed as a counterpart of MSCs in the body is advent building cells with the CD34+ CD31- CD146- phenotype, which after isolation and in vitro culture meet the criteria defining the population as MSCs. However, these cells also have the ability to differentiate into pericytes [18,19]. Although pericytes and MSCs have a very similar gene expression profile as well as an analogical capacity for differentiation, it has been shown that the functionality of these cells varies. In vitro studies of endothelial cell interactions in co-culture with MSCs or pericytes have shown that only pericytes are able to form highly branched, dense, cylindrical structures with large diameter, typical for well-organized blood vessels, while isolated from the bone marrow MSCs do not have such abilities. Currently, it is believed that there is a link between pericytes and MSCs, but their mutual relations are not well defined. There are speculations that MSCs are an intermediate form of pericytes or their subpopulation, but there is still no conclusive evidence confirming this hypothesis [20,21].

While the cells fulfilling criteria for MSCs can be harvested from various tissues at all developmental stages (fetal, young, adult and aged) using their plastic adherence property, there are profound differences between obtained MSC populations [22,23]. Bone marrow was historically the first source from which MSCs were obtained, however, over time, there have been reports of the possibility of isolation from other sources of cells with similar properties. Mesenchymal cells are obtained from both tissues and secretions of the adult body, such as adipose tissue, peripheral blood, dental pulp, yellow ligament, menstrual blood, endometrium, milk from mothers, as well as fetal tissues: amniotic fluid, membranes, chorionic villi, placenta, umbilical cord, Wharton jelly, and umbilical cord blood [2437]. MSCs of fetal origin as compared to cells isolated from tissues of adult organisms are characterized by a faster rate of proliferation as well as a greater number of in vitro passages until senescence [38]. However, MSCs derived from bone marrow and adipose tissue are able to create a larger number of CFU-F colonies, which indirectly indicates a higher degree of their stemness. The comparison of gene expression typical for pluripotent cells shows that only in cells isolated from the bone marrow we can observe the expression of the SOX2 gene, the activation of which is associated with the self-renewal process of stem cells as well as with neurogenesis during embryonic development [39]. Discrepancies in the ability of MSCs obtained from various sources to differentiate have also been described. The lack of differentiation of MSCs derived from umbilical cord blood towards adipocytes as well as the greater tendency of MSCs from bone marrow and adipose tissue to differentiate towards osteoblasts were observed [39,40].

In addition to the diverseness observed between MSCs from different sources, there are also differences associated with obtaining them from individual donors. Among the cells isolated from the bone marrow from donors of different ages and sexes, up to 12-fold differences in the rate of their proliferation and osteogenesis were found, combined with a 40-fold difference in the level of bone remodeling marker activity - ALP (alkaline phosphatase). At the same time, no correlations were found resulting from differences in the sex or age of donors [41]. However, the results of studies by other authors indicate that the properties of MSCs isolated from the bone marrow are strongly associated with the age of the donor. Cells collected from older donors are characterized by an increased percentage of apoptotic cells and slower rate of proliferation, which is associated with an increased population doubling time. There is also a weakened ability of MSCs from older donors to differentiate towards osteoblasts [42]. Heo in his work shows the different ability of MSCs to osteogenesis combining it with different levels of DLX5 gene expression (transcription factor with the homeodomain 5 motif) in individual donors, however independent of the type of tissue from which the cells were isolated [39].

The next stage in which we can observe diversity among the MSCs population is in vitro culture. The morphology of cultured cells that originate from the same isolation allows for differentiation into three sub-populations. There are observed spindle-shaped proliferating cells resembling fibroblasts (type I); large, flat cells with a clearly marked cytoskeleton structure, containing a number of granules (type II) and small, round cells with high self-renewal capacity [43,44]. The original hypothesis assumed that all cells that make up the MSCs population are multipotent, and each colony of CFU is capable of differentiating into adipocytes, chondrocytes and osteoblasts, as confirmed by appropriate studies [45]. However, in the literature we can find reports that cell lines derived from a common colony of CFU-F differ in their properties, characterized by uni-, di- or multipotence [46]. Some of the authors showed the division of clonogenic MSCs colonies into as much as eight groups distinct in their potential for differentiation. At the same time, it is suggested that there is a hierarchy within which cells subordinate to each other are increasingly directed towards osteo- chondro- or adipocytes and gradually lose their multipotential properties to di- and unipotential ones. This transformation may also be associated with a decrease in the rate of cell proliferation and the level of CD146 protein expression (CD; cluster of differentiation) - proposed as a marker of multipotency [47].

One of the main advantages of MSCs are their immunomodulatory properties. MSCs grown in vitro have the ability to interact and regulate the function of the majority of effector cells involved in the processes of primary and acquired immune response () [48]. They exert their immunomodulatory effects by inhibiting the complement-mediated effects of peripheral blood mononuclear cell proliferation [49,50], blocking apoptosis of native and activated neutrophils, as well as reducing the number of neutrophils binding to vascular endothelial cells, limiting the mobilization of these cells to the area of damage [51,52]. In addition, cytokines synthesized by activated MSCs stimulate neutrophil chemotaxis and secretion of pro-inflammatory chemokines involved in recruitment and stimulation of phagocytic macrophage properties [53]. Moreover MSCs limit mast cell degranulation, secretion of pro-inflammatory cytokines by these cells as well as their migration towards the chemotactic factors [54]. Native MSCs have the ability to block the proliferation of de novo-induced NK cells, but they are only able to partially inhibit the proliferation of already activated cells [55]. They also contribute to the reduction of cytotoxic activity of NK cells [56]. Moreover MSCs can block the differentiation of CD34 + cells isolated from the bone marrow or blood monocytes into mature dendritic cells both by direct contact as well as by secreted paracrine factors [57,58]. They inhibit the transformation of immature dendritic cells into mature forms and limit the mobilization of dendritic cells to the tissues [59]. Under their influence, M1 (pro-inflammatory) macrophages are transformed into M2 type cells with an anti-inflammatory phenotype, and the IL-10 (IL, interleukin) secreted by them inhibits T-cell proliferation [60,61]. In vitro studies have demonstrated a direct immunomodulatory effect of MSCs on lymphocytes. During the co-culture of MSCs with lymphocytes, suppression of activated CD4 + and CD8 + T cells and B lymphocytes was observed [62]. In addition, MSCs reduce the level of pro-inflammatory cytokines synthesized by T-lymphocytes, such as TNF- (tumor necrosis factor ) and IFN- (interferon ) [63], and increase synthesis of anti-inflammatory cytokines, e.g. IL-4. In the presence of MSCs, the inhibition of the differentiation of naive CD4 + T lymphocytes to Th17 + lymphocytes (Th; T helper cells) was observed, while the percentage of T cells differentiating towards CD4 + CD25 + regulatory T cells was found to increase [64,65]. Glennie et al. described this condition as anergy of activated T cells in the presence of MSCs [62]. MSCs also have the ability to limit the synthesis of immunoglobulins like IgM, IgG and IgA (Ig; immunoglobulin) classes secreted by activated B cells, thereby blocking the differentiation of these cells to plasma cells. They also reduce the expression of chemokines and their receptors on the surface of B lymphocytes, which probably have a negative effect on their ability to migrate [66].

The schematic representation of immunomodulatory capabilities of MSCs

Mesenchymal stem cells secrete a wide range of paracrine factors, collectively referred to as the secretome, which support regenerative processes in damaged tissues. They comprise the components of the extracellular matrix, proteins involved in the adhesion process, enzymes as well as their activators and inhibitors, growth factors and binding proteins, cytokines and chemokines, and probably many more [67]. These factors can have distinct impact on the processes they regulate (). MSCs secrete factors promoting angiogenesis, such as: vascular endothelial growth factor (VEGF) but they may also inhibit this process, through expression of monokine induced by interferon and tissue inhibitors of metalloproteinases 1 and 2 [68,69]. An important role is also played by chemokines secreted by MSCs in the process of blocking or stimulating cell chemotaxis, such as: CCL5 (RANTES, regulated by activation, expression and secretion by normal T lymphocytes), CXCL12 (SDF-1, stromal cell-derived factor 1) or CCL8 (MCP-2; monocyte chemoattractant protein 2). An essential group of factors from the point of view of regeneration processes are growth factors with an anti-apoptotic effect, including: HGF (hepatocyte growth factor), IGF-1 (insulin-like growth factor 1), VEGF, CINC-3 (cytokine induced by a chemoattractant for neutrophil chemoattractant), TIMP-1 (tissue inhibitor of metalloproteinases 1), TIMP-2 (tissue inhibitor of metalloproteinases 2), osteopontin, growth hormone, FGF-BP (bFGF binding protein), and BDNF (brain-derived growth factor; -derived neurotrophic factor) and stimulating proliferation as: TGF- (transforming growth factor ), HGF, EGF (epidermal growth factor), NGF (nerve growth factor; nerve growth factor), bFGF (basic fibroblast growth factor), IGFBP-1, IGFBP-2 (IGFBP; insulin-like growth factor 1 binding protein, IGF-Protein-1 protein) and M-CSF (stimulant factor t molar macrophage colony; macrophage colony-stimulating factor) [68,70,71]. Growth factors secreted by MSCs have also ability to reduce fibrosis of tissues during regeneration. These include KGF (keratinocyte growth factor), HGF, VEGF, and Ang-1 (angiopoietin-1), SDF1, IGF-1, EGF, HGF, NGF, TGF- [71,72]. There are reports about the antibacterial properties and interaction of the MSC secretome with cancer cells. Data on the impact of MSCs on neoplasia are not conclusive, however, it is assumed that both the tumor type and the origin of MSCs are of great importance for the final effect [73]. It was shown that factors enclosed within the MSCs secretome are able to reduce the proliferation, viability and migration of certain types of cancer cells (such as non-small-cell lung carcinoma) [74]. Others have shown that factors released by MSCs may increase motility, invasiveness and the ability to form metastases (including, for example, breast cancer cells) [75]. In response to bacteria, levels of cytokines such as IL- 6, IL-8, CCL5, PGE2, TNF-, IL-1, IL-10, VEGF and SDF-1 secreted by MSCs are subject to change [76]. MSCs contain also substances with antibacterial, anti-parasitic and antiviral activity [77].

The mechanisms mediating MSC-dependent trophic support

Another broad and dynamically developing field in recent years which is related to paracrine MSCs activity is their ability to secrete extracellular vesicles (EVs), which include exosomes, microvesicles and apoptotic bodies. Their composition largely coincides with the components contained in the cells from which they originate. Physiologically they play an important role in the regulation of biological functions, homeostasis and the immune response of the body. It is also postulated that the biological activity of microvesicles is comparable to that of MSCs [78]. Experiments conducted using supernatant derived from in vitro culture of MSCs showed that the factors contained in their secretome are responsible for a large part of the effects exerted by MSCs during the regeneration of the damaged area including the protection of other cells against apoptosis, induction of their proliferation, prevention of excessive fibrosis of tissues, stimulation of the angiogenesis process and immunomodulatory effects, as well as the induction of endogenous stem cells differentiation [65,68,69,7982].

As mentioned above, the ability to differentiate into three types of cells such as: osteocytes, chondrocytes and adipocytes is one of the criterion for MSCs [8]. This phenomenon can be traced in vitro by placing MSCs in a medium containing specific supplements, for the adipogenesis process they are mainly dexamethasone, indomethacin, insulin and isobutylmethylxanthin [83], for chondrogenesis cell culture in DMEM medium (Dulbecco / Vogt Modified Eagles Minimal Essential Medium) supplemented with insulin, transferrin, selenium, linoleic acid, selenium acid, pyruvate, ascorbic phosphate, dexamethasone and TGF- III [84], which may additionally be aided by the addition of IGF-1 and BMP-2 (BMP; bone morphogenetic proteins) [85]. In turn the osteogenesis is induced by the presence of ascorbic acid, -glycerophosphate and dexamethasone [86]. Differentiation of MSCs in the appropriate cell type is assessed by identifying the production of respectively: fat droplets (adipogenesis), proteoglycans and type II collagen synthesis (chondrogenesis) or mineralization of calcium deposits and the increase of alkaline phosphatase expression (osteogenesis). However, many literature reports indicate that by the treatment with appropriate factors MSCs might be also a source of other cell types. Caplan and Dennis in their work from 2006 present a process that they call mesengenesis, in which MSCs give also rise to myoblasts, bone marrow stromal cells, fibroblasts, cells co-creating connective tissue of the body as well as ligaments and tendons [87]. Addition of 5-azacytidine to MSCs allows to obtain muscle cells, including cardiomyocytes and myoblasts having the ability to create multinucleated miotubes and expressing markers such as: -myosin heavy chain, -actin cardiac form and desmin [88]. In addition, in vitro studies have made it possible to obtain from MSCs at least two types of cells derived from the endoderm through their transdifferentiation into hepatocytes and -cells of pancreatic islets. The liver cells are obtained from MSCs in two stages by culturing them in modified Dulbeccos medium supplemented with EGF, bFGF and nicotinamide, and in the next stage with the addition of oncostatin M, dexamethasone, insulin, transferrin and selenium. The resulting cells show the presence of markers typical for hepatocytes such as albumin, -fetoprotein and hepatocyte nuclear factor 4 (HNF-4) [89]. By the treatment with a mixture of growth factors secreted by regenerating cells of the pancreas as well as by the use of acitin A, sodium butyrate, taurine and nicotinamide the pancreatic islets of -cells capable of producing insulin were obtained from MSCs [90,91]. It has also been shown that stimulation with appropriate factors may result in the differentiation of MSCs into cells derived ontogenetically from ectoderm, such as neurons. The use of BME stimulation in vitro (-mercaptoethanol) followed by NGF leads to the differentiation of MSCs into cholinergic nerve cells expressing their typical proteins such as NF-68 neurofilaments (68 kDa Neurofilament protein with 68 kDa molecular mass), NF-200 (neurofilament protein with a molecular weight 200kDa, 200kDa neurofilament protein), NF-160 (neurofilament protein molecular weight 160kDa, 160kDa neurofilament protein), choline acetyltransferase and synapsin I [92]. Other factors mentioned as compounds inducing the transformation of MSCs into nerve cells are insulin, retinoic acid, bFGF, EGF, valproic acid, BME and hydrocortisol [93]. In addition, GNDF (glial cell-derived neurotrophic factor), BDNF (brain-derived neurotrophic factor), retinoic acid, 5-azacytidine, isobutylmethylxanthine and indomethacin stimulate the transformation of MSCs into mature neurons that express markers of nervous systems cells such as: nestin, -III tubulin, microtubule associated protein - MAP2 (microtubule associated protein 2) and neuron-specific enolase (ENO2; enolase 2) [94]. These studies show that under strictly controlled conditions prevailing during in vitro culture, in the presence of chemicals and growth factors, MSCs are able to turn into cells derived from all three embryonic germ layers ().

The differentiation potential of MSCs

It has been more than half a century since the curiosity has been revealed that not only hematopoietic cells, but also those capable of forming connective tissue reside in the bone marrow. Subsequent studies have begun to reveal the increasingly fascinating properties of these cells, which go far beyond forming connective tissue. This, combined with their easy derivation from various tissues, made them an attractive research object. Immunomodulatory properties, aiding repair of various tissues as well as differentiation potential to practically any types of cells stunned a whole host of scientists and established MSCs as a driving force of regenerative medicine and began also to play an increasingly important role in oncology [95]. We are currently observing a flood of clinical trials with the use of MSCs, and their number doubles every few years and currently reaches almost 1000 registered items on the clinicaltrials.gov website.

MSCs compose a negligible fraction of cells derived from in vivo tissues and there is no effective method to capture them directly. Therefore, MSCs need to be subjected to the process of in vitro expansion, which in clinical context is called biomanufacturing and biobanking and both terms are frequently used interchangeably to describe the process from procurement of cell source to deliver cells to the patients bed. The processing of MSCs must be performed according to current Good Manufacturing Practice (cGMP) as any other therapeutic agent and is subjected to extensive regulatory effort. Food and Drug Administration (FDA) is the main authority responsible for acceptance of medical products including those containing living cells such as MSCs in the USA. FDA has issued a perspective on MSC-based product characterization [96] and up-dated it in FDA Grand Round delivered by Steven Bauer, PhD, Chief of Cell and Tissue Therapies Branch at FDA on March 08, 2018. Both sources are an excellent overview of regulatory challenges related to the biobanking of MSCs. In general, any new product must obtain investigational new drug status (INDs) to be used in clinical trial before filing application for marketing, and there were 66 INDs submitted to FDA between 2006 and 2012. Based on that FDA engaged into regulatory research project called MSC consortium to characterize MSC based-products with an output of 16 research papers. The main organ responsible for the regulation of medical market in all Member States is European Medicines Agency (EMA) consisting of seven smaller committees. The MSCs-containing products should be classified as Advanced Therapy Medical Product (ATMP) and in detail considered as Somatic Cell Therapy Medicinal Product (CTMP) [97]. Its release on medical market has to be first accredited by Committee for Advanced Therapies (CAT) which creates the general opinion and evaluates the quality, safety and efficiency of the product. After CAT assessment the final acceptance should be then approved by Committee for the Medicinal Products for Human Use (CHMP). This type of legalization is called Centralized Marketing Authorization and it allows to use ATMP products in all European Union countries. Currently, there is a variety of protocols used for biomanufacturing and biobanking of MSCs, and once the successful stories become strong, the landscape of MSC production will probably solidify with predicted reduction of MSC production approaches due to economic and regulatory pressures.

Summing up, it seems that the MSCs are becoming a powerful global industry, ready to respond to the unmet needs of modern medicine struggling with the proper care and quality of life of rapidly aging societies, which is already affecting not only developed countries, but also very populous developing countries. In conclusion, we are beginning to observe the effect of the snowball in which ever new discoveries related to MSC are increasingly stimulating clinical applications of the MSC, which is beginning to contribute to the transformation of medical care.

Significance Statement

The research on bone marrow-derived stem cells of connective tissue is evolving and continuously expanding with a recent boost of interest in clinical applications reflected by an avalanche of nearly 1000 registered clinical trials. While, the current name: mesenchymal stem cells (MSCs) have been coined as late as early 90-ies, it is important to commemorate of the fiftieth anniversary of research on them and provide a big picture from roots of first paper in 1968, through identification of their various potential therapeutic activities such as immunomodulation, trophic support and capability for differentiation and taking role in cell replacement strategies.

This work was funded by NCR&D grant EXPLORE ME within the STRATEGMED I program and by NIH R01 NS091100-01A1.

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Mesenchymal stem cells: from roots to boost - PMC

For more in-depth learning, we recommend Different Approaches in our Patient Education program.

The challenges of gene and cell therapists can be divided into three broad categories based on disease, development of therapy, and funding.

Challenges based on the disease characteristics: Disease symptoms of most genetic diseases, such as Fabrys, hemophilia, cystic fibrosis, muscular dystrophy, Huntingtons, and lysosomal storage diseases are caused by distinct mutations in single genes. Other diseases with a hereditary predisposition, such as Parkinsons disease, Alzheimers disease, cancer, and dystonia may be caused by variations/mutations in several different genes combined with environmental causes. Note that there are many susceptible genes and additional mutations yet to be discovered. Gene replacement therapy for single gene defects is the most conceptually straightforward. However, even then the gene therapy agent may not equally reduce symptoms in patients with the same disease caused by different mutations, and even the samemutationcan be associated with different degrees of disease severity. Gene therapists often screen their patients to determine the type of mutation causing the disease before enrollment into a clinical trial.

The mutated gene may cause symptoms in more than one cell type. Cystic fibrosis, for example, affects lung cells and the digestive tract, so the gene therapy agent may need to replace the defective gene or compensate for its consequences in more than one tissue for maximum benefit. Alternatively, cell therapy can utilizestem cellswith the potential to mature into the multiple cell types to replace defective cells in different tissues.

In diseases like muscular dystrophy, for example, the high number of cells in muscles throughout the body that need to be corrected in order to substantially improve the symptoms makes delivery of genes and cells a challenging problem.

Some diseases, like cancer, are caused by mutations in multiple genes. Although different types of cancers have some common mutations, every tumor from a single type of cancer does not contain the same mutations. This phenomenon complicates the choice of a single gene therapy tactic and has led to the use of combination therapies and cell elimination strategies. For more information on gene and cell therapy strategies to treat cancer, please refer to the Cancer and Immunotherapy summary in the Disease Treatment section.

Disease models in animals do not completely mimic the human diseases and viralvectorsmay infect various species differently. The testing of vectors in animal models often resemble the responses obtained in humans, but the larger size of humans in comparison to rodents presents additional challenges in the efficiency of delivery and penetration of tissue.Gene therapy, cell therapy, and oligonucleotide-based therapy agents are often tested in larger animal models, including rabbit, dog, pig and nonhuman primate models. Testing human cell therapy in animal models is complicated by immune rejections. Furthermore, humans are a very heterogeneous population. Their immune responses to the vectors, altered cells, or cell therapy products may differ or be similar to results obtained in animal models.

Challenges in the development of gene and cell therapy agents: Scientific challenges include the development of gene therapy agents that express the gene in the relevant tissue at the appropriate level for the desired duration of time. There are a lot of issues in that once sentence, and while these issues are easy to state, each one requires extensive research to identify the best means of delivery, how to control sufficient levels or numbers of cells, and factors that influence duration of gene expression or cell survival. After the delivery modalities are determined, identification and engineering of a promoter and control elements (on/off switch and dimmer switch) that will produce the appropriate amount of protein in the target cell can be combined with the relevant gene. This gene cassette is engineered into a vector or introduced into thegenomeof a cell and the properties of the delivery vehicle are tested in different types of cells in tissue culture. Sometimes things go as planned and then studies can be moved onto examination in animal models. In most cases, the gene/cell therapy agent may need to be improved further by adding new control elements to obtain the desired responses in cells and animal models.

Furthermore, the response of the immune system needs to be considered based on the type of gene or cell therapy being undertaken. For example, in gene or cell therapy for cancer, one aim is to selectively boost the existing immune response to cancer cells. In contrast, to treat genetic diseases like hemophilia and cystic fibrosis the goal is for the therapeutic protein to be accepted as an addition to the patients immune system.

If the new gene is inserted into the patients cellularDNA, the intrinsic sequences surrounding the new gene can affect its expression and vice versa. Scientists are now examining short DNA segments that may insulate the new gene from surrounding control elements. Theoretically, these insulator sequences would also reduce the effect of vector control signals in the gene cassette on adjacent cellular genes. Studies are also focusing on means to target insertion of the new gene into safe areas of the genome, to avoid influence on surrounding genes and to reduce the risk of insertional mutagenesis.

Challenges of cell therapy include the harvesting of the appropriate cell populations and expansion or isolation of sufficient cells for one or multiple patients. Cell harvesting may require specific media to maintain the stem cells ability toself-renew and mature into the appropriate cells. Ideally extra cells are taken from the individual receiving therapy. Those additional cells can expand in culture and can be induced to becomepluripotent stem cells(iPS), thus allowing them to assume a wide variety of cell types and avoiding immune rejection by the patient. The long term benefit of stem cell administration requires that the cells be introduced into the correct target tissue and become established functioning cells within the tissue. Several approaches are being investigated to increase the number of stem cells that become established in the relevant tissue.

Another challenge is developing methods that allow manipulation of the stem cells outside the body while maintaining the ability of those cells to produce more cells that mature into the desired specialized cell type. They need to provide the correct number of specialized cells and maintain their normal control of growth and cell division, otherwise there is the risk that these new cells may grow into tumors.

Challenges in funding: In most fields, funding for basic or applied research for gene and cell therapy is available through the National Institutes of Health (NIH) and private foundations. These are usually sufficient to cover the preclinical studies that suggest a potential benefit from a particular gene and cell therapy. Moving into clinical trials remains a huge challenge as it requires additional funding for manufacturing of clinical grade reagents, formal toxicology studies in animals, preparation of extensive regulatory documents, and costs of clinical trials.Biotechnology companies and the NIH are trying to meet the demand for this large expenditure, but many promising therapies are slowed down by lack of funding for this critical next phase.

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Gene & Cell Therapy FAQs | ASGCT - American Society of Gene & Cell ...

Stem Cell Investig. 2019; 6: 19.

1Stem Cell Research Center, Tabriz University of Medical Sciences, Tabriz, Iran;

2Department of Clinical Sciences, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran;

2Department of Clinical Sciences, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran;

3Hematology and Oncology Research Center, Tabriz University of Medical Sciences, Tabriz, Iran

1Stem Cell Research Center, Tabriz University of Medical Sciences, Tabriz, Iran;

2Department of Clinical Sciences, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran;

3Hematology and Oncology Research Center, Tabriz University of Medical Sciences, Tabriz, Iran

Contributions: (I) Conception and design: E Fathi, R Farahzadi; (II) Administrative support: E Fathi, R Farahzadi; (III) Provision of study materials or patients: None; (IV) Collection and assembly of data: R Farahzadi, N Rajabzadeh; (V) Data analysis and interpretation: All authors; (VI) Manuscript writing: All authors; (VII) Final approval of manuscript: All authors.

#These authors contributed equally to this work.

Received 2018 Nov 11; Accepted 2019 Mar 17.

Recent developments in the stem cell biology provided new hopes in treatment of diseases and disorders that yet cannot be treated. Stem cells have the potential to differentiate into various cell types in the body during age. These provide new cells for the body as it grows, and replace specialized cells that are damaged. Since mesenchymal stem cells (MSCs) can be easily harvested from the adipose tissue and can also be cultured and expanded in vitro they have become a good target for tissue regeneration. These cells have been widespread used for cell transplantation in animals and also for clinical trials in humans. The purpose of this review is to provide a summary of our current knowledge regarding the important and types of isolated stem cells from different sources of animal models such as horse, pig, goat, dog, rabbit, cat, rat, mice etc. In this regard, due to the widespread use and lot of attention of MSCs, in this review, we will elaborate on use of MSCs in veterinary medicine as well as in regenerative medicine. Based on the studies in this field, MSCs found wide application in treatment of diseases, such as heart failure, wound healing, tooth regeneration etc.

Keywords: Mesenchymal stem cells (MSCs), animal model, cell-based therapy, regenerative medicine

Stem cells are one of the main cells of the human body that have ability to grow more than 200 types of body cells (1). Stem cells, as non-specialized cells, can be transformed into highly specialized cells in the body (2). In the other words, Stem cells are undifferentiated cells with self-renewal potential, differentiation into several types of cells and excessive proliferation (3). In the past, it was believed that stem cells can only differentiate into mature cells of the same organ. Today, there are many evidences to show that stem cells can differentiate into the other types of cell as well as ectoderm, mesoderm and endoderm. The numbers of stem cells are different in the tissues such as bone marrow, liver, heart, kidney, and etc. (3,4). Over the past 20 years, much attention has been paid to stem cell biology. Therefore, there was a profound increase in the understanding of its characteristics and the therapeutic potential for its application (5). Today, the utilization of these cells in experimental research and cell therapy represents in such disorders including hematological, skin regeneration and heart disease in both human and veterinary medicine (6).The history of stem cells dates back to the 1960s, when Friedenstein and colleagues isolated, cultured and differentiated to osteogenic cell lineage of bone marrow-derived cells from guinea pigs (7). This project created a new perspective on stem cell research. In the following, other researchers discovered that the bone marrow contains fibroblast-like cells with congenic potential in vitro, which were capable of forming colonies (CFU-F) (8). For over 60 years, transplantation of hematopoietic stem cells (HSCs) has been the major curative therapy for several genetic and hematological disorders (9). Almost in 1963, Till and McCulloch described a single progenitor cell type in the bone marrow which expand clonally and give rise to all lineages of hematopoietic cells. This research represented the first characterization of the HSCs (10). Also, the identification of mouse embryonic stem cells (ESCs) in 1981 revolutionized the study of developmental biology, and mice are now used extensively as one of the best option to study stem cell biology in mammals (11). Nevertheless, their application a model, have limitations in the regenerative medicine. But this model, relatively inexpensive and can be easily manipulated genetically (12). Failure to obtain a satisfactory result in the selection of many mouse models, to recapitulate particular human disease phenotypes, has forced researchers to investigate other animal species to be more probably predictive of humans (13). For this purpose, to study the genetic diseases, the pig has been currently determined as one the best option of a large animal model (14).

Stem cells, based on their differentiation ability, are classified into different cell types, including totipotent, pluripotent, multipotent, or unipotent. Also, another classification of these cells are based on the evolutionary stages, including embryonic, fetal, infant or umbilical cord blood and adult stem cells (15). shows an overview of stem cells classifications based on differentiation potency.

An overview of the stem cell classification. Totipotency: after fertilization, embryonic stem cells (ESCs) maintain the ability to form all three germ layers as well as extra-embryonic tissues or placental cells and are termed as totipotent. Pluripotency: these more specialized cells of the blastocyst stage maintain the ability to self-renew and differentiate into the three germ layers and down many lineages but do not form extra-embryonic tissues or placental cells. Multipotency: adult or somatic stem cells are undifferentiated cells found in postnatal tissues. These specialized cells are considered to be multipotent; with very limited ability to self-renew and are committed to lineage species.

Toti-potent cells have the potential for development to any type of cell found in the organism. In the other hand, the capacity of these cells to develop into the three primary germ cell layers of the embryo and into extra-embryonic tissues such as the placenta is remarkable (15).

The pluripotent stem cells are kind of stem cells with the potential for development to approximately all cell types. These cells contain ESCs and cells that are isolated from the mesoderm, endoderm and ectoderm germ layers that are organized in the beginning period of ESC differentiation (15).

The multipotent stem cells have less proliferative potential than the previous two groups and have ability to produce a variety of cells which limited to a germinal layer [such as mesenchymal stem cells (MSCs)] or just a specific cell line (such as HSCs). Adult stem cells are also often in this group. In the word, these cells have the ability to differentiate into a closely related family of cells (15).

Despite the increasing interest in totipotent and pluripotent stem cells, unipotent stem cells have not received the most attention in research. A unipotent stem cell is a cell that can create cells with only one lineage differentiation. Muscle stem cells are one of the example of this type of cell (15). The word uni is derivative from the Latin word unus meaning one. In adult tissues in comparison with other types of stem cells, these cells have the lowest differentiation potential. The unipotent stem cells could create one cell type, in the other word, these cells do not have the self-renewal property. Furthermore, despite their limited differentiation potential, these cells are still candidates for treatment of various diseases (16).

ESCs are self-renewing cells that derived from the inner cell mass of a blastocyst and give rise to all cells during human development. It is mentioned that these cells, including human embryonic cells, could be used as suitable, promising source for cell transplantation and regenerative medicine because of their unique ability to give rise to all somatic cell lineages (17). In the other words, ESCs, pluripotent cells that can differentiate to form the specialized of the various cell types of the body (18). Also, ESCs capture the imagination because they are immortal and have an almost unlimited developmental potential. Due to the ethical limitation on embryo sampling and culture, these cells are used less in research (19).

HSCs are multipotent cells that give rise to blood cells through the process of hematopoiesis (20). These cells reside in the bone marrow and replenish all adult hematopoietic lineages throughout the lifetime of the human and animal (21). Also, these cells can replenish missing or damaged components of the hematopoietic and immunologic system and can withstand freezing for many years (22).The mammalian hematopoietic system containing more than ten different mature cell types that HSCs are one of the most important members of this. The ability to self-renew and multi-potency is another specific feature of these cells (23).

Adult stem cells, as undifferentiated cells, are found in numerous tissues of the body after embryonic development. These cells multiple by cell division to regenerate damaged tissues (24). Recent studies have been shown that adult stem cells may have the ability to differentiate into cell types from various germ layers. For example, bone marrow stem cells which is derived from mesoderm, can differentiate into cell lineage derived mesoderm and endoderm such as into lung, liver, GI tract, skin, etc. (25). Another example of adult stem cells is neural stem cells (NSCs), which is derived from ectoderm and can be differentiate into another lineage such as mesoderm and endoderm (26). Therapeutic potential of adult stem cells in cell therapy and regenerative medicine has been proven (27).

For the first time in the late 1990s, CSCs were identified by John Dick in acute myeloid diseases. CSCs are cancerous cells that found within tumors or hematological cancers. Also, these cells have the characteristics of normal stem cells and can also give rise to all cell types found in a particular cancer sample (28). There is an increasing evidence supporting the CSCs hypothesis. Normal stem cells in an adult living creature are responsible for the repair and regeneration of damaged as well as aged tissues (29). Many investigations have reported that the capability of a tumor to propagate and proliferate relies on a small cellular subpopulation characterized by stem-like properties, named CSCs (30).

Embryonic connective tissue contains so-called mesenchymes, from which with very close interactions of endoderm and ectoderm all other connective and hematopoietic tissues originate, Whereas, MSCs do not differentiate into hematopoietic cell (31). In 1924, Alexander A. Maxi mow used comprehensive histological detection to identify a singular type of precursor cell within mesenchyme that develops into various types of blood cells (32). In general, MSCs are type of cells with potential of multi-lineage differentiation and self-renewal, which exist in many different kinds of tissues and organs such as adipose tissue, bone marrow, skin, peripheral blood, fallopian tube, cord blood, liver and lung et al. (4,5). Today, stem cells are used for different applications. In addition to using these cells in human therapy such as cell transplantation, cell engraftment etc. The use of stem cells in veterinary medicine has also been considered. The purpose of this review is to provide a summary of our current knowledge regarding the important and types of isolated stem cells from different sources of animal models such as horse, pig, goat, dog, rabbit, cat, rat, mice etc. In this regard, due to the widespread use and lot of attention of MSCs, in this review, we will elaborate on use of MSCs in veterinary medicine.

The isolation method, maintenance and culture condition of MSCs differs from the different tissues, these methods as well as characterization of MSCs described as (36). MSCs could be isolated from the various tissues such as adipose tissue, bone marrow, umbilical cord, amniotic fluid etc. (37).

Diagram for adipose tissue-derived mesenchymal stem cell isolation (3).

Diagram for bone marrow-derived MSCs isolation (33). MSC, mesenchymal stem cell.

Diagram for umbilical cord-derived MSCs isolation (34). MSC, mesenchymal stem cell.

Diagram for isolation of amniotic fluid stem cells (AFSCs) (35).

Diagram for MSCs characterization (35). MSC, mesenchymal stem cell.

The diversity of stem cell or MSCs sources and a wide aspect of potential applications of these cells cause to challenge for selecting an appropriate cell type for cell therapy (38). Various diseases in animals have been treated by cell-based therapy. However, there are immunity concerns regarding cell therapy using stem cells. Improving animal models and selecting suitable methods for engraftment and transplantation could help address these subjects, facilitating eventual use of stem cells in the clinic. Therefore, for this purpose, in this section of this review, we provide an overview of the current as well as previous studies for future development of animal models to facilitate the utilization of stem cells in regenerative medicine (14). Significant progress has been made in stem cells-based regenerative medicine, which enables researchers to treat those diseases which cannot be cured by conventional medicines. The unlimited self-renewal and multi-lineage differentiation potential to other types of cells causes stem cells to be frontier in regenerative medicine (24). More researches in regenerative medicine have been focused on human cells including embryonic as well as adult stem cells or maybe somatic cells. Today there are versions of embryo-derived stem cells that have been reprogrammed from adult cells under the title of pluripotent cells (39). Stem cell therapy has been developed in the last decade. Nevertheless, obstacles including unwanted side effects due to the migration of transplanted cells as well as poor cell survival have remained unresolved. In order to overcome these problems, cell therapy has been introduced using biocompatible and biodegradable biomaterials to reduce cell loss and long-term in vitro retention of stem cells.

Currently in clinical trials, these biomaterials are widely used in drug and cell-delivery systems, regenerative medicine and tissue engineering in which to prevent the long-term survival of foreign substances in the body the release of cells are controlled (40).

Today, the incidence and prevalence of heart failure in human societies is a major and increasing problem that unfortunately has a poor prognosis. For decades, MSCs have been used for cardiovascular regenerative therapy as one of the potential therapeutic agents (41). Dhein et al. [2006] found that autologous bone marrow-derived mesenchymal stem cells (BMSCs) transplantation improves cardiac function in non-ischemic cardiomyopathy in a rabbit model. In one study, Davies et al. [2010] reported that transplantation of cord blood stem cells in ovine model of heart failure, enhanced the function of heart through improvement of right ventricular mass, both systolic and diastolic right heart function (42). In another study, Nagaya et al. [2005] found that MSCs dilated cardiomyopathy (DCM), possibly by inducing angiogenesis and preventing cardial fibrosis. MSCs have a tremendous beneficial effect in cell transplantation including in differentiating cardiomyocytes, vascular endothelial cells, and providing anti-apoptotic as well angiogenic mediators (43). Roura et al. [2015] shown that umbilical cord blood mesenchymal stem cells (UCBMSCs) are envisioned as attractive therapeutic candidates against human disorders progressing with vascular deficit (44). Ammar et al., [2015] compared BMSCs with adipose tissue-derived MSCs (ADSCs). It was demonstrated that both BMSCs and ADSCs were equally effective in mitigating doxorubicin-induced cardiac dysfunction through decreasing collagen deposition and promoting angiogenesis (45).

There are many advantages of small animal models usage in cardiovascular research compared with large animal models. Small model of animals has a short life span, which allow the researchers to follow the natural history of the disease at an accelerated pace. Some advantages and disadvantages are listed in (46).

Despite of the small animal model, large animal models are suitable models for studies of human diseases. Some advantages and disadvantages of using large animal models in a study protocol planning was elaborated in (47).

Chronic wound is one of the most common problem and causes significant distress to patients (48). Among the types of tissues that stem cells derived it, dental tissuederived MSCs provide good sources of cytokines and growth factors that promote wound healing. The results of previous studies showed that stem cells derived deciduous teeth of the horse might be a novel approach for wound care and might be applied in clinical treatment of non-healing wounds (49). However, the treatment with stem cells derived deciduous teeth needs more research to understand the underlying mechanisms of effective growth factors which contribute to the wound healing processes (50). This preliminary investigation suggests that deciduous teeth-derived stem cells have the potential to promote wound healing in rabbit excisional wound models (49). In the another study, Lin et al. [2013] worked on the mouse animal model and showed that ADSCs present a potentially viable matrix for full-thickness defect wound healing (51).

Many studies have been done on dental reconstruction with MSCs. In one study, Khorsand et al. [2013] reported that dental pulp-derived stem cells (DPSCs) could promote periodontal regeneration in canine model. Also, it was shown that canine DPSCs were successfully isolated and had the rapid proliferation and multi-lineage differentiation capacity (52). Other application of dental-derived stem cells is shown in .

Diagram for application of dental stem cell in dentistry/regenerative medicine (53).

As noted above, stem cells have different therapeutic applications and self-renewal capability. These cells can also differentiate into the different cell types. There is now a great hope that stem cells can be used to treat diseases such as Alzheimer, Parkinson and other serious diseases. In stem cell-based therapy, ESCs are essentially targeted to differentiate into functional neural cells. Today, a specific category of stem cells called induced pluripotent stem (iPS) cells are being used and tested to generate functional dopamine neurons for treating Parkinson's disease of a rat animal model. In addition, NSC as well as MSCs are being used in neurodegenerative disorder therapies for Alzheimers disease, Parkinsons disease, and stroke (54). Previous studies have shown that BMSCs could reduce brain amyloid deposition and accelerate the activation of microglia in an acutely induced Alzheimers disease in mouse animal model. Lee et al. [2009] reported that BMSCs can increase the number of activated microglia, which effective therapeutic vehicle to reduce A deposits in AD patients (55). In confirmation of previous study, Liu et al. [2015] showed that transplantation of BMSCs in brain of mouse model of Alzheimers disease cause to decrease in amyloid beta deposition, increase in brain-derived neurotrophic factor (BDNF) levels and improvements in social recognition (56). In addition of BMSCs, NSCs have been proposed as tools for treating neurodegeneration disease because of their capability to create an appropriate cell types which transplanted. kerud et al. [2001] demonstrated that NSCs efficiently express high level of glial cell line-derived neurotrophic factor (GDNF) in vivo, suggesting a use of these cells in the treatment of neurodegenerative disorders, including Parkinsons disease (57). In the following, Venkataramana et al. [2010] transplanted BMSCs into the sub lateral ventricular zones of seven Parkinsons disease patients and reported encouraging results (58).

The human body is fortified with specialized cells named MSCs, which has the ability to self-renew and differentiate into various cell types including, adipocyte, osteocyte, chondrocyte, neurons etc. In addition to mentioned properties, these cells can be easily isolated, safely transplanted to injured sites and have the immune regulatory properties. Numerous in vitro and in vivo studies in animal models have successfully demonstrated the potential of MSCs for various diseases; however, the clinical outcomes are not very encouraging. Based on the studies in the field of stem cells, MSCs find wide application in treatment of diseases, such as heart failure, wound healing, tooth regeneration and etc. In addition, these cells are particularly important in the treatment of the sub-branch neurodegenerative diseases like Alzheimer and Parkinson.

The authors wish to thank staff of the Stem Cell Research Center, Tabriz University of Medical Sciences, Tabriz, Iran.

Funding: The project described was supported by Grant Number IR.TBZMED.REC.1396.1218 from the Stem Cell Research Center, Tabriz University of Medical Sciences, Tabriz, Iran.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Conflicts of Interest: The authors have no conflicts of interest to declare.

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Stem cell-based regenerative medicine - PMC

Introduction

Given the multi-lineage differentiation abilities of mesenchymal stem cells (MSCs) isolated from different tissues and organs, MSCs have been widely used in various medical fields, particularly regenerative medicine.13 The representative sources of MSCs are bone marrow, adipose, periodontal, muscle, and umbilical cord blood.410 Interestingly, slight differences have been reported in the characteristics of MSCs depending on the different sources, including their population in source tissues, immunosuppressive activities, proliferation, and resistance to cellular aging.11 Bone marrow-derived MSCs (BM-MSCs) are the most intensively studied and show clinically promising results for cartilage and bone regeneration.11 However, the isolation procedures for BM-MSCs are complicated because bone marrow contains a relatively small fraction of MSCs (0.0010.01% of the cells in bone marrow).12 Furthermore, bone marrow aspiration to harvest MSCs in human bones is a painful procedure and the slower proliferation rate of BM-MSCs is a clinical limitation.13 In comparison with BM-MSCs, adipose-derived MSCs (AD-MSCs) are relatively easy to collect and can produce up to 500 times the cell population of BM-MSCs.14 AD-MSCs showed a greater ability to regenerate damaged cartilage and bone tissues with increased immunosuppressive ability.14,15 Umbilical cord blood-derived MSCs (UC-MSCs) proliferate faster than BM-MSCs and are resistant to significant cellular aging.11

MSCs have been investigated and gained worldwide attention as potential therapeutic candidates for incurable diseases such as arthritis, spinal cord injury, and cardiac disease.3,1623 In particular, the inherent tropism of MSCs to inflammatory sites has been thoroughly studied.24 This inherent tropism, also known as homing ability, originates from the recognition of various chemokine sources in inflamed tissues, where profiled chemokines are continuously secreted and the MSCs migrate to the chemokines in a concentration-dependent manner.24 Rheumatoid arthritis (RA) is a representative inflammatory disease that primarily causes inflammation in the joints, and this long-term autoimmune disorder causes worsening pain and stiffness following rest. RA affects approximately 24.5 million people as of 2015, but only symptomatic treatments such as pain medications, steroids, and nonsteroidal anti-inflammatory drugs (NSAIDs), or slow-acting drugs that inhibit the rapid progression of RA, such as disease-modifying antirheumatic drugs (DMARDs) are currently available. However, RA drugs have adverse side effects, including hepatitis, osteoporosis, skeletal fracture, steroid-induced arthroplasty, Cushings syndrome, gastrointestinal (GI) intolerance, and bleeding.2527 Thus, MSCs are rapidly emerging as the next generation of arthritis treatment because they not only recognize and migrate toward chemokines secreted in the inflamed joints but also regulate inflammatory progress and repair damaged cells.28

However, MSCs are associated with many challenges that need to be overcome before they can be used in clinical settings.2931 One of the main challenges is the selective accumulation of systemically administered MSCs in the lungs and liver when they are administered intravenously, leading to insufficient concentrations of MSCs in the target tissues.32,33 In addition, most of the administered MSCs are typically initially captured by macrophages in the lungs, liver, and spleen.3234 Importantly, the viability and migration ability of MSCs injected in vivo differed from results previously reported as favorable therapeutic effects and migration efficiency in vitro.35

To improve the delivery of MSCs, researchers have focused on chemokines, which are responsible for MSCs ability to move.36 The chemokine receptors are the key proteins on MSCs that recognize chemokines, and genetic engineering of MSCs to overexpress the chemokine receptor can improve the homing ability, thus enhancing their therapeutic efficacy.37 Genetic engineering is a convenient tool for modifying native or non-native genes, and several technologies for genetic engineering exist, including genome editing, gene knockdown, and replacement with various vectors.38,39 However, safety issues that prevent clinical use persist, for example, genome integration, off-target effects, and induction of immune response.40 In this regard, MSC mimicking nanoencapsulations can be an alternative strategy for maintaining the homing ability of MSCs and overcoming the current safety issues.4143 Nanoencapsulation involves entrapping the core nanoparticles of solids or liquids within nanometer-sized capsules of secondary materials.44

MSC mimicking nanoencapsulation uses the MSC membrane fraction as the capsule and targeting molecules, that is chemokine receptors, with several types of nanoparticles, as the core.45,46 MSC mimicking nanoencapsulation consists of MSC membrane-coated nanoparticles, MSC-derived artificial ectosomes, and MSC membrane-fused liposomes. Nano drug delivery is an emerging field that has attracted significant interest due to its unique characteristics and paved the way for several unique applications that might solve many problems in medicine. In particular, the nanoscale size of nanoparticles (NPs) enhances cellular uptake and can optimize intracellular pathways due to their intrinsic physicochemical properties, and can therefore increase drug delivery to target tissues.47,48 However, the inherent targeting ability resulting from the physicochemical properties of NPs is not enough to target specific tissues or damaged tissues, and additional studies on additional ligands that can bind to surface receptors on target cells or tissues have been performed to improve the targeting ability of NPs.49 Likewise, nanoencapsulation with cell membranes with targeting molecules and encapsulation of the core NPs with cell membranes confer the targeting ability of the source cell to the NPs.50,51 Thus, MSC mimicking nanoencapsulation can mimic the superior targeting ability of MSCs and confer the advantages of each core NP. In addition, MSC mimicking nanoencapsulations have improved circulation time and camouflaging from phagocytes.52

This review discusses the mechanism of MSC migration to inflammatory sites, addresses the potential strategy for improving the tropism of MSCs using genetic engineering, and discusses the promising therapeutic agent, MSC mimicking nanoencapsulations.

The MSC migration mechanism can be exploited for diverse clinical applications.53 The MSC migration mechanism can be divided into five stages: rolling by selectin, activation of MSCs by chemokines, stopping cell rolling by integrin, transcellular migration, and migration to the damaged site (Figure 1).54,55 Chemokines are secreted naturally by various cells such as tumor cells, stromal cells, and inflammatory cells, maintaining high chemokine concentrations in target cells at the target tissue and inducing signal cascades.5658 Likewise, MSCs express a variety of chemokine receptors, allowing them to migrate and be used as new targeting vectors.5961 MSC migration accelerates depending on the concentration of chemokines, which are the most important factors in the stem cell homing mechanism.62,63 Chemokines consist of various cytokine subfamilies that are closely associated with the migration of immune cells. Chemokines are divided into four classes based on the locations of the two cysteine (C) residues: CC-chemokines, CXC-chemokine, C-chemokine, and CX3 Chemokine.64,65 Each chemokine binds to various MSC receptors and the binding induces a chemokine signaling cascade (Table 1).56,66

Table 1 Chemokine and Chemokine Receptors for Different Chemokine Families

Figure 1 Representation of stem cell homing mechanism.

The mechanisms underlying MSC and leukocyte migration are similar in terms of their migratory dynamics.55 P-selectin glycoprotein ligand-1 (PSGL-1) and E-selectin ligand-1 (ESL-1) are major proteins involved in leukocyte migration that interact with P-selectin and E-selectin present in vascular endothelial cells. However, these promoters are not present in MSCs (Figure 2).53,67

Figure 2 Differences in adhesion protein molecules between leukocytes and mesenchymal stem cells during rolling stages and rolling arrest stage of MSC. (A) The rolling stage of leukocytes starts with adhesion to endothelium with ESL-1 and PSGL-1 on leukocytes. (B) The rolling stage of MSC starts with the adhesion to endothelium with Galectin-1 and CD24 on MSC, and the rolling arrest stage was caused by chemokines that were encountered in the rolling stage and VLA-4 with a high affinity for VACM present in endothelial cells.

Abbreviations: ESL-1, E-selectin ligand-1; PSGL-1, P-selectin glycoprotein ligand-1 VLA-4, very late antigen-4; VCAM, vascular cell adhesion molecule-1.

The initial rolling is facilitated by selectins expressed on the surface of endothelial cells. Various glycoproteins on the surface of MSCs can bind to the selectins and continue the rolling process.68 However, the mechanism of binding of the glycoprotein on MSCs to the selectins is still unclear.69,70 P-selectins and E-selectins, major cell-cell adhesion molecules expressed by endothelial cells, adhere to migrated cells adjacent to endothelial cells and can trigger the rolling process.71 For leukocyte migration, P-selectin glycoprotein ligand-1 (PSGL-1) and E-selectin ligand-1 (ESL-1) expressed on the membranes of leukocytes interact with P-selectins and E-selectins on the endothelial cells, initiating the process.72,73 As already mentioned, MSCs express neither PSGL-1 nor ESL-1. Instead, they express galectin-1 and CD24 on their surfaces, and these bind to E-selectin or P-selectin (Figure 2).7476

In the migratory activation step, MSC receptors are activated in response to inflammatory cytokines, including CXCL12, CXCL8, CXCL4, CCL2, and CCL7.77 The corresponding activation of chemokine receptors of MSCs in response to inflammatory cytokines results in an accumulation of MSCs.58,78 For example, inflamed tissues release inflammatory cytokines,79 and specifically, fibroblasts release CXCL12, which further induces the accumulation of MSCs through ligandreceptor interaction after exposure to hypoxia and cytokine-rich environments in the rat model of inflammation.7982 Previous studies have reported that overexpressing CXCR4, which is a receptor to recognize CXCL12, in MSCs improves the homing ability of MSCs toward inflamed sites.83,84 In short, cytokines are significantly involved in the homing mechanism of MSCs.53

The rolling arrest stage is facilitated by integrin 41 (VLA-4) on MSC.85 VLA-4 is expressed by MSCs which are first activated by CXCL-12 and TNF- chemokines, and activated VLA-4 binds to VCAM-1 expressed on endothelial cells to stop the rotational movement (Figure 2).86,87

Karp et al categorized the migration of MSCs as either systemic homing or non-systemic homing. Systemic homing refers to the process of migration through blood vessels and then across the vascular endothelium near the inflamed site.67,88 The process of migration after passing through the vessels or local injection is called non-systemic homing. In non-systemic migration, stem cells migrate through a chemokine concentration gradient (Figure 3).89 MSCs secrete matrix metalloproteinases (MMPs) during migration. The mechanism underlying MSC migration is currently undefined but MSC migration can be advanced by remodeling the matrix through the secretion of various enzymes.9093 The migration of MSCs to the damaged area is induced by chemokines released from the injured site, such as IL-8, TNF-, insulin-like growth factor (IGF-1), and platelet-derived growth factors (PDGF).9496 MSCs migrate toward the damaged area following a chemokine concentration gradient.87

Figure 3 Differences between systemic and non-systemic homing mechanisms. Both systemic and non-systemic homing to the extracellular matrix and stem cells to their destination, MSCs secrete MMPs and remodel the extracellular matrix.

Abbreviation: MMP, matrix metalloproteinase.

RA is a chronic inflammatory autoimmune disease characterized by distinct painful stiff joints and movement disorders.97 RA affects approximately 1% of the worlds population.98 RA is primarily induced by macrophages, which are involved in the innate immune response and are also involved in adaptive immune responses, together with B cells and T cells.99 Inflammatory diseases are caused by high levels of inflammatory cytokines and a hypoxic low-pH environment in the joints.100,101 Fibroblast-like synoviocytes (FLSs) and accumulated macrophages and neutrophils in the synovium of inflamed joints also express various chemokines.102,103 Chemokines from inflammatory reactions can induce migration of white blood cells and stem cells, which are involved in angiogenesis around joints.101,104,105 More than 50 chemokines are present in the rheumatoid synovial membrane (Table 2). Of the chemokines in the synovium, CXCL12, MIP1-a, CXCL8, and PDGF are the main ones that attract MSCs.106 In the RA environment, CXCL12, a ligand for CXCR4 on MSCs, had 10.71 times higher levels of chemokines than in the normal synovial cell environment. MIP-1a, a chemokine that gathers inflammatory cells, is a ligand for CCR1, which is normally expressed on MSC.107,108 CXCL8 is a ligand for CXCR1 and CXCR2 on MSCs and induces the migration of neutrophils and macrophages, leading to ROS in synovial cells.59 PDGF is a regulatory peptide that is upregulated in the synovial tissue of RA patients.109 PDGF induces greater MSC migration than CXCL12.110 Importantly, stem cells not only have the homing ability to inflamed joints but also have potential as cell therapy with the anti-apoptotic, anti-catabolic, and anti-fibrotic effect of MSC.111 In preclinical trials, MSC treatment has been extensively investigated in collagen-induced arthritis (CIA), a common autoimmune animal model used to study RA. In the RA model, MSCs downregulated inflammatory cytokines such as IFN-, TNF-, IL-4, IL-12, and IL1, and antibodies against collagen, while anti-inflammatory cytokines, such as tumor necrosis factor-inducible gene 6 protein (TSG-6), prostaglandin E2 (PGE2), transforming growth factor-beta (TGF-), IL-10, and IL-6, were upregulated.112116

Table 2 Rheumatoid Arthritis (RA) Chemokines Present in the Pathological Environment and Chemokine Receptors Present in Mesenchymal Stem Cells

Genetic engineering can improve the therapeutic potential of MSCs, including long-term survival, angiogenesis, differentiation into specific lineages, anti- and pro-inflammatory activity, and migratory properties (Figure 4).117,118 Although MSCs already have an intrinsic homing ability, the targeting ability of MSCs and their derivatives, such as membrane vesicles, which are utilized to produce MSC mimicking nanoencapsulation, can be enhanced.118 The therapeutic potential of MSCs can be magnified by reprogramming MSCs via upregulation or downregulation of their native genes, resulting in controlled production of the target protein, or by introducing foreign genes that enable MSCs to express native or non-native products, for example, non-native soluble tumor necrosis factor (TNF) receptor 2 can inhibit TNF-alpha signaling in RA therapies.28

Figure 4 Genetic engineering of mesenchymal stem cells to enhance therapeutic efficacy.

Abbreviations: Sfrp2, secreted frizzled-related protein 2; IGF1, insulin-like growth factor 1; IL-2, interleukin-2; IL-12, interleukin-12; IFN-, interferon-beta; CX3CL1, C-X3-C motif chemokine ligand 1; VEGF, vascular endothelial growth factor; HGF, human growth factor; FGF, fibroblast growth factor; IL-10, interleukin-10; IL-4, interleukin-4; IL18BP, interleukin-18-binding protein; IFN-, interferon-alpha; SDF1, stromal cell-derived factor 1; CXCR4, C-X-C motif chemokine receptor 4; CCR1, C-C motif chemokine receptor 1; BMP2, bone morphogenetic protein 2; mHCN2, mouse hyperpolarization-activated cyclic nucleotide-gated.

MSCs can be genetically engineered using different techniques, including by introducing particular genes into the nucleus of MSCs or editing the genome of MSCs (Figure 5).119 Foreign genes can be transferred into MSCs using liposomes (chemical method), electroporation (physical method), or viral delivery (biological method). Cationic liposomes, also known as lipoplexes, can stably compact negatively charged nucleic acids, leading to the formation of nanomeric vesicular structure.120 Cationic liposomes are commonly produced with a combination of a cationic lipid such as DOTAP, DOTMA, DOGS, DOSPA, and neutral lipids, such as DOPE and cholesterol.121 These liposomes are stable enough to protect their bound nucleic acids from degradation and are competent to enter cells via endocytosis.120 Electroporation briefly creates holes in the cell membrane using an electric field of 1020 kV/cm, and the holes are then rapidly closed by the cells membrane repair mechanism.122 Even though the electric shock induces irreversible cell damage and non-specific transport into the cytoplasm leads to cell death, electroporation ensures successful gene delivery regardless of the target cell or organism. Viral vectors, which are derived from adenovirus, adeno-associated virus (AAV), or lentivirus (LV), have been used to introduce specific genes into MSCs. Recombinant lentiviral vectors are the most widely used systems due to their high tropism to dividing and non-dividing cells, transduction efficiency, and stable expression of transgenes in MSCs, but the random genome integration of transgenes can be an obstacle in clinical applications.123 Adenovirus and AAV systems are appropriate alternative strategies because currently available strains do not have broad genome integration and a strong immune response, unlike LV, thus increasing success and safety in clinical trials.124 As a representative, the Oxford-AstraZeneca COVID-19 vaccine, which has been authorized in 71 countries as a vaccine for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which spread globally and led to the current pandemic, transfers the spike protein gene using an adenovirus-based viral vector.125 Furthermore, there are two AAV-based gene therapies: Luxturna for rare inherited retinal dystrophy and Zolgensma for spinal muscular atrophy.126

Figure 5 Genetic engineering techniques used in the production of bioengineered mesenchymal stem cells.

Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 were recently used for genome editing and modification because of their simpler design and higher efficiency for genome editing, however, there are safety issues such as off-target effects that induce mutations at sites other than the intended target site.127 The foreign gene is then commonly transferred into non-integrating forms such as plasmid DNA and messenger RNA (mRNA).128

The gene expression machinery can also be manipulated at the cytoplasmic level through RNA interference (RNAi) technology, inhibition of gene expression, or translation using neutralizing targeted mRNA molecules with sequence-specific small RNA molecules such as small interfering RNA (siRNA) or microRNA (miRNA).129 These small RNAs can form enzyme complexes that degrade mRNA molecules and thus decrease their activity by inhibiting translation. Moreover, the pre-transcriptional silencing mechanism of RNAi can induce DNA methylation at genomic positions complementary to siRNA or miRNA with enzyme complexes.

CXC chemokine receptor 4 (CXCR4) is one of the most potent chemokine receptors that is genetically engineered to enhance the migratory properties of MSCs.130 CXCR4 is a chemokine receptor specific for stromal-derived factor-1 (SDF-1), also known as CXC motif chemokine 12 (CXCL12), which is produced by damaged tissues, such as the area of inflammatory bone destruction.131 Several studies on engineering MSCs to increase the expression of the CXCR4 gene have reported a higher density of the CXCR4 receptor on their outer cell membrane and effectively increased the migration of MSCs toward SDF-1.83,132,133 CXC chemokine receptor 7 (CXCR7) also had a high affinity for SDF-1, thus the SDF-1/CXCR7 signaling axis was used to engineer the MSCs.134 CXCR7-overexpressing MSCs in a cerebral ischemia-reperfusion rat hippocampus model promoted migration based on an SDF-1 gradient, cooperating with the SDF-1/CXCR4 signaling axis (Figure 6).37

Figure 6 Engineered mesenchymal stem cells with enhanced migratory abilities.

Abbreviations: CXCR4, C-X-C motif chemokine receptor 4; CXCR7, C-X-C motif chemokine receptor 7; SDF1, stromal cell-derived factor 1; CXCR1, C-X-C motif chemokine receptor 1; IL-8, interleukin-8; Aqp1, aquaporin 1; FAK, focal adhesion kinase.

CXC chemokine receptor 1 (CXCR1) enhances MSC migratory properties.59 CXCR1 is a receptor for IL-8, which is the primary cytokine involved in the recruitment of neutrophils to the site of damage or infection.135 In particular, the IL-8/CXCR1 axis is a key factor for the migration of MSCs toward human glioma cell lines, such as U-87 MG, LN18, U138, and U251, and CXCR1-overexpressing MSCs showed a superior capacity to migrate toward glioma cells and tumors in mice bearing intracranial human gliomas.136

The migratory properties of MSCs were also controlled via aquaporin-1 (Aqp1), which is a water channel molecule that transports water across the cell membrane and regulates endothelial cell migration.137 Aqp1-overexpressing MSCs showed enhanced migration to fracture gap of a rat fracture model with upregulated focal adhesion kinase (FAK) and -catenin, which are important regulators of cell migration.138

Nur77, also known as nerve growth factor IB or NR4A1, and nuclear receptor-related 1 (Nurr1), can play a role in improving the migratory capabilities of MSCs.139,140 The migrating MSCs expressed higher levels of Nur77 and Nurr1 than the non-migrating MSCs, and overexpression of these two nuclear receptors functioning as transcription factors enhanced the migration of MSCs toward SDF-1. The migration of cells is closely related to the cell cycle, and normally, cells in the late S or G2/M phase do not migrate.141 The overexpression of Nur77 and Nurr1 increased the proportion of MSCs in the G0/G1-phase similar to the results of migrating MSCs had more cells in the G1-phase.

MSC mimicking nanoencapsulations are nanoparticles combined with MSC membrane vesicles and these NPs have the greatest advantages as drug delivery systems due to the sustained homing ability of MSCs as well as the advantages of NPs. Particles sized 10150 nm have great advantages in drug delivery systems because they can pass more freely through the cell membrane by the interaction with biomolecules, such as clathrin and caveolin, to facilitate uptake across the cell membrane compared with micron-sized materials.142,143 Various materials have been used to formulate NPs, including silica, polymers, metals, and lipids.144,145 NPs have an inherent ability, called passive targeting, to accumulate at specific sites based on their physicochemical properties such as size, surface charge, surface hydrophilicity, and geometry.146148 However, physicochemical properties are not enough to target specific tissues or damaged tissues, and thus active targeting is a clinically approved strategy involving the addition of ligands that can bind to surface receptors on target cells or tissues.149,150 MSC mimicking nanoencapsulation uses natural or genetically engineered MSC membranes to coat synthetic NPs, producing artificial ectosomes and fusing them with liposomes to increase their targeting ability (Figure 7).151 Especially, MSCs have been studied for targeting inflammation and regenerative drugs, and the mechanism and efficacy of migration toward inflamed tissues have been actively investigated.152 MSC mimicking nanoencapsulation can mimic the well-known migration ability of MSCs and can be equally utilized without safety issues from the direct application of using MSCs. Furthermore, cell membrane encapsulations have a wide range of functions, including prolonged blood circulation time and increased active targeting efficacy from the source cells.153,154 MSC mimicking encapsulations enter recipient cells using multiple pathways.155 MSC mimicking encapsulations can fuse directly with the plasma membrane and can also be taken up through phagocytosis, micropinocytosis, and endocytosis mediated by caveolin or clathrin.156 MSC mimicking encapsulations can be internalized in a highly cell type-specific manner that depends on the recognition of membrane surface molecules by the cell or tissue.157 For example, endothelial colony-forming cell (ECFC)-derived exosomes were shown CXCR4/SDF-1 interaction and enhanced delivery toward the ischemic kidney, and Tspan8-alpha4 complex on lymph node stroma derived extracellular vesicles induced selective uptake by endothelial cells or pancreatic cells with CD54, serving as a major ligand.158,159 Therefore, different source cells may contain protein signals that serve as ligands for other cells, and these receptorligand interactions maximized targeted delivery of NPs.160 This natural mechanism inspired the application of MSC membranes to confer active targeting to NPs.

Figure 7 Mesenchymal stem cell mimicking nanoencapsulation.

Cell membrane-coated NPs (CMCNPs) are biomimetic strategies developed to mimic the properties of cell membranes derived from natural cells such as erythrocytes, white blood cells, cancer cells, stem cells, platelets, or bacterial cells with an NP core.161 Core NPs made of polymer, silica, and metal have been evaluated in attempts to overcome the limitations of conventional drug delivery systems but there are also issues of toxicity and reduced biocompatibility associated with the surface properties of NPs.162,163 Therefore, only a small number of NPs have been approved for medical application by the FDA.164 Coating with cell membrane can enhance the biocompatibility of NPs by improving immune evasion, enhancing circulation time, reducing RES clearance, preventing serum protein adsorption by mimicking cell glycocalyx, which are chemical determinants of self at the surfaces of cells.151,165 Furthermore, the migratory properties of MSCs can also be transferred to NPs by coating them with the cell membrane.45 Coating NPs with MSC membranes not only enhances biocompatibility but also maximizes the therapeutic effect of NPs by mimicking the targeting ability of MSCs.166 Cell membrane-coated NPs are prepared in three steps: extraction of cell membrane vesicles from the source cells, synthesis of the core NPs, and fusion of the membrane vesicles and core NPs to produce cell membrane-coated NPs (Figure 8).167 Cell membrane vesicles, including extracellular vesicles (EVs), can be harvested through cell lysis, mechanical disruption, and centrifugation to isolate, purify the cell membrane vesicles, and remove intracellular components.168 All the processes must be conducted under cold conditions, with protease inhibitors to minimize the denaturation of integral membrane proteins. Cell lysis, which is classically performed using mechanical lysis, including homogenization, sonication, or extrusion followed by differential velocity centrifugation, is necessary to remove intracellular components. Cytochalasin B (CB), a drug that affects cytoskeletonmembrane interactions, induces secretion of membrane vesicles from source cells and has been used to extract the cell membrane.169 The membrane functions of the source cells are preserved in CB-induced vesicles, forming biologically active surface receptors and ion pumps.170 Furthermore, CB-induced vesicles can encapsulate drugs and NPs successfully, and the vesicles can be harvested by centrifugation without a purification step to remove nuclei and cytoplasm.171 Clinically translatable membrane vesicles require scalable production of high volumes of homogeneous vesicles within a short period. Although mechanical methods (eg, shear stress, ultrasonication, or extrusion) are utilized, CB-induced vesicles have shown potential for generating membrane encapsulation for nano-vectors.168 The advantages of CB-induced vesicles versus other methods are compared in Table 3.

Table 3 Comparison of Membrane Vesicle Production Methods

Figure 8 MSC membrane-coated nanoparticles.

Abbreviations: EVs, extracellular vesicles; NPs, nanoparticles.

After extracting cell membrane vesicles, synthesized core NPs are coated with cell membranes, including surface proteins.172 Polymer NPs and inorganic NPs are adopted as materials for the core NPs of CMCNPs, and generally, polylactic-co-glycolic acid (PLGA), polylactic acid (PLA), chitosan, and gelatin are used. PLGA has been approved by FDA is the most common polymer of NPs.173 Biodegradable polymer NPs have gained considerable attention in nanomedicine due to their biocompatibility, nontoxic properties, and the ability to modify their surface as a drug carrier.174 Inorganic NPs are composed of gold, iron, copper, and silicon, which have hydrophilic, biocompatible, and highly stable properties compared with organic materials.175 Furthermore, some photosensitive inorganic NPs have the potential for use in photothermal therapy (PTT) and photodynamic therapy (PDT).176 The fusion of cell membrane vesicles and core NPs is primarily achieved via extrusion or sonication.165 Cell membrane coating of NPs using mechanical extrusion is based on a different-sized porous membrane where core NPs and vesicles are forced to generate vesicle-particle fusion.177 Ultrasonic waves are applied to induce the fusion of vesicles and NPs. However, ultrasonic frequencies need to be optimized to improve fusion efficiency and minimize drug loss and protein degradation.178

CMCNPs have extensively employed to target and treat cancer using the membranes obtained from red blood cell (RBC), platelet and cancer cell.165 In addition, membrane from MSC also utilized to target tumor and ischemia with various types of core NPs, such as MSC membrane coated PLGA NPs targeting liver tumors, MSC membrane coated gelatin nanogels targeting HeLa cell, MSC membrane coated silica NPs targeting HeLa cell, MSC membrane coated PLGA NPs targeting hindlimb ischemia, and MSC membrane coated iron oxide NPs for targeting the ischemic brain.179183 However, there are few studies on CMCNPs using stem cells for the treatment of arthritis. Increased targeting ability to arthritis was introduced using MSC-derived EVs and NPs.184,185 MSC membrane-coated NPs are proming strategy for clearing raised concerns from direct use of MSC (with or without NPs) in terms of toxicity, reduced biocompatibility, and poor targeting ability of NPs for the treatment of arthritis.

Exosomes are natural NPs that range in size from 40 nm to 120 nm and are derived from the multivesicular body (MVB), which is an endosome defined by intraluminal vesicles (ILVs) that bud inward into the endosomal lumen, fuse with the cell surface, and are then released as exosomes.186 Because of their ability to express receptors on their surfaces, MSC-derived exosomes are also considered potential candidates for targeting.187 Exosomes are commonly referred to as intracellular communication molecules that transfer various compounds through physiological mechanisms such as immune response, neural communication, and antigen presentation in diseases such as cancer, cardiovascular disease, diabetes, and inflammation.188

However, there are several limitations to the application of exosomes as targeted therapeutic carriers. First, the limited reproducibility of exosomes is a major challenge. In this field, the standardized techniques for isolation and purification of exosomes are lacking, and conventional methods containing multi-step ultracentrifugation often lead to contamination of other types of EVs. Furthermore, exosomes extracted from cell cultures can vary and display inconsistent properties even when the same type of donor cells were used.189 Second, precise characterization studies of exosomes are needed. Unknown properties of exosomes can hinder therapeutic efficiencies, for example, when using exosomes as cancer therapeutics, the use of cancer cell-derived exosomes should be avoided because cancer cell-derived exosomes may contain oncogenic factors that may contribute to cancer progression.190 Finally, cost-effective methods for the large-scale production of exosomes are needed for clinical application. The yield of exosomes is much lower than EVs. Depending on the exosome secretion capacity of donor cells, the yield of exosomes is restricted, and large-scale cell culture technology for the production of exosomes is high difficulty and costly and isolation of exosomes is the time-consuming and low-efficient method.156

Ectosome is an EV generated by outward budding from the plasma membrane followed by pinching off and release to the extracellular parts. Recently, artificially produced ectosome utilized as an alternative to exosomes in targeted therapeutics due to stable productivity regardless of cell type compared with conventional exosome. Artificial ectosomes, containing modified cargo and targeting molecules have recently been introduced for specific purposes (Figure 9).191,192 Artificial ectosomes are typically prepared by breaking bigger cells or cell membrane fractions into smaller ectosomes, similar size to natural exosomes, containing modified cargo such as RNA molecules, which control specific genes, and chemical drugs such as anticancer drugs.193 Naturally secreted exosomes in conditioned media from modified source cells can be harvested by differential ultracentrifugation, density gradients, precipitation, filtration, and size exclusion chromatography for exosome separation.194 Even though there are several commercial kits for isolating exosomes simply and easily, challenges in compliant scalable production on a large scale, including purity, homogeneity, and reproducibility, have made it difficult to use naturally secreted exosomes in clinical settings.195 Therefore, artificially produced ectosomes are appropriate for use in clinical applications, with novel production methods that can meet clinical production criteria. Production of artificially produced ectosomes begins by breaking the cell membrane fraction of cultured cells and then using them to produce cell membrane vesicles to form ectosomes. As mentioned above, cell membrane vesicles are extracted from source cells in several ways, and cell membrane vesicles are extracted through polycarbonate membrane filters to reduce the mean size to a size similar to that of natural exosomes.196 Furthermore, specific microfluidic devices mounted on microblades (fabricated in silicon nitride) enable direct slicing of living cells as they flow through the hydrophilic microchannels of the device.197 The sliced cell fraction reassembles and forms ectosomes. There are several strategies for loading exogenous therapeutic cargos such as drugs, DNA, RNA, lipids, metabolites, and proteins, into exosomes or artificial ectosomes in vitro: electroporation, incubation for passive loading of cargo or active loading with membrane permeabilizer, freeze and thaw cycles, sonication, and extrusion.198 In addition, protein or RNA molecules can be loaded by co-expressing them in source cells via bio-engineering, and proteins designed to interact with the protein inside the cell membrane can be loaded actively into exosomes or artificial ectosomes.157 Targeting molecules at the surface of exosomes or artificial ectosomes can also be engineered in a manner similar to the genetic engineering of MSCs.

Figure 9 Mesenchymal stem cell-derived exosomes and artificial ectosomes. (A) Wound healing effect of MSC-derived exosomes and artificial ectosomes,231 (B) treatment of organ injuries by MSC-derived exosomes and artificial ectosomes,42,232234 (C) anti-cancer activity of MSC-derived exosomes and artificial ectosomes.200,202,235

Most of the exosomes derived from MSCs for drug delivery have employed miRNAs or siRNAs, inhibiting translation of specific mRNA, with anticancer activity, for example, miR-146b, miR-122, and miR-379, which are used for cancer targeting by membrane surface molecules on MSC-derived exosomes.199201 Drugs such as doxorubicin, paclitaxel, and curcumin were also loaded into MSC-derived exosomes to target cancer.202204 However, artificial ectosomes derived from MSCs as arthritis therapeutics remains largely unexplored area, while EVs, mixtures of natural ectosomes and exosomes, derived from MSCs have studied in the treatment of arthritis.184 Artificial ectosomes with intrinsic tropism from MSCs plus additional targeting ability with engineering increase the chances of ectosomes reaching target tissues with ligandreceptor interactions before being taken up by macrophages.205 Eventually, this will decrease off-target binding and side effects, leading to lower therapeutic dosages while maintaining therapeutic efficacy.206,207

Liposomes are spherical vesicles that are artificially synthesized through the hydration of dry phospholipids.208 The clinically available liposome is a lipid bilayer surrounding a hollow core with a diameter of 50150 nm. Therapeutic molecules, such as anticancer drugs (doxorubicin and daunorubicin citrate) or nucleic acids, can be loaded into this hollow core for delivery.209 Due to their amphipathic nature, liposomes can load both hydrophilic (polar) molecules in an aqueous interior and hydrophobic (nonpolar) molecules in the lipid membrane. They are well-established biomedical applications and are the most common nanostructures used in advanced drug delivery.210 Furthermore, liposomes have several advantages, including versatile structure, biocompatibility, low toxicity, non-immunogenicity, biodegradability, and synergy with drugs: targeted drug delivery, reduction of the toxic effect of drugs, protection against drug degradation, and enhanced circulation half-life.211 Moreover, surfaces can be modified by either coating them with a functionalized polymer or PEG chains to improve targeted delivery and increase their circulation time in biological systems.212 Liposomes have been investigated for use in a wide variety of therapeutic applications, including cancer diagnostics and therapy, vaccines, brain-targeted drug delivery, and anti-microbial therapy. A new approach was recently proposed for providing targeting features to liposomes by fusing them with cell membrane vesicles, generating molecules called membrane-fused liposomes (Figure 10).213 Cell membrane vesicles retain the surface membrane molecules from source cells, which are responsible for efficient tissue targeting and cellular uptake by target cells.214 However, the immunogenicity of cell membrane vesicles leads to their rapid clearance by macrophages in the body and their low drug loading efficiencies present challenges for their use as drug delivery systems.156 However, membrane-fused liposomes have advantages of stability, long half-life in circulation, and low immunogenicity due to the liposome, and the targeting feature of cell membrane vesicles is completely transferred to the liposome.215 Furthermore, the encapsulation efficiencies of doxorubicin were similar when liposomes and membrane-fused liposomes were used, indicating that the relatively high drug encapsulation capacity of liposomes was maintained during the fusion process.216 Combining membrane-fused liposomes with macrophage-derived membrane vesicles showed differential targeting and cytotoxicity against normal and cancerous cells.217 Although only a few studies have been conducted, these results corroborate that membrane-fused liposomes are a potentially promising future drug delivery system with increased targeting ability. MSCs show intrinsic tropism toward arthritis, and further engineering and modification to enhance their targeting ability make them attractive candidates for the development of drug delivery systems. Fusing MSC exosomes with liposomes, taking advantage of both membrane vesicles and liposomes, is a promising technique for future drug delivery systems.

Figure 10 Mesenchymal stem cell membrane-fused liposomes.

MSCs have great potential as targeted therapies due to their greater ability to home to targeted pathophysiological sites. The intrinsic ability to home to wounds or to the tumor microenvironment secreting inflammatory mediators make MSCs and their derivatives targeting strategies for cancer and inflammatory disease.218,219 Contrary to the well-known homing mechanisms of various blood cells, it is still not clear how homing occurs in MSCs. So far, the mechanism of MSC tethering, which connects long, thin cell membrane cylinders called tethers to the adherent area for migration, has not been clarified. Recent studies have shown that galectin-1, VCAM-1, and ICAM are associated with MSC tethering,53,220 but more research is needed to accurately elucidate the tethering mechanism of MSCs. MSC chemotaxis is well defined and there is strong evidence relating it to the homing ability of MSCs.53 Chemotaxis involves recognizing chemokines through chemokine receptors on MSCs and migrating to chemokines in a gradient-dependent manner.221 RA, a representative inflammatory disease, is associated with well-profiled chemokines such as CXCR1, CXCR4, and CXCR7, which are recognized by chemokine receptors on MSCs. In addition, damaged joints in RA continuously secrete cytokines until they are treated, giving MSCs an advantage as future therapeutic agents for RA.222 However, there are several obstacles to utilizing MSCs as RA therapeutics. In clinical settings, the functional capability of MSCs is significantly affected by the health status of the donor patient.223 MSC yield is significantly reduced in patients undergoing steroid-based treatment and the quality of MSCs is dependent on the donors age and environment.35 In addition, when MSCs are used clinically, cryopreservation and defrosting are necessary, but these procedures shorten the life span of MSCs.224 Therefore, NPs mimicking MSCs are an alternative strategy for overcoming the limitations of MSCs. Additionally, further engineering and modification of MSCs can enhance the therapeutic effect by changing the targeting molecules and loaded drugs. In particular, upregulation of receptors associated with chemotaxis through genetic engineering can confer the additional ability of MSCs to home to specific sites, while the increase in engraftment maximizes the therapeutic effect of MSCs.36,225

Furthermore, there are several methods that can be used to exploit the targeting ability of MSCs as drug delivery systems. MSCs mimicking nanoencapsulation, which consists of MSC membrane-coated NPs, MSC-derived artificial ectosomes, and MSC membrane-fused liposomes, can mimic the targeting ability of MSCs while retaining the advantages of NPs. MSC-membrane-coated NPs are synthesized using inorganic or polymer NPs and membranes from MSCs to coat inner nanosized structures. Because they mimic the biological characteristics of MSC membranes, MSC-membrane-coated NPs can not only escape from immune surveillance but also effectively improve targeting ability, with combined functions of the unique properties of core NPs and MSC membranes.226 Exosomes are also an appropriate candidate for use in MSC membranes, utilizing these targeting abilities. However, natural exosomes lack reproducibility and stable productivity, thus artificial ectosomes with targeting ability produced via synthetic routes can increase the local concentration of ectosomes at the targeted site, thereby reducing toxicity and side effects and maximizing therapeutic efficacy.156 MSC membrane-fused liposomes, a novel system, can also transfer the targeting molecules on the surface of MSCs to liposomes; thus, the advantages of liposomes are retained, but with targeting ability. With advancements in nanotechnology of drug delivery systems, the research in cell-mimicking nanoencapsulation will be very useful. Efficient drug delivery systems fundamentally improve the quality of life of patients with a low dose of medication, low side effects, and subsequent treatment of diseases.227 However, research on cell-mimicking nanoencapsulation is at an early stage, and several problems need to be addressed. To predict the nanotoxicity of artificially synthesized MSC mimicking nanoencapsulations, interactions between lipids and drugs, drug release mechanisms near the targeted site, in vivo compatibility, and immunological physiological studies must be conducted before clinical application.

This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF-2019M3A9H1103690), by the Gachon University Gil Medical Center (FRD2021-03), and by the Gachon University research fund of 2020 (GGU-202008430004).

The authors report no conflicts of interest in this work.

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Stem Cell Mimicking Nanoencapsulation for Targeting Arthrit | IJN - Dove Medical Press

Int J Cell Biol. 2016; 2016: 6940283.

Department of Biological Sciences, Indian Institute of Science Education and Research (IISER), Bhopal, Madhya Pradesh 462066, India

Department of Biological Sciences, Indian Institute of Science Education and Research (IISER), Bhopal, Madhya Pradesh 462066, India

Academic Editor: Paul J. Higgins

Received 2016 Mar 13; Accepted 2016 Jun 5.

This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Regenerative medicine, the most recent and emerging branch of medical science, deals with functional restoration of tissues or organs for the patient suffering from severe injuries or chronic disease. The spectacular progress in the field of stem cell research has laid the foundation for cell based therapies of disease which cannot be cured by conventional medicines. The indefinite self-renewal and potential to differentiate into other types of cells represent stem cells as frontiers of regenerative medicine. The transdifferentiating potential of stem cells varies with source and according to that regenerative applications also change. Advancements in gene editing and tissue engineering technology have endorsed the ex vivo remodelling of stem cells grown into 3D organoids and tissue structures for personalized applications. This review outlines the most recent advancement in transplantation and tissue engineering technologies of ESCs, TSPSCs, MSCs, UCSCs, BMSCs, and iPSCs in regenerative medicine. Additionally, this review also discusses stem cells regenerative application in wildlife conservation.

Regenerative medicine, the most recent and emerging branch of medical science, deals with functional restoration of specific tissue and/or organ of the patients suffering with severe injuries or chronic disease conditions, in the state where bodies own regenerative responses do not suffice [1]. In the present scenario donated tissues and organs cannot meet the transplantation demands of aged and diseased populations that have driven the thrust for search for the alternatives. Stem cells are endorsed with indefinite cell division potential, can transdifferentiate into other types of cells, and have emerged as frontline regenerative medicine source in recent time, for reparation of tissues and organs anomalies occurring due to congenital defects, disease, and age associated effects [1]. Stem cells pave foundation for all tissue and organ system of the body and mediates diverse role in disease progression, development, and tissue repair processes in host. On the basis of transdifferentiation potential, stem cells are of four types, that is, (1) unipotent, (2) multipotent, (3) pluripotent, and (4) totipotent [2]. Zygote, the only totipotent stem cell in human body, can give rise to whole organism through the process of transdifferentiation, while cells from inner cells mass (ICM) of embryo are pluripotent in their nature and can differentiate into cells representing three germ layers but do not differentiate into cells of extraembryonic tissue [2]. Stemness and transdifferentiation potential of the embryonic, extraembryonic, fetal, or adult stem cells depend on functional status of pluripotency factors like OCT4, cMYC, KLF44, NANOG, SOX2, and so forth [35]. Ectopic expression or functional restoration of endogenous pluripotency factors epigenetically transforms terminally differentiated cells into ESCs-like cells [3], known as induced pluripotent stem cells (iPSCs) [3, 4]. On the basis of regenerative applications, stem cells can be categorized as embryonic stem cells (ESCs), tissue specific progenitor stem cells (TSPSCs), mesenchymal stem cells (MSCs), umbilical cord stem cells (UCSCs), bone marrow stem cells (BMSCs), and iPSCs (; ). The transplantation of stem cells can be autologous, allogenic, and syngeneic for induction of tissue regeneration and immunolysis of pathogen or malignant cells. For avoiding the consequences of host-versus-graft rejections, tissue typing of human leucocyte antigens (HLA) for tissue and organ transplant as well as use of immune suppressant is recommended [6]. Stem cells express major histocompatibility complex (MHC) receptor in low and secret chemokine that recruitment of endothelial and immune cells is enabling tissue tolerance at graft site [6]. The current stem cell regenerative medicine approaches are founded onto tissue engineering technologies that combine the principles of cell transplantation, material science, and microengineering for development of organoid; those can be used for physiological restoration of damaged tissue and organs. The tissue engineering technology generates nascent tissue on biodegradable 3D-scaffolds [7, 8]. The ideal scaffolds support cell adhesion and ingrowths, mimic mechanics of target tissue, support angiogenesis and neovascularisation for appropriate tissue perfusion, and, being nonimmunogenic to host, do not require systemic immune suppressant [9]. Stem cells number in tissue transplant impacts upon regenerative outcome [10]; in that case prior ex vivo expansion of transplantable stem cells is required [11]. For successful regenerative outcomes, transplanted stem cells must survive, proliferate, and differentiate in site specific manner and integrate into host circulatory system [12]. This review provides framework of most recent (; Figures ) advancement in transplantation and tissue engineering technologies of ESCs, TSPSCs, MSCs, UCSCs, BMSCs, and iPSCs in regenerative medicine. Additionally, this review also discusses stem cells as the tool of regenerative applications in wildlife conservation.

Promises of stem cells in regenerative medicine: the six classes of stem cells, that is, embryonic stem cells (ESCs), tissue specific progenitor stem cells (TSPSCs), mesenchymal stem cells (MSCs), umbilical cord stem cells (UCSCs), bone marrow stem cells (BMSCs), and induced pluripotent stem cells (iPSCs), have many promises in regenerative medicine and disease therapeutics.

ESCs in regenerative medicine: ESCs, sourced from ICM of gastrula, have tremendous promises in regenerative medicine. These cells can differentiate into more than 200 types of cells representing three germ layers. With defined culture conditions, ESCs can be transformed into hepatocytes, retinal ganglion cells, chondrocytes, pancreatic progenitor cells, cone cells, cardiomyocytes, pacemaker cells, eggs, and sperms which can be used in regeneration of tissue and treatment of disease in tissue specific manner.

TSPSCs in regenerative medicine: tissue specific stem and progenitor cells have potential to differentiate into other cells of the tissue. Characteristically inner ear stem cells can be transformed into auditory hair cells, skin progenitors into vascular smooth muscle cells, mesoangioblasts into tibialis anterior muscles, and dental pulp stem cells into serotonin cells. The 3D-culture of TSPSCs in complex biomaterial gives rise to tissue organoids, such as pancreatic organoid from pancreatic progenitor, intestinal tissue organoids from intestinal progenitor cells, and fallopian tube organoids from fallopian tube epithelial cells. Transplantation of TSPSCs regenerates targets tissue such as regeneration of tibialis muscles from mesoangioblasts, cardiac tissue from AdSCs, and corneal tissue from limbal stem cells. Cell growth and transformation factors secreted by TSPSCs can change cells fate to become other types of cell, such that SSCs coculture with skin, prostate, and intestine mesenchyme transforms these cells from MSCs into epithelial cells fate.

MSCs in regenerative medicine: mesenchymal stem cells are CD73+, CD90+, CD105+, CD34, CD45, CD11b, CD14, CD19, and CD79a cells, also known as stromal cells. These bodily MSCs represented here do not account for MSCs of bone marrow and umbilical cord. Upon transplantation and transdifferentiation these bodily MSCs regenerate into cartilage, bones, and muscles tissue. Heart scar formed after heart attack and liver cirrhosis can be treated from MSCs. ECM coating provides the niche environment for MSCs to regenerate into hair follicle, stimulating hair growth.

UCSCs in regenerative medicine: umbilical cord, the readily available source of stem cells, has emerged as futuristic source for personalized stem cell therapy. Transplantation of UCSCs to Krabbe's disease patients regenerates myelin tissue and recovers neuroblastoma patients through restoring tissue homeostasis. The UCSCs organoids are readily available tissue source for treatment of neurodegenerative disease. Peritoneal fibrosis caused by long term dialysis, tendon tissue degeneration, and defective hyaline cartilage can be regenerated by UCSCs. Intravenous injection of UCSCs enables treatment of diabetes, spinal myelitis, systemic lupus erythematosus, Hodgkin's lymphoma, and congenital neuropathies. Cord blood stem cells banking avails long lasting source of stem cells for personalized therapy and regenerative medicine.

BMSCs in regenerative medicine: bone marrow, the soft sponge bone tissue that consisted of stromal, hematopoietic, and mesenchymal and progenitor stem cells, is responsible for blood formation. Even halo-HLA matched BMSCs can cure from disease and regenerate tissue. BMSCs can regenerate craniofacial tissue, brain tissue, diaphragm tissue, and liver tissue and restore erectile function and transdifferentiation monocytes. These multipotent stem cells can cure host from cancer and infection of HIV and HCV.

iPSCs in regenerative medicine: using the edge of iPSCs technology, skin fibroblasts and other adult tissues derived, terminally differentiated cells can be transformed into ESCs-like cells. It is possible that adult cells can be transformed into cells of distinct lineages bypassing the phase of pluripotency. The tissue specific defined culture can transform skin cells to become trophoblast, heart valve cells, photoreceptor cells, immune cells, melanocytes, and so forth. ECM complexation with iPSCs enables generation of tissue organoids for lung, kidney, brain, and other organs of the body. Similar to ESCs, iPSCs also can be transformed into cells representing three germ layers such as pacemaker cells and serotonin cells.

Stem cells in wildlife conservation: tissue biopsies obtained from dead and live wild animals can be either cryopreserved or transdifferentiated to other types of cells, through culture in defined culture medium or in vivo maturation. Stem cells and adult tissue derived iPSCs have great potential of regenerative medicine and disease therapeutics. Gonadal tissue procured from dead wild animals can be matured, ex vivo and in vivo for generation of sperm and egg, which can be used for assistive reproductive technology oriented captive breeding of wild animals or even for resurrection of wildlife.

Application of stem cells in regenerative medicine: stem cells (ESCs, TSPSCs, MSCs, UCSCs, BMSCs, and iPSCs) have diverse applications in tissue regeneration and disease therapeutics.

For the first time in 1998, Thomson isolated human ESCs (hESCs) [13]. ESCs are pluripotent in their nature and can give rise to more than 200 types of cells and promises for the treatment of any kinds of disease [13]. The pluripotency fate of ESCs is governed by functional dynamics of transcription factors OCT4, SOX2, NANOG, and so forth, which are termed as pluripotency factors. The two alleles of the OCT4 are held apart in pluripotency state in ESCs; phase through homologues pairing during embryogenesis and transdifferentiation processes [14] has been considered as critical regulatory switch for lineage commitment of ESCs. The diverse lineage commitment potential represents ESCs as ideal model for regenerative therapeutics of disease and tissue anomalies. This section of review on ESCs discusses transplantation and transdifferentiation of ESCs into retinal ganglion, hepatocytes, cardiomyocytes, pancreatic progenitors, chondrocytes, cones, egg sperm, and pacemaker cells (; ). Infection, cancer treatment, and accidents can cause spinal cord injuries (SCIs). The transplantation of hESCs to paraplegic or quadriplegic SCI patients improves body control, balance, sensation, and limbal movements [15], where transplanted stem cells do homing to injury sites. By birth, humans have fixed numbers of cone cells; degeneration of retinal pigment epithelium (RPE) of macula in central retina causes age-related macular degeneration (ARMD). The genomic incorporation of COCO gene (expressed during embryogenesis) in the developing embryo leads lineage commitment of ESCs into cone cells, through suppression of TGF, BMP, and Wnt signalling pathways. Transplantation of these cone cells to eye recovers individual from ARMD phenomenon, where transplanted cone cells migrate and form sheet-like structure in host retina [16]. However, establishment of missing neuronal connection of retinal ganglion cells (RGCs), cones, and PRE is the most challenging aspect of ARMD therapeutics. Recently, Donald Z Jacks group at John Hopkins University School of Medicine has generated RGCs from CRISPER-Cas9-m-Cherry reporter ESCs [17]. During ESCs transdifferentiation process, CRIPER-Cas9 directs the knock-in of m-Cherry reporter into 3UTR of BRN3B gene, which is specifically expressed in RGCs and can be used for purification of generated RGCs from other cells [17]. Furthermore, incorporation of forskolin in transdifferentiation regime boosts generation of RGCs. Coaxing of these RGCs into biomaterial scaffolds directs axonal differentiation of RGCs. Further modification in RGCs generation regime and composition of biomaterial scaffolds might enable restoration of vision for ARMD and glaucoma patients [17]. Globally, especially in India, cardiovascular problems are a more common cause of human death, where biomedical therapeutics require immediate restoration of heart functions for the very survival of the patient. Regeneration of cardiac tissue can be achieved by transplantation of cardiomyocytes, ESCs-derived cardiovascular progenitors, and bone marrow derived mononuclear cells (BMDMNCs); however healing by cardiomyocytes and progenitor cells is superior to BMDMNCs but mature cardiomyocytes have higher tissue healing potential, suppress heart arrhythmias, couple electromagnetically into hearts functions, and provide mechanical and electrical repair without any associated tumorigenic effects [18, 19]. Like CM differentiation, ESCs derived liver stem cells can be transformed into Cytp450-hepatocytes, mediating chemical modification and catabolism of toxic xenobiotic drugs [20]. Even today, availability and variability of functional hepatocytes are a major a challenge for testing drug toxicity [20]. Stimulation of ESCs and ex vivo VitK12 and lithocholic acid (a by-product of intestinal flora regulating drug metabolism during infancy) activates pregnane X receptor (PXR), CYP3A4, and CYP2C9, which leads to differentiation of ESCs into hepatocytes; those are functionally similar to primary hepatocytes, for their ability to produce albumin and apolipoprotein B100 [20]. These hepatocytes are excellent source for the endpoint screening of drugs for accurate prediction of clinical outcomes [20]. Generation of hepatic cells from ESCs can be achieved in multiple ways, as serum-free differentiation [21], chemical approaches [20, 22], and genetic transformation [23, 24]. These ESCs-derived hepatocytes are long lasting source for treatment of liver injuries and high throughput screening of drugs [20, 23, 24]. Transplantation of the inert biomaterial encapsulated hESCs-derived pancreatic progenitors (CD24+, CD49+, and CD133+) differentiates into -cells, minimizing high fat diet induced glycemic and obesity effects in mice [25] (). Addition of antidiabetic drugs into transdifferentiation regime can boost ESCs conservation into -cells [25], which theoretically can cure T2DM permanently [25]. ESCs can be differentiated directly into insulin secreting -cells (marked with GLUT2, INS1, GCK, and PDX1) which can be achieved through PDX1 mediated epigenetic reprogramming [26]. Globally, osteoarthritis affects millions of people and occurs when cartilage at joints wears away, causing stiffness of the joints. The available therapeutics for arthritis relieve symptoms but do not initiate reverse generation of cartilage. For young individuals and athletes replacement of joints is not feasible like old populations; in that case transplantation of stem cells represents an alternative for healing cartilage injuries [27]. Chondrocytes, the cartilage forming cells derived from hESC, embedded in fibrin gel effectively heal defective cartilage within 12 weeks, when transplanted to focal cartilage defects of knee joints in mice without any negative effect [27]. Transplanted chondrocytes form cell aggregates, positive for SOX9 and collagen II, and defined chondrocytes are active for more than 12wks at transplantation site, advocating clinical suitability of chondrocytes for treatment of cartilage lesions [27]. The integrity of ESCs to integrate and differentiate into electrophysiologically active cells provides a means for natural regulation of heart rhythm as biological pacemaker. Coaxing of ESCs into inert biomaterial as well as propagation in defined culture conditions leads to transdifferentiation of ESCs to become sinoatrial node (SAN) pacemaker cells (PCs) [28]. Genomic incorporation TBox3 into ESCs ex vivo leads to generation of PCs-like cells; those express activated leukocyte cells adhesion molecules (ALCAM) and exhibit similarity to PCs for gene expression and immune functions [28]. Transplantation of PCs can restore pacemaker functions of the ailing heart [28]. In summary, ESCs can be transdifferentiated into any kinds of cells representing three germ layers of the body, being most promising source of regenerative medicine for tissue regeneration and disease therapy (). Ethical concerns limit the applications of ESCs, where set guidelines need to be followed; in that case TSPSCs, MSCs, UCSCs, BMSCs, and iPSCs can be explored as alternatives.

TSPSCs maintain tissue homeostasis through continuous cell division, but, unlike ESCs, TSPSCs retain stem cells plasticity and differentiation in tissue specific manner, giving rise to few types of cells (). The number of TSPSCs population to total cells population is too low; in that case their harvesting as well as in vitro manipulation is really a tricky task [29], to explore them for therapeutic scale. Human body has foundation from various types of TSPSCs; discussing the therapeutic application for all types is not feasible. This section of review discusses therapeutic application of pancreatic progenitor cells (PPCs), dental pulp stem cells (DPSCs), inner ear stem cells (IESCs), intestinal progenitor cells (IPCs), limbal progenitor stem cells (LPSCs), epithelial progenitor stem cells (EPSCs), mesoangioblasts (MABs), spermatogonial stem cells (SSCs), the skin derived precursors (SKPs), and adipose derived stem cells (AdSCs) (; ). During embryogenesis PPCs give rise to insulin-producing -cells. The differentiation of PPCs to become -cells is negatively regulated by insulin [30]. PPCs require active FGF and Notch signalling; growing more rapidly in community than in single cell populations advocates the functional importance of niche effect in self-renewal and transdifferentiation processes. In 3D-scaffold culture system, mice embryo derived PPCs grow into hollow organoid spheres; those finally differentiate into insulin-producing -cell clusters [29]. The DSPSCs, responsible for maintenance of teeth health status, can be sourced from apical papilla, deciduous teeth, dental follicle, and periodontal ligaments, have emerged as regenerative medicine candidate, and might be explored for treatment of various kinds of disease including restoration neurogenic functions in teeth [31, 32]. Expansion of DSPSCs in chemically defined neuronal culture medium transforms them into a mixed population of cholinergic, GABAergic, and glutaminergic neurons; those are known to respond towards acetylcholine, GABA, and glutamine stimulations in vivo. These transformed neuronal cells express nestin, glial fibrillary acidic protein (GFAP), III-tubulin, and voltage gated L-type Ca2+ channels [32]. However, absence of Na+ and K+ channels does not support spontaneous action potential generation, necessary for response generation against environmental stimulus. All together, these primordial neuronal stem cells have possible therapeutic potential for treatment of neurodental problems [32]. Sometimes, brain tumor chemotherapy can cause neurodegeneration mediated cognitive impairment, a condition known as chemobrain [33]. The intrahippocampal transplantation of human derived neuronal stem cells to cyclophosphamide behavioural decremented mice restores cognitive functions in a month time. Here the transplanted stem cells differentiate into neuronal and astroglial lineage, reduce neuroinflammation, and restore microglial functions [33]. Furthermore, transplantation of stem cells, followed by chemotherapy, directs pyramidal and granule-cell neurons of the gyrus and CA1 subfields of hippocampus which leads to reduction in spine and dendritic cell density in the brain. These findings suggest that transplantation of stem cells to cranium restores cognitive functions of the chemobrain [33]. The hair cells of the auditory system produced during development are not postmitotic; loss of hair cells cannot be replaced by inner ear stem cells, due to active state of the Notch signalling [34]. Stimulation of inner ear progenitors with -secretase inhibitor ({"type":"entrez-nucleotide","attrs":{"text":"LY411575","term_id":"1257853995","term_text":"LY411575"}}LY411575) abrogates Notch signalling through activation of transcription factor atonal homologue 1 (Atoh1) and directs transdifferentiation of progenitors into cochlear hair cells [34]. Transplantation of in vitro generated hair cells restores acoustic functions in mice, which can be the potential regenerative medicine candidates for the treatment of deafness [34]. Generation of the hair cells also can be achieved through overexpression of -catenin and Atoh1 in Lrg5+ cells in vivo [35]. Similar to ear progenitors, intestine of the digestive tract also has its own tissue specific progenitor stem cells, mediating regeneration of the intestinal tissue [34, 36]. Dysregulation of the common stem cells signalling pathways, Notch/BMP/TGF-/Wnt, in the intestinal tissue leads to disease. Information on these signalling pathways [37] is critically important in designing therapeutics. Coaxing of the intestinal tissue specific progenitors with immune cells (macrophages), connective tissue cells (myofibroblasts), and probiotic bacteria into 3D-scaffolds of inert biomaterial, crafting biological environment, is suitable for differentiation of progenitors to occupy the crypt-villi structures into these scaffolds [36]. Omental implementation of these crypt-villi structures to dogs enhances intestinal mucosa through regeneration of goblet cells containing intestinal tissue [36]. These intestinal scaffolds are close approach for generation of implantable intestinal tissue, divested by infection, trauma, cancer, necrotizing enterocolitis (NEC), and so forth [36]. In vitro culture conditions cause differentiation of intestinal stem cells to become other types of cells, whereas incorporation of valproic acid and CHIR-99021 in culture conditions avoids differentiation of intestinal stem cells, enabling generation of indefinite pool of stem cells to be used for regenerative applications [38]. The limbal stem cells of the basal limbal epithelium, marked with ABCB5, are essential for regeneration and maintenance of corneal tissue [39]. Functional status of ABCB5 is critical for survival and functional integrity of limbal stem cells, protecting them from apoptotic cell death [39]. Limbal stem cells deficiency leads to replacement of corneal epithelium with visually dead conjunctival tissue, which can be contributed by burns, inflammation, and genetic factors [40]. Transplanted human cornea stem cells to mice regrown into fully functional human cornea, possibly supported by blood eye barrier phenomena, can be used for treatment of eye diseases, where regeneration of corneal tissue is critically required for vision restoration [39]. Muscle degenerative disease like duchenne muscular dystrophy (DMD) can cause extensive thrashing of muscle tissue, where tissue engineering technology can be deployed for functional restoration of tissue through regeneration [41]. Encapsulation of mouse or human derived MABs (engineered to express placental derived growth factor (PDGF)) into polyethylene glycol (PEG) fibrinogen hydrogel and their transplantation beneath the skin at ablated tibialis anterior form artificial muscles, which are functionally similar to those of normal tibialis anterior muscles [41]. The PDGF attracts various cell types of vasculogenic and neurogenic potential to the site of transplantation, supporting transdifferentiation of mesoangioblasts to become muscle fibrils [41]. The therapeutic application of MABs in skeletal muscle regeneration and other therapeutic outcomes has been reviewed by others [42]. One of the most important tissue specific stem cells, the male germline stem cells or spermatogonial stem cells (SSCs), produces spermatogenic lineage through mesenchymal and epithets cells [43] which itself creates niche effect on other cells. In vivo transplantation of SSCs with prostate, skin, and uterine mesenchyme leads to differentiation of these cells to become epithelia of the tissue of origin [43]. These newly formed tissues exhibit all physical and physiological characteristics of prostate and skin and the physical characteristics of prostate, skin, and uterus, express tissue specific markers, and suggest that factors secreted from SSCs lead to lineage conservation which defines the importance of niche effect in regenerative medicine [43]. According to an estimate, more than 100 million people are suffering from the condition of diabetic retinopathy, a progressive dropout of vascularisation in retina that leads to loss of vision [44]. The intravitreal injection of adipose derived stem cells (AdSCs) to the eye restores microvascular capillary bed in mice. The AdSCs from healthy donor produce higher amounts of vasoprotective factors compared to glycemic mice, enabling superior vascularisation [44]. However use of AdSCs for disease therapeutics needs further standardization for cell counts in dose of transplant and monitoring of therapeutic outcomes at population scale [44]. Apart from AdSCs, other kinds of stem cells also have therapeutic potential in regenerative medicine for treatment of eye defects, which has been reviewed by others [45]. Fallopian tubes, connecting ovaries to uterus, are the sites where fertilization of the egg takes place. Infection in fallopian tubes can lead to inflammation, tissue scarring, and closure of the fallopian tube which often leads to infertility and ectopic pregnancies. Fallopian is also the site where onset of ovarian cancer takes place. The studies on origin and etiology of ovarian cancer are restricted due to lack of technical advancement for culture of epithelial cells. The in vitro 3D organoid culture of clinically obtained fallopian tube epithelial cells retains their tissue specificity, keeps cells alive, which differentiate into typical ciliated and secretory cells of fallopian tube, and advocates that ectopic examination of fallopian tube in organoid culture settings might be the ideal approach for screening of cancer [46]. The sustained growth and differentiation of fallopian TSPSCs into fallopian tube organoid depend both on the active state of the Wnt and on paracrine Notch signalling [46]. Similar to fallopian tube stem cells, subcutaneous visceral tissue specific cardiac adipose (CA) derived stem cells (AdSCs) have the potential of differentiation into cardiovascular tissue [47]. Systemic infusion of CA-AdSCs into ischemic myocardium of mice regenerates heart tissue and improves cardiac function through differentiation to endothelial cells, vascular smooth cells, and cardiomyocytes and vascular smooth cells. The differentiation and heart regeneration potential of CA-AdSCs are higher than AdSCs [48], representing CA-AdSCs as potent regenerative medicine candidates for myocardial ischemic therapy [47]. The skin derived precursors (SKPs), the progenitors of dermal papilla/hair/hair sheath, give rise to multiple tissues of mesodermal and/or ectodermal origin such as neurons, Schwann cells, adipocytes, chondrocytes, and vascular smooth muscle cells (VSMCs). VSMCs mediate wound healing and angiogenesis process can be derived from human foreskin progenitor SKPs, suggesting that SKPs derived VSMCs are potential regenerative medicine candidates for wound healing and vasculature injuries treatments [49]. In summary, TSPSCs are potentiated with tissue regeneration, where advancement in organoid culture (; ) technologies defines the importance of niche effect in tissue regeneration and therapeutic outcomes of ex vivo expanded stem cells.

MSCs, the multilineage stem cells, differentiate only to tissue of mesodermal origin, which includes tendons, bone, cartilage, ligaments, muscles, and neurons [50]. MSCs are the cells which express combination of markers: CD73+, CD90+, CD105+, CD11b, CD14, CD19, CD34, CD45, CD79a, and HLA-DR, reviewed elsewhere [50]. The application of MSCs in regenerative medicine can be generalized from ongoing clinical trials, phasing through different state of completions, reviewed elsewhere [90]. This section of review outlines the most recent representative applications of MSCs (; ). The anatomical and physiological characteristics of both donor and receiver have equal impact on therapeutic outcomes. The bone marrow derived MSCs (BMDMSCs) from baboon are morphologically and phenotypically similar to those of bladder stem cells and can be used in regeneration of bladder tissue. The BMDMSCs (CD105+, CD73+, CD34, and CD45), expressing GFP reporter, coaxed with small intestinal submucosa (SIS) scaffolds, augment healing of degenerated bladder tissue within 10wks of the transplantation [51]. The combinatorial CD characterized MACs are functionally active at transplantation site, which suggests that CD characterization of donor MSCs yields superior regenerative outcomes [51]. MSCs also have potential to regenerate liver tissue and treat liver cirrhosis, reviewed elsewhere [91]. The regenerative medicinal application of MSCs utilizes cells in two formats as direct transplantation or first transdifferentiation and then transplantation; ex vivo transdifferentiation of MSCs deploys retroviral delivery system that can cause oncogenic effect on cells. Nonviral, NanoScript technology, comprising utility of transcription factors (TFs) functionalized gold nanoparticles, can target specific regulatory site in the genome effectively and direct differentiation of MSCs into another cell fate, depending on regime of TFs. For example, myogenic regulatory factor containing NanoScript-MRF differentiates the adipose tissue derived MSCs into muscle cells [92]. The multipotency characteristics represent MSCs as promising candidate for obtaining stable tissue constructs through coaxed 3D organoid culture; however heterogeneous distribution of MSCs slows down cell proliferation, rendering therapeutic applications of MSCs. Adopting two-step culture system for MSCs can yield homogeneous distribution of MSCs in biomaterial scaffolds. For example, fetal-MSCs coaxed in biomaterial when cultured first in rotating bioreactor followed with static culture lead to homogeneous distribution of MSCs in ECM components [7]. Occurrence of dental carries, periodontal disease, and tooth injury can impact individual's health, where bioengineering of teeth can be the alternative option. Coaxing of epithelial-MSCs with dental stem cells into synthetic polymer gives rise to mature teeth unit, which consisted of mature teeth and oral tissue, offering multiple regenerative therapeutics, reviewed elsewhere [52]. Like the tooth decay, both human and animals are prone to orthopedic injuries, affecting bones, joint, tendon, muscles, cartilage, and so forth. Although natural healing potential of bone is sufficient to heal the common injuries, severe trauma and tumor-recession can abrogate germinal potential of bone-forming stem cells. In vitro chondrogenic, osteogenic, and adipogenic potential of MSCs advocates therapeutic applications of MSCs in orthopedic injuries [53]. Seeding of MSCs, coaxed into biomaterial scaffolds, at defective bone tissue, regenerates defective bone tissues, within fourwks of transplantation; by the end of 32wks newly formed tissues integrate into old bone [54]. Osteoblasts, the bone-forming cells, have lesser actin cytoskeleton compared to adipocytes and MSCs. Treatment of MSCs with cytochalasin-D causes rapid transportation of G-actin, leading to osteogenic transformation of MSCs. Furthermore, injection of cytochalasin-D to mice tibia also promotes bone formation within a wk time frame [55]. The bone formation processes in mice, dog, and human are fundamentally similar, so outcomes of research on mice and dogs can be directional for regenerative application to human. Injection of MSCs to femur head of Legg-Calve-Perthes suffering dog heals the bone very fast and reduces the injury associated pain [55]. Degeneration of skeletal muscle and muscle cramps are very common to sledge dogs, animals, and individuals involved in adventurous athletics activities. Direct injection of adipose tissue derived MSCs to tear-site of semitendinosus muscle in dogs heals injuries much faster than traditional therapies [56]. Damage effect treatment for heart muscle regeneration is much more complex than regeneration of skeletal muscles, which needs high grade fine-tuned coordination of neurons with muscles. Coaxing of MSCs into alginate gel increases cell retention time that leads to releasing of tissue repairing factors in controlled manner. Transplantation of alginate encapsulated cells to mice heart reduces scar size and increases vascularisation, which leads to restoration of heart functions. Furthermore, transplanted MSCs face host inhospitable inflammatory immune responses and other mechanical forces at transplantation site, where encapsulation of cells keeps them away from all sorts of mechanical forces and enables sensing of host tissue microenvironment, and respond accordingly [57]. Ageing, disease, and medicine consumption can cause hair loss, known as alopecia. Although alopecia has no life threatening effects, emotional catchments can lead to psychological disturbance. The available treatments for alopecia include hair transplantation and use of drugs, where drugs are expensive to afford and generation of new hair follicle is challenging. Dermal papillary cells (DPCs), the specialized MSCs localized in hair follicle, are responsible for morphogenesis of hair follicle and hair cycling. The layer-by-layer coating of DPCs, called GAG coating, consists of coating of geletin as outer layer, middle layer of fibroblast growth factor 2 (FGF2) loaded alginate, and innermost layer of geletin. GAG coating creates tissue microenvironment for DPCs that can sustain immunological and mechanical obstacles, supporting generation of hair follicle. Transplantation of GAG-coated DPCs leads to abundant hair growth and maturation of hair follicle, where GAG coating serves as ECM, enhancing intrinsic therapeutic potential of DPCs [58]. During infection, the inflammatory cytokines secreted from host immune cells attract MSCs to the site of inflammation, which modulates inflammatory responses, representing MSCs as key candidate of regenerative medicine for infectious disease therapeutics. Coculture of macrophages (M) and adipose derived MSCs from Leishmania major (LM) susceptible and resistant mice demonstrates that AD-MSCs educate M against LM infection, differentially inducing M1 and M2 phenotype that represents AD-MSC as therapeutic agent for leishmanial therapy [93]. In summary, the multilineage differentiation potential of MSCs, as well as adoption of next-generation organoid culture system, avails MSCs as ideal regenerative medicine candidate.

Umbilical cord, generally thrown at the time of child birth, is the best known source for stem cells, procured in noninvasive manner, having lesser ethical constraints than ESCs. Umbilical cord is rich source of hematopoietic stem cells (HSCs) and MSCs, which possess enormous regeneration potential [94] (; ). The HSCs of cord blood are responsible for constant renewal of all types of blood cells and protective immune cells. The proliferation of HSCs is regulated by Musashi-2 protein mediated attenuation of Aryl hydrocarbon receptor (AHR) signalling in stem cells [95]. UCSCs can be cryopreserved at stem cells banks (; ), in operation by both private and public sector organization. Public stem cells banks operate on donation formats and perform rigorous screening for HLA typing and donated UCSCs remain available to anyone in need, whereas private stem cell banks operation is more personalized, availing cells according to donor consent. Stem cell banking is not so common, even in developed countries. Survey studies find that educated women are more eager to donate UCSCs, but willingness for donation decreases with subsequent deliveries, due to associated cost and safety concerns for preservation [96]. FDA has approved five HSCs for treatment of blood and other immunological complications [97]. The amniotic fluid, drawn during pregnancy for standard diagnostic purposes, is generally discarded without considering its vasculogenic potential. UCSCs are the best alternatives for those patients who lack donors with fully matched HLA typing for peripheral blood and PBMCs and bone marrow [98]. One major issue with UCSCs is number of cells in transplant, fewer cells in transplant require more time for engraftment to mature, and there are also risks of infection and mortality; in that case ex vivo propagation of UCSCs can meet the demand of desired outcomes. There are diverse protocols, available for ex vivo expansion of UCSCs, reviewed elsewhere [99]. Amniotic fluid stem cells (AFSCs), coaxed to fibrin (required for blood clotting, ECM interactions, wound healing, and angiogenesis) hydrogel and PEG supplemented with vascular endothelial growth factor (VEGF), give rise to vascularised tissue, when grafted to mice, suggesting that organoid cultures of UCSCs have promise for generation of biocompatible tissue patches, for treating infants born with congenital heart defects [59]. Retroviral integration of OCT4, KLF4, cMYC, and SOX2 transforms AFSCs into pluripotency stem cells known as AFiPSCs which can be directed to differentiate into extraembryonic trophoblast by BMP2 and BMP4 stimulation, which can be used for regeneration of placental tissues [60]. Wharton's jelly (WJ), the gelatinous substance inside umbilical cord, is rich in mucopolysaccharides, fibroblast, macrophages, and stem cells. The stem cells from UCB and WJ can be transdifferentiated into -cells. Homogeneous nature of WJ-SCs enables better differentiation into -cells; transplantation of these cells to streptozotocin induced diabetic mice efficiently brings glucose level to normal [7]. Easy access and expansion potential and plasticity to differentiate into multiple cell lineages represent WJ as an ideal candidate for regenerative medicine but cells viability changes with passages with maximum viable population at 5th-6th passages. So it is suggested to perform controlled expansion of WJ-MSCS for desired regenerative outcomes [9]. Study suggests that CD34+ expression leads to the best regenerative outcomes, with less chance of host-versus-graft rejection. In vitro expansion of UCSCs, in presence of StemRegenin-1 (SR-1), conditionally expands CD34+ cells [61]. In type I diabetic mellitus (T1DM), T-cell mediated autoimmune destruction of pancreatic -cells occurs, which has been considered as tough to treat. Transplantation of WJ-SCs to recent onset-T1DM patients restores pancreatic function, suggesting that WJ-MSCs are effective in regeneration of pancreatic tissue anomalies [62]. WJ-MSCs also have therapeutic importance for treatment of T2DM. A non-placebo controlled phase I/II clinical trial demonstrates that intravenous and intrapancreatic endovascular injection of WJ-MSCs to T2DM patients controls fasting glucose and glycated haemoglobin through improvement of -cells functions, evidenced by enhanced c-peptides and reduced inflammatory cytokines (IL-1 and IL-6) and T-cells counts [63]. Like diabetes, systematic lupus erythematosus (SLE) also can be treated with WJ-MSCs transplantation. During progression of SLE host immune system targets its own tissue leading to degeneration of renal, cardiovascular, neuronal, and musculoskeletal tissues. A non-placebo controlled follow-up study on 40 SLE patients demonstrates that intravenous infusion of WJ-MSC improves renal functions and decreases systematic lupus erythematosus disease activity index (SLEDAI) and British Isles Lupus Assessment Group (BILAG), and repeated infusion of WJ-MSCs protects the patient from relapse of the disease [64]. Sometimes, host inflammatory immune responses can be detrimental for HSCs transplantation and blood transfusion procedures. Infusion of WJ-MSC to patients, who had allogenic HSCs transplantation, reduces haemorrhage inflammation (HI) of bladder, suggesting that WJ-MSCs are potential stem cells adjuvant in HSCs transplantation and blood transfusion based therapies [100]. Apart from WJ, umbilical cord perivascular space and cord vein are also rich source for obtaining MSCs. The perivascular MSCs of umbilical cord are more primitive than WJ-MSCs and other MSCs from cord suggest that perivascular MSCs might be used as alternatives for WJ-MSCs for regenerative therapeutics outcome [101]. Based on origin, MSCs exhibit differential in vitro and in vivo properties and advocate functional characterization of MSCs, prior to regenerative applications. Emerging evidence suggests that UCSCs can heal brain injuries, caused by neurodegenerative diseases like Alzheimer's, Krabbe's disease, and so forth. Krabbe's disease, the infantile lysosomal storage disease, occurs due to deficiency of myelin synthesizing enzyme (MSE), affecting brain development and cognitive functions. Progression of neurodegeneration finally leads to death of babies aged two. Investigation shows that healing of peripheral nervous system (PNS) and central nervous system (CNS) tissues with Krabbe's disease can be achieved by allogenic UCSCs. UCSCs transplantation to asymptomatic infants with subsequent monitoring for 46 years reveals that UCSCs recover babies from MSE deficiency, improving myelination and cognitive functions, compared to those of symptomatic babies. The survival rate of transplanted UCSCs in asymptomatic and symptomatic infants was 100% and 43%, respectively, suggesting that early diagnosis and timely treatment are critical for UCSCs acceptance for desired therapeutic outcomes. UCSCs are more primitive than BMSCs, so perfect HLA typing is not critically required, representing UCSCs as an excellent source for treatment of all the diseases involving lysosomal defects, like Krabbe's disease, hurler syndrome, adrenoleukodystrophy (ALD), metachromatic leukodystrophy (MLD), Tay-Sachs disease (TSD), and Sandhoff disease [65]. Brain injuries often lead to cavities formation, which can be treated from neuronal parenchyma, generated ex vivo from UCSCs. Coaxing of UCSCs into human originated biodegradable matrix scaffold and in vitro expansion of cells in defined culture conditions lead to formation of neuronal organoids, within threewks' time frame. These organoids structurally resemble brain tissue and consisted of neuroblasts (GFAP+, Nestin+, and Ki67+) and immature stem cells (OCT4+ and SOX2+). The neuroblasts of these organoids further can be differentiated into mature neurons (MAP2+ and TUJ1+) [66]. Administration of high dose of drugs in divesting neuroblastoma therapeutics requires immediate restoration of hematopoiesis. Although BMSCs had been promising in restoration of hematopoiesis UCSCs are sparely used in clinical settings. A case study demonstrates that neuroblastoma patients who received autologous UCSCs survive without any associated side effects [12]. During radiation therapy of neoplasm, spinal cord myelitis can occur, although occurrence of myelitis is a rare event and usually such neurodegenerative complication of spinal cord occurs 624 years after exposure to radiations. Transplantation of allogenic UC-MSCs in laryngeal patients undergoing radiation therapy restores myelination [102]. For treatment of neurodegenerative disease like Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), traumatic brain injuries (TBI), Parkinson's, SCI, stroke, and so forth, distribution of transplanted UCSCs is critical for therapeutic outcomes. In mice and rat, injection of UCSCs and subsequent MRI scanning show that transplanted UCSCs migrate to CNS and multiple peripheral organs [67]. For immunomodulation of tumor cells disease recovery, transplantation of allogenic DCs is required. The CD11c+DCs, derived from UCB, are morphologically and phenotypically similar to those of peripheral blood derived CTLs-DCs, suggesting that UCB-DCs can be used for personalized medicine of cancer patient, in need for DCs transplantation [103]. Coculture of UCSCs with radiation exposed human lung fibroblast stops their transdifferentiation, which suggests that factors secreted from UCSCs may restore niche identity of fibroblast, if they are transplanted to lung after radiation therapy [104]. Tearing of shoulder cuff tendon can cause severe pain and functional disability, whereas ultrasound guided transplantation of UCB-MSCs in rabbit regenerates subscapularis tendon in fourwks' time frame, suggesting that UCB-MSCs are effective enough to treat tendons injuries when injected to focal points of tear-site [68]. Furthermore, transplantation of UCB-MSCs to chondral cartilage injuries site in pig knee along with HA hydrogel composite regenerates hyaline cartilage [69], suggesting that UCB-MSCs are effective regenerative medicine candidate for treating cartilage and ligament injuries. Physiologically circulatory systems of brain, placenta, and lungs are similar. Infusion of UCB-MSCs to preeclampsia (PE) induced hypertension mice reduces the endotoxic effect, suggesting that UC-MSCs are potential source for treatment of endotoxin induced hypertension during pregnancy, drug abuse, and other kinds of inflammatory shocks [105]. Transplantation of UCSCs to severe congenital neutropenia (SCN) patients restores neutrophils count from donor cells without any side effect, representing UCSCs as potential alternative for SCN therapy, when HLA matched bone marrow donors are not accessible [106]. In clinical settings, the success of myocardial infarction (MI) treatment depends on ageing, systemic inflammation in host, and processing of cells for infusion. Infusion of human hyaluronan hydrogel coaxed UCSCs in pigs induces angiogenesis, decreases scar area, improves cardiac function at preclinical level, and suggests that the same strategy might be effective for human [107]. In stem cells therapeutics, UCSCs transplantation can be either autologous or allogenic. Sometimes, the autologous UCSCs transplants cannot combat over tumor relapse, observed in Hodgkin's lymphoma (HL), which might require second dose transplantation of allogenic stem cells, but efficacy and tolerance of stem cells transplant need to be addressed, where tumor replace occurs. A case study demonstrates that second dose allogenic transplants of UCSCs effective for HL patients, who had heavy dose in prior transplant, increase the long term survival chances by 30% [10]. Patients undergoing long term peritoneal renal dialysis are prone to peritoneal fibrosis and can change peritoneal structure and failure of ultrafiltration processes. The intraperitoneal (IP) injection of WJ-MSCs prevents methylglyoxal induced programmed cell death and peritoneal wall thickening and fibrosis, suggesting that WJ-MSCs are effective in therapeutics of encapsulating peritoneal fibrosis [70]. In summary, UCB-HSCs, WJ-MSCs, perivascular MSCs, and UCB-MSCs have tissue regeneration potential.

Bone marrow found in soft spongy bones is responsible for formation of all peripheral blood and comprises hematopoietic stem cells (producing blood cells) and stromal cells (producing fat, cartilage, and bones) [108] (; ). Visually bone marrow has two types, red marrow (myeloid tissue; producing RBC, platelets, and most of WBC) and yellow marrow (producing fat cells and some WBC) [108]. Imbalance in marrow composition can culminate to the diseased condition. Since 1980, bone marrow transplantation is widely accepted for cancer therapeutics [109]. In order to avoid graft rejection, HLA typing of donors is a must, but completely matched donors are limited to family members, which hampers allogenic transplantation applications. Since matching of all HLA antigens is not critically required, in that case defining the critical antigens for haploidentical allogenic donor for patients, who cannot find fully matched donor, might relieve from donor constraints. Two-step administration of lymphoid and myeloid BMSCs from haploidentical donor to the patients of aplastic anaemia and haematological malignancies reconstructs host immune system and the outcomes are almost similar to fully matched transplants, which recommends that profiling of critically important HLA is sufficient for successful outcomes of BMSCs transplantation. Haploidentical HLA matching protocol is the major process for minorities and others who do not have access to matched donor [71]. Furthermore, antigen profiling is not the sole concern for BMSCs based therapeutics. For example, restriction of HIV1 (human immune deficiency virus) infection is not feasible through BMSCs transplantation because HIV1 infection is mediated through CD4+ receptors, chemokine CXC motif receptor 4 (CXCR4), and chemokine receptor 5 (CCR5) for infecting and propagating into T helper (Th), monocytes, macrophages, and dendritic cells (DCs). Genetic variation in CCR2 and CCR5 receptors is also a contributory factor; mediating protection against infection has been reviewed elsewhere [110]. Engineering of hematopoietic stem and progenitor cells (HSPCs) derived CD4+ cells to express HIV1 antagonistic RNA, specifically designed for targeting HIV1 genome, can restrict HIV1 infection, through immune elimination of latently infected CD4+ cells. A single dose infusion of genetically modified (GM), HIV1 resistant HSPCs can be the alternative of HIV1 retroviral therapy. In the present scenario stem cells source, patient selection, transplantation-conditioning regimen, and postinfusion follow-up studies are the major factors, which can limit application of HIV1 resistant GM-HSPCs (CD4+) cells application in AIDS therapy [72, 73]. Platelets, essential for blood clotting, are formed from megakaryocytes inside the bone marrow [74]. Due to infection, trauma, and cancer, there are chances of bone marrow failure. To an extent, spongy bone marrow microenvironment responsible for lineage commitment can be reconstructed ex vivo [75]. The ex vivo constructed 3D-scaffolds consisted of microtubule and silk sponge, flooded with chemically defined organ culture medium, which mimics bone marrow environment. The coculture of megakaryocytes and embryonic stem cells (ESCs) in this microenvironment leads to generation of functional platelets from megakaryocytes [75]. The ex vivo 3D-scaffolds of bone microenvironment can stride the path for generation of platelets in therapeutic quantities for regenerative medication of burns [75] and blood clotting associated defects. Accidents, traumatic injuries, and brain stroke can deplete neuronal stem cells (NSCs), responsible for generation of neurons, astrocytes, and oligodendrocytes. Brain does not repopulate NSCs and heal traumatic injuries itself and transplantation of BMSCs also can heal neurodegeneration alone. Lipoic acid (LA), a known pharmacological antioxidant compound used in treatment of diabetic and multiple sclerosis neuropathy when combined with BMSCs, induces neovascularisation at focal cerebral injuries, within 8wks of transplantation. Vascularisation further attracts microglia and induces their colonization into scaffold, which leads to differentiation of BMSCs to become brain tissue, within 16wks of transplantation. In this approach, healing of tissue directly depends on number of BMSCs in transplantation dose [76]. Dental caries and periodontal disease are common craniofacial disease, often requiring jaw bone reconstruction after removal of the teeth. Traditional therapy focuses on functional and structural restoration of oral tissue, bone, and teeth rather than biological restoration, but BMSCs based therapies promise for regeneration of craniofacial bone defects, enabling replacement of missing teeth in restored bones with dental implants. Bone marrow derived CD14+ and CD90+ stem and progenitor cells, termed as tissue repair cells (TRC), accelerate alveolar bone regeneration and reconstruction of jaw bone when transplanted in damaged craniofacial tissue, earlier to oral implants. Hence, TRC therapy reduces the need of secondary bone grafts, best suited for severe defects in oral bone, skin, and gum, resulting from trauma, disease, or birth defects [77]. Overall, HSCs have great value in regenerative medicine, where stem cells transplantation strategies explore importance of niche in tissue regeneration. Prior to transplantation of BMSCs, clearance of original niche from target tissue is necessary for generation of organoid and organs without host-versus-graft rejection events. Some genetic defects can lead to disorganization of niche, leading to developmental errors. Complementation with human blastocyst derived primary cells can restore niche function of pancreas in pigs and rats, which defines the concept for generation of clinical grade human pancreas in mice and pigs [111]. Similar to other organs, diaphragm also has its own niche. Congenital defects in diaphragm can affect diaphragm functions. In the present scenario functional restoration of congenital diaphragm defects by surgical repair has risk of reoccurrence of defects or incomplete restoration [8]. Decellularization of donor derived diaphragm offers a way for reconstruction of new and functionally compatible diaphragm through niche modulation. Tissue engineering technology based decellularization of diaphragm and simultaneous perfusion of bone marrow mesenchymal stem cells (BM-MSCs) facilitates regeneration of functional scaffolds of diaphragm tissues [8]. In vivo replacement of hemidiaphragm in rats with reseeded scaffolds possesses similar myography and spirometry as it has in vivo in donor rats. These scaffolds retaining natural architecture are devoid of immune cells, retaining intact extracellular matrix that supports adhesion, proliferation, and differentiation of seeded cells [8]. These findings suggest that cadaver obtained diaphragm, seeded with BM-MSCs, can be used for curing patients in need for restoration of diaphragm functions (; ). However, BMSCs are heterogeneous population, which might result in differential outcomes in clinical settings; however clonal expansion of BMSCs yields homogenous cells population for therapeutic application [8]. One study also finds that intracavernous delivery of single clone BMSCs can restore erectile function in diabetic mice [112] and the same strategy might be explored for adult human individuals. The infection of hepatitis C virus (HCV) can cause liver cirrhosis and degeneration of hepatic tissue. The intraparenchymal transplantation of bone marrow mononuclear cells (BMMNCs) into liver tissue decreases aspartate aminotransferase (AST), alanine transaminase (ALT), bilirubin, CD34, and -SMA, suggesting that transplanted BMSCs restore hepatic functions through regeneration of hepatic tissues [113]. In order to meet the growing demand for stem cells transplantation therapy, donor encouragement is always required [8]. The stem cells donation procedure is very simple; with consent donor gets an injection of granulocyte-colony stimulating factor (G-CSF) that increases BMSCs population. Bone marrow collection is done from hip bone using syringe in 4-5hrs, requiring local anaesthesia and within a wk time frame donor gets recovered donation associated weakness.

The field of iPSCs technology and research is new to all other stem cells research, emerging in 2006 when, for the first time, Takahashi and Yamanaka generated ESCs-like cells through genetic incorporation of four factors, Sox2, Oct3/4, Klf4, and c-Myc, into skin fibroblast [3]. Due to extensive nuclear reprogramming, generated iPSCs are indistinguishable from ESCs, for their transcriptome profiling, epigenetic markings, and functional competence [3], but use of retrovirus in transdifferentiation approach has questioned iPSCs technology. Technological advancement has enabled generation of iPSCs from various kinds of adult cells phasing through ESCs or direct transdifferentiation. This section of review outlines most recent advancement in iPSC technology and regenerative applications (; ). Using the new edge of iPSCs technology, terminally differentiated skin cells directly can be transformed into kidney organoids [114], which are functionally and structurally similar to those of kidney tissue in vivo. Up to certain extent kidneys heal themselves; however natural regeneration potential cannot meet healing for severe injuries. During kidneys healing process, a progenitor stem cell needs to become 20 types of cells, required for waste excretion, pH regulation, and restoration of water and electrolytic ions. The procedure for generation of kidney organoids ex vivo, containing functional nephrons, has been identified for human. These ex vivo kidney organoids are similar to fetal first-trimester kidneys for their structure and physiology. Such kidney organoids can serve as model for nephrotoxicity screening of drugs, disease modelling, and organ transplantation. However generation of fully functional kidneys is a far seen event with today's scientific technologies [114]. Loss of neurons in age-related macular degeneration (ARMD) is the common cause of blindness. At preclinical level, transplantation of iPSCs derived neuronal progenitor cells (NPCs) in rat limits progression of disease through generation of 5-6 layers of photoreceptor nuclei, restoring visual acuity [78]. The various approaches of iPSCs mediated retinal regeneration including ARMD have been reviewed elsewhere [79]. Placenta, the cordial connection between mother and developing fetus, gets degenerated in certain pathophysiological conditions. Nuclear programming of OCT4 knock-out (KO) and wild type (WT) mice fibroblast through transient expression of GATA3, EOMES, TFAP2C, and +/ cMYC generates transgene independent trophoblast stem-like cells (iTSCs), which are highly similar to blastocyst derived TSCs for DNA methylation, H3K7ac, nucleosome deposition of H2A.X, and other epigenetic markings. Chimeric differentiation of iTSCs specifically gives rise to haemorrhagic lineages and placental tissue, bypassing pluripotency phase, opening an avenue for generation of fully functional placenta for human [115]. Neurodegenerative disease like Alzheimer's and obstinate epilepsies can degenerate cerebrum, controlling excitatory and inhibitory signals of the brain. The inhibitory tones in cerebral cortex and hippocampus are accounted by -amino butyric acid secreting (GABAergic) interneurons (INs). Loss of these neurons often leads to progressive neurodegeneration. Genomic integration of Ascl1, Dlx5, Foxg1, and Lhx6 to mice and human fibroblast transforms these adult cells into GABAergic-INs (iGABA-INs). These cells have molecular signature of telencephalic INs, release GABA, and show inhibition to host granule neuronal activity [81]. Transplantation of these INs in developing embryo cures from genetic and acquired seizures, where transplanted cells disperse and mature into functional neuronal circuits as local INs [82]. Dorsomorphin and SB-431542 mediated inhibition of TGF- and BMP signalling direct transformation of human iPSCs into cortical spheroids. These cortical spheroids consisted of both peripheral and cortical neurons, surrounded by astrocytes, displaying transcription profiling and electrophysiology similarity with developing fetal brain and mature neurons, respectively [83]. The underlying complex biology and lack of clear etiology and genetic reprogramming and difficulty in recapitulation of brain development have barred understanding of pathophysiology of autism spectrum disorder (ASD) and schizophrenia. 3D organoid cultures of ASD patient derived iPSC generate miniature brain organoid, resembling fetal brain few months after gestation. The idiopathic conditions of these organoids are similar with brain of ASD patients; both possess higher inhibitory GABAergic neurons with imbalanced neuronal connection. Furthermore these organoids express forkhead Box G1 (FOXG1) much higher than normal brain tissue, which explains that FOXG1 might be the leading cause of ASD [84]. Degeneration of other organs and tissues also has been reported, like degeneration of lungs which might occur due to tuberculosis infection, fibrosis, and cancer. The underlying etiology for lung degeneration can be explained through organoid culture. Coaxing of iPSC into inert biomaterial and defined culture leads to formation of lung organoids that consisted of epithelial and mesenchymal cells, which can survive in culture for months. These organoids are miniature lung, resemble tissues of large airways and alveoli, and can be used for lung developmental studies and screening of antituberculosis and anticancer drugs [87]. The conventional multistep reprogramming for iPSCs consumes months of time, while CRISPER-Cas9 system based episomal reprogramming system that combines two steps together enables generation of ESCs-like cells in less than twowks, reducing the chances of culture associated genetic abrasions and unwanted epigenetic [80]. This approach can yield single step ESCs-like cells in more personalized way from adults with retinal degradation and infants with severe immunodeficiency, involving correction for genetic mutation of OCT4 and DNMT3B [80]. The iPSCs expressing anti-CCR5-RNA, which can be differentiated into HIV1 resistant macrophages, have applications in AIDS therapeutics [88]. The diversified immunotherapeutic application of iPSCs has been reviewed elsewhere [89]. The -1 antitrypsin deficiency (A1AD) encoded by serpin peptidase inhibitor clade A member 1 (SERPINA1) protein synthesized in liver protects lungs from neutrophils elastase, the enzyme causing disruption of lungs connective tissue. A1AD deficiency is common cause of both lung and liver disease like chronic obstructive pulmonary disease (COPD) and liver cirrhosis. Patient specific iPSCs from lung and liver cells might explain pathophysiology of A1AD deficiency. COPD patient derived iPSCs show sensitivity to toxic drugs which explains that actual patient might be sensitive in similar fashion. It is known that A1AD deficiency is caused by single base pair mutation and correction of this mutation fixes the A1AD deficiency in hepatic-iPSCs [85]. The high order brain functions, like emotions, anxiety, sleep, depression, appetite, breathing heartbeats, and so forth, are regulated by serotonin neurons. Generation of serotonin neurons occurs prior to birth, which are postmitotic in their nature. Any sort of developmental defect and degeneration of serotonin neurons might lead to neuronal disorders like bipolar disorder, depression, and schizophrenia-like psychiatric conditions. Manipulation of Wnt signalling in human iPSCs in defined culture conditions leads to an in vitro differentiation of iPSCs to serotonin-like neurons. These iPSCs-neurons primarily localize to rhombomere 2-3 segment of rostral raphe nucleus, exhibit electrophysiological properties similar to serotonin neurons, express hydroxylase 2, the developmental marker, and release serotonin in dose and time dependent manner. Transplantation of these neurons might cure from schizophrenia, bipolar disorder, and other neuropathological conditions [116]. The iPSCs technology mediated somatic cell reprogramming of ventricular monocytes results in generation of cells, similar in morphology and functionality with PCs. SA note transplantation of PCs to large animals improves rhythmic heart functions. Pacemaker needs very reliable and robust performance so understanding of transformation process and site of transplantation are the critical aspect for therapeutic validation of iPSCs derived PCs [28]. Diabetes is a major health concern in modern world, and generation of -cells from adult tissue is challenging. Direct reprogramming of skin cells into pancreatic cells, bypassing pluripotency phase, can yield clinical grade -cells. This reprogramming strategy involves transformation of skin cells into definitive endodermal progenitors (cDE) and foregut like progenitor cells (cPF) intermediates and subsequent in vitro expansion of these intermediates to become pancreatic -cells (cPB). The first step is chemically complex and can be understood as nonepisomal reprogramming on day one with pluripotency factors (OCT4, SOX2, KLF4, and hair pin RNA against p53), then supplementation with GFs and chemical supplements on day seven (EGF, bFGF, CHIR, NECA, NaB, Par, and RG), and two weeks later (Activin-A, CHIR, NECA, NaB, and RG) yielding DE and cPF [86]. Transplantation of cPB yields into glucose stimulated secretion of insulin in diabetic mice defines that such cells can be explored for treatment of T1DM and T2DM in more personalized manner [86]. iPSCs represent underrated opportunities for drug industries and clinical research laboratories for development of therapeutics, but safety concerns might limit transplantation applications (; ) [117]. Transplantation of human iPSCs into mice gastrula leads to colonization and differentiation of cells into three germ layers, evidenced with clinical developmental fat measurements. The acceptance of human iPSCs by mice gastrula suggests that correct timing and appropriate reprogramming regime might delimit human mice species barrier. Using this fact of species barrier, generation of human organs in closely associated primates might be possible, which can be used for treatment of genetic factors governed disease at embryo level itself [118]. In summary, iPSCs are safe and effective for treatment of regenerative medicine.

The unstable growth of human population threatens the existence of wildlife, through overexploitation of natural habitats and illegal killing of wild animals, leading many species to face the fate of being endangered and go for extinction. For wildlife conservation, the concept of creation of frozen zoo involves preservation of gene pool and germ plasm from threatened and endangered species (). The frozen zoo tissue samples collection from dead or live animal can be DNA, sperms, eggs, embryos, gonads, skin, or any other tissue of the body [119]. Preserved tissue can be reprogrammed or transdifferentiated to become other types of tissues and cells, which opens an avenue for conservation of endangered species and resurrection of life (). The gonadal tissue from young individuals harbouring immature tissue can be matured in vivo and ex vivo for generation of functional gametes. Transplantation of SSCs to testis of male from the same different species can give rise to spermatozoa of donor cells [120], which might be used for IVF based captive breeding of wild animals. The most dangerous fact in wildlife conservation is low genetic diversity, too few reproductively capable animals which cannot maintain adequate genetic diversity in wild or captivity. Using the edge of iPSC technology, pluripotent stem cells can be generated from skin cells. For endangered drill, Mandrillus leucophaeus, and nearly extinct white rhinoceros, Ceratotherium simum cottoni, iPSC has been generated in 2011 [121]. The endangered animal drill (Mandrillus leucophaeus) is genetically very close to human and often suffers from diabetes, while rhinos are genetically far removed from other primates. The progress in iPSCs, from the human point of view, might be transformed for animal research for recapturing reproductive potential and health in wild animals. However, stem cells based interventions in wild animals are much more complex than classical conservation planning and biomedical research has to face. Conversion of iPSC into egg or sperm can open the door for generation of IVF based embryo; those might be transplanted in womb of live counterparts for propagation of population. Recently, iPSCs have been generated for snow leopard (Panthera uncia), native to mountain ranges of central Asia, which belongs to cat family; this breakthrough has raised the possibilities for cryopreservation of genetic material for future cloning and other assisted reproductive technology (ART) applications, for the conservation of cat species and biodiversity. Generation of leopard iPSCs has been achieved through retroviral-system based genomic integration of OCT4, SOX2, KLF4, cMYC, and NANOG. These iPSCs from snow leopard also open an avenue for further transformation of iPSCs into gametes [122]. The in vivo maturation of grafted tissue depends both on age and on hormonal status of donor tissue. These facts are equally applicable to accepting host. Ectopic xenografts of cryopreserved testis tissue from Indian spotted deer (Moschiola indica) to nude mice yielded generation of spermatocytes [123], suggesting that one-day procurement of functional sperm from premature tissue might become a general technique in wildlife conservation. In summary, tissue biopsies from dead or live animals can be used for generation of iPSCs and functional gametes; those can be used in assisted reproductive technology (ART) for wildlife conservation.

The spectacular progress in the field of stem cells research represents great scope of stem cells regenerative therapeutics. It can be estimated that by 2020 or so we will be able to produce wide array of tissue, organoid, and organs from adult stem cells. Inductions of pluripotency phenotypes in terminally differentiated adult cells have better therapeutic future than ESCs, due to least ethical constraints with adult cells. In the coming future, there might be new pharmaceutical compounds; those can activate tissue specific stem cells, promote stem cells to migrate to the side of tissue injury, and promote their differentiation to tissue specific cells. Except few countries, the ongoing financial and ethical hindrance on ESCs application in regenerative medicine have more chance for funding agencies to distribute funding for the least risky projects on UCSCs, BMSCs, and TSPSCs from biopsies. The existing stem cells therapeutics advancements are more experimental and high in cost; due to that application on broad scale is not feasible in current scenario. In the near future, the advancements of medical science presume using stem cells to treat cancer, muscles damage, autoimmune disease, and spinal cord injuries among a number of impairments and diseases. It is expected that stem cells therapies will bring considerable benefits to the patients suffering from wide range of injuries and disease. There is high optimism for use of BMSCs, TSPSCs, and iPSCs for treatment of various diseases to overcome the contradictions associated with ESCs. For advancement of translational application of stem cells, there is a need of clinical trials, which needs funding rejoinder from both public and private organizations. The critical evaluation of regulatory guidelines at each phase of clinical trial is a must to comprehend the success and efficacy in time frame.

Dr. Anuradha Reddy from Centre for Cellular and Molecular Biology Hyderabad and Mrs. Sarita Kumari from Department of Yoga Science, BU, Bhopal, India, are acknowledged for their critical suggestions and comments on paper.

There are no competing interests associated with this paper.

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Stem Cells Applications in Regenerative Medicine and ...

-- Biohaven initiates a clinical trial of the novel antibody recruiting molecule BHV-1100 to assess safety, tolerability, and exploratory clinical activity in Multiple Myeloma

Published: Oct. 27, 2021 at 7:30 AM EDT|Updated: 18 hours ago

NEW HAVEN, Conn., Oct. 27, 2021 /PRNewswire/ --Biohaven Pharmaceutical Holding Company Ltd. (NYSE: BHVN), announced the enrollment of the first patient in a Phase 1a/1b trial in Multiple Myeloma using the ARM, BHV-1100, in combination with autologous cytokine induced memory-like (CIML) natural killer (NK) cells and immunoglobulin (Ig) to target and kill multiple myeloma cells expressing the cell surface protein CD38 (Figure 1). BHV-1100 is the lead clinical asset from Biohaven's ARM Platform, developed from a strategic alliance with PeptiDream Inc. This clinical trial will assess the safety and tolerability, as well as exploratory efficacy endpoints, in newly diagnosed multiple myeloma patients who have tested positive for minimal residual disease (MRD+) in first remission prior to autologous stem cell transplant (ASCT).

NK cells are part of the innate immune system, which is designed to recognize and destroy "non-self" or diseased cells in the body. However, tumor cells can evade detection by immune effector cells, allowing the tumor to advance. BHV-1100 targets a cell-surface protein, CD38, that is heavily overexpressed on multiple myeloma and binds to it, recruiting primed autologous cytokine induced memory-like (CIML) natural killer (NK) cells to destroy the tumor.

Charlie Conway, Ph.D., Chief Scientific Officer at Biohaven commented, "While many recent advances have been made to benefit multiple myeloma patients, most patients will unfortunately still relapse. We are excited to investigate BHV-1100 for its ability to recruit autologous CIML NK cells to the site of the tumor. Based on preclinical data from Biohaven Labs, we anticipate that our CD38 targeting ARM-enabled NK cells will kill CD38-positive multiple myeloma cells, and recruit other immune effector cells to assist in reducing the tumor burden."

Biohaven has initiated enrollment in the clinical trial and plans to enroll 25 patients for this single-center, open-label study (ClinicalTrials.gov Identifier: NCT04634435; https://clinicaltrials.gov/ct2/show/NCT04634435). The study will enroll newly diagnosed multiple myeloma patients who have minimal residual disease (MRD+) in first remission prior to an autologous stem cell transplant (ASCT).

David Spiegel M.D., PhD, inventor of the ARM technology and Professor of Chemistry and Pharmacology at Yale University, commented, "This is an important milestone in the development of the ARM therapeutic platform taking a novel technology from 'benchtop to bedside'. It also highlights Biohaven's commitment to benefit patients in need."

About ARMs: Antibody Recruiting Molecules

ARMs,antibody recruiting molecules, are engineered with modular components that are readily interchangeable, giving the platform tremendous flexibility and rapid development timelines. ARM compounds are being developed at Biohaven Labs to redirect a patient's own antibodies for therapeutic effect with multiple benefits over traditional monoclonal antibody therapies, including the potential for oral dosing. For BHV

1100, the ARM platform is being used to provide antigen targeting to NK cell-based therapies without genetic engineering. This NK cell targeting approach is also being investigated with allogeneic, or 'off-the-shelf', immune cell-based therapies.

About Multiple Myeloma Multiple myeloma is a type of blood cancer of the plasma cell that develops in the bone marrow, the soft tissue inside our bones. Healthy plasma cells produce antibodies, which are critical for the immune system's ability to recognize disease-causing entities, such as bacteria, viruses and tumor cells. In multiple myeloma, however, genetic abnormalities in a single plasma cell cause it to divide uncontrollably. This leads to the over-production of a single (monoclonal) antibody protein, referred to as an "M protein". Also, these cancerous cells divide to the point of crowding out normal, healthy cells that reside in the bone marrow. Many patients are diagnosed due to symptoms such as bone pain or fractures, kidney failure (thirst, dehydration, confusion), nerve pain, fever, and weakness. The American Cancer Society estimates that approximately 34,920 new cases will be diagnosed, and 12,410 deaths will occur in 2021 from multiple myeloma.

About BiohavenBiohaven is a commercial-stage biopharmaceutical company with a portfolio of innovative, best-in-class therapies to improve the lives of patients with debilitating neurological and neuropsychiatric diseases, including rare disorders and areas of unmet need. Biohaven's neuro-innovation portfolio includes FDA-approved NURTEC ODT (rimegepant) for the acute and preventive treatment of migraine and a broad pipeline of late-stage product candidates across three distinct mechanistic platforms: CGRP receptor antagonism for the acute and preventive treatment of migraine; glutamate modulation for obsessive-compulsive disorder, Alzheimer's disease, and spinocerebellar ataxia; and MPO inhibition for amyotrophic lateral sclerosis. More information about Biohaven is available atwww.biohavenpharma.com.

About PeptiDream PeptiDream Inc. is a public(Tokyo Stock Exchange 1st Section 4587) biopharmaceutical company founded in 2006 employing their proprietary Peptide Discovery Platform System (PDPS), a state-of-the-art highly versatile discovery platform which enables the production of highly diverse (trillions) non-standard peptide libraries with high efficiency, for the identification of highly potent and selective hit candidates, which then can be developed into peptide-based, small molecule-based, or peptide-drug-conjugate-based therapeutics. PeptiDream aspires to be a world leader in drug discovery and development to address unmet medical needs and improve the quality of life of patients worldwide. Further information regarding PeptiDream can be found at: http://www.peptidream.com.

Forward-looking Statement This news release includes forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. These forward-looking statements involve substantial risks and uncertainties, including statements that are based on the current expectations and assumptions of Biohaven's management about BHV-1100 as a treatment for multiple myeloma. Forward-looking statements include those related to: Biohaven's ability to effectively develop and commercialize BHV-1100, delays or problems in the supply or manufacture of BHV-1100, complying with applicableU.S.regulatory requirements, the expected timing, commencement and outcomes of Biohaven's planned and ongoing clinical trials, the timing of planned interactions and filings with the FDA, the timing and outcome of expected regulatory filings, the potential commercialization of Biohaven's product candidates, the potential for Biohaven's product candidates to be firstin class or best in class therapies and the effectiveness and safety of Biohaven's product candidates. Various important factors could cause actual results or events to differ materially from those that may be expressed or implied by our forward-looking statements. Additional important factors to be considered in connection with forward-looking statements are described in the "Risk Factors" section of Biohaven's Annual Report on Form 10-K for the year ended December 31, 2020, filed with the Securities and Exchange Commission onMarch 1, 2021, and Biohaven's subsequent filings with the Securities and Exchange Commission. The forward-looking statements are made as of this date and Biohaven does not undertake any obligation to update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

NURTEC and NURTEC ODT are registered trademarks of Biohaven Pharmaceutical Ireland DAC.Neuroinnovation is a trademark of Biohaven Pharmaceutical Holding Company Ltd.

ARM is a trademark of Kleo Pharmaceuticals, Inc.

Biohaven ContactDr. Vlad CoricChief Executive OfficerVlad.Coric@biohavenpharma.com

Media ContactMike BeyerSam Brown Inc.mikebeyer@sambrown.com312-961-2502

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SOURCE Biohaven Pharmaceutical Holding Company Ltd.

The above press release was provided courtesy of PRNewswire. The views, opinions and statements in the press release are not endorsed by Gray Media Group nor do they necessarily state or reflect those of Gray Media Group, Inc.

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Biohaven Enrolls Phase 1a/1b Clinical Trial of BHV-1100, Lead Asset from its ARM (Antibody Recruiting Molecule) Platform, in Combination with NK Cell...

Researchers have been looking for something that can help the body heal itself. Although studies are ongoing, stem cell research brings this notion of regenerative medicine a step closer. However, many of its ideas and concepts remain controversial. So, what are stem cells, and why are they so important?

Stem cells are cells that can develop into other types of cells. For example, they can become muscle or brain cells. They can also renew themselves by dividing, even after they have been inactive for a long time.

Stem cell research is helping scientists understand how an organism develops from a single cell and how healthy cells could be useful in replacing cells that are not working correctly in people and animals.

Researchers are now studying stem cells to see if they could help treat a variety of conditions that impact different body systems and parts.

This article looks at types of stem cells, their potential uses, and some ethical concerns about their use.

The human body requires many different types of cells to function, but it does not produce every cell type fully formed and ready to use.

Scientists call a stem cell an undifferentiated cell because it can become any cell. In contrast, a blood cell, for example, is a differentiated cell because it has already formed into a specific kind of cell.

The sections below look at some types of stem cells in more detail.

Scientists extract embryonic stem cells from unused embryos left over from in vitro fertilization procedures. They do this by taking the cells from the embryos at the blastocyst stage, which is the phase in development before the embryo implants in the uterus.

These cells are undifferentiated cells that divide and replicate. However, they are also able to differentiate into specific types of cells.

There are two main types of adult stem cells: those in developed bodily tissues and induced pluripotent stem (iPS) cells.

Developed bodily tissues such as organs, muscles, skin, and bone include some stem cells. These cells can typically become differentiated cells based on where they exist. For example, a brain stem cell can only become a brain cell.

On the other hand, scientists manipulate iPS cells to make them behave more like embryonic stem cells for use in regenerative medicine. After collecting the stem cells, scientists usually store them in liquid nitrogen for future use. However, researchers have not yet been able to turn these cells into any kind of bodily cell.

Scientists are researching how to use stem cells to regenerate or treat the human body.

The list of conditions that stem cell therapy could help treat may be endless. Among other things, it could include conditions such as Alzheimers disease, heart disease, diabetes, and rheumatoid arthritis. Doctors may also be able to use stem cells to treat injuries in the spinal cord or other parts of the body.

They may do this in several ways, including the following.

In some tissues, stem cells play an essential role in regeneration, as they can divide easily to replace dead cells. Scientists believe that knowing how stem cells work can help treat damaged tissue.

For instance, if someones heart contains damaged tissue, doctors might be able to stimulate healthy tissue to grow by transplanting laboratory-grown stem cells into the persons heart. This could cause the heart tissue to renew itself.

One study suggested that people with heart failure showed some improvement 2 years after a single-dose administration of stem cell therapy. However, the effect of stem cell therapy on the heart is still not fully clear, and research is still ongoing.

Another investigation suggested that stem cell therapies could be the basis of personalized diabetes treatment. In mice and laboratory-grown cultures, researchers successfully produced insulin-secreting cells from stem cells derived from the skin of people with type 1 diabetes.

Study author Jeffrey R. Millman an assistant professor of medicine and biomedical engineering at the Washington University School of Medicine in St. Louis, MO said, What were envisioning is an outpatient procedure in which some sort of device filled with the cells would be placed just beneath the skin.

Millman hopes that these stem cell-derived beta cells could be ready for research in humans within 35 years.

Stem cells could also have vast potential in developing other new therapies.

Another way that scientists could use stem cells is in developing and testing new drugs.

The type of stem cell that scientists commonly use for this purpose is the iPS cell. These are cells that have already undergone differentiation but which scientists have genetically reprogrammed using genetic manipulation, sometimes using viruses.

In theory, this allows iPS cells to divide and become any cell. In this way, they could act like undifferentiated stem cells.

For example, scientists want to grow differentiated cells from iPS cells to resemble cancer cells and use them to test anticancer drugs. This could be possible because conditions such as cancer, as well as some congenital disabilities, happen because cells divide abnormally.

However, more research is taking place to determine whether or not scientists really can turn iPS cells into any kind of differentiated cell and how they can use this process to help treat these conditions.

In recent years, clinics have opened that offer different types of stem cell treatments. One 2016 study counted 570 of these clinics in the United States alone. They appear to offer stem cell-based therapies for conditions ranging from sports injuries to cancer.

However, most stem cell therapies are still theoretical rather than evidence-based. For example, researchers are studying how to use stem cells from amniotic fluid which experts can save after an amniocentesis test to treat various conditions.

The Food and Drug Administration (FDA) does allow clinics to inject people with their own stem cells as long as the cells are intended to perform only their normal function.

Aside from that, however, the FDA has only approved the use of blood-forming stem cells known as hematopoietic progenitor cells. Doctors derive these from umbilical cord blood and use them to treat conditions that affect the production of blood. Currently, for example, a doctor can preserve blood from an umbilical cord after a babys birth to save for this purpose in the future.

The FDA lists specific approved stem cell products, such as cord blood, and the medical facilities that use them on its website. It also warns people to be wary of undergoing any unproven treatments because very few stem cell treatments have actually reached the earliest phase of a clinical trial.

Historically, the use of stem cells in medical research has been controversial. This is because when the therapeutic use of stem cells first came to the publics attention in the late 1990s, scientists were only deriving human stem cells from embryos.

Many people disagree with using human embryonic cells for medical research because extracting them means destroying the embryo. This creates complex issues, as people have different beliefs about what constitutes the start of human life.

For some people, life starts when a baby is born, while for others, it starts when an embryo develops into a fetus. Meanwhile, other people believe that human life begins at conception, so an embryo has the same moral status and rights as a human child.

Former U.S. president George W. Bush had strong antiabortion views. He believed that an embryo should be considered a life and not be used for scientific experiments. Bush banned government funding for human stem cell research in 2001, but former U.S. president Barack Obama then revoked this order. Former U.S. president Donald Trump and current U.S. president Joe Biden have also gone back and forth with legislation on this.

However, by 2006, researchers had already started using iPS cells. Scientists do not derive these stem cells from embryonic stem cells. As a result, this technique does not have the same ethical concerns. With this and other recent advances in stem cell technology, attitudes toward stem cell research are slowly beginning to change.

However, other concerns related to using iPS cells still exist. This includes ensuring that donors of biological material give proper consent to have iPS cells extracted and carefully designing any clinical studies.

Researchers also have some concerns that manipulating these cells as part of stem cell therapy could lead to the growth of cancerous tumors.

Although scientists need to do much more research before stem cell therapies can become part of regular medical practice, the science around stem cells is developing all the time.

Scientists still conduct embryonic stem cell research, but research into iPS cells could help reduce some of the ethical concerns around regenerative medicine. This could lead to much more personalized treatment for many conditions and the ability to regenerate parts of the human body.

Learn more about stem cells, where they come from, and their possible uses here.

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Stem cells: Therapy, controversy, and research

Introduction

The growing burden of ischemic heart disease (IHD) is a major public health issue. The most harmful type of IHD is acute myocardial infarction (MI), which leads to loss of tissue and impaired cardiac performance, accounting for two in five deaths in China.1 Timely revascularization after MI, including percutaneous coronary intervention, thrombolytic treatment and bypass surgery, is key to improving cardiac function and preventing post-infarction pathophysiological remodeling.2 However, these effective but invasive approaches cannot be used in all patients owing to their applicability, which is limited based on specific clinical characteristics, and the possibility of severe complications such as bleeding and reperfusion injury.2,3 Attempts to limit infarct size and improve prognosis using pharmacotherapy (including antiplatelet and antiarrhythmic drugs and angiotensin-converting enzyme inhibitors) without reperfusion has been proven generally inefficient, due to non-targeted drug distribution and side effects, and short half-life of some drugs.1,3,4 Consequently, many patients in which this approach is used still progress to cardiac hypertrophy and heart failure.1 Growth and rupture of atherosclerotic plaques and the ensuing thrombosis are the major causes of acute MI.4 Currently available interventions for atherosclerosis (AS) including statins can reduce acute MI, but the effects vary between individuals, and leave significant residual risks.58 Some chemotherapies, such as docetaxel9 and methotrexate,10,11 also seem to have beneficial effects in AS; however, systemic administration of these drugs is limited because of their adverse effects.12 The demand for safer and more efficient therapies and prevention strategies for MI is therefore increasing.

Several optimized strategies have so far been explored, one of which is the application of nanoparticles (NPs). These nanoscale particles have been widely used in the treatment of tumors and neural diseases.13,14 NPs enable delivery of therapeutic compounds to target sites with high spatial and temporal resolution, enhancement of tissue engineering processes and regulation of the behaviour of transplants such as stem cells. The application of NPs improves the therapeutic effects and minimizes the adverse effects of traditional or novel therapies, increasing the likelihood that they can be successfully translated to clinical settings.1518 However, research on NPs in this field is still in its infancy.5,1921 This review summarizes the latest NP-based strategies for managing acute MI, mostly published within the past 7 years, with a particular focus on effects and mechanisms rather than particle types, which have been extensively covered in other reviews (Figure 1). In addition, we offer an initial viewpoint on the value of function-based systems over those based on materials, and discuss future prospects in this field.

Figure 1 Overview of nanoparticle-based strategies for the treatment and prevention of myocardial infarction. Nanoparticles are capable of delivering therapeutic agents and nucleic acids in a stable and targeted manner, improving the properties of tissue engineering scaffolds, labeling transplanted cells and regulating cell behaviors, thus promoting the cardioprotective effects of traditional or novel therapies.

A multitude of NP types are currently under investigation, including lipid-based NPs, polymeric NPs, micelles, inorganic NPs, and exosomes. Virus can also be considered as NPs; however they will not be discussed in this review.22 NPs made from different materials show similar in vivo metabolic kinetic characteristics and protective effects on infarcted heart.19,20 Function-based NP types, oriented towards a specific purpose, may be preferable compared with traditional types, on account of their practicality in basic research and clinical translation. In this review, we discuss NPs used in the treatment and prevention of MI that fall into the following four categories: 1) circulation-stable nanocarriers (polymeric, lipid or inorganic particles); 2) targeted delivery vectors (magnetic or particles modified to improve target specificity); 3) enhancers of tissue engineering; and 4) regulators of cell behavior (Figure 1). We propose that the choice of each NP for any given application should be primarily based on the roles or mechanisms they perform.

Many NPs, whether composed of either naturally occurring or synthetic materials, act as nanocarriers to improve the circulating stability of therapeutic agents.15,16 Polymeric NPs comprise one of the most widely employed types, with excellent biocompatibility, tunable mechanical properties, and the ability be easily modified with therapeutic agents using a broad range of chemical techniques.23,24 The most commonly used polymer for these NPs is polylactide-co-glycolide (PLGA), which has Food and Drug Administration approval.25,26 Recently, there has been a therapeutic emphasis on polydopamine (PDA), from which several related nanomaterials have been created, including PDA NPs and PDA NP-knotted hydrogels.27,28 NPs made from polylactic acid (PLA),29,30 poly--caprolactone (PCL),31 polyoxalates,32 polyacrylonitrile,33 chitosan29,34 and hollow mesoporous organosilica35 have also been constructed and administered in vitro in cells and in vivo in animal models.

Lipid NPs or liposomes are also considered promising candidates for the delivery of therapeutic agents, due to their morphology, which is similar to that of cellular membranes and ability to carry both lipophilic and hydrophilic drugs. These non-toxic, non-immunogenic and biodegradable amphipathic nanocarriers can be designed to reduce capture by reticuloendothelial cells, increase circulation time, and achieve satisfactory targeting.36,37 Solid lipid NPs (SLNs) combine the advantages of polymeric NPs, fat emulsions, and liposomes, remaining in a solid state at room temperature. Active key components of SLNs are mainly physiological lipids, dispersed in aqueous solution containing a stabilizer (surfactant).38 Micelles are made by colloidal aggregation in a solution through self-assembly of amphiphilic polymers, or a simple lipidic layer of transfer vehicles;39 these have been used in cellular and molecular imaging40 and treatment41 for a long time.

Inorganic NPs used in basic IHD research are classified as metal, metal compounds, carbon,42 or silicon NPs;43 these are relatively inert, stable, and biocompatible. Gold (Au),44 silver (Ag)45 and copper (Cu)46 are commonly used materials in their production. These NPs can be delivered orally,47 or injected intravenously48 or intraperitoneally.56 However, they are more widely used to construct electrically conductive myocardial scaffolds in tissue engineering.49,50 Myocardial patches and scaffolds are promising therapeutic approaches to repairing heart tissue after IHD; incorporating conductive NPs can further improve functionality, introducing beneficial physical properties and electroconductivity. Some organic particles, such as liposomes anchored with poly(N-isopropylacrylamide)-based copolymer groups, are also suitable for the production of effective nanogels or patches for this purpose.37

Several metal compounds have been used for treatment of IHD.5154 The application of magnetic particles made from iron oxide has been of particular interest in recent research. These NPs are more prone to manipulation with an external magnetic field, and thus serve as powerful tools for targeted delivery of therapeutics. In addition, modification with targeted peptides or antibodies is another approach to the construction of targeted delivery systems.

Another strategy to protect cardiac performance after MI is the transplantation of cells; however, the beneficial effects of this are currently limited.58 Many NPs can improve the behavior of cells; in this context, they may stimulate cardioprotective potential. In particular, exosomes a major subgroup of extracellular vesicles (EVs) with a diameter of 30150nm, which are secreted via exocytosis55 represent novel, heterogeneous, biological NPs with an endogenous origin. They are able to carry a variety of proteins, lipids, nucleic acids, and other bioactive substances.5557 Mechanistic studies have confirmed that exosomes offer a cell-free strategy to rescue ischemic cardiomyocytes (CMs).59,60

The physical properties of NPs, including size, shape, and surface charge, impact on how biological processes behave, and consequently, responses in the body.61 The recommended definition of NPs in pharmaceutical technology and biomedicine includes a limitation that more than 50% of particles should be in a size distribution range of 10100 nm.39 However, this is not strictly distinguished in studies, so for the purposes of this review, we have relaxed this definition. Small NPs have a faster uptake and processing speed and longer blood circulation half-lives than larger ones; a decreased surface area results in increased reactivity to the microenvironment and greater speed of release of the compounds they carry.6163 However, an exception to this principle is that, among particles of less than 50 nm diameter, larger NPs have longer circulatory half-lives.64,65 NPs can be spherical, discoidal, tubular or dendritic.61,63 The impact of NP shape on uptake and clearance has also been revealed;66,67 for instance, spheres endocytose more easily,20 while micelles and filomicelles target aortic macrophages, B cells, and natural killer (NK) cells in the immune system more effectively than polymersomes.68 In terms of charge, cationic NPs are more likely to interact with cells than negatively charged or neutral particles because the mammalian cell membrane is negatively charged.62 As a result, positively charged particles are reported to be more likely to destabilize blood cell membranes and cause cell lysis.61 Additionally, the rate of drug release is largely determined by the diameter of the pore. Motivated by the idea, Palma-Chavez et al developed a multistage delivery system by encapsulating PLGA NPs in micron-sized PLGA outer shells.69

Some types of NPs, such as micelles, possess coreshell morphological structures: a core composed of hydrophobic block segments is surrounded by hydrophilic polymer blocks in a shell that stabilizes the entire micelle. The core provides enough space to accommodate compounds, while the shell protects drug molecules from hydrolysis and enzymatic degradation.36 Surface chemical composition largely governs the chemical interactions between NPs and molecules in the body. Appropriate surface coatings can create a defensive layer, protect encapsulated cargo, and affect biological behaviors. Coating with inert polymers like polyethylene glycol (PEG) is the most commonly used method, which hinders interactions with proteins, alters the composition of the protein corona, attenuate NP recognition by opsonins which tag particles for phagocytosis, and extend the half-life of particles.36,70 Additionally, PEG coating helps the therapeutic agents reach ischemic sites, because PEGylated macromolecules tend to diffuse in the interstitial space of the heart.71 Functionalization of gangliosides can further attenuate the immunogenicity of PEGylated liposomes without damaging therapeutic efficacy.72 Removal of detachable PEG conjugates in the microenvironment of the target sites improves capture by cells. Wang and colleagues synthesized PDA-coated tanshinone IIA NPs by spontaneous hydrophobic self-assembly.73 Polyethyleneimine (PEI) is capable of condensing nucleic acid and overcoming hamper of cell membrane. Therefore, modification with PEI is mainly used for the transport of DNA and RNA.74 Of note, despite their inertness, novel NPs composed of metals can also be modified with compounds such as PEG, thiols, and disulfides.48,75 Hydrogels mixed with peptide-coated Au NPs attain greater viscosity than hydrogels mixed with Au NPs.24

Targeted delivery is a primary goal in the development of nanocarriers. Passive targeting is based on enhanced permeability in ischemic heart tissue, which does not meet the needs of clinical application.76 This fact has prompted work on targeting agent modification and magnetic guidance. Conjugation with specific monoclonal antibodies is a feasible method for delivering drug payloads targeted to ischemic lesions. Copper sulfide (CuS) NPs coupled to antibodies targeting transient receptor potential vanilloid subfamily 1 (TRPV1), permit specific binding to vascular smooth muscle cells (SMCs), and can also act as a switch for photothermal activation of TRPV1 signaling.52 In another study conducted by Liu and colleagues, two types of antibodies, binding CD63 (expressed on the surface of exosomes) or myosin light chain (MLC, expressed on injured CMs) are utilized to allow NPs to capture exosomes and accumulate in ischemic heart tissue. These NPs have a unique structure comprising an ferroferric oxide core and PEG-decorated silica shell, which simultaneously enables magnetic manipulation and molecule conjugation via hydrazone bonds.21 Targeted peptides such as atrial natriuretic peptide (ANP),43 S2P peptide (plague-targeting peptide),77 and stearyl mannose (type 2 macrophage-targeting ligand)16 allow NPs to precisely target atherosclerotic tissue and ischemic heart lesions. Modification with EMMPRIN-binding peptide (AP9) has been shown to enable more rapid uptake of micelles by H9C2 myoblasts and primary CMs and to deliver drug payloads targeted to lesions in vivo.78,79 Another strategy for targeted nanocarriers is to produce cell mimetic carriers. Using the inflammatory response as a marker after MI,76 Boada and colleagues synthesized biomimetic NPs (leukosomes) by integrating membrane proteins purified from activated J774 macrophages into the phospholipid bilayer of NPs. Local chronic inflammatory lesions demonstrated overexpression of adhesion molecules, which bound leukosomes efficiently.80

The biocompatibility of NPs is difficult to predict because any interaction with molecules or cells can cause toxic effects. Generally, NPs remain in blood, but can also extravasate from vasculature with enhanced permeability, or accumulate in the mononuclear phagocyte system.81 Important causes of NP-associated toxicity include: oxidative stress injury and cell apoptosis secondary to the production of free radicals, lack of anti-oxidants, phagocytic cell responses, and the composition of some types of particles.61 Hepatotoxicity, nephrotoxicity and any other potential off-target organ damage caused by accumulation of particles, especially those with poor degradability and slow clearance, are also essential to explore in toxicity tests.82 Additionally, the evaluation of evoked immune responses according to the expression of inflammatory factors and stimulation of leukocytes in cell lines and animal models is also important.83

A few studies have reported NP-associated acute and chronic hazards in pharmacological applications, although some of these observations may be contentious. Specifically, aggregation of non-functionalized carbon nanotubes (CNTs) has been observed owing to inherent hydrophobicity of these particles.61 Aside from inflammation and T lymphocyte apoptosis, multi-walled CNTs can rupture cell membranes, resulting in macrophage cytotoxic effects.84,85 Silica NPs induce vascular endothelial dysfunction and promoted the release of proinflammatory and procoagulant factors, mediated by miR-451a negative regulation of the interleukin 6 receptor/signal transducer and activator of transcription/transcription factor (IL6R/STAT/TF) signaling pathway.8688 Metal NPs, such as Au and Ag, can also penetrate the cell membrane, increase oxidative stress and decrease cell viability.89,90 Consequently, exposure to Au may cause nephrotoxicity91 and reversible cardiac hypertrophy.92 El-Hussainy and colleagues observed myocardial dysfunction in rats given alumina NPs.93,94 Nemmar and colleagues investigated the toxicity of ultrasmall superparamagnetic iron oxide nanoparticles (SPIONs) administered intravenously, which resulted in cardiac oxidative stress and DNA damage as well as thrombosis.95 Cell-derived exosomes and a majority of natural polymers are considered relatively safe;83 however, Babiker and colleagues demonstrated that dendritic polyamidoamine NPs compromise recovery from ischemia/reperfusion (I/R) injury in isolated rat hearts.96 The effects of degradation byproducts are also of concern.83 An advantage of the nanoscale size of NPs is that their injection is unlikely to block the microvascular system; however, it remains controversial whether NPs give rise to arrhythmias.97 These factors highlight that examining the biocompatibility of NPs both in vitro and in vivo is a vital component of preclinical or clinical research.

NP toxicity depends on many parameters, including material composition, coating, size, shape, surface charges and concentration.39 For instance, larger particles seem to be more favorable from a toxicology standpoint.83 However, single-walled CNTs are considered more harmful than multi-walled CNTs, due to their smaller size resulting in less aggregation and increased uptake by macrophages.61 Cationic AuNPs are more toxic compared with anionic AuNPs, which appear to be nontoxic.98 Generally speaking, NP-associated toxicity can be lowered by functionalization with nontoxic surface molecules, stabilization and localization in the region of interest by using scaffolds.24,99 The toxicity of CNTs mediated by oxidative stress and inflammation was reduced using these strategies in several studies.24,100 Local application and targeted delivery also enabled dose reduction and concurrently decreased the incidence of adverse effects. Administration of therapeutic agents directly into the infarcted or peri-infarcted myocardium is a conventional approach with a low risk of inducing embolization.

NP is a suitable method for the administration of therapeutic agents in terms of the minimization of side effects, enhanced stability of cargo, and possibility of controlled delivery and release.76 Detailed information on the experimental design and results of the latest studies on the use of NPs as therapeutic vectors are provided in Table 1. Recently, several drugs approved for clinical use as immunosuppressants have been suggested as potentially effective cardioprotective agents. For example, NPs containing cyclosporine A inhibited apoptosis and inflammation in ischemic myocardium by improving mitochondrial function.25,101 Commercial methotrexate also showed minor cardioprotective effects; additionally, when loaded into lipid core NPs, adenosine bioavailability and echocardiographic and morphometric results were all improved a rats model of MI.102 Margulis and colleagues developed a method to fabricate NPs via a supercritical fluids setup, which loaded and transferred celecoxib, a lipophilic nonsteroidal anti-inflammatory drug, into the NPs. These celecoxib-containing NPs alleviated ejection function damage and ventricular dilation by inducing significant levels of neovascularization.103 Furthermore, a series of investigations indicated that drugs used for hypoglycemia (eg pioglitazone, exenatide and liraglutide)104106 and lipid lowering (statins)107 attenuate the progression of post-MI heart failure, and are therefore also potential therapeutic cargoes for NPs in the treatment of MI.

NP systems also offer an alternative method for delivering plant-derived therapeutic agents, most of which belong to traditional Chinese medicine. Its of vital importance because of the criticization on adverse reactions caused by direct injection of such complexes. Cheng and colleagues designed a dual-shell polymeric NP as a multistage, continuous, targeted vehicle of resveratrol, a reactive oxygen species (ROS) scavenger. Due to the severe oxide stress in areas of infarction, the proposed antioxidant-delivery NPs represent a new method to effectively treat MI. These NPs are modified with two peptides, targeting ischemic myocardium and mitochondria, respectively; cardioprotective effects have been confirmed in both hypoxia/reoxygenated (H/R) H9C2 cells and I/R rats.108 In addition, Dong and colleagues also demonstrated that puerarin-SLNs produced smaller areas of infarction in a MI rat model, evaluated by 2,3,5-triphenyltetrazolium chloride (TTC) staining. These particles were modified with cyclic arginyl-glycyl-aspartic acid peptide, a specific targeting moiety to v3 integrin receptors, which are highly expressed on endothelial cells (ECs) during angiogenesis.109 In a recent study, quercetin was loaded into mesoporous silica NPs, which enhanced the inhibition of cell apoptosis and oxidative stress, improving ventricular remodeling and promoting the recovery of cardiac function by activating the janus kinase 2 (JAK2)/STAT3 pathway.110 Similarly, curcuminpolymer NPs, administered by gavage, improved serum inflammatory cytokine levels compared with direct administration of curcumin.111

Translation of novel bioactive agents into clinical practice has been limited, owing to lack of sufficient bioavailability and systemic toxicity.76 Encapsulating small molecules such as 3i-1000 (an inhibitor of the GATA4NKX2-5 interaction),43 TAK-242 (inhibitor of toll-like receptor 4, TLR4)112 and C143 (inhibitor of ERK1/2)113 in NPs promotes myocardial repair after MI without the risk of uncontrolled and off-target adverse effects. Administration of vascular endothelial growth factor (VEGF) causes elevated vascular permeability and tissue edema. The cardioprotective effects of VEGF-loaded polymeric NPs injected either intravenously114 or intramyocardially115 eliminated vascular leakage due to promotion of lymphangiogenesis. Further studies have confirmed these results and add to the evidence that combined delivery of VEGF with other growth factors is recommended, since VEGF primarily drives the formation of new capillaries.116 Furthermore, in line with previous research, similar therapeutic effects have been demonstrated in studies using polymeric NPs loaded with stromal cell derived factor 1 (SDF-1) and insulin-like growth factor 1 (IGF-1).117,118

We also notice that some novel payloads in NPs-based therapy for MI have been studied. For example, deoxyribozyme-AuNP can silence tumor necrosis factor- (TNF-).119 A target that is implicated in irreversible heart damage after MI; its effects are mediated by free radical production, downregulation of contractile proteins, and initiation of pro-inflammatory cytokine cascades. Mesoporous iron oxide NPs containing the hydrogen sulfide donor compound diallyl trisulfide act as a platform for the controlled and sustained release of this therapeutic gas molecule. The application of these NPs at appropriate concentrations, resulted in the preservation of cardiac systolic performance without any observable detrimental effects on homeostasis in vivo.15

With increasing insight into the molecular mechanisms of MI, a particular emphasis on gene therapy has emerged. Gene expression can be modulated by DNA fragments, messenger RNA (mRNA), microRNA (miRNA) and small interfering RNA (siRNA), which thus represent new approaches for treating ischemia. Currently available nucleic acid delivery systems are mainly divided into viral and non-viral systems. However, virus-based approaches are limited by their potential for uncontrollable mutagenesis.36 From a clinical point of view, NP represents a suitable choice as novel non-viral nucleic acid vector, which could feasibly transfect in a stable, targeted, and sustained manner (as shown in Table 2).

Table 2 NPs-Based Nucleic Acid Delivery Systems for Treatment for MI Reported in the Last 7 Years

As a common gene vehicle, plasmids face the risk of being destroyed by DNase and immunoreactivity in the serum, and transduction in non-target organs.120 A recent study by Kim and colleagues aligns with current research trends focused on virus-free therapies, in which carboxymethylcellulose NPs were designed to transfer 5-azacytidine to halt proliferation, and deliver plasmid DNA containing GATA4, myocyte enhancer factor 2C (MEF2C), and TBX5 to induce reprogramming and cardiogenesis of mature normal human dermal fibroblasts.121 In a methodological study, lipidoid NPs were used to successfully deliver pseudouridine-modified mRNA, encoding enhanced green fluorescent protein.122

MiRNAs act as essential regulators of cellular processes through post-transcriptional suppression; increasing evidence reveals miRNAs play critical roles in cardiovascular diseases. An miRNA-transferring platform with self-accelerating nucleic acid release, containing a heparin core and an ethanolamine-modified poly(glycidyl methacrylate) shell, has been constructed and used as an efficient vector of miR-499, which inhibits cardiomyocyte apoptosis.123 Intravenous administration of anionic hyaluronan-sulfate NPs (mean diameter 130 nm) enable the stable delivery of miR-21 mimics, thus modulating the expression of TNF, transforming growth factor (TGF), and suppressor of cytokine signaling 1 (SOCS1). Consequently, these NPs switch the phenotype of macrophages from pro-inflammatory to reparative, promote neovascularization and reduced collagen deposition.124 Interestingly, silencing miR-21 using antagomiR-21a-5p in a nanoparticle formulation has also been shown to reduce expression of pro-inflammatory cytokines in vitro, and attenuate inflammation and fibrosis in mice with autoimmune myocarditis.125 A number of other potentially therapeutic miRNAs have also been successfully transferred to CMs in recent works, including miR-146a, miR-146b-5p, miR-181b, miR-199-3p, miR-214-3p, miR-194-5p and miR-122-5p.126128 Evaluation of angiogenesis, cardiac function, and scar size in these studies indicated that injectable miRNANPs can deliver miRNA to restore injured myocardium efficiently and safely. Yang and colleagues developed an in vivo miRNA delivery system incorporating a shear-thinning hydrogel and NPs characterized by surface presence of miRNA and cell-penetrating peptide (CPP).126 Additionally, angiotensin II type 1 receptor-targeting peptide-modified NPs serve as targeted carriers for anti-miR-1 antisense oligonucleotide, significantly reducing apoptosis and infarct size.129

SiRNAs inhibit gene expression by mediating mRNA cleavage in a sequence-specific manner, highlighting NP-based RNA interference as another viable approach to modulate cellular phenotype and attenuate cardiac failure. Dosta and colleagues demonstrated that poly(-amino ester) particles modified by adding lysine-/histidine-oligopeptides could represent a system for the transfer of siRNA.130 Studies have now revealed that chemokine CC motif ligand 2 (CCL2) and its cognate receptor CC chemokine receptor 2 (CCR2) promoted excessive Ly6Chigh inflammatory monocyte infiltration in infarcted area and aggravate myocardial injury.131 Photoluminescent mesoporous silicon nanoparticles (MSNPs) carrying siCCR2 have been reported to improve the effectiveness of transplanted mesenchymal stem cells (MSCs) in reducing myocardial remodeling after acute MI.131 Targeted transportation and enhanced uptake with minimum leakage improved the efficiency of delivery via NPs, significantly outperforming the control group. Taken together, these studies demonstrate that NPs act as promising drug delivery systems in the treatment of MI.

Myocardial patches and scaffolds, consisting of either bioactive hydrogels or nanofibers, are minimally invasive, relatively localized, and targeted approaches to repair the heart after IHD. Those biomaterials must have an anisotropic structure, mechanical elasticity, electrical conductivity, and the ability to promote ischemic heart repair.132 A variety of NPs have been applied in this field, among which inorganic NPs have been the focus of most research efforts.42 These investigations of inorganic NPs can be divided into four categories based on their effects and the mechanisms involved, which are described in this section.

NPs enhance physical properties and electroconductivity, which is essential for the biomaterials to properly accommodate cardiac cells and subsequently resulted in cell retention, cell-cell coupling and robust synchronized beating behavior. CNTs are able to increase the required physical properties of scaffolds, such as maximum load, elastic modulus, and toughness.133,134 Gelatin methacrylate (GelMA) also has decreased impedance, hydrogel swelling ratio, and pore diameter, as well as increased Youngs modulus when combined with gold nanorods (AuNRs).135 Given this insight, highly electroconductive NPs have been increasingly investigated.34,99 Specifically, Ahadian and colleagues revealed that a higher integrated CNT concentration in gels resulted in greater conductivity.136 Zhou and colleagues verified the therapeutic effects of patches incorporating single-walled CNT for myocardial ischemia, which halted progressive cardiac dysfunction and regenerated the infarcted myocardium.137 Spherical AuNPs have also been shown to increase the conductivity of chitosan hydrogels in a concentration-dependent manner.138 Interestingly, silicon NPs mimic the effects of AuNRs without affecting conductivity or stiffness, as reported by Navaei and colleagues.139

Several studies demonstrate the effects of CNT on CM functions. When CMs are cultured on multi-walled CNT substrates or treated with CNT-integrated patches, these cells show spontaneous electrical activity.34,99,140 Brisa and colleagues functionalized reverse thermal gels with AuNPs, investigating the phenotype of CMs in vitro; the growth of cells with a CM phenotype was observed, along with gap junction formation.141 CMs exposed to AuNR-containing GelMa show higher affinity, leading to packed and uniform tissue structure.135 These conductive scaffolds also facilitate the robustness and synchrony of spontaneous beating in CMs without damaging their viability and metabolic activity.

Combined incorporation of inorganic NPs and cells represents a feasible strategy to promote therapeutic effects. Despite some reports on the cytotoxicity of Au,89,90 no significant loss of viability, metabolism, migration, or proliferation of MSCs in scaffolds containing AuNP is reported. A CNT-embedded, electrospun chitosan/polyvinyl alcohol mesh is reported to promote the differentiation of MSCs to CMs.142 In another approach, Baei and colleagues added AuNPs to chitosan thermosensitive hydrogels seeded with MSCs.138 There was a significant increase in expression of early and mature cardiac markers, indicating enhanced cardiomyogenic differentiation of MSCs compared to the matrix alone, while no difference in growth was observed. Gao et al created a fibrin scaffold, in which cells and AuNPs were suspended simultaneously; these bioactive patches were shown to promote left ventricular function and decrease infarct size and apoptosis in the periscar boarder zone myocardium in swine models of acute MI.97 These studies of AuNP-containing scaffolds demonstrated reduced infarct and fibrotic size, as well as facilitated angiogenesis and cardiac function, which can be attributed at least in part to the enhanced expression of connexin 43 and atrial natriuretic peptide, and activation of the integrin-linked kinase(ILK)/serine-threonine kinase (p-AKT)/GATA4 pathway.49,143,144 Scaffolds containing Ag NPs evoke M2 polarization of macrophages in vitro;145 which may also play a role in cardioprotective action because M2 macrophages are capable of promoting cardiac recovery via the secretion of anti-inflammatory cytokines, collagen deposition, and neovascularization.146

Similarly, CNT also act synergically with poly(N-isopropylacrylamide) scaffolds containing adipose-derived stem cells;147 significant improvement of cardiac function and increased implantation and proliferation of stem cells has been observed with these scaffolds, compared with scaffolds without CNT.147 Selenium NPs148 and titania NPs53 have been shown to improve the mechanical and conductive properties of chitosan patches, promoting their ability to support proliferation and the synchronous activity of cells growing on these patches.

Mounting evidence demonstrates the unique benefits of using cardiac scaffolds with magnetic NPs such as SPIONs; these benefits include, but are not limited to, significant improvements in cell proliferation149 and assembly of electrochemical junctions.150 Given that magnetic manipulation enhances the therapeutic efficacy of iron oxide NPs in cardiac scaffolds, Chouhan and colleagues designed a magnetic actuator device by incorporating magnetic iron oxide NPs (MIONs) in silk nanofibers; this resulted in more controlled drug release properties, as well as the promotion of proliferation and maturation in CMs.151 Magnetic NPs can be used to label induced pluripotent stem cell (iPSC)-derived CMs via conjugation with antibodies against signal-regulatory protein . Zwi-Dantsis and colleagues reported the construction of tailored cardiac tissue microstructures, achieved by orienting MION-labelled cells along the applied field to impart different shapes without any mechanical support.152 However, the interactions between and effects of NPs and cells in scaffolds, and the cardioprotective efficacy of patches in which NP-labelled cells are suspended, require further elucidation.

Polymeric nanomaterials have also been investigated in the context of cardiac bioengineering materials; for instance, water-swollen polymer NPs have been used to prepare nanogels. With a 3D structure containing cross-linked biopolymer networks, nanogels can encapsulate, protect, and deliver various agents.83,153 PDA-coated tanshinone IIA NPs suspended in a ROS-sensitive, injectable hydrogel via PDA-thiol bonds significantly improved cardiac performance, accompanied by inhibition of the expression of inflammation factors in rat model.73 After implanting cryogel patches consisting of GelMa and linked conductive polypyrrole NPs154 or scaffolds of electrospun GelMA/polycaprolactone with GelMA-polypyrrole NPs,155 left ventricular (LV) ejection fraction (EF) has been shown to increase, with a concurrent decrease in infarct size, in MI animal models.

Progenitor or stem cell-based therapy in the form of injections and engineered cardiac patches, discussed in the previous section, has been recognized as a promising strategy to improve the cardiac niche and ameliorate adverse remodeling processes and fibrosis after acute MI.56,156,157 However, poor survival and low engraftment rates for transplanted cells are still major challenges in this field.157 Among possible optimization strategies, combining NPs with stem cell therapy is of great interest (Table 3).

Table 3 Studies Combining NPs and Cell Therapy Reported in the Last 7 Years

Accumulating evidence has shown two main mechanisms for NP-loaded cell therapy in the context of MI treatment. Firstly, various NP types could efficiently improve survival and cell proliferation, modulating differentiation of implanted cells in the ischemic microenvironment.62,158 Specifically, electrically driven nanomanipulators could guide cardiomyogenic differentiation of MSCs: in a previous study, electroactuated gold NPs were administrated with pulsed electric field stimulation, and tube-like morphological alterations were observed, along with upregulation of cardiac specific markers.143 Adipose-derived stem cells that load PLGA-simvastatin NPs promoted differentiation of these cells into SMCs and ECs, and had cardioprotective effects in a mouse model of MI induced by left anterior descending ligation.17 Secondly, engraftment rate is another important factor affecting treatment efficacy in this context.159 Zhang and colleagues designed silica-coated, MION-labelled endothelial progenitor cells; intravenous administration of these cells in a rat model of MI significantly improved cardiac performance, as indicated by echocardiogram, morphological, and histological evidence, and neovascularization. This indicates magnetic guidance may potentially address the problem of low levels of stem cell retention, which has typically been observed.51 In particular, NPs can link the therapeutic cells to injured CMs, thereby promoting cell anchorage and engraftment. To this end, Cheng and colleagues established a magnetic, bifunctional cell connector by conjugating NPs with two antibodies: one against cell determinant (CD)45, which is expressed on bone marrow-derived stem cells, and one against MLC. The magnetic core of this NP also enabled physical enrichment in ischemic heart tissue using external magnets.160 More than one mechanism may be involved in a study. Chen and colleagues fabricated a sustained release carrier of insulin-like growth factor (IGF), a pro-survival agent, via in situ growth of Fe3O4 NPs on MSNPs. In this study, the NPs promoted both the survival and retention of MSCs, and intramyocardial injection of the NP-labeled MSCs was able to ameliorate functional and histological damage without any obvious toxicity in vivo.161 However, SPION labeling does not seem to improve therapeutic efficiency, as demonstrated by Wang and colleagues in a study using hypoxia-preconditioned SPION-labeled adipose-derived stem cells (ASCs).162

Primary criticisms of cell-based therapies include their potential immunogenicity, arrhythmogenicity and tumorigenicity. It is widely accepted that the beneficial effects of cell-based therapy are mainly attributable to paracrine effects rather than directly replenishing lost CMs;56 researchers are therefore investigating of cell-free approaches. Exosomes have attractive properties including stable transport, homing to target tissues or cells, and penetration of biological barriers, as well as being more biocompatible with lower immunogenicity than cell-based approaches. Interestingly, post-MI circulating exosomes serve as important cardioprotective messengers.163,164 Manipulating their biodistribution has proven to be a viable strategy to reduce infarct size, promoting angiogenesis and ejection functions.21 However, from a therapeutic standpoint, the lack of control over endogenous exosome production and cargo encapsulation limits the use of this naturally-present mechanism for therapeutic enhancement. The low purity and weak targeting of natural exosomes are two further obstacles to overcome before clinical application. Strategies to address these include finding robust sources; optimized isolation methods for higher yields, efficiency and purity; and improving therapeutic payloads. These have been systematically summarized in other reviews.165167

AS is considered a low-grade, chronic inflammatory disease, characterized by accumulation and deposition of cholesterol in arteries, as well as remodeling of the extracellular matrix in the intima and inner media.12,168 Inflammation of ECs, proliferation of SMCs, and recruitment of monocytes and macrophages play a critical role in the development of AS. NPs allow for the packaging of large amounts of therapeutic compounds in a compact nanostructure, specifically targeting pathological mechanisms and attenuating atherogenesis. Optimization of the loaded drug and NP target together lead to enhanced efficacy while minimizing side effects.169 In this section, we summarize recent breakthroughs in the order of pathological progression, as shown in Table 4.

Primary prevention refers to control of the risk factors of AS, one of which is hypertension.170 PLA NPs have been shown to improve the efficacy of aliskiren, the first oral direct renin inhibitor and the first in a new class of antihypertensive agents.29 Encapsulation in nanocarriers also renders the application of anandamide viable, which was once limited; recent research revealed that this new therapy could lower blood pressure and LV mass index in rats.171 Similar results were observed in a study in which angiotensinogen was silenced using small hairpin RNA.172 NPs may also help to make more anti-hypertensive drugs available, reduce side effects such as asthma, and lessen the effective dosage by providing sustained drug release over time. The link between AS and diabetes mellitus, which describes a group of metabolic disorders, has also been investigated in numerous studies.173 Possible mechanisms include oxidative stress, altered protein kinase signaling, and epigenetic modifications. Cetin and colleagues successfully constructed NP-based drug delivery systems for the administration of metformin, an oral antihyperglycemic agent with low oral bioavailability and short biological half-life.174 NPs are also promising tools for improving the oral bioavailability of insulin, which is of great interest because oral insulin will significantly increase patients compliance.175,176

The inflammatory hypothesis of AS is now widely established, making selective targeting and accumulation of NPs in inflammatory lesions attractive therapeutic strategies. Targeting macrophages in apoE-/- mice has been shown to result in decreased phagocytosis and suppression of inflammatory genes in lesional macrophages, thus lessening burden of atherosclerotic plaques.177 Tom and colleagues used NPs consisting of high-density lipoprotein (HDL), a known atheroprotective bionanomaterial, as carriers for TNF receptor-associated factor in mice, and observed reductions in both leukocyte recruitment and macrophage activation.178 Both single-walled CNT and HDL-NPs have a favorable safety profile. In a pathological context, activated endothelial tissue expresses more adhesion molecules, such as selectins, than usual. These molecules are thus potential targets for cardiovascular nanomedicine. Glycoprotein Ib (GPIb)179 and biotinylated Sialyl Lewis A (sLeA)69 specifically bind to selectins, leading to the accumulation of conjugated NPs in injured vessels; an in vitro study demonstrated that GPIb-conjugated NPs could bind to target surfaces, where they were taken up by activated ECs under shear stress conditions. In another study, Sager and colleagues simultaneously inhibited five adhesion molecules associated with leukocyte recruitment in post-MI apoE-/- mice. Inflammation in plaque and ischemic heart, rendering acute coronary events and post-MI complications less likely to occur.180 However, targeting inflammatory process may have heterogeneous effects in humans because the targeting moieties and target receptors may be overexpressed in several different pathologic conditions in addition to AS. Oxidation is another factor involved in the development of AS. Upregulation of endothelial nitric oxide synthase (eNOS) leads to vascular construction and other AS-promoting effects. Pechanova and colleagues observed that the application of PLA NPs resulted in larger decreases in NOS than direct administration.29

Aside from these processes, avoiding plaque rupture and thrombosis could be another therapeutic aim. Nakashiro and colleagues showed that delivering pioglitazone via NPs inhibited plaque rupture in apoE-/- mice.181 The integrin 3 is upregulated in angiogenic vasculature, which is ubiquitous in plaque ruptures, which may lead to MI.182 3 integrin-targeted NPs provide a site-specific drug delivery platform that has been shown to successfully stabilize plaques in rabbits.182 Ji and colleagues used NPs composed of albumin with an average diameter of 225.6 nm to deliver a plasmid containing the tissue-type plasminogen activator gene (t-PA); this system plays a role in preventing thrombosis in addition to attenuating intimal thickness and proliferation of vascular SMCs.183 NPs consisting of engineered amphipathic cationic peptide and serine/threonine protein kinase JNK2 siRNA also reduces thrombotic risk, plaque necrotic area, and vascular barrier disorder in mice given the equivalent of a 14-week western diet.184

Innovation and development of therapies based on NPs in recent years has led to significant advances towards complete repair of the injured myocardium following acute MI. Nevertheless, developing clinically relevant solutions remains difficult for several reasons. Firstly, as shown in tables, there is little consistency among studies regarding the characteristics of NPs, their payloads, and their methods of administration, as well as methods used for evaluating cardiac repair. It can be difficult to control characteristics such as the size of the synthesized particles in a narrow range, even within single studies. Such significant heterogeneity can lead to differences in observed results in repeated experiments, or under different conditions. Secondly, although many studies have focused on the health effects of unintentional exposure to NPs by inhalation or ingestion,185,186 most of the studies on medical applications of NPs have not reported on toxicity of NP systems until recently.73 Remarkably, there has not been a consensus on NP-associated adverse effects in existing reports, making assessments of biocompatibility a priority for NP characterization.

NPs have emerged as a powerful tool for controlling cell signaling pathways in regenerative strategies using novel therapeutics and drugs that are unsuitable for direct administration. One advantage of the application of NP systems is the ability to release the drug payload or regulate gene expression in a stable and controlled manner. Therefore, many otherwise serious side effects, such as sudden arrhythmic deaths resulting from persistent and uncontrolled expression of miRNA by viral vectors, may be completely avoided.187 More research is required to develop stable and efficient methods of NP production, improve encapsulation efficiency of drugs, and achieve satisfactory targeting. In particular, a greater focus on investigating NP-based switches, including optical, electrical and magnetic methods, has enabled the regulation of cell signaling, exemplified by the development of a CuS NP-based photothermal switch.52 Optimizing tissue engineering scaffolds containing conductive NPs is a promising strategy for the protection of the myocardium after ischemia by mimicking the myocardial extracellular matrix. Improvements in understanding of cardiac repair mechanisms, and how these biomaterials may interfere with them, is therefore urgently needed. Furthermore, heart repair is complex and involves many processes, including apoptosis, angiogenesis, inflammatory infiltration, and fibrosis. Therefore, novel treatments should be designed using NP-based integrative strategies based on these multiple different mechanisms. However, its important to highlight that synergistic effects of different drug payloads, NPs, and NPcell combined strategies should be addressed, as not all may be compatible with one another. Future research should focus on these aspects to translate NP-based therapeutic strategies for MI into practical and effective clinical use.

The authors report no conflicts of interest in this work.

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Read the original here:
Therapy and Prevention Strategies for Myocardial Infarction | IJN - Dove Medical Press

Imagine being able to reverse blindness, cure multiple sclerosis (MS), or rebuild your heart muscles after a heart attack. For the past few decades, research into stem cells, the building blocks of tissues and organs, has raised the prospect of medical advances of this kind yet it has produced relatively few approved treatments. But that could be about to change, says Robin Ali, professor of human molecular genetics of Kings College London. Just as gene therapy went from being a fantasy with little practical value to becoming a major area of treatment, stem cells are within a few years of reaching the medical mainstream. Whats more, developments in synthetic biology, the process of engineering and re-engineering cells, could make stem cells even more effective.

Stem cells are essentially the bodys raw material: basic cells from which all other cells with particular functions are generated. They are found in various organs and tissues, including the brain, blood, bone marrow and skin. The primary promise of adult stem cells lies in regenerative medicine, says Professor Ali.

Stem cells go through several rounds of division in order to produce specialist cells; a blood stem cell can be used to produce blood cells and skin stem cells can be used to produce skin cells. So in theory you can take adult stem cells from one person and transplant them into another person in order to promote the growth of new cells and tissue.

In practice, however, things have proved more complicated, since the number of stem cells in a persons body is relatively limited and they are hard to access. Scientists were also previously restricted by the fact that adult stem cells could only produce one specific type of cell (so blood stem cells couldnt produce skin cells, for instance).

In their quest for a universal stem cell, some scientists initially focused on stem cells from human embryos, but that remains a controversial method, not only because harvesting stem cells involves destroying the embryo, but also because there is a much higher risk of rejection of embryonic stem cells by the recipients immune system.

The good news is that in 2006 Japanese scientist Shinya Yamanaka of Kyoto University and his team discovered a technique for creating what they call induced pluripotent stem cells (iPSC). The research, for which they won a Nobel Prize in 2012, showed that you can rewind adult stem cells development process so that they became embryo-like stem cells. These cells can then be repurposed into any type of stem cells. So you could turn skin stem cells into iPSCs, which could in turn be turned into blood stem cells.

This major breakthrough has two main benefits. Firstly, because iPSCs are derived from adults, they dont come with the ethical problems associated with embryonic stem cells. Whats more, the risk of the body rejecting the cells is much lower as they come from another adult or are produced by the patient. In recent years scientists have refined this technique to the extent that we now have a recipe for making all types of cells, as well as a growing ability to multiply the number of stem cells, says Professor Ali.

Having the blueprint for manufacturing stem cells isnt quite enough on its own and several barriers remain, admits Professor Ali. For example, we still need to be able to manufacture large numbers of stem cells at a reasonable cost. Ensuring that the stem cells, once they are in the recipient, carry out their function of making new cells and tissue remains a work in progress. Finally, regulators are currently taking a hard line towards the technology, insisting on exhaustive testing and slowing research down.

The good news, Professor Ali believes, is that all these problems are not insurmountable as scientists get better at re-engineering adult cells (a process known as synthetic biology). The costs of manufacturing large numbers of stem cells are falling and this can only speed up as more companies invest in the area. There are also a finite number of different human antigens (the parts of the immune system that lead a body to reject a cell), so it should be possible to produce a bank of iPSC cells for the most popular antigen types.

While the attitude of regulators is harder to predict, Professor Ali is confident that it needs only one major breakthrough for the entire sector to secure a large amount of research from the top drug and biotech firms. Indeed, he believes that effective applications are likely in the next few years in areas where there are already established transplant procedures, such as blood transfusion, cartilage and corneas. The breakthrough may come in ophthalmology (the treatment of eye disorders) as you only need to stimulate the development of a relatively small number of cells to restore someones eyesight.

In addition to helping the body repair its own tissues and organs by creating new cells, adult stem cells can also indirectly aid regeneration by delivering other molecules and proteins to parts of the body where they are needed, says Ralph Kern, president and chief medical officer of biotechnology company BrainStorm Cell Therapeutics.

For example, BrainStorm has developed NurOwn, a cellular technology using peoples own cells to deliver neurotrophic factors (NTFs), proteins that can promote the repair of tissue in the nervous system. NurOwn works by modifying so-called Mesenchymal stem cells (MSCs) from a persons bone marrow. The re-transplanted mesenchymal stem cells can then deliver higher quantities of NTFs and other repair molecules.

At present BrainStorm is using its stem-cell therapy to focus on diseases of the brain and nervous system, such as amyotrophic lateral sclerosis (ALS, also known as Lou Gehrigs disease), MS and Huntingtons disease. The data from a recent final-stage trial suggests that the treatment may be able to halt the progression of ALS in those who have the early stage of the disease. Phase-two trial (the second of three stages of clinical trials) of the technique in MS patients also showed that those who underwent the treatment experienced an improvement in the functioning of their body.

Kern notes that MSCs are a particularly promising area of research. They are considered relatively safe, with few side effects, and can be frozen, which improves efficiency and drastically cuts down the amount of bone marrow that needs to be extracted from each patient.

Because the manufacture of MSC cells has become so efficient, NurOwn can be used to get years of therapy in one blood draw. Whats more, the cells can be reintroduced into patients bodies via a simple lumbar puncture into the spine, which can be done as an outpatient procedure, with no need for an overnight stay in hospital.

Kern emphasises that the rapid progress in our ability to modify cells is opening up new opportunities for using stem cells as a molecular delivery platform. Through taking advantage of the latest advances in the science of cellular therapies, BrainStorm is developing a technique to vary the molecules that its stem cells deliver so they can be more closely targeted to the particular condition being treated. BrainStorm is also trying to use smaller fragments of the modified cells, known as exosomes, in the hope that these can be more easily delivered and absorbed by the body and further improve its ability to avoid immune-system reactions to unrelated donors. One of BrainStorms most interesting projects is to use exosomes to repair the long-term lung damage from Covid-19, a particular problem for those with long Covid-19. Early preclinical trials show that modified exosomes delivered into the lungs of animals led to remarkable improvements in their condition. This included increasing the lungs oxygen capacity, reducing inflammation, and decreasing clotting.

Overall, while Kern admits that you cant say that stem cells are a cure for every condition, there is a lot of evidence that in many specific cases they have the potential to be the best option, with fewer side effects. With Americas Food and Drug Administration recently deciding to approve Biogens Alzheimers drug, Kern thinks that they have become much more open to approving products in diseases that are currently considered untreatable. As a result, he thinks that a significant number of adult stem-cell treatments will be approved within the next five to ten years.

Adult stem cells and synthetic biology arent just useful in treatments, says Dr Mark Kotter, CEO and founder of Bit Bio, a company spun out of Cambridge University. They are also set to revolutionise drug discovery. At present, companies start out by testing large numbers of different drug combinations in animals, before finding one that seems to be most effective. They then start a process of clinical trials with humans to test whether the drug is safe, followed by an analysis to see whether it has any effects.

Not only is this process extremely lengthy, but it is also inefficient, because human and animal biology, while similar in many respects, can differ greatly for many conditions. Many drugs that seem promising in animals end up being rejected when they are used on humans. This leads to a high failure rate. Indeed, when you take the failures into account, it has been estimated that it may cost as much to around $2bn to develop the typical drug.

As a result, pharma companies are now realising that you have to insert the human element at a pre-clinical stage by at least using human tissues, says Kotter. The problem is that until recently such tissues were scarce, since they were only available from biopsies or surgery. However, by using synthetic biology to transform adult stem cells from the skin or other parts of the body into other types of stem cells, researchers can potentially grow their own cells, or even whole tissues, in the laboratory, allowing them to integrate the human element at a much earlier stage.

Kotter has direct experience of this himself. He originally spent several decades studying the brain. However, because he had to rely on animal tissue for much of his research he became frustrated that he was turning into a rat doctor.

And when it came to the brain, the differences between human and rat biology were particularly stark. In fact, some human conditions, such as Alzheimers, dont even naturally appear in rodents, so researchers typically use mice and rats engineered to develop something that looks like Alzheimers. But even this isnt a completely accurate representation of what happens in humans.

As a result of his frustration, Kotter sought a way to create human tissues. It initially took six months. However, his company, Bit Bio, managed to cut costs and greatly accelerate the process. The companys technology now allows it to grow tissues in the laboratory in a matter of days, on an industrial scale. Whats more, the tissues can also be designed not just for particular conditions, such as dementia and Huntingdons disease, but also for particular sub-types of diseases.

Kotter and Bit Bio are currently working with Charles River Laboratories, a global company that has been involved in around 80% of drugs approved by the US Food and Drug Administration over the last three years, to commercialise this product. They have already attracted interest from some of the ten largest drug companies in the world, who believe that it will not only reduce the chances of failure, but also speed up development. Early estimates suggest that the process could double the chance of a successful trial, effectively cutting the cost of each approved drug by around 50% from $2bn to just $1bn. This in turn could increase the number of successful drugs on the market.

Two years ago my colleague Dr Mike Tubbs tipped Fate Therapeutics (Nasdaq: FATE). Since then, the share price has soared by 280%, thanks to growing interest from other drug companies (such as Janssen Biotech and ONO Pharmaceutical) in its cancer treatments involving genetically modified iPSCs.

Fate has no fewer than seven iPSC-derived treatments undergoing trials, with several more in the pre-clinical stage. While it is still losing money, it has over $790m cash on hand, which should be more than enough to support it while it develops its drugs.

As mentioned in the main story, the American-Israeli biotechnology company BrainStorm Cell Therapeutics (Nasdaq: BCLI) is developing treatments that aim to use stem cells as a delivery mechanism for proteins. While the phase-three trial (the final stage of clinical trials) of its proprietary NurOwn system for treatment of Amyotrophic lateral sclerosis (ALS, or Lou Gehrigs disease) did not fully succeed, promising results for those in the early stages of the disease mean that the company is thinking about running a new trial aimed at those patients. It also has an ongoing phase-two trial for those with MS, a phase-one trial in Alzheimers patients, as well as various preclinical programmes aimed at Parkinsons, Huntingtons, autistic spectrum disorder and peripheral nerve injury. Like Fate Therapeutics, BrainStorm is currently unprofitable.

Australian biotechnology company Mesoblast (Nasdaq: MESO) takes mesenchymal stem cells from the patient and modifies them so that they can absorb proteins that promote tissue repair and regeneration. At present Mesoblast is working with larger drug and biotech companies, including Novartis, to develop this technique for conditions ranging from heart disease to Covid-19. Several of these projects are close to being completed.

While the US Food and Drug Administration (FDA) controversially rejected Mesoblasts treatment remestemcel-L for use in children who have suffered from reactions to bone-marrow transplants against the advice of the Food and Drug Administrations own advisory committee the firm is confident that the FDA will eventually change its mind.

One stem-cell company that has already reached profitability is Vericel (Nasdaq: VCEL). Vericels flagship MACI products use adult stem cells taken from the patient to grow replacement cartilage, which can then be re-transplanted into the patient, speeding up their recovery from knee injuries. It has also developed a skin replacement based on skin stem cells.

While earnings remain relatively small, Vericel expects profitability to soar fivefold over the next year alone as the company starts to benefit from economies of scale and runs further trials to expand the range of patients who can benefit.

British micro-cap biotech ReNeuron (Aim: RENE) is developing adult stem-cell treatments for several conditions. It is currently carrying out clinical trials for patients with retinal degeneration and those recovering from the effects of having a stroke. ReNeuron has also developed its own induced pluripotent stem cell (iPSC) platform for research purposes and is seeking collaborations with other drug and biotech companies.

Like other small biotech firms in this area, it is not making any money, so it is an extremely risky investment although the rewards could be huge if any of its treatments show positive results from their clinical trials.

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Investing in stem cells, the building blocks of the body - MoneyWeek

Introduction

Extracellular vesicles (EVs) including exosomes, microvesicles, and apoptotic bodies are produced and released by almost all types of cell. EVs vary in size, properties, and secretion pathway depending on the originating cell.1,2 Exosomes are small EVs (sEVs) which are formed by a process of inward budding in early endosomes to form multivesicular bodies (MVBs) with an average size of 100 nm, and released into the extracellular microenvironment to transfer their components.3,4 Microvesicles are composed of lipid components of the plasma membrane and their sizes range from 1001000 nm, whereas apoptotic bodies result from programmed cell death.5 Initially, EVs were considered to maintain cellular waste through release of unwanted proteins and biomolecules; later, these organelles were considered important for intercellular communications through various cargo molecules such as lipids, proteins, DNA, RNA, and microRNAs (miRNAs).6 Previously, it was suggested that EVs play a critical role in normal cells to maintain homeostasis and prevent cancer initiation. Inhibition of EVs secretion causes accumulation of nuclear DNA in the cytoplasm, leading to apoptosis.1 The induction of apoptosis is the principal event of the reactive oxygen species (ROS) dependent DNA damage response.7,8

Several studies reported that exosomes are synthesized by means of two major pathways, the endosomal sorting complexes required for transport (ESCRT)-dependent and ESCRT-independent, and the processes are highly regulated by multiple signal transduction cascades.18 Exosomes released from the cell through normal exocytosis mechanisms are characterized by vesicular docking and fusion with the aid of SNARE complexes. Exosomes are considered to be organelle responsible for garbage disposal agents. However, at a later stage, these secretory bodies play a critical role in maintaining the physiological and pathological conditions of the surrounding cells by transferring information from donor cells to recipient cells. Exosome development begins with endocytosis to form early endosomes, later forming multivesicular endosomes (MVEs), and finally generating late endosomes by inward budding. MVEs merge with the cell membrane and release intraluminal endosomal vesicles that become exosomes into the extracellular space.9,10 Exosome biogenesis is dependent on various critical factors including the site of biogenesis, protein sorting, physicochemical aspects, and transacting mediators.11

Exosomes contain various types of cargo molecules including lipids, proteins, DNAs, mRNAs, and miRNAs. Most of the cargo is involved in the biogenesis and transportation ability of exosomes.12,13 Exosomes are released by fusion of MVBs with the cell membrane via activation of Rab-GTPases and SNAREs. Exosomes are abundant and can be isolated from a wide variety of body fluids and also cell culture medium.14 Exosomes contain tetraspanins that are responsible for cell penetration, invasion, and fusion events. Exosomes are released onto the external surface by the MVB formation proteins Alix and TSG101. Exosome-bound proteins, annexins and Rab protein, govern membrane transport and fusion whereas Alix, flotillin, and TSG101 are involved in exosome biogenesis.15,16 Exosomes contain various types of proteins such as integral exosomal membrane proteins, lipid-anchored outer and inner membrane proteins, peripheral surface and inner membrane proteins, exosomal enzymes, and soluble proteins that play critical roles in exosome functions.11

The functions of exosomes depend on the origin of the cell/tissue, and are involved in the immune response, antigen presentation programmed cell death, angiogenesis, inflammation, coagulation, and morphogen transporters in the creation of polarity during development and differentiation.1720 Ferguson and Nguyen reported that the unique functions of exosomes depend on the availability of unique and specific proteins and also the type of cell.21 All of these categories influence cellular aspects of proteins such as the cell junction, chaperones, the cytoskeleton, membrane trafficking, structure, and transmembrane receptor/regulatory adaptor proteins. The role of exosomes has been explored in different pathophysiological conditions including metabolic diseases. Exosomes are extremely useful in cancer biology for the early detection of cancer, which could increase prognosis and survival. For example, the presence of CD24, EDIL3, and fibronectin proteins on circulating exosomes has been proposed as a marker of early-stage breast cancer.22 Cancer-derived exosomes promoted tumor growth by directly activating the signaling pathways such as P13K/AKT or MAPK/ERK.23 Tumor-derived exosomes are significantly involved in the immune system, particularly stimulating the immune response against cancer and delivering tumor antigens to dendric cells to produce exosomes, which in turn stimulates the T-cell-mediated antitumor immune response.24 Exosomal surface proteins are involved in immunotherapies through the regulation of the tumor immune microenvironment by aberrant cancer signaling.25 A study demonstrated that exosomes have the potential to affect health and pathology of cells through contents of the vesicle.26 Exosomes derived from mesenchymal stem cells exhibit protective effects in stroke models following neural injury resulting from middle cerebral artery occlusion.27 The structural region of the exosome facilitate the release of misfolded and prion proteins, and are also involved in the propagation of neurodegenerative diseases such as Huntington disease, Alzheimers disease (AD), and Parkinsons disease (PD).28,29

Exosomes serve as novel intercellular communicators due to their cell-specific cargo of proteins, lipids, and nucleic acids. In addition, exosomes released from parental cells may interact with target cells, and it can influence cell behavior and phenotype features30 and also it mediate the horizontal transfer of genetic material via interaction of surface adhesion proteins.31 Exosomes are potentially serving as biomarkers due to the wide-spread and cell-specific availability of exosomes in almost all body fluids.13 Therefore, exosomes are exhibited as delivery vehicles for the efficient delivery of biological therapeutics across different biological barriers to target cells.3234

In this review, first, we comprehensively describe the factors involved in exosome biogenesis and the role of exosomes in intercellular signaling and cell-cell communications, immune responses, cellular homeostasis, autophagy, and infectious diseases. In addition, we discuss the role of exosomes as diagnostic markers, and the therapeutic and clinical implications. Finally, we discuss the challenges and outstanding developments in exosome research.

The extracellular vesicles play critical role in inter cellular communication by serving as vehicles for transfer of biomolecules. These vesicles are generally classified into microvesicles, ectosomes, shedding vesicles, or microparticles. MVs bud directly from the plasma membrane, whereas exosomes are represented by small vesicles of different sizes that are formed as the ILV by budding into early endosomes and MVBs and are released by fusion of MVBs with the plasma membrane (Figure 1). Invagination of late endosomal membranes results in the formation of intraluminal vesicles (ILVs) within large MVBs.35 Biogenesis of exosomes occurs in three ways including vesicle budding into discrete endosomes that mature into multivesicular bodies, which release exosomes upon plasma membrane fusion; direct vesicle budding from the plasma membrane; and delayed release by budding at intracellular plasma membrane-connected compartments (IPMCs) followed by deconstruction of IPMC neck(s).11 The mechanisms of biogenesis of exosomes are governed by various types of proteins including the ESCRT proteins Hrs, CHMP4, TSG101, STAM1, VPS4, and other proteins such as the Syndecan-syntenin-ALIX complex, nSMase2, PLD2, and CD9.14,3639 After formation, the MVB can either fuse with the lysosome to degrade its content or fuse with the plasma membrane to release the ILVs as exosomes. The release of exosomes to the extracellular milieu is driven by proteins of the Rab-GTPase family including RAB2B, 5A, 7, 9A, 11, 27, and 35. SNARE family proteins VAMP7 and YKT6 have also been implicated in the release.14,38,4042 Biogenesis of exosomes is influenced by several external factors including cell type, cell confluency, serum conditions, and the presence and absence of cytokines and growth factors. In addition, biogenesis is also regulated by the sites of exosomes, protein sorting, physico-chemical aspects, and trans-acting mediators (Figure 2). For example, THP-1 cells were cultured in RPMI-1640 cell culture medium supplemented with 10% FCS secreted low level of exosomes compared to cells grown on cell culture medium supplemented with 1% FCS (Figure 3). The exogenous factor like serum starvation influences biogenesis and secretion of exosomes.

Figure 1 Biogenesis and cargoes of exosomes.

Figure 2 Effect of various factors on biogenesis of exosomes.

Figure 3 Serum deprivation causes an increase of the number of cellular exosomes in THP-1 cells. Panel (A); 10% FCS. Panel (B); 1% FCS. Panel (C) Quantification of exosomes using DLS and NTA.

Exosome release depends on expression of Rab27 or Ral. For example, exosomes released from the MVB significantly decrease in cells depleted of Rab2741 or Ral.43 The most efficient EV-producing cell types have yet to be determined44 and few reports suggest that immature dendritic cells produce limited amounts of EVs45,46 whereas mesenchymal stem cells secrete vast amounts, relevant for the production of EV therapeutics on a clinical scale.47,48 A few proteins play a critical role in the biogenesis of EVs, such as Rab27a and Rab27b.49 Over expression of Rab27a and Rab27b produce significant amounts of EVs in cancer cells. For example, overexpression of Rab27a and Rab27b in breast cancer cells,50 hepatocellular carcinoma cells,51 glioma cells,52 and pancreas cancer cells53 produces significant levels of EVs. Although all types of cells secrete and release EVs, cancer cells seem to produce higher levels than normal cells.54 Furthermore, the presence of invadopodia that are docking sites for Rab27a-positive MVBs induces secretion of EVs, and also enhances secretion of EVs in cancer cells.55 Thus, inhibition of invadopodia formation greatly reduces exosome secretion into conditioned media. This evidence demonstrates that cancer cells potentially release more EVs than non-cancer cells.

The rate of origin of exosomes from the plasma membrane of stem cells is vigorous, at rates equal to the production of exosomes,56 which is consistent with a report suggesting that stem cells bud ~50100 nm-diameter vesicles directly from the plasma membrane.57 Plasma membrane-derived exosomes contain selectively enriched protein and lipid markers in leukocytes.58 Plasma membrane exosomal budding is also observed for glioblastoma exosomes.59 Conventional transmission electron microscopy revealed that certain cell types contain deep invaginations of the plasma membrane that are indistinguishable from MVBs.6062 Certain cell types secrete exosomes containing cargo proteins, which primarily bud from the plasma membrane, and exosome composition is determined predominantly by intracellular protein trafficking pathways, rather than by the distinct mechanisms of exosome biogenesis.63 Biogenesis of exosomes is regulated by syndecan heparan sulphate proteoglycans and their cytoplasmic adaptor syntenin. Syntenin interacts directly with ALIX through LYPX (n) L motifs.64 Glycosylation is an essential factor in the biogenesis of exosomes and N-linked glycosylation directs glycoprotein sorting into EMVs.65 Collectively, these reports suggest that exosomes are made at both plasma and endosome membranes rather than endosome alone. Oligomerization is a critical factor for exosomal protein sorting and it was found to be sufficient to target plasma membrane proteins to exosomes. High-order oligomeric proteins target them to exosomes.66 Further, plasma membrane anchors support exosomal protein budding. For example, budding of CD63 and CD9 from the plasma membrane is much more efficient than endosome-targeted budding of CD63 and CD9.63 Protein clustering is another factor that induces membrane scission.67

Physico-chemical properties determine budding efficiency and are crucial factors of exosome biogenesis, a fundamental process involving the budding of vesicles that are 30200 nm in size. In particular, lipids are critical players in exosome biogenesis, especially those able to form cone and inverse cone shapes. Generally, exosome membranes contain phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylethanolamine (PE), phosphatidylinositols (PIs), phosphatidic acid (PA), cholesterol, ceramides, sphingomyelin, glycosphingolipids, and a number of lower abundance lipids.68,69 Exosomes have a rich content of PE and PS, which increase budding efficiency and promote exosome genesis and release. PA promotes exosome biogenesis and PLD2 is involved in the budding of certain exosomal cargoes.70 Besides these factors, ceramide is an important lipid molecule regulating exosome biogenesis and facilitating membrane curvature, which is essential for vesicular budding. Inhibition of an enzyme that generates ceramide impairs exosome biogenesis.71

The next critical factor is trans-acting mediators that are involved in the biogenesis of exosomes through regulating plasma membrane homeostasis, intracellular protein trafficking pathways, MVB maturation and trafficking, IPMC biogenesis, vesicle budding, and scission.11 For example, Rab proteins regulate exosome biogenesis via endosomes and the plasma membrane by determining organelle membrane identity, recruiting mechanistic effectors, and mediating organelle dynamics.72 The functions of Rab proteins in the control and biogenesis of exosomes depends on cell type. MVB biogenesis is regulated by Rab27a, Rab27b, their effectors Slp4, Slac2b, and Munc13-4, and also Rab 35 and Rab 11.73 Loss of Rab27 function leads to a ~5075% drop in exosome production, and is also involved in assembling the plasma membrane microdomains involved in plasma membrane vesicle budding, by regulating plasma membrane PIP2 dynamics.74 Overall, Rab27 proteins control exosome biogenesis at both endosomes and plasma membranes. In addition, Rab35 also contributes to exosome biogenesis by regulating PIP2 levels of plasma membrane, and its loss leads to a reduction of exosome release by ~50%.75 Gurunathan et al76 reported that yeast produces two classes of secretory vesicles, low density and high density, and dynamin and clathrin are required for the biogenesis of these two different types of vesicle.

The Ral family is involved in the biogenesis of exosomes, and inhibition of Ral causes an accumulation of MVBs near the plasma membrane and a ~50% decrease in the vesicular secretion of exosomes and exosomal marker proteins.43 Ral GTPases function through various effectors proteins, including Arf6 and the phospholipase PLD2, which are involved in exosomal release of SDCs.37 The ESCRT complex machinery (0 through III) are involved in MVB biogenesis on a major level including membrane deformation, sealing, and repair during a wide array of processes. The major contributions of the ESCRT complex to the biogenesis of vesicles are the recognition and sequestration of ubiquitinated proteins to specific domains of the endosomal membrane via ubiquitin binding subunits of ESCRT-0. After interaction with the ESCRT-I and -II complexes, the total complex will then combine with ESCRT-III, a protein complex that is involved in promoting the budding process. Finally, following cleaving of the buds to form ILVs, the ESCRT-III complex separates from the MVB membrane using energy supplied by the sorting protein Vps4.77 In addition, other proteins such as Alix, which is associated with several ESCRT (TSG101 and CHMP4) proteins, are involved in endosomal membrane budding and abscission, as well as exosomal cargo selection via interaction with syndecan.39 Another important factor, autophagy, is critically involved in exosome secretion. Autophagy related (Atg) proteins coordinate initiation, nucleation, and elongation during autophagosome biogenesis in the presence of ESCRT-III components including CHMP2A and VPS4. For instance, the absence of Atg5 in cancer cells causes a reduction in exosome production.78 Conversely, CRISPR/Cas9-mediated knockout of Atg5 in neuronal cells increases the release of exosomes and exosome-associated prions from neuronal cells.79

Exosomes play a critical role in the physiologic regulation of mammary gland development and are important mediators of breast tumorigenesis.80 Biogenesis of exosomes occurs in all cell types; however, production depends on cell type. For example, breast cancer cells (BCC) produce increased numbers of exosomes compared to normal mammary epithelial cells. Studies revealed that patients with BC have increased numbers of MVs in their blood.81 Kavanagh et al reported that several fold changes were observed from exosomes isolated from triple negative breast cancer (TNBC) chemoresistant therapeutic induced senescent (TIS) cells compared with control EVs.82 TIS cells release significantly more EVs compared with control cells, containing chemotherapy and key proteins involved in cell proliferation, ATP depletion, and apoptosis, and exhibit the senescence-associated secretory phenotype (SASP). Cannabidiol (CBD), inhibits exosome and microvesicle (EMV) release in three different types of cancer cells including prostate cancer (PC3), hepatocellular carcinoma (HEPG2), and breast adenocarcinoma (MDA-MB-231). All three different cell lines show variability in the release of exosomes in a dose-dependent manner. These variabilities are all due to mitochondrial function, including modulation of STAT3 and prohibitin expression. This study suggests that the anticancer agent CBD plays critical role in EMV biogenesis.83 Sulfisoxazole (SFX) inhibits sEV secretion from breast cancer cells through interference with endothelin receptor A (ETA) through the reduced expression of proteins involved in the biogenesis and secretion of sEV, and triggers co-localization of multivesicular endosomes with lysosomes for degradation.84 Secreted EVs from human colorectal cancer cells contain 957 vesicular proteins. The direct protein interactions between cellular proteins play a critical role in protein sorting during EV formation. SRC signaling plays a major role in EV biogenesis, and inhibition of SRC kinase decreases the intracellular biogenesis and cell surface release of EVs.85 Proteomic analysis revealed that the exosomes released from imatinib-sensitive GIST882 cell line exhibit 764 proteins. The authors found that significant amount of proteins belong to protein release function and involved in the classical pathway and overlap to a high degree with proteins of exosomal origin.86 Exosomes secreted by antigen-presenting cells contain high levels of MHC class II proteins and costimulatory proteins, whereas exosomes released from other cell types lack these proteins.1,87

The biogenesis of exosomes depends on a percentage of confluency of approximately 6090%, which influences the yield and functions of EVs.44 Gal et al88 observed a 10-fold decreased level of cholesterol metabolism in confluent cell cultures compared to cells in the preconfluent state. The high level of cholesterol content in confluent cells leads to a decreased level of EVs in prostate cancer.68 The major reason behind for the reduced level of vesicle production is contact inhibition, which triggers confluent cells to enter quiescence and/or alters their characteristics compared to actively dividing cells.89,90 Exogenous stimulation could influence the condition of the cells including the phenotype and efficacy of secretion. Previously, several studies demonstrated that various external factors increase biogenesis of EVs such as Ca2+ ionophores,91 hypoxia,9294 and detachment of cells,95 whereas lipopolysaccharide reduces biogenesis and release of EVs.96 Furthermore, serum, which supports adherence of the cells, plays a critical role in the biogenesis of EVs.97 For example, FCS has noticeable effects on cultured cells; however, the effects depend on cell type and differentiation status.97,98 To avoid the immense amounts of vesicles present in FCS, the use of conditioned media has been suggested. Culture viability and health status of cells are important aspects for producing an adequate amount of vesicles with proper cargo molecules such as protein and RNA.99,100 Exogenous stress, such as starvation, can induce phenotypic alterations and changes in proliferation. These changes cause alterations in the cells metabolism and eventually lead to low yields.101,102

Cellular stresses, such as hypoxia, inflammation, and hyperglycemia, influence the RNA and protein content in exosomes. To examine these factors, the effects of cellular stresses on endothelial cells were studied.99 Endothelial cells were exposed to different types of cellular stress such as hypoxia, tumor necrosis factor- (TNF-)-induced activation, and high glucose and mannose concentrations. The mRNA and protein content of exosomes produced by these cells were compared using microarray analysis and a quantitative proteomics approach. The results indicated that endothelial cell-derived exosomes contain 1354 proteins and 1992 mRNAs. Several proteins and mRNAs showed altered levels after exposure of their producing cells to cellular stress. Interestingly, cells exposed to high sugar concentrations had altered exosome protein composition only to a minor extent, and exosome RNA composition was not affected. Low-intensity ultrasound-induced (LIUS) anti-inflammatory effects have been achieved by upregulation of extracellular vesicle/exosome biogenesis. These exosomes carry anti-inflammatory cytokines and anti-inflammatory microRNAs, which inhibit inflammation of target cells via multiple shared and specific pathways. A study suggested that exosome-mediated anti-inflammatory effects of LIUS are feasible and that these techniques are potential novel therapeutics for cancers, inflammatory disorders, tissue regeneration, and tissue repair.103 Another factor, called manumycin-A (MA), a natural microbial metabolite, was analyzed in exosome biogenesis and secretion in castration-resistant prostate cancer (CRPC) C4-2B, cells. The effect of MA on cell growth was observed, and the results revealed that there was no effect on cell growth. However, MA attenuated the ESCRT-0 proteins Hrs, ALIX, and Rab27a, and exosome biogenesis and secretion by CRPC cells. The inhibitory effect of MA on exosome biogenesis and secretion was primarily mediated via targeted inhibition of Ras/Raf/ERK1/2 signaling. These findings suggest that MA is a potential drug candidate for the suppression of exosome biogenesis and secretion by CRPC cells.104

Methods of isolation of exosomes play critical roles in functions and delivery. Although several methods such as ultracentrifugation, density gradient centrifugation, chromatography, filtration, polymer-based precipitation, and immunoaffinity have been adopted to isolate pure exosomes without contamination, there is still a lack of consistency and agreement.105 Isolation of exosomes along with non-exosomal materials and damaged exosomal membranes creates artifacts and alters the protein and RNA profiles. Since exosomes are obtained from a variety of sources, the composition of proteins/lipids influences the sedimentation properties and isolation. Thus, precise and consistent techniques are warranted for the isolation, purification, and application of exosomes.

Although several functions of exosomes have been explored, the precise function of exosomes remains a mystery. Historically, exosomes have been known to function as cellular garbage bags, recyclers of cell surface proteins, cellular signalers, intercellular signaling and cell-cell communications, immune responses, cellular homeostasis, autophagy, and infectious diseases.106 (Figure 4) ECVs are secreted cell-derived membrane particles involved in intercellular signaling and cell-cell communications, and contain immense bioactive information. Most cell types produce exosomes and release these into the extracellular environment, circulating through different bodily fluids such as urine, blood, and saliva and transferring their cargo to recipient cells. These vesicles play a significant role in various pathological conditions, such as different types of cancer, neurodegenerative diseases, infectious diseases, pregnancy complications, obesity, and autoimmune diseases, as reviewed elsewhere.107 Exosomes play a significant role in intercellular communication between cells by interacting with target cells via endocytosis.108 More specifically, exosomes are involved in cancer development, survival and metastasis of tumors, drug resistance, remodeling of the extracellular matrix, angiogenesis, thrombosis, and proliferation of tumor cells.94,109111 Exosomes contribute significantly to tumor vascularization and hypoxia-mediated inter-tumor communication during cancer progression, and premetastatic niches, which are significant players in cancer.16,94,109,112 Exosomes derived from hepatic epithelial cells increase the expression of enhancer zeste homolog 2 (EZH2) and cyclin-D1, and subsequently promotes G1/S transition.113

Figure 4 Multifunctional aspects biological functions of exosomes.

Conventionally, cells communicate with adjacent cells through direct cell-cell contact through gap junctions and cell surface protein/protein interactions, whereas cells communicating with distant cells do so through secreted soluble factors, such as hormones and cytokines, to facilitate signal propagation.114 Cells also communicate through electrical and chemical signals.115 Several studies have suggested that exosomes play vital roles in intercellular communication by serving as vehicles for transferring various cellular constituents, such as proteins, lipids, and nucleic acids, between cells.6,116118 Exosomes function as exosomal shuttle RNAs in which some exosomal RNAs from donor cells functions in recipient cells,6 a form of genetic exchange. Recently, researchers found that cells communicating with other cells through exosomes carrying cell-specific cargoes of proteins, lipids, and nucleic acids may employ novel intercellular communication mechanisms.30 Exosomes exert influences through various mechanistic approaches, such as direct stimulation of target cells via surface-bound ligands; transfer of activated receptors to recipient cells; and epigenetic reprogramming of recipient cells.119,120 Exosomes play critical roles in immunoregulation, including antigen presentation, immune activation, immune suppression, and immune tolerance via exosome-mediated intercellular communication. Mesenchymal stem cell (MSC)-derived exosomes play significant roles in wound healing processes.121 Exosomes from platelet-rich plasma (PRP) inhibit the release of TNF-. PRP-Exos significantly decreases the apoptotic rate of osteoarthritis (OA) chondrocytes compared with activated PRP (PRP-As).122 Extracellular vesicle (ECV)-modified polyethylenimine (PEI) complexes enhance short interfering RNA (siRNA) delivery by forming non-covalent complexes with small RNA molecules, including siRNAs and anti-miRs, in both conditions, in vitro and in vivo.123 Non-GSC glioma cells were treated with GSC-released exosomes. The results showed that GSC-released exosomes increase proliferation, neurosphere formation, invasive capacities, and tumorigenicity of non-GSC glioma cells through the Notch1 signaling pathway and stemness-related protein expressions.124

Exosomal miR-1910-3p promotes proliferation and migration of breast cancer cells in vitro and in vivo through downregulation of myotubularin-related protein 3 and activation of the nuclear factor-B (NF-B) and wnt/-catenin signaling pathway, and promotes breast cancer progression.125 Human hepatic progenitor cell (CdH)-derived exosomes (EXOhCdHs) play a crucial role in maintaining cell viability and inhibit oxidative stress-induced cell death. Experimental evidence suggests that inhibition of exosome secretion treatment with GW4869 results in the acceleration of reactive oxygen species (ROS) production, thereby causing a decrease in cell viability.126 Tumor-derived EXs (TDEs) are vehicles that enable communication between cells by transferring bioactive molecules, also delivering oncogenic molecules and containing different molecular cargoes compared to EXs delivered from normal cells. They can therefore be used as non-invasive biomarkers for the early diagnosis and prognosis of most cancers, including breast and ovarian cancers.127 Exosomes released by ER-stressed HepG2 cells significantly enhance the expression levels of several cytokines, including IL-6, monocyte chemotactic protein-1, IL-10, and tumor necrosis factor- in macrophages. ER stress-associated exosomes mediate macrophage cytokine secretion in the liver cancer microenvironment, and also indicate the potential of treating liver cancer via an ER stress-exosomal-STAT3 pathway.128 Mesenchymal stem cell-derived exosomal miR-223 protects neuronal cells from apoptosis, enhances cell migration and increases miR-223 by targeting PTEN, thus activating the PI3K/Akt pathway. In addition, exosomes isolated from the serum of AD patients promote cell apoptosis through the PTEN-PI3K/Akt pathway and these studies indicate a potential therapeutic approach for AD.129 A mouse model of diabetes demonstrated that mesenchymal stromal cell-derived exosomes ameliorate peripheral neuropathy through increased nerve conduction velocity. In addition, MSC-derived exosomes substantially suppress proinflammatory cytokines.130

Exosomes derived from activated astrocytes promote microglial M2 phenotype transformation following traumatic brain injury (TBI). miR-873a-5p significantly inhibits LPS-induced microglial M1 phenotype transformation.131 Several studies reported that exosomes are involved in cancer progression and metastasis; however, this depends on the type of cells the exosomes were derived from. For example, human umbilical vein endothelial cells (HUVEC) were treated with exosomes derived from HeLa cells (ExoHeLa), and the expression of tight junctions (TJ) proteins, such as zonula occludens-1 (ZO-1) and Claudin-5, was significantly reduced compared with exosomes from human cervical epithelial cells. Thus, permeability of the endothelial monolayer was increased after the treatment with ExoHeLa. Mice studies have shown that injection of ExoHeLa into mice increased vascular permeability and tumor metastasis. The results from this study demonstrated that HeLa cell-derived exosomes promote metastasis by triggering ER stress in endothelial cells and break down endothelial integrity. Such effects of exosomes are microRNA-independent.132 Exosomes mediate the gene expression of target cells and regulate pathological and physiological processes including promoting angiogenesis, inhibiting ventricular remodeling and improving cardiac function, as well as inhibiting local inflammation and regulating the immune response. Accumulating evidence shows that exosomes possess therapeutic potential through their anti-apoptotic and anti-fibrotic roles.

The functions of exosomes in immune responses are well established and do not cause any severe immune responses. A mouse study demonstrated that administration of a low dose of mouse or human cell-derived exosomes for extended periods of time caused no severe immune reactions.133 The function of exosomes in immune regulation is regulated by the transfer and presentation of antigenic peptides. Exosomes contain antigen-presenting cells (APCs) carrying peptide MHC-II and costimulatory signals and directly present the peptide antigen to specific T cells to induce their activation.134 For example, intradermal injection of APC-derived exosomes with MHC-II loaded with tumor peptide delayed tumor progression and growth.135 Exosome-derived immunogenic peptides activate immature mouse dendritic cells and indirectly activate APCs, and induce specific CD4+ T cell proliferation.136 Exosomes containing IFNa and IFNg, tumor necrosis factor a (TNFa), and IL from macrophages promoted dendritic cell maturation, CD4+ and CD8+ T cell activation, and the regulation of macrophage IL expression.137 The cargo of exosomes, such as DNA and miRNA, regulate the innate and adaptive immune responses. Exosomes are able to regulate the immune response by controlling gene expression and signaling pathways in recipient cells through transfer of miRNAs, and eventually control dendritic cell maturation.138 Exosomes containing miR-212-3p derived from tumors down-regulate the MHC-II transcription factor RFXAP (regulatory factor X associated protein) in dendritic cells, possibly promoting immune evasion by cancer cells.139 Exosomes containing miR-222-3p down regulate expression of SOCS3 (suppressor of cytokine signaling 3) in monocytes, which is involved in STAT3-mediated M2 polarization of macrophages.140 In mice, exosomes stimulate adaptive immune responses, including the activation of dendritic cells, with the uptake of breast cancer cell-derived exosomal genomic DNA and activation of cGAS-STING signaling and antitumor responses.141 The priming of dendritic cells is associated with the uptake of exosomal genomic and mitochondrial DNA (mtDNA) from T cells, inducing type I IFN production by cGAS-STING signaling.142 Inhibition of EGFR leads to increased levels of DNA in the exosomes and induces cGAS-STING signaling in dendritic cells, contributing to the overall suppression of tumor growth.143 Conversely, uptake of tumor-derived exosomal DNA by circulating neutrophils was shown to enhance the production of tissue factor and IL-8, which play a role in promoting tumor inflammation and paraneoplastic events.144 Melanoma-derived exosomes containing PD-L1 (programmed cell death ligand 1) suppress CD8+ T cell antitumor function and cancer cell-derived exosomes block dendritic cell maturation and migration in a PD-L1-dependent manner. Engineered cancer cell-derived exosomes promote dendritic cell maturation, resulting in increased proliferation of T cells and antitumor activity.145147

Inflammation is an important process for maintaining homeostasis in cellular systems. Systemic inflammation is an essential component in the pathogenesis of several diseases.148,149 Exosomes seem to play a crucial role in inflammation processes through cargo molecules, such as miRNA and proteins, which act on nearby as well as distant target tissues. Exosomes play a vital role in intercellular communication between cells via endocytosis and are associated with modulation of inflammation, coagulation, angiogenesis, and apoptosis.20,150153 Exosomes derived from dendritic cells, B lymphocytes, and tumor cells release exosomes that can regulate immunological memory through the surface expression of antigen-presenting MHC I and MHC II molecules, and subsequently elicit T cell activation and maturation.134,137,154156 Exosomes play a crucial role in carrying and presenting functional MHC-peptide complexes to modulate antigen-specific CD8+ and CD4+ responses.157,158 Exosomes containing miR-Let-7d influence the growth of T helper 1 (Th1) cells and inhibit IFN- secretion.159 Exosomes derived from choroid plexus epithelial cells containing miR-146a and miR-155 upregulate the expression of inflammatory cytokines in astrocytes and microglia.160 Exosomes containing miR-181c suppress the expression of Toll-like receptor 4 (TLR-4) and subsequently lower TNF- and IL-1 levels in burn-induced inflammation.161 Exosomal miR-155 from bone marrow cells (BMCs) increases the level of TNF- and subsequently enhances innate immune responses in chronic inflammation.162 Exosomes containing miR-150-5p and miR-142-3p derived from dendritic cells (DCs) increase expression of interleukin 10 (IL-10) and a decrease in IL-6 expression.163 Exosomal miR-138 can protect against inflammation by decreasing the expression level of NF-B, a transcription factor that regulates inflammatory cytokines such as TNF- and IL-18.164 HIF-1-inducing exosomal microRNA-23a expression from tubular epithelial cells mediates the cross talk between tubular epithelial cells and macrophages, promoting macrophage activation and triggering tubulointerstitial inflammation.165 A rat model study demonstrated that bone marrow mesenchymal stem cell (BMSC)-derived exosomes reduced inflammatory responses by modulating microglial polarization and maintaining the balance between M2-related and M1-related cytokines.165 Melatonin-stimulated mesenchymal stem cell (MSC)-derived exosomes improve diabetic wound healing through regulating macrophage M1 and M2 polarization by targeting the PTEN/AKT pathway, and significantly suppressed the pro-inflammatory factors IL-1 and TNF- and reduced the relative gene expression of IL-1, TNF-, and iNOS. Increasing levels of anti-inflammatory factor IL-10 are associated with increasing relative expression of Arg-1.166

Immunomodulators are essential factors for the prevention and treatment of disorders occurring due to an over high-spirited immune response, such as the SARS-CoV-2-triggered cytokine storm leading to lung pathology and mortality seen during the ongoing viral pandemic.167 MSC-secreted extracellular vesicles exhibit immunosuppressive capacity, which facilitates the regulation of the migration, proliferation, activation, and polarization of various immune cells, promoting a tolerogenic immune response while inhibiting inflammatory responses.168 Collagen scaffold umbilical cord-derived mesenchymal stem cell (UC-MSC)-derived exosomes induce collagen remodeling, endometrium regeneration, increasing the expression of the estrogen receptor /progesterone receptor, and restoring fertility. Furthermore, exosomes modulate CD163+ M2 macrophage polarization, reduce inflammation, increase anti-inflammatory responses, facilitate endometrium regeneration, and restore fertility through the immunomodulatory functions of miRNAs.169 Exosomes released into the airways during influenza virus infection trigger pulmonary inflammation and carry viral antigens and it facilitate the induction of a cellular immune response.170 Shenoy et al171 reported that exosomes derived from chronic inflammatory microenvironments contribute to the immune suppression of T cells. These exosomes arrest the activation of T cells stimulated via the T cell checkpoint (TCR). Exosomes secreted by normal retinal pigment epithelial cells (RPE) by rotenone-stimulated ARPE-19 cells induce apoptosis, oxidative injury, and inflammation in ARPE-19 cells. Exosomes secreted under oxidative stress induce retinal function damage in rats and upregulate expression of Apaf1. Overexpression of Apaf1 in exosomes secreted under oxidative stress (OS) can cause the inhibition of cell proliferation, increase in apoptosis, and elicitation of inflammatory responses in ARPE-19 cells. Exosomes derived from ARPE-19 cells under OS regulate Apaf1 expression to increase apoptosis and to induce oxidative injury and inflammatory response through a caspase-9 apoptotic pathway.172 Collectively, these findings highlight the critical role of exosomes in inflammation and suggest the possibility of utilizing exosomes as an inducer to attenuate inflammation and restore impaired immune responses in various diseases including cancer.

The endomembrane system of eukaryotic cells is a complex series of interconnected membranous organelles that play vital roles in protecting cells from adverse conditions, such as stress, and maintaining cell homeostasis during health and disease.173 To preserve cellular homeostasis, higher eukaryotic cells are equipped with various potent self-defense mechanisms, such as cellular senescence, which blocks the abnormal proliferation of cells at risk of neoplastic transformation and is considered to be an important tumor-suppressive mechanism.174,175 Exosomes contribute to reduce intracellular stress and preservation of cellular homeostasis through clearance of damaged or toxic material, including proteins, lipids, and even nucleic acids. Therefore, exosomes serve as quality controller in cells.176 The vesicular transport system plays pivotal roles in the maintenance of cell homeostasis in eukaryote cells, which involves the cytoplasmic trafficking of biomolecules inside and outside of cells. Several types of membrane-bound organelles, such as the Golgi apparatus, endoplasmic reticulum (ER), endosomes and lysosomes, in association with cytoskeleton elements, are involved in the intracellular vesicular system. Molecules are transported through exocytosis and endocytosis to maintain homeostasis through the intracellular vesicular system and regulate cells responses to the internal and external environment. To maintain homeostasis and protect cells from various stress conditions, autophagy is an intracellular vesicular-related process that plays an important role through the endocytosis/lysosomal/exocytosis pathways through degradation and expulsion of damaged molecules out of the cytoplasm.177179 Autophagy, as an intracellular waste elimination system, is a synchronized process that actively participates in cellular homeostasis through clearance and recycling of damaged proteins and organelles from the cytoplasm to autophagosomes, and then to lysosomes.38,180182 Cells maintain homeostasis by autophagosomes, which are vesicles derived from autophagic and endosomal compartments. These processes are involved in adaption to nutrient deprivation, cell death, growth, and tumor progression or suppression. Autophagy flux contributes to maintaining homeostasis in the tumor microenvironment of endothelial cells. To support this concept, a study provided evidence suggesting that depletion of Atg5 in ECs could intensify the abnormal function of tumor vessels.183 Exosome secretion plays a crucial role in maintaining cellular homeostasis in exosome-secreting cells. As a consequence of blocking exosome secretion, nuclear DNA accumulates in the cytoplasm, thereby causing the activation of cytoplasmic DNA sensing machinery. Blocking exosome secretion aggravates the innate immune response, leading to ROS-dependent DNA damage responses and thus inducing senescence-like cell-cycle arrest or apoptosis in normal human cells. Thus, cells remove harmful cytoplasmic DNA, protecting them from adverse effects.182 Salomon and Rice reported that the involvement of exosomes in placental homeostasis and pregnancy disorders. EVs of placental origin are found in a variety of body fluids including urine and blood. Moreover, the number of exosomes throughout gestation is higher in complications of pregnancy, such as preeclampsia and gestational diabetes mellitus, compared to normal pregnancies.184

The endolysosomal system is critically involved in maintaining homeostasis through the highly regulated processes of internalization, sorting, recycling, degradation, and secretion. For example, endocytosis allows the internalization of various receptor proteins into cells, and vesicles formed from the plasma membrane fuse and deliver their membrane and protein content to early endosomes. Similarly, significant amounts of internalized content are recycled back to the plasma membrane via recycling endosomes,76 while the remaining material is sequestered in ILVs in late endosomes, also known as multivesicular bodies.185,186 Tetraspanin proteins, such as CD63 and CD81, are regulators of ILV formation. Once ILVs are formed, MVBs can degrade their cargo by fusing with lysosomes or, alternatively, MVBs can secrete their ILVs by fusing with the plasma membrane and release their content into extracellular milieu.187190 Exosomes play an important role in regulating intracellular RNA homeostasis by promoting the release of misfolded or degraded RNA products, and toxic RNA products. Y RNAs are involved in the degradation of structured and misfolded RNAs. Further studies have demonstrated that proteins involved in RNA processing are abundant in exosomes, and the half-lives of secreted RNAs are almost twice as short as those of intracellular mRNAs. These studies suggest that cells maintain intracellular RNA homeostasis through the release of distinct RNA species in extracellular vesicles.191193 Exosomes reduce cholesterol accumulation in Niemann-Pick type C disease, a lysosomal storage disease in which cells accumulate unesterified cholesterol and sphingolipids within the endosomal and lysosomal compartment.194

Autophagy is the intracellular vesicular-related process that regulates the cell environment against pathological and stress conditions. In order to maintain homeostasis and protect the cells against stress conditions, internal vesicles or secreted vesicles serve as a canal to degrade and expel damaged molecules out of the cytoplasm.38,181,182 Autophagy protects the cell from various stress conditions and maintains cellular homeostasis, regulating cell survival and differentiation through clearance and recycling of damaged proteins and organelles from the cytoplasm to autophagosomes, and then to lysosomes.180 Several studies have demonstrated that proteins are involved in controlling tumor cell function and fate, and mediate crosstalk between exosome biogenesis and autophagy. Coordination between exosome-autophagy networks serves as a tool to conserve cellular homeostasis via the lysosomal degradative pathway and/or secretion of cargo into the extracellular milieu.176,195 Autophagy is a multi-step process that occurs by initiation, membrane nucleation, maturation and finally the fusion of autophagosomes with lysosomes. The autophagy process is not only linked with endocytosis but is also linked with the biogenesis of exosomes. For example, subsets of the autophagy machinery involved in the biogenesis of exosomes and the autophagic process itself appear dispensable.78,196 Crosstalk between exosomal and autophagic pathways has been reported in a growing number of diseases. Proteomic studies were performed to analyze the involvement of key proteins in the interconnection between exosome and autophagy pathways. They found that almost all proteins were identified; however, their involvement differed between them. Among 100 proteins, four proteins were highly ranked including HSPA8 (3/100), HSP90AA1 (8/100), VCP (24/100), and Rab7A (81/100). These data suggest an interconnection between the exosome and autophagy.197,198 Endosomal autophagy plays a significant role in the interconnection between exosomes and autophagy. Stress is a major factor for autophagy. In particular, the starvation of cells is a key inducer of autophagy, and induces enlargement of MVB structures and a co-localization of Rab11 and LC3 in these structures, an indication that autophagy-related processes are associated with the MVB.199 The sorting of autophagy-related cargo into MVBs is dependent on Hsc70 (HSPA8), VPS4, and TSG101, and independent on LAMP-2A, thereby excluding a role for, the lysosome.200 Several proteins are involved in the regulation and biogenesis of secretory autophagy compartments such as GRASPs, LC3, Rab8a, ESCRTs, and SNAREs, along with several Atg proteins.181,201,202 Autophagosomes could fuse with MVBs to form amphisomes and release vesicles to the external environment.203

Autophagy and exosome biogenesis and function are interconnected by microRNA. Over-expression of miR-221/222 inhibits the level of PTEN and activates Akt signaling, and subsequently reduces the expression of hallmarks that positively relate to autophagy including LC3, ATG5 and Beclin1, and increases the expression of SQSTM1/p62.204 MiR-221/222 from human aortic smooth muscle cell (HAoSMC)-derived exosomes inhibit autophagy in HUVECs by modulating the PTEN/Akt signaling pathway. miRNA-223 attenuates hypoxia-induced apoptosis and excessive autophagy in neonatal rat cardiomyocytes and H9C2 cells via the Akt/mTOR pathway, by targeting poly(ADP-ribose) polymerase 1 (PARP-1) through increased autophagy via the AMPK/mTOR and Akt/mTOR pathways205 ATG5 mediates the dissociation of vacuolar proton pumps (V1Vo-ATPase) from MVBs, which prevents acidification of the MVB lumen and allows MVB-PM fusion and exosome release. Accordingly, knockout of ATG5 or ATG16L1 significantly reduces exosome release and attenuates the exosomal enrichment of lipidated LC3B. These findings demonstrate that autophagic mechanisms possibly regulate the fate of MVBs and subsequent exosome biogenesis.78 Bone marrow MSC (BMMSC)-derived exosomes contain a high level of miR-29c, which regulates autophagy under hypoxia/reoxygenation (H/R) conditions.206 Human umbilical cord MSC-derived exosomes (HucMDEs) promote hepatic glycolysis, glycogen storage, and lipolysis, and reduce gluconeogenesis. Additionally, autophagy potentially contributes to the effects of HucMDE treatment and increases formation of autophagosomes and the autophagy marker proteins BECN1, MAP, and 1LC3B. These findings suggest that HucMDEs improve hepatic glucose and lipid metabolism in T2DM rats by activating autophagy via the AMPK pathway.207 Liver fibrosis is a serious disorder caused by prolonged parenchymal cell death, leading to the activation of fibrogenic cells, extracellular matrix accumulation, and eventually liver fibrosis. Exosomes derived from adipose-derived mesenchymal stem cells (ADSCs) have been used to deliver circular RNAs mmu_circ_0000623 to treat liver fibrosis. The findings from this study suggest that Exos from ADSCs containing mmu_circ_0000623 significantly suppress CCl4-induced liver fibrosis by promoting autophagy activation. Autophagy inhibitor treatment significantly reverses the treatment effects of Exos.208 Inhibition of autophagy by PDGF and its downstream molecule SHP2 (Src homology 2-containing protein tyrosine phosphatase 2) increased hepatic stellate cell (HSC)-derived EV release. Disruption of mTOR signaling abolishes PDGF-dependent EV release. Activation of mTOR signaling induces the release of MVB-derived exosomes by inhibiting autophagy, as well as microvesicles, through activation of ROCK1 signaling. Furthermore, deletion of SHP2 attenuates CCl4 or BDL-induced liver fibrosis.209 The therapeutic effects of exosomes containing high concentrations of mmu_circ_0000250 were analyzed in diabetic mice. The findings indicated that a high concentration of mmu_circ_0000250 had a better therapeutic effect on wound healing when compared with wild-type exosomes from ADSCs. The results also showed that exosome treatment with mmu_circ_0000250 increased angiopoiesis in wounded skin and suppressed apoptosis by inducing miR-128-3p/SIRT1-mediated autophagy.210 A study showed that mice treated with differentiated cardiomyocyte (iCM) exosomes exhibited significant cardiac improvement post-myocardial infarction, with significantly reduced apoptosis and fibrosis. Apoptosis was associated with reduced levels of hypoxia and inhibition of exosome biogenesis. iCM-exosome-treated groups showed upregulation of autophagosome production and autophagy flux. Hence, these findings indicate that iCM-Ex can improve post-myocardial infarction cardiac function by regulating autophagy in hypoxic cardiomyocytes.211 Exosomes of hepatocytes play a crucial role in inhibiting hepatocyte apoptosis and promoting hepatocyte regeneration. Mesenchymal stem cell-derived hepatocyte-like cell exosomes (MSC-Heps-Exo) were injected into a mouse hepatic Ischemia/reperfusion (I/R) I/R model through the tail. The results demonstrated that MSC-Heps-Exo effectively relieve hepatic I/R damage, reduce hepatocyte apoptosis, and decrease liver enzyme levels. A possible mechanism of reduced hepatic ischemia/reperfusion injury is the enhancement of autophagy.212

Exosomes play a critical role in viral infections, particularly of retroviruses and retroviruses, and use preexisting pathways for intracellular protein trafficking and formation of infectious particles. Exosomes and viruses share several features including biogenesis, uptake by cells, and the intracellular transfer of RNAs, mRNAs, and cellular proteins. Some features are different, including self-replication after infection of new cells, regulation of viral expression, and complex viral entry mechanisms.213,214 Exosomes secreted from virus-infected cells carry mostly cargo molecules such as viral proteins, genomic RNA, mRNA, miRNA, and genetic regulatory elements.215218 These cargo molecules are involved in the alteration of recipient cell behavior, regulating cellular responses, and enabling infection by various types of viruses such as human T-cell lymphotropic virus (HTLV), hepatitis C virus (HCV), dengue virus, and human immunodeficiency virus (HIV).215 Exosomes communicate with host cells through contact between exosomes and their recipient cells, via different kinds of mechanisms. Initially, the transmembrane proteins of exosomes build a network directly with the signaling receptors of target cells and then join with the plasma membrane of recipient cells to transport their content to the cytosol. Finally, the exosomes are incorporated into the recipient cells.219221 A report suggested that disruption of exosomal lipid rafts leads to the inhibition of internalization of exosomes.95 Exosomes derived from HIV-infected patients contain the trans-activating response element, which is responsible for HIV-1 replication in recipient cells through downregulation of apoptosis.222 While exosomes serving as carrier molecules, exosomes contain miRNAs that induce viral replication and immune responses either by direct targeting of viral transcripts or through indirect modulation of virus-related host pathways. In addition, exosomes have been found to act as nanoscale carriers involved in HIV pathogenesis. For example, exosomes enhance HIV-1 entry into human monocytic and T cell lines through the exosomal tetraspanin proteins CD9 and CD81.223 Influenza virus infection causes accumulation of various types of microRNAs in bronchoalveolar lavage fluid, which are responsible for the potentiation of the innate immune response in mouse type II pneumocytes. Serum of influenza virus-infected mice show significant levels of miR-483-3p, which increases the expression of proinflammatory cytokine genes and inflammatory pathogenesis of H5N1 influenza virus infection in vascular endothelial cells.224 Exosomes are involved in the transmission of inflammatory, apoptotic, and regenerative signals through RNAs. Chen et al investigated the potential functions of exosomal RNAs by RNA sequencing analysis in exosomes derived from clinical specimens of healthy control (HC) individuals and patients with chronic hepatitis B (CHB) and acute-on-chronic liver failure caused by HBV (HBV-ACLF). The results revealed that the samples contained unique and distinct types of RNAs in exosomes.225 Zika virus (ZIKV) infection causes severe neurological malfunctions including microcephaly in neonates and other complications associated with Guillain-Barr syndrome in adults. Interestingly, ZIKV uses exosomes as mediators of viral transmission between neurons and increases production of exosomes from neuronal cells. Exosomes derived from ZIKV-infected cells contained both ZIKV viral RNA and protein(s) which are highly infectious to nave cells. ZIKV uses neutral Sphingomyelinase (nSMase)-2/SMPD3 to regulate production and release of exosomes.226

During infections, viruses replicate in host cells through vesicular trafficking through a sequence of complexes known as ESCRT, and assimilate viral constituents into exosomes. Exosomes encapsulate viral antigens to maximize infectivity by hiding viral genomes, entrapping the immune system, and maximizing viral infection in uncontaminated cells. Exosomes can be used as a source of viral antigens that can be targeted for therapeutic use. A Variety of infectious diseases caused by viruses such as HCV, ZIKV, West Nile virus (WNV), and DENV enter into the host cells using clathrin-mediated or receptor-mediated endocytosis. For example, HCV infects host cells by specific targeting of cells through cellular contact, and hepatocyte-derived exosomes that contain HCV RNA can stimulate innate immune cells.217,227230 Exosomes show structural and molecular similarity to HIV-1 and HIV-2, which are enclosed by a lipid bilayer, and in the vital features of size and density, RNA species, and macro biomolecules including carbohydrates, lipids, and proteins. HIV-infected cells release enriched viral RNAs containing exosomes derived from HIV-infected cells and are enhanced with viral RNAs and Nef protein.6,38,231236 Izquierdo-Useros et al reported that both exosomes and HIV-1 express sialyllactose-containing gangliosides and interact with each other via sialic-acid-binding immunoglobulin-like lectins (Siglecs)-1. Siglecs-1 stimulates mature dendritic cell (mDC) capture and storage of both exosomes and HIV-1 in mDCs.237 Exosomes released from HIV-infected T cells contain transactivation response (TAR) element RNA, which stimulate proliferation, migration, and invasion of oral/oropharyngeal and lung cancer cells.238 Nuclear VP40 from Ebola virus VP40 upregulates cyclin D1 levels, resulting in dysregulated cell cycle and EV biogenesis. Synthesized extracellular vesicles contain cytokines and EBOV proteins from infected cells, which are responsible for the destruction of immune cells during EBOV pathogenesis.239 HIV enters into the host cells through human T-cell immunoglobin mucin (TIM) proteins. TIMs are a group of proteins (TIM-1, TIM-3, and TIM-4) that promote phagocytosis of apoptotic cells.240 TIM-4 is involved in HIV-1 exosome-dependent cellular entry mechanisms. Substantiating this hypothesis, neural stem cell (NSC)-derived exosomes containing TIM-4 protein increase HIV-1 exosome-dependent cellular entry into host cells, and antibody against TIM4 inhibits exosome-mediated entry of HIV in various types of cell.241

Exosomes show immense promise in biomedical applications due to their potential in drug delivery, the carriage of biomolecular markers of many diseases, and cellular protection. In addition, they can be used in non-invasive diagnostics or minimum invasive diagnostics.150 Detection of biomarkers is vital for early diagnosis of cancer and also critical for treatment. Several studies have documented the importance of exosomes in a variety of diseases, although further examination of the biology and functions of exosomes is warranted due to the continuing emergence of new diseases in the present world. The complex cargo of exosomes facilitates the exploration of a variety of diagnostic windows into disease detection, monitoring, and treatment. Exosomes are found in all biological fluids and are secreted by all cells, rendering them attractive for use through minimally invasive liquid biopsies, and they have the potential for use in longitudinal sampling to follow disease progression.242 Exosomes are produced and secreted by almost all body fluids, including blood, urine, saliva, breast milk, cerebrospinal fluid, semen, amniotic fluid, and ascites. These exosomes contain micro RNAs, proteins, and lipids serving as diagnostic markers.120 Exosomes are used in diagnostic applications in various kinds of diseases, such as cardiovascular diseases (CVDs),243 diseases of the central nervous system (CNS),244 cancer,245 and other prominent diseases including in the liver,246 kidney,247 and lung.248 Exosomes are potentially used to detect cancer-associated mutations in serum and also for the transfer of genomic DNA from donor cells to recipient cells.249 Exosomes carrying specific miRNAs or groups of miRNAs can be used as diagnostic markers to detect cancer. For example, exosomes containing oncogenic Kras, which have tumor-suppressor miRNAs-100, seem to have high diagnostic value, which could facilitate the differentiation of the expression pattern between cancer cells and normal cells.250,251 Similarly, miR-21 is considered to be diagnostic marker for various types of cancer including glioblastomas and pancreatic, colorectal, colon, liver, breast, ovarian, and esophageal cancers.252 Tumor suppressor miRNAs, such as miR-146a and miR-34a, function as diagnostic tools to detect liver, breast, colon, pancreatic, and hematologic malignancies.251 Exosomes containing GPC1 (glypican 1) are used as diagnostic markers to detect pancreatic, breast, and colon cancer.253,254

Exosomes play critical roles in various types of disease, and particularly in cancer progression and resistance to therapy. The unique biogenesis of exosomes and their biological features have generated excitement for their potential use as biomarkers for cancer.255 Generally, exosomes are produced and secreted by most cells and contain all the biological components of a cell. Hence, exosomes are found in all biological fluids and provide excellent opportunities for use as biomarkers.242 Surface proteins of exosomes are involved in the regulation of the tumor immune microenvironment and the monitoring of immunotherapies. Hence, exosome proteins play a critical role in cancer signaling.256 Exosomes from patients with metastatic pancreatic cancer show a higher mutant Kras allele frequency than exosomes from patients with local disease. In addition, the exosomes also accumulate a significantly higher level of cancer cell-specific DNA such as cytoplasmic DNA.8,257 Exosomes protect DNA and RNA from enzymatic degradation by encapsulation and stability in exosomes. The enhanced stability and retention of exosomes in liquid biopsies increases the availability and performance of exosomes as cancer biomarkers.258 Cancer cells contain cargo molecules, such as nucleic acid, proteins, metabolites, and lipids that are relatively different from normal cells, which is a contributing factor for their candidacy as cancer biomarkers. Exosomes isolated and purified from patient plasma samples enriched for miR-10b-5p, miR-101-3p, and miR-143-5p have been identified as potential diagnostic markers for gastric cancer with lymph node metastasis, gastric cancer with ovarian metastasis, and gastric cancer with liver metastasis, respectively.259 Kato et al analyzed the expression of CD44 protein and mRNA from cell lysates and exosomes from prostate cancer cells.260 Exosomes from serum containing CD44v8-10 mRNA was used as a diagnostic marker for docetaxel resistance in prostate cancer patients. The study was performed to evaluate plasma exosomal mRNA-125a-5p and miR-141-5p miRNAs as biomarkers for the diagnosis of prostate cancer from 19 healthy individuals and 31 prostate cancer patients. In comparing the miR-125a-5p/miR-141-5p level ratio, prostate cancer patients had significantly higher levels of miR-125a-5p/miR-141-5p. The findings from this study demonstrated that plasma exosomal expression of miR-141-3p and miR-125a-5p are markers of specific tumor traits associated with prostate cancer.261 Serum samples from 81 patients with gastric cancer showed that exosomes contained significant levels of long non-coding RNA (lncRNA) H19, which could be a diagnostic marker for gastric cancer.262 Plasma exosomes are suitable candidates as biomarkers for various diseases. For instance, plasma exosome lncRNA expression profiles were examined in esophageal squamous cell carcinoma (ESCC) patients. The findings suggest that five different types of lncRNAs were at significantly higher levels in exosomes from ESCC patients than in non-cancer controls. These lncRNAs may serve as highly effective, noninvasive biomarkers for ESCC diagnosis.263 Differential expression of lncRNAs, such as LINC00462, HOTAIR, and MALAT1, are significantly upregulated in hepatocellular carcinoma (HCC) tissues. The exosomes of the control group had a larger number of lncRNAs with a high amount of alternative splicing compared to hepatic disease patients.264 To demonstrate exosomes as a non-invasive cancer diagnostic tool, RNA-sequencing analysis was performed between three pairs of non-small-cell lung cancer (NSCLC) patients and controls from Chinese populations. The results show that circ_0047921, circ_0056285, and circ_0007761 were significantly expressed and that these exosomal circRNAs are promising biomarkers for NSCLC diagnosis.265 Exosomes were isolated from the serum of 34 patients with acute myocardial infarction (AMI), 31 patients with unstable angina (UA), and 22 healthy controls. The isolated exosomes exhibited higher levels of miR-126 and miR-21 in the patients with UA and AMI than in the healthy controls.266 Xu et al designed a study to examine tumor-derived exosomes as diagnostic biomarkers. In this study exosome miRNA microarray analysis was performed in the peripheral blood from four lung adenocarcinoma patients, including two with metastasis and two without metastasis. The results found that miR-4436a and miR-4687-5p were upregulated in the metastasis and non-metastasis group, while miR-22-3p, miR-3666, miR-4448, miR-4449, miR-6751-5p, and miR-92a-3p were downregulated. Exosomes containing miR-4448 have served as a diagnostic marker of patients with adenocarcinoma metastasis. Increased understanding of exosome biogenesis, structure, and function would enhance the performance of biomarkers in various kinds of disease diagnosis, prognosis, and surveillance.267

Exosomes have unique features such as ease of handling, molecular composition, and critical immunogenicity, and it is particularly easy to use them to transfer genes and proteins into cells. These unique characteristic features can inhibit angiogenesis and cancer metastasis, which are the two main targets of cancer therapy.268,269 Exosomes have potential therapeutic applications in a variety of diseases due to their potential capacity as vehicles for the delivery of therapeutic agents (Figure 5). Exosomes from colon cancer cells contain the highly immunogenic antigens MelanA/Mart-1 and gp100, serving as an indicator of tumor origin in particular organelles. Animal studies have demonstrated that tumor-derived antigen-containing exosomes induce potent antitumor T-cell responses and tumor regression.270 Exosomes containing tumor antigens are able to stimulate CD4+and CD8+T cells, and antigen-presenting exosomes inhibit tumor growth.135,271,272 MSC-derived exosomes exhibit the immunomodulatory and cytoprotective activities of their parent cells.273,274 Similarly, exosomes derived from bone marrow show protective roles in myocardial ischemia/reperfusion injury,109 hypoxia-induced pulmonary hypertension,275 and brain injury,276,277 and inhibit breast cancer growth via vascular endothelial growth factor down-regulation and miR-16 transfer in mice.278 Mesenchymal cell- and epithelial cell-derived exosomes exhibit tolerance and without any undesired side effects in patients and also act as therapeutic agents themselves.48,279 Exosomes engineered with ligands containing RGD peptide are used to induce signaling in specific cell types, and doxorubicin-loaded exosomes derived from dendritic cells show therapeutic responses in mammary tumor-bearing mice.46 Exosomal microRNAs are able to control other cells, and the delivery of miRNA or siRNA payload promotes anticancer activity in mammary carcinoma and glioma.280,281 Rabies virus glycoprotein (RVG)-modified dendritic cell-derived exosomes suppress the expression of BACE1 in the brain, which indicates the therapeutic potential of exosomes to target AD.282 Furthermore, these exosomes stimulated neurite outgrowth in cultured astrocytes by transferring miR-133b between cells.27 Immunotherapy is able to induce tumor-targeting immunity or an antitumor host immune response. For example, tumor-associated antigen-loaded mature autologous dendritic cells increase survival of metastatic castration-resistant patients.283 Exosome therapy induces upregulation of CD122 molecules in CD4+ T cells, whereas the lymphocyte pool is stable. Multiple vaccinations with exosomes increase circulating CD3-/CD56+ natural killer (NK) cells.284 An in vitro study demonstrated that adipose stem cell-derived exosomes up-regulate the peroxisome proliferator-activated receptor gamma coactivator 1, phosphorylate the cyclic AMP response element binding protein, and ameliorate abnormal apoptotic protein levels.285 Exosomes are used as potential carriers to carry anti-inflammatory drugs. Curcumin-encapsulated exosomes show significant anti-inflammatory activity, and exosomes are also used to deliver anti-inflammatory drugs to the brain through a noninvasive intranasal route.286,287 Turturici et al reported that specific progenitor cell-derived EVs contain biological cargo that promotes angiogenesis and tissue repair, and modulates immune functions.288

Figure 5 Therapeutic potential and versatile clinical implications of exosomes.

Generally, exosomes serve as vehicles for the delivery of drugs and are also actively involved as therapeutic agents. Conversely, injected exosomes enter into other cells and deliver functional cargo molecules very efficiently and rapidly, with minimal immune clearance and are well tolerated.16,21,245,289,290 Intravenous administration of human MSC-derived exosomes supports neuroprotection in a swine model of traumatic brain injury.291 In vitro and in vivo models demonstrate that exosomes from human-induced pluripotent stem cell-derived mesenchymal stromal Cells (hiPSC-MSCs) protect the liver against hepatic ischemia/reperfusion injury through increasing the level of proliferation of primary hepatocytes, activity of sphingosine kinase, and synthesis of sphingosine-1-phosphate (S1P).292 Exosomes derived from macrophages show potential for use in neurological diseases because of their easy entry into the brain by crossing the blood-brain barrier (BBB). Catalase-loaded exosomes displayed a neuroprotective effect in a mouse model of PD and exosomes loaded with dopamine entered into the brain better in comparison to free dopamine.33,293 Treatment of tumor-bearing mice with autologous exosomes loaded with gemcitabine significantly suppressed tumor growth and increase longevity, and caused only minimal damage to normal tissues. The study demonstrated that autologous exosomes are safe and effective vehicles for targeted delivery of GEM against pancreatic cancer.294

Generally, lipid-based nanoparticles such as liposomes or micelles, or synthetic delivery systems have been adopted to transport active molecules. However, the merits of synthetic systems are limited due to various factors including inefficiency, cytotoxicity and/or immunogenicity. Therefore, the development of natural carrier systems is indispensable. One of the most prominent examples of such natural carriers are exosomes, which are used to transport drug and active biomolecules. Exosomes are more compatible with other cells because they carry various targeting molecules from their cells of origin. Exosomes are nano-sized membrane vesicles derived from almost all cell types, which carry a variety of cargo molecules from their parent cells to other cells. Due to their natural biogenesis and unique qualities, including high biocompatibility, enhanced stability, and limited immunogenicity, they have advantages as drug delivery systems (DDSs) compared to traditional synthetic delivery vehicles. For instance, extracellular vesicles, including exosomes, carry and protect a wide array of nucleic acids and can potentially deliver these into recipient cells.6 EVs possess inherent targeting properties due to their lipid composition and protein content enabling them to cross biological barriers, and these salient features exploit endogenous intracellular trafficking mechanisms and trigger a response upon uptake by recipient cells.45,295297 The lipid composition and protein content of exocytic vesicles have specific tropism to specific organs.296 The integrin of exosomes determines the ability to alter the pharmacokinetics of EVs and increase their accumulation in various type of organs including brain, lungs, or liver.117 For example, EVs containing Tspan8 in complex with integrin alpha4 were shown to be preferentially taken up by pancreatic cells.298 Similarly, the lipid composition of EVs influences the cellular uptake of EVs by macrophages.299 EVs derived from dendritic cell achieved targeted knockdown by fusion between expression of Lamp2b and neuron-specific RVG peptide by using siRNA in neuronal cell.45 EVs loaded with Cre recombinase protein were able to deliver functional CreFRB to recipient cells through active and passive mechanisms in the presence of endosomal escape, enhancing the compounds chloroquine and UNC10217832A.300 EVs from cardiosphere-derived cells achieved targeted delivery by fusion of the N-terminus of Lamp2b to a cardiomyocyte-specific peptide (CMP).301 RVG-exosomes were used to deliver anti-alpha-synuclein shRNA minicircle (shRNA-MC) therapy to the alpha-synuclein preformed-fibril-induced mouse model of parkinsonism. This therapy decreased alpha-synuclein aggregation, reduced the loss of dopaminergic neurons, and improved clinical symptoms. RVG exosome-mediated therapy prolonged the effectiveness and was specifically delivered into the brain.302 Zhang et al evaluated the effects of umbilical cord-derived macrophage exosomes loaded with cisplatin on the growth and drug resistance of ovarian cancer cells. High loading efficiency of cisplatin was achieved by membrane disruption of exosomes by sonication.303 Incorporation of cisplatin into umbilical cord blood-derived M1 macrophage exosomes increased cytotoxicity 3.3-fold in drug-resistant A2780/DDP cells and 1.4-fold in drug-sensitive A2780 cells, compared to chemotherapy alone. Loading of cisplatin into M2 exosomes increased cytotoxicity by nearly 1.7-fold in drug-resistant A2780/DDP cells and 1.4-fold in drug-sensitive A2780 cells. The findings suggest that cisplatin-loaded M1 exosomes are potentially powerful tools for the delivery of chemotherapeutics to treat cancers regardless of drug resistance. Shandilya et al developed a chemical-free and non-mechanical method for the encapsulation and intercellular delivery of siRNA using milk-derived exosomes through conjugation between bovine lactoferrin with poly-L-lysine, wherein lactoferrin as a ligand was captured by the GAPDH present in exosomes, loading siRNA in an effortless manner.304 Targeted drug delivery was achieved with low immunogenicity and toxicity using exosomes derived from immature dendritic cells (imDCs) from BALB/c mice by expressing the fusion protein RGD. Recombinant methioninase (rMETase) was loaded into tumor-targeting iRGD-Exos. The findings suggest that the iRGD-Exos-rMETase group exhibited significant antitumor activity compared to the rMETase group.305 Several diseases show high inflammatory responses; therefore, amelioration of inflammatory responses is a critical factor. The inflammatory responses in various disease models can be attenuated through introduction of super-repressor IB (srIB), which is the dominant active form of IB, and can inhibit translocation of nuclear factor B into the nucleus. Intraperitoneal injection of purified srIB-loaded exosomes (Exo-srIBs) showed diminished mortality and systemic inflammation in septic mouse models.306 Systemic administration of macrophage-derived exosomes modified with azide and conjugated with dibenzocyclooctyne-modified antibodies of CD47 and SIRP (aCD47 and aSIRP) through pH-sensitive linkers can actively and specifically target tumors through distinguishing between aCD47 and CD47 on the tumor cell surface.307 SPION-decorated exosomes prepared using fusion proteins of cell-penetrating peptides (CPP) and TNF- (CTNF-)-anchored exosomes coupled with superparamagnetic iron oxide nanoparticles (CTNF--exosome-SPIONs) significantly enhanced tumor cell growth inhibition via induction of the TNFR I-mediated apoptotic pathway. Furthermore, in vivo studies in murine melanoma subcutaneous cancer models showed that TNF--loaded exosome-based vehicle delivery enhanced cancer targeting under an external magnetic field and suppressed tumor growth with mitigating toxicity.308 Yu et al309 developed a formulation of erastin-loaded exosomes labeled with folate (FA) to form FA-vectorized exosomes loaded with erastin (erastin@FA-exo) to target triple-negative breast cancer (TNBC) cells with overexpression of FA receptors. Erastin@FA-exo increased the uptake efficiency of erastin and also significantly inhibited the proliferation and migration of MDA-MB-231 cells compared with erastin@exo and free erastin. Interestingly, erastin@FA-exo promoted ferroptosis with intracellular depletion of glutathione and ROS generation. Plasma exosomes (Exo) loaded with quercetin (Exo-Que) improved the drug bioavailability, enhanced the brain targeting of Que and potently ameliorated cognitive dysfunction in okadaic acid (OA)-induced AD mice compared to free quercetin by inhibiting phosphorylated tau-mediated neurofibrillary tangles.310 Spinal cord injury (SCI) causes paralysis of the limbs. To determine the role of resveratrol in SCI, exosomes derived from resveratrol-treated primary microglia were used as carriers which are able to enhance the solubility of resveratrol and enhance penetration of the drug through the BBB, thereby increasing its concentration in the CNS. The findings demonstrated that Exo + Res are highly effective at crossing the BBB with good stability, suggesting they have potential for enhancing targeted drug delivery and recovering neuronal function in SCI therapy, and is likely associated with the induction of autophagy and inhibition of apoptosis via the PI3K signaling pathway.311 Delivery of miR-204-5p by exosomes inhibits cancer cell proliferation and tumor growth, and induces apoptosis and chemoresistance by specifically suppressing the target genes of miR-204-5p in human cancer cells.312 Engineered exosomes with RVG peptide on the surface for neuron targeting and NGF-loaded exosomes (NGF@ExoRVG) were efficiently delivered into ischemic cortex, with a burst release of encapsulated NGF protein and de novo NGF protein translated from the delivered mRNA. The delivered NGF protein showed high stability and a long retention time, and also reduced inflammation by reshaping microglia polarization, promoted cell survival, and increased the population of double cortin-positive cells, a neuroblast marker.313 Intranasal delivery of mesenchymal stem cell-derived extracellular vesicles exerts immunomodulatory and neuroprotective effects in a 3xTg model of AD by activation of microglia cells and increased dendritic spine density.314 Exosome-encapsulated paclitaxel showed efficacy in the treatment of multi-drug resistant cancer cells and it overcomes MDR in cancer cells.315,316 Saari et al found that the loading of Paclitaxel to autologous prostate cancer cell-derived EVs increased its cytotoxic effect.316 Exosome loaded doxorubicin (exoDOX) avoids undesired and unnecessary heart toxicity by partially limiting the crossing of DOX through the myocardial endothelial cells.317 Studies from in vitro and in vivo demonstrate that exosome loaded doxorubicin showed that exosomes did not decrease the efficacy of DOX and there is no cardiotoxicity in DOX-treated mice.318

The intrinsic properties of exosomes have been exploited to control various types of diseases, including neurodegenerative conditions and cancer, through promoting or restraining the delivery of proteins, metabolites, and nucleic acids into recipient cells effectively, eventually altering their biological response. Furthermore, exosomes can be engineered to deliver diverse therapeutic payloads to the target site, including siRNAs, antisense oligonucleotides, chemotherapeutic agents, and immune modulators. The natural lipid and protein composition of exosomes increases bioavailability and minimizes undesirable side effects to the recipients. Due to the availability of exosomes in biological fluid, they can be easily used as potential biomarkers for diagnosis of diseases. Exosomes are naturally decorated with numerous ligands on the surface that can be beneficial for preferential tumor targeting.282 Due to their unique properties, including superior targeting capabilities and safety profile, exosomes are the subject of clinical trials as cancer therapeutic agents.284 Exosomes derived from DCs loaded with tumor antigens have been used to vaccinate cancer patients with the goal of enhancing anti-tumor immune responses.284,319,320

Due to the potential level of various types of cargoes and salient features, exosomes are involved in intercellular messaging and disease diagnosis. As a result of dedicated studies, exosomes have been identified as natural drug delivery vehicles. However, we still face challenges regarding the purity of exosomes due to the lack of standardized techniques for their isolation and purification, inefficient separation methods, difficulties in characterization, and lack of specific biomarkers.321 The first challenge is the use of conventional methods, which are laborious for isolation and purification, time consuming, and vulnerable to contamination by other impurities, which will affect drug delivery processes. The second challenge is the various cellular origins of exosomes, which could affect specific applications. For example, in the application of exosomes in cancer therapy, we should avoid the use of exosomes derived from cancer cells, due to their oncogenic properties. Finally, exosomes have variable properties due to extraction from different types of cell and different cell culture techniques. Therefore, there is a necessity to address and overcome the challenges. There is also a need for an exosome consortium to develop common protocols for the development of rapid and precise methods of exosome isolation, and to assist the selection of sources that are dependent upon the specific therapeutic application. The most important challenge of exosome biology is the clinical translation of exosome-based research using different cell sources. Further characterization studies based on therapeutic applications are needed. Finally, important steps need to be taken to purify exosomes in a feasible, rapid, cost-effective, and scalable manner, which are free from downstream processing and have minimal processing times, that are specifically targeted to therapeutic applications and clinical settings.

The achievement of exosome therapy is based on success rate of clinical trials. Exosomes with size ranges from 60 to 200nm have been used as an active pharmaceutical ingredient or drug carrier in disease treatment. Exosomes derived from human and plant-derived exosomes are registered in clinical trials, but more complete reports are available for humanderived exosomes.322 There are two major exosomes from DCs and MSCs are frequently used in clinical trials, which potentially induce inflammation response and inflammation treatment. The more crucial aspect of exosomes in clinical trials needs to comply with good manufacturing practice (GMP) including upstream, downstream and quality control. Recently, France and USA conducted clinical trials using EVs containing MHCpeptide complexes derived from dendritic could alter tumor growth in immune competent mice and a Phase I anti-non-small cell lung cancer319,320 and several other clinical trial studies are shown in Table 1. Recent clinical case shows promising results with MSC-EVs derived from unrelated bone marrow donors for the treatment of a steroid-refractory graft-vs-host disease patient.279 Similarly, exosomes were used for the treatment of various types of diseases such as melanoma, non-small-cell-lung cancer, colon cancer and chronic kidney disease.284,319,320,323,324

Table 1 Summary of the Exosome Used in Clinical Trials (Source: clinicaltrials.com)

Exosomes are nano-sized membrane vesicles released by the fusion of an organelle of the endocytic pathway, a multivesicular body, with the plasma membrane. Since the last decade, exosomes have played a critical role in nanomedicine and studies related to exosome biology have increased immensely. Exosomes are secreted by almost all cell types and they are found in almost all types of body fluids. They function as mediators of cell-cell communications and play a significant role in both physiological and pathological processes. Exosomes carry a wide range of cargoes including proteins, lipids, RNAs, and DNA, which mediate signaling to recipient cells or tissues, making them a promising diagnostic biomarker and therapeutic tool for the treatment of cancers and other pathologies. In this review, we summarized what is known to date about the factors involved in exosome biogenesis and the role of exosomes in intercellular signaling and cell-cell communications, immune responses, cellular homeostasis, autophagy, and infectious diseases. Further, we reviewed the role of exosomes as diagnostic markers, and their therapeutic and clinical implications. Furthermore, we highlighted the challenges and outstanding developments in exosome research. The clinical application of exosomes is inevitable and they represent multicomponent biomarkers for several diseases including cancer and neurological diseases, etc. Recently, the mortality rate due to various types of cancers has increased. Therefore, therapies are essential to reduce mortality rates. At this juncture, we need sensitive, rapid, cost-effective, and large-scale production of exosomes to use as cancer biomarkers in diagnosis, prognosis, and surveillance. Furthermore, novel technologies are required for further tailoring exosomes as drug delivery vesicles with high drug pay loads, high specificity and low immunogenicity, and free of toxicity undesired side-effects. In addition, standardized and uniform protocols are necessary to isolate and purify exosomes for clinical applications, and more precise isolation and characterization procedures are required to increase understanding of the heterogeneity of exosomes, their cargo, and functions. There is an urgent need for information regarding the composition and mechanisms of action of the various substances in exosomes and to determine how to obtain highly purified exosomes at the right dosage for their clinical use. Currently, exosomes represent a promising tool in the field of nanomedicine and may provide solutions to a variety of todays medical mysteries.

The future direction of exosome research must focus on addressing the differential responses of communication between normal cells and cancer cells, how normal cells rapidly become cancerous, and how exosomes plays critical role in cancer progression via cell-cell communications. In vivo studies need to urgently address the critical factors such as biogenesis, trafficking, and cellular entry of exosomes originating from unmanipulated exosomes that control regulatory pathological functions. Further studies are required to decipher the mechanism of the cell-specific secretion and transport of exosomes, and the biological controls exerted by target cells. Exosomes represent a clinically significant nanoplatform. To substantiate this idea, numerous systematic in vivo studies are necessary to demonstrate the potency and toxicology of exosomes, which could help bring this novel idea a step closer to clinical reality. The most vital part of the system is to optimize the conditions for the engineering of exosomes that are non-toxic, for use in clinical trials. Furthermore, the translation of exosomes into clinical therapies requires their categorization as active drug components or drug delivery vehicles. Finally, future research should focus on the nanoengineering of exosomes that are tailored specifically for drug delivery and clinical efficacy.

Although we are the authors of this review, we would never have been able to complete it without the great many people who have contributed to the field of exosomes biogenesis, functions, therapeutic and clinical implications of exosomes aspects. We owe our gratitude to all those researchers who have made this review possible. We have cited as many references as permitted and apologize to the authors of those publications that we have not cited due to the limitation of references. We apologize to other authors who have worked on these aspects but whom we have unintentionally overlooked.

This study was supported by the KU-Research Professor Program of Konkuk University.

This work was supported by a grant from the Science Research Center (2015R1A5A1009701) of the National Research Foundation of Korea.

The authors report no conflicts of interest related to this work..

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[Full text] A Comprehensive Review on Factors Influences Biogenesis, Functions, Th | IJN - Dove Medical Press

Introduction

Bone remodelling is a tightly coupled lifelong process, whereby old bone is removed by osteoclasts (bone resorption) and new bone is formed by osteoblasts (bone formation).1,2 Osteocytes, which act as mechanosensors/endocrine cells, and bone lining cells3 are also involved in bone remodelling.4 Myriad pathophysiological factors affecting bone remodelling have been observed in skeletal diseases such as osteoporosis, arthritis and periodontal disease.5 Oxidative stress is one of the pathophysiological factors affecting bone remodelling. Oxidative stress stimulates osteoclast differentiation, thereby enhancing bone resorption.6,7 Reactive oxygen species (ROS) stimulate the apoptosis of osteoblasts and osteocytes, thus affecting bone formation. ROS also activate mitogen-activated protein kinases (MAPKs), such as extracellular signal-regulated kinases (ERK1/2), c-Jun-N terminal kinase (JNK) and p38, and enhance osteoclastogenesis and bone resorption.811 These phenomena skew the bone remodelling process in favour of bone loss.

Antioxidants are compounds which reduce free radicals and oxidative stress.12 Antioxidants have been reported to promote differentiation of osteoblasts, bone formation and survival of osteocytes, as well as suppressing osteoclast differentiation and activity.8,1315 Some studies associate the age-related reduction in circulating antioxidants to osteoporosis in rats and women.1618 A decline in antioxidant levels has been reported to promote bone loss by triggering the tumour necrosis factor-alpha (TNF)-dependent signalling pathway,6 while administration of antioxidants, such as vitamin C, E, N-acetylcysteine and lipoic acid, have been reported to exert favourable effects in animal models of osteoporosis1921 and individuals with osteoporosis.2225

Caffeic acid (CA) is a metabolite of hydroxycinnamate and phenylpropanoid commonly synthesized by all plant species. It is a polyphenol present in many food sources like coffee, tea, wine, blueberries, apples, cider, honey and propolis.26 CA and its major derivatives including caffeic acid phenethyl ester (CAPE) and caffeic acid 3,4-dihydroxy-phenethyl ester (CADPE) are reported to possess potential antibacterial, antidiabetic, antioxidant, anti-inflammatory, antineoplastic and cardioprotective activities (reviewed in2729). As a potent antioxidant, CA has been demonstrated to decrease lipoperoxyl radicals (ROO) by donating a hydrogen atom to its corresponding hydroperoxide, which terminates the lipid peroxidation chain reaction. It also inhibits human low-density lipoprotein (LDL) oxidation induced by cupric ions.30 Furthermore, it interacts with other compounds, such as -tocopherol, chlorogenic and caftaric acids, to exert more potent antioxidant activity in a variety of different systems.3133 Therefore, the antioxidant activities of CA might protect against the negative effects of oxidative stress on bone cells and the skeletal system. This systematic review aims to summarise the effects of CA and its derivatives on bone cells and bone in literature.

A systematic literature search was conducted from July until November 2020 using PubMed, Scopus, Cochrane Library and Web of Science databases to identify studies on the effects of caffeic acid on bone and bone cells including osteoblasts, osteoclasts and osteocytes. The search string used was (1) caffeic acid AND (2) (bone OR osteoporosis OR osteoblasts OR osteoclasts OR osteocytes).

Studies with the following characteristics were included: (1) original research article with the primary objective of determining the effects of caffeic acid on bone and bone cells; (2) studies using cellular or animal models, or humans; (3) studies administering caffeic acid as a single compound but not in a mixture or food. Articles were excluded if they (1) do not contain original data; (2) use food rich in caffeic acid or mixtures containing caffeic acid. The bibliography of relevant review articles was traced for potential articles missed during database search. The search results were organised using EndNoteTM software (Clarivate Analytics, Philadelphia, USA). Duplicates were identified using EndNoteTM and confirmed by manual checking.

Two authors (S.O.E. and K.L.P.) searched the same databases using the search string mentioned and screened the search results. All the articles that did not match the selection criteria were excluded. Next, the articles which used caffeic acid in treating models other than bone-related diseases were removed. Finally, articles which used caffeic acid in combination with other compounds were also excluded. Any disagreement on the inclusion or exclusion of articles was resolved through discussion among the two authors. The corresponding author (K.Y.C.) had the final decision on articles included if a consensus could not be reached between authors responsible for screening. This systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and checklist.34 Steps in the selection process, from identification, screening, eligibility to the inclusion of articles, are shown in Figure 1.

Figure 1 Flowchart of the article selection process.

From the literature search, 381 articles were identified, of which 87 were obtained from PubMed, 182 were from Scopus, 3 from Cochrane Library and 109 from Web of Science. A total of 155 duplicate articles were identified and removed. Of the 226 articles screened, 202 articles were excluded based on the selection criteria, whereby 51 articles did not contain primary data (3 book chapters, 2 commentary and 46 review articles), 147 articles and 2 conference abstracts presented topics irrelevant to the current review, a conference abstract had been published as a full-length research article and another conference abstract did not contain sufficient experiment details (Supplementary Material). Finally, 24 articles fulfilling all criteria mentioned were included in the review.

The included studies were published between 2006 and 2020. Seven studies were in vitro experiments using mouse bone marrow macrophages (BMMs), RAW264.7, RAW D and MG63 osteoblast cell lines3541 while 19 studies were in vivo studies using Sprague Dawley/Sprague Dawley albino rats, Wistar/Wistar albino rats, Balb/c mice, lipopolysaccharide (LPS)-resistant C3H/HEJ mice, C57BL/6J mice and ICR mice.35,38,4258 No human studies on this topic were reported.

Six in vitro studies focused on the effects of CA on osteoclast differentiation from haematopoietic cells using macrophage colony-stimulating factor (M-CSF), receptor activator of NF-B (RANK) ligand (RANKL) or TNF-,3539,41 while one in vitro study focused on the effect of CA on osteoblasts using MG63 osteoblast cell line.40 Four in vitro studies used CA doses between 0.15 M.35,37,38,40 Ang et al.36 used doses between 00.3 M and Sandra et al.41 and Sandra and Ketherin39 used a dose of 10 g/mL (55.5 M). The treatment period was 57 days for the differentiation of osteoclasts.

For animal studies, Duan et al.,55 Zawawi et al.,58 William et al.,51 Wu et al.,38 Zych et al.49 and Folwarczna et al.48,52 used CA or its derivatives at doses between 0.550 mg/kg via oral or intraperitoneal (i.p.) administration. Ucan et al.,57 Erdem et al.,53 Cicek et al.,54 Yigit et al.,45 Yildiz et al.50 and Tolba et al.56 used doses between 1020 mol/kg/day (2.845.69 mg/kg/day) via i.p. administration. Kizilda et al.4244 and Kazanciolu et al.46,47 used the dose of 10 mmol/kg/day (2.843 g/kg/day) for an i.p. administration, Kazanciolu et al.47 employed 50100 mmol/kg/day (14.2228.43 g/kg/day) for a localised administration, while Ha et al.35 used a collagen sponge soaked with CAPE with the final dose of 250 g/mouse. For oral administration, first-pass effect might affect the enteric absorption of CA or its derivatives.59 For i.p. administration, the injection is commonly performed at the lower left or right quadrant of the abdomen. The peritoneum can absorb the compounds fast and reach systemic circulation with greater bioavailability with fewer handling errors.60

The bone-related disease models used included ovariectomy (OVX)- or glucocorticoids (dexamethasone)-induced osteoporosis, polyethylene particle-induced bone defect and osteolysis, electromagnetic force (EMF)-stimulated bone loss, osteotomy- or anti-collagen antibody-induced arthritis (CAIA) and rapid maxillary expansion (RME) and LPS-induced periodontitis. The endpoints studied included bone microstructure, histomorphometry, bone remodelling and oxidative status. The effects of CA and its derivatives on bone remodelling have been summarized in Table 1.

Melguizo-Rodrguez et al. reported that 24-hour CA (1 M) incubation increased the number of MG63 osteoblast cells compared with control.40 Gene expression studies revealed that CA increased the expression of osteoblast-related genes such as bone morphogenetic protein-2 and -7 (BMP-2 and BMP-7), transforming growth factor-beta 1 (TGF-1), transforming growth factor-beta receptor 1, 2 and 3 (TGF-R1, TGF-R2 and TGF-R3) and osteoblastogenesis genes including Runt-related transcription (RUNX-2), alkaline phosphatase (ALP), collagen type 1 (COL-I), osterix (OSX) and osteocalcin (OSC).40 Additionally, pretreatment of CA (10 g/mL or 55.5 M) on RAW D cells for 2 h also significantly inhibited the RANKL and TNF-induced osteoclastogenesis with the suppression of p38 MAPK phosphorylation and tartrate-resistant acid phosphatase (TRAP)-positive osteoclast-like cells (OCLs) formation.39 Similarly, pretreatment of CA (0.1, 1 and 10 g/mL or 0.555, 5.55 and 55.5 M) on RAW D cells and BMMs for 3 days significantly inhibited the RANKL and TNF-induced osteoclastogenesis and NF-B activity in RAW-D cells and RANKL, TNF and M-CSF-induced osteoclastogenesis in BMMs.41

On the other hand, CAPE treatment (00.3 M; 57 days) suppressed the formation of TRAP-positive OCLs on RANKL-treated RAW264.7 cells and BMMs.36 Apoptosis occurred in CAPE-treated RAW264.7 cells with the disruption of the microtubule network in OCLs.36 Similarly, Kwon et al. reported that CAPE treatment (0.15 M) for 5 days suppressed OCLs formation from RANKL-stimulated RAW264.7 cells.37 Another study by Ha et al. treating M-CSF and RANKL-stimulated BMMs with CAPE (05 M for 57 days) also showed decreased OCLs formation in a concentration-dependent manner.35 The amount of TRAP-positive OCLs was decreased upon 0.1 and 0.5 M CAPE treatment by 30% and 95% respectively.35 No OCL formation was observed upon 1 M CAPE treatment.35 The anti-osteoclastogenic activities of CAPE are mainly contributed by its anti-inflammatory and antioxidant properties. Mechanistically, CAPE reduces superoxide anion generation by downregulating the nicotinamide adenine dinucleotide phosphate oxidase 1 (Nox1) expression through the interruption of nuclear factor-kappa B (NF-B) and c-Jun N-terminal kinase (JNK) signalling pathways.37 CAPE suppresses RANKL-mediated activation of the NF-B pathway by downregulating NF-B p65 subunit expression and its nuclear translocation,37 suppressing nuclear factor of activated T cells (NFAT) activities36 and degradation of NF-B inhibitor (IB),36,37 as well as inducing the degradation of IB kinase (IKK).37 CAPE also suppresses the expression and activation of JNK and its downstream transcription factors, such as c-Fos and c-Jun, which subsequently interrupt the protein activator-1 (AP-1) complex formation.37 Additionally, CAPE suppressed RANKL-induced activation of the Nox1 by inhibiting the Nox p47PHOX subunit translocation to the cell membrane and downregulation of Ras-related C3 botulinum toxin substrate 1 (Rac1) expression.37

On the other hand, Wu et al. reported that CADPE (0.15 M for 7 days) also concentration-dependently reduced OCL formation in the M-CSF and RANKL-stimulated BMMs and RAW264.7 cells.38 Mechanistic and characterisation examination revealed that CADPE suppressed RANKL-induced tumour necrosis factor receptor-associated factor 6 (TRAF6) activation and protein kinase B (PKB or also known as Akt) and activation of major MAPKs including ERK, JNK and p38.38 Subsequently, CADPE suppressed downstream expression of nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), nuclear translocation of c-Fos protein and expression of osteoclastic markers, such as TRAP and cathepsin K, possibly through the non-receptor tyrosine kinase c-Src signalling.38 Interestingly, CADPE did not significantly affect the NF-kB signalling pathway and M-CSF-induced proliferation and differentiation of BMMs.

Supplementation of CA in animal models of bone loss yielded heterogeneous findings.48,49,52 This observation might be attributable to oral administration. Folwarczna et al. reported that CA (5 and 50 mg/kg, by stomach tube for 4 weeks) improved the bone mechanical properties by increasing the width of the trabecular metaphysis of the femur and decreasing the transverse growth in endosteal of the femur in OVX rats.48 Folwarczna et al. then demonstrated that CA (10 mg/kg/day; oral administration for 4 weeks) could reduce the width of tibial periosteal and endosteal osteoid compared with untreated OVX rats.52 However, CA did not promote or reduce the resorption of compact bone in the tibia of OVX-induced osteoporotic rats as evidenced by negligible changes of bone mass, bone mineral mass, bone mass/body mass ratio and bone mineral mass/body mass ratio.52 On the other hand, Zych et al. reported that CA at a similar dose (10 mg/kg/day; by stomach tube for 4 weeks) worsened the bone mechanical properties of healthy female Wistar Cmd:(WI)WU rats by decreasing the load of fracture at the femoral neck, decreasing the width of periosteal osteoid in the tibia and decreasing the width of the epiphysis and metaphysis trabecular in the femur compared with the negative control group.49

CAPE is the most extensively studied caffeic acid derivative in animal studies. The beneficial effects on new bone formation and healing upon systemic administration of CAPE had been reported.46,47,53,57 Erdem et al. reported that a low dose of CAPE (10 mol/kg; i.p. injection for 22 days) increased new bone formation and bone strength by increasing maximum torsional fracture momentum and degree of rigidity compared with negative control in rats that underwent unilateral femoral lengthening (osteotomy).53 Similarly, a 30-day i.p. injection of CAPE (10 mol/kg/day) also increased bone healing level in Sprague Dawley rats with cranial critical size bone defect.57 A higher dose of CAPE (10 mmol/kg/day, i.p. for 20 days) also further promoted the RME procedure-induced new bone formation in midpalatal suture of male Sprague Dawley rats.47 Similarly, a longer treatment period of CAPE (10 mmol/kg/day; i.p. injection for 28 days) also significantly promoted bone healing by increasing the total new bone areas in surgical-induced calvarial defects of male Wistar rats compared with the negative control.46 However, localised administration of CAPE (28 days) on surgical-induced calvarial defects by pre-mixing 50 and 100 mmol/kg CAPE solutions with gelatin sponges did not significantly improve the new bone formation.46

Localised and systemic administration of CAPE was reported to be beneficial in reducing osteolysis and bone loss.35,4245,50,5456,58 Ha et al. reported that collagen sponge implant impregnated with 250 g CAPE and RANKL could reduce osteoclastogenesis with significantly lesser TRAP-stained area in mouse calvariae compared with implants with RANKL only.35 Subcutaneous injection of CAPE (1 mg/kg/day for 10 days) reduced the polyethylene particle-induced calvarial osteolysis, surface bone resorption and TRAP-positive cells formation with an increase of bone volume (BV) on LPS-resistant C3H/HEJ female mice.58 However, no significant changes were observed in carboxy-terminal cross-linked type 1 collagen (CTX-1) and osteoclast-associated receptor levels among untreated and CAPE-treated rats with calvarial osteolysis.58

Similarly, Duan et al. reported that lower dose and frequency of CAPE injection (0.5 mg/kg twice a week; i.p. injection for 4 weeks) also increased the BV and trabecular number (Tb.N) due to the decrease of bone osteoclast formation (evidenced by decreased osteoclast number/bone perimeter) in OVX mice.55 Tolba et al. also reported that i.p. injection of CAPE (10 and 20 mol/kg) for 3 weeks increased femur weight and length in rats with dexamethasone-induced bone loss.56 The preservation of skeletal health in their study was associated with an improved antioxidant defence, such as higher levels of glutathione (GSH) and superoxide dismutase (SOD), and the reduction of malondialdehyde (MDA, lipid peroxidation product).56 This event led to an increase of osteoblastogenesis indicated by upregulation of RUNX-2 and ALP (osteoblast marker) levels56 On the other hand, decreased RANKL/osteoprotegerin (OPG) ratio was observed with CAPE treatment, indicating the suppression of osteoclastogenesis, which was further confirmed by lower acid phosphatase level and TRAP activity.56 In another study by Yildiz et al., CAPE (10 mol/kg/day; i.p. injection for 22 days) also increased the spine and femur BMD in rats with EMF-induced bone loss.50 Similarly, Cicek et al. reported a longer treatment of CAPE (10 mol/kg/day; i.p. injection for 28 days) also significantly improved the mechanical strength of cortical bone by increasing the breaking force, bending strength and total fracture energy in rats with EMF-induced bone loss compared with negative control.54

Additionally, a study by Wu et al. treated mice with an OVX-induced bone loss with a moderately high dose of CADPE (10 mg/kg; i.p. injection) every 2 days for 3 months.38 Results showed that CADPE could increase the BV fraction (BV/TV) and Tb.N, as well as decreased trabecular spacing (Tb.Sp) compared with the negative control.38 The improvement in the bone structure was contributed by reduced osteoclast number and eroded surface on the bone.38 Assessment of bone remodelling markers also revealed that serum TRAP5b and CTX-1 levels were reduced in CADPE-treated group compared with the negative control.38

On the other hand, CAPE was effective in reducing periodontitis-related bone loss and osteolysis.4245 CAPE (10 mol/kg/day, i.p. for 14 days) significantly reduced the subgingival ligature placement-induced periodontitis-mediated articular bone loss, histopathological features and severity of periodontal inflammation with lesser polymorphonuclear cells (PMNLs) infiltration in the junctional epithelium and connective tissues among Wistar albino rats.45 CAPE also suppressed the periodontitis-upregulated interleukin (IL)-1, IL-6, IL-10, TNF, MDA levels and the percentage of gingival apoptosis with the parallel restoration of periodontitis-downregulated GSH and glutathione peroxidase (GPx).45 Administration of high-dose CAPE (10 mmol/kg/day; i.p. for 15 days) in streptozotocin (STZ)-induced diabetic male Sprague Dawley rats reduced RANKL-positive osteoclast number, IL-1 levels, oxidative stress index (OSI), alveolar bone loss and histological analysis score in LPS-induced periodontitis. The treated rats also suffered lesser inflammatory reactions, ulcers and hyperemia.42 Similar changes of osteoclast number, IL-1 and OSI were observed in male Sprague Dawley rats with chronic stress and LPS-induced periodontitis treated with CAPE (10 mmol/kg/day, i.p. for 14 days).44 In addition, CAPE also increased the mesial and distal periodontal bone supports (MPBS and DPBS) in these rats.44 The effects of CAPE were sustained with a longer treatment period of CAPE (10 mmol/kg/day, i.p. for 28 days) on male Sprague Dawley rats with LPS-induced periodontitis.43

In contrast to the above findings, Williams et al. reported that subcutaneous injection of CAPE (1 mg/kg; at day 3, 7 and 10) did not reduce paw inflammation or bone loss in CAIA mice.51 Cartilage and bone degradation, as well as TRAP-positive cells on the bone surface and soft tissues, were still apparent in the supplemented CAIA group compared with the normal control.51

This systematic review found that although CA and its derivatives is a potential anti-osteoporosis agent by suppressing the formation of osteoclasts and their bone resorption activity, it worsened bone mechanical properties in some cases. The anti-osteoclastogenesis action of CA and its derivatives was mediated by the antioxidant activities, which blocked RANKL-induced TRAF6/Akt and MAPK signalling, as well as M-CSF/c-Src signalling. In animals, CA and its derivatives (mainly CAPE) prevented bone resorption in rodent calvariae when implanted in situ, facilitated the healing of bone defects, preserved bone structure and improved mechanical strength in osteoporosis models induced by OVX, dexamethasone, osteotomy, LPS-mediated periodontitis and EMF. However, CA did not alter bone resorption in OVX-induced osteoporotic rats and worsened the mechanical properties in normal rats. Additionally, CAPE did not suppress bone loss in rats with CAIA-induced bone loss.

Osteoblasts are bone-forming cells derived from bone marrow mesenchymal stem cells and are responsible for the synthesis, secretion and mineralisation of bone matrix.61 The expression of osteoblast markers was increased following CA or CAPE supplementation, an indication that CA and CAPE stimulated osteoblast proliferation, differentiation and maturation.40,56 Osteoblasts and osteocytes regulate the formation of osteoclasts through RANKL/OPG axis. Osteoblasts and osteocytes synthesise RANKL, which binds to RANK to activate the canonical pathway for osteoclastogenesis. They also secrete OPG, which is a decoy receptor for RANKL to suppress osteoclastogenesis. The production of RANKL is stimulated under conditions such as oestrogen deficiency62 and oxidative stress.63 Osteoclastogenesis can also be stimulated via a non-canonical pathway, for instance, through the binding of TNF with TNF receptor I or II.64 Glucocorticoids are potential modulators of RANKL/OPG axis, whereby dexamethasone is shown to downregulate OPG levels in osteoblasts.65 Tolba et al. showed that the RANKL/OPG level reduced in rats induced with dexamethasone with CAPE treatment.56 Other cellular studies showed that CA and its derivatives suppressed RANKL- and TNF-induced formation of OCLs from haematopoietic cells,3539 indicating that CA and its derivatives suppressed both canonical and non-canonical osteoclastogenesis.

The complex formed by the binding of RANKL to RANK causes the recruitment of the adaptor molecules tumour necrosis factor receptor-associated factors (TRAFs), including TRAF6.66 This event leads to the activation of several downstream signalling pathways, including c-Src/Akt/phosphatidylinositol 3-kinase and MAPKs (ERK/p38/JNK). CADPE was shown to suppress RANKL-induced activation of TRAF6 activation and the subsequent signalling pathways in multiple osteoclast progenitors, such as BMMs,38 RAW264.738 and RAW D cells.39 Sandra and Ketherin suggested that the downregulation of p38 is the key step of CA-mediated osteoclastogenesis.39 Upon activation, p38 initiates osteoclastogenesis by inducing NF-B and NFATc1 expression.67,68 Inhibition of p38 MAPK reduces RANKL (canonical) and TNF-induced (non-canonical) osteoclast formation.69

The NF-B pathway is another signalling pathway downstream of TRAFs critical for osteoclast differentiation and bone reabsorption activity. Upon activation, IKK (consisting of IKK, IKK and IKK) phosphorylates and degrades IB, which enables translocation of NF-B p65/p50 heterodimers into the nucleus to allow transcription of osteoclast-related genes.70 Kwon et al. demonstrated that the anti-osteoclastogenesis effects of CAPE were mediated via the degradation of total IKK, thereby preventing the phosphorylation and degradation of IB and subsequently suppresses the nuclear translation of p65.37 On the other hand, Wu et al. reported that CADPE did not affect phosphorylation or degradation of IB, as well as nuclear translocation, and DNA-binding activity of p65.38 This observation suggests that compared with CAPE, CADPE does not influence the NF-B signalling pathway.

ROS are one of the important secondary signals in the early stages of osteoclast differentiation.71,72 These ROS are mainly produced as superoxide anions by Nox1.73 Blocking of Nox1 ameliorates ROS production and the downstream MAPKs (JNK, p38 and ERK) and NF-B activation74 and subsequently suppresses the osteoclast formation.71 The reduction of Nox 1 and Rac1 expression by CAPE is accompanied by RANKL-downstream signalling, denoting that anti-osteoclastogenesis effects of CAPE are dependent on suppression of Nox1-mediated superoxide anion production. Besides, dexamethasone has been reported to increase the expression of oxidative stress-related genes in human osteoblasts.75 Tolba et al. showed that CAPE increased GSH and SOD but reduced MDA in the bone of the rats exposed to dexamethasone, indicating an improvement of redox status in the skeletal environment.56 Additionally, CAPE also reduced the OSI and bone loss with an improvement of bone support in rats with LPS-induced periodontitis.

NFATc1 is the master regulator of osteoclast-related gene expression, and it is activated by c-Fos and NF-B.76 Ha et al. observed that CAPE inhibited the recruitment of NF-B to NFATc1 promoter, and the combined effect of NF-B inhibition on c-Fos and NFATc1 may have caused CAPE to suppress osteoclastogenesis effectively.35 Holland et al. demonstrated a new fluorinated derivative of CAPE possesses potent anti-osteoclastogenic properties on RAW 264.7 cells by downregulating NFATc1 via suppression of c-Fos and NF-B signalling pathways.77 Besides, this new fluorinated CAPE also exhibits improved stability with a 2-fold higher potency than CAPE.77 On the other hand, although CADPE did not alter NF-B signalling, it still could suppress NFATc1 and other osteoclast-related markers, indicating other mechanisms of suppression could be involved, for instance, c-Src and MAPKs signalling pathways.38

Matrix metalloproteinases (MMPs), including gelatinases (MMP-2 and MMP-9) are examples of zinc-dependent extracellular matrix-degrading enzymes, which actively participate in bone resorption.78 MMPs are expressed as inactive proenzymes or zymogens that can be activated by several mediators including AP-1, NF-B, TNF and TGF.78 Currently, there is no study conducted to investigate the inhibitory effects of CA and CAPE on osteoclastic MMPs activity and its subsequent linkage in bone resorption; interestingly, CA and CAPE were reported to inhibit MMP-9 activity in human hepatocellular carcinoma HEP3B cells.79,80 This observation renders an interesting research gap in osteoclastic MMP inhibition upon CA and its derivatives treatment.

Suppression of osteoclastogenesis by CA or its derivatives have significant therapeutic potential against bone disorders induced by excessive bone resorption. Bone loss after osteotomy is a rapid process that affects both fractured and unfractured bone and may be incompletely reversible.81 CAPE was reported to improve bone formation and mechanical strength of bone in osteotomy.53 Exposure to EMF radiation caused by high-voltage transmission lines and transformers could affect bone health through decreased BMD, serum calcium and ALP level leading to the increase of bone resorption.82 CAPE increased the spine and femur BMD levels50 and increased mechanical strength of bones54 in rats exposed to EMF radiation. Total hip arthroplasty without cement often caused osteolysis induced by polyethylene particles.83 CAPE was shown by Zawawi et al. to prevent calvarial bone resorption in a murine polyethylene particle-induced osteolysis model.58 Therefore, biomaterials impregnated with CA or its derivatives could be adopted to prevent osteolysis in the arthroplasty procedure. CA has been incorporated in chitosan/(3-chloropropyl) trimethoxysilane scaffold for hard-tissue engineering applications and this adopted material exhibits antibacterial and anticancer effects.84 Ucan et al. observed that CAPE increased cranial bone healing in rats with critical size bone defect, suggesting that it could be administered systematically or locally to treat bone fracture/defect healing.57

Similarly, CAPE also effectively reduced the articular bone loss, inflammatory cytokines production and oxidative stress in rats with LPS-mediated periodontitis. Additionally, Wu et al.38 and Duan et al.55 demonstrated that CADPE prevented the ovariectomy-induced bone loss by suppressing osteoclast activity in a mouse model, while Folwarczna et al. showed increased width of trabecular metaphysis in the femur of OVX rats.48 Similarly, Tolba et al. showed improved bone formation and skeletal health in rats with dexamethasone-induced bone loss upon receiving CAPE.56 Additionally, CA and its derivatives may be involved in oestrogen production and signalling. Zych et al. reported that an oral administration of CA (10 mg/kg/day for 4 weeks) significantly restored the serum oestradiol levels in OVX rats.85 Interestingly, CA at 10 and 100 M did not cause any alteration in calcium content in the femoral-diaphyseal and metaphyseal ex vivo culture, suggesting its bone-protecting effect may not involve calcium metabolism and regulation.86 Additionally, CAPE was reported as a selective human oestrogen receptor agonist with the EC50 value of 3.72 M in oestrogen-responsive element transcription.87 A recent in silico study by Zhao et al. suggested potential osteoimmunological effects of CAPE, which may explain its biological activities on both immune and skeletal systems.88 However, the findings from this modelling study requires further validation through in vitro and in vivo models. As oestrogen deficiency due to menopause and glucocorticoids present the most significant cause of primary and secondary osteoporosis globally, CA and its derivatives have the potential to be used as an adjuvant therapy to existing osteoporosis management strategies. The mechanisms of action of CA and its derivatives in osteoclastogenesis have been summarized in Figure 2.

Figure 2 Mechanism of action of caffeic acid and its derivatives.

Abbreviations: , decrease or downregulate; ?, unknown mechanism; Akt, protein kinase B; AP-1, activator protein 1; CA, caffeic acid; CADPE; caffeic acid 3,4-dihydroxy-phenethyl ester; CAPE, caffeic acid phenethyl ester; c-Src, cellular sarcoma tyrosine kinase; ERK1/2, extracellular signal-regulated kinases 1/2; GM-CSF, granulocyte-macrophage colony-stimulating factor; Grb2, growth factor receptor-bound protein 2; IFN-, interferon-gamma; IL, interleukin; IL1R, interleukin-1 receptor; IB, NF-B inhibitor protein; IKK, IB kinase; LPS, lipopolysaccharide; M-CSF, macrophage colony-stimulating factor; M-CSF-R, M-CSF receptor; MAPKs, mitogen-activated protein kinases; NFAT, nuclear factor of activated T cells; NF-B, nuclear factor kappa B; NIK, MAPK kinase kinase 14; Nox1, nicotinamide adenine dinucleotide phosphate oxidase 1; OPG, osteoprotegerin; PI3k, phosphoinositide 3-kinase; Rac1, Ras-related C3 botulinum toxin substrate 1; RANK, receptor activator of NF-B; RANKL, receptor activator of NF-B ligand; ROS, reactive oxygen species; TAK, MAPK kinase kinase 7; TLR4, Toll-like receptor 4; TNF, tumour necrosis factor-alpha; TNFR1/2, TNF receptor 1/2; TRAF2, tumour necrosis factor receptor-associated factor 2; TRAF6; tumour necrosis factor receptor-associated factor 6.

Regardless of the positive effects of CA on bone status, some studies have reported negative effects associated with supplementation of CA and its derivatives. CA supplementation did not affect the bone resorption52 and reduced transverse growth of endosteal in femur48 of rats with OVX-induced osteoporosis. In normal rats, CA supplementation even negatively affected their bone mechanical properties.49 Moreover, CAPE supplementation has been reported to stimulate the synthesis of PGE2,89 which mediates osteoclastogenesis through RANKL stimulation and activation of the NF-B pathway.90 This event will eventually increase TRAP-positive OCLs. Similarly, Williams et al. showed that CAPE did not suppress osteoclastogenesis in rats with CAIA.51

In term of safety, the International Agency for Cancer Research classifies CA as Class 2B (possibly carcinogenic to humans),91 and it was reported to induce renal tubular cell hyperplasia, forestomach hyperplasia, renal cell adenoma and forestomach cancer in rodents.9294 CA has been reported to be non-mutagenic and non-clastogenic.91 Therefore, its carcinogenicity may involve epigenetic modification. Human toxicity and carcinogenicity of CA and its derivatives remain unknown. CA also showed anti-implantation activity in pregnant mice at a median effective dose of 4.26 mg/kg/day.95 Similarly, 5 mg/kg/day and 150 mg/kg of CA in mice demonstrated anti-implantation activity in early pregnancy.96 On the other hand, 0.15 mg/kg/day, 5 mg/kg/day and 150 mg/kg/day of CA for 21 days in mice showed no maternal toxicity, foetal teratogenesis or post-natal effects on pup development and mortality.96 The same experiment stated that the no-observed-adverse-effect level of CA for pregnant female mice was 0.15 mg/kg/day.96 Therefore, high-dose CA should be cautioned in humans, especially pregnant women.

Several common limitations can be identified from the studies reviewed. Most studies did not adopt a positive control to compare against the anti-osteoclastogenesis or anti-osteoporosis effect of CA. Therefore, the therapeutic effects of CA and currently available anti-resorptive therapy cannot be compared. Although osteoblastogenesis and bone formation are also important in bone remodelling, evidence of CA on these processes is limited in the literature. The actions of CA in humans cannot be confirmed due to the lack of human clinical trials. These aspects can be improved in future studies.

The current review also has several limitations. We only considered articles indexed by PubMed, Scopus, Cochrane Library and Web of Science; therefore, non-indexed articles could be overlooked. We only selected articles studying CA or its derivatives as a single compound to understand its mechanism of action properly without other interference, but not a mixture of compounds or natural products rich in CA. CA are present in foods, and interaction with other compounds in the food matrix might alter its absorption, bioavailability and action on the target tissue. Moreover, the heterogeneous findings of CA in bone loss reduction upon oral administration further emphasise these possibilities.

The current preclinical evidence agrees that CA and its derivatives exert promising skeletal protective effects by inhibiting osteoclastogenesis and bone resorption, but literature on bone formation is limited. Notwithstanding that, the skeletal effects of CA and its derivatives in models of normal bone health should be investigated because the limited studies available show undesirable effects. Human clinical trials to validate the skeletal effects of CA are lacking. Therefore, a well-planned clinical trial should be conducted to confirm the potential of CA as an antiresorptive agent. This information is critical for CA and its derivatives to be incorporated as part of the strategies to prevent bone loss.

The researchers are funded by Universiti Kebangsaan Malaysia through Research University Grant (GUP-2020-021). S.O.E. and K.L.P. are post-doctoral researchers funded by Universiti Kebangsaan Malaysia through FPR-1 and RGA-1 grants.

The authors report no conflicts of interest in this work.

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[Full text] Effects of Caffeic Acid and Its Derivatives on Bone: A Systematic Revi | DDDT - Dove Medical Press

Abstract

Enzyme replacement therapy, in which a functional copy of an enzyme is injected either systemically or directly into the brain of affected individuals, has proven to be an effective strategy for treating certain lysosomal storage diseases. The inefficient uptake of recombinant enzymes via the mannose-6-phosphate receptor, however, prohibits the broad utility of replacement therapy. Here, to improve the efficiency and efficacy of lysosomal enzyme uptake, we exploited the strategy used by diphtheria toxin to enter into the endolysosomal network of cells by creating a chimera between the receptor-binding fragment of diphtheria toxin and the lysosomal hydrolase TPP1. We show that chimeric TPP1 binds with high affinity to target cells and is efficiently delivered into lysosomes. Further, we show superior uptake of chimeric TPP1 over TPP1 alone in brain tissue following intracerebroventricular injection in mice lacking TPP1, demonstrating the potential of this strategy for enhancing lysosomal storage disease therapy.

Lysosomal storage diseases (LSDs) are a group of more than 70 inherited childhood diseases characterized by an accumulation of cellular metabolites arising from deficiencies in a specific protein, typically a lysosomal hydrolase. Although each individual disease is considered rare, LSDs have a combined incidence of between 1/5000 and 1/8000 live births, and together, they account for a substantial proportion of the neurodegenerative diseases in children (1). The particular age of onset for a given LSD varies depending on the affected protein and the percentage of enzymatic activity still present; however, in most cases, symptoms manifest early in life and progress insidiously, affecting multiple tissues and organs (2). In all but the mildest of cases, disease progression results in severe physical disability, possible intellectual disability, and a shortened life expectancy, with death occurring in late childhood or early adolescence.

As they are monogenic diseases, reintroducing a functional form of the defective enzyme into lysosomes is in principle a viable strategy for treating LSDs. Enzyme replacement therapy (ERT) is now approved for the treatment of seven LSDs, and clinical trials are ongoing for five others (3). However, delivering curative doses of recombinant lysosomal enzymes into lysosomes remains a major challenge in practice. ERT typically takes advantage of a specific N-glycan posttranslational modification, mannose-6-phosphorylation (M6P), which controls trafficking of endogenous lysosomal enzymes, as well as exogenous uptake of lysosomal enzymes from circulation by cells having the cation-independent M6P receptor (CIMPR) (4). Hence, a combination of factors including (i) the abundance of the M6P receptor in the liver, (ii) poor levels of CIMPR expression in several key target tissue types such as bone and skeletal muscle, (iii) incomplete and unpredictable M6P labeling of recombinant enzymes, and (iv) the highly variable affinity of recombinant lysosomal enzymes for CIMPR [viz., Kds (dissociation constants) ranging from low to mid micromolar (5, 6)] all contribute to diminishing the overall effectiveness of therapies using CIMPR for cell entry (3).

To improve the delivery of therapeutic lysosomal enzymes, we drew inspiration from bacterial toxins, which, as part of their mechanism, hijack specific host cellsurface receptors to gain entry into the endolysosomal pathway. While we and others have explored exploiting this pathway to deliver cargo into the cytosol (7, 8), here we asked whether this same approach could be used to enhance the delivery of lysosomal enzymes into lysosomes. We choose the diphtheria toxin (DT)diphtheria toxin receptor (DTR) system owing to the ubiquitous nature of the DTR, in particular its high expression levels on neurons.

Corynebacterium diphtheriae secretes DT exotoxin, which is spread to distant organs by the circulatory system, where it affects the lungs, heart, liver, kidneys, and the nervous system (9). It is estimated that 75% of individuals with acute disease also develop some form of peripheral or cranial neuropathy. This multiorgan targeting results from the fact that the DTR, heparin-binding EGF (epidermal growth factor)like growth factor (HBEGF), is ubiquitously expressed. The extent to which DT specifically targets difficult-to-access tissues such as muscle and bone, however, is not currently known.

DT is a three-domain protein that consists of an N-terminal ADP (adenosine diphosphate)ribosyl transferase enzyme (DTC), a central translocation domain (DTT), and a C-terminal receptorbinding domain (DTR). The latter is responsible for both binding cell surface HBEGF with high affinity [viz., Kd = 27 nM (10)] and triggering endocytosis into early endosomes (Fig. 1A). Within endosomes, DTT forms membrane-spanning pores that serve as conduits for DTC to enter the cytosol where it inactivates the host protein synthesis machinery. The remaining portions of the toxin remain in the endosomes and continue to lysosomes where they are degraded (11, 12). We hypothesized that the receptor-binding domain, lacking any means to escape endosomes, would proceed with any attached cargo to lysosomes and, thus, serve as a means to deliver cargo specifically into lysosomes following high-affinity binding to HBEGF.

(A) DT intoxication pathway (left), DT domain architecture, and LTM structure (right). (B and C) DTK51E/E148K, LTM, mCherry-LTM, and LTM-mCherry compete with wild-type DT for binding and inhibit its activity in a dose-dependent manner with IC50 (median inhibitory concentration) values of 46.9, 10.1, 52.7, and 76.1 nM, respectively (means SD; n = 3). (D and E) C-terminal and N-terminal fusions of LTM to mCherry were immunostained (red) and observed to colocalize with the lysosomal marker LAMP1 (39). (F) Fractional co-occurrence of the red channel with the green channel (Manders coefficient M2) were calculated for mCherry-LTM and LTM-mCherry and were found to be 0.61 0.10 and 0.52 0.11, respectively (means SD; n = 6).

In this study, we generated a series of chimeric proteins containing the DTR-binding domain, DTR, with the goal of demonstrating the feasibility of delivering therapeutic enzymes into lysosomes through the DT-HBEGF internalization pathway. We showed that DTR serves as a highly effective and versatile lysosome-targeting moiety (LTM). It can be placed at either the N or C terminus of the cargo, where it retains its high-affinity binding to HBEGF and the ability to promote trafficking into lysosomes both in vitro and in vivo. On the basis of its advantages, over M6P-mediated mechanisms, we further investigated the utility of LTM for the lysosomal delivery of human tripeptidyl peptidase-1 (TPP1) with the long-term goal of treating Batten disease.

To evaluate whether the DTR-binding fragment could function autonomously to traffic cargo into lysosomes, we first asked whether the isolated 17-kDa DTR fragment could be expressed independently from DT holotoxin and retain its affinity for HBEGF. We cloned, expressed, and purified the receptor-binding fragment and evaluated its ability to compete with full-length DT for the DTR, HBEGF. Before treating cells with a fixed dose of wild-type DT that completely inhibits protein synthesis, cells were incubated with a range of concentrations of LTM or a full-length, nontoxic mutant of DT (DTK51E/E148K). LTM-mediated inhibition of wild-type DT-mediated toxicity was equivalent to nontoxic DT (Fig. 1B), demonstrating that the receptor-binding fragment can be isolated from the holotoxin without affecting its ability to fold and bind cell surface HBEGF. Next, we evaluated whether LTM had a positional bias (i.e., was able to bind HBEGF with a fusion partner when positioned at either terminus). To this end, we generated N- and C-terminal fusions of LTM to the model fluorescent protein mCherry (i.e., mCherry-LTM and LTM-mCherry). To determine binding of each chimera to HBEGF, we quantified the ability of each chimera to compete with wild-type DT on cells in the intoxication assay. Both constructs competed with wild-type DT to the same extent as LTM alone and DTK51E/E148K (Fig. 1C), demonstrating that LTM is versatile and autonomously folds in different contexts.

To evaluate intracellular trafficking, HeLa cells were treated with either LTM-mCherry or mCherry-LTM and then fixed and stained 4 hours later with an antibody against the lysosomal marker LAMP1. In both cases, we observed significant uptake of the fusion protein (Fig. 1, D and E). We calculated Manders coefficients (M2) to quantify the extent to which signal in the red channel (LTM-mCherry and mCherry-LTM) was localizing with signal in the green channel (LAMP1). The fraction of red/green co-occurrence was calculated to be 0.61 for mCherry-LTM and 0.52 for LTM-mCherry, indicating trafficking to the lysosomal compartments of the cells and no significant difference (P = 0.196) between the two orientations of chimera (Fig. 1F). Together, these results confirm that the LTM is capable of binding HBEGF and trafficking associated cargo into cells and that the LTM can function in this manner at either terminus of a fusion construct.

With minimal positional bias observed in the mCherry fusion proteins, we next screened LTM fusions to TPP1 to identify a design that maximizes expression, stability, activity, and, ultimately, delivery. TPP1 is a 60-kDa lysosomal serine peptidase encoded by the CLN2 gene, implicated in neuronal ceroid lipofuscinosis type 2 or Batten disease. Loss of function results in the accumulation of lipofuscin, a proteinaceous, autofluorescent storage material (13). Exposure to the low-pH environment of the lysosome triggers autoproteolytic activation of TPP1 and release of a 20-kDa propeptide that occludes its active site. From a design perspective, we favored an orientation in which the LTM was N terminal to TPP1, as autoprocessing of TPP1 would result in the release of the upstream LTM-TPP1 propeptide, liberating active, mature TPP1 enzyme in the lysosome (Fig. 2A). Given the need for mammalian expression of lysosomal enzymes, we generated synthetic genetic fusions of the LTM to TPP1, in which we converted the codons from bacterially derived DT into the corresponding mammalian codons. Human embryonic kidney (HEK) 293F suspension cells stably expressing recombinant TPP1 (rTPP1) and TPP1 with an N-terminal LTM fusion (LTM-TPP1) were generated using the piggyBac transposon system (14). A C-terminal construct (TPP1-LTM) was also produced; however, expression of this chimera was poor in comparison with rTPP1 and LTM-TPP1 (~0.4 mg/liter, cf. 10 to 15 mg/liter).

(A) Design of LTM-TPP1 fusion protein and delivery schematic. (B) Enzyme kinetics of rTPP1 and LTM-TPP1 against the synthetic substrate AAF-AMC are indistinguishable. Michaelis-Menten plots were generated by varying [AAF-AMC] at a constant concentration of 10 nM enzyme (means SD; n = 3). Plots and kinetic parameters were calculated with GraphPad Prism 7.04. (C) Maturation of TPP1 is unaffected by the N-terminal fusion of LTM. (D) LTM-TPP1 inhibits wild-type DT activity in a dose-dependent manner (IC50 of 17.2 nM), while rTPP1 has no effect on protein synthesis inhibition by DT (means SD; n = 3). (E) LTM and DTR-TPP1 bind HBEGF with apparent Kds of 13.3 and 19.1 nM, respectively. (F) LTM-TPP1 (39) colocalizes with LAMP1 staining (red).

The activity of rTPP1 and LTM-TPP1 against the tripeptide substrate Ala-Ala-Phe-AMC (AAF-AMC) was assessed to determine any effects of the LTM on TPP1 activity. The enzyme activities of rTPP1 and LTM-TPP1 were determined to be equivalent, as evidenced through measurements of their catalytic efficiency (Fig. 2B), demonstrating that there is no inference by LTM on the peptidase activity of TPP1. Maturation of LTM-TPP1 through autocatalytic cleavage of the N-terminal propeptide was analyzed by SDSpolyacrylamide gel electrophoresis (PAGE) (Fig. 2C). Complete processing of the zymogen at pH 3.5 and 37C occurred between 5 and 10 min, which is consistent with what has been observed for the native recombinant enzyme (15).

The ability of LTM-TPP1 to compete with DT for binding to extracellular HBEGF was first assessed with the protein synthesis competition assay. Similar to LTM, mCherry-LTM, and LTM-mCherry, LTM-TPP1 prevents protein synthesis inhibition by 10 pM DT with an IC50 (median inhibitory concentration) of 17.2 nM (Fig. 2D). As expected, rTPP1 alone was unable to inhibit DT-mediated entry and cytotoxicity. To further characterize this interaction, we measured the interaction between LTM and LTM-TPP1 and recombinant HBEGF using surface plasmon resonance (SPR) binding analysis (Fig. 2E). By SPR, LTM and LTM-TPP1 were calculated to have apparent Kds of 13.3 and 19.1 nM, respectively, values closely corresponding to the IC50 values obtained from the competition experiments (10.1 and 17.2 nM, respectively). Consistent with these results, LTM-TPP1 colocalizes with LAMP1 by immunofluorescence (Fig. 2F).

To study uptake of chimeric fusion proteins in cell culture, we generated a cell line deficient in TPP1 activity. A CRISPR RNA (crRNA) was designed to target the signal peptide region of TPP1 in exon 2 of CLN2. Human HeLa Kyoto cells were reverse transfected with a Cas9 ribonucleoprotein complex and then seeded at low density into a 10-cm dish. Single cells were expanded to colonies, which were picked and screened for TPP1 activity. A single clone deficient in TPP1 activity was isolated and expanded, which was determined to have ~4% TPP1 activity relative to wild-type HeLa Kyoto cells plated at the same density (Fig. 3A). The small residual activity observed is likely the result of another cellular enzyme processing the AAFAMC (7-amido-4-methlycoumarin) substrate used in this assay, as there is no apparent TPP1 protein being produced (Fig. 3B). Sanger sequencing of the individual alleles confirmed complete disruption of the CLN2 gene (fig. S1). In total, three unique mutations were identified within exon 2 of CLN2: a single base insertion resulting in a frameshift mutation and two deletions of 24 and 33 base pairs (bp), respectively.

(A) CLN2 knockout cells exhibit ~4% TPP1 activity relative to wild-type HeLa Kyoto cells (means SD; n = 3). (B) Western blotting against TPP1 reveals no detectable protein in the knockout cells. (C) (Left) In vitro maturation of pro-rTPP1 and LTM-TPP1 (16 ng) was analyzed by Western blot. (Right) TPP1 present in wild-type (WT) and TPP1/ cells, and TPP1/ cells treated with 100 nM rTPP1 and LTM-TPP1. (D) Uptake of rTPP1 and LTM-TPP1 into HeLa Kyoto TPP1/ cells was monitored by TPP1 activity (means SD; n = 4). (E) TPP1 activity present in HeLa Kyoto TPP1/ cells following a single treatment with 50 nM LTM-TPP1 (means SD; n = 3).

Next, we compared the delivery and activation of rTPP1 and LTM-TPP1 into lysosomes by treating TPP1/ cells with a fixed concentration of the enzymes (100 nM) and by analyzing entry and processing by Western blot (Fig. 3C). In both cases, most enzymes were present in the mature form, indicating successful delivery to the lysosome; however, the uptake of LTM-TPP1 greatly exceeded the uptake of rTPP1. As both rTPP1 and LTM-TPP1 receive the same M6P posttranslational modifications promoting their uptake by CIMPR, differences in their respective uptake should be directly attributable to uptake by HBEGF. To quantify the difference in uptake and lysosomal delivery, cells were treated overnight with varying amounts of each enzyme, washed, lysed, and assayed for TPP1 activity. The activity assays were performed without a preactivation step, so signal represents protein that has been activated in the lysosome. For both constructs, we observed a dose-dependent increase in delivery of TPP1 to the lysosome (Fig. 3D). Delivery of LTM-TPP1 was significantly enhanced compared with TPP1 alone at all doses, further demonstrating that uptake by HBEGF is more efficient than that by CIMPR alone. TPP1 activity in cells treated with LTM-TPP1 was consistently ~10 greater than that of cells treated with rTPP1, with the relative difference increasing at the highest concentrations tested. This may speak to differences in abundance, replenishment, and/or recycling of HBEGF versus CIMPR, in addition to differences in receptor-ligand affinity. Uptake of LTM-TPP1 and rTPP1 into several other cell types yielded similar results (fig. S2). To assess the lifetime of the delivered enzyme, cells were treated with LTM-TPP1 (50 nM) and incubated overnight. Cells were washed and incubated with fresh media, and TPP1 activity was assayed over the course of several days. Cells treated with LTM-TPP1 still retained measurable TPP1 activity at 1 week after treatment (Fig. 3E).

While the DT competition experiment demonstrated that HBEGF is involved in the uptake of LTM-TPP1 but not rTPP1 (Fig. 2D), it does not account for the contribution of CIMPR to uptake. Endoglycosidase H (EndoH) cleaves between the core N-acetylglucosamine residues of high-mannose N-linked glycans, leaving behind only the asparagine-linked N-acetylglucosamine moiety. Both rTPP1 and LTM-TPP1 were treated with EndoH to remove any M6P moieties, and delivery into Hela TPP1/ was subsequently assessed. While rTPP1 uptake is completely abrogated by treatment with EndoH, LTM-TPP1 uptake is only partially decreased (Fig. 4), indicating that while HBEGF-mediated endocytosis is the principal means by which LTM-TPP1 is taken up into cells, uptake via CIMPR still occurs. The fact that CIMPR uptake is still possible in the LTM-TPP1 fusion means that the fusion is targeted to two receptors simultaneously, increasing its total uptake and, potentially, its biodistribution.

Uptake of LTM-TPP1 via the combination of HBEGF and CIMPR was shown to be 3 to 20 more efficient than CIMPR alone in cellulo (fig. S2). To interrogate this effect in vivo, TPP1-deficient mice (TPP1tm1pLob or TPP1/) were obtained as a gift from P. Lobel at Rutgers University. Targeted disruption of the CLN2 gene was achieved by insertion of a neo cassette into intron 11 in combination with a point mutation (R446H), rendering these mice TPP1 null by both Western blot and enzyme activity assay (16). Prior studies have demonstrated that direct administration of rTPP1 into the cerebrospinal fluid (CSF) via intracerebroventricular or intrathecal injection results in amelioration of disease phenotype (17) and even extension of life span in the disease mouse (18). To compare the uptake of LTM-TPP1 and rTPP1 in vivo, the enzymes were injected into the left ventricle of 6-week-old TPP1/ mice. Mice were euthanized 24 hours after injection, and brain homogenates of wild-type littermates, untreated, and treated mice were assayed for TPP1 activity (Fig. 5A). Assays were performed without preactivation, and therefore, the results report on enzyme that has been taken up into cells, trafficked to the lysosome, and processed to the mature form.

(A) Assay schematic. (B) TPP1 activity in brain homogenates of 6-week-old mice injected with two doses (5 and 25 g) of either rTPP1 or LTM-TPP1 (5 g, P = 0.01; 25 g, P = 0.002). (C) TPP1 activity in brain homogenates following a single 25-g dose of LTM-TPP1, 1, 7, and 14 days postinjection. Data are presented as box and whisker plots, with whiskers representing minimum and maximum values from n 4 mice per group. Statistical significance was calculated using paired t tests with GraphPad Prism 7.04.

While both enzymes resulted in a dose-dependent increase in TPP1 activity, low (5 g) and high (25 g) doses of rTPP1 resulted in only modest increases of activity, representing ~6 and ~26% of the wild-type levels of activity, respectively (Fig. 5B). At the same doses, LTM-TPP1 restored ~31 and ~103% of the wild-type activity. To assess the lifetime of enzyme in the brain, mice were injected intracerebroventricularly with 25 g of LTM-TPP1 and euthanized either 1 or 2 weeks postinjection. Remarkably, at 1 week postinjection, ~68% of TPP1 activity was retained (compared with 1 day postinjection), and after 2 weeks, activity was reduced to ~31% (Fig. 5C).

ERT is a lifesaving therapy that is a principal method of treatment in non-neurological LSDs. Uptake of M6P-labeled enzymes by CIMPR is relatively ineffective due to variable receptor affinity (5, 6), heterogeneous expression of the receptor, and incomplete labeling of recombinantly produced enzymes (19). Despite its inefficiencies and high cost (~200,000 USD per patient per year) (20), it remains the standard of care for several LSDs, as alternative treatment modalities (substrate reduction therapy, gene therapy, and hematopoietic stem cell transplantation) are not effective, not as well developed, or inherently riskier (2125). Improving the efficiency and distribution of recombinant enzyme uptake may help address some of the current shortcomings in traditional ERT.

Several strategies have been used to increase the extent of M6P labeling on recombinantly produced lysosomal enzymes: engineering mammalian and yeast cell lines to produce more specific/uniform N-glycan modification (19, 26, 27), chemical or enzymatic modification of N-glycans posttranslationally (28), and covalent coupling of M6P (29). M6P-independent uptake of a lysosomal hydrolase by CIMPR has been demonstrated for both -glucuronidase (28) and acid -glucosidase (30, 31). In the latter work, a peptide tag (GILT) targeting insulin-like growth factor II receptor (IGF2R) was fused to recombinant alpha glucosidase, which enabled receptor-mediated entry into cells. CIMPR is a ~300-kDa, 15-domain membrane protein with 3 M6P-binding domains and 1 IGF2R domain. By targeting the IGF2R domain with a high-affinity (low nanomolar) peptide rather than the low-affinity M6P-binding domain, the authors were able to demonstrate a >20-fold increase in the uptake of a GAA-peptide fusion protein in cell culture and a ~5-fold increase in the ability to clear built-up muscle glycogen in GAA-deficient mice.

In this study, we have demonstrated efficient uptake and lysosomal trafficking of a model lysosomal enzyme, TPP1, via a CIMPR-independent route, using the receptor-binding domain of a bacterial toxin. HBEGF is a member of the EGF family of growth factors, and DT is its only known ligand. Notably, it plays roles in cardiac development, wound healing, muscle contraction, and neurogenesis; however, it does not act as a receptor in any of these physiological processes (32). Intracellular intoxication by DT is the only known process in which HBEGF acts as a receptor, making it an excellent candidate receptor for ERT, as there is no natural ligand with which to compete. Upon binding, DT is internalized via clathrin-mediated endocytosis and then trafficked toward lysosomes for degradation (33, 34). Acidification of endosomal vesicles by vacuolar ATPases (adenosine triphosphatases) promotes insertion of DTT into the endosomal membrane and subsequent translocation of the catalytic DTC domain into the cytosol. In the absence of an escape mechanism, the majority of internalized LTM should be trafficked to the lysosome, as we have demonstrated with our chimera (Figs. 2F and 3C). Uptake of LTM-TPP1 in vitro is robustly relative to rTPP1 (Fig. 3D and fig. S2), and TPP1 activity is sustained in the lysosome for a substantial length of time (Fig. 3E). We have also demonstrated that the increase in uptake efficiency that we observed in cell culture persists in vivo. TPP1 activity in the brains of CLN2-null mice was significantly greater in animals treated with intracerebroventricularly injected LTM-TPP1, as compared with those treated with TPP1 at two different doses (Fig. 5B), and, remarkably, this activity persists with an apparent half-life of ~8 days (Fig. 5C).

An important consideration for further development of the LTM platform for clinical development is the potential immunogenicity of using a bacterial fragment in this context. Previously, we demonstrated that the receptor-binding fragment of DT could be replaced with a human scFv (single-chain fragment variable) targeting HBEGF (8). With our demonstration of the potential for targeting HBEGF for LSDs, future efforts will focus on increasing the affinity and specificity of these first-generation humanized LTMs to develop high-affinity chimeras with greatly reduced immunogenicity for further development.

While the ability of LTM-TPP1 to affect disease progression has yet to be determined, recent positive clinical trial results (35) and the subsequent approval of rTPP1 (cerliponase alfa) for treatment of neuronal ceroid lipofuscinosis 2 (NCL2) provide support for this approach. In that clinical trial, 300 mg of rTPP1 was administered by biweekly intracerebroventricular injection to 24 affected children, and this was able to prevent disease progression. While this dose is of the same order of magnitude as other approved ERTs (<1 to 40 mg/kg) (36, 37), it represents a substantial dose, especially considering that it was delivered to a single organ. Improving the efficiency of uptake by targeting an additional receptor as we have done here, is expected to greatly decrease the dose required to improve symptoms, while at the same time decreasing costs and the chances of dose-dependent side effects.

DTK51E/E148K, LTM, LTM-mCherry, mCherry-LTM, and HBEGF constructs were cloned using the In-Fusion HD cloning kit (Clontech) into the Champion pET SUMO expression system (Invitrogen). Recombinant proteins were expressed as 6His-SUMO fusion proteins in Escherichia coli BL21(DE3)pLysS cells. Cultures were grown at 37C until an OD600 (optical density at 600 nm) of 0.5, induced with 1 mM IPTG (isopropyl--d-thiogalactopyranoside) for 4 hours at 25C. Cell pellets harvested by centrifugation were resuspended in lysis buffer [20 mM tris (pH 8.0), 160 mM NaCl, 10 mM imidazole, lysozyme, benzonase, and protease inhibitor cocktail] and lysed by three passages through an EmulsiFlex C3 microfluidizer (Avestin). Following clarification by centrifugation at 18,000g for 20 min and syringe filtration (0.2 m), soluble lysate was loaded over a 5-ml His-trap FF column (GE Healthcare) using an AKTA FPLC. Bound protein was washed and eluted over an imidazole gradient (20 to 150 mM). Fractions were assessed for purity by SDS-PAGE, pooled, concentrated, and frozen on dry ice in 25% glycerol for storage at 80C.

TPP1 cDNA was obtained from the SPARC BioCentre (The Hospital for Sick Children) and cloned into the piggyBac plasmid pB-T-PAF (J.M.R., University of Toronto) using Not I and Asc I restriction sites to generate two expression constructs (pB-T-PAF-ProteinA-TEV-LTM-TPP1 and pB-T-PAF-ProteinA-TEV-TPP1). Stably transformed expression cell lines (HEK293F) were then generated using the piggyBac transposon system, as described (14). Protein expression was induced with doxycycline, and secreted fusion protein was separated from expression media using immunoglobulin G (IgG) Sepharose 6 fast flow resin (GE Healthcare) in a 10-ml Poly-Prep chromatography column (Bio-Rad). Resin was washed with 50 column volumes of wash buffer [10 mM tris (pH 7.5) and 150 mM NaCl] and then incubated overnight at 4C with TEV (Tobacco Etch Virus) protease to release the recombinant enzyme from the Protein A tag. Purified protein was then concentrated and frozen on dry ice in 50% glycerol for storage at 80C.

Cellular intoxication by DT was measured using a nanoluciferase reporter strain of Vero cells (Vero NlucP), as described previously (8). Briefly, Vero NlucP cells were treated with a fixed dose of DT at EC99 (10 pM) and a serial dilution of LTM, LTM-mCherry, mCherry-LTM, DTK51E/E148K, LTM-TPP1, or rTPP1 and incubated overnight (17 hours) at 37C. Cell media was then replaced with a 1:1 mixture of fresh media and Nano-Glo luciferase reagent (Promega), and luminescence was measured using a SpectraMax M5e (Molecular Devices). Results were analyzed with GraphPad Prism 7.04.

SPR analysis was performed on a Biacore X100 system (GE Healthcare) using a CM5 sensor chip. Recombinant HBEGF was immobilized to the chip using standard amine coupling at a concentration of 25 g/ml in 10 mM sodium acetate (pH 6.0) with a final response of 1000 to 2500 resonance units (RU). LTM and LTM-TPP1 were diluted in running buffer [200 mM NaCl, 0.02% Tween 20, and 20 mM tris (pH 7.5)] at concentrations of 6.25 to 100 nM and injected in the multicycle analysis mode with a contact time of 180 s and a dissociation time of 600 s. The chip was regenerated between cycles with 10 mM glycine (pH 1.8). Experiments were performed in duplicate using two different chips. Binding data were analyzed with Biacore X100 Evaluation Software version 2.0.2, with apparent dissociation constants calculated using the 1:1 steady-state affinity model.

HeLa cells were incubated with LTM-mCherry (0.5 M), mCherry-LTM (0.5 M), or LTM-TPP1 (2 M) for 2 hours. Cells were washed with ice-cold phosphate-buffered saline (PBS), fixed with 4% paraformaldehyde, and permeabilized with 0.5% Triton X-100. mCherry constructs were visualized with a rabbit polyclonal antibody against mCherry (Abcam, ab16745) and anti-rabbit Alexa Fluor 568 (Thermo Fisher Scientific). LAMP1 was stained with a mouse primary antibody (DSHB 1D4B) and anti-mouse Alexa Fluor 488 (Thermo Fisher Scientific).

Colocalization was quantified using the Volocity (PerkinElmer) software package to measure Manders coefficients of mCherry signal with LAMP1 signal. The minimal threshold for the 488- and 568-nm channels was adjusted to correct the background signal. The same threshold for both channels was used for all the cells examined.

CLN2/ fibroblast 19494 were incubated with LTM-TPP1 (2 M) for 2 hours. Cells were washed with ice-cold PBS, fixed with 4% paraformaldehyde, and permeabilized with 0.5% Triton X-100. LTM-TPP1 was visualized with a mouse monoclonal against TPP1 (Abcam, ab54685) and anti-mouse Alexa Fluor 488 (Thermo Fisher Scientific). LAMP1 was stained with rabbit anti-LAMP1 and anti-rabbit Alexa Fluor 568 (Thermo Fisher Scientific).

TPP1 protease activity was measured using the synthetic substrate AAF-AMC using a protocol adapted from Vines and Warburton (38). Briefly, enzyme was preactivated in 25 l of activation buffer [50 mM NaOAc (pH 3.5) and 100 mM NaCl] for 1 hour at 37C. Assay buffer [50 mM NaOAc (pH 5.0) and 100 mM NaCl] and substrate (200 M AAF-AMC) were then added to a final volume of 100 l. Fluorescence (380 nm excitation/460 nm emission) arising from the release of AMC was monitored in real time using a SpectraMax M5e (Molecular Devices). TPP1 activity in cellulo was measured similarly, without the activation step. Cells in a 96-well plate were incubated with 25 l of 0.5% Triton X-100 in PBS, which was then transferred to a black 96-well plate containing 75 l of assay buffer with substrate in each well.

crRNA targeting the signal peptide sequence in exon 2 of CLN2 was designed using the Integrated DNA Technologies (www.idtdna.com) design tool. The gRNA:Cas9 ribonucleoprotein complex was assembled according to the manufacturers protocol (Integrated DNA Technologies) and reverse transfected using Lipofectamine RNAiMAX (Thermo Fisher Scientific) into HeLa Kyoto cells (40,000 cells in a 96-well plate). Following 48 hours of incubation, 5000 cells were seeded into a 10-cm dish. Clonal colonies were picked after 14 days and transferred to a 96-well plate. Clones were screened for successful CLN2 knockout by assaying TPP1 activity and confirmed by Sanger sequencing and Western blot against TPP1 antibody (Abcam, ab54385).

The pro-form of TPP1 was matured in vitro to the active form in 50 mM NaOAc (pH 3.5) and 100 mM NaCl for 1 to 30 min at 37C. The autoactivation reaction was halted by the addition of 2 Laemmli SDS sample buffer containing 10% 2-mercaptoethanol and boiled for 5 min. Pro and mature TPP1 were separated by SDS-PAGE and imaged on a ChemiDoc gel imaging system (Bio-Rad).

Proteins or cellular lysate were separated by 4 to 20% gradient SDS-PAGE before being transferred to a nitrocellulose membrane using the iBlot (Invitrogen) dry transfer system. Membranes were then blocked for 1 hour with a 5% milktris-buffered saline (TBS) solution and incubated overnight at room temperature with a 1:100 dilution of mouse monoclonal antibody against TPP1 (Abcam, ab54685) in 5% milk-TBS. Membranes were washed 3 5 min with 0.1% Tween 20 (Sigma-Aldrich) in TBS before a 1-hour incubation with a 1:5000 dilution of sheep anti-mouse IgG horseradish peroxidase secondary antibody (GE Healthcare) in 5% milk-TBS. Chemiluminescent signal was developed with Clarity Western ECL substrate (Bio-Rad) and visualized on a ChemiDoc gel imaging system (Bio-Rad).

rTTP1 and LTM-TPP1 were treated with EndoH (New England Biolabs) to remove N-glycan modifications. Enzymes were incubated at 1 mg/ml with 2500 U of EndoH for 48 hours at room temperature in 20 mM tris (pH 8.0) and 150 mM NaCl in a total reaction volume of 20 l. Cleavage of N-glycans was assessed by SDS-PAGE, and concentrations were normalized to native enzyme-specific activities.

Cryopreserved TPP1+/ embryos were obtained from P. Lobel at Rutgers University and rederived in a C57/BL6 background at The Centre for Phenogenomics in Toronto. Animal maintenance and all procedures were approved by The Centre for Phenogenomics Animal Care Committee and are in compliance with the CCAC (Canadian Council on Animal Care) guidelines and the OMAFRA (Ontario Ministry of Agriculture, Food, and Rural Affairs) Animals for Research Act.

TPP1/ mice (60 days old) were anesthetized with isoflurane (inhaled) and injected subcutaneously with sterile saline (1 ml) and meloxicam (2 mg/kg). Mice were secured to a stereotactic system, a small area of the head was shaved, and a single incision was made to expose the skull. A high-speed burr was used to drill a hole at stereotaxic coordinates: anteroposterior (A/P), 1.0 mm; mediolateral (M/L), 0.3 mm; and dorsoventral (D/V), 3.0 mm relative to the bregma, and a 33-gauge needle attached to a 10-l Hamilton syringe was used to perform the intracerebroventricular injection into the left ventricle. Animals received either 1 or 5 l of enzyme (5 g/l), injected at a constant rate. Isoflurane-anesthetized animals were euthanized by transcardial perfusion with PBS. Brains were harvested and frozen immediately, then thawed and homogenized in lysis buffer [500 mM NaCl, 0.5% Triton X-100, 0.1% SDS, and 50 mM Tris (pH 8.0)] using 5-mm stainless steel beads in TissueLyser II (Qiagen). In vitro TPP1 assay was performed, as described, minus the activation step.

Acknowledgments: We thank P. Lobel at Rutgers University for providing the TPP1-deficient mice. Funding: We are grateful to the Canadian Institutes of Health Research for funding. Author contributions: S.N.S.-M. devised and performed experiments and drafted the initial manuscript. G.L.B. provided materials and assisted in conceptualization and experimental design. X.Z., D.Z., and R.H. contributed to the experimental design and performed experiments. P.K.K. and B.A.M. contributed to the experimental design. J.M.R. contributed to the experimental design and revised the manuscript. R.A.M. assisted in conceptualization, contributed to the experimental design, and assisted in writing the manuscript. Competing interests: B.A.M. is a chief medical advisor at Taysha Gene Therapies. The authors declare that they have no other competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.

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Exploiting the diphtheria toxin internalization receptor enhances delivery of proteins to lysosomes for enzyme replacement therapy - Science Advances

ANDOVER, Mass. The liquid that many hope could help end the Covid-19 pandemic is stored in a nondescript metal tank in a manufacturing complex owned by Pfizer, one of the worlds biggest drug companies. There is nothing remarkable about the container, which could fit in a walk-in closet, except that its contents could end up in the worlds first authorized Covid-19 vaccine.

Pfizer, a 171-year-old Fortune 500 powerhouse, has made a billion-dollar bet on that dream. So has a brash, young rival just 23 miles away in Cambridge, Mass. Moderna, a 10-year-old biotech company with billions in market valuation but no approved products, is racing forward with a vaccine of its own. Its new sprawling drug-making facility nearby is hiring workers at a fast clip in the hopes of making history and a lot of money.

In many ways, the companies and their leaders couldnt be more different. Pfizer, working with a little-known German biotech called BioNTech, has taken pains for much of the year to manage expectations. Moderna has made nearly as much news for its stream of upbeat press releases, executives stock sales, and spectacular rounds of funding as for its science.

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Each is well-aware of the other in the race to be first.

But what the companies share may be bigger than their differences: Both are banking on a genetic technology that has long held huge promise but has so far run into biological roadblocks. It is called synthetic messenger RNA, an ingenious variation on the natural substance that directs protein production in cells throughout the body. Its prospects have swung billions of dollars on the stock market, made and imperiled scientific careers, and fueled hopes that it could be a breakthrough that allows society to return to normalcy after months living in fear.

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Both companies have been frequently name-checked by President Trump. Pfizer reported strong, but preliminary, data on Monday, and Moderna is expected to follow suit soon with a glimpse of its data. Both firms hope these preliminary results will allow an emergency deployment of their vaccines millions of doses likely targeted to frontline medical workers and others most at risk of Covid-19.

There are about a dozen experimental vaccines in late-stage clinical trials globally, but the ones being tested by Pfizer and Moderna are the only two that rely on messenger RNA.

For decades, scientists have dreamed about the seemingly endless possibilities of custom-made messenger RNA, or mRNA.

Researchers understood its role as a recipe book for the bodys trillions of cells, but their efforts to expand the menu have come in fits and starts. The concept: By making precise tweaks to synthetic mRNA and injecting people with it, any cell in the body could be transformed into an on-demand drug factory.

But turning scientific promise into medical reality has been more difficult than many assumed. Although relatively easy and quick to produce compared to traditional vaccine-making, no mRNA vaccine or drug has ever won approval.

Even now, as Moderna and Pfizer test their vaccines on roughly 74,000 volunteers in pivotal vaccine studies, many experts question whether the technology is ready for prime time.

I worry about innovation at the expense of practicality, Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine and an authority on vaccines, said recently. The U.S. governments Operation Warp Speed program, which has underwritten the development of Modernas vaccine and pledged to buy Pfizers vaccine if it works, is weighted toward technology platforms that have never made it to licensure before.

Whether mRNA vaccines succeed or not, their path from a gleam in a scientists eye to the brink of government approval has been a tale of personal perseverance, eureka moments in the lab, soaring expectations and an unprecedented flow of cash into the biotech industry.

It is a story that began three decades ago, with a little-known scientist who refused to quit.

Before messenger RNA was a multibillion-dollar idea, it was a scientific backwater. And for the Hungarian-born scientist behind a key mRNA discovery, it was a career dead-end.

Katalin Karik spent the 1990s collecting rejections. Her work, attempting to harness the power of mRNA to fight disease, was too far-fetched for government grants, corporate funding, and even support from her own colleagues.

It all made sense on paper. In the natural world, the body relies on millions of tiny proteins to keep itself alive and healthy, and it uses mRNA to tell cells which proteins to make. If you could design your own mRNA, you could, in theory, hijack that process and create any protein you might desire antibodies to vaccinate against infection, enzymes to reverse a rare disease, or growth agents to mend damaged heart tissue.

In 1990, researchers at the University of Wisconsin managed to make it work in mice. Karik wanted to go further.

The problem, she knew, was that synthetic RNA was notoriously vulnerable to the bodys natural defenses, meaning it would likely be destroyed before reaching its target cells. And, worse, the resulting biological havoc might stir up an immune response that could make the therapy a health risk for some patients.

It was a real obstacle, and still may be, but Karik was convinced it was one she could work around. Few shared her confidence.

Every night I was working: grant, grant, grant, Karik remembered, referring to her efforts to obtain funding. And it came back always no, no, no.

By 1995, after six years on the faculty at the University of Pennsylvania, Karik got demoted. She had been on the path to full professorship, but with no money coming in to support her work on mRNA, her bosses saw no point in pressing on.

She was back to the lower rungs of the scientific academy.

Usually, at that point, people just say goodbye and leave because its so horrible, Karik said.

Theres no opportune time for demotion, but 1995 had already been uncommonly difficult. Karik had recently endured a cancer scare, and her husband was stuck in Hungary sorting out a visa issue. Now the work to which shed devoted countless hours was slipping through her fingers.

I thought of going somewhere else, or doing something else, Karik said. I also thought maybe Im not good enough, not smart enough. I tried to imagine: Everything is here, and I just have to do better experiments.

In time, those better experiments came together. After a decade of trial and error, Karik and her longtime collaborator at Penn Drew Weissman, an immunologist with a medical degree and Ph.D. from Boston University discovered a remedy for mRNAs Achilles heel.

The stumbling block, as Kariks many grant rejections pointed out, was that injecting synthetic mRNA typically led to that vexing immune response; the body sensed a chemical intruder, and went to war. The solution, Karik and Weissman discovered, was the biological equivalent of swapping out a tire.

Every strand of mRNA is made up of five molecular building blocks called nucleosides. But in its altered, synthetic form, one of those building blocks, like a misaligned wheel on a car, was throwing everything off by signaling the immune system. So Karikand Weissman simply subbed it out for a slightly tweaked version, creating a hybrid mRNA that could sneak its way into cells without alerting the bodys defenses.

That was a key discovery, said Norbert Pardi, an assistant professor of medicine at Penn and frequent collaborator. Karik and Weissman figured out that if you incorporate modified nucleosides into mRNA, you can kill two birds with one stone.

That discovery, described in a series of scientific papers starting in 2005, largely flew under the radar at first, said Weissman, but it offered absolution to the mRNA researchers who had kept the faith during the technologys lean years. And it was the starter pistol for the vaccine sprint to come.

And even though the studies by Karik and Weissman went unnoticed by some, they caught the attention of two key scientists one in the United States, another abroad who would later help found Moderna and Pfizers future partner, BioNTech.

Derrick Rossi, a native of Toronto who rooted for the Maple Leafs and sported a soul patch, was a 39-year-old postdoctoral fellow in stem cell biology at Stanford University in 2005 when he read the first paper. Not only did he recognize it as groundbreaking, he now says Karik and Weissman deserve the Nobel Prize in chemistry.

If anyone asks me whom to vote for some day down the line, I would put them front and center, he said. That fundamental discovery is going to go into medicines that help the world.

But Rossi didnt have vaccines on his mind when he set out to build on their findings in 2007 as a new assistant professor at Harvard Medical School running his own lab.

He wondered whether modified messenger RNA might hold the key to obtaining something else researchers desperately wanted: a new source of embryonic stem cells.

In a feat of biological alchemy, embryonic stem cells can turn into any type of cell in the body. That gives them the potential to treat a dizzying array of conditions, from Parkinsons disease to spinal cord injuries.

But using those cells for research had created an ethical firestorm because they are harvested from discarded embryos.

Rossi thought he might be able to sidestep the controversy. He would use modified messenger molecules to reprogram adult cells so that they acted like embryonic stem cells.

He asked a postdoctoral fellow in his lab to explore the idea. In 2009, after more than a year of work, the postdoc waved Rossi over to a microscope. Rossi peered through the lens and saw something extraordinary: a plate full of the very cells he had hoped to create.

Rossi excitedly informed his colleague Timothy Springer, another professor at Harvard Medical School and a biotech entrepreneur. Recognizing the commercial potential, Springer contacted Robert Langer, the prolific inventor and biomedical engineering professor at the Massachusetts Institute of Technology.

On a May afternoon in 2010, Rossi and Springer visited Langer at his laboratory in Cambridge. What happened at the two-hour meeting and in the days that followed has become the stuff of legend and an ego-bruising squabble.

Langer is a towering figure in biotechnology and an expert on drug-delivery technology. At least 400 drug and medical device companies have licensed his patents. His office walls display many of his 250 major awards, including the Charles Stark Draper Prize, considered the equivalent of the Nobel Prize for engineers.

As he listened to Rossi describe his use of modified mRNA, Langer recalled, he realized the young professor had discovered something far bigger than a novel way to create stem cells. Cloaking mRNA so it could slip into cells to produce proteins had a staggering number of applications, Langer thought, and might even save millions of lives.

I think you can do a lot better than that, Langer recalled telling Rossi, referring to stem cells. I think you could make new drugs, new vaccines everything.

Langer could barely contain his excitement when he got home to his wife.

This could be the most successful company in history, he remembered telling her, even though no company existed yet.

Three days later Rossi made another presentation, to the leaders of Flagship Ventures. Founded and run by Noubar Afeyan, a swaggering entrepreneur, the Cambridge venture capital firm has created dozens of biotech startups. Afeyan had the same enthusiastic reaction as Langer, saying in a 2015 article in Nature that Rossis innovation was intriguing instantaneously.

Within several months, Rossi, Langer, Afeyan, and another physician-researcher at Harvard formed the firm Moderna a new word combining modified and RNA.

Springer was the first investor to pledge money, Rossi said. In a 2012 Moderna news release, Afeyan said the firms promise rivals that of the earliest biotechnology companies over 30 years ago adding an entirely new drug category to the pharmaceutical arsenal.

But although Moderna has made each of the founders hundreds of millions of dollars even before the company had produced a single product Rossis account is marked by bitterness. In interviews with the Globe in October, he accused Langer and Afeyan of propagating a condescending myth that he didnt understand his discoverys full potential until they pointed it out to him.

Its total malarkey, said Rossi, who ended his affiliation with Moderna in 2014. Im embarrassed for them. Everybody in the know actually just shakes their heads.

Rossi said that the slide decks he used in his presentation to Flagship noted that his discovery could lead to new medicines. Thats the thing Noubar has used to turn Flagship into a big company, and he says it was totally his idea, Rossi said.

Afeyan, the chair of Moderna, recently credited Rossi with advancing the work of the Penn scientists. But, he said, that only spurred Afeyan and Langer to ask the question, Could you think of a code molecule that helps you make anything you want within the body?

Langer, for his part, told STAT and the Globe that Rossi made an important finding but had focused almost entirely on the stem cell thing.

Despite the squabbling that followed the birth of Moderna, other scientists also saw messenger RNA as potentially revolutionary.

In Mainz, Germany, situated on the left bank of the Rhine, another new company was being formed by a married team of researchers who would also see the vast potential for the technology, though vaccines for infectious diseases werent on top of their list then.

A native of Turkey, Ugur Sahin moved to Germany after his father got a job at a Ford factory in Cologne. His wife, zlem Treci had, as a child, followed her father, a surgeon, on his rounds at a Catholic hospital. She and Sahin are physicians who met in 1990 working at a hospital in Saarland.

The couple have long been interested in immunotherapy, which harnesses the immune system to fight cancer and has become one of the most exciting innovations in medicine in recent decades. In particular, they were tantalized by the possibility of creating personalized vaccines that teach the immune system to eliminate cancer cells.

Both see themselves as scientists first and foremost. But they are also formidable entrepreneurs. After they co-founded another biotech, the couple persuaded twin brothers who had invested in that firm, Thomas and Andreas Strungmann, to spin out a new company that would develop cancer vaccines that relied on mRNA.

That became BioNTech, another blended name, derived from Biopharmaceutical New Technologies. Its U.S. headquarters is in Cambridge. Sahin is the CEO, Treci the chief medical officer.

We are one of the leaders in messenger RNA, but we dont consider ourselves a messenger RNA company, said Sahin, also a professor at the Mainz University Medical Center. We consider ourselves an immunotherapy company.

Like Moderna, BioNTech licensed technology developed by the Pennsylvania scientist whose work was long ignored, Karik, and her collaborator, Weissman. In fact, in 2013, the company hired Karik as senior vice president to help oversee its mRNA work.

But in their early years, the two biotechs operated in very different ways.

In 2011, Moderna hired the CEO who would personify its brash approach to the business of biotech.

Stphane Bancel was a rising star in the life sciences, a chemical engineer with a Harvard MBA who was known as a businessman, not a scientist. At just 34, he became CEO of the French diagnostics firm BioMrieux in 2007 but was wooed away to Moderna four years later by Afeyan.

Moderna made a splash in 2012 with the announcement that it had raised $40 million from venture capitalists despite being years away from testing its science in humans. Four months later, the British pharmaceutical giant AstraZeneca agreed to pay Moderna a staggering $240 million for the rights to dozens of mRNA drugs that did not yet exist.

The biotech had no scientific publications to its name and hadnt shared a shred of data publicly. Yet it somehow convinced investors and multinational drug makers that its scientific findings and expertise were destined to change the world. Under Bancels leadership, Moderna would raise more than $1 billion in investments and partnership funds over the next five years.

Modernas promise and the more than $2 billion it raised before going public in 2018 hinged on creating a fleet of mRNA medicines that could be safely dosed over and over. But behind the scenes the companys scientists were running into a familiar problem. In animal studies, the ideal dose of their leading mRNA therapy was triggering dangerous immune reactions the kind for which Karik had improvised a major workaround under some conditions but a lower dose had proved too weak to show any benefits.

Moderna had to pivot. If repeated doses of mRNA were too toxic to test in human beings, the company would have to rely on something that takes only one or two injections to show an effect. Gradually, biotechs self-proclaimed disruptor became a vaccines company, putting its experimental drugs on the back burner and talking up the potential of a field long considered a loss-leader by the drug industry.

Meanwhile BioNTech has often acted like the anti-Moderna, garnering far less attention.

In part, that was by design, said Sahin. For the first five years, the firm operated in what Sahin called submarine mode, issuing no news releases, and focusing on scientific research, much of it originating in his university lab. Unlike Moderna, the firm has published its research from the start, including about 150 scientific papers in just the past eight years.

In 2013, the firm began disclosing its ambitions to transform the treatment of cancer and soon announced a series of eight partnerships with major drug makers. BioNTech has 13 compounds in clinical trials for a variety of illnesses but, like Moderna, has yet to get a product approved.

When BioNTech went public last October, it raised $150 million, and closed with a market value of $3.4 billion less than half of Modernas when it went public in 2018.

Despite his role as CEO, Sahin has largely maintained the air of an academic. He still uses his university email address and rides a 20-year-old mountain bicycle from his home to the office because he doesnt have a drivers license.

Then, late last year, the world changed.

Shortly before midnight, on Dec. 30, the International Society for Infectious Diseases, a Massachusetts-based nonprofit, posted an alarming report online. A number of people in Wuhan, a city of more than 11 million people in central China, had been diagnosed with unexplained pneumonia.

Chinese researchers soon identified 41 hospitalized patients with the disease. Most had visited the Wuhan South China Seafood Market. Vendors sold live wild animals, from bamboo rats to ostriches, in crowded stalls. That raised concerns that the virus might have leaped from an animal, possibly a bat, to humans.

After isolating the virus from patients, Chinese scientists on Jan. 10 posted online its genetic sequence. Because companies that work with messenger RNA dont need the virus itself to create a vaccine, just a computer that tells scientists what chemicals to put together and in what order, researchers at Moderna, BioNTech, and other companies got to work.

A pandemic loomed. The companies focus on vaccines could not have been more fortuitous.

Moderna and BioNTech each designed a tiny snip of genetic code that could be deployed into cells to stimulate a coronavirus immune response. The two vaccines differ in their chemical structures, how the substances are made, and how they deliver mRNA into cells. Both vaccines require two shots a few weeks apart.

The biotechs were competing against dozens of other groups that employed varying vaccine-making approaches, including the traditional, more time-consuming method of using an inactivated virus to produce an immune response.

Moderna was especially well-positioned for this moment.

Forty-two days after the genetic code was released, Modernas CEO Bancel opened an email on Feb. 24 on his cellphone and smiled, as he recalled to the Globe. Up popped a photograph of a box placed inside a refrigerated truck at the Norwood plant and bound for the National Institute of Allergy and Infectious Diseases in Bethesda, Md. The package held a few hundred vials, each containing the experimental vaccine.

Moderna was the first drug maker to deliver a potential vaccine for clinical trials. Soon, its vaccine became the first to undergo testing on humans, in a small early-stage trial. And on July 28, it became the first to start getting tested in a late-stage trial in a scene that reflected the firms receptiveness to press coverage.

The first volunteer to get a shot in Modernas late-stage trial was a television anchor at the CNN affiliate in Savannah, Ga., a move that raised eyebrows at rival vaccine makers.

Along with those achievements, Moderna has repeatedly stirred controversy.

On May 18, Moderna issued a press release trumpeting positive interim clinical data. The firm said its vaccine had generated neutralizing antibodies in the first eight volunteers in the early-phase study, a tiny sample.

But Moderna didnt provide any backup data, making it hard to assess how encouraging the results were. Nonetheless, Modernas share price rose 20% that day.

Some top Moderna executives also drew criticism for selling shares worth millions, including Bancel and the firms chief medical officer, Tal Zaks.

In addition, some critics have said the government has given Moderna a sweetheart deal by bankrolling the costs for developing the vaccine and pledging to buy at least 100 million doses, all for $2.48 billion.

That works out to roughly $25 a dose, which Moderna acknowledges includes a profit.

In contrast, the government has pledged more than $1 billion to Johnson & Johnson to manufacture and provide at least 100 million doses of its vaccine, which uses different technology than mRNA. But J&J, which collaborated with Beth Israel Deaconess Medical Centers Center for Virology and Vaccine Research and is also in a late-stage trial, has promised not to profit off sales of the vaccine during the pandemic.

Over in Germany, Sahin, the head of BioNTech, said a Lancet article in January about the outbreak in Wuhan, an international hub, galvanized him.

We understood that this would become a pandemic, he said.

The next day, he met with his leadership team.

I told them that we have to deal with a pandemic which is coming to Germany, Sahin recalled.

He also realized he needed a strong partner to manufacture the vaccine and thought of Pfizer. The two companies had worked together before to try to develop mRNA influenza vaccines. In March, he called Pfizers top vaccine expert, Kathrin Jansen.

Here is the original post:
The story of mRNA: From a loose idea to a tool that may help curb Covid - STAT

Acute Lymphoblastic Leukemia (AML), also called acute myeloblastic leukemia, acute myelogenous leukemia, acute myeloid leukemia, or acute nonlymphocytic leukemia, is an aggressive, fast-growing, heterogenous group of blood cancers that arise as a result of clonal expansion of myeloid hematopoietic precursors in the bone marrow. Not only are circulating leukemia (blast) cells seen in the peripheral blood, but granulocytopenia, anemia, and thrombocytopenia are also common as proliferating leukemia cells interfere with normal hematopoiesis.

Approximately 40-45% of younger and 10-20% of older adults diagnosed with AML are cured with current standard chemotherapy. However, the outlook for patients with relapsed and/or refractory disease is gloomy. Relapse following conventional chemotherapy remains is a major cause of death.

The process of manufacturing chimeric antigen receptor (CAR) T-cell therapies. [1] T-cells (represented by objects labeled as t) are removed from the patients blood. [2] Then in a lab setting the gene that encodes for the specific antigen receptors is incorporated into the T-cells. [3] Thus producing the CAR receptors (labeled as c) on the surface of the cells. [4] The newly modified T-cells are then further harvested and grown in the lab. [5]. After a certain time period, the engineered T-cells are infused back into the patient. This file is licensed by Reyasingh56 under the Creative Commons Attribution-Share Alike 4.0 International license.Today, the only curative treatment option for patients with AML is allogeneic hematopoietic stem cell transplantation or allo-HSCT, which through its graft-vs.-leukemia effects has the ability to eliminate residual leukemia cells. But it is an ption for only a minority. And despite a long history of success, relapse following allo-HSCT is still a major challenge and is associated with poor prognosis.

In recent years, rresearchers learned a lot about the genomic and epigenomic landscapes of AML. This understanding has paved the way for rational drug development as new drugable targets, resulting in treatments including the antibody-drug conjugate (ADC) gemtuzumab ozogamycin (Mylotarg; Pfizer/Wyeth-Ayerst Laboratories).

CAR T-cell TherapiesChimeric antigen receptor (CAR) T-cells therapies, using a patients own genetically modified T-cells to find and kill cancer, are one of the most exciting recent developments in cancer research and treatment.

Traditional CAR T-cell therapies are an autologous, highly personalised, approach in which T-cells are collected from the patient by leukopheresis and engineered in the laboratory to express a receptor directed at a cancer antigen such as CD19. The cells are then infused back into the patient after administration of a lymphodepletion regimen, most commonly a combination of fludarabine and cyclophosphamide. Durable remissions have been observed in pediatric patients with B-ALL and adults with NHL.

CD19-targeted CAR T-cell therapies, have, over the last decade, yielded remarkable clinical success in certain types of B-cell malignancies, and researchers have made substantial efforts aimed at translating this success to myeloid malignancies.

While complete ablation of CD19-expressing B cells, both cancerous and healthy, is clinically tolerated, the primary challenge limiting the use of CAR T-cells in myeloid malignancies is the absence of a dispensable antigen, as myeloid antigens are often co-expressed on normal hematopoietic stem/progenitor cells (HSPCs), depletion of which would lead to intolerable myeloablation.

A different approachBecause autologous CAR T-cell therapies are patient-specific, each treatment can only be used for that one patient. Furthermore, because CAR T-cells are derived from a single disease-specific antibody, they are, by design, only recognized by one specific antigen. As a consequence, only a small subset of patients with any given cancer may be suited for the treatment.

This specificity means that following leukopheresis, a lot of work needs to be done to create this hyper personalised treatment option, resulting in 3 5 weeks of manufacturing time.

The manufacturing process of CAR T-cell therapies, from a single academic center to a large-scale multi-site manufacturing center further creates challenges. Scaling out production means developing processes consistent across many collection, manufacturing, and treatment sites. This complexity results in a the realitively high cost of currently available CAR T-cell therapies.

To solve some of the concerns with currently available CAR T-cell therapies, researchers are investigating the option to develop allogenic, off-the-shelf Universal CAR T-cell (UCARTs) treatments that can be mass manufactured and be used for multiple patients.

Allogeneic CAR T-cell therapy are generally created from T-cells from healthy donors, not patients. Similar to the autologous approach, donor-derived cells are shipped to a manufacturing facility to be genetically engineered to express the antibody or CAR, however, in contrast to autologous CAR T-cells, allogeneic CAR T-cells are also engineered with an additional technology used to limit the potential for a graft versus host reaction when administered to patients different from the donor.

One unique benefit ofn this approach is that because these therapies hey are premade and available for infusion, there is no requirement to leukopheresis or a need to wait for the CAR T-cells to be manufactured. This strategy also will benefit patients who are cytopenic (which is not an uncommon scenario for leukemia patients) and from whom autologous T-cell collection is not possible.

PioneersAmong the pioneers of developing allogeneic CAR-T therapies are companies including Celyad Oncology, Cellectis, Allogene Therapeutics, and researchers at University of California, Los Angeles (UCLA) in colaboration with Kite/Gilead.

Researchers at UCLA were, for example, able to turn pluripotent stem cells into T-cells through structures called artificial thymic organoids. These organoids mimic the thymus, the organ where T-cells are made from blood stem cells in the body.

Celyad OncologyBelgium-based Celyad Oncology is advancing a number of both autologous and allogeneic CAR T-cell therapies, including proprietary, non-gene edited allogeneic CAR T-cell candidates underpinned by the companys shRNA technology platform. The shRNA platform coupled with Celyads all-in-one vector approach provides flexibility, versatility, and efficiency to the design of novel, off-the-shelf CAR T-cell candidates through a single step engineering process.

In July 2020, the company announced the start of Phase I trials with CYAD-211, Celyads first-in-class short hairpin RNA (shRNA)-based allogeneic CAR T candidate and second non-gene edited off-the-shelf program. CYAD-211 targets B-cell maturation antigen (BCMA) for the treatment of relapsed/refractory multiple myeloma and is engineered to co-express a BCMA-targeting chimeric antigen receptor and a single shRNA, which interferes with the expression of the CD3 component of the T-cell receptor (TCR) complex.

During the 2020 American Society of Clinical Oncology (ASCO) Virtual Scientific Program in May 2020, the company presented updates from its allogeneic programs, including additional data from the alloSHRINK study, an open-label, dose-escalation Phase I trial assessing the safety and clinical activity of three consecutive administrations of CYAD-101, an investigational, non-gene edited, allogeneic CAR T-cell candidate engineered to co-express a chimeric antigen receptor based on NKG2D (a receptor expressed on natural killer (NK) cells that binds to eight stress-induced ligands and the novel inhibitory peptide TIM TCR Inhibitory Molecule), for the treatment of metastatic colorectal cancer (mCRC).

The expression of TIM reduces signalling of the TCR complex, which is responsible for graft-versus host disease.every two weeks administered concurrently with FOLFOX (combination of 5-fluorouracil, leucovorin and oxaliplatin) in patients with refractory metastatic colorectal cancer (mCRC).

The safety and clinical activity data from the alloSHRINK trial in patients with mCRC demonstrated CYAD-101s differentiated profile as an allogeneic CAR T-cell candidate. Furthermore, the absence of clinical evidence of graft-versus-host-disease (GvHD) for CYAD-101 confirms the potential of non-gene edited approaches for the development of allogeneic CAR-T candidates.

Interim data from the alloSHRINK trial showed encouraging anti-tumor activity, with two patients achieving a confirmed partial response (cPR) according to RECIST 1.1 criteria, including one patient with a KRAS-mutation, the most common oncogenic alteration found in all human cancers. In addition, nine patients achieved stable disease (SD), with seven patients demonstrating disease stabilization lasting more than or equal to three months of duration.

Based on these results, clinical trials were broadened to include evaluating CYAD-101 following FOLFIRI (combination of 5-fluorouracil, leucovorin and irinotecan) preconditioning chemotherapy in refractory mCRC patients, at the recommended dose of one billion cells per infusion as an expansion cohort of the alloSHRINK trial. Enrollment in the expansion cohort of the trial is expected to begin during the fourth quarter of 2020.

CellectisCellectis is developping a universal CAR T-cell (UCART) platform in an attempy to create off-the-shelf CAR T-cell therapies. The companys pipeline includes UCART123, a CAR T-cell therapy designed to targets CD123+ leukemic cells in acute myeloid leukemia (AML). The investigational agent is being studied in two open-label Phase I trials: AML123 studying the therapys safety and efficacy in an estimated 156 AML patients, and ABC123 studying the therapys safety and activity in an estimated 72 patients with blastic plasmacytoid dendritic cell neoplasm (BPDCN).

UCART22Another investigational agent in clinical trials is UCART22 which is designed to treat both CD22+ B-cell acute lymphoblastic leukemia (B-ALL) and CD22+ B-cell non-Hodgkin lymphoma (NHL). Cellectis reported that UCART22 is included in an open-label, dose-escalating Phase I trial to study its safety and activity in relapsed or refractory CD22+ B-ALL patients.

UCART22 harbors a surface expression of an anti-CD22 CAR (CD22 scFv-41BB-CD3z) and the RQR8 ligand, a safety feature rendering the T-cells sensitive to the antibody rituximab. Further, to reduce the potential for alloreactivity, the cell surface expression of the T-cell receptor is abrogated through the inactivation of the TCR constant (TRAC) gene using Cellectis TALEN gene-editing technology.[1]

Preclinical data supporting the development of UCART22 was presented by Marina Konopleva, M.D., Ph.D. and her vteam during the 2017 annual meeting of the American Society of Hematology (ASH) meeting. [1]

Cellectis is also developing UCARTCS1 which is developed to treat CS1-expressing hematologic malignancies, such as multiple myeloma (MM). UCARTCLL1 is in preclinical development for treating CLL1-expressing hematologic malignancies, such as AML.

Cellectis and Allogene Therapeutics, another biotech company involved in the developmen t of CAR T-cell therapies, are developing ALLO-501, another CAR T-cell therapy which targets CD19 and is being developed for the the treatment of patients with relapsed or refractory NHL. Allogene Therapeutics is also developing ALLO-715, an investigational CAR T-cell therapy targeting the B-cell maturation antigen (BCMA) for treating relapsed or refractory multiple myeloma and ALLO-819, which targets CD135 (also called FLT3), for treating relapsed or refractory AML.

Allogene, in collaboration with both Cellectis, Pfizer (which has a 25% stake in Allogene) and Servier have numerous active open-label, single-arm Phase I trials for an off-the-shelf allogeneic CAR-T therapy UCART19* in patients with relapsed or refractory CD19+ B-ALL. Participating patients receive lymphodepletion with fludarabine and cyclophosphamide with alemtuzumab, followed by UCART19 infusion. Adults patients with R/R B-ALL are eligible.

The PALL aims to evaluate the safety and feasibility of UCART19 to induce molecular remission in pediatric patients with relapsed or refractory CD19-positive B-cell acute lymphoblastic leukemia (B-ALL) in 18 pediatric patients.

The CALM trial is a dose-escalating study evaluating the therapys safety and tolerability in 40 adult patients; and a long-term safety and efficacy follow-up study in 200 patients with advanced lymphoid malignancies.

Allogene reported preliminary proof-of-concept results during the annual meeting of the American Society of Hematology (ASH) in December 2018.

Data from the first 21 patients from both the PALL (n=7) and CALM (n=14) Phase I studies were pooled. The median age of the participating patients was 22 years (range, 0.8-62 years) and the median number of prior therapies was 4 (range, 1-6). Sixty-two percent of the patients (13/21) had a prior allogeneic stem cell transplant.

Of the 17 patients who received treatment with UCART19 and who received lymphodepletion with fludarabine, cyclophosphamide and alemtuzumab, an anti-CD52 monoclonal antibody, 14 patients (82%) achieved CR/CRi, and 59% of them (10/17) achieved MRD-negative remission.

In stark contrast, the four patients who only received UCART19 and fludarabine and cyclophosphamide without alemtuzumab did not see a response and minimal UCART19 expansion.

Based on these results, researchers noted that apparent importance of an anti-CD52 antibody for the efficacy of allogeneic CAR-T therapies. In addition, safety data also looked promising. The trial results did not include grade 3 or 4 neurotoxicity and only 2 cases of grade 1 graft-versus-host disease (10%), 3 cases of grade 3 or 4 cytokine release syndrome which were considered manageable (14%), 5 cases of grade 3 or 4 viral infections (24%), and 6 cases of grade 4 prolonged cytopenia (29%).

Precision BiosciencesPrecision Biosciences is developing PBCAR0191, an off-the-shelf investigational allogeneic CAR T-cell candidate targeting CD19. The drug candidate is being investigated in a Phase I/IIa multicenter, nonrandomized, open-label, parallel assignment, dose-escalation, and dose-expansion study for the treatment of patients with relapsed or refractory (R/R) non-Hodgkin lymphoma (NHL) or R/R B-cell precursor acute lymphoblastic leukemia (B-ALL).

The NHL cohort includes patients with mantle cell lymphoma (MCL), an aggressive subtype of NHL, for which Precision has received both Orphan Drug and Fast Track Designations from the U.S. Food and Drug Administration (FDA).

A clinical trial with PBCAR0191 Precision Biosciences is exploring some novel lymphodepletion strategies in addition to fludarabine and cyclophosphamide. Patients with R/R ALL, R/R CLL, R/R Richter transformation, and R/R NHL are eligible. Patients with MRD+ B-ALL are eligible as well. This trial is enrolling patients.

In late September 2020, Precision BioSciences, a clinical stage biotechnology amd Servier, announced the companies have added two additional hematological cancer targets beyond CD19 and two solid tumor targets to its CAR T-cell development and commercial license agreement.

PBCAR20APBCAR20A is an investigational allogeneic anti-CD20 CAR T-cell therapy being developed by Precision Biosciences for the treartment of patients with relapsed/refractory (R/R) non-Hodgkin lymphoma (NHL) and patients with R/R chronic lymphocytic leukemia (CLL) or R/R small lymphocytic lymphoma (SLL). The NHL cohort will include patients with mantle cell lymphoma (MCL), an aggressive subtype of NHL, for which Precision BioSciences has received orphan drug designation from the United States Food and Drug Administration (FDA).

PBCAR20A is being evaluated in a Phase I/IIa multicenter, nonrandomized, open-label, dose-escalation and dose-expansion clinical trial in adult NHL and CLL/SLL patients. The trial will be conducted at multiple U.S. sites.

PBCAR269APrecision Biosciences is, in collaboration with Springworks Therapeutics, also developing PBCAR269A, an allogeneic BCMA-targeted CAR T-cell therapy candidate being evaluated for the safety and preliminary clinical activity in a Phase I/IIa multicenter, nonrandomized, open-label, parallel assignment, single-dose, dose-escalation, and dose-expansion study of adults with relapsed or refractory multiple myeloma. In this trial, the starting dose of PBCAR269A is 6 x 105 CAR T cells/kg body weight with subsequent cohorts receiving escalating doses to a maximum dose of 6 x 106 CAR T cells/kg body weight.

PBCAR269A is Precision Biosciencess third CAR T-cell candidate to advance to the clinic and is part of a pipeline of cell-phenotype optimized allogeneic CAR T-cell therapies derived from healthy donors and then modified via a simultaneous TCR knock-out and CAR T-cell knock-in step with the =companys proprietary ARCUS genome editing technology.

The FDA recently granted Fast Track Designation to PBCAR269A for the treatment of relapsed or refractory multiple myeloma for which the FDA previously granted Orphan Drug Designation.

TCR2 TherapeuticsTCR2 Therapeutics is developing a proprietary TRuC (TCR Fusion Construct) T-cells designed to harness the natural T cell receptor complex to recognize and kill cancer cells using the full power of T-cell signaling pathways independent of the human leukocyte antigen (HLA).

While succesful in hematological malignancies, CAR T-cells therapies have generally struggled to show efficacy against solid tumors. Researchers at TCR2 Therapeutics believe this is is caused by the fact that CAR T-cell therapies only utilize a single TCR subunit, and, as a result, do not benefit from all of the activation and regulatory elements of the natural TCR complex. By engineering TCR T-cells, which are designed to utilize the complete TCR, they have demonstrated clinical activity in solid tumors. However, this approach has also shown major limitations. TCR T-cells require tumors to express HLA to bind tumor antigens. HLA is often downregulated in cancers, preventing T-cell detection. In addition, each specific TCR-T cell therapy can only be used in patients with one of several specific HLA subtypes, limiting universal applicability of this approach and increasing the time and cost of patient enrollment in clinical trials.

In an attempt to solve this problem, researchers at TCR2 Therapeutics have developped a proprieatarry TRuC-T Cells which are designed to incorporate the best features of CAR-T and TCR-T cell therapies and overcome the limitations. The TRuC platform is a novel T cell therapy platform, which uses the complete TCR complex without the need for HLA matching.

By conjugating the tumor antigen binder to the TCR complex, the TRuC construct recognizes highly expressed surface antigens on tumor cells without the need for HLA and engage the complete TCR machinery to drive the totality of T-cell functions required for potent, modulated and durable tumor killing.

In preclinical studies, TCR2 Therapeutics TRuC T-cells technology has demonstrated superior anti-tumor activity in vivo compared to CAR T-cells therapies, while, at the same time, releasing lower levels of cytokines. These data are encouraging for the treatment of solid tumors where CAR T-cells have not shown significant clinical activity due to very short persistence and for hematologic tumors where a high incidence of severe cytokine release syndrome remains a major concern.

TCR2 Therapeutics product candidates include TC-210 and TC-110.

TC-210 is designed to targets mesothelin-positive solid tumors. While its expression in normal tissues is low, mesothelin is highly expressed in many solid tumors. Mesothelin overexpression has also been correlated with poorer prognosis in certain cancer types and plays a role in tumorigenesis. TC-210 is being developed for the treatment of non-small cell lung cancer, ovarian cancer, malignant pleural/peritoneal mesothelioma and cholangiocarcinoma.

The companys TRuC-T cell targeting CD19-positive B-cell hematological malignancies, TC-110, is being developed to improve upon and address the unmet needs of current CD19-directed CAR T-cell therapies. The clinical development TC-110 focus on the treatment of adult acute lymphoblastic leukemia (ALL), diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL). Preclinical data demonstrates that TC-110 is superior to CD19-CAR-T cells (carrying either 4-1BB or CD28 co-stimulatory domains) both in anti-tumor activity as well as the level of cytokine release which may translate into lower rates of adverse events. The development of TC-110 starts with autologous T-cells collection by leukopheresis. These T-cells undergo genetic engineering to create TRuC-T cells targeting CD19.

This strategy combines the best features of CAR T-cells and the native T-cell receptor. It is open for R/R NHL and R/R B-ALL.

AUTO1Auto1 is an autologous CD19 CAR T-cell investigational therapyis being developped by Autolus Therapeutics. The investigational drug uses a single-chain variable fragment (scFv) called CAT with a lower affinity for CD19 and a faster off-rate compared to the FMC63 scFv used in other approved CD19 CAR T-cell therapies. The investigational therapy is designed to overcome the limitations in safety while maintaining similar levels of efficacy compared to current CD19 CAR T-cell therapies.

Designed to have a fast target binding off-rate to minimize excessive activation of the programmed T-cells, AUTO1 may reduce toxicity and be less prone to T-cell exhaustion, which could enhance persistence and improve the T-cells abilities to engage in serial killing of target cancer cells.

In 2018, Autolus signed a license agreement UCL Business plc (UCLB), the technology-transfer company of UCL, to develop and commercialize AUTO1 for the treatment of B cell malignancies. AUTO1 is currently being evaluated in two Phase I studies, one in pediatric ALL and one in adult ALL.

CARPALL trialInitial results from the ongoing Phase I CARPALL trial of AUTO1 were presented during European Hematology Association 1st European CAR T Cell Meeting held in Paris, France, February 14-16, 2019.

Enrolled patients had a median age of 9 years with a median of 4 lines of prior treatment. Seventeen patients were enrolled, and 14 patients received an infusion of CAR T cells. Ten of 14 patients had relapsed post allogeneic stem cell transplant. Eight patients were treated in second relapse, 5 in > second relapse and 3 had relapsed after prior blinatumomab or inotuzumab therapy. Two patients had ongoing CNS disease at enrollment.

This data confirmed that AUTO1 did not induces severe cytokine release syndrome (CRS) (Grade 3-5). Nine patients experienced Grade 1 CRS, and 4 patients experienced Grade 2 CRS. No patients required tociluzumab or steroids. As previously reported, one patient experienced Grade 4 neurotoxicity; there were no other reports of severe neurotoxicity (Grade 3-5). The mean cumulative exposure to AUTO1 CAR T-cells in the first 28 days as assessed by AUC was 1,721,355 copies/g DNA. Eleven patients experienced cytopenia that was not resolved by day 28 or recurring after day 28: 3 patients Grades 1-3 and 8 patients Grade 4. Two patients developed significant infections, and 1 patient died from sepsis while in molecular complete response (CR).

With a single dose of CAR T cells at 1 million cells/kg dose, 12/14 (86%) achieved molecular CR. Five patients relapsed with CD19 negative disease. Event free survival (EFS) based on morphological relapse was 67% (CI 34-86%) and 46% (CI 16-72%) and overall survival (OS) was 84% (CI 50-96%) and 63% (CI 27-85%) at 6 and 12 months, respectively.

CAR T cell expansion was observed in all responding patients (N=12), with CAR T cells comprising up to 84% of circulating T cells at the point of maximal expansion. The median persistence of CAR T-cells was 215 days.

The median duration of remission in responding patients was 7.3 months with a median follow-up of 14 months. Five of 14 patients (37%) remain in CR with ongoing persistence of CAR T-cells and associated B cell aplasia.

Fate TherapeuticsFT819 is an off-the-shelf CAR T-cell therapy targeting CD19 being developed by Fate Therapeutics. The T-cells are derived from a clonal engineered master induced pluripotent stem cell line (iPSCs) with a novel 1XX CAR targeting CD19 inserted into the T-cell receptor alpha constant (TRAC) locus and edited for elimination of T-cell receptor (TCR) expression.

Patients participating in the companys clinbical trial will receive lymphodepletion with fludarabine and cyclophosphamide. Some patients will also receive IL-2. Patients with R/R ALL, R/R CLL, R/R Richter transformation, and R/R NHL are eligible. Patients with MRD+ B-ALL are eligible as well.

At the Annual Meeting of the American Societ of Hematology held in December 2019, researchers from Fate Therapeutics presented new in vivo preclinical data demonstrating that FT819 exhibits durable tumor control and extended survival. In a stringent xenograft model of disseminated lymphoblastic leukemia, FT819 demonstrated enhanced tumor clearance and control of leukemia as compared to primary CAR19 T-cells. At Day 35 following administration, a bone marrow assessment showed that FT819 persisted and continued to demonstrate tumor clearance, whereas primary CAR T cells, while persisting, were not able to control tumor growth. [2]

CAR-NK CD19Allogeneic cord blood-derived Natural Killer (NK) cells are another off-the-shelf product that does not require the collection of cells from each patient.

Unlike T-cells, NK-cells do not cause GVHD and can be given safely in the allogeneic setting. At MD Anderson Cancer Center, Katy Rezvani, M.D., Ph.D, Professor, Stem Cell Transplantation and Cellular Therapy, and her team broadly focuses their research on the role of natural killer (NK) cells in mediating protection against hematologic malignancies and solid tumors and strategies to enhance killing function against various cancer.

As part of their research, the team has developed a novel cord blood-derived NK-CAR product that expresses a CAR against CD19; ectopically produces IL-15 to support NK-cell proliferation and persistence in vivo; and expresses a suicide gene, inducible caspase 9, to address any potential safety concerns.

In this phase I and II trial researchers administered HLA-mismatched anti-CD19 CAR-NK cells derived from cord blood to 11 patients with relapsed or refractory CD19-positive cancers (non-Hodgkins lymphoma or chronic lymphocytic leukemia [CLL]). NK cells were transduced with a retroviral vector expressing genes that encode anti-CD19 CAR, interleukin-15, and inducible caspase 9 as a safety switch. The cells were expanded ex vivo and administered in a single infusion at one of three doses (1105, 1106, or 1107 CAR-NK cells per kilogram of body weight) after lymphodepleting chemotherapy. The preliminarry resilts of the trials confirmed that administration of CAR-NK cells was not associated with the development of cytokine release syndrome, neurotoxicity, or graft-versus-host disease, and there was no increase in the levels of inflammatory cytokines, including interleukin-6, over baseline.

The study results also demonstrated that of the 11 patients who were treated, 8 patients (73%) had a response. Of these patients, 7 (4 with lymphoma and 3 with CLL) had a complete remission ICR), and 1 had remission of the Richters transformation component but had persistent CLL. Noteworthy was that responses were rapid and seen within 30 days after infusion at all dose levels. The infused CAR-NK cells expanded and persisted at low levels for at least 12 months. The researchers also noted that a majority of the 11 participating patients with relapsed or refractory CD19-positive cancers had a response to treatment with CAR-NK cells without the development of major toxic effects.[3]

Note* Servier will hold ex-US commercial rights. Servier is the sponsor of the UCART19 trials.

Clinical trialsalloSHRINK Standard cHemotherapy Regimen and Immunotherapy With Allogeneic NKG2D-based CYAD-101 Chimeric Antigen Receptor T-cells NCT03692429Study Evaluating Safety and Efficacy of UCART123 in Patients With Relapsed/ Refractory Acute Myeloid Leukemia (AMELI-01) NCT03190278Study to Evaluate the Safety and Clinical Activity of UCART123 in Patients With BPDCN (ABC123) NCT03203369Study of UCART19 in Pediatric Patients With Relapsed/Refractory B Acute Lymphoblastic Leukemia (PALL) NCT02808442Dose Escalation Study of UCART19 in Adult Patients With Relapsed / Refractory B-cell Acute Lymphoblastic Leukaemia (CALM) NCT02746952Dose-escalation Study of Safety of PBCAR0191 in Patients With r/r NHL and r/r B-cell ALL NCT03666000.Dose-escalation Study of Safety of PBCAR20A in Subjects With r/r NHL or r/r CLL/SLL NCT04030195A Dose-escalation Study to Evaluate the Safety and Clinical Activity of PBCAR269A in Study Participants With Relapsed/Refractory Multiple Myeloma NCT04171843TC-110 T Cells in Adults With Relapsed or Refractory Non-Hodgkin Lymphoma or Acute Lymphoblastic Leukemia NCT04323657Phase 1/2 Trial of TC-210 T Cells in Patients With Advanced Mesothelin-Expressing Cancer NCT03907852CARPALL: Immunotherapy With CD19 CAR T-cells for CD19+ Haematological Malignancies NCT02443831Umbilical & Cord Blood (CB) Derived CAR-Engineered NK Cells for B Lymphoid Malignancies NCT03056339

Reference[1] Petti F. Broadening the Applicability of CAR-T Immunotherapy to Treat the Untreatable. OncoZine. October 24, 2019 [Article][2] Wells J, Cai T, Schiffer-Manniou C, Filipe S, Gouble A, Galetto R, Jain N, Jabbour EJ, Smith J, Konopleva M. Pre-Clinical Activity of Allogeneic Anti-CD22 CAR-T Cells for the Treatment of B-Cell Acute Lymphoblastic Leukemia Blood (2017) 130 (Supplement 1): 808. https://doi.org/10.1182/blood.V130.Suppl_1.808.808%5B3%5D Chang C, Van Der Stegen S, Mili M, Clarke R, Lai YS, Witty A, Lindenbergh P, Yang BH, et al. FT819: Translation of Off-the-Shelf TCR-Less Trac-1XX CAR-T Cells in Support of First-of-Kind Phase I Clinical Trial. Blood (2019) 134 (Supplement_1): 4434.https://doi.org/10.1182/blood-2019-130584%5B4%5D Liu E, Marin D, Banerjee P, Macapinlac HA, Thompson P, Basar R, Nassif Kerbauy L, Overman B, Thall P, Kaplan M, Nandivada V, Kaur I, Nunez Cortes A, Cao K, Daher M, Hosing C, Cohen EN, Kebriaei P, Mehta R, Neelapu S, Nieto Y, Wang M, Wierda W, Keating M, Champlin R, Shpall EJ, Rezvani K. Use of CAR-Transduced Natural Killer Cells in CD19-Positive Lymphoid Tumors. N Engl J Med. 2020 Feb 6;382(6):545-553. doi: 10.1056/NEJMoa1910607. PMID: 32023374; PMCID: PMC7101242.

Featured image: T-cells attacking a cancer cell. Photo courtesy: Fotolia/Adobe 2016 2020. Used with permission.

Link:
CAR T-cell Therapies for the Treatment of Patients with Acute Lymphoblastic Leukemia - OncoZine

Concerning heart failure (HF), the current COVID-19 pandemic is having a dramatic effect on the daily life of each individual, ranging from social distancing measures applied in most countries to getting severely diseased due to the virus. Cardiovascular Disease (CVD) is among the most common conditions in people that die of the infection. The burden of CVD accounts for over 60 million people in the EU alone, therefore, it is the leading cause of death in the world.

Although COVID-19 shows us the direct impact of a potential treatment for peoples health, CVD is a stealthy pandemic killer. HF is a chronic disease condition in which the heart is not able to fill properly or efficiently pump blood throughout your body, caused by different stress conditions including myocardial infarction, atherosclerosis, diabetes and high blood pressure. Several measures are commonly used to treat heart disease, such as lifestyle changes and medications like beta-blockers and ACE inhibitors, yet these typically only slow down the progression of the disease.

Biomedical research is exploring new avenues by combining scientific insights with new technologies to overcome chronic diseases like HF. Among the most appealing and promising technologies are the use of cardiac tissue engineering and extracellular vesicles-mediated repair strategies.

Upon an initial cell loss post-infarction, it is appealing to replace this massive loss in contractile cells for new cells and thereby not treating patients symptoms, but repairing the cause of the disease. Cardiac cell therapy has been pursued for many years with variable results in small initial trials upon injection into patients. Different cell types have been used to help the myocardium in need, but the most promising approaches aim to use induced pluripotent cells (iPS) from reprogrammed cells from the patient themselves that can be directed towards contractile myocardial cells. These cells in combination with natural materials, in which the cells are embedded in the heart, can be used for tissue engineering strategies (1). Together with different international partners, Sluijters team are trying to develop strategies to use these iPS-derived contractile cells for myocardial repair via direct myocardial injection (H2020-Technobeat-66724) or to make a scaffold that can be used as a personalised biological ventricular assist device (H2020-BRAV-874827). A combination of engineering and biology to mimic the native myocardium aims to replace the chronically ill tissue for healthy and well-coupled heart tissue that can enhance the contractile performance of the heart.

Recently, a Dutch national programme started, called RegMedXB, in which the reparative treatment of the heart is aimed to be performed outside the patients body. During the time the heart is outside the body; the patient is connected to the heart-lung machine, and after restoring function, it will be re-implanted. The so-called Cardiovascular Moonshot aims to create a therapy that best suits the individual patient, by having their heart beating in a bioreactor, outside the body. Although it sounds very futuristic, many small lessons will be learned to feet novel therapeutic insights.

The initial injection of stem cells did result in a nice improvement of myocardial performance. We have now learned that rather than these delivered cells helping the heart themselves, the release of small lipid carriers called extracellular vesicles (EVs) (2) from these cells occur. These EVs carry different biological molecules, including nucleotides, proteins and lipids, and are considered to be the bodies nanosized messengers for communication. The use of stem cell-derived EVs are now being explored as a powerful means to change the course of the disease. Via these small messengers, natural biologics are delivered to diseased cells and thereby help them to overcome the stressful circumstances. EVs carry reparative signals that can be transferred to the diseased heart and thereby change the course of heart disease in some patients.

Within the EVICARE program (3) (H2020-ERC-725229), Sluijters team are using stem cell-derived EVs to change the response of the heart to injury. Also, to understand which heart cells and processes are being affected, they use materials to facilitate a slow release of biomaterials over an extended period rather than a single dose, which is probably essential for a chronic disease like HF. For now, improved blood flow is the main aim but the team have seen other effects as well, such as cardiovascular cell proliferation (4) by which the heart cells themselves start to repair the organ.

The use of EVs basically aims to enhance the endogenous repair mechanisms of the heart. These natural carriers can be mimicked with synthetic materials, or used as a hybrid of the two, thereby creating an engineered nanoparticle, that is superior in the intracellular delivery of genetic materials. The possibility of loading different biological materials allows a further tuning of its effectiveness and use in different disease conditions, creating a new off-the-shelf delivery system for nanomedicine to treat cancer and CVD (H2020-Expert-825828).

As is true of the current COVID-19 pandemic, HF is also a growing chronic disease that affects millions of people worldwide. The chronic damaged myocardium needs reparative strategies in the future to lower the social burden for patients, but also to keep the economic consequences affordable. New scientific insights with cutting edge technological developments will help to address these needs of CVD patients and their families.

References

(1) Madonna R, Van Laake LW, Botker HE, Davidson SM, De Caterina R, Engel FB, Eschenhagen T, Fernandez-Aviles F, Hausenloy DJ, Hulot JS, Lecour S, Leor J, Menasch P, Pesce M, Perrino C, Prunier F, Van Linthout S, Ytrehus K, Zimmermann WH, Ferdinandy P, Sluijter JPG. ESC Working Group on Cellular Biology of the Heart: position paper for Cardiovascular Research: tissue engineering strategies combined with cell therapies for cardiac repair in ischaemic heart disease and heart failure. Cardiovasc Res. 2019 Mar 1;115(3):488-500.

(2) Sluijter JPG, Davidson SM, Boulanger, CM, Buzs EI, de Kleijn DPV, Engel FB, Giricz Z, Hausenloy DJ, Kishore R, Lecour S, Leor J, Madonna R, Perrino C, Prunier F, Sahoo S, Schiffelers RM, Schulz R, Van Laake LW, Ytrehus K, Ferdinandy P. Extracellular vesicles in diagnostics and therapy of the ischaemic heart: Position Paper from the Working Group on Cellular Biology of the Heart of the European Society of Cardiology. Cardiovasc Res. 2018 Jan 1;114(1):19-34.

(3) https://www.sluijterlab.com/extracellular-vesicle-inspired-ther

(4) Maring JA, Lodder K, Mol E, Verhage V, Wiesmeijer KC, Dingenouts CKE, Moerkamp AT, Deddens JC, Vader P, Smits, AM, Sluijter JPG, Goumans MJ. Cardiac Progenitor Cell-Derived Extracellular Vesicles Reduce Infarct Size and Associate with Increased Cardiovascular Cell Proliferation. J Cardiovasc Transl Res. 2019 Feb;12(1):5-17.

Please note: this is a commercial profile.

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Innovative treatments for heart failure - Open Access Government

The study on the Anti-Ageing Drugs Marketby Brand Essence Market Research is a compilation of systematic details in terms of market valuation, market size, revenue estimation, and geographical spectrum of the business vertical. The study also offers a precise analysis of the key challenges and growth prospects awaiting key players of the Anti-Ageing Drugs market, including a concise summary of their corporate strategies and competitive setting.

In 2018, the Global Anti-Ageing Drugs Market size was xx million US$ and it is expected to reach xx million US$ by the end of 2025, with a CAGR of xx% during 2019-2025.

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In this report, 2018 has been considered as the base year and 2019 to 2025 as the forecast period to estimate the market size for Anti-Ageing Drugs.

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In global market, the following companies are covered: Nu Skin BIOTIME Elysium Health La Roche-Posay DermaFix

Market Segment by Product Type Hormonal Therapy Antioxidants Enzymes Stem Cells Others

Market Segment by Application Skin Hair Others

Anti-Ageing Drugs market report consists of the worlds crucial region market share, size (volume), trends including the product profit, price, value, production, capacity, capability utilization, supply, and demand. Besides, market growth rate, size, and forecasts at the global level have been provided. The geographic areas covered in this report:North America (United States, Canada and Mexico), Europe (Germany, France, UK, Russia and Italy), Asia-Pacific (China, Japan, Korea, India and Southeast Asia), South America (Brazil, Argentina, Colombia etc.), Middle East and Africa (Saudi Arabia, UAE, Egypt, Nigeria and South Africa).

This research study involved the extensive usage of both primary and secondary data sources. The research process involved the study of various factors affecting the industry, including the government policy, market environment, competitive landscape, historical data, present trends in the market, technological innovation, upcoming technologies and the technical progress in related industry, and market risks, opportunities, market barriers and challenges. Top-down and bottom-up approaches are used to validate the global market size market and estimate the market size for manufacturers, regions segments, product segments and applications (end users). All possible factors that influence the markets included in this research study have been accounted for, viewed in extensive detail, verified through primary research, and analyzed to get the final quantitative and qualitative data. The market size for top-level markets and sub-segments is normalized, and the effect of inflation, economic downturns, and regulatory & policy changes or other factors are not accounted for in the market forecast. This data is combined and added with detailed inputs and analysis from BrandEssenceResearch and presented in this report.

After complete market engineering with calculations for market statistics; market size estimations; market forecasting; market breakdown; and data triangulation, extensive primary research was conducted to gather information and verify and validate the critical numbers arrived at. In the complete market engineering process, both top-down and bottom-up approaches were extensively used, along with several data triangulation methods, to perform market estimation and market forecasting for the overall market segments and sub segments listed in this report. Extensive qualitative and further quantitative analysis is also done from all the numbers arrived at in the complete market engineering process to list key information throughout the report.

The study objectives are: To analyze and research the Anti-Ageing Drugs status and future forecast in United States, European Union and China, involving sales, value (revenue), growth rate (CAGR), market share, historical and forecast. To present the key Anti-Ageing Drugs manufacturers, presenting the sales, revenue, market share, and recent development for key players. To split the breakdown data by regions, type, companies and applications To analyze the global and key regions market potential and advantage, opportunity and challenge, restraints and risks. To identify significant trends, drivers, influence factors in global and regions To analyze competitive developments such as expansions, agreements, new product launches, and acquisitions in the market

In this study, the years considered to estimate the market size of Anti-Ageing Drugs are as follows: History Year: 2014-2018 Base Year: 2018 Estimated Year: 2019 Forecast Year 2019 to 2025

Table of Contents

1 Report Overview1.1 Study Scope1.2 Key Market Segments1.3 Players Covered1.4 Market Analysis by Type1.4.1 Global Anti-Ageing Drugs Market Size Growth Rate by Type (2014-2025)1.4.2 Topical Products1.4.3 Botulinum1.4.4 Dermal Fillers1.4.5 Chemical Peels1.4.6 Microabrasion Equipment1.4.7 Laser Surfacing Treatments1.5 Market by Application1.5.1 Global Anti-Ageing Drugs Market Share by Application (2014-2025)1.5.2 Hospitals1.5.3 Dermatology Clinics1.6 Study Objectives1.7 Years Considered

2 Global Growth Trends2.1 Anti-Ageing Drugs Market Size2.2 Anti-Ageing Drugs Growth Trends by Regions2.2.1 Anti-Ageing Drugs Market Size by Regions (2014-2025)2.2.2 Anti-Ageing Drugs Market Share by Regions (2014-2019)2.3 Industry Trends2.3.1 Market Top Trends2.3.2 Market Drivers2.3.3 Market Opportunities

3 Market Share by Key Players3.1 Anti-Ageing Drugs Market Size by Manufacturers3.1.1 Global Anti-Ageing Drugs Revenue by Manufacturers (2014-2019)3.1.2 Global Anti-Ageing Drugs Revenue Market Share by Manufacturers (2014-2019)3.1.3 Global Anti-Ageing Drugs Market Concentration Ratio (CR5 and HHI)3.2 Anti-Ageing Drugs Key Players Head office and Area Served3.3 Key Players Anti-Ageing Drugs Product/Solution/Service3.4 Date of Enter into Anti-Ageing Drugs Market3.5 Mergers & Acquisitions, Expansion Plans

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US Biotherapeutics Cell Line Market Insights and Forecast 2020 to 2025 - Cole of Duty

INTRODUCTION

After injury or tissue damage, cells must migrate to the wound site and deposit new tissue to restore function (1). While many tissues provide a permissive environment for such interstitial [three-dimensional (3D)] cell migration (i.e., skin), adult dense connective tissues (such as the knee meniscus, articular cartilage, and tendons) do not support this migratory behavior. Rather, the extracellular matrix (ECM) density and micromechanics increase markedly with tissue maturation (2, 3) and, as a consequence, act as a barrier for cells to reach the wound interface. It follows then that healing of these tissues in adults is poor (4, 5) and that wound interfaces remain susceptible to refailure over the long term due to insufficient repair tissue formation. Similarly, fibrous scaffolds used in repair applications also impede cell infiltration when the scaffolds become too dense (6).

This raises an important conundrum in dense connective tissues and repair scaffolds; while the dense ECM and fibrous scaffold properties are critical for mechanical function, they, at the same time, can compromise cell migration, with endogenous cells locked in place and unable to participate in repair processes. This concept is supported by in vitro studies documenting that, in 3D collagen gels, the migration of mesenchymal lineage cells is substantially attenuated once the gel density and/or stiffness has reached a certain threshold (79). Consistent with this, our recent in vitro models exploring cell invasion into devitalized dense connective tissue (knee meniscus sections) showed reduced cellular invasion in adult tissues compared to less dense fetal tissues (3). The density of collagen in most adult dense connective tissues is 30 to 40 times higher than that used within in vitro collagen gel migration assay systems (2, 3), emphasizing the substantial barrier to migration that the dense ECM plays in these tissues.

To address this ECM impediment to successful healing, we and others have developed strategies to loosen the matrix (via local release of degradative enzymes) in an attempt to expedite repair and/or encourage migration to the wound site (10), with promising results both in vitro and in vivo (10, 11). Despite the potential of this approach, it is cognitively dissonant to disrupt ECM to repair it, and any such therapy would have to consider any adverse consequences on tissue mechanical function.

This led us to consider alternative controllable parameters that might regulate interstitial cell mobility while preserving the essential mechanical functionality of the matrix. It is well established that increasing matrix density decreases the effective pore size within dense connective tissues. The nucleus is the largest (and stiffest) organelle in eukaryotic cells (12), and it must physically deform as a cell passes through constructures that are smaller than its own smallest diameter (9). When artificial pores of decreasing diameter are introduced along an in vitro migration path (e.g., in an in vitro Boyden chamber system), cell motion can be completely arrested (13). If cells are forced to transit through these tight passages, then nuclear rupture and DNA damage can occur (14, 15). Conversely, under conditions where nuclear stiffness is low, as is the case in neutrophils (16) and some particularly invasive cancer cells (17), migration through small pores occurs quite readily.

Given the centrality of the nucleus in migration through small pores, methods to transiently regulate nuclear stiffness or deformability might therefore serve as an effective modulator of interstitial cell migration through dense tissues and scaffolds. Nuclear stiffness is defined by two primary featuresthe density of packing of the genetic material contained within (i.e., the heterochromatin content) and the intermediate filament network that underlies the nuclear envelope (the nuclear lamina, composed principally of the proteins Lamin B and Lamin A/C) (12, 16, 18, 19). Increasing chromatin condensation increases nuclear stiffness, while decreasing Lamin A/C content decreases nuclear stiffness (19, 20). Both increasing the stiffness of the microenvironment in which a cell resides (21) and the mechanical loading history of a cell promotes heterochromatin formation and Lamin A/C accumulation (2224), resulting in stiffer nuclei. Since both matrix stiffening and mechanical loading are features of dense connective tissue maturation, these inputs may drive nuclear mechanoadaptation (25), resulting in endogenous cells with stiff nuclei that are locked in place.

On this basis, the goal of this study was to determine whether nuclear softening could enhance migration through dense connective tissues and repair scaffolds to increase colonization of the wound site and the potential for repair by endogenous cells. We took the approach of transiently decreasing nuclear stiffness in adult meniscus cells through decreasing heterochromatin content [using Trichostatin A (TSA), a histone deacetylase (HDAC) inhibitor] that promotes chromatin relaxation (26) and confirmed the importance of nuclear stiffness by reducing Lamin A/C protein content (using lentiviral-mediated knockdown). Our experimental findings and theoretical models demonstrate that nuclear softening decreases the barriers to interstitial migration through small pores, both in vitro and in vivo, resulting in the improved colonization of dense fibrous networks and transit through native tissue by adult meniscus cells. By addressing the inherent limitations to repair imposed by nuclear mechanoadaptation that accompanies cell differentiation and ECM maturation, this work defines a promising strategy to promote the repair of damaged dense connective tissues in adults.

We first determined whether TSA treatment alters chromatin organization in adult meniscal fibrochondrocytes (MFCs). Super-resolution images of the core histone protein Histone-H2B in MFC nuclei were obtained by stochastic optical reconstruction microscopy (STORM) and revealed a notable organization of Histone-H2B inside MFC nuclei (STORM; Fig. 1A), which could not be observed with conventional microscopy (conventional; Fig. 1A). It has recently been shown that super-resolution images can be segmented at multiple length scales using Voronoi tessellation (27, 28). To segment the H2B super-resolution images, we carried out Voronoi tessellation, used a threshold to remove large polygons corresponding to regions of the nucleus containing sparse localizations, and color-coded the localizations with the same color if their polygons were connected in space and shared at least one edge. This segmentation showed that H2B localizations clustered to form discrete and spatially separated nanodomains in control nuclei [()TSA]. Nuclei treated with TSA, on the other hand, contained smaller domains. These results were quantitatively recapitulated by a decrease in the number of H2B localizations in individual domains and an overall decrease in the area of domains in MFCs treated with TSA [(+)TSA] (Fig. 1, B to D). These results are in line with a more folded chromatin confirmation in ()TSA cells, which opens and decondenses after TSA treatment. These results are also consistent with recent super-resolution analysis, which showed that TSA-treated fibroblasts have small nucleosome nanodomains that are more uniformly distributed in the nuclear space compared to control fibroblasts (29, 30). This decondensation was also confirmed in TSA-treated bovine mesenchymal stem cells (MSCs), where TSA treatment decreased the number and area of H2B nanodomains (fig. S1A). This increased acetylation at H3K9 (Ac-H3K9) was apparent at the nanoscale (fig. S1B) and via conventional fluorescence imaging of the nuclei (fig. S1C). Conversely, there were no significant changes in H3K27me3 with TSA treatment when evaluated using STORM or conventional fluorescent microscopy (fig. S1, D and E).

(A) Representative conventional fluorescent and STORM imaging of Histone-H2B in a control [top; ()TSA] or TSA-treated MFC nucleus [bottom; (+)TSA]. (B) Corresponding Voronoi-based image segmentation, which allows for visualization and quantification of Histone-H2B nanodomains. (C and D) Quantification of the number of H2B localizations per cluster and the cluster area with TSA treatment. The box, line, and dot correspond to the interdecile range (10th to 90th percentile), median, and mean, respectively, Mann-Whitney U test, n 10,584 clusters from five cells. Next to each Voronoi image, higher-magnification zoom-ins of the region inside the squares are shown. (E) TSA treatment for 3 hours decreases chromatin condensation in 4,6-diamidino-2-phenylindole (DAPI)stained nuclei (scale bar, 5 m), and the number of visible edges (left). Quantification of the chromatin condensation parameter (CCP) with TSA treatment [right; *P < 0.05 versus ()TSA, n = ~20]. (F) Schematic showing experimental design to evaluate nuclear deformability and changes in nuclear aspect ratio (NAR = b/a) with cell stretch. (G) Representative DAPI-stained nuclei on scaffolds before and after 15% stretch (left; scale bar, 20 m) and NAR at 3 and 15% stretch (n = 32 to 58 cells, *P < 0.05 versus ()TSA and +P < 0.05 versus 3%). (H) 2D wound closure assay shows no differences in gap filling in the presence or absence of TSA [()TSA; left: scale bar, 200 m; right: P > 0.05, n = 6). (I) Schematic of Boyden chamber chemotaxis assay (left) and migrated cell signal intensity through 3-, 5-, and 8-m-diameter pores, with and without TSA pretreatment [right; n = 5 samples per group, *P < 0.05 versus ()TSA and +P < 0.05 versus 3 m, means SD]. All experiments were carried out at least in triplicate, except for the wound closure assay (which was performed in duplicate). RFU, relative fluorescence units.

In addition, TSA treatment for 3 hours [(+)TSA] also resulted in marked chromatin decondensation in MFCs seeded on aligned (AL) nanofibrous scaffolds that are commonly used for dense connective tissue repair, as evidenced by decreases in the number of visible edges in 4,6-diamidino-2-phenylindole (DAPI)stained nuclei compared to control cells [()TSA] and a reduction (~40%) in the image-based chromatin condensation parameter (CCP) (Fig. 1E).

To assess whether this TSA-mediated chromatin decondensation changed nuclear stiffness and deformability, we stretched MFC-seeded AL scaffolds (from 0 to 15% grip-to-grip strain) and determined the change in nuclear aspect ratio (NAR) (Fig. 1F). Nuclei that were pretreated with TSA [(+)TSA] showed increased nuclear deformation compared to control nuclei [()TSA] (Fig. 1G); however, TSA did not change cell/nuclear morphology (fig. S2, A to C) or cell migration on planar surfaces (Fig. 1H), and only minor changes in focal adhesions were observed (fig. S2, D and E). MFC spread area and traction force generation were also unaffected by TSA treatment when cells were plated on soft substrates (E = 10 kPa) (fig. S2, F to I). These observations suggest that TSA treatment decreases nuclear deformability by chromatin decondensation without changing overall cell migration capacity in 2D culture.

We next assessed the ability of MFCs to migrate through small pores using a commercial transwell migration assay (Fig. 1I). Cells treated with TSA [(+)TSA] (200 ng/ml) showed enhanced migration compared to controls [()TSA] across all pore sizes, including 3-m pores that supported the lowest migration in controls (Fig. 1I). This improved migration with TSA treatment was dose dependent (fig. S3). Together, these data show that while TSA treatment does not change cell morphology, contractility, or planar migration on 2D substrates, chromatin relaxation increases MFC nuclear deformability, which improves cell migration through micron-sized pores.

Having observed increased migration through rigid micron-sized pores with nuclear softening, we next assayed whether TSA treatment would enhance migration through dense fibrillar networks. A custom microfluidic cell migration chamber was designed, consisting of a top reservoir containing basal medium (BM), a bottom reservoir containing BM supplemented with platelet-derived growth factor (PDGF) as a chemoattractant and an interposed nanofibrous poly(-caprolactone) (PCL) layer (labeled with CellTracker Red, ~150-m thickness) (Fig. 2, A and B). With this design, a gradient of soluble factors is presented across the fibrous layer, as evidenced by Trypan blue diffusion over time (Fig. 2C).

(A) Schematic (top) and a top view (bottom) of the PDMS [poly(dimethylsiloxane)]/nanofiber migration chamber. (B) Schematic showing meniscus cells (green) seeded onto fluorescently labeled nanofibers interposed between the top reservoir containing BM and a bottom reservoir containing BM supplemented with PDGF (100 ng/ml) as a chemoattractant. (C) Visual representation of soluble factor gradient in microdevice showing the slow accumulation of trypan blue in the upper chamber as a function of time. (D) Experimental schematic showing meniscus cell (MFC) isolation and seeding onto nanofiber substrates (passage 1, isolated from adult bovine menisci). One day after seeding, TSA or PDGF was added to the top reservoir or the bottom reservoir, respectively, and cells were cultured for additional 2 days. On day 3, scaffolds were imaged by confocal microscopy to determine the degree of cell penetrance into the scaffold. (E) 3D confocal reconstructions of cell (green) migration through AL or non-AL (NAL) nanofibrous networks (AL or NAL; red) with and without TSA treatment. Scale bar, 30 m. (F) Cross-sectional views of cells (green) within nanofibrous substrates (red). Scale bar, 30 m. Quantification of the percentage of infiltrated cells (G) [n = 5 to 8 images, *P < 0.05 versus ()TSA and +P < 0.05 versus AL, means SD] and cell infiltration depth (H) [n = 33 cells, *P < 0.05 versus ()TSA and +P < 0.05 versus AL, means SEM, normalized to the ()TSA/AL group]. Quantification of the percentage of infiltrated cells (I) [n = 5 images, *P < 0.05 versus ()TSA, P < 0.05 versus 0% poly(ethylene oxide) (PEO), and aP < 0.05 versus 25% PEO, means SD] and cell infiltration depth (J) [n = 33 cells, *P < 0.05 versus ()TSA, P < 0.05 versus 0% PEO, and aP < 0.05 versus 25% PEO, means SD] normalized to the control PCL/0% PEO group] as a function of PEO content. All experiments were carried out in triplicate.

MFCs were seeded atop the fibrous layer, and their migration was evaluated as a function of nuclear deformability (TSA) and fiber alignment [AL or non-AL (NAL)]. MFCs were cultured in BM for 1 day for attachment and then were treated for 2 days either with or without TSA (Fig. 2D). Confocal imaging (Fig. 2, E and F, and movie S1, A and B) and scanning electron microscopy (fig. S4A) showed increased MFC invasion into the fibrous networks with TSA treatment [(+)TSA] when compared to untreated MFCs [()TSA]. Without TSA, MFCs remained largely on the surface of the fibers with some cytoplasmic extensions into the fibers (fig. S4B), whereas TSA treatment increased the number of nuclei entering the fiber network (fig. S4C). When quantified, infiltration was higher in the NAL group compared to the AL group (P < 0.05; Fig. 2, G and H), likely due to the increased pore size in the NAL scaffolds (6, 31), and TSA treatment improved migration to similar levels in both NAL and AL groups (P < 0.05; Fig. 2, G and H). As expected, cells in AL scaffolds showed higher aspect ratios and solidity compared to cells on NAL scaffolds, yet TSA treatment did not influence cell morphology (fig. S4D). Nuclei in NAL groups were rounder (lower NAR) than in AL groups, and TSA treatment resulted in more elongated nuclei (higher NAR) in both AL and NAL groups (fig. S4E). While promoting cell invasion, TSA treatment did not result in any change in DNA damage (as assessed by phospho-histone H2AX-positive nuclei; fig. S4F) and slightly reduced cell proliferation at this time point (fig. S4G). Thus, it appears that TSA increased nuclear deformability, resulting in enhanced cell migration into these dense fibrous networks.

To verify that nuclear softening is the primary mechanism for enhanced migration into fibrous networks, we also knocked down Lamin A/C in MFCs before seeding. In previous studies, cells lacking Lamin A/C showed increased nuclear deformability and increased mobility in collagen gels and through small pores in Boyden chambers (13, 32). Consistent with these studies (12, 19, 33), reduction of Lamin A/C protein levels in MFCs and MSCs (fig. S5, A to C) increased nuclear deformability in response to applied stretch (fig. S5D). When MFCs with Lamin A/C knockdown were seeded onto fibrous networks, a greater fraction entered into the scaffold and reached greater infiltration depths (fig. S5, E to G). To further illustrate that nuclear stiffening reduces migration, we cultured MSCs in transforming growth factor3 (TGF-3)containing media for 1 week before seeding onto the fibers. As we reported previously (23), these conditions induce differentiation in MSCs, resulting in stiffer nuclei with increased chromatin condensation and decreased nuclear deformability. Compared to undifferentiated MSCs, these differentiated MSCs were found largely on the scaffold surface (fig. S6, A to D) and had a lower infiltration rate and depth. While many factors change during cell differentiation, these findings also support that a less deformable nucleus is an impediment to interstitial cell migration. Together, these studies support that a stiff nucleus is a limiting factor in the invasion of the small pores of dense fibrous networks.

To investigate the combined role of porosity and nuclear softening on migration, we next fabricated fibrous networks through the combined electrospinning of both PCL and poly(ethylene oxide) (PEO), where PEO acts as a sacrificial fiber fraction to enhance porosity (6, 31). Consistent with our previous findings, cell infiltration percentage and depth progressively increased as a function of increasing PEO content (Fig. 2, I and J). When nuclei were softened with TSA treatment, we observed greater infiltration into low-porosity scaffolds (PEO content, <25%), but no difference in high porosity scaffolds (Fig. 2, I and J). This suggests that increasing nuclear deformability is only beneficial in the context of dense networks, where the nucleus impedes migration.

To better define the relationship between pore size and nuclear stiffness on cellular migration, we developed a computational model to predict the critical force (Fc) required for the nucleus to enter a small channel (Fig. 3). This model was motivated by studies of cellular transmigration through endothelium in the context of cancer invasion, where the surrounding matrix properties (stiffness), endothelium properties (stiffness and pore size), and the cell properties (in particular, the nuclear stiffness) appear to regulate transmigration (34). Here, we considered cell migration into a narrow and long channel to mimic migration into a porous fiber network, where network properties are defined by fiber density (Fig. 3A). When the cell enters the channel, the resistance force encountered by the nucleus increases monotonically as the cell advances, reaching a maximal resistance force (defined as the critical force, Fc). Following this, the nucleus snaps through the opening, leading to a drop in the resistance force, which vanishes after the nucleus fully enters the channel (Fig. 3B and movie S2). Thus, the cells must generate a sufficient force to overcome this critical force to migrate into a channel. As the channel size (rg) becomes smaller and the ECM modulus (EECM) becomes greater, the critical force required for the nucleus to enter the channel increases (Fig. 3C and fig. S7). As this required force increases, it eventually exceeds the force generation capacity of the cell, resulting in a situation where the cell cannot enter the pore.

(A) Schematic showing a nucleus (blue) above a narrow channel representing the small pores in a dense fiber network (orange). The geometric parameters are the radius of the nucleus (rn) and the half width of the channel (rg). The stiffness parameters are the modulus of the nucleus (En) and the fiber network (EECM). The nucleus is treated as a spheroid for simplicity. (B) Simulation of a nucleus moving into and through the channel in the dense fiber network. The normalized resistant force (F/Enrn2) encountered by the nucleus is plotted as a function of the normalized displacement of the nucleus (un/rn). The maximum normalized resistance force is defined as the critical force. (C) The critical force as a function of the normalized ECM modulus (with respect to En) and normalized channel size (with respect to rn). The critical force is larger as the ECM becomes stiffer or the channel becomes smaller. (D) The critical force decreases as the PEO content increases. TSA treatment also decreases the critical force, particularly for dense networks (low PEO content). (E) Normalized NAR after entry into the channel increases as the ECM becomes stiffer or the nucleus becomes softer (both lead to a larger normalized ECM modulus, EECM/En).

To better understand the influence of PEO content (affecting both the channel size and ECM modulus) and dose of TSA (affecting nuclear modulus) on cell migration, we used the normalized critical force data obtained from the model. Our previous work (6) defined the influence of PEO content on matrix mechanical properties and pore size; the effect of TSA on nuclear stiffness has also been measured quantitatively by other groups (26). Using these data, we predicted the critical force at different PEO contents for both TSA-treated and control cells (Fig. 3D). Results from this model showed that critical force decreased monotonically as PEO content increased, given that a higher PEO content results in larger pores (31). This indicates that infiltrated cell numbers should increase as the PEO content increases, consistent with our experimental results. Likewise, since TSA results in a softer nucleus (26), the critical force drops significantly compared to control conditions. This is particularly important at low PEO contents (denser networks), where the critical force for TSA-treated nuclei drops markedly. In networks with larger pores, the difference in critical force between TSA-treated groups vanishes. We included the model to gain, in general, insight into how a change in nuclear deformability (with TSA) might broadly affect cell migration in 3D and chose a simple configuration to gain some initial insight. While this model is simple (i.e., it does not represent the geometry of our fiber networks or native tissue), its predictions were consistent with our experimental findings, where the percentage of infiltrated cells was higher with TSA treatment at 0% PEO but the difference between groups disappeared at 50% PEO (Fig. 2I). The model also predicted that the NAR (after fully embedded in the channel) should increase as the nucleus becomes softer or the ECM becomes stiffer [with both resulting in a larger normalized ECM modulus (Fig. 3E), EECM/En]; this also is consistent with our experimental results showing that the NAR of TSA-treated nuclei within scaffolds was larger than nuclei in the control group.

The above data demonstrate that TSA treatment decreases chromatin condensation for a sufficient period of time to permit migration. However, prolonged exposure to this agent may have deleterious effects on cell phenotype and function. To assess this, we queried how long changes in MFC nuclear condensation persist after TSA withdrawal. MFCs were treated with TSA for 1 day as above, followed by five additional days of culture in fresh BM (Fig. 4A). Consistent with our previous findings, TSA decreased chromatin condensation and CCP after 1 day of treatment (Fig. 4, B and C). Upon removal of TSA, CCP values progressively increased, reaching baseline levels by day 5 (Fig. 4, B and C). A similar finding was noted in H2B localizations and domain area via STORM imaging, where these values returned to baseline levels within 5 days of TSA withdrawal (fig. S8, A to C). Similarly, nuclei in MFCs treated with TSA showed increased deformation compared to control MFC nuclei that were not treated with TSA (Fig. 4D) and increased Ac-H3K9 levels (Fig. 4, E and F), but these values gradually returned to the baseline levels within 5 days with TSA removal (Fig. 4, D to F). Over this same time course, proliferation was decreased in TSA-treated cells but returned to baseline levels within 5 days of TSA withdrawal on both tissue culture plastic (TCP) and on AL nanofibrous scaffolds (fig. S8, D and E). No change in levels of apoptosis (caspase activity) was observed over this time course (fig. 8F). Further, to investigate phenotypic behavior of cells after TSA treatment in the context of tissue repair, we next assayed whether cells exposed to TSA showed alterations in fibrochondrogenic gene expression and collagen production in MFCs. Although the sample size was small in this study, we did not detect a significant change in gene expression for any of the major collagen isoforms or proteoglycans normally produced by meniscus cells (fig. S9A). To further assess this, MFCs were treated with TSA for 1 day, followed by culture in fresh BM or TGF-3 containing chemically defined media (to accelerate collagen production) for an additional 3 days. Collagen produced by these cells and released to the media was not altered by TSA treatment (fig. S9B). Together, these data support that TSA treatment decreases chromatin condensation by increasing acetylation of histones in MFCs but this change is transient and baseline levels are restored gradually after TSA is removed, without alterations in collagen production.

(A) Schematic showing experimental setup; adult MFCs seeded on AL nanofibrous scaffolds were treated with/without TSA in BM for 1 day, followed by culture in fresh BM without TSA for an additional 5 days. (B) Representative DAPI-stained nuclei (top) and corresponding detection of visible edges (bottom) (scale bar, 3 m) and (C) CCP for time points indicated in (A) (red line; BM control at day 0, n = ~20 nuclei, *P < 0.05 versus Ctrl, means SEM). (D) NAR with 3 and 15% of applied stretch (normalized to NAR with 0%, n = 65 ~80 cells, *P < 0.05 versus 3%, +P < 0.05 versus Ctrl, P < 0.05 versus day 0, and aP < 0.05 versus day1, means SEM). (E) Immunostaining for Ac-H3K9 (green) in nuclei (blue) and quantification of mean intensity of the immunostaining (F) (n = ~28 cells, *P < 0.05 versus Ctrl and +P < 0.05 versus day 0, means SEM]. a.u., arbitrary units. All experiments were carried out in triplicate.

Given that transient TSA treatment softened MFC nuclei, resulting in enhanced interstitial cell migration, and did not perturb collagen production in the short term, we next investigated longer-term maturation of a tissue engineered construct with TSA treatment. For this, MFCs were seeded onto AL-PCL/PEO 25% scaffolds and cultured in TGF-3 containing chemically defined media for 4 weeks with/without TSA treatments (once a week for 1 day) as illustrated in Fig. 5A. In controls [()TSA], collagen deposition occurred mostly at the construct border (Fig. 5B), but both deposition and cell distribution were improved with TSA treatment [(+)TSA] (Fig. 5, B and C). Quantification showed that ~50% of cells were located within 50 m of the scaffold edge in controls [()TSA], while TSA treatment [(+)TSA] increased the number of cells deeper within the scaffold (250- to 400-m range; Fig. 5D).

(A) Experimental schematic showing MFCs seeded on PCL/25% PEO nanofibrous scaffolds that were cultured in chemically defined media for 4 weeks with TSA treatment once per week. After 4 weeks, ECM production and cell infiltration with/without TSA treatment were evaluated. Representative cross sections of MFC-laden nanofibrous constructs at week 4 stained for collagen (B) and cell nuclei (C). Scale bar, 100 m. (D) Quantification of MFC infiltration with/without TSA treatment (n = 3 images from three separate samples, *P < 0.05 versus ()TSA, means SEM). Experiments were carried out in duplicate. PSR, Picrosirius Red.

Toward meniscus repair, it is important to evaluate MFC migration through the dense fibrous ECM of meniscus tissue in the context of TSA treatment. For this, adult meniscus explants (, 5 mm) were cultured for ~2 weeks, donor cells in these vital explants were stained with CellTracker, and the explants were placed onto devitalized tissue substrates and cultured for an additional 48 hours, with/without TSA treatment [(/+)TSA] (Fig. 6A). During this 48-hour period, the cells derived from the donor explants adhered to the tissue substrates (Fig. 6B). In control groups [()TSA], cells were found predominantly on the substrate surface, whereas TSA-treated MFCs were found below the substrate surface (Fig. 6, B and C). Quantification showed that both the percent infiltration and the infiltration depth were significantly greater with TSA treatment (Fig. 6D).

(A) Schematic showing processing of vital tissue explants and devitalized tissue sections for invasion assay. Cell migration from the vital tissue and infiltration into the devitalized tissue section were evaluated by confocal microscopy. (B) 3D reconstructions (scale bar, 200 m) and (C) cross-sectional views (scale bar, 50 m) of cells (green) migrating through the devitalized tissue sections (blue), with and without TSA treatment. (D) Quantification of the percentage of infiltrated cells [n = 6 images, *P < 0.05 versus ()TSA, means SD] and cell infiltration depth [n = ~40 cells, *P < 0.05 versus ()TSA, means SEM]. Experiments were carried out in triplicate. (E) Electrospinning schematic showing two independent fiber jets collected simultaneously onto a common rotating mandrel. Discrete fiber populations are composed of PEO containing TSA and PCL. (F) Experimental schematic showing meniscus cell seeding onto nanofiber substrates. One day after seeding, the composite PCL/PEO TSA-releasing (PPT) scaffold was added to the microfluidic chamber reservoir, and cells were cultured for an additional 2 days, followed by confocal imaging. (G) 3D confocal reconstructions of cell (green) migration through AL nanofibrous networks with and without scaffold-mediated TSA delivery (scale bar, 100 m) and quantifications of the percentage of infiltrated cells [n = 5 images, *P < 0.05 versus ()TSA, +P < 0.05 versus (+)TSA, and #P < 0.05 versus 100 ng, means SD; biomolecule loading (mass per scaffold) is based on electrospinning parameters and scaffold mass]. (H) Schematic of repair construct assembly and subcutaneous evaluation in a rat model. (I) Images of DAPI-stained nuclei (blue) at the center of repair constructs after 1 week of subcutaneous implantation, with and without TSA delivery. Dashed lines indicate tissue-scaffold interfaces; dotted lines indicate separation into outer one-third (A), middle (B), and inner one-third (C) sections for quantification. Scale bar, 300 m. (J) Number of cells within each region of the scaffold with and without biomaterial-mediated TSA release (n = 3 samples from three different animals, *P < 0.05 versus PCL/PEO).

Next, we developed an assay to evaluate endogenous cell migration within native tissue. For this, tissue explants (, 6 mm) were excised from adult menisci, and the cells on the periphery of the explants were devitalized using a two-cycle freeze-thaw process (freezing in 20C for 30 min, followed by thawing at room temperature for 30 min, repeated twice on day 2; fig. S10A). This resulted in a ring of dead cells at the periphery of the tissue and a vital core. Processed explants were then treated with TSA for 1 day (day 1) and cultured in fresh media for an additional 3 days (fig. S10A). At the end of culture, living cells along the explant border were quantified. In controls that had not been treated by freeze-thaw (Ctrl), live cells occupied the periphery (fig. S10, B and D). With the two-cycle freeze-thaw process, there was a significant decrease in the number of live cells in this region (fig. S10, B and D), while cells in the center of the explant remained vital (day 2; fig. S10, B and D). With TSA treatment [(+)TSA], the number of vital cells that had migrated from the vital core to the periphery was significantly increased (day 3; fig. S10, C and D).

Last, to demonstrate the clinical potential of these findings, we developed an integrated biomaterial implant system to improve tissue repair in vivo (10, 35) via TSA delivery (Fig. 6E). Here, TSA was released from the PEO fiber fraction of a composite nanofibrous scaffold when this fiber fraction dissolves when placed in an aqueous environment. To first demonstrate bioactivity of the scaffold, we directly included small segments of these TSA-releasing composite scaffolds in the top chamber of the microfluidic migration device to treat seeded MFCs (Fig. 6F). Consistent with findings from soluble delivery, the percentage of infiltrated cells increased with the addition of the TSA-releasing composite scaffold (Fig. 6G): scaffolds releasing ~200 ng of TSA resulted in similar cell migration as direct addition of TSA (200 ng/ml) to the chamber (Fig. 6G). These results show our ability to deliver TSA to the wound site in a controlled fashion. To determine whether these TSA-releasing scaffolds could improve interstitial migration of endogenous meniscus cells in an in vivo setting, we subcutaneously placed meniscal repair constructs in nude rats with empty (PCL/PEO) or TSA-releasing scaffolds (PCL/PEO/TSA) interposed between the cut surfaces and histologically evaluated cellularity of the tissue and implant at 1 week (Fig. 6H). Results showed that interfacial cellularity was markedly higher for repair constructs with the scaffolds releasing ~100 ng of TSA (PCL/PEO/TSA) compared to control scaffolds (PCL/PEO; Fig. 6I), with cells occupying the full thickness of the TSA-releasing scaffold (Fig. 6J). Together, these data indicate that biomaterial-mediated nuclear softening of endogenous meniscus cells increases their capacity for interstitial migration through the tissue and into the scaffold in an in vivo setting.

PCL nanofibrous scaffolds were fabricated via electrospinning as in (6). Briefly, a PCL solution (80 kDa; Shenzhen Bright China Industrial Co. Ltd., China; 14.3% (w/v) in 1:1 tetrahydrofuran and N,N-dimethylformamide) was extruded through a stainless steel needle (2.5 ml/hour, 18-gauge, charged to +13 kV). To form NAL scaffolds, fibers were collected on a mandrel rotating with a surface velocity of <0.5 m/s. For AL scaffolds, fibers were collected at a high surface velocity (~10 m/s) (36). In some studies, to enhance cell infiltration, PCL/PEO (PEO, 200 kDa; Polysciences Inc., Warrington, PA) composite AL fibrous scaffolds were produced by coelectrospinning two fiber fractions onto the same mandrel, as in (6). For this, solutions of PCL (14.3%, w/v) and PEO (10%, w/v, in 90% ethanol) were electrospun simultaneously onto a centrally located mandrel (~10 m/s, 2.5 ml/hour). Resulting composite scaffolds were produced with PEO content of 0, 25, and 50% by scaffold dry mass. To visualize fibers, CellTracker Red (0.0005%, w/v) was mixed into the PCL solutions before electrospinning. Scaffolds were hydrated and sterilized in ethanol (100, 70, 50, and 30%; 30 min per step) and incubated in a fibronectin (20 g/ml) solution overnight to enhance initial cell attachment. TSA-releasing scaffolds contained a semipermanent (very slow degrading) fiber population (PCL) and a transient (water soluble) fiber population (PEO). The PEO fibers released TSA as they dissolve. To form this fiber fraction, TSA was added to the PEO solution (1% wt/vol) 2 days before spinning. PCL (10 ml) and PEO/TSA (10 ml) solutions were loaded into individual syringes and electrospun simultaneously by coelectrospinning onto a common centrally located mandrel, as above. Estimates of TSA content (mass per scaffold) were based on electrospinning parameters and the mass of each fiber fraction (Fig. 6E).

MFCs were isolated from the outer zone of adult bovine (20 to 30 months; Animal Technologies Inc.) or porcine menisci (6 to 9 months; Yucatan, Sinclair BioResources). For this, meniscal tissue segments were minced into ~1-mm3 cubes and placed onto TCP and incubated at 37C in a BM consisting of Dulbeccos modified Eagles medium (DMEM) with 10% fetal bovine serum and 1% penicillin/streptomycin/fungizone (PSF). Cells gradually emerged from the small tissue segments over 2 weeks, after which the remaining tissue was removed and the cells were passaged one time before use. MSCs were isolated from juvenile bovine bone marrow as in (37) and expanded in BM. To induce MSC fibrochondrogenesis, passage 1 MSCs were seeded on AL PCL scaffolds and cultured in a chemically defined serum free medium consisting of high glucose DMEM with 1 PSF, 0.1 M dexamethasone, ascorbate 2-phosphate (50 g/ml), l-proline (40 g/ml), sodium pyruvate (100 g/ml), insulin (6.25 g/ml), transferrin (6.25 g/ml), selenous acid (6.25 ng/ml), bovine serum albumin (BSA; 1.25 mg/ml), and linoleic acid (5.35 g/ml) (Life Technologies, NY, USA). This base medium (Ctrl) was further supplemented with TGF-3 (10 ng/ml) to induce differentiation (Ctrl/Diff, R&D Systems, Minneapolis, MN). Cell-seeded constructs were cultured in this medium for up to 7 days.

MFCs or MSCs were plated into eight-well Lab-Tek 1 cover glass chambers (Nunc), followed by preculture in BM for 2 days. At this time point, cells were treated with TSA for 3 hours, followed by fixation in methanol-ethanol (1:1) at 20C for 6 min. After a 1-hour incubation in blocking buffer containing 10 weight % BSA (Sigma-Aldrich) in phosphate-buffered saline (PBS), samples were incubated overnight with anti-H2B (1:50; abcam1790, Abcam), anti-H3K4me4 (1:100; MA5-11199, Thermo Fisher Scientific), or anti-H3K27me3 (1:100; PA5-31817, Thermo Fisher Scientific) at 4C. Next, samples were washed and incubated for 40 min with secondary antibodies custom labeled with activator-reporter dye pairs (Alexa Fluor 405Alexa Fluor 647, Invitrogen) for STORM imaging (29, 38). All imaging experiments were carried out with a commercial STORM microscope system from Nikon Instruments (N-STORM). For imaging, the 647-nm laser was used to excite the reporter dye (Alexa Fluor 647, Invitrogen) to switch it to the dark state. Next, a 405-nm laser was used to reactivate the Alexa Fluor 647 in an activator dye (Alexa Fluor 405)facilitated manner. An imaging cycle was used in which one frame belonging to the activating light pulse (405 nm) was alternated with three frames belonging to the imaging light pulse (647 nm). Imaging was carried out in a previously described imaging buffer [Cysteamine (#30070-50G, Sigma-Aldrich), GLOX solution: 1 glucose oxidase (0.5 mg/ml), 1 catalase (40 mg/ml) (all from Sigma-Aldrich), and 10% glucose in PBS] (39). STORM images were analyzed and rendered using custom-written software (Insight3, gift of B. Huang, University of California, San Francisco, USA) as previously described (39). For quantitative analysis, a previously described method was adapted that segments super-resolution images based on Voronoi tessellation of the fluorophore localizations (27, 28). Voronoi tessellation of a STORM image assigns a Voronoi polygon to each localization, such that the polygon area is inversely proportional to the local localization density (40). The spatial distribution of localizations is represented by a set of Voronoi polygons such that smaller polygon areas correspond to regions of higher density. Domains were segmented by grouping adjacent Voronoi polygons with areas less than a selected threshold, and imposing a minimum of three localizations per domain criteria generates the final segmented dataset.

MFCs (P1) were seeded onto AL PCL (0% PEO) scaffolds in BM for 2 days. To induce chromatin decondensation, TSA, a HDAC inhibitor (26) was added to the media for 3 hours. Chromatin condensation state and nuclear deformability were evaluated 3 hours after TSA treatment. For chromatin condensation analysis, constructs were fixed in 4% paraformaldehyde for 30 min at 37C, followed by PBS washing and permeabilization (with 0.05% Triton X-100 in PBS supplemented with 320 mM sucrose and 6 mM magnesium chloride). Nuclei were visualized by DAPI (ProLong Gold Antifade Reagent with DAPI, P36935, Molecular Probes, Grand Island, NY) and imaged at their mid-section using a confocal microscope (Leica TCS SP8, Leica Microsystems Inc., IL). Edge density in individual nuclei was measured using a Sobel edge detection algorithm in MATLAB to calculate the CCP as described in (24).

To assess nuclear deformability, the NAR (NAR = a/b) was evaluated before (0%) and after 9 and 15% grip-to-grip static deformation of constructs. Nuclear shape was captured on an inverted fluorescent microscope (Nikon T30, Nikon Instruments, Melville, NY) equipped with a charge-coupled device camera at each deformation level. NAR was calculated using a custom MATLAB code. Changes in NAR were tracked for individual MSC nuclei at each strain step as in (41).

To assess MFC migration on 2D substrates, a scratch assay was performed with or without TSA treatment. For this, passage 1 MFCs were plated into a six-well tissue culture dish (2 105 cells per well) and cultured to confluence (for 2 to 3 days). Confluent monolayers were then scratched with a 2.5-l pipette tip, and cell debris was removed via PBS washing. Images were taken using an inverted microscope at regular intervals and wound closure computed using ImageJ.

In addition, as an initial assessment of MFC migration, 96-well transwell migration assay kits (Chemicon QCM 96-well Migration Assay; membrane pore size, 3, 5, or 8 m) were used to assess cell migration. Briefly, human recombinant PDGF-AB (100 ng/ml in 150 l of BM; Prospect Bio) was added to the bottom chamber, and passage 1 MFCs (50,000 cells per well) were seeded into the top chamber. Cells were allowed to migrate for 18 hours at 37C with/without TSA treatment. In some studies, different dosages of TSA (0 to 800 nM) were applied (at a pore size of 5 m).

To assess initial cell migration through dense nanofiber networks, a custompoly(dimethylsiloxane) (PDMS) migration assay chamber was implemented (Fig. 2A). Top and bottom pieces containing holes (top, 6, 7, 6 mm in diameter; bottom, 6, 5, 6 mm in diameter) and a channel (bottom, 2 mm in width and 20 mm in length) were designed via SOLIDWORKS software for 3D printed templates (Acura SL 5530, Protolabs), and these were cast from the templates with PDMS (Sylgard 184, Dow Corning). To assemble the multilayered chamber, bottom PDMS pieces, the periphery of PCL electrospun fiber networks, and top PDMS pieces were coated with uncured PDMS base and curing agent mixture (10:1 ratio) and placed on cover glasses sequentially. For firm adhesion of each layer, chambers were incubated at 40C overnight. The final device consisted of a top reservoir containing BM and a bottom reservoir containing BM + PDGF (100 ng/ml) as a chemoattractant (Fig. 2A). To simulate chemoattactant diffusion from bottom to top reservoirs, trypan blue 0.4% solution (MP Biomedicals) was introduced to one of the side holes to fill the bottom reservoir, and the central top reservoir was filled with PBS. Cell migration chambers were kept in incubator (37C, 5% CO2), and images were obtained at regular intervals (Fig. 2D).

Fluorescently labeled (CellTracker Red) AL or NAL nanofibrous PCL scaffolds (thickness, ~150 m) were interposed between the reservoirs, and MFCs (2000 cells, passage 1) were seeded onto the top of each scaffold, followed by 1 day before culture in BM. Cells in chambers were cultured in BM with/without TSA for an additional 2 days. At the end of 3 days, cells were fixed and visualized by actin/DAPI staining. Confocal z-stacks were obtained at 40 magnification, and maximum z-stack projections were used to assess cellular morphology (cell/nuclear aspect ratio, area, circularity, and solidity). The percentage of infiltrated cells was quantified from confocal z stacks, with cells located beneath fibers categorized as infiltrated (fig. S3C) and the infiltration depth measured on cross-sectional images using ImageJ. For scanning electron microscopy imaging, additional samples were fixed and dehydrated in ethanol (30, 50, 70, and 100%, 60 min per step) and then hexamethyldisilane for terminal dehydration under vacuum.

Details on the model have been described previously (34). Briefly, to understand the influence of both intracellular and extracellular cues on cell migration through the fibrous ECM, we considered a model in which a cell with a spherical nucleus of radius rn is invading ECM through a deformable gap (with radius rg) smaller than the diameter of the nucleus (Fig. 3A). For simplicity, the nucleus is modeled by a spheroid and treated as a compressible neo-Hookean hyperelastic material to capture the mechanical response. An infinitely long small channel is created in the ECM to mimic the path a cell would migrate through in the migration assay. A neo-Hookean hyperelastic material was used to capture the ECM mechanical properties. The model parameters are shown in Table 1.

To assess how fast the TSA-mediated MFC chromatin organization and deformability was restored after TSA removal, MFCs seeded on AL scaffolds were treated with TSA for 1 day, followed by additional culture for 5 days in fresh BM (Fig. 4A). At each time point, the CCP and nuclear deformability were evaluated as described above. In addition, Ac-H3 levels in MFC nuclei were assessed by immunostaining with an Ac-H3K9 monoclonal antibody (MA5-11195, Thermo Fisher Scientific; 1:400, overnight at 4C). All images were collected using a confocal microscope (Leica TCS SP8, Leica Microsystems Inc., IL) at 63 magnification, with staining intensity quantified using ImageJ.

For long-term evaluation of matrix production after TSA treatment, MFCs were seeded on PCL/PEO 25% AL nanofibrous scaffolds (P1, 105 cells, 1 cm by 1 cm by 0.1 cm) and were cultured in TGF-3 containing chondrogenic media for 4 weeks. TSA was applied once each week for 24 hours. After 4 weeks, constructs were fixed with 4% paraformaldehyde and embedded in CryoPrep frozen section embedding medium [optimal cutting temperature (OCT) compound, Thermo Fisher Scientific, Pittsburgh, PA]. Using a cryostat microtome (Microm HM-500 M Cryostat, Ramsey, MN), constructs were sectioned to 8 m in thickness through their depth and stained with Picrosirius Red and DAPI to visualize collagen and nuclei, respectively. Stained sections were visualized and imaged by brightfield and fluorescent microscopy (Nikon Eclipse TS 100, Melville, NY). To quantify cell infiltration in the scaffolds, the number of migrated cells as a function of scaffold depth was determined for each experimental group (n = 3 scaffolds per group) using ImageJ.

To isolate fresh MFCs, cylindrical tissue explants (6 mm in diameter and 3 mm in height) were excised using biopsy punches from the middle zone of the meniscus, and these explants incubated in BM for ~2 weeks to allow cells to occupy the periphery. To fabricate devitalized tissue substrates, additional cylindrical tissue explants (8 mm in diameter) were embedded in OCT sectioning medium (Sakura Finetek, Torrance, CA) and axially cut (to ~50 m in thickness) using a cryostat microtome. These devitalized sections were placed onto positively charged glass slides and stored at 20C until use. After ~2 weeks of in vitro culture, the living explants were incubated in 5-chloromethylfluorescein diacetate (5 g/ml) (CellTracker Green, Thermo Fisher Scientific, Waltham, MA) in serum-free media (DMEM with 1% PSF) for 1 hour to fluorescently label cells in the explants. The explants were placed atop tissue substrates to allow for cell egress onto and invasion into the sections, and slides with explants were incubated at 37C with/without TSA treatment in BM for 2 days, at which point maximum z-stack projections were acquired using a confocal microscope (Leica TCS SP8, Leica Microsystems Inc., IL). Cell infiltration depth was measured as the distance between the apical tissue surface and the basal cell surface using a custom MATLAB code (3), and the total number of cells and the number of migrated cells (those entirely embedded within the tissue) were counted (n = 3 per group) using ImageJ.

In addition, to observe endogenous meniscus cell migration in the native ECM, a tissue-based migration assay was developed. Cylindrical meniscus tissue explants (6 mm in diameter and ~6 mm in height) were excised from the middle zone of adult menisci. To kill the cells on the border of the tissue, explants were frozen at 20C for 30 min and then thawed at room temperature for 30 min; this process was repeated twice (two-cycle) (day 2; fig. S10A). After devitalizing the periphery, explants were cultured in BM for 1 day, and TSA was added for 1 day (day 1; fig. S10A). After TSA treatment, explants were washed with PBS (day 0; fig. S10A), followed by culture in fresh BM for an additional 3 days. At day 3, LIVE/DEAD staining was performed, and explants cross sections were imaged (day 3; fig. S10A). Images were acquired from eight regions distributed evenly around the boundary (Leica TCS SP8, Leica Microsystems Inc., IL). The number of live cells located within 1 mm of the boundary was determined using ImageJ.

To evaluate the impact of biomaterial-mediated TSA delivery on endogenous meniscus cell migration in an in vivo setting, a nude rat xenotransplant model was used, as in (10). All animal procedures were approved by the Animal Care and Use Committee of the Corporal Michael Crescenz VA Medical Center. Before subcutaneous implantation, horizontal defects were created in adult bovine meniscal explants (8 mm in diameter and 4 mm in height, n = 3 donors; Fig. 6H). Electrospun PCL/PEO scaffolds with/without TSA were prepared (6 mm in diameter with a 2-mm-diameter central fenestration). Control PCL/PEO scaffolds or scaffolds releasing TSA (PCL/PEO/TSA, ~100 ng) were placed into the defect, which was closed with absorbable sutures. The repair construct was implanted subcutaneously into the dorsum of male athymic nude rats (n = 3, Hsd:RH-Foxn1rnu, 8 to 10 weeks old, ~300 g, Harlan) (Fig. 6H) (10). At 1 week, rats were euthanized, and constructs were removed from the subcutaneous space. Samples were fixed with para-formaldehyde and embedded in OCT sectioning medium (Sakura Finetek, Torrance, CA), sectioned to 8 m in thickness, stained with DAPI for cell nuclei, and imaged using a fluorescence microscope. Cell number in the center and edges of the implanted scaffold were determined using ImageJ.

Statistical analysis was performed using Student t tests or analysis of variance (ANOVA) with Tukeys honestly significantly different post hoc tests (SYSTAT v.10.2, Point Richmond, CA). For datasets that were not normally distributed, nonparametric Mann-Whitney or Kruskal-Wallis tests were performed, followed by post hoc testing with Dunns correction using GraphPad Prism version 6 (GraphPad Software Inc., La Jolla, CA, USA). Results are expressed as the means SEM or SD, as indicated in the figure legends. Differences were considered statistically significant at P < 0.05.

Acknowledgments: We acknowledge S. Gullbrand, D. H. Kim, and E. Henning for technical support. Funding: This work was supported by the NIH (R01 AR056624), the Department of Veterans Affairs (I01 RX000174), the NSF Science and Technology Center for Engineering Mechanobiology (CMMI-1548571), and the Penn Center for Musculoskeletal Disorders (P30 AR069619). Author contributions: S.-J.H., K.H.S., S.T., X.C., A.P.P., B.N.S., F.Q., V.B.S., M.L., J.A.B., and R.L.M. designed the studies. S.-J.H., K.H.S., S.T., X.C., A.P.P., and B.N.S. performed the experiments. S.-J.H., K.H.S., S.T., X.C., A.P.P., B.N.S., F.Q., V.B.S., M.L., J.A.B., and R.L.M. analyzed and interpreted the data. S.-J.H., S.T., X.C., V.B.S., M.L., J.A.B., and R.L.M. drafted the manuscript, and all authors edited the final submission. Competing interests: The authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.

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Nuclear softening expedites interstitial cell migration in fibrous networks and dense connective tissues - Science Advances