Acta Naturae. 2010 Jul; 2(2): 1828.

Institute of Cytology and Genetics, Siberian Branch, Russian Academy of Sciences

Institute of Cytology and Genetics, Siberian Branch, Russian Academy of Sciences

Institute of Cytology and Genetics, Siberian Branch, Russian Academy of Sciences

Research Center of Clinical and Experimental Medicine, Siberian Branch, Russian Academy of Medical Sciences

Institute of Cytology and Genetics, Siberian Branch, Russian Academy of Sciences

Research Center of Clinical and Experimental Medicine, Siberian Branch, Russian Academy of Medical Sciences

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

Induced pluripotent stem cells (iPSCs) are a new type of pluripotent cellsthat can be obtained by reprogramming animal and human differentiated cells. In this review,issues related to the nature of iPSCs are discussed and different methods ofiPSC production are described. We particularly focused on methods of iPSC production withoutthe genetic modification of the cell genome and with means for increasing the iPSC productionefficiency. The possibility and issues related to the safety of iPSC use in cell replacementtherapy of human diseases and a study of new medicines are considered.

Keywords: induced pluripotent stem cells, directed stem cell differentiation, cell replacement therapy

Pluripotent stem cells are a unique model for studying a variety of processes that occur inthe early development of mammals and a promising tool in cell therapy of human diseases. Theunique nature of these cells lies in their capability, when cultured, for unlimitedselfrenewal and reproduction of all adult cell types in the course of theirdifferentiation [1]. Pluripotency is supported by acomplex system of signaling molecules and gene network that is specific for pluripotent cells.The pivotal position in the hierarchy of genes implicated in the maintenance of pluripotency isoccupied by Oct4, Sox2 , and Nanog genes encodingtranscription factors [2, 3]. The mutual effect of outer signaling molecules and inner factors leads tothe formation of a specific expression pattern, as well as to the epigenome statecharacteristic of stem cells. Both spontaneous and directed differentiations are associatedwith changes in the expression pattern and massive epigenetic transformations, leading totranscriptome and epigenome adjustment to a distinct cell type.

Until recently, embryonic stem cells (ESCs) were the only wellstudied source ofpluripotent stem cells. ESCs are obtained from either the inner cell mass or epiblast ofblastocysts [46]. A series of protocols has been developed for the preparation of variouscell derivatives from human ESCs. However, there are constraints for ESC usein cell replacement therapy. The first constraint is the immune incompatibility between thedonor cells and the recipient, which can result in the rejection of transplanted cells. Thesecond constraint is ethical, because the embryo dies during the isolation of ESCs. The firstproblem can be solved by the somatic cell nuclear transfer into the egg cell and then obtainingthe embryo and ESCs. The nuclear transfer leads to genome reprogramming, in which ovariancytoplasmic factors are implicated. This way of preparing pluripotent cells from certainindividuals was called therapeutic cloning. However, this method is technologyintensive,and the reprogramming yield is very low. Moreover, this approach encounters theabovementioned ethic problem that, in this case, is associated with the generation ofmany human ovarian cells [7].

In 2006, the preparation of pluripotent cells by the ectopic expression of four genes Oct4 , Sox2 , Klf4 , and cMyc in both embryonic and adult murine fibroblasts was first reported[8]. The pluripotent cells derived from somatic ones werecalled induced pluripotent stem cells (iPSCs). Using this set of factors(Oct4, Sox2, Klf4, and cMyc), iPSCs were prepared later from variousdifferentiated mouse [914] and human [1517] cell types. Human iPSCs were obtainedwith a somewhat altered gene set: Oct4 , Sox2 , Nanog , and Lin28 [18].Induced PSCs closely resemble ESCs in a broad spectrum of features. They possess similarmorphologies and growth manners and are equally sensitive to growth factors and signalingmolecules. Like ESCs, iPSCs can differentiate in vitro intoderivatives of all three primary germ layers (ectoderm, mesoderm, and endoderm) and formteratomas following their subcutaneous injection into immunodeficient mice. MurineiPSCs injected into blastocysts are normally included in the development toyield animals with a high degree of chimerism. Moreover, murine iPSCs, wheninjected into tetraploid blastocycts, can develop into a whole organism [19, 20]. Thus, an excellent method thatallows the preparation of pluripotent stem cells from various somatic cell types whilebypassing ethical problems has been uncovered by researchers.

In the first works on murine and human iPSC production, either retro or lentiviralvectors were used for the delivery of Oct4 , Sox2 , Klf4 , and cMyc genes into somatic cells. Theefficiency of transduction with retroviruses is high enough, although it is not the same fordifferent cell types. Retroviral integration into the host genome requires a comparatively highdivision rate, which is characteristic of the relatively narrow spectrum of cultured cells.Moreover, the transcription of retroviral construct under the control of a promoter localizedin 5LTR (long terminal repeat) is terminated when the somatic celltransform switches to the pluripotent state [21]. Thisfeature makes retroviruses attractive in iPSC production. Nevertheless, retroviruses possesssome properties that make iPSCs that are produced using them improper for celltherapy of human diseases. First, retroviral DNA is integrated into the host cell genome. Theintegration occurs randomly; i.e., there are no specific sequences or apparent logic forretroviral integration. The copy number of the exogenous retroviral DNA that is integrated intoa genome may vary to a great extent [15]. Retrovirusesbeing integrated into the cell genome can introduce promoter elements and polyadenylationsignals; they can also interpose coding sequences, thus affecting transcription. Second, sincethe transcription level of exogenous Oct4 , Sox2 , Klf4 , and cMyc in the retroviral constructdecreases with cell transition into the pluripotent state, this can result in a decrease in theefficiency of the stable iPSC line production, because the switch from the exogenous expressionof pluripotency genes to their endogenous expression may not occur. Third, some studies showthat the transcription of transgenes can resume in the cells derived fromiPSCs [22]. The high probability thatthe ectopic Oct4 , Sox2 , Klf4 , and cMyc gene expression will resume makes it impossible to applyiPSCs produced with the use of retroviruses in clinical trials; moreover,these iPSCs are hardly applicable even for fundamental studies onreprogramming and pluripotency principles. Lentiviruses used for iPSC production can also beintegrated into the genome and maintain their transcriptional activity in pluripotent cells.One way to avoid this situation is to use promoters controlled by exogenous substances added tothe culture medium, such as tetracycline and doxycycline, which allows the transgenetranscription to be regulated. iPSCs are already being produced using suchsystems [23].

Another serious problem is the gene set itself that is used for the induction of pluripotency[22]. The ectopic transcription of Oct4 , Sox2 , Klf4 , and cMyc can lead to neoplastic development from cells derived from iPSCs,because the expression of Oct4 , Sox2 , Klf4, and cMyc genes is associated with the development ofmultiple tumors known in oncogenetics [22, 24]. In particular, the overexpression of Oct4 causes murine epithelial cell dysplasia [25],the aberrant expression of Sox2 causes the development of serrated polypsand mucinous colon carcinomas [26], breast tumors arecharacterized by elevated expression of Klf4 [27] , and the improper expression of cMyc is observed in 70% of human cancers [28].Tumor development is oberved in ~50% of murine chimeras obtained through the injection ofretroviral iPSCs into blastocysts, which is very likely associated with thereactivation of exogenous cMyc [29, 30].

Several possible strategies exist for resolving the above-mentioned problems:

The search for a less carcinogenic gene set that is necessary and sufficient for reprogramming;

The minimization of the number of genes required for reprogramming and searching for the nongenetic factors facilitating it;

The search for systems allowing the elimination of the exogenous DNA from the host cell genome after the reprogramming;

The development of delivery protocols for nonintegrated genetic constructs;

The search for ways to reprogram somatic cells using recombinant proteins.

The ectopic expression of cMyc and Klf4 genes isthe most dangerous because of the high probability that malignant tumors will develop [22]. Hence the necessity to find other genes that couldsubstitute cMyc and Klf4 in iPSC production. Ithas been reported that these genes can be successfully substituted by Nanog and Lin28 for reprogramming human somatic cells [18;] . iPSCs were prepared from murine embryonic fibroblastsby the overexpression of Oct4 and Sox2 , as well as the Esrrb gene encoding the murine orphan nuclear receptor beta. It has alreadybeen shown that Esrrb , which acts as a transcription activator of Oct4 , Sox2 , and Nanog , is necessary for theselfrenewal and maintenance of the pluripotency of murine ESCs. Moreover, Esrrb can exert a positive control over Klf4 . Thus, the genes causingelevated carcinogenicity of both iPSCs and their derivatives can besuccessfully replaced with less dangerous ones [31].

The Most Effectively Reprogrammed Cell Lines . Murine and humaniPSCs can be obtained from fibroblasts using the factors Oct4, Sox2, and Klf4,but without cMyc . However, in this case, reprogramming deceleratesand an essential shortcoming of stable iPSC clones is observed [32, 33]. The reduction of a number ofnecessary factors without any decrease in efficiency is possible when iPSCsare produced from murine and human neural stem cells (NSCs) [12, 34, 35]. For instance, iPSCs were produced fromNSCs isolated from adult murine brain using two factors, Oct4 and Klf4, aswell as even Oct4 by itself [12, 34]. Later, human iPSCs were produced by the reprogramming offetal NSCs transduced with a retroviral vector only carrying Oct4 [35] . It is most likely that the irrelevanceof Sox2, Klf4, and cMyc is due to the high endogenous expression level of these genes inNSCs.

Successful reprogramming was also achieved in experiments withother cell lines, in particular, melanocytes of neuroectodermal genesis [36]. Both murine and human melanocytes are characterized by a considerableexpression level of the Sox2 gene, especially at early passages.iPSCs from murine and human melanocytes were produced without the use of Sox2or cMyc. However, the yield of iPSC clones produced from murine melanocytes was lower(0.03% without Sox2 and 0.02% without cMyc) in comparison with that achieved when allfour factors were applied to melanocytes (0.19%) and fibroblasts (0.056%). A decreasedefficiency without Sox2 or cMyc was observed in human melanocyte reprogramming (0.05%with all four factors and 0.01% without either Sox2 or cMyc ). All attempts to obtain stable iPSC clones in the absence of both Sox2 andcMyc were unsuccessful [36]. Thus, theminimization of the number of factors required for iPSC preparation can be achieved by choosingthe proper somatic cell type that most effectively undergoes reprogramming under the action offewer factors, for example, due to the endogenous expression of pluripotencygenes. However, if human iPSCs are necessary, these somatic cellsshould be easily accessible and wellcultured and their method of isolation should be asnoninvasive as possible.

One of these cell types can be adipose stem cells (ASCs). This is aheterogeneous group of multipotent cells which can be relatively easily isolated in largeamounts from adipose tissue following liposuction. Human iPSCs weresuccessfully produced from ASCs with a twofold reprogramming rate and20fold efficiency (0.2%), exceeding those of fibroblasts [37].

However, more accessible resources for the effective production of humaniPSCs are keratinocytes. When compared with fibroblasts, human iPSC productionfrom keratinocytes demonstrated a 100fold greater efficiency and a twofold higherreprogramming rate [38].

It has recently been found that the reprogramming of murine papillary dermal fibroblasts(PDFs) into iPSCs can be highly effective with theoverexpression of only two genes, Oct4 and Klf4 ,inserted into retroviral vectors [39;].PDFs are specialized cells of mesodermal genesis surrounding the stem cells ofhair follicles . One characteristic feature of these cells is the endogenous expression of Sox2 , Klf4 , and cMyc genes,as well as the geneencoding alkaline phosphatase, one of the murine and humanESC markers. PDFs can be easily separated from other celltypes by FACS (fluorescenceactivated cell sorting) using life staining with antibodiesagainst the surface antigens characteristic of one or another cell type. The PDF reprogrammingefficiency with the use of four factors (Oct4, Sox2, Klf4, and cMyc) retroviral vectorsis 1.38%, which is 1,000fold higher than the skin fibroblast reprogramming efficiency inthe same system. Reprogramming PDFs with two factors, Oct4 and Klf4 , yields 0.024%, which is comparable to the efficiency of skinfibroblast reprogramming using all four factors. The efficiency of PDF reprogramming iscomparable with that of NSCs, but PDF isolation is steady and far lessinvasive [39]. It seems likely that human PDF lines arealso usable, and this cell type may appear to be one of the most promising for human iPSCproduction in terms of pharmacological studies and cell replacement therapy. The use of suchcell types undergoing more effective reprogramming, together with methods providing thedelivery of pluripotency genes without the integration of foreign DNA into thehost genome and chemical compounds increasing the reprogramming efficiency and substitutingsome factors required for reprogramming, is particularly relevant.

Chemical Compounds Increasing Cell Reprogramming Efficiency. As was noted above,the minimization of the factors used for reprogramming decreases the efficiency of iPSCproduction. Nonetheless, several recent studies have shown that the use of genetic mechanisms,namely, the initiation of ectopic gene expression, can be substituted by chemical compounds,most of them operating at the epigenetic level. For instance, BIX01294 inhibitinghistone methyltransferase G9a allows murine fibroblast reprogramming using only two factors,Oct4 and Klf4, with a fivefold increased yield of iPSC clones in comparison with the controlexperiment without BIX01294 [40]. BIX01294taken in combination with another compound can increase the reprogramming efficiency even more.In particular, BIX01294 plus BayK8644 elevated the yield of iPCSs 15 times, andBIX01294 plus RG108 elevated it 30 times when only two reprogramming factors, Oct4 andKlf4, were used. RG108 is an inhibitor of DNA methyltransferases, and its role in reprogrammingis apparently in initiating the more rapid and effective demethylation of promoters ofpluripotent cellspecific genes, whereas BayK8644 is an antagonist of Ltypecalcium channels, and its role in reprogramming is not understood very well [40]. However, more considerable results were obtained inreprogramming murine NSCs. The use of BIX01294 allowed a 1.5foldincrease in iPSC production efficiency with two factors, Oct4 and Klf4, in comparison withreprogramming with all four factors. Moreover, BIX01294 can even substitute Oct4 in thereprogramming of NSCs, although the yield is very low [41]. Valproic (2propylvaleric) acid inhibiting histone deacetylases canalso substitute cMyc in reprogramming murine and human fibroblasts. Valproic acid (VPA)increases the reprogramming efficiency of murine fibroblasts 50 times, and human fibroblastsincreases it 1020 times when three factors are used [42, 43]. Other deacetylase inhibitors,such as TSA (trichostatin A) and SAHA (suberoylanilide hyroxamic acid), also increase thereprogramming efficiency. TSA increases the murine fibroblast reprogramming efficiency 15times, and SAHA doubles it when all four factors are used [42]. Besides epigenetic regulators, the substances inhibiting the proteincomponents of signaling pathways implicated in the differentiation of pluripotent cells arealso applicable in the substitution of reprogramming factors. In particular, inhibitors of MEKand GSK3 kinases (PD0325901 and CHIR99021, respectively) benefit the establishment of thecomplete and stable pluripotency of iPSCs produced from murineNSCs using two factors, Oct4 and Klf4 [41, 44].

It has recently been shown that antioxidants can considerably increase the efficiency ofsomatic cell reprogramming. Ascorbic acid (vitamin C) can essentially influence the efficiencyof iPSC production from various murine and human somatic cell types [45]. The transduction of murine embryonic fibroblasts (mEFs) with retrovirusescarrying the Oct4 , Sox2 , and Klf4 genes results in a significant increase in the production level of reactive oxygen species(ROS) compared with that of both control and Efs tranduced with Oct4 , Sox2 , cMyc , and Klf4 . Inturn, the increase in the ROS level causes accelerated aging and apoptosis of the cell, whichshould influence the efficiency of cell reprogramming. By testing several substances possessingantioxidant activity such as vitamin B1, sodium selenite, reduced glutathione, and ascorbicacid, the authors have found that combining these substances increases the yield ofGFPpositive cells in EF reprogramming (the Gfp genewas under the control of the Oct4 gene promoter). The use of individualsubstances has shown that only ascorbate possesses a pronounced capability to increase thelevel of GFPpositive cells, although other substances keep theirROSdecreasing ability. In all likelihood, this feature of ascorbates is not directlyassociated with its antioxidant activity [45]. The scoreof GFPpositive iPSC colonies expressing an alkaline phosphatase hasshown that the efficiency of iPSC production from mEFs with three factors (Oct4, Sox2, andKlf4) can reach 3.8% in the presence of ascorbate. When all four factors (Oct4, Sox2, Klf4, andcMyc) are used together with ascorbate, the efficiency of iPSC production may reach8.75%. A similar increase in the iPSC yield was also observed in the reprogramming of murinebreast fibroblasts; i.e., the effect of vitamin C is not limited by one cell type. Moreover,the effect of vitamin C on the reprogramming efficiency is more profound than that of thedeacetylase inhibitor valproic (2propylvaleric) acid. The mutual effect of ascorbate andvalproate is additive; i.e., these substances have different action mechanisms. Moreover,vitamin C facilitates the transition from preiPSCs to stablepluripotent cells. This feature is akin to the effects of PD0325901 and CHIR99021, which areinhibitors of MEK and GSK3 kinases, respectively. This effect of vitamin C expands to humancells as well [45]. Following the transduction of humanfibroblasts with retroviruses carrying Oct4 , Sox2 , Klf4 , and cMyc and treatment with ascorbate, theauthors prepared iPSCs with efficiencies reaching 6.2%. The reprogrammingefficiency of ASCs under the same conditions reached 7.06%. The mechanism ofthe effect that vitamin C has on the reprogramming efficiency is not known in detail.Nevertheless, the acceleration of cell proliferation was observed at the transitional stage ofreprogramming. The levels of the p53 and p21 proteins decreased in cells treated withascorbate, whereas the DNA repair machinery worked properly [45]. It is interesting that an essential decrease in the efficiency of iPSCproduction has been shown under the action of processes initiated by p53 and p21 [4650].

As was mentioned above, for murine and human iPSC production, both retro andlentiviruses were initially used as delivery vectors for the genes required for cellreprogramming. The main drawback of this method is the uncontrolled integration of viral DNAinto the host cells genome. Several research groups have introduced methods fordelivering pluripotency genes into the recipient cell which either do notintegrate allogenic DNA into the host genome or eliminate exogenous genetic constructs from thegenome.

CreloxP Mediated Recombination. To prepareiPSCs from patients with Parkinsons disease, lentiviruses were used,the proviruses of which can be removed from the genome by Cre recombinase. To do this, the loxP site was introduced into thelentiviral 3LTRregions containing separate reprogramming genesunder the control of the doxycyclineinducible promoter. During viral replication, loxP was duplicated in the 5LTR of the vector. As aresult, the provirus integrated into the genome was flanked with two loxP sites. The inserts were eliminated using the temporary transfection ofiPSCs with a vector expressing Cre recombinase[51].

In another study, murine iPSCs were produced using a plasmid carrying the Oct4 , Sox2 , Klf4I, and cMyc genes in the same reading frame in which individual cDNAs were separatedby sequences encoding 2 peptides, and practically the whole construct was flanked with loxP sites [52]. The use ofthis vector allowed a notable decrease in the number of exogenous DNA inserts in the hostcells genome and, hence, the simplification of their following excision [52]. It has been shown using lentiviruses carrying similarpolycistronic constructs that one copy of transgene providing a high expression level of theexogenous factors Oct4, Sox2, Klf4, and cMyc is sufficient for the reprogramming ofdifferentiated cells into the pluripotent state [53,54].

The drawback of the CreloxP system is the incomplete excisionof integrated sequences; at least the loxP site remains in thegenome, so the risk of insertion mutations remains.

Plasmid Vectors . The application of lentiviruses and plasmids carrying the loxP sites required for the elimination of transgene constructsmodifies, although insignificantly, the host cells genome. One way to avoid this is touse vector systems that generally do not provide for the integration of the whole vector orparts of it into the cells genome. One such system providing a temporary transfectionwith polycistronic plasmid vectors was used for iPSC production from mEFs [29]. A polycistronic plasmid carrying the Oct4 , Sox2 , and Klf4 gene cDNAs, as well as aplasmid expressing cMyc , was transfected into mEFs one, three, five,and seven days after their primary seeding. Fibroblasts were passaged on the ninth day, and theiPSC colonies were selected on the 25th day. Seven out of ten experiments succeeded inproducing GFPpositive colonies (the Gfp gene wasunder the control of the Nanog gene promoter). The iPSCsthat were obtained were similar in their features to murine ESCs and did not contain inserts ofthe used DNA constructs in their genomes. Therefore, it was shown that wholesome murineiPSCs that do not carry transgenes can be reproducibly produced, and that thetemporary overexpression of Oct4 , Sox2 , Klf4 , and cMyc is sufficient for reprogramming. The maindrawback of this method is its low yield. In ten experiments the yield varied from 1 to 29 iPSCcolonies per ten million fibroblasts, whereas up to 1,000 colonies per ten millions wereobtained in the same study using retroviral constructs [29].

Episomal Vectors . Human iPSCs were successfully produced fromskin fibroblasts using single transfection with polycistronic episomal constructs carryingvarious combinations of Oct4 , Sox2 , Nanog , Klf4 , cMyc , Lin28 , and SV40LT genes. These constructs were designed on the basis of theoriP/EBNA1 (EpsteinBarr nuclear antigen1) vector [55]. The oriP/EBNA1 vector contains the IRES2 linker sequence allowing theexpression of several individual cDNAs (encoding the genes required for successfulreprogramming in this case) into one polycistronic mRNA from which several proteins aretranslated. The oriP/EBNA1 vector is also characterized by lowcopy representation in thecells of primates and can be replicated once per cell cycle (hence, it is not rapidlyeliminated, the way common plasmids are). Under nonselective conditions, the plasmid iseliminated at a rate of about 5% per cell cycle [56]. Inthis work, the broad spectrum of the reprogramming factor combinations was tested, resulting inthe best reprogramming efficiency with cotransfection with three episomes containing thefollowing gene sets: Oct4 + Sox2 + Nanog + Klf4 , Oct4 + Sox2 + SV40LT + Klf4 , and cMyc + Lin28 . SV40LT ( SV40 large T gene )neutralizes the possible toxic effect of overexpression [57]. The authors have shown thatwholesome iPSCs possessing all features of pluripotent cells can be producedfollowing the temporary expression of a certain gene combination in human somatic cells withoutthe integration of episomal DNA into the genome. However, as in the case when plasmid vectorsare being used, this way of reprogramming is characterized by low efficiency. In separateexperiments the authors obtained from 3 to 6 stable iPSC colonies per 106transfected fibroblasts [55]. Despite the fact that skinfibroblasts are wellcultured and accessible, the search for other cell types which arerelatively better cultured and more effectively subject themselves to reprogramming throughthis method is very likely required. Another drawback of the given system is that this type ofepisome is unequally maintained in different cell types.

PiggyBacTransposition . One promising system used foriPSC production without any modification of the host genome is based on DNA transposons.Socalled PiggyBac transposons containing2linkered reprogramming genes localized between the 5 and3terminal repeats were used for iPSC production from fibroblasts. The integrationof the given constructs into the genome occurs due to mutual transfection with a plasmidencoding transposase. Following reprogramming due to the temporary expression of transposase,the elimination of inserts from the genome took place [58, 59]. One advantage of the PiggyBac system on CreloxP is that the exogenous DNA iscompletely removed [60].

However, despite the relatively high efficiency of exogenous DNA excision from the genome by PiggyBac transposition, the removal of a large number of transposoncopies is hardly achievable.

Nonintegrating Viral Vectors . Murine iPSCs were successfullyproduced from hepatocytes and fibroblasts using four adenoviral vectors nonintegrating into thegenome and carrying the Oct4 , Sox2 , Klf4 , and cMyc genes. An analysis of the obtainediPSCs has shown that they are similar to murine ESCs in their properties(teratoma formation, gene promoter DNA methylation, and the expression of pluripotent markers),but they do not carry insertions of viral DNA in their genomes [61]. Later, human fibroblastderived iPSCs wereproduced using this method [62].

The authors of this paper cited the postulate that the use of adenoviral vectors allows theproduction of iPSCs, which are suitable for use without the risk of viral oroncogenic activity. Its very low yield (0.00010.001%), the deceleration ofreprogramming, and the probability of tetraploid cell formation are the drawbacks of themethod. Not all cell types are equally sensitive to transduction with adenoviruses.

Another method of gene delivery based on viral vectors was recently employed for theproduction of human iPSCs. The sendaivirus (SeV)based vector wasused in this case [63]. SeV is a singlestrandedRNA virus which does not modify the genome of recipient cells; it seems to be a good vector forthe expression of reprogramming factors. Vectors containing either all pluripotencyfactors or three of them (without ) were used for reprogramming the human fibroblast. The construct based on SeV is eliminatedlater in the course of cell proliferation. It is possible to remove cells with the integratedprovirus via negative selection against the surface HN antigen exposed on the infected cells.The authors postulate that reprogramming technology based on SeV will enable the production ofclinically applicable human iPSCs [63].

Cell Transduction with Recombinant Proteins . Although the methods for iPSCproduction without gene modification of the cells genome (adenoviral vectors, plasmidgene transfer, etc.) are elaborated, the theoretical possibility for exogenous DNA integrationinto the host cells genome still exists. The mutagenic potential of the substances usedpresently for enhancing iPSC production efficiency has not been studied in detail. Fullychecking iPSC genomes for exogenous DNA inserts and other mutations is a difficult task, whichbecomes impossible to solve in bulk culturing of multiple lines. The use of protein factorsdelivered into a differentiated cell instead of exogenous DNA may solve this problem. Tworeports have been published to date in which murine and human iPSCs wereproduced using the recombinant Oct4, Sox2, Klf4, and cMyc proteins [64, 65] . T he methodused to deliver the protein into the cell is based on the ability of peptides enriched withbasic residues (such as arginine and lysine) to penetrate the cells membrane. MurineiPSCs were produced using the recombinant Oct4, Sox2, Klf4, and cMycproteins containing eleven Cterminal arginine residues and expressed in E. coli . The authors succeeded in producing murine iPSCs during four roundsof protein transduction into embryonic fibroblasts [65].However, iPSCs were only produced when the cells were additionally treatedwith 2propylvalerate (the deacetylase inhibitor). The same principle was used for theproduction of human iPSCs, but protein expression was carried out in humanHEK293 cells, and the proteins were expressed with a fragment of nine arginins at the proteinCend. Researchers have succeeded in producing human iPSCs after sixtransduction rounds without any additional treatment [64]. The efficiency of producing human iPSC in this way was 0.001%, which isone order lower than the reprogramming efficiency with retroviruses. Despite some drawbacks,this method is very promising for the production of patientspecificiPSCs.

The first lines of human pluripotent ESCs were produced in 1998 [6]. In line with the obvious fundamental importance of embryonic stem cellstudies with regard to the multiple processes taking place in early embryogenesis, much of theinterest of investigators is associated with the possibility of using ESCs and theirderivatives as models for the pathogenesis of human diseases, new drugs testing, and cellreplacement therapy. Substantial progress is being achieved in studies on directed humanESC differentiation and the possibility of using them to correct degenerativedisorders. Functional cell types, such as motor dopaminergic neurons, cardiomyocytes, andhematopoietic cell progenitors, can be produced as a result of ESCdifferentiation. These cell derivatives, judging from their biochemical and physiologicalproperties, are potentially applicable for the therapy of cardiovascular disorders, nervoussystem diseases, and human hematological disorders [66].Moreover, derivatives produced from ESCs have been successfully used for treating diseasesmodeled on animals. Therefore, bloodcell progenitors produced from ESCs weresuccessfully used for correcting immune deficiency in mice. Visual functions were restored inblind mice using photoreceptors produced from human ESCs, and the normal functioning of thenervous system was restored in rats modeling Parkinsons disease using the dopaminergicneurons produced from human ESCs [6770]. Despite obvious success, the fullscale applicationof ESCs in therapy and the modeling of disorders still carry difficulties, because of thenecessity to create ESC banks corresponding to all HLAhaplotypes, whichis practically unrealistic and hindered by technical and ethical problems.

Induced pluripotent stem cells can become an alternative for ESCs in the area of clinicalapplication of cell replacement therapy and screening for new pharmaceuticals.iPSCs closely resemble ESCs and, at the same time, can be produced in almostunlimited amounts from the differentiated cells of each patient. Despite the fact that thefirst iPSCs were produced relatively recently, work on directed iPSCdifferentiation and the production of patientspecific iPSCs isintensive, and progress in this field is obvious.

Dopamine and motor neurons were produced from human iPSCs by directeddifferentiation in vitro [71, 72]. These types of neurons are damaged in many inherited oracquired human diseases, such as spinal cord injury, Parkinsons disease, spinal muscularatrophy, and amyotrophic lateral sclerosis. Some investigators have succeeded in producingvarious retinal cells from murine and human iPSCs [7375]. HumaniPSCs have been shown to be spontaneously differentiated in vitro into the cells of retinal pigment epithelium [76]. Another group of investigators has demonstrated that treating human andmurine iPSCs with Wnt and Nodal antagonists in a suspended culture induces theappearance of markers of cell progenitors and pigment epithelium cells. Further treating thecells with retinoic acid and taurine activates the appearance of cells expressing photoreceptormarkers [75].

Several research groups have produced functional cardiomyocytes (CMs) in vitro from murine and human iPSCs [7781]. Cardiomyocytes producedfrom iPSC are very similar in characteristics (morphology, marker expression,electrophysiological features, and sensitivity to chemicals) to the CMs ofcardiac muscle and to CMs produced from differentiated ESCs. Moreover, murineiPSCs, when injected, can repair muscle and endothelial cardiac tissuesdamaged by cardiac infarction [77].

Hepatocytelike cell derivatives, dendritic cells, macrophages, insulinproducingcell clusters similar to the duodenal islets of Langerhans, and hematopoietic and endothelialcells are currently produced from murine and human iPSCs, in addition to thealreadylisted types of differentiated cells [8285].

In addition to directed differentiation in vitro , investigators apply mucheffort at producing patientspecific iPSCs. The availability ofpluripotent cells from individual patients makes it possible to study pathogenesis and carryout experiments on the therapy of inherited diseases, the development of which is associatedwith distinct cell types that are hard to obtain by biopsy: so the use ofiPSCs provides almost an unlimited resource for these investigations.Recently, the possibility of treating diseases using iPSCs was successfullydemonstrated, and the design of the experiment is presented in the figure. A mutant allele wassubstituted with a normal allele via homologous recombination in murine fibroblastsrepresenting a model of human sickle cell anemia. iPSCs were produced fromrepaired fibroblasts and then differentiated into hematopoietic cell precursors.The hematopoietic precursors were then injected into a mouse from which the skin fibroblastswere initially isolated (). As a result, the initialpathological phenotype was substantially corrected [86].A similar approach was applied to the fibroblasts and keratinocytes of a patient withFanconis anemia. The normal allele of the mutant gene producing anemia was introducedinto a somatic cell genome using a lentivirus, and then iPSCs were obtainedfrom these cells. iPSCs carrying the normal allele were differentiated intohematopoietic cells maintaining a normal phenotype [87].The use of lentiviruses is unambiguously impossible when producing cells to be introduced intothe human body due to their oncogenic potential. However, new relatively safe methods of genomemanipulation are currently being developed; for instance, the use of synthetic nucleasescontaining zinc finger domains allowing the effective correction of genetic defects invitro [88].

Design of an experiment on repairing the mutant phenotype in mice modeling sickle cell anemia development [2]. Fibroblasts isolatedfrom the tail of a mouse (1) carrying a mutant allele of the gene encoding the human hemoglobin -chain (hs) were used for iPSCproduction (2). The mutation was then repaired in iPSCs by means of homological recombination (3) followed by cell differentiationvia the embryoid body formation (4). The directed differentiation of the embryoid body cells led to hematopoietic precursor cells (5)that were subsequently introduced into a mouse exposed to ionizing radiation (6).

The induced pluripotent stem cells are an excellent model for pathogenetic studies at the celllevel and testing compounds possessing a possible therapeutic effect.

The induced pluripotent stem cells were produced from the fibroblasts of a patient with spinalmuscular atrophy (SMA) (SMAiPSCs). SMA is an autosomalrecessive disease caused by a mutation in the SMN1 ( survival motorneuron 1 ) gene, which is manifested as the selective nonviability of lower motor neurons. Patients with this disorder usually die at the age of about two years.Existing experimental models of this disorder based on the use of flatworms, drosophila, andmice are not satisfactory. The available fibroblast lines from patients withSMA cannot provide the necessary data on the pathogenesis of this disordereither. It was shown that motor neurons produced from SMAiPSCs canretain the features of SMA development, selective neuronal death, and the lackof SMN1 transcription. Moreover, the authors succeeded in elevating the SMNprotein level and aggregation (encoded by the SMN2 gene, whose expressioncan compensate for the shortage in the SMN1 protein) in response to the treatment of motorneurons and astrocytes produced from SMAiPSCs with valproate andtorbomycin [89;]. iPSCs and theirderivatives can serve as objects for pharmacological studies, as has been demonstrated oniPSCs from patients with familial dysautonomia (FDA) [90]. FDA is an inherited autosomal recessive disorder manifested as thedegeneration of sensor and autonomous neurons. This is due to a mutation causing thetissuespecific splicing of the IKBKAP gene, resulting in a decreasein the level of the fulllength IKAP protein. iPSCs were produced fromfibroblasts of patients with FDA. They possessed all features of pluripotent cells. Neuralderivatives produced from these cells had signs of FDA pathogenesis and low levels of thefulllength IKBKAP transcript. The authors studied the effect of threesubstances, kinetin, epigallocatechin gallate, and tocotrienol, on the parameters associatedwith FDA pathogenesis. Only kinetin has been shown to induce an increase in the level offulllength IKBKAP transcript. Prolonged treatment with kinetininduces an increase in the level of neuronal differentiation and expression of peripheralneuronal markers.

Currently, a broad spectrum of iPSCs is produced from patients with variousinherited pathologies and multifactorial disorders, such as Parkinsons disease, Downsyndrome, type 1 diabetes, Duchenne muscular dystrophy, talassemia, etc., whichare often lethal and can scarcely be treated with routine therapy [51, 87, 89, 9194]. The data on iPSCs produced by reprogramming somaticcells from patients with various pathologies are given in the .

Functional categories of M. tuberculosis genes with changed expression level during transition to the NC state

One can confidently state that both iPSCs themselves and their derivativesare potent instruments applicable in biomedicine, cell replacement therapy, pharmacology, andtoxicology. However, the safe application of iPSCbased technologies requires the use ofmethods of iPSCs production and their directed differentiation which minimizeboth the possibility of mutations in cell genomes under in vitro culturingand the probability of malignant transformation of the injected cells. The development ofmethods for human iPSC culturing without the use of animal cells (for instance, the feederlayer of murine fibroblasts) is necessary; they make a viralorigin pathogen transferfrom animals to humans impossible. There is a need for the maximum standardization ofconditions for cell culturing and differentiation.

This study was supported by the Russian Academy of Sciences Presidium ProgramMolecular and Cell Biology.

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Induced Pluripotent Stem Cells: Problems and Advantages ...

SUNNYVALE, Calif., April 12, 2022 (GLOBE NEWSWIRE) -- BioCardia, Inc.[Nasdaq: BCDA], a developer of cellular and cell-derived therapeutics for the treatment of cardiovascular and pulmonary diseases, today announced that the U.S. Food and Drug Administration (FDA) has approved the Company's Investigational New Drug (IND) application for BCDA-04, a proprietary allogeneic mesenchymal cell (MSC) population that is Neurokinin-1 receptor positive (NK1R+). This allows BioCardia to initiate its First-in-Human Phase I/II trial in adult patients recovering from Acute Respiratory Distress Syndrome (ARDS) due to COVID-19, with trial initiation expected in the third quarter of 2022.

The first part of the clinical trial will evaluate increasing doses of the NK1R+ MSCs and the optimal dose will be taken to Phase II in a randomized study in adult patients recovering from ARDS due to COVID-19. "This investigational cell therapy is administered intravenously (IV) and follows a significant body of compelling clinical results by NIH investigators and peer companies," said Ian McNiece, Ph.D., BioCardias Chief Scientific Officer. "After IV delivery, the cells migrate to the lungs for local therapeutic benefit. We expect the anti-inflammatory nature of these mesenchymal stem cells to have a positive impact in ARDS because of the interaction of the Neurokinin-1 receptors with Substance P, a neuropeptide that has long been known to be a primary mediator of inflammation in the lungs. Our goal is to help recovering patients with ARDS due to COVID-19 recover faster and more fully, while avoiding longer term respiratory issues."

"In addition to our critically important autologous cell therapies being studied for ischemic heart failure and chronic myocardial ischemia with refractory angina, the FDA's acceptance of this IND for patients recovering from ARDS is an important milestone in the development of our allogeneic mesenchymal stem cell therapy platform and validation for its potential to provide therapeutic benefit beyond the cardiovascular system," said Peter Altman, Ph.D., Chief Executive Officer. "Our off the shelf MSC platform may have significant advantages over others in clinical development for multiple indications because the MSCs express the biologically important NK1 receptor which binds Substance P. Our in-house clinical cell manufacturing is also expected to be an important strategic asset that enables rapid and cost-effective development."

About ARDS

Acute respiratory distress syndrome (ARDS) occurs when fluid builds up in the tiny, elastic air sacs (alveoli) in the lungs. The fluid keeps the lungs from filling with enough air, which means less oxygen reaches the bloodstream. This deprives organs of the oxygen they need to function. ARDS typically occurs in people who are already critically ill or who have significant injuries. Severe shortness of breath the main symptom of ARDS usually develops within a few hours to a few days after the precipitating injury or infection. Many people who develop ARDS don't survive. The risk of death increases with age and severity of illness. Of the people who do survive ARDS, some recover completely while others experience lasting damage to their lungs1. Based on preliminary clinical reports on COVID-19, respiratory failure complicated by ARDs is the leading cause of death for COVID-19 patients.2 Despite multiple clinical studies, no pharmacological treatments have proven effective for ARDS.3, 4

About BioCardia

BioCardia, Inc., headquartered in Sunnyvale, California, is developing cellular and cell-derived therapeutics for the treatment of cardiovascular and pulmonary disease. CardiAMP autologous and NK1R+ allogeneic cell therapies are the Companys biotherapeutic platforms that enable four product candidates in clinical development. The CardiAMP Cell Therapy Heart Failure Trial investigational product has been granted Breakthrough designation by the FDA, has CMS reimbursement, and is supported financially by the Maryland Stem Cell Research Fund. The CardiAMP Chronic Myocardial Ischemia Trial also has CMS reimbursement. For more information visit:www.BioCardia.com.

FORWARD LOOKING STATEMENTS

This press release contains forward-looking statements that are subject to many risks and uncertainties. Forward-looking statements include, among other things, initiation of our BCDA-04 clinical trial, and the mechanism of action and ease of administration of our NK1R+ MSC therapy.

We may use terms such as believes, estimates, anticipates, expects, plans, intends, may, could, might, will, should, approximately or other words that convey the uncertainty of future events or outcomes to identify these forward-looking statements. Although we believe that we have a reasonable basis for each forward-looking statement contained herein, we caution you that forward-looking statements are not guarantees of future performance and that our actual results may differ materially from the forward-looking statements contained in this press release. As a result of these factors, we cannot assure you that the forward-looking statements in this press release will prove to be accurate. Additional factors that could materially affect actual results can be found in BioCardias Form 10-K filed with the Securities and Exchange Commission on March 29, 2022, under the caption titled Risk Factors. BioCardia expressly disclaims any intent or obligation to update these forward-looking statements, except as required by law.

_________________________________________________________________________________________________________

Media Contact:Anne Laluc, MarketingEmail:alaluc@BioCardia.comPhone: 650-226-0120

Investor Contact:David McClung, Chief Financial OfficerEmail:dmcclung@BioCardia.comPhone: 650-226-0120

(1)MayoClinic.Org

(2)Rajagopal K, Keller SP, Akkanti B, et al. Advanced pulmonary and cardiac support of COVID-19 patients, emerging recommendations from ASAIOa living working document. Circ Heart Fail. 2020 May;13(5).

(3)Thompson BT, Chambers RC, Liu KD (2017) Acute respiratory distress syndrome. N Engl J Med 377(19):19041905.

(4)3. Group RC, Horby P, Lim WS et al (2020) Dexamethasone in hospitalized patients with Covid-19preliminary report. N Engl J Med.

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BioCardia Announces FDA Approval of Its IND for NK1R+ Mesenchymal Stem Cells for the Treatment of Patients Recovering from Acute Respiratory Distress...

The latest study of the Personalized Cell Therapy MarketStatistics2022Report providesan elaborative analysis of the market size, industry share, growth, development, and competitive landscape. The report also provides a comprehensive analysis of the sales volume, revenue, gross margin, and price growth in the Personalized Cell TherapyMarket. Many key points covered in the report, include recent development in the global market, such as mergers and acquisitions, SWOT analysis, competitive landscape, industry trends, and company profiles.

Leading Key Players Covered in the GlobalPersonalized Cell Therapy Market Research Report:

Novartis AG, Vericel Corporation, Bellicum Pharmaceuticals, MolMed SpA, Cytori Therapeutics Inc, Gilead Sciences, Inc, Celgene Corporation, Bluebird Bio, Aurora Biopharma Inc, Saneron CCEL TherapeuticsInc, Kuur Therapeutics, MediGene AG, Sangamo Therapeutics

Get a Sample PDF of the Report @ https://www.alexareports.com/report-sample/2856089

Market Segment by Types:

By Cell Type, Hematopoietic Stem Cell, Skeletal Muscle Stem Cell/Mesenchymal Stem Cells/Lymphocytes, By Technique, Platelet Transfusions/Bone Marrow Transplantation/Packed Red Cell Transfusions/Organ Transplantation

Market Segment by Applications:

Cardiovascular Diseases, Neurological Disorders, Inflammatory Diseases, Diabetes, Cancer

Market Segment by Regions:

Table of Contents

Section 1 Personalized Cell Therapy Market Overview

Section 2 Global Personalized Cell Therapy Market Key Players Share

Section 3 Key PlayersPersonalized Cell Therapy Business Introduction

Section 4 Global Personalized Cell Therapy Market Segmentation (By Region)

Section 5 Global Personalized Cell Therapy Market Segmentation (by Product Type)

Section 6 Global Personalized Cell Therapy Market Segmentation (by Application)

Section 7 Global Personalized Cell Therapy Market Segmentation (by Channel)

Section 8 Personalized Cell Therapy Market Forecast 2021-2026

Section 9 Personalized Cell Therapy Application and Client Analysis

Section 10 Personalized Cell Therapy Manufacturing Cost of Analysis

Section 11 Conclusion

Section 12 Methodology and Data Source

If any customization or requirements in the research study, please let us know Alexa Reportsoffer the report as you want.

Customized Report @ https://www.alexareports.com/send-an-enquiry/2856089

About Us:

Alexa Reports is a globally celebrated premium market research service provider, with a strong legacy of empowering businesses with years of experience. We help our clients by implementing a decision support system through progressive statistical surveying, in-depth market analysis, and reliable forecast data.

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Personalized Cell Therapy Market Size by Applications, Company Profiles, Product Types, Revenue and Forecast to 2026 ChattTenn Sports - ChattTenn...

Relatlimab is the third immune checkpoint inhibitor from Bristol Myers Squibb, adding to the Company's growing and differentiated oncology portfolio

Bristol Myers Squibb (NYSE: BMY) today announced that Opdualag TM (nivolumab and relatlimab-rmbw), a new, first-in-class, fixed-dose combination of nivolumab and relatlimab, administered as a single intravenous infusion, was approved by the U.S. Food and Drug Administration (FDA) for the treatment of adult and pediatric patients 12 years of age or older with unresectable or metastatic melanoma. 1 The approval is based on the Phase 2/3 RELATIVITY-047 trial, which compared Opdualag (n=355) to nivolumab alone (n=359). 1,2

This press release features multimedia. View the full release here: https://www.businesswire.com/news/home/20220304005561/en/

Opdualag Logo, Bristol Myers Squibb

The trial met its primary endpoint, progression-free survival (PFS), and Opdualag more than doubled the median PFS when compared to nivolumab monotherapy, 10.1 months (95% Confidence Interval [CI]: 6.4 to 15.7) versus 4.6 months (95% CI: 3.4 to 5.6); (Hazard Ratio [HR] 0.75; 95% CI: 0.62 to 0.92, P =0.0055). 1 The Opdualag safety profile was similar to that previously reported for nivolumab. 1,2 No new safety events were identified with the combination when compared to nivolumab monotherapy. 1,2 Grade 3/4 drug-related adverse events were 18.9% in the Opdualag arm compared to 9.7% in the nivolumab arm. 2 Drug-related adverse events leading to discontinuation were 14.6% in the Opdualag arm compared to 6.7% in the nivolumab arm. 2

"Since the approval of the first immune checkpoint inhibitor more than 10 years ago, we've seen immunotherapy, alone and in combination, revolutionize the treatment of patients with advanced melanoma," said F. Stephen Hodi, M.D., director of the Melanoma Center and the Center for Immuno-Oncology at Dana-Farber Cancer Institute. 3 "Today's approval is particularly significant, as it introduces an entirely new combination of two immunotherapies that may act together to help improve anti-tumor response by targeting two different immune checkpoints LAG-3 and PD-1." 1,2

Opdualag is associated with the following Warnings & Precautions: severe and fatal immune-mediated adverse reactions (IMARs) including pneumonitis, colitis, hepatitis, endocrinopathies, nephritis with renal dysfunction, dermatologic adverse reactions, myocarditis and other immune-mediated adverse reactions; infusion-related reactions; complications of allogeneic hematopoietic stem cell transplantation (HSCT); and embryo-fetal toxicity. 1 Please see Important Safety Information below.

"While we have made great progress in the treatment of advanced melanoma over the past decade, we are committed to expanding dual immunotherapy treatment options for these patients," said Samit Hirawat, chief medical officer, global drug development, Bristol Myers Squibb. 3 "Inhibiting LAG-3 with relatlimab, in a fixed-dose combination with nivolumab, represents a new treatment approach that builds on our legacy of bringing innovative immunotherapy options to patients. The approval of a new medicine that includes our third distinct checkpoint inhibitor marks an important step forward in giving patients more options beyond monotherapy treatment."

Lymphocyte activation gene-3 (LAG-3) and programmed death-1 (PD-1) are two distinct inhibitory immune checkpoints that are often co-expressed on tumor-infiltrating lymphocytes, thus contributing to tumor-mediated T-cell exhaustion. 2 The combination of nivolumab (anti-PD-1) and relatlimab (anti-LAG-3) results in increased T-cell activation compared to the activity of either antibody alone. 1 Relatlimab (in combination with nivolumab) is the first LAG-3-blocking antibody to demonstrate a benefit in a Phase 3 study. 1 It is the third checkpoint inhibitor (along with anti-PD-1 and anti-CTLA-4) for Bristol Myers Squibb.

"Today's approval is exciting news and offers new hope to the melanoma community. The availability of this treatment combination may enable patients to potentially benefit from a new, first-in-class dual immunotherapy," said Michael Kaplan, president and CEO, Melanoma Research Alliance.

The FDA-approved dosing for adult patients and pediatric patients 12 years of age or older who weigh at least 40 kg is 480 mg nivolumab and 160 mg relatlimab administered intravenously every four weeks. 1 The recommended dosage for pediatric patients 12 years of age or older who weigh less than 40 kg, and pediatric patients younger than 12 years of age, has not been established. 1

This application was approved under the FDA's Real-Time Oncology Review (RTOR) pilot program, which aims to ensure that safe and effective treatments are available to patients as early as possible. 4 The review was also conducted under the FDA's Project Orbis initiative, which enabled concurrent review by the health authorities in Australia, Brazil and Switzerland, where the application remains under review.

About RELATIVITY-047

RELATIVITY-047 is a global, randomized, double-blind Phase 2/3 study evaluating the fixed-dose combination of nivolumab and relatlimab versus nivolumab alone in patients with previously untreated metastatic or unresectable melanoma. 1,2 The trial excluded patients with active autoimmune disease, medical conditions requiring systemic treatment with moderate or high dose corticosteroids or immunosuppressive medications, uveal melanoma, and active or untreated brain or leptomeningeal metastases. 1 The primary endpoint of the trial is progression-free survival (PFS) determined by Blinded Independent Central Review (BICR) using Response Evaluation Criteria in Solid Tumors (RECIST v1.1). 1 The secondary endpoints are overall survival (OS) and objective response rate (ORR). 1 A total of 714 patients were randomized 1:1 to receive a fixed-dose combination of nivolumab (480 mg) and relatlimab (160 mg) or nivolumab (480 mg) by intravenous infusion every four weeks until disease progression or unacceptable toxicity. 1

Select Safety Profile From RELATIVITY-047

Adverse reactions leading to permanent discontinuation of Opdualag occurred in 18% of patients. 1 Opdualag was interrupted due to an adverse reaction in 43% of patients. 1 Serious adverse reactions occurred in 36% of patients treated with Opdualag. 1 The most frequent (1%) serious adverse reactions were adrenal insufficiency (1.4%), anemia (1.4%), colitis (1.4%), pneumonia (1.4%), acute myocardial infarction (1.1%), back pain (1.1%), diarrhea (1.1%), myocarditis (1.1%), and pneumonitis (1.1%). 1 Fatal adverse reactions occurred in three (0.8%) patients treated with Opdualag and included hemophagocytic lymphohistiocytosis, acute edema of the lung, and pneumonitis. 1 The most common (20%) adverse reactions were musculoskeletal pain (45%), fatigue (39%), rash (28%), pruritus (25%), and diarrhea (24%). 1 The Opdualag safety profile was similar to that previously reported for nivolumab. 1,2 No new safety events were identified with the combination when compared to nivolumab monotherapy. 1,2 Grade 3/4 drug-related adverse events were 18.9% in the Opdualag arm compared to 9.7% in the nivolumab arm. 2 Drug-related adverse events leading to discontinuation were 14.6% in the Opdualag arm compared to 6.7% in the nivolumab arm. 2

About Melanoma

Melanoma is a form of skin cancer characterized by the uncontrolled growth of pigment-producing cells (melanocytes) located in the skin. 5 Metastatic melanoma is the deadliest form of the disease and occurs when cancer spreads beyond the surface of the skin to other organs. 5,6 The incidence of melanoma has been increasing steadily for the last 30 years. 5,6 In the United States, approximately 99,780 new diagnoses of melanoma and about 7,650 related deaths are estimated for 2022. 5 Melanoma can be mostly treatable when caught in its very early stages; however, survival rates can decrease as the disease progresses. 6

OPDUALAG INDICATION

Opdualag TM (nivolumab and relatlimab-rmbw) is indicated for the treatment of adult and pediatric patients 12 years of age or older with unresectable or metastatic melanoma.

OPDUALAG IMPORTANT SAFETY INFORMATION

Severe and Fatal Immune-Mediated Adverse Reactions

Immune-mediated adverse reactions (IMARs) listed herein may not include all possible severe and fatal immune-mediated adverse reactions.

IMARs which may be severe or fatal, can occur in any organ system or tissue. IMARs can occur at any time after starting treatment with a LAG-3 and PD-1/PD-L1 blocking antibodies. While IMARs usually manifest during treatment, they can also occur after discontinuation of Opdualag. Early identification and management of IMARs are essential to ensure safe use. Monitor patients closely for symptoms and signs that may be clinical manifestations of underlying IMARs. Evaluate clinical chemistries including liver enzymes, creatinine, and thyroid function at baseline and periodically during treatment. In cases of suspected IMARs, initiate appropriate workup to exclude alternative etiologies, including infection. Institute medical management promptly, including specialty consultation as appropriate.

Withhold or permanently discontinue Opdualag depending on severity (please see section 2 Dosage and Administration in the accompanying Full Prescribing Information). In general, if Opdualag requires interruption or discontinuation, administer systemic corticosteroid therapy (1 to 2 mg/kg/day prednisone or equivalent) until improvement to Grade 1 or less. Upon improvement to Grade 1 or less, initiate corticosteroid taper and continue to taper over at least 1 month. Consider administration of other systemic immunosuppressants in patients whose IMARs are not controlled with corticosteroid therapy. Toxicity management guidelines for adverse reactions that do not necessarily require systemic steroids (e.g., endocrinopathies and dermatologic reactions) are discussed below.

Immune-Mediated Pneumonitis

Opdualag can cause immune-mediated pneumonitis, which may be fatal. In patients treated with other PD-1/PD-L1 blocking antibodies, the incidence of pneumonitis is higher in patients who have received prior thoracic radiation. Immune-mediated pneumonitis occurred in 3.7% (13/355) of patients receiving Opdualag, including Grade 3 (0.6%), and Grade 2 (2.3%) adverse reactions. Pneumonitis led to permanent discontinuation of Opdualag in 0.8% and withholding of Opdualag in 1.4% of patients.

Immune-Mediated Colitis

Opdualag can cause immune-mediated colitis, defined as requiring use of corticosteroids and no clear alternate etiology. A common symptom included in the definition of colitis was diarrhea. Cytomegalovirus infection/reactivation has been reported in patients with corticosteroid-refractory immune-mediated colitis. In cases of corticosteroid-refractory colitis, consider repeating infectious workup to exclude alternative etiologies.

Immune-mediated diarrhea or colitis occurred in 7% (24/355) of patients receiving Opdualag, including Grade 3 (1.1%) and Grade 2 (4.5%) adverse reactions. Colitis led to permanent discontinuation of Opdualag in 2% and withholding of Opdualag in 2.8% of patients.

Immune-Mediated Hepatitis

Opdualag can cause immune-mediated hepatitis, defined as requiring the use of corticosteroids and no clear alternate etiology.

Immune-mediated hepatitis occurred in 6% (20/355) of patients receiving Opdualag, including Grade 4 (0.6%), Grade 3 (3.4%), and Grade 2 (1.4%) adverse reactions. Hepatitis led to permanent discontinuation of Opdualag in 1.7% and withholding of Opdualag in 2.3% of patients.

Immune-Mediated Endocrinopathies

Opdualag can cause primary or secondary adrenal insufficiency, hypophysitis, thyroid disorders, and Type 1 diabetes mellitus, which can be present with diabetic ketoacidosis. Withhold or permanently discontinue Opdualag depending on severity (please see section 2 Dosage and Administration in the accompanying Full Prescribing Information).

For Grade 2 or higher adrenal insufficiency, initiate symptomatic treatment, including hormone replacement as clinically indicated. In patients receiving Opdualag, adrenal insufficiency occurred in 4.2% (15/355) of patients receiving Opdualag, including Grade 3 (1.4%) and Grade 2 (2.5%) adverse reactions. Adrenal insufficiency led to permanent discontinuation of Opdualag in 1.1% and withholding of Opdualag in 0.8% of patients.

Hypophysitis can present with acute symptoms associated with mass effect such as headache, photophobia, or visual field defects. Hypophysitis can cause hypopituitarism; initiate hormone replacement as clinically indicated. Hypophysitis occurred in 2.5% (9/355) of patients receiving Opdualag, including Grade 3 (0.3%) and Grade 2 (1.4%) adverse reactions. Hypophysitis led to permanent discontinuation of Opdualag in 0.3% and withholding of Opdualag in 0.6% of patients.

Thyroiditis can present with or without endocrinopathy. Hypothyroidism can follow hyperthyroidism; initiate hormone replacement or medical management as clinically indicated. Thyroiditis occurred in 2.8% (10/355) of patients receiving Opdualag, including Grade 2 (1.1%) adverse reactions. Thyroiditis did not lead to permanent discontinuation of Opdualag. Thyroiditis led to withholding of Opdualag in 0.3% of patients. Hyperthyroidism occurred in 6% (22/355) of patients receiving Opdualag, including Grade 2 (1.4%) adverse reactions. Hyperthyroidism did not lead to permanent discontinuation of Opdualag. Hyperthyroidism led to withholding of Opdualag in 0.3% of patients. Hypothyroidism occurred in 17% (59/355) of patients receiving Opdualag, including Grade 2 (11%) adverse reactions. Hypothyroidism led to the permanent discontinuation of Opdualag in 0.3% and withholding of Opdualag in 2.5% of patients.

Monitor patients for hyperglycemia or other signs and symptoms of diabetes; initiate treatment with insulin as clinically indicated. Diabetes occurred in 0.3% (1/355) of patients receiving Opdualag, a Grade 3 (0.3%) adverse reaction, and no cases of diabetic ketoacidosis. Diabetes did not lead to the permanent discontinuation or withholding of Opdualag in any patient.

Immune-Mediated Nephritis with Renal Dysfunction

Opdualag can cause immune-mediated nephritis, which is defined as requiring use of steroids and no clear etiology. In patients receiving Opdualag, immune-mediated nephritis and renal dysfunction occurred in 2% (7/355) of patients, including Grade 3 (1.1%) and Grade 2 (0.8%) adverse reactions. Immune-mediated nephritis and renal dysfunction led to permanent discontinuation of Opdualag in 0.8% and withholding of Opdualag in 0.6% of patients.

Withhold or permanently discontinue Opdualag depending on severity (please see section 2 Dosage and Administration in the accompanying Full Prescribing Information).

Immune-Mediated Dermatologic Adverse Reactions

Opdualag can cause immune-mediated rash or dermatitis, defined as requiring use of steroids and no clear alternate etiology. Exfoliative dermatitis, including Stevens-Johnson syndrome, toxic epidermal necrolysis, and Drug Rash with eosinophilia and systemic symptoms has occurred with PD-1/L-1 blocking antibodies. Topical emollients and/or topical corticosteroids may be adequate to treat mild to moderate non-exfoliative rashes.

Withhold or permanently discontinue Opdualag depending on severity (please see section 2 Dosage and Administration in the accompanying Full Prescribing Information).

Immune-mediated rash occurred in 9% (33/355) of patients, including Grade 3 (0.6%) and Grade 2 (3.4%) adverse reactions. Immune-mediated rash did not lead to permanent discontinuation of Opdualag. Immune-mediated rash led to withholding of Opdualag in 1.4% of patients.

Immune-Mediated Myocarditis

Opdualag can cause immune-mediated myocarditis, which is defined as requiring use of steroids and no clear alternate etiology. The diagnosis of immune-mediated myocarditis requires a high index of suspicion. Patients with cardiac or cardio-pulmonary symptoms should be assessed for potential myocarditis. If myocarditis is suspected, withhold dose, promptly initiate high dose steroids (prednisone or methylprednisolone 1 to 2 mg/kg/day) and promptly arrange cardiology consultation with diagnostic workup. If clinically confirmed, permanently discontinue Opdualag for Grade 2-4 myocarditis.

Myocarditis occurred in 1.7% (6/355) of patients receiving Opdualag, including Grade 3 (0.6%), and Grade 2 (1.1%) adverse reactions. Myocarditis led to permanent discontinuation of Opdualag in 1.7% of patients.

Other Immune-Mediated Adverse Reactions

The following clinically significant IMARs occurred at an incidence of ardiac/Vascular: pericarditis, vasculitis; Nervous System: meningitis, encephalitis, myelitis and demyelination, myasthenic syndrome/myasthenia gravis (including exacerbation), Guillain-Barr syndrome, nerve paresis, autoimmune neuropathy; Ocular: uveitis, iritis, and other ocular inflammatory toxicities can occur. Some cases can be associated with retinal detachment. Various grades of visual impairment, including blindness, can occur. If uveitis occurs in combination with other IMARs, consider a Vogt-Koyanagi-Haradalike syndrome, as this may require treatment with systemic steroids to reduce the risk of permanent vision loss; Gastrointestinal: pancreatitis including increases in serum amylase and lipase levels, gastritis, duodenitis; Musculoskeletal and Connective Tissue: myositis/polymyositis, rhabdomyolysis (and associated sequelae including renal failure), arthritis, polymyalgia rheumatica; Endocrine: hypoparathyroidism; Other (Hematologic/Immune) : hemolytic anemia, aplastic anemia, hemophagocytic lymphohistiocytosis, systemic inflammatory response syndrome, histiocytic necrotizing lymphadenitis (Kikuchi lymphadenitis), sarcoidosis, immune thrombocytopenic purpura, solid organ transplant rejection.

Infusion-Related Reactions

Opdualag can cause severe infusion-related reactions. Discontinue Opdualag in patients with severe or life-threatening infusion-related reactions. Interrupt or slow the rate of infusion in patients with mild to moderate infusion-related reactions. In patients who received Opdualag as a 60-minute intravenous infusion, infusion-related reactions occurred in 7% (23/355) of patients.

Complications of Allogeneic Hematopoietic Stem Cell Transplantation (HSCT)

Fatal and other serious complications can occur in patients who receive allogeneic hematopoietic stem cell transplantation (HSCT) before or after being treated with a PD-1/PD-L1 receptor blocking antibody. Transplant-related complications include hyperacute graft-versus-host disease (GVHD), acute GVHD, chronic GVHD, hepatic veno-occlusive disease after reduced intensity conditioning, and steroid-requiring febrile syndrome (without an identified infectious cause). These complications may occur despite intervening therapy between PD-1/PD-L1 blockade and allogeneic HSCT.

Follow patients closely for evidence of transplant-related complications and intervene promptly. Consider the benefit versus risks of treatment with a PD-1/PD-L1 receptor blocking antibody prior to or after an allogeneic HSCT.

Embryo-Fetal Toxicity

Based on its mechanism of action and data from animal studies, Opdualag can cause fetal harm when administered to a pregnant woman. Advise pregnant women of the potential risk to a fetus. Advise females of reproductive potential to use effective contraception during treatment with Opdualag for at least 5 months after the last dose of Opdualag.

Lactation

There are no data on the presence of Opdualag in human milk, the effects on the breastfed child, or the effect on milk production. Because nivolumab and relatlimab may be excreted in human milk and because of the potential for serious adverse reactions in a breastfed child, advise patients not to breastfeed during treatment with Opdualag and for at least 5 months after the last dose.

Serious Adverse Reactions

In Relativity-047, fatal adverse reaction occurred in 3 (0.8%) patients who were treated with Opdualag; these included hemophagocytic lymphohistiocytosis, acute edema of the lung, and pneumonitis. Serious adverse reactions occurred in 36% of patients treated with Opdualag. The most frequent serious adverse reactions reported in 1% of patients treated with Opdualag were adrenal insufficiency (1.4%), anemia (1.4%), colitis (1.4%), pneumonia (1.4%), acute myocardial infarction (1.1%), back pain (1.1%), diarrhea (1.1%), myocarditis (1.1%), and pneumonitis (1.1%).

Common Adverse Reactions and Laboratory Abnormalities

The most common adverse reactions reported in 20% of the patients treated with Opdualag were musculoskeletal pain (45%), fatigue (39%), rash (28%), pruritus (25%), and diarrhea (24%).

The most common laboratory abnormalities that occurred in 20% of patients treated with Opdualag were decreased hemoglobin (37%), decreased lymphocytes (32%), increased AST (30%), increased ALT (26%), and decreased sodium (24%).

Please see U.S. Full Prescribing Information for Opdualag .

OPDIVO + YERVOY INDICATIONS

OPDIVO (nivolumab), as a single agent, is indicated for the treatment of patients with unresectable or metastatic melanoma.

OPDIVO (nivolumab), in combination with YERVOY (ipilimumab), is indicated for the treatment of patients with unresectable or metastatic melanoma.

OPDIVO + YERVOY IMPORTANT SAFETY INFORMATION

Severe and Fatal Immune-Mediated Adverse Reactions

Immune-mediated adverse reactions listed herein may not include all possible severe and fatal immune-mediated adverse reactions.

Immune-mediated adverse reactions, which may be severe or fatal, can occur in any organ system or tissue. While immune-mediated adverse reactions usually manifest during treatment, they can also occur after discontinuation of OPDIVO or YERVOY. Early identification and management are essential to ensure safe use of OPDIVO and YERVOY. Monitor for signs and symptoms that may be clinical manifestations of underlying immune-mediated adverse reactions. Evaluate clinical chemistries including liver enzymes, creatinine, adrenocorticotropic hormone (ACTH) level, and thyroid function at baseline and periodically during treatment with OPDIVO and before each dose of YERVOY. In cases of suspected immune-mediated adverse reactions, initiate appropriate workup to exclude alternative etiologies, including infection. Institute medical management promptly, including specialty consultation as appropriate.

Withhold or permanently discontinue OPDIVO and YERVOY depending on severity (please see section 2 Dosage and Administration in the accompanying Full Prescribing Information). In general, if OPDIVO or YERVOY interruption or discontinuation is required, administer systemic corticosteroid therapy (1 to 2 mg/kg/day prednisone or equivalent) until improvement to Grade 1 or less. Upon improvement to Grade 1 or less, initiate corticosteroid taper and continue to taper over at least 1 month. Consider administration of other systemic immunosuppressants in patients whose immune-mediated adverse reactions are not controlled with corticosteroid therapy. Toxicity management guidelines for adverse reactions that do not necessarily require systemic steroids (e.g., endocrinopathies and dermatologic reactions) are discussed below.

Immune-Mediated Pneumonitis

OPDIVO and YERVOY can cause immune-mediated pneumonitis. The incidence of pneumonitis is higher in patients who have received prior thoracic radiation. In patients receiving OPDIVO monotherapy, immune-mediated pneumonitis occurred in 3.1% (61/1994) of patients, including Grade 4 (

In patients receiving OPDIVO 1 mg/kg with YERVOY 3 mg/kg every 3 weeks, immune-mediated pneumonitis occurred in 7% (31/456) of patients, including Grade 4 (0.2%), Grade 3 (2.0%), and Grade 2 (4.4%).

Immune-Mediated Colitis

OPDIVO and YERVOY can cause immune-mediated colitis, which may be fatal. A common symptom included in the definition of colitis was diarrhea. Cytomegalovirus (CMV) infection/reactivation has been reported in patients with corticosteroid-refractory immune-mediated colitis. In cases of corticosteroid-refractory colitis, consider repeating infectious workup to exclude alternative etiologies. In patients receiving OPDIVO monotherapy, immune-mediated colitis occurred in 2.9% (58/1994) of patients, including Grade 3 (1.7%) and Grade 2 (1%). In patients receiving OPDIVO 1 mg/kg with YERVOY 3 mg/kg every 3 weeks, immune-mediated colitis occurred in 25% (115/456) of patients, including Grade 4 (0.4%), Grade 3 (14%) and Grade 2 (8%).

Immune-Mediated Hepatitis and Hepatotoxicity

OPDIVO and YERVOY can cause immune-mediated hepatitis. In patients receiving OPDIVO monotherapy, immune-mediated hepatitis occurred in 1.8% (35/1994) of patients, including Grade 4 (0.2%), Grade 3 (1.3%), and Grade 2 (0.4%). In patients receiving OPDIVO 1 mg/kg with YERVOY 3 mg/kg every 3 weeks, immune-mediated hepatitis occurred in 15% (70/456) of patients, including Grade 4 (2.4%), Grade 3 (11%), and Grade 2 (1.8%).

Immune-Mediated Endocrinopathies

OPDIVO and YERVOY can cause primary or secondary adrenal insufficiency, immune-mediated hypophysitis, immune-mediated thyroid disorders, and Type 1 diabetes mellitus, which can present with diabetic ketoacidosis. Withhold OPDIVO and YERVOY depending on severity (please see section 2 Dosage and Administration in the accompanying Full Prescribing Information). For Grade 2 or higher adrenal insufficiency, initiate symptomatic treatment, including hormone replacement as clinically indicated. Hypophysitis can present with acute symptoms associated with mass effect such as headache, photophobia, or visual field defects. Hypophysitis can cause hypopituitarism; initiate hormone replacement as clinically indicated. Thyroiditis can present with or without endocrinopathy. Hypothyroidism can follow hyperthyroidism; initiate hormone replacement or medical management as clinically indicated. Monitor patients for hyperglycemia or other signs and symptoms of diabetes; initiate treatment with insulin as clinically indicated.

In patients receiving OPDIVO monotherapy, adrenal insufficiency occurred in 1% (20/1994), including Grade 3 (0.4%) and Grade 2 (0.6%).In patients receiving OPDIVO 1 mg/kg with YERVOY 3 mg/kg every 3 weeks, adrenal insufficiency occurred in 8% (35/456), including Grade 4 (0.2%), Grade 3 (2.4%), and Grade 2 (4.2%). In patients receiving OPDIVO 1 mg/kg with YERVOY 3 mg/kg every 3 weeks, adrenal insufficiency occurred in 8% (35/456), including Grade 4 (0.2%), Grade 3 (2.4%), and Grade 2 (4.2%).

In patients receiving OPDIVO monotherapy, hypophysitis occurred in 0.6% (12/1994) of patients, including Grade 3 (0.2%) and Grade 2 (0.3%). In patients receiving OPDIVO 1 mg/kg with YERVOY 3 mg/kg every 3 weeks, hypophysitis occurred in 9% (42/456), including Grade 3 (2.4%) and Grade 2 (6%).

In patients receiving OPDIVO monotherapy, thyroiditis occurred in 0.6% (12/1994) of patients, including Grade 2 (0.2%).

In patients receiving OPDIVO monotherapy, hyperthyroidism occurred in 2.7% (54/1994) of patients, including Grade 3 (

In patients receiving OPDIVO monotherapy, hypothyroidism occurred in 8% (163/1994) of patients, including Grade 3 (0.2%) and Grade 2 (4.8%). In patients receiving OPDIVO 1 mg/kg with YERVOY 3 mg/kg every 3 weeks, hypothyroidism occurred in 20% (91/456) of patients, including Grade 3 (0.4%) and Grade 2 (11%).

In patients receiving OPDIVO monotherapy, diabetes occurred in 0.9% (17/1994) of patients, including Grade 3 (0.4%) and Grade 2 (0.3%), and 2 cases of diabetic ketoacidosis.

Immune-Mediated Nephritis with Renal Dysfunction

OPDIVO and YERVOY can cause immune-mediated nephritis. In patients receiving OPDIVO monotherapy, immune-mediated nephritis and renal dysfunction occurred in 1.2% (23/1994) of patients, including Grade 4 (

Immune-Mediated Dermatologic Adverse Reactions

OPDIVO can cause immune-mediated rash or dermatitis. Exfoliative dermatitis, including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and drug rash with eosinophilia and systemic symptoms (DRESS) has occurred with PD-1/PD-L1 blocking antibodies. Topical emollients and/or topical corticosteroids may be adequate to treat mild to moderate nonexfoliative rashes.

YERVOY can cause immune-mediated rash or dermatitis, including bullous and exfoliative dermatitis, SJS, TEN, and DRESS. Topical emollients and/or topical corticosteroids may be adequate to treat mild to moderate non-bullous/exfoliative rashes.

Withhold or permanently discontinue OPDIVO and YERVOY depending on severity (please see section 2 Dosage and Administration in the accompanying Full Prescribing Information).

In patients receiving OPDIVO monotherapy, immune-mediated rash occurred in 9% (171/1994) of patients, including Grade 3 (1.1%) and Grade 2 (2.2%). In patients receiving OPDIVO 1 mg/kg with YERVOY 3 mg/kg every 3 weeks, immune-mediated rash occurred in 28% (127/456) of patients, including Grade 3 (4.8%) and Grade 2 (10%).

Other Immune-Mediated Adverse Reactions

The following clinically significant immune-mediated adverse reactions occurred at an incidence of ocular: uveitis, iritis, and other ocular inflammatory toxicities can occur; gastrointestinal: pancreatitis to include increases in serum amylase and lipase levels, gastritis, duodenitis; musculoskeletal and connective tissue: myositis/polymyositis, rhabdomyolysis, and associated sequelae including renal failure, arthritis, polymyalgia rheumatica; endocrine: hypoparathyroidism; other (hematologic/immune): hemolytic anemia, aplastic anemia, hemophagocytic lymphohistiocytosis (HLH), systemic inflammatory response syndrome, histiocytic necrotizing lymphadenitis (Kikuchi lymphadenitis), sarcoidosis, immune thrombocytopenic purpura, solid organ transplant rejection.

In addition to the immune-mediated adverse reactions listed above, across clinical trials of YERVOY monotherapy or in combination with OPDIVO, the following clinically significant immune-mediated adverse reactions, some with fatal outcome, occurred in nervous system: autoimmune neuropathy (2%), myasthenic syndrome/myasthenia gravis, motor dysfunction; cardiovascular: angiopathy, temporal arteritis; ocular: blepharitis, episcleritis, orbital myositis, scleritis; gastrointestinal: pancreatitis (1.3%); other (hematologic/immune): conjunctivitis, cytopenias (2.5%), eosinophilia (2.1%), erythema multiforme, hypersensitivity vasculitis, neurosensory hypoacusis, psoriasis.

Some ocular IMAR cases can be associated with retinal detachment. Various grades of visual impairment, including blindness, can occur. If uveitis occurs in combination with other immune-mediated adverse reactions, consider a Vogt-Koyanagi-Haradalike syndrome, which has been observed in patients receiving OPDIVO and YERVOY, as this may require treatment with systemic corticosteroids to reduce the risk of permanent vision loss.

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Despite progress involving the use of induced pluripotent stem cells (iPSCs) within disease modeling and drug discovery applications, it will be a long path to achieve the broad-scale use of iPSC-derived cell types in human patients.

Within a preclinical context, cell types differentiated from iPSCs are tested for their therapeutic response. Then, clinical trials are conducted to assure that essential parameters, such as tumorigenicity, dose toxicity, and immunogenicity, are assessed before authorizing the product for use in human patients. iPSC-derived cells have the potential to be used as therapies for treating cardiovascular, neurological, and metabolic diseases, as well as repairing damaged cartilage, spinal, motor neuron and eye tissues resulting from genetic defects or injuries.

In general, the targets for iPSC-derived therapies include any diseases or disorders for which there are no other viable treatments and where there is a need to repair or replace dysfunctional tissue.

Today, the following companies and organizations are forging the path toward iPSC-derived cell therapeutics.

While the groups above are involved with the development of iPSC-based cell therapeutics, not all of them have reached clinical-stage. Companies and organizations developing clinical-stage iPSC-derived therapeutics are described below.

In 2016, Cynata Therapeutics received a landmark approval to launch the worlds first formal clinical trial of an allogeneic iPSC-derived cell product (CYP-001) for the treatment of GvHD. In collaboration with Fujifilm, Cynata Therapeutics completed this Phase I trial in December 2018, reporting positive results.

Cynata Therapeutics is now testing its product candidate CYP-004 in a Phase 3 clinical trial enrolling up to 440 patients. CYP-004 is an allogeneic, iPSC-derived mesenchymal stem cell (MSC) product derived using Cynatas proprietary Cymerus technology. Led by the University of Sydney and funded by the Australian Government National Health and Medical Research Council (NHMRC), the trial will assess whether the cells can improve patient outcomes in osteoarthritis (OA).

It will be the worlds first clinical trial involving an iPSC-derived cell therapeutic to enter Phase 3 and the largest one ever completed.

In December 2019, the National Institutes of Health (NIH) announced it would be undertaking the first U.S. clinical trial of an iPSC-derived therapeutic. The goal of this trial is to restore dying cells of the retina. The Phase I/IIa clinical trial involves 12 patients with advanced-stage geographic atrophy who received an iPSC-derived retinal pigment epithelial (RPE) implant into a single eye. This trial is supported by the Ocular and Stem Cell Translational Research Section of the National Eye Institute (NEI). The NEI is part of the NIH.

In February 2019, allogeneic iPSC-derived NK cells produced by scientists from the University of Minnesota in collaboration with Fate Therapeutics were granted approval by FDA for a clinical trial. Specifically, Fate Therapeutics is exploring the clinical use of FT516 and FT500, which are its off-the-shelf, iPSC-derived natural killer (NK) cell product candidates. In December 2019, the company released promising clinical data from its Phase 1 studies.

In July 2020, Fate Therapeutics subsequently announced FDA clearance of its IND application for the worlds first iPSC-derived CAR T-cell therapy, FT819.FT819 is an off-the-shelf allogeneic chimeric antigen receptor (CAR) T-cell therapy targeting CD19+ malignancies. Notably, the use of a clonal master iPSC line as the starting cell source will position Fate to mass produce CAR T-cells to be delivered off-the-shelf to patients.

The Japanese company Healios K.K. is preparing, in collaboration with Sumitomo Dainippon Pharma, for a clinical trial using allogeneic iPSC-derived retinal cells to treat age-related macular degeneration (AMD).

Of course, there are also numerous physician-led studies underway in Japan investigating the use of iPSC-derived cellular products inhuman patients. These clinical trials are for diseases such as macular degeneration, ischemic cardiomyopathy, Parkinsons disease, solid tumors, spinal cord injury (SCI) and platelet production.

Details on each of these Japanese trials are provided below:

Significant progress has been made for retinal degeneration diseases, particularly for age-related macular degeneration (AMD). In 2009, preclinical data showed for the first time the recovery of visual function in patients injected with retinal pigment epithelium (RPE) differentiated from iPSCs in a rat models retina. A major breakthrough was made when the group led by Masayo Takahashi at the Riken Centre for Developmental Biology in Japan produced iPSC-RPE cell sheets in 2014.

The above-mentioned successes led to the initiation of the first iPSCs clinical trial in 2014 itself. Scientists at the RIKEN Centre in Japan transplanted an autologous iPSC-RPE cell sheet just below the affected retina, without immunosuppression, in a 77-year-old woman with AMD. One year after the transplantation, the progression of the degeneration simply halted, an area with photoreceptors recovery was observed, and the patients vision remained stable. There were no symptoms of immune rejection or tumor development.

In March 2017, Japanese scientists announced that a 60-year-old man was the first patient to receive iPSC-RPE cells derived from another person (an allogeneic source). A clinical-grade iPSC bank for collecting and storing healthy HLA homozygous donors is now being established at the Centre for iPS Cell Research and Application (CiRA) in Kyoto (Japan).

Also in 2017, iPSC-derived cardiomyocytes were grafted on to a porcine model of ischemic cardiomyopathy by Kawamura, et al., using a cell-sheet technique. Cardiac function was significantly improved, and neovasculogenesis was observed. Recently, scientists from Osaka University were granted approval for a clinical trial to transplant allogeneic sheets of tissue derived from iPSCs onto the diseased hearts of three human patients.

Several preclinical studies in spinal cord injuries using iPSC-derived neural progenitor cells in animal models have provided evidence for remyelination and locomotor function recovery. In February 2018, the Japanese government gave an approval to Professor Hideyuki Okano for a clinical trial that will involve the treatment of patients with spinal cord injuries at Keio University.

In September 2018, group of scientists from Kyoto University were granted approval to begin a transfusion trial using platelets derived from iPSCs into an individual with aplastic anemia. The hope is that iPSC-derived platelets could replace transfusions of donated blood.

As early as 2008, it was confirmed that iPSC-derived dopaminergic neurons improved the symptoms and dopaminergic function of a rat model of Parkinsons disease. Approximately a decade later, in October 2018, dopamine precursor cells were created from allogeneic iPSCs produced by Jun Takahashis research group at Kyoto University. Physicians at Kyoto University Hospital then transplanted these cells into subjects with Parkinsons disease. A total of seven patients were involved.

In July 2019, scientists at Osaka University started a clinical trial for limbal stem cell deficiency, a condition in which corneal stem cells are lost. The scientists grafted a sheet of iPSC-derived corneal cells onto the cornea of a patient. Within one month, her vision seemed to have improved.

What questions do you have about the development of iPSC-derived cell therapeutics? Ask them in the comments below.

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The Pipeline for of iPSC-Derived Cell Therapeutics in 2022 ...

Report Oceanpresents a new report onglobalcell therapy processing marketsize, share, growth, industry trends, and forecast 2030, covering various industry elements and growth trends helpful for predicting the markets future.

The global cell therapy processing market was valued at $1,695 million in 2018, and is projected to reach $12,062 million by 2026, registering a CAGR of 27.80% from 2019 to 2026.

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In order to produce a holistic assessment of the market, a variety of factors is considered, including demographics, business cycles, and microeconomic factors specific to the market under study. Global cell therapy processing market report 2021 also contains a comprehensive business analysis of the state of the business, which analyzes innovative ways for business growth and describes critical factors such as prime manufacturers, production value, key regions, and growth rate.

The Centers for Medicare and Medicaid Services report that US healthcare expenditures grew by 4.6% to US$ 3.8 trillion in 2019, or US$ 11,582 per person, and accounted for 17.7% of GDP. Also, the federal government accounted for 29.0% of the total health expenditures, followed by households (28.4%). State and local governments accounted for 16.1% of total health care expenditures, while other private revenues accounted for 7.5%.

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This study aims to define market sizes and forecast the values for different segments and countries in the coming eight years. The study aims to include qualitative and quantitative perspectives about the industry within the regions and countries covered in the report. The report also outlines the significant factors, such as driving factors and challenges, that will determine the markets future growth.

Cell therapy is the administration of living cells to replace a missing cell type or to offer a continuous source of a necessary factor to achieve a truly meaningful therapeutic outcome. There are different forms of cell therapy, ranging from transplantation of cells derived from an individual patient or from another donor. The manufacturing process of cell therapy requires the use of different products such as cell lines and instruments. These cell therapies are used for the treatment of various diseases such as cardiovascular disease and neurological disorders.

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Increase in the incidence of cardiovascular diseases, rise in the demand for chimeric antigen receptor (CAR) T cell therapy, increase in the R&D for the advancement in the research associated with cell therapy, increase in the potential of cell therapies in the treatment of diseases associated with lungs using stem cell therapies, and rise in understanding of the role of stem cells in inducing development of functional lung cells from both embryonic stem cells (ESCs) & induced pluripotent stem (iPS) cells are the key factors that fuel the growth of the cell therapy processing market.

Moreover, increase in a number of clinical studies relating to the development of cell therapy processing, rise in adoption of regenerative drug, introduction of novel technologies for cell therapy processing, increase in government investments for cell-based research, increase in number of GMP-certified production facilities, large number of oncology-oriented cell-based therapy clinical trials, and rise in the development of allogeneic cell therapy are other factors that augment the growth of the market. However, high-costs associated with the cell therapies, and bottlenecks experienced by manufacturers during commercialization of cell therapies are expected to hinder the growth of the market.

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The cell therapy processing market is segmented into offering type, application, and region. By type, the market is categorized into products, services, and software. The application covered in the segment include cardiovascular devices, bone repair, neurological disorders, skeletal muscle repair, cancer, and others. On the basis of region, the market is analyzed across North America (U.S., Canada, and Mexico), Europe (Germany, France, UK, Italy, Spain, and rest of Europe), Asia-Pacific (Japan, China, India, and rest of Asia-Pacific), and LAMEA (Latin America, Middle East, and Africa).

KEY BENEFITS FOR STAKEHOLDERS The study provides an in-depth analysis of the market along with the current trends and future estimations to elucidate the imminent investment pockets. It offers a quantitative analysis from 2018 to 2026, which is expected to enable the stakeholders to capitalize on the prevailing market opportunities. A comprehensive analysis of all the geographical regions is provided to determine the existing opportunities. The profiles and growth strategies of the key players are thoroughly analyzed to understand the competitive outlook of the global market.

LIST OF KEY PLAYERS PROFILED IN THE REPORT Cell Therapies Pty Ltd Invitrx Inc. Lonza Ltd Merck & Co., Inc. (FloDesign Sonics) NantWorks, LLC Neurogeneration, Inc. Novartis AG Plasticell Ltd. Regeneus Ltd StemGenex, Inc.

LIST OF OTHER PLAYERS IN THE VALUE CHAIN (These players are not profiled in the report. The same will be included on request.) Beckman Coulter, Inc. Stemcell Technologies MiltenyiBiotec GmbH

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KEY MARKET SEGMENTSBy Offering Type Products Services Software

By Application Cardiovascular Devices Bone Repair Neurological Disorders Skeletal Muscle Repair Cancer Others

By Region North Americao U.S.o Canadao Mexico Europeo Germanyo Franceo UKo Italyo Spaino Rest of Europe Asia-Pacifico Japano Chinao Indiao Rest of Asia-Pacific LAMEAo Latin Americao Middle Easto Africa

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What are the aspects of this report that relate to regional analysis?

The reports geographical regions include North America, Europe, Asia Pacific, Latin America, the Middle East, and Africa.

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Reports on the market include the growth rates of each region, which includes their countries, over the coming years.

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This report provides a comprehensive analysis of leading competitors in the market.

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This market report shows the projected market size for the cell therapy processing market at the end of the forecast period. The report also examines the historical and current market sizes.

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The report analyzes companies across the globe in detail.

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Cell Therapy Processing Market CAGR of 27.80% Share, Scope, Stake, Trends, Industry Size, Sales & Revenue, Growth, Opportunities and Demand with...

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Cardiac muscle cells or cardiomyocytes (also known as cardiac myocytes) are the muscle cells (myocytes) that make up the heart muscle. Cardiomyocytes go through a contraction-relaxation cycle that enables cardiac muscles to pump blood throughout the body.

[In this image] Immunostaining of human cardiomyocytes with antibodies for actin (red), myomesin (green), and nuclei (blue).Photo source: https://www.fujifilmcdi.com/products/cardiac-cells/icell-cardiomyocytes

Cardiomyocytes are highly specialized cell types in terms of their structures and functions. Each cardiomyocyte contains myofibrils, unique organelles consisting of long chains of sarcomeres, the fundamental contractile units of muscle cells.

[In this image] Cardiomyocyte geometry and cellular architecture are controlled by micropatterned ECM substrate. Scientists used this technique to study how cells sense and respond to mechanical forces.Photo source: https://diseasebiophysics.seas.harvard.edu/research/mechanotransduction/

The heart is a muscular organ that pumps blood through the blood vessels of the circulatory system. It is composed of individual heart muscle cells (cardiomyocytes) and several other cell types.

[In this figure] The anatomy of the human heart showing 4 heart chambers (left atrium, left ventricle, right atrium, right ventricle) and the blood flow. The myocardium is referred to the cardiac muscle layers building the wall of each chamber.

[In this figure] The thickness of the heart wall (or myocardium) consists of cardiac muscle cells.Photo source: biologydictionary

[In this video] Structure of the human heart.

Cardiovascular disease is a leading cause of death worldwide. Nearly 2,400 Americans die of cardiac causes each day, one death every 37 seconds.

As the chief cell type of the heart, cardiac muscle cells primarily dedicate to the contractile function of the heart and enable the pumping of blood around the body. If anything goes wrong in the heart, it can lead to a catastrophic outcome. A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow ceases to a part of the heart, causing massive cardiomyocyte death in that area. Severe cases can, ultimately, lead to heart failure and death.

[In this figure] The progress of myocardial infarction or heart attack. At time post-infarction:

0-12 hours: Beginning of necrotic coagulation due to the blockage of coronary arteries Cardiomyocytes suffer the lack of oxygen (hypoxia)

12-72 hours: Culmination of necrotic coagulation Neutrophils infiltrate by an inflammatory response.

1-3 weeks: Disintegration of death myocytes and formation of granulation tissue (collagenous fibers, macrophages, and fibroblasts)

> 1 month: Formation of fibrous scar (fewer cells with an abundance of collagenous fibers)

A human heart contains an estimated 23 billion cardiomyocytes. There are several non-myocyte populations in the heart, including endothelial cells, smooth muscle cells, myofibroblasts, epicardial cells, endocardial cells, valve interstitial cells, resident macrophages, and other immune system-related cells, and potentially, adult stem cells (mesenchymal stem cells and cardiac stem cells). These distinct cell pools are not isolated from one another within the heart but interact physically to maintain the function of the whole organ. Overall, cardiomyocytes only account for less than a third of the total cell number in the heart.

[In this image] Immunostaining showing highly vascularized heart muscle.Cardiomyocytes are labeled by the striated pattern of sarcomeric -actinin (green). Capillaries are red and nuclei are blue.Photo source: biocompare.

The three main types of muscle include: Cardiac muscle, Skeletal muscle, and Smooth muscle.

[In this figure] Morphology and comparison of cardiac, skeleton, and smooth muscles.

Note: Involuntary muscles are the muscles that cannot be controlled by will or conscious.

There are two types of cells within the heart: the cardiomyocytes and the cardiac pacemaker cells.

The heart is composed of cardiac muscle cells that have specialized features that relate to their function:

These structural features contribute to the unique functional properties of the cardiac tissue:

Like other animal cells, cardiomyocytes contain all the cell organelles that are essential for normal cell physiology. Moreover, cardiomyocytes have several unique cellular structures that allow them to perform their function effectively. Here are five main characteristics of mature cardiomyocytes: (1) striated; (2) uninucleated; (3) branched; (4) connected by intercalated discs; (5) high mitochondrial content.

[In this figure] Main characteristics of cardiac myocytes.Modified from lumen Anatomy and Physiology I.

Lets get closer to look inside a cardiomyocyte and learn its unique ultrastructure.

All cardiomyocytes and pacemaker cells are linked by cellular bridges. Intercalated discs, which form porous junctions, bring the membranes of adjacent cardiomyocytes very close together. These pores (gap junctions) permit ions, such as sodium, potassium, and calcium, to easily diffuse from cell to cell, establishing a cell-cell communication. This joining is called electric coupling, and it allows the quick transmission of action potentials and the coordinated contraction of the entire heart.

Intercalated discs also function as mechanical anchor points that enable the transmission of contractile force from one cardiomyocyte to another (by desmosomes and adherens junctions). This allows for the heart to work as a single coordinated unit.

[In this figure] Cardiac muscle cells are connected together to coordinate the cardiac contraction. This joining is called electric coupling and is achieved by the presence of irregularly-spaced dark bands between cardiomyocytes. These bands are known as intercalated discs.Photo source: bioninja.

[In this figure] Cardiac myocytes are branched and interconnected from end to end by structures called intercalated disks, visible as dark lines in the light microscope.Photo source: https://doctorlib.info/physiology/medical/49.html

There are 3 main types of junctional complexes within the intercalated discs. They work in different ways to maintain cardiac tissue integrity and cardiomyocyte synchrony.

The term desmosome came from Greek words of bonding (desmo) and body (soma). Desmosomes serve as the anchor points to bring the cardiac muscle fibers together. Desmosomes can withstand mechanical stress, which allows them to hold cells together. Without desmosomes, the cells of the cardiac muscles will fall apart during contraction.

The ability of desmosome to resist mechanical stress comes from its unique 3-D structure. Desmosome is an asymmetrical protein complex bridging between two adjacent cardiomyocytes, with each end residing in the cytoplasm. The intracellular part anchors intermediate filaments in the cytoskeleton to the cell surface. The middle part bridges the intercellular space between two cytoplasmic membranes.

[In this figure] Desmosomes connect intermediate filaments from two adjust cardiomyocytes. This job is accomplished by the formation of a dense protein complex or plaque in the intercalated discs. Major protein players include transmembrane cadherins: desmogleins (Dsgs) and desmocollins (Dscs), cytoplasmic anchors: plakophilins (PKPs) and plakoglobin (PG), and cytoskeleton adaptor: desmoplakin (DP). Cadherins link cells together, and other proteins form a dense complex called plaque.

In addition to desmosomes, adherens junctions (Ajs) are another type of mechanical intercellular junctions in cardiomyocytes. The difference is that adherens junctions link the intercalated disc to the actin cytoskeleton and desmosomes attach to intermediate filaments.

Adherens junctions keep the cardiac muscle cells tightly together as the heart pump. Adherens junctions are also the anchor point where myofibrils are attached, enabling transmission of contractile force from one cell to another.

[In this figure] Adherens junctions link actin cytoskeleton from two adjust cardiomyocytes together.Adherens junctions are constructed from cadherins and catenins. Cadherins (in cardiomyocytes N-Cadherin is the main cadherin) are transmembrane proteins that zip together adjacent cells in a homophilic manner. The transmembrane cadherins form complexes with cytosolic catenins, thereby establishing the connection to the actin cytoskeleton. At the adherens junctions, the opposing membranes become separated by 20nm.

Gap junctions are essential for the chemical and electrical coupling of neighboring cells. Gap junctions work like intercellular channels connecting the cytoplasm of neighboring cells, enabling passive diffusion of various compounds, like metabolites, water, and ions, up to a molecular mass of 1000 Da. Thereby they establish direct communication between adjacent cells.

[In this figure] Neonatal rat cardiac myocytes in cell culture.Cells were immunostained for actinin (green), gap junctions (red), and counterstained with DAPI (blue).Photo source: bioscience

Gap junctions are present in nearly all tissues and cells throughout the entire body. In cardiac muscle, gap junctions ensure proper propagation of the electrical impulse (from pacemaker cells to neighboring cardiomyocytes). This electrical wave triggers sequential and coordinated contraction of the cardiomyocytes as a whole.

[In this figure] A gap junction channel consists of twelve connexin proteins, six of which are contributed by each cell. The six connexin subunits form a hemi-channel in the plasma membrane, which is called a connexon. A connexon docks to another connexon in the intercellular space to create a complete gap junction channel. The intercellular space between adjacent cells at the site of a gap junction is 2-4 nm.

A second feature of cardiomyocytes is the sarcomeres, which are also present in skeletal muscles. The sarcomeres give cardiac muscle their striated appearance and are the repeating sections that make up myofibrils.

[In this image] Freshly isolated heart muscle cells showing intercalated discs (green), sarcomeres (red), and nuclei (blue).Photo source: https://christianz.artstation.com/

Cardiac muscle cells are equipped with bundles of myofibrils that contain myofilaments. These fiber-like structures can occupy 45-60% of the volume of cardiomyocytes. The myofibrils are formed of distinct, repeating units, termed sarcomeres. The sarcomeres, which are composed of thick and thin myofilaments, represent the basic contractile units of a muscle cell and are defined as the region of myofilament structures between two Z-lines (see image below). The distance between Z-lines in human hearts ranges from around 1.6 to 2.2 m.

[In this figure] Labeled diagram of myofibril showing the unit of a sarcomere. A sarcomere is defined as a segment between two neighboring Z-discs.

[In this image] Immunofluorescence image of adult mouse cardiomyocytes showing the Z-lines of the sarcomeres. 3D color projection of alpha-actinin 2 acquired with a confocal microscope.Photo source: Dylan Burnette.

The thick filaments are composed of myosin II. Each myosin contains two ATPase sites on its head. ATPase hydrolyzes ATP and this process is required for actin and myosin cross-bridge formation. These heads bind to actin on the thin filaments. There are about 300 molecules of myosin per thick filament.

The thin filaments are composed of single units of actin known as globular actin (G-actin). Two strands of actin filaments form a helix, which is stabilized by rod-shaped proteins termed tropomyosin. Troponin proteins, which function as regulators, bind to the tropomyosin at regular intervals. Whereas troponin lies in the grooves between the actin filaments, tropomyosin covers the sites on which actin binds to myosin. Their respective actions, therefore, control the binding of myosin to actin and consequently in the contraction and relaxation of cardiac muscles.

To generate muscular contraction, the myosin heads bind to actin filaments, allowing myosin to function as a motor that drives filament sliding. The actin filaments slide past the myosin filaments toward the middle of the sarcomere. This results in the shortening of the sarcomere without any change in filament length.

[In this figure] Sliding-filament model of muscle contraction.

Sarcolemma (also called myolemma) is a specialized cell membrane of cardiomyocytes and skeletal muscle cells. It consists of a lipid bilayer and a thin outer coat of polysaccharide material (glycocalyx) that contacts the basement membrane. The sarcolemma is also part of the intercalated disks as well as the T-tubules of the cardiac muscle.

Basement membrane is an extracellular matrix (ECM) coat that cover individual cardiomyocytes. Its composed of glycoproteins laminin and fibronectin, type IV collagen as well as proteoglycans that contribute to its overall width of about 50nm. Basement membrane provides a scaffold to which the muscle fiber can adhere.

[In this figure] A cross-section of a mouse heart showing the basement membrane (green) wrapping around an individual myocyte.

In cardiomyocytes and skeletal muscle cells, the sarcolemma (i.e. the plasma membrane) forms deep invaginations known as T-tubules (or transverse tubules). These invaginations increase the total surface area and allow depolarization of the membrane to penetrate quickly to the interior of the cell.

Without t-tubules, the wave of calcium ions (Ca2+) takes time to propagate from the periphery of the cell into the center. This time lag will first activate the peripheral sarcomeres and then the deeper sarcomeres, resulting in sub-maximal force production.

The t-tubules make it possible that current is simultaneously relayed to the core of the cell, and trigger near to all sarcomeres simultaneously, resulting in a maximal force output. T-tubules also stay close to sarcoplasmic reticulum (SR) networks, which is the modified endoplasmic reticulum (ER) of calcium storage in myocytes.

[In this figure] T-tubules (transverse tubules) are extensions of the cell membrane that penetrate into the center of skeletal and cardiac muscle cells. T-tubules permit the rapid transmission of the action potential into the cell and also play an important role in regulating cellular calcium concentration.

Mitochondria are the powerhouse of the cell because they generate most of the cells energy supply of adenosine triphosphate (ATP). It is no doubt that the normal functions of cardiomyocytes require a lot of energy. Effective heart pumping is primarily dependent on oxidative energy production by mitochondria. Cardiomyocytes have a densely packed mitochondrial network, which allows them to produce ATP quickly, making them highly resistant to fatigue.

Different types of mitochondria can be distinguished within cardiomyocytes, and their morphological features are usually defined according to their location: intermyofibrillar mitochondria, subsarcolemmal mitochondria, and perinuclear mitochondria.

[In this figure] Mitochondrial morphology in cardiomyocytes.(Top) The anatomy of a mitochondrion. (Bottom left) Schematic diagram of the location of subsarcolemmal mitochondria (SSM), interfibrillar mitochondria (IFM), and perinuclear mitochondria (PNM). (Bottom right) TEM images of mitochondria in cardiomyocytes.Photo source: researchgate, wiki

Intermyofibrilar Mitochondria are found deeper within the cells and strictly ordered between rows of contractile proteins, apparently isolated from each other by repeated arrays. They play a huge role in producing enough energy for muscle contractions.

[In this figure] Immunofluorescent confocal imaging showing the densely packed mitochondria in cardiomyocytes. (A): Z-line (actinin); (B): Mitochondria; (C): Merge image.Photo source: MDPI

Subsarcolemmal Mitochondria reside beneath the sarcolemma. They collect oxygen from the circulating blood in the arteries and are responsible for providing the energy needed for conserving the integrity of the sarcolemma.

Perinuclear mitochondria are organized in clusters around the nucleus to provide energy for transcription and translation processes.

The cardiac function requires high energy demands; therefore, the adult cardiomyocytes contain numerous mitochondria, which can occupy at least 30% of cell volume. They meet >90% of the energy requirements by oxidative phosphorylation (OXPHOS) in the mitochondria, which requires a huge demand for oxygen consumption.

In humans, at a heart rate of 6070 beats per minute, the oxygen consumption of the myocardium is 20-fold higher than that of skeletal muscle at rest (compared by a normalization per gram of cell mass). In order to meet this high oxygen demand, the capillary density in the heart is 2-8 times higher than that in skeletal muscle (3,0004,000/mm2 compared to 5002,000 capillaries/mm2, respectively). Also, cardiomyocytes maintain a very high level of oxygen extraction (from blood) of 7080% compared with 3040% in skeletal muscle.

[In this image] Myofibrils in cultured cardiomyocytes.Photo source: https://christianz.artstation.com/

Cardiomyocytes go through a contraction-relaxation cycle that enables cardiac muscles to pump blood throughout the body. This is achieved through a process known as excitation-contraction coupling (ECC) that converts action potential (an electric stimulus) into muscle contraction.

[In this figure] Schematic diagram of the process of cardiac excitation-contraction coupling.Key steps in the cardiac excitation-contraction coupling:

Step 1: An action potential is induced by pacemaker cells. It travels along the sarcolemma and down into the T-tubule system to depolarize the cell membrane.

Step 2: Calcium channels in the T-tubules are activated by the action potential and permit calcium entry into the cell.

Step 3: Calcium influx triggers a subsequent release of calcium that is stored in the sarcoplasmic reticulum (SR).

Step 4: Free calcium binds troponin-C (TN-C) that is part of the regulatory complex attached to the thin filaments. Calcium binding moves the troponin complex from the actin binding site. As a result, actin is free to bind myosin. The actin and myosin filaments slide past each other thereby shortening the sarcomere length, thus initiating contraction.

Step 5: At the end of a contraction, calcium entry into the cell slows and calcium is sequestered by the SR by calcium pumps. Lowering the cytosolic calcium concentration releases myosin-actin binding and the initial sarcomere length is restored.

In human beings (and many other animals), cardiomyocytes are the first cells to terminally differentiate, thus making the heart one of the first organs to form in a developing fetus. This makes sense because the function of the circulatory system is so crucial for a growing embryo so that the heart is the top priority.

In the embryo of a mouse, for instance, precursor cells of the cardiac muscles have been shown to start developing about 6 days after fertilization. In human embryos, the heart begins to beat at about 22-23 days, with blood flow beginning in the 4th week. The heart is therefore one of the earliest differentiating and functioning organs.

The heart forms initially in the embryonic disc as a simple paired tube (heart tube formation; week 3) derived from mesoderm. Then, the heart tubes loop and begin segmenting to separate chambers primitive atrium, and primitive ventricle. During this period, the first heartbeat begins.

[In this figure] The timeline of heart development.LA means left atrium; RA means right atrium. For more details, seehttps://embryology.med.unsw.edu.au/embryology/index.php/Cardiovascular_System_-_Heart_Development

Here, cardiomyocytes grow into a spongy-like tissue (cardiac jelly), called trabeculation, to build up the thickness of myocardial muscles. Thus, the heart begins to resemble the adult heart in that it has two atria, two ventricles, and the aorta forming a connection with the left ventricle while the pulmonary trunk forms a connection with the right ventricle.

As you can see that our hearts went through a complex developmental process. Inevitably, heart developmental abnormalities could happen (affect 8-10 of every 1000 births in the United States).

Can cardiomyocytes divide? Scientists used to believe that damaged human cardiac muscles cannot regenerate themselves by cell division in adults. In other words, all cardiomyocytes are terminally differentiated. In humans, our cardiomyocytes lose the ability to divide at around 7 days after birth. However, studies have recently shown that myocytes renew at a significantly low rate throughout the life of an individual. For instance, for younger people, about 25 years of age, the annual turnover of cardiomyocytes is about 1 percent. This, however, decreases to about 0.45 percent for older individuals (75 and above). Over the lifespan of an individual, less than 50 percent of these cells are renewed. Comparing to many of the other cells, cardiomyocytes have a very long lifespan. In contrast, small intestine epithelium renews every 2-7 days and hepatocytes (liver cells) renew every 0.5-1 year.

[In this figure] Radiocarbon dating establishes the age of human cardiomyocytes.Scientists used a pretty smart way to estimate the turnover of human heart cells. Generally speaking, the half-life of 14C is too long to date a lifetime of less than a century. However, the dramatic increase in the atmospheric 14C caused by nuclear bomb tests (during the Cool War) in the 1950s and 1960s increased the sensitivity of radiocarbon dating to a temporal resolution of 1-2years.Photo source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5837331/

Low turnover of human cardiomyocytes suggests that the regenerative ability of cardiac muscles may be poor (another example is neural cells in the brain). In the event of injuries or myocardial infarction, the injured heart muscles of human beings do not regenerate sufficiently to allow the heart to heal itself. Instead, fibrotic scar tissue forms in the injured site (fibrosis), and the heart functions are compromised, leading to heart failure.

Currently, a number of methods have been studied to repair a broken heart by regenerating cardiomyocytes. These new inventions benefit from the recent advances in biotechnology, especially stem cell biology, regenerative medicine, and tissue engineering. Hopefully, this can bring new therapeutic options to patients with cardiovascular diseases in the near future.

Studies suggested that even in adults, a very small population of progenitor cells reside in the heart and are capable of producing new cardiac myocytes. These cells, known as cardiac stem cells, may not be able to regenerate fast enough to repair a large area of damaged myocardium naturally in humans. However, these cells have shown to be powerful in regenerative capability in other species, like zebrafish.

Scientists believe that once we understand these cardiac progenitors more, we may isolate and expand these cells in quantity, and transplant them to repair damaged heart tissues. For example, we already learned that these cardiac stem cells express cell surface markers like c-Kit (sca-1 in mouse) and aggregate into cardiac spheres.

[In this figure] Multiple different stem cell populations have been described in the adult heart, including c-Kit and Sca-1 cells that were shown to be cardiac progenitors.Photo source: https://dev.biologists.org/content/143/8/1242

Induced pluripotent stem cell (iPSC) technology is a huge revolution in biotechnology. Patients cells (easily obtained from skin biopsy or even urine) can be converted into powerful pluripotent stem cells that have unlimited proliferation capacity and can differentiate any cell type of our body. This eliminates the need to use human embryos for this purpose. Furthermore, these cells are autologous, meaning they wont be rejected by the immune system after transplantation.

Using iPSC technology, researchers have been able to obtain unlimited amounts of functional cardiomyocytes for cell transplantation. Basically, they control the Wnt pathway to convert iPSCs to mesodermal progenitor cells, then play with several growth factors to direct the cardiac vascular progenitors (Flk1+). Following glucose starvation, pure cardiomyocytes can be selected. You can even see these cells beating in the dish.

Therapeutic implantation of iPSC-derived cardiomyocytes progresses pretty fast. We already witnessed successful cell engraftment and cardiac repairing in non-human primates and human patients.

[In this video] Heart cells derived from iPSC stem cells beating in a cell culture dish.

Cardiac fibroblasts make up a significant portion of the total cardiac cells. In the injured heart, these fibroblasts will become active myofibroblasts and form scar tissue. Myofibroblasts survive very well and have ability to coupled with neighboring cells; therefore, myofibroblasts have been shown to be particularly ideal for direct reprogramming to convert them into cells that resemble cardiomyocytes.

Over the past decade, a number of studies have been successfully conducted, reprogramming fibroblasts into cardiomyocyte-like cells. In principle, scientists expressed transcription factors (i.e., Gata4, Mef2c, and Tbx5) that play critical roles in cardiomyocyte differentiation to force the conversion of fibroblasts. Ideally, these genes can be delivered directly to the injured heart via viruses or nanoparticles to perform in situ reprogramming.

Scientists also put their efforts into how to stimulate mature cardiomyocytes to proliferate again (Mature cardiomyocytes typically do not proliferate.) This strategy, called cell cycle re-entry, recently gained success by screening many cell-cycle regulators. Scientists found a combination of cyclin-dependent kinases (CDK) and cyclins, or regulators of the Hippo-YAP signaling pathway can do so. These findings reveal the possibility to efficiently unlock the proliferative potential in cells that had terminally exited the cell cycle.

[In this figure] Potential cardiac regenerative therapies.Photo source: https://www.nature.com/articles/s41536-017-0024-1

Cardiomyocytes can be observed by staining of histological sections of the heart. Since the heart is a 3-D organ, make sure you cut the heart at the right angle.

[In this figure] (Left) A longitudinal section through both ventricles should be made from the base to the apex of the heart. (Right) A cross-section of the heart. H&E staining.(Ao: aorta, At: atrium, Lv: left ventricle, Rv: right ventricle)

Common histological staining for heart tissues includes Hematoxylin and eosin (H&E) and Massons trichrome staining.

[In this figure] A cross section of mouse heart stained by Massons trichrome. Blue color indicates the formation of fibrous scar tissues in the infarction area.

Read more from the original source:
Cardiomyocytes (Cardiac Muscle Cells) - Structure ...

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

1Regenerative Medicine Centre, Arabian Gulf University, Manama, Bahrain; 2Department of Molecular Medicine, College of Medicine and Medical Sciences, Arabian Gulf University, Manama, Bahrain

Introduction: Stroke is a leading cause of death and disability worldwide. The disease is caused by reduced blood flow into the brain resulting in the sudden death of neurons. Limited spontaneous recovery might occur after stroke or brain injury, stem cell-based therapies have been used to promote these processes as there are no drugs currently on the market to promote brain recovery or neurogenesis. Adult stem cells (ASCs) have shown the ability of differentiation and regeneration and are well studied in literature. ASCs have also demonstrated safety in clinical application and, therefore, are currently being investigated as a promising alternative intervention for the treatment of stroke.Methods: Eleven studies have been systematically selected and reviewed to determine if autologous adult stem cells are effective in the treatment of stroke. Collectively, 368 patients were enrolled across the 11 trials, out of which 195 received stem cell transplantation and 173 served as control. Using data collected from the clinical outcomes, a broad comparison and a meta-analysis were conducted by comparing studies that followed a similar study design.Results: Improvement in patients clinical outcomes was observed. However, the overall results showed no clinical significance in patients transplanted with stem cells than the control population.Conclusion: Most of the trials were early phase studies that focused on safety rather than efficacy. Stem cells have demonstrated breakthrough results in the field of regenerative medicine. Therefore, study design could be improved in the future by enrolling a larger patient population and focusing more on localized delivery rather than intravenous transplantation. Trials should also introduce a more standardized method of analyzing and reporting clinical outcomes to achieve a better comparable outcome and possibly recognize the full potential that these cells have to offer.

Keywords: adult stem cells, autologous, neurogenesis, inflammation, clinical application, stroke, stroke recovery, systematic review, meta-analysis

Stroke is the second leading cause of death worldwide and one of the leading causes of disability.1 The blockade or the rupture of a blood vessel to the brain leads to either ischemic or hemorrhagic stroke, respectively.2,3 The extent and the location of the damaged brain tissue may be associated with irreversible cognitive impairment or decline in speech, comprehension, memory, and partial or total physical paralysis.4

Four chronological phases, namely hyperacute, acute, subacute, and chronic, describe the strokes cellular manifestations.5 The hyperacute phase is immediate and associated with glutamate-mediated excitotoxicity and a progressive neuronal death that can last a few hours.6 The glutamate, a potent excitatory neurotransmitter, is also an inducer of neurodegeneration following stroke.7 The acute phase, which could last over a week after the stroke, is associated with the delayed and progressive neuronal death and the infiltration of immune cells.5 The following subacute phase can extend up to three months after the stroke and is mainly associated with reduced inflammation and increased plasticity of neurons, astrocytes, microglia, and endothelial cells, allowing spontaneous recovery.8 In the chronic phase that follows, the plasticity of cells is reduced and only permits rehabilitation-induced recovery.5

The immediate treatments differ for ischemic and hemorrhagic strokes. Immediate intervention is required to restore the blood flow to the brain following an ischemic stroke. Thrombolytic agents, such as activase (Alteplase), a recombinant tissue plasminogen activator (tPA), are commonly given intravenously to dissolve the blood clots. Other more invasive approaches, such as a thrombectomy, use stents or catheters to remove the blood clot.9 Antiplatelet agents like Aspirin, anticoagulants, blood pressure medicines, or statins are generally given to reduce the risk of recurrence. Some ischemic strokes are caused by the narrowing of the carotid artery due to the accumulation of fatty plaques; a carotid endarterectomy is performed to correct the constriction.

The treatment of a hemorrhagic stroke requires a different approach. An emergency craniotomy is usually performed to remove the blood accumulating in the brain and repair the damaged blood vessels. Accumulation of cerebrospinal fluid in brain ventricles (hydrocephalus) is also a frequent complication following a hemorrhagic stroke, which requires surgery to drain the fluid. Medications to lower blood pressure are given before surgery and to prevent further seizures.10

These immediate treatments are critical to minimize the long-term consequence of the stroke but do not address the post-stroke symptoms caused by neurodegeneration. New therapeutic approaches adapted to the physiology of each phase of the stroke are currently developed. A promising therapy has been the use of stem cells.11 In this review, different clinical trials involving the use of various stem cells for the treatment of stroke are presented and compared using a meta-analysis of the published results.

To narrow down the relevant literature, a search strategy focused on original literature and reporting the clinical application of stem cells in stroke was established. An NCBI PubMed word search for stroke, stem cells, and adult stem cells yielded 146 clinical studies between 2010 and 2021. Finally, 11 studies, using autologous adult stem cells in the treatment of stroke, were considered. A PRISMA flow diagram detailing an overview of the study selection procedure and the inclusion and exclusion of papers is included in Appendix I. The inclusion criteria comprise the injection of autologous adult stem cells at any stroke stages (hyperacute, acute, sub-acute, chronic), and clinical trials whose results have been published in the last 11 years. The exclusion criteria include studies published more than 11 years ago, studies not published in English, all preclinical studies, other diseases related to stroke (ex. cardiovascular diseases), embryonic or induced pluripotent stem cells, allogeneic stem cells, and other cell therapies. Two independent researchers reviewed and filtered the 146 studies by reading the titles and abstracts. All three authors approved the final selected studies.

Stem cells are undifferentiated and unspecialized cells characterized by their ability to self-renew and their potential to differentiate into specialized cell types.12 Ischemic stroke causes severe damage to the brain cells by destroying the heterogeneous cell population and neuronal connections along with vascular systems. The regenerative potential of several types of stem cells like embryonic stem cells, neural stem cells, adult stem cells (mesenchymal stem cells), and induced pluripotent stem cells have been assessed for treating stroke.

Adult stem cells exhibit multipotency and the ability to self-renew and differentiate into specialized cell types. They have been widely used in clinical trials and a safe option thus far in treating various diseases.12,13,14 The plasticity of these cells allow their differentiation across tissue lineages when exposed to defined cell culture conditions.15 There are multiple easily accessible sources of adult stem cells, mainly the bone marrow, blood, and adipose tissue. In clinical settings, both autologous and HLA-matched allogeneic cells have been transplanted and are deemed to be safe.

Adult stem cells can secrete a variety of bioactive substances into the injured brain following a stroke in the form of paracrine signals.1618 The paracrine signals include growth factors, trophic factors, and extracellular vesicles, which may be associated with enhanced neurogenesis, angiogenesis, and synaptogenesis (Figure 1). Also, mesenchymal stem cells (MSCs) are thought to contribute to the resolution of the stroke by attenuating inflammation,19 reducing scar thickness, enhancing autophagy, normalizing microenvironmental and metabolic profiles and possibly replacing damaged cells.20

Figure 1 Schematic depicting the clinical application of different cells in stroke patients. The cells were delivered in one of three ways, intravenously, intra-arterially, or via stereotactic injections. Once administered, the cells play a role in providing paracrine signals and growth factors to facilitate angiogenesis and cell regeneration, immunomodulatory effects that serve to protect the neurons from further damage caused by inflammation, and finally, trans-differentiation of stem cells. Data from Dabrowska S, Andrzejewska A, Lukomska B, Janowski M.19 Created with BioRender.com.

A few routes of administration have been used to deliver the stem cells to the patients. The most common is through intravenous injection. Intra-arterial delivery is also performed; but this mode can be extremely painful to patients compared to an intravenous transfusion. The third approach is via stereotactic injections. This is an invasive surgery that involves injecting the cells directly into the site of affected in the brain.

Also known as mesenchymal stromal cells or medicinal signaling cells, MSCs can be derived from different sources including bone marrow, peripheral blood, lungs, heart, skeletal muscle, adipose tissue, dental pulp, dermis, umbilical cord, placenta, amniotic fluid membrane and many more.21 MSCs are characterized by positive cell surface markers, including Stro-1, CD19, CD44, CD90, CD105, CD106, CD146, and CD166. The cells are also CD14, CD34, and CD45 negative.22,23 The cells are thought to provide a niche to stem cells in normal tissue and releases paracrine factors that promote neurogenesis (Figure 2).19,20,24 During the acute and subacute stage of stroke, MSCs may inhibit inflammation, thus, reducing the incidence of debilitating damage and symptoms that may occur post-stroke.

Figure 2 Schematic describing the role of mesenchymal stem cells in stroke. The cells release different growth factors, signals, and cytokines that serve to facilitate various functions. Through the release of cytokines, they can modulate inflammation and block apoptosis. The growth factors aid in promoting angiogenesis and neurogenesis. Data from Maleki M, Ghanbarvand F, Behvarz MR, Ejtemaei M, Ghadirkhomi E.23 Created with BioRender.com.

Derived from the bone marrow, mononuclear cells contain several types of stem cells, including mesenchymal stem cells and hematopoietic progenitor cells that give rise to hematopoietic stem cells and various other differentiated cells. They can produce and secrete multiple growth factors and cytokines. They are also attracted to the lesion or damage site where they can accelerate angiogenesis and promote repair endogenously through the proliferation of the hosts neural stem cells. Mononuclear cells have also demonstrated the ability to decrease neurodegeneration, modulate inflammation, and prevent apoptosis in animal models.25,26

Blood stem cells are a small number of bone marrow stem cells that have been mobilized into the blood by hematopoietic growth factors, which regulate the differentiation and proliferation of cells. They are increasingly used in cell therapies, most recently for the regeneration of non-hematopoietic tissue, including neurons. Recombinant human granulocyte colony-stimulating factor (G-CSF) has been used as a stimulator of hematopoiesis, which in turn amplifies the yield of peripheral blood stem cells.27

The literature review considered 11 clinical trials that satisfied the inclusion criteria. A total of 368 patients were enrolled including 179 patients treated with various types of adult stem cells. The clinical trial number 7 contained a historical control of 59 patients included in the data analysis (Figure 3). The analysis was done on the published clinical and functional outcomes of various tests such as mRS, and mBI. The analysis compared the patients clinical outcomes post stem cell therapy to the baseline clinical results. The variance in the patient population should be noted.

Figure 3 Schematic representing an overview of the total number of patients enrolled in all 11 clinical trials and the number of patients administered with each type of adult stem cell.

Abbreviations: MSC, mesenchymal stem cells; PBSC, peripheral blood stem cells; MNC, mononuclear stem cells; ADSVF, adipose derived stromal vascular fraction; ALD401, aldehyde dehydrogenase-bright stem cells.

Meta-analyses were conducted using modified Rankin scale (mRS) and Barthel Index (BI) scores. In the clinical trials, mRS and BI scores are commonly used scales to assess functional outcome in stroke patients. The BI score was developed to measures the patients performance in 10 activities of daily life from self-care to mobility. An mRS score follows a similar outcome but measures the patients independence in daily tasks rather than performance. OpenMeta[Analyst], an open-source meta-analysis software, was used to produce random-effects meta-analyses and create the forest plots. The number of patients, mean, and standard deviation (SD) of the scores were calculated to determine the study weights and create the forest plots.

All 11 clinical trials were compared based on their clinical and functional outcomes (Table 1; Figure 4). The data shows that stem cell therapy is relatively safe and viable in the treatment of stroke, indicating an improvement in patients overall health. However, when compared to the control, the improvement is not significant as patients in the control group also exhibited an improved clinical and functional outcome. Across trials that assigned a control group, the patients either received a placebo, or alternative form of treatment including physiotherapy. Variance in functional and clinical tests used to assess patients, and the number of patients enrolled in each trial results in a discrepancy in reporting. Most of the trials failed to report whether the patients suffered from an acute, subacute or chronic stroke which also affects the results of the treatments, with acute and subacute being the optimal periods to receive treatment due to cell plasticity and inhibiting unwarranted inflammation.39 The deaths in both the treatment and control population were attributed to the progression of the disease and are likely not the result of the treatment. Albeit, it has been noted down as they had occurred during the follow-up period.

Table 1 Overview of Selected Clinical Trials

Figure 4 Overview of clinical outcomes of the 11 clinical trials (N=368). (A) The chart shows the percentages of patients who have either improved, remained stable, deteriorated, or deceased. Some clinical trials are without a control arm. (B) The plot shows the overall percentage of patients that have improved after receiving either the stem cell treatment versus the standard of care. (C) The plot shows the overall percentage of patients that have remained stable and showed no clinical or functional improvement in the follow up period. (D) The plot shows the overall percentage of the patients whose condition has deteriorated in the follow up period.

A meta-analysis was conducted using modified Rankin scale (mRS) and Barthel Index (BI) scores. The results of the mRS scores were analyzed (Figure 5A; Table 2). In terms of study weights, CT6 is the highest (40.07%) as shown in Table 2. The combined results of the mRS functional test from CT1, CT5, CT6, and CT11 show a non-significant statistical heterogeneity in the studies (p-value 0.113). In conjunction, BI scores were analyzed and a meta-analysis was conducted using four comparable trials (Figure 5B; Table 3). In terms of study weights, CT3 is the highest (32.384%) as shown in Table 3. The combined results of BI scores from CT5, CT3, CT10, and CT11 show a statistical heterogeneity in the results of the studies (p-value 0.004) thus, precision of results is uncertain. More comparable studies are needed to have a better outcome. Therefore, standardized testing in trails should be considered in future trials.

Table 2 Clinical Outcomes of mRS Test

Table 3 Clinical Outcomes of BI Test

Figure 5 Meta-analysis conducted using three comparable trials. (A) Meta-analysis conducted using four comparable trials (CT1, CT5, CT6, CT11) for the mRS test. (B) Meta-analysis conducted using four comparable trials (CT3, CT5, CT10, and CT11) for the BI test.

Across all trials, patients injected with the MSCs, and other cell types did not trigger a degradation of the patient conditions demonstrating the safety of the procedures. However, the efficacy of the use of adult stem cells is less clear when compared to patients in the control group. This discrepancy could, however, exhibit improvement in patients receiving the treatment compared to the baseline clinical outcomes. However, when therapy results are compared to the patients in the control population that either received a placebo, physiotherapy, or prescribed medication, the efficacy of the use of adult stem cells is less clear.

Although multiple adult stem cell types have been used, mesenchymal stem cells have been widely used in many clinical trials. Albeit there is a consensus that the therapeutic and clinical outcomes of mesenchymal stem cell treatments are not yet significantly effective compared to the control treatment. Some trials have shown patient improvements, such as CT6 and CT8, where the investigators used PBSCs or BMMNSC, respectively. Although subjectively, the cells appear to be therapeutic, objectively, there are many limitations to the study designs included in this review. Not all the trials enrolled a control arm for a better comparison as some were only testing safety rather than efficacy. Therefore, we cannot conclude whether autologous adult stem cells are an effective therapeutic stroke treatment. Only autologous cells were included in this review as they are non-immunogenic.

Another factor to consider is the evident discrepancy in the number of patients enrolled in each trial. The trials included in this review are in Phase I and II trials, which primarily focus on safety rather than efficacy. Intravenous injection was the most used method of cell delivery due to its convenience and safety. However, it is commonly considered that this approach is not the most effective way of delivery, as the majority of the transplanted cells get absorbed by non-targeted organs, and the remaining cells find difficulty passing the blood-brain barrier. Due to this dilemma, the most obvious approach would be to inject the cells directly into the brain. However, a stereotactic procedure is invasive and will require general anesthesia, which may compromise patients health, especially ones suffering from acute ischemic stroke.40 Thus, an intra-arterial delivery seems feasible to accomplish the task as it is less invasive and might be more effective than an intravenous treatment such as the cases observed in CT3 and CT8. In CT11, the patients demonstrated a visible fmRI recovery as well as recovery of motor function in patients that have received a stem cell treatment. However, the analysis and test scores show no significance between the treatment group and the control group.

Only a few studies were comparable using a similar evaluation approach. Considering these factors, better study designs enrolling a higher number of patients in randomized clinical trial against the standard of care are needed. Moreover, a better grouping of the patients based on the type and stage of stroke may provide more relevant information for the safety and efficacy of adult stem cells for the recovery and prevention of recurrence of stroke patients.

ADSVF, Adipose-derived stromal vascular fraction; ASCs, Adult stem cells; ALD-401, Aldehyde dehydrogenase 401; BI, Barthel Index; BM-MNC, Bone marrow-derived mononuclear cells; FLAIR, Fluid attenuated inversion recovery; fMRI, Functional magnetic resonance imaging; G-CSF, Granulocyte colony-stimulating factor; MRI, Magnetic resonance imaging; MSCs, Mesenchymal stem cells; mRS, modified Rankin Scale; NIHSS, National Institute of Health Stroke Scale; PBSC, Peripheral blood stem cells; SD, Standard deviation; tPA, tissue plasminogen activator.

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

There is no funding to report.

We declare there is no conflict of interest.

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The rest is here:
Autologous Adult Stem Cells in the Treatment of Stroke | SCCAA - Dove Medical Press

DUBLIN--(BUSINESS WIRE)--The "Global Regenerative Medicine Market Size, Share & Trends Analysis Report by Product (Cell-based Immunotherapies, Gene Therapies), by Therapeutic Category (Cardiovascular, Oncology), and Segment Forecasts, 2021-2027" report has been added to ResearchAndMarkets.com's offering.

The global regenerative medicine market size is expected to reach USD 57.08 billion by 2027, growing at a CAGR of 11.27% over the forecast period.

Recent advancements in biological therapies have resulted in a gradual shift in preference toward personalized medicinal strategies over the conventional treatment approach. This has resulted in rising R&D activities in the regenerative medicine arena for the development of novel regenerative therapies.

Furthermore, advancements in cell biology, genomics research, and gene-editing technology are anticipated to fuel the growth of the industry. Stem cell-based regenerative therapies are in clinical trials, which may help restore damaged specialized cells in many serious and fatal diseases, such as cancer, Alzheimer's, neurodegenerative diseases, and spinal cord injuries.

For instance, various research institutes have adopted Human Embryonic Stem Cells (hESCs) to develop a treatment for Age-related Macular Degeneration (AMD).

Constant advancements in molecular medicines have led to the development of gene-based therapy, which utilizes targeted delivery of DNA as a medicine to fight against various disorders.

Gene therapy developments are high in oncology due to the rising prevalence and genetically driven pathophysiology of cancer. The steady commercial success of gene therapies is expected to accelerate the growth of the global market over the forecast period.

Regenerative Medicine Market Report Highlights

Key Topics Covered:

Market Variables, Trends, & Scope

Competitive Analysis

Covid-19 Impact Analysis

Regenerative Medicine Market: Product Business Analysis

Regenerative Medicine Market: Therapeutic Category Business Analysis

Regenerative Medicine Market: Regional Business Analysis

Companies Mentioned

For more information about this report visit https://www.researchandmarkets.com/r/kovhgl

Here is the original post:
Global Regenerative Medicine Market is Expected to Reach USD 57.08 Billion by 2027, Growing at a CAGR of 11.27% Over the Forecast Period. -...

Advance Market Analytics published a new research publication on Stem Cells Market Insights, to 2026 with 232 pages and enriched with self-explained Tables and charts in presentable format. In the Study you will find new evolving Trends, Drivers, Restraints, Opportunities generated by targeting market associated stakeholders. The growth of the Stem Cells Market was mainly driven by the increasing R&D spending across the world.

Some of the key players profiled in the study are:

Smith & Nephew (United Kingdom),Celgene Corporation (United States),BIOTIME, INC. (United States),Cynata (Australia),Applied Cell Technology (Hungary),STEMCELL Technologies Inc. (Canada),BioTime Inc. (United States),Cytori Therapeutics, Inc. (United States),Astellas Pharma Inc. (Japan),U.S. Stem Cell, Inc. (United States),Takara Holdings. (Japan)

Get Free Exclusive PDF Sample Copy of This Research @ https://www.advancemarketanalytics.com/sample-report/72815-global-stem-cells-market-1

Scope of the Report of Stem Cells

The stem cell is used for treating chronic diseases such as cardiovascular disorders, cancer, diabetes, and others. Growing research and development in stem cell isolation techniques propelling market growth. For instance, a surgeon from Turkey developed a method for obtaining stem cells from the human body without enzymes which are generally used for the isolation of stem cells. Further, growing healthcare infrastructure in the developing economies and government spending on the life science research and development expected to drive the demand for stem cell market over the forecasted period.

Market Trend:

Emphasizing On Development of Regenerative Medicine

Technological Advancement in Stem Cell Harvesting and Isolation Techniques

Market Drivers:

Rising Prevalence of Chronic Diseases such as Cardiovascular Disorders, Cancer, and others

Growing Healthcare Infrastructure in the Developing Economies

Challenges:

Lack of Awareness Regarding Stem Cell Therapy in the Low and Middle Income Group Countries

Opportunities:

Growing Demand for Cellular Therapies

Rising Application of Autologous Therapy

The titled segments and sub-section of the market are illuminated below:by Type (Adult Stem Cells (Neuronal, Hematopoietic, Mesenchymal, Umbilical Cord, Others), Human Embryonic Stem Cells (hESC), Induced Pluripotent Stem Cells, Very Small Embryonic-Like Stem Cells), Application (Regenerative Medicine (Neurology, Orthopedics, Oncology, Hematology, Cardiovascular and Myocardial Infraction, Injuries, Diabetes, Liver Disorder, Incontinence, Others), Drug Discovery and Development), Technology (Cell Acquisition (Bone Marrow Harvest, Umbilical Blood Cord, Apheresis), Cell Production (Therapeutic Cloning, In-vitro Fertilization, Cell Culture, Isolation), Cryopreservation, Expansion and Sub-Culture), Therapy (Autologous, Allogeneic)

Have Any Questions Regarding Global Financial Advisory Market Report, Ask Our [emailprotected] https://www.advancemarketanalytics.com/enquiry-before-buy/72815-global-stem-cells-market-1

Region Included are: North America, Europe, Asia Pacific, Oceania, South America, Middle East & Africa

Country Level Break-Up: United States, Canada, Mexico, Brazil, Argentina, Colombia, Chile, South Africa, Nigeria, Tunisia, Morocco, Germany, United Kingdom (UK), the Netherlands, Spain, Italy, Belgium, Austria, Turkey, Russia, France, Poland, Israel, United Arab Emirates, Qatar, Saudi Arabia, China, Japan, Taiwan, South Korea, Singapore, India, Australia and New Zealand etc.

Strategic Points Covered in Table of Content of Global Stem Cells Market:

Chapter 1: Introduction, market driving force product Objective of Study and Research Scope the Stem Cells market

Chapter 2: Exclusive Summary the basic information of the Stem Cells Market.

Chapter 3: Displaying the Market Dynamics- Drivers, Trends and Challenges of the Stem Cells

Chapter 4: Presenting the Stem Cells Market Factor Analysis Porters Five Forces, Supply/Value Chain, PESTEL analysis, Market Entropy, Patent/Trademark Analysis.

Chapter 5: Displaying market size by Type, End User and Region 2015-2020

Chapter 6: Evaluating the leading manufacturers of the Stem Cells market which consists of its Competitive Landscape, Peer Group Analysis, BCG Matrix & Company Profile

Chapter 7: To evaluate the market by segments, by countries and by manufacturers with revenue share and sales by key countries (2021-2026).

Chapter 8 & 9: Displaying the Appendix, Methodology and Data Source

Finally, Stem Cells Market is a valuable source of guidance for individuals and companies in decision framework.

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Stem Cells Market to Witness Gigantic Growth by 2026 LSMedia - LSMedia

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 ...

Report Ocean presents a new report on Mesenchymal Stem Cells Market size, share, growth, industry trends, and forecast 2026, covering various industry elements and growth trends helpful for predicting the markets future. The global mesenchymal stem cells market size to reach USD 2,518.5 Million by 2026, growing at a CAGR of 7.0% during forecast period, according to a new research report published . The report Mesenchymal Stem Cells Market, [By Source (Bone Marrow, Umbilical Cord Blood, Peripheral Blood, Lung Tissue, Synovial Tissues, Amniotic Fluids, Adipose Tissues); By Application (Injuries, Drug Discovery, Cardiovascular Infraction, Others); By Region]: Market Size & Forecast, 2018 2026 provides an extensive analysis of present market dynamics and predicted future trends. The market was valued at USD 1,335.1 million in 2017. In 2017, the drug discovery application dominated the market, in terms of revenue. North America region is observed to be the leading contributor in the global market revenue in 2017.

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In order to produce a holistic assessment of the market, a variety of factors is considered, including demographics, business cycles, and microeconomic factors specific to the market under study. Mesenchymal Stem Cells Market report 2021 also contains a comprehensive business analysis of the state of the business, which analyzes innovative ways for business growth and describes critical factors such as prime manufacturers, production value, key regions, and growth rate.

The Centers for Medicare and Medicaid Services report that US healthcare expenditures grew by 4.6% to US$ 3.8 trillion in 2019, or US$ 11,582 per person, and accounted for 17.7% of GDP. Also, the federal government accounted for 29.0% of the total health expenditures, followed by households (28.4%). State and local governments accounted for 16.1% of total health care expenditures, while other private revenues accounted for 7.5%.

This study aims to define market sizes and forecast the values for different segments and countries in the coming eight years. The study aims to include qualitative and quantitative perspectives about the industry within the regions and countries covered in the report. The report also outlines the significant factors, such as driving factors and challenges, that will determine the markets future growth.

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These stem cells mainly function for the replacement of damaged cell and tissues. The potential of these cell is to heal the damaged tissue with no pain to the individual. Scientists are majorly focusing on developing new and innovative treatment options for the various chronic diseases like cancer. Additionally, the local governments have also taken various steps for promoting the use of these stem cells.

The significant aspects that are increasing the development in market for mesenchymal stem cells consist of enhancing need for these stem cells as an efficient therapy option for knee replacement. Raising senior populace throughout the world, as well as increasing frequency of numerous persistent conditions consisting of cancer cells, autoimmune illness, bone and cartilage diseases are elements anticipated to enhance the market development throughout the forecast period. The mesenchymal stem cells market is obtaining favorable assistance by the reliable federal government policies, as well as funding for R&D activities which is anticipated to influence the market growth over coming years. According to the reports released by world health organization (WHO), by 2050 individuals aged over 60 will certainly make up greater than 20% of the globes population. Of that 20%, a traditional quote of 15% is estimated to have symptomatic OA, as well as one-third of these individuals are expected to be influenced by extreme specials needs. Taking into consideration all these aspects, the market for mesenchymal stem cells will certainly witness a substantial development in the future.

Increasing demand for better healthcare facilities, rising geriatric population across the globe, and continuous research and development activities in this area by the key players is expected to have a positive impact on the growth of Mesenchymal Stem Cells market. North America generated the highest revenue in 2017, and is expected to be the leading region globally during the forecast period. The Asia Pacific market is also expected to witness significant market growth in coming years. Developing healthcare infrastructure among countries such as China, India in this region is observed to be the major factor promoting the growth of this market during the forecast period.

The major key players operating in the industry are Cell Applications, Inc., Cyagen Biosciences Inc. Axol Bioscience Ltd., Cytori Therapeutics Inc., Stem cell technologies Inc., Celprogen, Inc. BrainStorm Cell Therapeutics, Stemedica Cell Technologies, Inc. These companies launch new products and undertake strategic collaboration and partnerships with other companies in this market to expand presence and to meet the increasing needs and requirements of consumers.

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Polaris Market Research has segmented the global mesenchymal stem cells market on the basis of source type, application and region:

Mesenchymal Stem Cells Source Type Outlook (Revenue, USD Million, 2015 2026)

Bone Marrow

Umbilical Cord Blood

Peripheral Blood

Lung Tissue

Synovial Tissues

Amniotic Fluids

Adipose Tissues

Mesenchymal Stem Cells Application Outlook (Revenue, USD Million, 2015 2026)

Injuries

Drug Discovery

Cardiovascular Infraction

Others

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Mesenchymal Stem Cells Regional Outlook (Revenue, USD Million, 2015 2026)

North America

U.S.

Canada

Europe

Germany

UK

France

Italy

Spain

Russia

Rest of Europe

Asia-Pacific

China

India

Japan

Singapore

Malaysia

Australia

Rest of Asia-Pacific

Latin America

Mexico

Brazil

Argentina

Rest of LATAM

Middle East & Africa

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The report provides a comprehensive analysis of market trends, including information on usage and consumption at the regional level.

Reports on the market include the growth rates of each region, which includes their countries, over the coming years.

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This report provides a comprehensive analysis of leading competitors in the market.

The report includes information about the key vendors in the market.

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A market report includes details on recent market developments, mergers, and acquisitions involving the key players mentioned.

What is the key information extracted from the report?

Extensive information on factors estimated to affect the Market growth and market share during the forecast period is presented in the report.The report offers the present scenario and future growth prospects Market in various geographical regions.The competitive landscape analysis on the market as well as the qualitative and quantitative information is delivered.The SWOT analysis is conducted along with Porters Five Force analysis.The in-depth analysis provides an insight into the Market, underlining the growth rate and opportunities offered in the business.

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Mesenchymal Stem Cells Market Growth Drivers 2021, Industry Share-Size, Global Demand, Emerging Trends, Opportunities in Grooming Regions, Key Players...

BURLINGTON, Mass.--(BUSINESS WIRE)--PharmaEssentia USA Corporation, a subsidiary of PharmaEssentia Corporation (TPEx:6446), a global biopharmaceutical innovator based in Taiwan leveraging deep expertise and proven scientific principles to deliver new biologics in hematology and oncology, today announced that BESREMi (ropeginterferon alfa-2b-njft) is now commercially available in the U.S. to eligible patients with polycythemia vera (PV). BESREMi was approved by the FDA in November as the only interferon for adults with polycythemia vera. BESREMi was approved with a boxed warning for risk of serious disorders including aggravation of neuropsychiatric, autoimmune, ischemic and infectious disorders.

Today marks the beginning of a new chapter in the treatment of PV. Our team is delivering on our goal to bring an innovative solution that may help more people manage not only the symptoms of PV, but target the disease itself to gain durable control with potential to reduce progression over time, said Meredith Manning, U.S. General Manager. We look forward to working closely with U.S. providers to raise awareness of this therapy and help advance treatment goals.

PharmaEssentia SOURCE Now Available to Support People with PV in the U.S.

With the commercial availability of BESREMi, PharmaEssentia is also launching a comprehensive patient support program, which can be found at http://www.pharmaessentiaSOURCE.com.

The SOURCE program is available for patients prescribed BESREMi and offers a full suite of services designed to help patients start and stay on therapy. Services include insurance navigation support, titration and injection training, and ongoing adherence guidance. The program also includes physician resources, including guides to help patients get started on treatment and ordering processes.

As part of this program, PharmaEssentia will help patients with financial barriers to starting therapy. The company is offering co-pay and co-insurance programs to assist eligible patients who experience financial need. Programs include a $0 copay card for commercially insured patients, temporary product supply in case of insurance delays and/or gaps in coverage, free drug for the uninsured and under-insured as well as assistance identifying additional support as needed.

Weve designed SOURCE with active input from the PV community to simplify the process for appropriate patients to initiate and maintain access to BESREMi and to benefit from its effects over the long-term, added Manning. Our goal is to ensure that any appropriate person with PV who is prescribed BESREMi is able to receive the therapy.

About Polycythemia Vera

Polycythemia Vera (PV) is a cancer originating from a disease-initiating stem cell in the bone marrow resulting in a chronic increase of red blood cells, white blood cells, and platelets. PV may result in cardiovascular complications such as thrombosis and embolism, and often transforms to secondary myelofibrosis or leukemia. While the molecular mechanism underlying PV is still subject of intense research, current results point to a set of acquired mutations, the most important being a mutant form of JAK2.1

About BESREMi

BESREMi is an innovative monopegylated, long-acting interferon. With its unique pegylation technology, BESREMi has a long duration of activity in the body and is aimed to be administered once every two weeks (or every four weeks with hematological stability for at least one year), allowing flexible dosing that helps meet the individual needs of patients. After one year, patients with stable complete hematologic response (CHR) can be treated with BESREMi every four weeks.

BESREMi has orphan drug designation for treatment of PV in the United States. The product was approved by the European Medicines Agency (EMA) in 2019 and has received approval in Taiwan and South Korea. BESREMi was invented and is manufactured by PharmaEssentia.

Important Safety Information

IMPORTANT SAFETY INFORMATION AND INDICATIONS

WARNING: RISK OF SERIOUS DISORDERS

Interferon alfa products may cause or aggravate fatal or life-threatening neuropsychiatric, autoimmune, ischemic, and infectious disorders. Patients should be monitored closely with periodic clinical and laboratory evaluations. Therapy should be withdrawn in patients with persistently severe or worsening signs or symptoms of these conditions. In many, but not all cases, these disorders resolve after stopping therapy.

CONTRAINDICATIONS

WARNINGS AND PRECAUTIONS

Other central nervous system effects, including suicidal ideation, attempted suicide, aggression, bipolar disorder, mania and confusion have been observed with other interferon alfa products.

Closely monitor patients for any symptoms of psychiatric disorders and consider psychiatric consultation and treatment if such symptoms emerge. If psychiatric symptoms worsen, it is recommended to discontinue BESREMi therapy.

ADVERSE REACTIONS

The most common adverse reactions reported in > 40% of patients in the PEGINVERA study (n=51) were influenza-like illness, arthralgia, fatigue, pruritis, nasopharyngitis, and musculoskeletal pain. In the pooled safety population (n=178), the most common adverse reactions greater than 10%, were liver enzyme elevations (20%), leukopenia (20%), thrombocytopenia (19%), arthralgia (13%), fatigue (12%), myalgia (11%), and influenza-like illness (11%).

DRUG INTERACTIONS

Patients on BESREMi who are receiving concomitant drugs which are CYP450 substrates with a narrow therapeutic index should be monitored to inform the need for dosage modification for these concomitant drugs. Avoid use with myelosuppressive agents and monitor patients receiving the combination for effects of excessive myelosuppression. Avoid use with narcotics, hypnotics or sedatives and monitor patients receiving the combination for effects of excessive CNS toxicity.

USE IN SPECIFIC POPULATIONS

Please see accompanying full Prescribing Information, including Boxed Warning.

About PharmaEssentia

PharmaEssentia Corporation (TPEx: 6446), based in Taipei, Taiwan, is a rapidly growing biopharmaceutical innovator. Leveraging deep expertise and proven scientific principles, the company aims to deliver effective new biologics for challenging diseases in the areas of hematology and oncology, with one approved product and a diversifying pipeline. Founded in 2003 by a team of Taiwanese-American executives and renowned scientists from U.S. biotechnology and pharmaceutical companies, today the company is expanding its global presence with operations in the U.S., Japan, China, and Korea, along with a world-class biologics production facility in Taichung. For more information, visit our website or find us on LinkedIn and Twitter.

Forward Looking Statement

This press release contains forward looking statements, including statements regarding the timing of BESREMis availability in the United States, the commercialization plans and expectations for commercializing BESREMi in the United States, and the potential benefits or competitive position of BESREMi. For those statements, we claim the protection of the safe harbor for forward-looking statements contained in the Private Securities Litigation Reform Act of 1995 and similar legislation and regulations under Taiwanese law. These forward-looking statements are based on management expectations and assumptions as of the date of this press release, and actual results may differ materially from those in these forward-looking statements as a result of various factors. These factors include PharmaEssentias ability to launch BESREMi in the United States, whether BESREMi is successfully commercialized and adopted by physicians and patients, the extent to which reimbursement is available for BESREMi, and the ability to receive FDA and other regulatory approvals for additional indications for BESREMi. Any forward-looking statements set forth in this press release speak only as of the date of this press release. We do not undertake to update any of these forward-looking statements to reflect events or circumstances that occur after the date hereof. The information found on our website, and the FDA website, is not incorporated by reference into this press release and is included for reference purposes only.

1 Cerquozzi S, Tefferi A. Blast Transformation and Fibrotic Progression in Polycythemia Vera and Essential Thrombocythemia: A Literature Review of Incidence and Risk Factors. Blood Cancer Journal (2015) 5, e366; doi:10.1038/bcj.2015.95.

2021 PharmaEssentia Corporation. All rights reserved. US-BSRM-2100225 11/21

BESREMi and PharmaEssentia are registered trademarks of PharmaEssentia Corporation, and the PharmaEssentia logo and PharmaEssentia SOURCE are trademarks of PharmaEssentia Corporation.

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PharmaEssentia's BESREMi (ropeginterferon alfa-2b-njft) Now Available for the Treatment of People With Polycythemia Vera in the United States -...

Twenty years ago, cardiologist and stem-cell scientist Piero Anversa published an exciting paper. He was then a prominent researcher at New York Medical College in Valhalla, and his data in mice showed that injured hearts could regenerate with the help of stem cells taken from bone marrow1contrary to prevailing wisdom.

Myocardial infarction, commonly known as a heart attack, deprives cardiac muscle cells of oxygen, causing them to perish. The human heart responds by laying scar tissue over lost muscle. But these reconstituted areas dont pump blood as competently as before. In time, this can lead to heart failureparticularly if other heart attacks follow. The implications of Anversas work were clear: stem cells, through their growth and proliferation, had the potential to reverse the damage caused by heart attacks and thereby prevent heart failure.

But other researchers who attempted to replicate these mouse studies found themselves coming up short. Allegations of faked results eventually began to surface, and Anversa, who had since joined Harvard Medical School, and Brigham and Womens Hospital in Boston, Massachusetts, was forced to leave his posts in 2015. Two years later, Brigham and Womens Hospital paid the US government US$10 million to settle allegations that Anversa and his colleagues had used fraudulent data to apply for federal funding. And a 2018 investigation conducted by Harvard called for 31 of Anversas papers to be retracted.

This saga has dampened the enthusiasm that once surrounded research into stem-cell therapy, says Michael Schneider, a research cardiologist at Imperial College London. The controversy, overt scientific misconduct and evidence against Anversas claims has cast aspersions on the field more generally, he admits. Thats unfortunate, because many other stem-cell scientists are conducting legitimate research.

Meanwhile, another heart-healing strategy has emerged, drawing inspiration from species that, unlike humans, can regrow cardiac muscle after trauma. Researchers are seeking to learn more about the molecules produced by zebrafish (Danio rerio) hearts as they heal themselvesand are investigating whether injectable drugs containing the same substances could also yield reparative results.

The question is now whether it will be stem cells, small-molecule drugs or a combination of the two that achieve the goal of convincing the heart to heal instead of scar.

In the wake of the Anversa scandal, there has been an important evolution of thinking on the stem-cells front. A 2019 literature review pointed out that newer studies tend to show the most significant impact from stem-cell therapy comes from the substances the cells secrete, rather than their proliferation2. After many years of work, we find that when we deliver cells into the heart, the benefit of replaced damaged cells is only minor, says the reviews author Javaria Tehzeeb, an internal-medicine specialist at the Albany Medical Center in New York. The real work of regeneration happens, she explains, when the cells produce growth factors, which in turn affect heart repair by reducing inflammation and stimulating the development of new heart muscle.

That means stem-cell therapies share some similarities with the drug strategyessentially it comes down to molecules secreted by the stem cells versus molecules that are directly injected. But they also have important differences.

First, part of the stem-cell therapy benefits might still come from the cells proliferation, even if that bonus is relatively small. Second, theres little control over what substances the stem cells produce once theyre injected, whereas specific molecules can be administered at known doses. And finally, the logistics of scaling up and delivering these two therapies will be very different.

A study published in 2020 showcased the importance of stem-cell-produced molecules by looking at the structural integrity of proteins found in infarcted mouse hearts3. The scientists artificially induced heart attacks in eight adult mice. Four weeks later, they administered stem cells to half the rodents. After a further four weeks, their hearts were removed and washed with a series of buffer solutions and chemical reagents to extract the proteins, which were then analysed. We essentially did a massive scan of every single protein in the heart, says Andre Terzic, lead author of the study. The authors were able to identify almost 4,000 proteins, and showed that heart attacks distorted the structure of 450 of them. But with stem-cell therapy, that number fell to 283.

Proteins are the intimate components that make our hearts work properly, and when the heart is diseased, they become damaged, says Terzic, who is director of the Mayo Clinic Center for Regenerative Medicine in Rochester, Minnesota. The ability of these stem cells to secrete healing signals is probably a key element to what weve observed.

All cells and tissues are constantly telling each other what they need and whether theyre stressed through molecular signalling. When you lose a chunk of cells in a heart attack, you lose part of that conversation, explains Charles Murry, an experimental pathologist and director of the Institute for Stem Cell and Regenerative Medicine at the University of Washington in Seattle. Injected stem cells could be filling in the missing dialogue by secreting signalling and rescue molecules, he explains.

Although this sounds encouraging, there are still parts of the stem-cell-therapy approach that need to be finessed. In a 2018 study, Murry and colleagues transplanted approximately 750 million cardiomyocytes into macaque monkeys that had experienced major heart attacks4. One month after the intervention, the amount of blood pumped by their hearts had increased by 10.6% compared with just 2.5% in the control group. This advantage persisted three months later, but one out of the five stem-cell-treated monkeys suffered arrhythmias. The onset of arrhythmia wasnt previously observed in small-animal studies, but it is a known complication of heart attacks. Nevertheless, the researchers thought it could be a potential side effect of the stem-cell infusion. Obviously it isnt statistically significant, but common sense led us to classify this as a treatment complication, says Murry.

In addition to safety concerns, stem-cell therapies are also beset by questions of practicality. Think of a lab with all these cell culture flasks where you have to grow millions of cells just to create a single dose, says Terzic. Now imagine tens of thousands of patients. Its a formidable effort to be ready, especially if you want to intervene rapidly. You dont have the luxury of time to build up supplies.

Thats one reason why some people think the promise of cardiac rejuvenation lies elsewhere. Theres been an awful lot of time and money spent on stem-cell therapy, raising false hope in patientsand so far, the clinical outcomes have been largely disappointing, says Paul Riley, a cardiovascular scientist at the University of Oxford, UK. Riley is investigating whether inserting specific molecules into the heart might be more effective.

Human hearts cant regenerate on their own, but other animals do have such abilities. Zebrafish, for example, can regrow their hearts after as much as 20% is removed. Newborn mice can also regenerate heart tissue. Observing the molecular pathways in these animals might make similar results possible in humans.

Research has shown that following a myocardial infarction in zebrafish, the epicardiuma membrane surrounding the heart muscleproduces molecular signals that might kick-start muscle-cell regeneration5. The hope is that manipulating the human epicardium could elicit the same therapeutic results. There are probably approaches we can take to target the cells that exist in the heart with small molecules or drugs, that could invoke repair and regeneration, says Riley.

Back in 2011, Riley and colleagues showed that this is theoretically possible6. They pre-treated adult mice with a daily injection of a protein called thymosin 4 for one week before inducing an infarction, and found that these mice were able to produce new cardiac muscle. This offers a road map to a pre-emptive therapy. If an individual is at high risk of a heart attack, says Riley, then its conceivable they could be advised to take a priming or preventative therapeutic, which may counteract an event, but its not quite the holy grail of restoring lost tissue after a heart attack that were searching for. In other studies, Riley has since shown that other proteins besides thymosin 4 might also have a role in stimulating the epicardium to regenerate the heart7.

Its easier to see how the drug route offers clearer prospects for scaling upbut the science behind this approach is newer, and there havent been any clinical trials in humans yet. What goes in stem cells favour is the body of work behind them, says Tehzeeb.

It might be that stem-cell therapies achieve government approvals first, but then drugs overtake them once the science and research have had time to catch up. When we get to the end of the line with molecules, then maybe we can say stem cells are a thing of the past, Tehzeeb says. But until then, we should continue to pursue their potential.

Murry echoes that sentiment, arguing that findings from both camps could end up helping everyones research. We need an ecosystem with a competition of ideas, and as long as its all openly published then well figure it out, he says. Thats the better approach, rather than saying my idea is better than your idea.

This article is part ofNature Outlook: Heart health, an editorially independent supplement produced with the financial support of third parties.About this content.

Orlic, D.et al.Nature410, 701705 (2001).

Tehzeeb, J., Manzoor, A. & Ahmed, M. M.Cureus11, e5959 (2019).

Arrell, D. K., Rosenow, C. S., Yamada, S., Behfar, A. & Terzic, A.npj Regen. Med.5, 5 (2020).

Liu, Y.-W.et al.Nature Biotechnol.36, 597605 (2018).

Cao, J. & Poss, K. D.Nature Rev. Cardiol.15, 631647 (2018).

Smart, N.et al.Nature474, 640644 (2011).

McManus, S.et al.J. Mol. Cell. Cardiol.140, 3031 (2020).

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Cells or drugs? The race to regenerate the heart - Scientific American

The COVID-19 pandemic has created a sense of urgency to generate new drugs and vaccines. In many cases, this urgency became a regulatory opportunity to bypass established regulatory pathways for new drugs.

While this has led to the fast emergence of many useful drugs and vaccines for COVID-19, it has also led to a general reduction in the quality of medical research from which to derive conclusions.

For example, according to Janet Woodcock, former director of the Food and Drug Administrations (FDA) Center for Drug Evaluation and Research, an FDA analysis found that 6% of clinical trials are yielding results the agency deems actionable.

The lack of regulation coupled with a sense of urgency has also led to overhype and rushed development of certain treatments, including cell-based therapies often sold as stem cell treatments.

While some of these products have undergone well-designed, adequately controlled trials, most are in the early stages. Some clinics are nevertheless offering these unproven and unlicensed treatments to people, promising to boost their immune system or overall health to protect against COVID-19.

Promoting and selling unproven and unlicensed treatments can harm public health and could lead many to undergo untested and potentially harmful treatments.

Recently, a group of researchers from the University of California, Irvine, the Georgia Institute of Technology, the University at Buffalo, NY, and the University of Melbourne in Australia, published a report outlining misinformation around cell-based treatments for COVID-19, calling for their stronger regulation.

Efforts to rapidly develop therapeutic interventions should never occur at the expense of the ethical and scientific standards that are at the heart of responsible clinical research and innovation, said Dr. Laertis Ikonomou, assistant professor of Oral Biology at the University at Buffalo, and co-author of the study.

Scientists, regulators, and policymakers must guard against the proliferation of poorly designed, underpowered, and duplicative studies that are launched with undue haste because of the pandemic, but are unlikely to provide convincing, clinically meaningful safety and efficacy data, said co-author Dr. Leigh Turner, professor of Health, Society and Behavior at the University of California, Irvine.

The researchers published their report in Stem Cell Reports.

Researchers conducted a study in August 2020 of 70 clinical trials involving cell-based treatments for COVID-19. They found that most were small, with an average of 51.8 participants, and only 22.8% were randomized, double-blinded, and controlled experiments.

The authors concluded that the cell-based interventions for COVID-19 were likely to have a relatively small collective clinical impact.

Cell-based treatments for COVID-19 are still at an experimental stage, Dr. Ikonomou told Medical News Today. There are tens of clinical trials, of varied complexity and rigor, that evaluate various cell types, such as mesenchymal stromal cells, for COVID-19 treatment.

Expanded or compassionate use of cell-based interventions has also been reported, but these individual cases are unlikely to tell us whether and how cell therapies could help with COVID-19 and do not substitute for the systematic clinical evaluation of cell-based products, he added.

A few completed phase 1/2 trials have shown a favorable safety profile, but larger size trials are required. Eventually, properly-powered, controlled, randomized, double-blinded clinical trials will help determine whether cell-based treatments are a viable therapeutic option for COVID-19 and its complications, he explained.

The urgency of the pandemic has made it easy to exaggerate early-stage research. The scientists highlight this is especially the case in press releases, where media professionals can over-hype findings and understate or omit limitations to gain more media coverage.

The researchers also say that even when online media include limitations and key aspects of studies, other communication channels can strip these away easily. What is left then gets amplified, as the public is desperate to see positive news.

To address this, the researchers say science communicators should ensure they have an accurate understanding of the information they report and highlight the required steps for the science to advance without exaggerating its speed.

The researchers also say that simply feeding the public more information in what is known as the information deficit model alone is insufficient. They also suggest science communicators should strive for an engaged or dialogue-based communication approach.

Over-hyping of promising treatments and in particular cell-based treatments has been a longstanding problem, and it did not first emerge with the COVID-19 pandemic, said Dr. Ikonomou. It has become a salient issue during these times due to the global nature of this health emergency and the resulting devastation and health toll.

Therefore, it is even more important to communicate promising developments in COVID-19-related science and clinical management [responsibly]. Key features of good communication are an accurate understanding of new findings, including study limitations and avoidance of sensationalist language, he explained.

Realistic timeframes for clinical translation are equally important as is the realization that promising interventions at preliminary stages may not always translate to proven treatments following rigorous testing, he added.

The researchers say that commercial investments by biotechnology companies to develop cell-based therapies for COVID-19 have led to well-designed and rigorous clinical trials.

However, some other businesses have overlooked the demanding process of pre-marketing authorization of their products. Instead, they made unsubstantiated and inaccurate claims about their stem cell products for COVID-19 based on hyperbolic reporting of cell-based therapies in early testing.

Some clinics advertise unproven and unlicensed mesenchymal stem cell treatments or exosome therapies as immune boosters that prevent COVID-19 and repair and regenerate lungs.

Often, these businesses make their treatments available via infusion or injection. However, one anti-aging clinic in California shipped its kits to clients, where they were to self-administer with a nebulizer and mask.

Such companies often market stem cell treatments via online and social media. In an initial review of many of these brands, the researchers could not find published findings from preclinical studies and clinical trials to support their commercial activities.

Instead, they found that these companies drew from uncritical news media reports, preliminary clinical studies, or case reports in which those diagnosed with COVID-19 received stem cell interventions.

Promoting such therapies that have not undergone proper tests for safety and efficacy have the potential for significant physical and financial harm.

Health experts have documented adverse events due to unlicensed stem cell products, including vision loss and autoimmune, infectious, neurological, and cardiovascular complications.

Early in the pandemic, scientific and professional societies, including the Alliance for Regenerative Medicine and the International Society for Stem Cell Research, have warned the public against businesses engaged in the marketing of cell-based treatments that have not undergone adequate testing.

The researchers highlight that it is unclear whether these warnings reached individuals and their loved ones or significantly affected public understanding of the risks of receiving unlicensed and unproven stem cell treatments for COVID-19.

They also indicate that it is unclear whether these societies and organizations have an important role in convincing regulatory bodies to increase enforcement in this space. Nevertheless, at the time of writing, the FDA and Federal Trade Commission have issued 22 letters to businesses selling unproven and unlicensed cell-based therapies.

And while many of these companies have ceased market activity, the presence of other companies continuing to pedal the same claims makes it clear that regulatory bodies must increase their enforcement.

Additionally, the researchers question whether warning letters are sufficient to disincentivize clinicians and others to sell unlicensed products. They write:

If companies and affiliated clinicians are not fined, forced to return to patients whatever profits they have made, confronted with criminal charges, subject to revocation of medical licensure, or otherwise subject to serious legal and financial consequences, it is possible that more businesses will be drawn to this space because of the profits that can be generated from selling unlicensed and unproven cell-based products in the midst of a pandemic.

The researchers conclude that regulators should increase enforcement against unproven and unlicensed therapies for COVID-19.

They also say that science communicators should report on scientific claims more realistically and include the public in more discourse.

In the U.S. and elsewhere, there are regulations and enforcement mechanisms that deal with harms caused by unproven and unlicensed cell-based interventions and false advertising claims, said Dr. Ikonomou. It may be preferable to implement existing regulations more vigorously than introduce new ones.

Stakeholders, such as scientific, professional, and medical associations, can contribute towards this goal with reporting and monitoring of cell therapy misinformation. There is a shared responsibility to combat cell-therapy related misinformation and disinformation that undercuts legitimate research and clinical efforts and portrays unproven interventions as silver bullets for COVID-19, he concluded.

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COVID-19: Researchers warn against overhyping early-stage therapies - Medical News Today

J Cardiovasc Nurs. Author manuscript; available in PMC 2014 Jul 21.

Published in final edited form as:

PMCID: PMC4104807

NIHMSID: NIHMS100185

1Department of Bioengineering, University of Illinois at Chicago

2Department of Physiology and Biophysics and Department of Bioengineering, University of Illinois at Chicago

1Department of Bioengineering, University of Illinois at Chicago

2Department of Physiology and Biophysics and Department of Bioengineering, University of Illinois at Chicago

Stem cells have the ability to differentiate into specific cell types. The two defining characteristics of a stem cell are perpetual self-renewal and the ability to differentiate into a specialized adult cell type. There are two major classes of stem cells: pluripotent that can become any cell in the adult body, and multipotent that are restricted to becoming a more limited population of cells. Cell sources, characteristics, differentiation and therapeutic applications are discussed. Stem cells have great potential in tissue regeneration and repair but much still needs to be learned about their biology, manipulation and safety before their full therapeutic potential can be achieved.

Stem cells have the ability to build every tissue in the human body, hence have great potential for future therapeutic uses in tissue regeneration and repair. In order for cells to fall under the definition of stem cells, they must display two essential characteristics. First, stem cells must have the ability of unlimited self-renewal to produce progeny exactly the same as the originating cell. This trait is also true of cancer cells that divide in an uncontrolled manner whereas stem cell division is highly regulated. Therefore, it is important to note the additional requirement for stem cells; they must be able to give rise to a specialized cell type that becomes part of the healthy animal.1

The general designation, stem cell encompasses many distinct cell types. Commonly, the modifiers, embryonic, and adult are used to distinguish stem cells by the developmental stage of the animal from which they come, but these terms are becoming insufficient as new research has discovered how to turn fully differentiated adult cells back into embryonic stem cells and, conversely, adult stem cells, more correctly termed somatic stem cells meaning from the body, are found in the fetus, placenta, umbilical cord blood and infants.2 Therefore, this review will sort stem cells into two categories based on their biologic properties - pluripotent stem cells and multipotent stem cells. Their sources, characteristics, differentiation and therapeutic applications are discussed.

Pluripotent stem cells are so named because they have the ability to differentiate into all cell types in the body. In natural development, pluripotent stem cells are only present for a very short period of time in the embryo before differentiating into the more specialized multipotent stem cells that eventually give rise to the specialized tissues of the body (). These more limited multipotent stem cells come in several subtypes: some can become only cells of a particular germ line (endoderm, mesoderm, ectoderm) and others, only cells of a particular tissue. In other words, pluripotent cells can eventually become any cell of the body by differentiating into multipotent stem cells that themselves go through a series of divisions into even more restricted specialized cells.

During natural embryo development, cells undergo proliferation and specialization from the fertilized egg, to the blastocyst, to the gastrula during natural embryo development (left side of panel). Pluripotent, embryonic stem cells are derived from the inner cell mass of the blastoctyst (lightly shaded). Multipotent stem cells (diamond pattern, diagonal lines, and darker shade) are found in the developing gastrula or derived from pluripotent stem cells and are restricted to give rise to only cells of their respective germ layer.

Based on the two defining characteristics of stem cells (unlimited self-renewal and ability to differentiate), they can be described as having four outcomes or fates3 (). A common fate for multipotent stem cells is to remain quiescent without dividing or differentiating, thus maintaining its place in the stem cell pool. An example of this is stem cells in the bone marrow that await activating signals from the body. A second fate of stem cells is symmetric self-renewal in which two daughter stem cells, exactly like the parent cell, arise from cell division. This does not result in differentiated progeny but does increase the pool of stem cells from which specialized cells can develop in subsequent divisions. The third fate, asymmetric self-renewal, occurs when a stem cell divides into two daughter cells, one a copy of the parent, the other a more specialized cell, named a somatic or progenitor cell. Asymmetric self-renewal results in the generation of differentiated progeny needed for natural tissue development/regeneration while also maintaining the stem cell pool for the future. The fourth fate is that in which a stem cell divides to produce two daughters both different from the parent cell. This results in greater proliferation of differentiated progeny with a net loss in the stem cell pool.

Four potential outcomes of stem cells. A) Quiescence in which a stem cell does not divide but maintains the stem cell pool. B) Symmetric self-renewal where a stem cell divides into two daughter stem cells increasing the stem cell pool. C) Asymmetric self-renewal in which a stem cell divides into one differentiated daughter cell and one stem cell, maintaining the stem cell pool. D) Symmetric division without self-renewal where there is a loss in the stem cell pool but results in two differentiated daughter cells. (SC- Stem cell, DP-Differentiated progeny)

The factors that determine the fate of stem cells is the focus of intense research. Knowledge of the details could be clinically useful. For example, clinicians and scientists might direct a stem cell population to expand several fold through symmetrical self-renewal before differentiation into multipotent or more specialized progenitor cells. This would ensure a large, homogeneous population of cells at a useful differentiation stage that could be delivered to patients for successful tissue regeneration.

Pluripotent stem cells being used in research today mainly come from embryos, hence the name, embryonic stem cells. Pre-implantation embryos a few days old contain only 10-15% pluripotent cells in the inner cell mass (). Those pluripotent cells can be isolated, then cultured on a layer of feeder cells which provide unknown cues for many rounds of proliferation while sustaining their pluripotency.

Recently, two different groups of scientists induced adult cells back into the pluripotent state by molecular manipulation to yield induced pluripotent stem cells (iPS) that share some of the same characteristics as embryonic stem cells such as proliferation, morphology and gene expression (in the form of distinct surface markers and proteins being expressed).4-8 Both groups used retroviruses to carry genes for transcription factors into the adult cells. These genes are transcribed and translated into proteins that regulate the expression of other genes designed to reprogram the adult nucleus back into its embryonic state. Both introduced the embryonic transcription factors known as Sox2 and Oct4. One group also added Klf4 and c-Myc4, and the other group added Lin28 and Nanog.6 Other combinations of factors would probably also work, but, unfortunately, neither the retroviral carrier method nor the use of the oncogenic transcription factor c-Myc are likely to be approved for human therapy. Consequently, a purely chemical approach to deliver genes into the cells, and safer transcription factors are being tried. Results of these experiments look promising.9

Multipotent stem cells may be a viable option for clinical use. These cells have the plasticity to become all the progenitor cells for a particular germ layer or can be restricted to become only one or two specialized cell types of a particular tissue. The multipotent stem cells with the highest differentiating potential are found in the developing embryo during gastrulation (day 14-15 in humans, day 6.5-7 in mice). These cells give rise to all cells of their particular germ layer, thus, they still have flexibility in their differentiation capacity. They are not pluripotent stem cells because they have lost the ability to become cells of all three germ layers (). On the low end of the plasticity spectrum are the unipotent cells that can become only one specialized cell type such as skin stem cells or muscle stem cells. These stem cells are typically found within their organ and although their differentiation capacity is restricted, these limited progenitor cells play a vital role in maintaining tissue integrity by replenishing aging or injured cells. There are many other sub-types of multipotent stem cells occupying a range of differentiation capacities. For example, multipotent cells derived from the mesoderm of the gastrula undergo a differentiation step limiting them to muscle and connective tissue; however, further differentiation results in increased specialization towards only connective tissue and so on until the cells can give rise to only cartilage or only bone.

Multipotent stem cells found in bone marrow are best known, because these have been used therapeutically since the 1960s10 (their potential will be discussed in greater detail in a later section). Recent research has found new sources for multipotent stem cells of greater plasticity such as the placenta and umbilical cord blood.11 Further, the heart, until recently considered void of stem cells, is now known to contain stem cells with the potential to become cardiac myocytes.12 Similarly, neuro-progenitor cells have been found within the brain.13

The cardiac stem cells are present in such small numbers, that they are difficult to study and their function has not been fully determined. The second review in this series will discuss their potential in greater detail.

Since Federal funding for human embryonic stem cells is restricted in the United States, many scientists use the mouse model instead. Besides their ability to self-renew indefinitely and differentiate into cell types of all three germ layers, murine and human pluripotent stem cells have much in common. It should not be surprising that so many pluripotency traits are conserved between species given the shared genomic sequences and intra-cellular structure in mammals. Both mouse and human cells proliferate indefinitely in culture, have a high nucleus to cytoplasm ratio, need the support of growth factors derived from other live cells, and display similar surface antigens, transcription factors and enzymatic activity (i.e. high alkaline phosphatase activity).14 However, differences between mouse and human pluripotent cells, while subtle, are very important. Although the transcription factors mentioned above to induce pluripotency from adult cells (Oct3/4 and Sox2) are shared, the extracellular signals needed to regulate them differ. Mouse embryonic stem cells need the leukemia inhibitory factor and bone morphogenic proteins while human require the signaling proteins Noggin and Wnt for sustained pluripotency.15 Surface markers used to identify pluripotent cells also differ slightly between the two species as seen in the variants of the adhesion molecule SSEA (SSEA-1 in mouse, SSEA-3 & 4 in humans).16 Thus, while pluripotency research in mouse cells is valuable, a direct correlation to the human therapy is not likely.

Last, but certainly not least, a big difference between mouse and human stem cells are the moral and ethical dilemmas that accompany the research. Some people consider working with human embryonic stem cells to be ethically problematic while very few people have reservations on working with the mouse models. However, given the biological differences between human and mouse cells, most scientists believe that data relevant for human therapy will be missed by working only on rodents.

Cell surface markers are typically also used to identify multipotent stem cells. For example, mesenchymal stem cells can be purified from the whole bone marrow aspirate by eliminating cells that express markers of committed cell types, a step referred to as lineage negative enrichment, and then further separating the cells that express the sca-1 and c-Kit surface markers signifying mesenchymal stem cells. Both the lineage negative enrichment step and the sca-1/c-Kit isolation can be achieved by using flow cytometry and is discussed in further detail in the following review. The c-Kit surface marker also is used to distinguish the recently discovered cardiac stem cells from the rest of the myocardium. A great deal of recent work in cardiovascular research has centered on trying to find which markers indicate early multipotent cells that will give rise to pre-cardiac myocytes. Cells with the specific mesodermal marker, Kdr, give rise to the progenitor cells of the cardiovascular system including contracting cardiac myocytes, endothelial cells and vascular smooth muscle cells and are therefore considered to be the earliest cells with specification towards the cardiovascular lineage.17 Cells at this early stage still proliferate readily and yet are destined to become cells of the cardiovascular system and so may be of great value therapeutically.

Scientists are still struggling to reliably direct differentiation of stem cells into specific cell types. They have used a virtual alphabet soup of incubation factors toward that end (including trying a variety of growth factors, chemicals and complex substrates on which the cells are grown), with, so far, only moderate success. As an example of this complexity, one such approach to achieve differentiation towards cardiac myocytes is to use the chemical activin A and the growth factor BMP-4. When these two factors are administered to pluripotent stem cells in a strictly controlled manner, both in concentration and temporally, increased efficiency is seen in differentiation towards cardiac myocytes, but still, only 30% of cells can be expected to become cardiac.18

Multipotent cells have also been used as the starting point for cell therapy, again with cocktails of growth factors and/or chemicals to induce differentiation toward a specific, desired lineage. Some recipes are simple, such as the use of retinoic acid to induce mesenchymal stem cells into neuronal cells,19 or transforming growth factor- to make bone marrow-derived stem cells express cardiac myocyte markers.20 Others are complicated or ill-defined such as addition of the unknown factors secreted by cells in culture. Physical as well as chemical cues cause differentiation of stem cells. Simply altering the stiffness of the substrate on which cells are cultured can direct stem cells to neuronal, myogenic or osteogenic lineages.21 Cells evolve in physical and chemical environments so a combination of both will probably be necessary for optimal differentiation of stem cells. The importance of physical cues in the cells environment will be discussed in greater detail in the final review of this series. Ideally, for stem cells to be used therapeutically, efficient, uniform protocols must be established so that cells are a well-controlled and well-defined entity.

Pluripotent stem cells have not yet been used therapeutically in humans because many of the early animal studies resulted in the undesirable formation of unusual solid tumors, called teratomas. Teratomas are made of a mix of cell types from all the early germ layers. Later successful animal studies used pluripotent cells modified to a more mature phenotype which limits this proliferative capacity. Cells derived from pluripotent cells have been used to successfully treat animals. For example, animals with diabetes have been treated by the creation of insulin-producing cells responsive to glucose levels. Also, animals with acute spinal cord injury or visual impairment have been treated by creation of new myelinated neurons or retinal epithelial cells, respectively. Commercial companies are currently in negotiations with the FDA regarding the possibility of advancing to human trials. Other animal studies have been conducted to treat several maladies such as Parkinsons disease, muscular dystrophy and heart failure.18,22,23

Scientists hope that stem cell therapy can improve cardiac function by integration of newly formed beating cardiac myocytes into the myocardium to produce greater force. Patches of cardiac myocytes derived from human embryonic stem cells can form viable human myocardium after transplantation into animals,24 with some showing evidence of electrical integration.25,26 Damaged rodent hearts showed slightly improved cardiac function after injection of cardiac myocytes derived from human embryonic stem cells.21 The mechanisms for the gain in function are not fully understood but it may be only partially due to direct integration of new beating heart cells. It is more likely due to paracrine effects that benefit other existing heart cells (see next review).

Multipotent stem cells harvested from bone marrow have been used since the 1960s to treat leukemia, myeloma and lymphoma. Since cells there give rise to lymphocytes, megakaryocytes and erythrocytes, the value of these cells is easily understood in treating blood cancers. Recently, some progress has been reported in the use of cells derived from bone marrow to treat other diseases. For example, the ability to form whole joints in mouse models27 has been achieved starting with mesenchymal stem cells that give rise to bone and cartilage. In the near future multipotent stem cells are likely to benefit many other diseases and clinical conditions. Bone marrow-derived stem cells are in clinical trials to remedy heart ailments. This is discussed in detail in the next review of this series.

Pluripotent and multipotent stem cells have their respective advantages and disadvantages. The capacity of pluripotent cells to become any cell type is an obvious therapeutic advantage over their multipotent kin. Theoretically, they could be used to treat diseased or aging tissues in which multipotent stem cells are insufficient. Also, pluripotent stem cells proliferate more rapidly so can yield higher numbers of useful cells. However, use of donor pluripotent stem cells would require immune suppressive drugs for the duration of the graft28 while use of autologous multipotent stem cells (stem cells from ones self) would not. This ability to use ones own cells is a great advantage of multipotent stem cells. The immune system recognizes specific surface proteins on cells/objects that tell them whether the cell is from the host and is healthy. Autologous, multipotent stem cells have the patients specific surface proteins that allow it to be accepted by the hosts immune system and avoid an immunological reaction. Pluripotent stem cells, on the other hand, are not from the host and therefore, lack the proper signals required to stave off rejection from the immune system. Research is ongoing trying to limit the immune response caused by pluripotent cells and is one possible advantage that iPS cells may have.

The promises of cures for human ailments by stem cells have been much touted but many obstacles must still be overcome. First, more human pluripotent and multipotent cell research is needed since stem cell biology differs in mice and men. Second, the common feature of unlimited cell division shared by cancer cells and pluripotent stem cells must be better understood in order to avoid cancer formation. Third, the ability to acquire large numbers of the right cells at the right stage of differentiation must be mastered. Fourth, specific protocols must be developed to enhance production, survival and integration of transplanted cells. Finally, clinical trials must be completed to assure safety and efficacy of the stem cell therapy. When it comes to stem cells, knowing they exist is a long way from using them therapeutically.

Supported by NIH (HL 62426 and T32 HL 007692)

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Introduction to Stem Cell Therapy

Abstract

Traumatic spinal cord injury (SCI) is a life changing neurological condition with substantial socioeconomic implications for patients and their care-givers. Recent advances in medical management of SCI has significantly improved diagnosis, stabilization, survival rate and well-being of SCI patients. However, there has been small progress on treatment options for improving the neurological outcomes of SCI patients. This incremental success mainly reflects the complexity of SCI pathophysiology and the diverse biochemical and physiological changes that occur in the injured spinal cord. Therefore, in the past few decades, considerable efforts have been made by SCI researchers to elucidate the pathophysiology of SCI and unravel the underlying cellular and molecular mechanisms of tissue degeneration and repair in the injured spinal cord. To this end, a number of preclinical animal and injury models have been developed to more closely recapitulate the primary and secondary injury processes of SCI. In this review, we will provide a comprehensive overview of the recent advances in our understanding of the pathophysiology of SCI. We will also discuss the neurological outcomes of human SCI and the available experimental model systems that have been employed to identify SCI mechanisms and develop therapeutic strategies for this condition.

Keywords: spinal cord injury, secondary injury mechanisms, clinical classifications and demography, animal models, glial and immune response, glial scar, chondroitin sulfate proteoglycans (CSPGs), cell death

Spinal cord injury (SCI) is a debilitating neurological condition with tremendous socioeconomic impact on affected individuals and the health care system. According to the National Spinal Cord Injury Statistical Center, there are 12,500 new cases of SCI each year in North America (1). Etiologically, more than 90% of SCI cases are traumatic and caused by incidences such as traffic accidents, violence, sports or falls (2). There is a reported male-to-female ratio of 2:1 for SCI, which happens more frequently in adults compared to children (2). Demographically, men are mostly affected during their early and late adulthood (3rd and 8th decades of life) (2), while women are at higher risk during their adolescence (1519 years) and 7th decade of their lives (2). The age distribution is bimodal, with a first peak involving young adults and a second peak involving adults over the age of 60 (3). Adults older than 60 years of age whom suffer SCI have considerably worse outcomes than younger patients, and their injuries usually result from falls and age-related bony changes (1).

The clinical outcomes of SCI depend on the severity and location of the lesion and may include partial or complete loss of sensory and/or motor function below the level of injury. Lower thoracic lesions can cause paraplegia while lesions at cervical level are associated with quadriplegia (4). SCI typically affects the cervical level of the spinal cord (50%) with the single most common level affected being C5 (1). Other injuries include the thoracic level (35%) and lumbar region (11%). With recent advancements in medical procedures and patient care, SCI patients often survive these traumatic injuries and live for decades after the initial injury (5). Reports on the clinical outcomes of patients who suffered SCI between 1955 and 2006 in Australia demonstrated that survival rates for those suffering from tetraplegia and paraplegia is 91.2 and 95.9%, respectively (5). The 40-year survival rate of these individuals was 47 and 62% for persons with tetraplegia and paraplegia, respectively (5). The life expectancy of SCI patients highly depends on the level of injury and preserved functions. For instance, patients with ASIA Impairment Scale (AIS) grade D who require a wheelchair for daily activities have an estimated 75% of a normal life expectancy, while patients who do not require wheelchair and catheterization can have a higher life expectancy up to 90% of a normal individual (6). Today, the estimated life-time cost of a SCI patient is $2.35 million per patient (1). Therefore, it is critical to unravel the cellular and molecular mechanisms of SCI and develop new effective treatments for this devastating condition. Over the past decades, a wealth of research has been conducted in preclinical and clinical SCI with the hope to find new therapeutic targets for traumatic SCI.

SCI commonly results from a sudden, traumatic impact on the spine that fractures or dislocates vertebrae. The initial mechanical forces delivered to the spinal cord at the time of injury is known as primary injury where displaced bone fragments, disc materials, and/or ligaments bruise or tear into the spinal cord tissue (79). Notably, most injuries do not completely sever the spinal cord (10). Four main characteristic mechanisms of primary injury have been identified that include: (1) Impact plus persistent compression; (2) Impact alone with transient compression; (3) Distraction; (4) Laceration/transection (8, 11). The most common form of primary injury is impact plus persistent compression, which typically occurs through burst fractures with bone fragments compressing the spinal cord or through fracture-dislocation injuries (8, 12, 13). Impact alone with transient compression is observed less frequently but most commonly in hyperextension injuries (8). Distraction injuries occur when two adjacent vertebrae are pulled apart causing the spinal column to stretch and tear in the axial plane (8, 12). Lastly, laceration and transection injuries can occur through missile injuries, severe dislocations, or sharp bone fragment dislocations and can vary greatly from minor injuries to complete transection (8). There are also distinct differences between the outcomes of SCI in military and civilian cases. Compared to civilian SCI, blast injury is the common cause of SCI in battlefield that usually involves multiple segments of the spinal cord (14). Blast SCI also results in higher severity scores and is associated with longer hospital stays (15). A study on American military personnel, who sustained SCI in a combat zone from 2001 to 2009, showed increased severity and poorer neurological recovery compared to civilian SCI (15). Moreover, lower lumbar burst fractures and lumbosacral dissociation happen more frequently in combat injuries (1). Regardless of the form of primary injury, these forces directly damage ascending and descending pathways in the spinal cord and disrupt blood vessels and cell membranes (11, 16) causing spinal shock, systemic hypotension, vasospasm, ischemia, ionic imbalance, and neurotransmitter accumulation (17). To date, the most effective clinical treatment to limit tissue damage following primary injury is the early surgical decompression (< 24 h post-injury) of the injured spinal cord (18, 19). Overall, the extent of the primary injury determines the severity and outcome of SCI (20, 21).

Functional classification of SCI has been developed to establish reproducible scoring systems by which the severity of SCI could be measured, compared, and correlated with the clinical outcomes (20). Generally, SCI can be classified as either complete or incomplete. In complete SCI, neurological assessments show no spared motor or sensory function below the level of injury (4). In the past decades, several scoring systems have been employed for clinical classification of neurological deficits following SCI. The first classification system, Frankel Grade, was developed by Frankel and colleagues in 1969 (22). They assessed the severity and prognosis of SCI using numerical sensory and motor scales (22). This was a 5-grade system in which Grade A was the most severe SCI with complete loss of sensory and motor function below the level of injury. Grade B represented complete motor loss with preserved sensory function and sacral sparing. Patients in Grade C and D had different degrees of motor function preservation and Grade E represented normal sensory and motor function. The Frankel Grade was widely utilized after its publication due to its ease of use. However, lack of clear distinction between Grades C and D and inaccurate categorization of motor improvements in patients over time, led to its replacement by other scoring systems (20).

Other classification methods followed Frankel's system. In 1987, Bracken et al. at Yale University School of Medicine classified motor and sensory functions separately in a 5 and 7-scale systems, respectively (23). However, this scoring system failed to account for sacral function (20). Moreover, integration of motor and sensory classifications was impossible in this system and it was abandoned due to complexity and impracticality in clinical settings (20). Several other scoring systems were developed in 1970' and 1980's by different groups such as Lucas and Ducker at the Maryland Institute for Emergency Medical Services in late 1970's (24), Klose and colleagues at the University of Miami Neuro-spinal Index (UMNI) in early 1980s (25) and Chehrazi and colleagues (Yale Scale) in 1981 (26). These scoring systems also became obsolete due to their disadvantage in evaluation of sacral functions, difficulty of use or discrepancies between their motor and sensory scoring sub-systems (20).

The ASIA scoring system is currently the most widely accepted and employed clinical scoring system for SCI. ASIA was developed in 1984 by the American Spinal Cord Injury Association and has been updated over time to improve its reliability (). In this system, sensory function is scored from 02 and motor function from 0 to 5 (20). The ASIA impairment score (AIS) ranges from complete loss of sensation and movement (AIS = A) to normal neurological function (AIS = E). The first step in ASIA system is to identify the neurological level of injury (NLI). In this assessment, except upper cervical vertebrae that closely overlay the underlying spinal cord segments, the anatomical relationship between the spinal cord segments and their corresponding vertebra is not reciprocally aligned along the adult spinal cord (20). At thoracic and lumbar levels, each vertebra overlays a spinal cord segment one or two levels below and as the result, a T11 vertebral burst fracture results in neurological deficit at and below L1 spinal cord segment. Hence, the neurological level of injury (NLI) is defined as the most caudal neurological level at which all sensory and motor functions are normal (20). Upon identifying the NLI, if the injury is complete (AIS = A), zone of partial preservation (ZPP) is determined (20). ZPP is defined as all the segments below the NLI that have some preserved sensory or motor function. A precise record of ZPP enables the examiners to distinguish spontaneous from treatment-induced functional recovery, thus, essential for evaluating the therapeutic efficacy of treatments (20). Complete loss of motor and preservation of some sensory functions below the neurological level of the injury is categorized as AIS B (20). If motor function is also partially spared below the level of the injury, AIS score can be C or D (20). The AIS is scored D when the majority of the muscle groups below the level of the injury exhibit strength level of 3 or higher (for more details see ). ASIA classification combines the assessments of motor, sensory and sacral functions, thus addressing the shortcomings of previous scoring systems (20). The validity and reproducibility of ASIA system combined with its accuracy in prediction of patients' outcome have made it the most accepted and reliable clinical scoring system utilized for neurological classification of SCI (20).

ASIA scoring for the neurological classification of the SCI. A sample scoring sheet used for ASIA scoring in clinical setting is provided (adopted from: http://asia-spinalinjury.org).

In clinical management of SCI, neurological outcomes are generally determined at 72 h after injury using ASIA scoring system (20, 27). This time-point has shown to provide a more precise assessment of neurological impairments after SCI (28). One important predictor of functional recovery is to determine whether the injury was incomplete or complete. As time passes, SCI patients experience some spontaneous recovery of motor and sensory functions. Most of the functional recovery occurs during the first 3 months and in most cases reaches a plateau by 9 months after injury (20). However, additional recovery may occur up to 1218 months post-injury (20). Long term outcomes of SCI are closely related to the level of the injury, the severity of the primary injury and progression of secondary injury, which will be discussed in this review.

Depending on the level of SCI, patients experience paraplegia or tetraplegia. Paraplegia is defined as the impairment of sensory or motor function in lower extremities (27, 28). Patients with incomplete paraplegia generally have a good prognosis in regaining locomotor ability (~76% of patients) within a year (27). Complete paraplegic patients, however, experience limited recovery of lower limb function if their NLI is above T9 (29). An NLI below T9 is associated with 38% chance of regaining some lower extremity function (29). In patients with complete paraplegia, the chance of recovery to an incomplete status is only 4% with only half of these patients regaining bladder and bowel control (29). Tetraplegia is defined as partial or total loss of sensory or motor function in all four limbs. Patients with incomplete tetraplegia will gain better recovery than complete tetra- and paraplegia (30). Unlike complete SCI, recovery from incomplete tetraplegia usually happens at multiple levels below the NLI (20). Patients generally reach a plateau of recovery within 912 months after injury (20). Regaining some motor function within the first month after the injury is associated with a better neurological outcome (20). Moreover, appearance of muscle flicker (a series of local involuntary muscle contractions) in the lower extremities is highly associated with recovery of function (31). Patients with complete tetraplegia, often (6690%) regain function at one level below the injury (28, 30). Importantly, initial muscle strength is an important predictor of functional recovery in these patients (20). Complete tetraplegic patients with cervical SCI can regain antigravity muscle function in 27% of the cases when their initial muscle strength is 0 on a 5-point scale (32). However, the rate of regaining antigravity muscle strength at one caudal level below the injury increases to 97% when the patients have initial muscle strength of 12 on a 5-point scale (33).

An association between sensory and motor recovery has been demonstrated in SCI where spontaneous sensory recovery usually follows the pattern of motor recovery (20, 34). Maintenance of pinprick sensation at the zone of partial preservation or in sacral segments has been shown as a reliable predictor of motor recovery (35). One proposed reason for this association is that pinprick fibers in lateral spinothalamic tract travel in proximity of motor fibers in the lateral corticospinal tract, and thus, preservation of sensory fibers can be an indicator of the integrity of motor fiber (20). Diagnosis of an incomplete injury is of great importance and failure to detect sensory preservation at sacral segments results in an inaccurate assessment of prognosis (20).

In the past few decades, various animal models have been developed to allow understanding the complex biomedical mechanisms of SCI and to develop therapeutic strategies for this condition. An ideal animal model should have several characteristics including its relevance to the pathophysiology of human SCI, reproducibility, availability, and its potential to generate various severities of injury (36).

Small rodents are the most frequently employed animals in SCI studies due to their availability, ease of use and cost-effectiveness compared to primates and larger non-primate models of SCI (36, 37). Among rodents, rats more closely mimic pathophysiological, electrophysiological, functional, and morphological features of non-primate and human SCI (38). In rat (39), cat (40), monkey (41), and human SCI (17), a cystic cavity forms in the center of the spinal cord, which is a surrounded by a rim of anatomically preserved white matter. A study by Metz and colleagues compared the functional and anatomical outcomes of rat contusive injuries and human chronic SCI (42). High resolution MRI assessments identified that SCI-induced neuroanatomical changes such as spinal cord atrophy and size of the lesion were significantly correlated with the electrophysiological and functional outcomes in both rat and human contusive injuries (42). Histological assessments in rats also showed a close correlation between the spared white matter and functional preservation following injury (42). These studies provide evidence that rat models of contusive SCI could serve as an adequate model to develop and evaluate the structural and functional benefits of therapeutic strategies for SCI (42).

Mice show different histopathology than human SCI in which the lesion site is filled with dense fibrous connective-like tissue (4346). Mouse SCI studies show the presence of fibroblast-like cells expressing fibronectin, collagen, CD11b, CD34, CD13, and CD45 within the lesion core of chronic SCI, while it is absent in the injured spinal cord of rats (47). Another key difference between rat and mice SCI is the time-point of inflammatory cell infiltration. While microglia/macrophage infiltration is relatively consistent between rat and mouse models of SCI (47), there is a temporal difference in infiltration of neutrophils and T cells between the two species (47, 48). In SCI rats, infiltration of neutrophils, the first responders, peaks at 6 h post injury, followed by a significant decline at 2448 h after SCI (48). Similarly, in mouse SCI, neutrophil infiltration occurs within 6 h following injury; however, their numbers continue to rise and do not peak until 314 days post injury (49). T cell infiltration also varies between rat and mouse SCI models (50). In rats, T cell infiltration occurs between 3 and 7 days post injury and declines by 50% in the following 2 weeks (47), whereas in mice, T cell infiltration is not detected until 14 days post injury and their number doubles between 2 and 6 weeks post injury (47). Regardless of their pathophysiological relevance, mice have been used extensively in SCI studies primarily due to the availability of transgenic and mutant mouse models that have allowed uncovering molecular and cellular mechanisms of SCI (38).

In recent years, there has been emerging interest in employment of non-human primates and other larger animals such as pig, dog and cat as intermediate pre-clinical models (5153) to allow more effective translation of promising treatments from rodent models to human clinical trials (50). Although rodents have served as invaluable models for studying SCI mechanisms and therapeutic development, larger mammals, in particular non-human primates, share a closer size, neuroanatomy, and physiology to humans. Importantly, their larger size provides a more relevant platform for drug development, bioengineering inventions, and electrophysiological and rehabilitation studies. Nonetheless, both small and large animal models of SCI have limitations in their ability to predict the outcome in human SCI. One important factor is high degree of variability in the nature of SCI incidence, severity and location of the injury in human SCI, while in laboratory animal models, these variabilities are less (36). Values acquired by clinical scoring systems such as ASIA or Frankel scoring systems lack the consistency of the data acquired from laboratory settings, which makes the translation of therapeutic interventions from experimental to clinical settings challenging (36). A significant effect from an experimental treatment in consistent laboratory settings may not be reproducible in clinical settings due to high variability and heterogeneity in human populations and their injuries (36). To date, several pharmacological and cellular preclinical discoveries have led to human clinical trials based on their efficacy in improving the outcomes of SCI in small animal models. However, the majority of these trials failed to reproduce the same efficacy in human SCI. Thus, in pre-clinical studies, animal models, and study designs should be carefully chosen to reflect the reality of clinical setting as closely as possible (36). Larger animals provide the opportunity to refine promising therapeutic strategies prior to testing in human SCI; however, their higher cost, need for specialized facilities and small subject (sample) size have limited their use in SCI research (50). Thus, rodents are currently the most commonly employed models for preclinical discoveries and therapeutic development, while the use of larger animals is normally pursued for late stage therapies that have shown efficacy and promise in small animal models. provides a summary of available SCI models.

Animal models are also classified based on the type of SCI. The following sections will provide an overview on the available SCI models that are developed based on injury mechanisms, their specifications and relevance to human SCI ().

A complete transection model of SCI is relatively easy to reproduce (51). However, this model is less relevant to human SCI as a complete transection of the spinal cord rarely happens (51). While they do not represent clinical reality of SCI, transection models are specifically suitable for studying axonal regeneration or developing biomaterial scaffolds to bridge the gap between proximal and distal stamps of the severed spinal cord (51). Due to complete disconnection from higher motor centers, this model is also suitable for studying the role of propriospinal motor and sensory circuits in recovery of locomotion following SCI (51, 80). Partial transection models including hemi-section, unilateral transection and dorsal column lesions are other variants of transection models (51). Partial transection models are valuable for investigation of nerve grafting, plasticity and where a comparison between injured and non-injured pathways is needed in the same animal (51). However, these models lead to a less severe injury and higher magnitude of spontaneous recovery rendering them less suitable for development and evaluation of new therapies (51).

Contusion is caused by a transient physical impact to the spinal cord and is clinically-relevant. There are currently three types of devices that can produce contusion injury in animal models: weight-drop apparatus, electromagnetic impactor, and a recently introduced air gun device (51). The impactor model was first introduced by Gruner at New York University (NYU) in 1992 (81). The original NYU impactor included a metal rod of specific weight (10 g) that could be dropped on the exposed spinal cord from a specific height to induce SCI (51). This model allowed induction of a defined severity of SCI by adjusting the height, which the rod fell on the spinal cord (81). Parameters such as time, velocity at impact and biomechanical response of the tissue can be recorded for analysis and verification (51). The NYU impactor was later renamed to Multicenter Animal Spinal Cord Injury Study (MASCIS) impactor, and conditions surrounding the study and use of the MASCIS impactor were standardized (51). Since its introduction, the MASCIS impactor has been updated twice. The most recent version, MACIS III, was introduced in 2012 and included both electromagnetic control and digital recording of the impact parameters (51). However, inability to control duration of impact and weight bounce, that could cause multiple impacts, have been known limitations of MASCIS impactors (51).

The Infinite Horizon (IH) impactor is another type of impactor that utilizes a stepping motor to generate force-controlled impact in contrast to free fall in the MASICS impactor (51). This feature allows for better control over the force of impact and prevents weight bounce as the computer-controlled metal impounder can be immediately retracted upon transmitting a desired force to the spinal cord (51). IH impactor can be set to different force levels to provide mild, moderate and severe SCI in rats (ex. 100, 150, and 200 kdyn) (51). A limitation with IH impactors is unreliability of their clamps in holding the spinal column firmly during the impact that can cause inconsistent parenchymal injury and neurological deficits (51).

Ohio State University (OSU) impactor is a computer controlled electromagnetic impactor that was originally invented in 1987 and refined in 1992 to improve reliability (58). As the OSU impactor is electromagnetically controlled, multiple strikes are avoided (51). Subsequently, a modified version of the OSU impactor was developed in 2000 for use in mice (43). However, the OSU impactor is limited by its inability to determine the precise initial contact point with the spinal cord due to displacement of CSF upon loading the device (51). To date, MASCIS, IH and OSU impactor devices have been employed extensively and successfully to induce SCI. These impactor devices are available for small and large animals such as mice, rats, marmosets, cats, and pigs (51, 82).

Compressive models of SCI have been also employed for several decades (61). While contusion injury is achieved by applying a force for a very brief period (milliseconds), the compression injury consists of an initial contusion for milliseconds followed by a prolonged compression through force application for a longer duration (seconds to minutes) (51). Thus, compression injury can be categorized as contusive-compressive models (51). Various models of compressive SCI are available.

Clip compression is the most commonly used compression model of SCI in rat and mice (51, 61, 62, 83). It was first introduced by Rivlin and Tator in 1978 (61). In this model, following laminectomy, a modified aneurism clip with a calibrated closing force is applied to the spinal cord for a specific duration of time (usually 1 min) to induce a contusive-compressive injury (51). The severity of injury can be calibrated and modified by adjusting the force of the clip and the duration of compression (51). For example, applying a 50 g clip for 1 min typically produces a severe SCI, while a 35 g clip creates a moderate to severe injury with the same duration (83). Aneurysm clips were originally designed for use in rat SCI, however, in recent years smaller and larger clips have been developed to accommodate its use in mice (62) and pig models (52). The clip compression model has several advantages compared to contusion models. This method is less expensive and easier to perform (51). Importantly, in contrast to the impactor injury that contusion is only applied dorsally to the spinal cord, the clip compression model provides contusion and compression simultaneously both dorsally and ventrally. Hence, clip compression model more closely mimics the most common form of human SCI, which is primarily caused by dislocation and burst compression fractures (83). Despite its advantages, clip compression model can create variabilities such as the velocity of closing and actual delivered force that cannot be measured precisely at the time of application (51).

Calibrated forceps compression has been also employed to induce SCI in rodents. This simple and inexpensive compressive model was first utilized in 1991 for induction of SCI in guinea pigs (64). In this method, a calibrated forceps with a spacer is used to compress the spinal cord bilaterally (51). This model lacks the initial impact and contusive injury, which is associated with most cases of human traumatic SCI. Accordingly, this model is not a clinically relevant model for reproducing human SCI pathology and therapeutic development (51).

Balloon Compression model has been also utilized extensively in primates and larger animals such as dogs and cats (8486). In this model, a catheter with an inflatable balloon is inserted in the epidural or subdural space. The inflation of the balloon with air or saline for a specific duration of time provides the force for induction of SCI (51). Generally, all compression models (clip, forceps, and balloon) have the same limitation as the velocity and amount of force are unmeasurable (51).

In conclusion, while existing animal models do not recapitulate all clinical aspects of human SCI, the compression and contusion models are considered to be the most relevant and commonly employed methods for understanding the secondary injury mechanisms and therapeutic development for SCI.

Secondary injury begins within minutes following the initial primary injury and continues for weeks or months causing progressive damage of spinal cord tissue surrounding the lesion site (7). The concept of secondary SCI was first introduced by Allen in 1911 (87). While studying SCI in dogs, he observed that removal of the post traumatic hematomyelia improved neurological outcome. He hypothesized that presence of some biochemical factors in the necrotic hemorrhagic lesion causes further damage to the spinal cord (87). The term of secondary injury is still being used in the field and is referred to a series of cellular, molecular and biochemical phenomena that continue to self-destruct spinal cord tissue and impede neurological recovery following SCI () (20).

Summary of secondary injury processes following traumatic spinal cord injury. Diagram shows the key pathophysiological events that occur after primary injury and lead to progressive tissue degeneration. Vascular disruption and ischemia occur immediately after primary injury that initiate glial activation, neuroinflammation, and oxidative stress. These acute changes results in cell death, axonal injury, matrix remodeling, and formation of a glial scar.

Secondary injury can be temporally divided into acute, sub-acute, and chronic phases. The acute phase begins immediately following SCI and includes vascular damage, ionic imbalance, neurotransmitter accumulation (excitotoxicity), free radical formation, calcium influx, lipid peroxidation, inflammation, edema, and necrotic cell death (7, 20, 88). As the injury progresses, the sub-acute phase of injury begins which involves apoptosis, demyelination of surviving axons, Wallerian degeneration, axonal dieback, matrix remodeling, and evolution of a glial scar around the injury site (). Further changes occur in the chronic phase of injury including the formation of a cystic cavity, progressive axonal die-back, and maturation of the glial scar (7, 8992). Here, we will review the key components of acute secondary injury that contribute to the pathophysiology of SCI (, ).

Pathophysiology of traumatic spinal cord injury. This schematic diagram illustrates the composition of normal and injured spinal cord. Of note, while these events are shown in one figure, some of the pathophysiological events may not temporally overlap and can occur at various phases of SCI, which are described here. Immediately after primary injury, activation of resident astrocytes and microglia and subsequent infiltration of blood-borne immune cells results in a robust neuroinflammatory response. This acute neuroinflammatory response plays a key role in orchestrating the secondary injury mechanisms in the sub-acute and chronic phases that lead to cell death and tissue degeneration, as well as formation of the glial scar, axonal degeneration and demyelination. During the acute phase, monocyte-derived macrophages occupy the epicenter of the injury to scavenge tissue debris. T and B lymphocytes also infiltrate the spinal cord during sub-acute phase and produce pro-inflammatory cytokines, chemokines, autoantibodies reactive oxygen and nitrogen species that contribute to tissue degeneration. On the other hand, M2-like macrophages and regulatory T and B cells produce growth factors and pro-regenerative cytokines such as IL-10 that foster tissue repair and wound healing. Loss of oligodendrocytes in acute and sub-acute stages of SCI leads to axonal demyelination followed by spontaneous remyelination in sub-acute and chronic phases. During the acute and sub-acute phases of SCI; astrocytes, OPCs and pericytes, which normally reside in the spinal cord parenchyma, proliferate and migrate to the site of injury and contribute to the formation of the glial scar. The glial scar and its associated matrix surround the injury epicenter and create a cellular and biochemical zone with both beneficial and detrimental roles in the repair process. Acutely, the astrocytic glial scar limits the spread of neuroinflammation from the lesion site to the healthy tissue. However, establishment of a mature longstanding glial scar and upregulation of matrix chondroitin sulfate proteoglycans (CSPGs) are shown to inhibit axonal regeneration/sprouting and cell differentiation in subacute and chronic phases.

Disruption of spinal cord vascular supply and hypo-perfusion is one of the early consequences of primary injury (93). Hypovolemia and hemodynamic shock in SCI patients due to excessive bleeding and neurogenic shock result in compromised spinal cord perfusion and ischemia (93). Larger vessels such as anterior spinal artery usually remain intact (94, 95), while rupture of smaller intramedullary vessels and capillaries that are susceptible to traumatic damage leads to extravasation of leukocytes and red blood cells (93). Increased tissue pressure in edematous injured spinal cord and hemorrhage-induced vasospasm in intact vessels further disrupts blood flow to the spinal cord (93, 95). In rat and monkey models of SCI, there is a progressive reduction in blood flow at the lesion epicenter within the first few hours after injury which remains low for up to 24 h (96). The gray matter is more prone to ischemic damage compared to the white matter as it has a 5-fold higher density of capillary beds and contains neurons with high metabolic demand (95, 97, 98). After injury, white matter blood flow typically returns to normal levels within 15 min post injury, whereas there are multiple hemorrhages in the gray matter and as a result, re-perfusion usually does not occur for the first 24 h (9, 99, 100). Vascular insult, hemorrhage and ischemia ultimately lead to cell death and tissue destruction through multiple mechanisms, including oxygen deprivation, loss of adenosine triphosphate (ATP), excitotoxicity, ionic imbalance, free radical formation, and necrotic cell death. Cellular necrosis and release of cytoplasmic content increase the extracellular level of glutamate causing glutamate excitotoxicity (93, 101). Moreover, re-establishment of blood flow in ischemic tissue leads to further damage through generating free radicals and eliciting an inflammatory response (93, 102) that will be discussed in this review.

Within few minutes after primary SCI, the combination of direct cellular damage and ischemia/hypoxia triggers a significant rise of extracellular glutamate, the main excitatory neurotransmitter in the CNS (7). Glutamate binds to ionotropic (NMDA, AMPA, and Kainate receptors) as well as metabotropic receptors resulting in calcium influx inside the cells (103105) (93). The effect of glutamate is not restricted to neurons as its receptors are vastly expressed on the surface of all glia and endothelial cells (103106). Astrocytes can also release excess glutamate extracellularly upon elevation of their intracellular Ca2+ levels. Reduced ability of activated astrocytes for glutamate re-uptake from the interstitial space due to lipid peroxidation results in further accumulation of glutamate in the SCI milieu (93). Using microdialysis, elevated levels of glutamate have been detected in the white matter in the acute stage of injury (107). Based on a study by Panter and colleagues, glutamate increase is detected during the first 2030 min post SCI and returns to the basal levels after 60 min (108).

Under normal condition, concentration of free Ca2+ can considerably vary in different parts of the cell (109). In the cytosol, Ca2+ ranges from 50100 nM while it approaches 0.51.0 mM in the lumen of endoplasmic reticulum (110112). A long-lasting abnormal increase in Ca2+ concentration in cytosol, mitochondria or endoplasmic reticulum has detrimental consequences for the cell (109113). Mitochondria play a central role in calcium dependent neuronal death (113). In neurons, during glutamate induced excitotoxicity, NMDA receptor over-activity leads to mitochondrial calcium overload, which can cause apoptotic or necrotic cell death (113). Shortly after SCI, Ca2+ enters mitochondria through the mitochondrial calcium uniporter (MCU) (114). While the amount of mitochondrial calcium is limited during the resting state of a neuron, they can store a high amount of Ca2+ following stimulation (113). Calcium overload also activates a host of protein kinases and phospholipases that results in calpain mediated protein degradation and oxidative damage due to mitochondrial failure (93). In the injured white matter, astrocytes, oligodendrocytes and myelin are also damaged by the increased release of glutamate and Ca2+-dependent excitotoxicity (115). Within the first few hours after injury, oligodendrocytes show signs of caspase-3 activation and other apoptotic features, and their density declines (116). Interestingly, while glutamate excitotoxicity is triggered by ionic imbalance in the white matter, in the gray matter, it is largely associated with the activity of neuronal NMDA receptors (117, 118). Altogether, activation of NMDA receptors and consequent Ca2+ overload appears to induce intrinsic apoptotic pathways in neurons and oligodendrocytes and causes cell death in the first week of SCI in the rat (119, 120). Administration of NMDA receptor antagonist (MK-801) shortly following SCI has been associated with improved functional recovery and reduced edema (121).

Mitochondrial calcium overload also impedes mitochondrial respiration and results in ATP depletion disabling Na+/K+ ATPase and increasing intracellular Na+ (119, 122124). This reverses the function of the Na+ dependent glutamate transporter that normally utilizes Na+ gradient to transfer glutamate into the cells (119, 125, 126). Moreover, the excess intracellular Na+ reverses the activity of Na+/Ca2+ exchanger allowing more Ca+ influx (127). Cellular depolarization activates voltage gated Na+ channels that results in entry of Cl and water into the cells along with Na+ causing swelling and edema (128). Increased Na+ concentration over-activates Na+/H+ exchanger causing a rise in intracellular H+ (101, 129). Resultant intracellular acidosis increases membrane permeability to Ca2+ that exacerbates the injury-induced ionic imbalance (101, 129). Axons are more susceptible to the damage caused by ionic imbalance due to their high concentration of voltage gated Na+ channels in the nodes of Ranvier (7). Accumulating evidence shows that administration of Na+ channel blockers such as Riluzole attenuates tissue damage and improves functional recovery in SCI underlining sodium as a key player in secondary injury mechanisms (130133).

SCI results in production of free radicals and nitric oxide (NO) (114). Mitochondrial Ca2+ overload activates NADPH oxidase (NOX) and induces generation of superoxide by electron transport chain (ETC) (114). Reactive oxygen and nitrogen species (ROS and RNS) produced by the activity of NOX and ETC activates cytosolic poly (ADP ribose) polymerase (PARP). PARP consumes and depletes NAD+ causing failure of glycolysis, ATP depletion and cell death (114). Moreover, PAR polymers produced by PARP activity, induce the release of apoptosis inducing factor (AIF) from mitochondria and induce cell death (114). On the other hand, acidosis caused by SCI results in the release of intracellular iron from ferritin and transferrin (93). Spontaneous oxidation of Fe2+ to Fe3+ gives rise to more superoxide radicals (93). Subsequently, the Fenton reaction between Fe3+ and hydrogen peroxide produces highly reactive hydroxyl radicals (134). The resultant ROS and RNS react with numerous targets including lipids in the cell membrane with the most deleterious effects (93, 135). Because free radicals are short-lived and difficult to assess, measurements of their activity and final products, such as Malondialdehyde (MDA), are more reliable following SCI. Current evidence indicates that MDA levels are elevated as early as 1 h and up to 1 week after SCI (136, 137).

Oxidation of lipids and proteins is one of the key mechanisms of secondary injury following SCI (93). Lipid peroxidation starts when ROSs interact with polyunsaturated fatty acids in the cell membrane and generate reactive lipids that will then form lipid peroxyl radicals upon interacting with free superoxide radicals (138, 139). Each lipid peroxyl radical can react with a neighboring fatty acid, turn it into an active lipid and start a chain reaction that continues until no more unsaturated lipids are available or terminates when the reactive lipid quenches with another radical (93). The final products of this termination step of the lipid peroxidation is 4-hydroxynonenal (HNE) and 2-propenal, which are highly toxic to the cells (138140). Lipid peroxidation is also an underlying cause of ionic imbalance through destabilizing cellular membranes such as cytoplasmic membrane and endoplasmic reticulum (93). Moreover, lipid peroxidation leads to Na+/K+ ATPase dysfunction that exacerbates the intracellular Na+ overload (141). In addition to ROS associated lipid peroxidation, amino acids are subject to significant RNS associated oxidative damage following SCI (93). RNSs (containing ONOO) can nitrate the tyrosine residues of amino acids to form 3-nitrotyrosine (3-NT), a marker for peroxynitrite (ONOO) mediated protein damage (139). Lipid and protein oxidation following SCI has a number of detrimental consequences at cellular level including mitochondrial respiratory and metabolic failure as well as DNA alteration that ultimately lead to cell death (141).

Cell death is a major event in the secondary injury mechanisms that affects neurons and glia after SCI (142145). Cell death can happen through various mechanisms in response to various injury-induced mediators. Necrosis and apoptosis were originally identified as two major cell death mechanisms following SCI (146148). However, recent research has uncovered additional forms of cell death. In 2012, the Nomenclature Committee on Cell Death (NCCD) NCCD defined 12 different forms of cell death such as necroptosis, pyroptosis, and netosis (149). Among the identified modes of cell death, to date, necrosis, necroptosis, apoptosis, and autophagy have been studied more extensively in the context of SCI and will be discussed in this review.

Following SCI, neurons and glial cells die through necrosis as the result of mechanical damage at the time of primary injury that also continues to the acute and subacute stages of injury (7, 150). Necrosis occurs due to a multitude of factors including accumulation of toxic blood components (151), glutamate excitotoxicity and ionic imbalance (152), ATP depletion (153), pro-inflammatory cytokine release by neutrophils and lymphocytes (154, 155), and free radical formation (142, 156158). It was originally thought that necrosis is caused by a severe impact on a cell that results in rapid cell swelling and lysis. However, follow up evidence showed that in the case of seizure, ischemia and hypoglycemia, necrotic neurons show signs of shrunken, pyknotic, and condensed nuclei, with swollen, irreversibly damaged mitochondria and plasma membrane that are surrounded by astrocytic processes (159). Moreover, necrosis was conventionally viewed as instantaneous energy-independent non-programmed cell death (142, 156). However, recent research has identified another form of necrosis, termed as necroptosis, that is executed by regulated mechanisms.

Programmed necrosis or necroptosis has been described more recently as a highly regulated, caspase-independent cell death with similar morphological characteristics as necrosis (160). Necroptosis is a receptor-mediated process. It is induced downstream of the TNF receptor 1 (TNFR1) and is dependent on the activity of the receptor interacting protein kinase 1 (RIPK1) and RIPK3. Recent studies has uncovered a key role for RIPK1 as the mediator of necroptosis and a regulator of the innate immune response involved in both inflammation and cell death (161). Evidence from SCI studies show that lysosomal damage can potentiate necroptosis by promoting RIPK1 and RIPK3 accumulation (161). Interestingly, inhibition of necroptosis by necrostatin-1, a RIPK1 inhibitor, improves functional outcomes after SCI (150). These initial findings suggest that modulation of necroptosis pathways seems to be a promising target for neuroprotective strategies after SCI.

Apoptosis is the most studied mechanism of cell death after SCI. Apoptosis represents a programmed, energy dependent mode of cell death that begins within hours of primary injury (7). This process takes place in cells that survive the primary injury but endure enough insult to activate their apoptotic pathways (142). In apoptosis, the cell shrinks and is eventually phagocytosed without induction of an inflammatory response (156). Apoptosis typically occurs in a delayed manner in areas more distant to the injury site and most abundantly affects oligodendrocytes. In rat SCI, apoptosis happens as early as 4 h after the injury and reaches a peak at 7 day (156). At the site of injury majority of oligodendrocytes are lost within 7 days after SCI (162). However, apoptosis can be observed at a diminished rate for weeks after SCI (162, 163). Microglia and astrocytes also undergo apoptosis (156, 164). Interestingly, apoptotic cell death occurs in the chronically injured spinal cord in rat, monkey and human models of SCI, which is thought to be due to loss of trophic support from degenerating axons (146, 165).

Apoptosis is induced through extrinsic and intrinsic pathways based on the triggering mechanism (166). The extrinsic pathway is triggered by activation of death receptors such as FAS and TNFR1, which eventually activates caspase 8 (167). The intrinsic pathway, however, is regulated through a balance between intracellular pro- and anti-apoptotic proteins and is triggered by the release of cytochrome C from mitochondria and activating caspase 9 (167). In SCI lesion, apoptosis primarily happens due to injury induced Ca2+ influx, which activates caspases and calpain; enzymes involved in breakdown of cellular proteins (7). Moreover, it is believed that the death of neurons and oligodendrocytes in remote areas from the lesion epicenter can be mediated through cytokines such as TNF-, free radical damage and excitotoxicity since calcium from damaged cells within the lesion barely reaches these remote areas (8, 168). Fas mediated cell death has been suggested as a key mechanism of apoptosis following SCI (144, 169172). Post-mortem studies on acute and chronic human SCI and animal models revealed that Fas mediated apoptosis plays a role in oligodendrocyte apoptosis and inflammatory response at acute and subacute stages of SCI (173). Fas deficient mice exhibit a significant reduction in apoptosis and inflammatory response evidenced by reduced macrophage infiltration and inflammatory cytokine expression following SCI (173). Interestingly, Fas deficient mice show a significantly improved functional recovery after SCI (173) suggesting the promise of anti-apoptotic strategies for SCI.

SCI also results in a dysregulated autophagy (174). Normally, autophagy plays an important role in maintaining the homeostasis of cells by aiding in the turnover of proteins and organelles. In autophagy, cells degrade harmful, defective or unnecessary cytoplasmic proteins and organelles through a lysosomal dependent mechanism (175, 176). The process of autophagy starts with the formation of an autophagosome around the proteins and organelles that are tagged for autophagy (176). Next, fusion of the phagosome with a lysosome form an autolysosome that begins a recycling process (176). In response to cell injury and endoplasmic reticulum (ER) stress, autophagy is activated and limits cellular loss (177, 178). Current evidence suggests a neuroprotective role for autophagy after SCI (175, 179). Dysregulation of autophagy contributes to neuronal loss (174, 180). Accumulation of autophagosomes in ventral horn motor neurons have been detected acutely following SCI (181). Neurons with dysregulated autophagy exhibit higher expression of caspase 12 and become more prone to apoptosis (174). Moreover, blocking autophagy has been associated with neurodegenerative diseases such as Parkinson's and Alzheimer's disease (182184). Autophagy promotes cell survival through elimination of toxic proteins and damaged mitochondria (185, 186). Interestingly, autophagy is crucial in cytoskeletal remodeling and stabilizes neuronal microtubules by degrading SCG10, a protein involved in microtubule disassembly (179). Pharmacological induction of autophagy in a hemi-section model of SCI in mice has been associated with improved neurite outgrowth and axon regeneration, following SCI (179). Altogether, although further studies are needed, autophagy is currently viewed as a beneficial mechanism in SCI.

Neuroinflammation is a key component of the secondary injury mechanisms with local and systemic consequences. Inflammation was originally thought to be detrimental for the outcome of SCI (187). However, now it is well-recognized that inflammation can be both beneficial and detrimental following SCI, depending on the time point and activation state of immune cells (188). There are multiple cell types involved in the inflammatory response following injury including neutrophils, resident microglia, and astrocytes, dendritic cells (DCs), blood-born macrophages, B- and T-lymphocytes (189) (). The first phase of inflammation (02 days post injury) involves the recruitment of resident microglia and astrocytes and blood-born neutrophils to the injury site (190). The second phase of inflammation begins approximately 3 days post injury and involves the recruitment of blood-born macrophages, B- and T-lymphocytes to the injury site (189, 191193). T lymphocytes become activated in response to antigen presentation by macrophages, microglia and other antigen presenting cells (APCs) (194). CD4+ helper T cells produce cytokines that stimulate B cell antibody production and activate phagocytes (195) (). In SCI, B cells produce autoantibodies against injured spinal cord tissue, which exacerbate neuroinflammation and cause tissue destruction (196). While inflammation is more pronounced in the acute phase of injury, it continues in subacute and chronic phase and may persist for the remainder of a patients' life (193). Interestingly, composition and phenotype of inflammatory cells change based on the injury phase and the signals present in the injury microenvironment. It is established that microglia/macrophages, T cells, B cells are capable of adopting a pro-inflammatory or an anti-inflammatory pro-regenerative phenotype in the injured spinal cord (191, 197199). The role of each immune cell population in the pathophysiology of SCI will be discussed in detail in upcoming sections.

Immune response in spinal cord injury. Under normal circumstances, there is a balance between pro-inflammatory effects of CD4+ effector T cells (Teff) and anti-inflammatory effects of regulatory T and B cells (Treg and Breg). Treg and Breg suppress the activation of antigen specific CD4+ Teff cells through production of IL-10 and TGF-. Injury disrupts this balance and promote a pro-inflammatory environment. Activated microglia/macrophages release pro-inflammatory cytokines and chemokines and present antigens to CD4+ T cells causing activation of antigen specific effector T cells. Teff cells stimulate antigen specific B cells to undergo clonal expansion and produce autoantibodies against spinal cord tissue antigens. These autoantibodies cause neurodegeneration through FcR mediated phagocytosis or complement mediated cytotoxicity. M1 macrophages/microglia release pro-inflammatory cytokines and reactive oxygen species (ROS) that are detrimental to neurons and oligodendrocytes. Breg cells possess the ability to promote Treg development and restrict Teff cell differentiation. Breg cells could also induce apoptosis in Teff cells through Fas mediate mechanisms.

Astrocytes are not considered an immune cell per se; however, they play pivotal roles in the neuroinflammatory processes in CNS injury and disease. Their histo-anatomical localization in the CNS has placed them in a strategic position for participating in physiological and pathophysiological processes in the CNS (200). In normal CNS, astrocytes play major roles in maintaining CNS homeostasis. They contribute to the structure and function of blood-brain-barrier (BBB), provide nutrients and growth factors to neurons (200), and remove excess fluid, ions, and neurotransmitters such as glutamate from synaptic spaces and extracellular microenvironment (200). Astrocytes also play key roles in the pathologic CNS by regulating BBB permeability and reconstruction as well as immune cell activity and trafficking (201). Astrocytes contribute to both innate and adaptive immune responses following SCI by differential activation of their intracellular signaling pathways in response to environmental signals (201).

Astrocytes react acutely to CNS injury by increasing cytokine and chemokine production (202). They mediate chemokine production and recruitment of neutrophils through an IL-1R1-Myd88 pathway (202). Activation of the nuclear factor kappa b (NF-B) pathway, one of the key downstream targets of interleukin (IL)1R-Myd88 axis, increases expression of intracellular adhesion molecule (ICAM) and vascular cell adhesion molecule (VCAM), which are necessary for adhesion and extravasation of leukocytes in inflammatory conditions such as SCI (201, 202). Within minutes of injury, production of IL-1 is significantly elevated in astrocytes and microglia (203). Moreover, chemokines such as monocyte chemoattractant protein (MCP)-1, chemokine C-C motif ligand 2 (CCL2), C-X-C motif ligand 1 (CXCL1), and CXCL2 are produced by astrocytes, and enhance the recruitment of neutrophils and pro-inflammatory macrophages following injury (201, 202). Astrocytes also promote pro-inflammatory M1-like phenotype in microglia/macrophages in the injured spinal cord through their production of TNF-, IL-12, and IFN- (204206). Interestingly, astrocytes also produce anti-inflammatory cytokines, such as TGF- and IL-10, which can promote a pro-regenerative M2-like phenotype in microglia/macrophages (201, 207, 208).

Immunomodulatory role of astrocytes is defined by activity of various signaling pathways through a wide variety of surface receptors (200). For example, gp130, a member of IL-6 cytokine family, activates SHP2/Ras/Erk signaling cascade in astrocytes and limits neuroinflammation in autoimmune rodent models (209). TGF- signaling in astrocytes has been implicated in modulation of neuroinflammation through inhibition of NF-B activity and nuclear translocation (201, 210). STAT3 is another key signaling pathway in astrocytes with beneficial properties in neuroinflammation. Increase in STAT3 phosphorylation enhances astrocytic scar formation and restricts the expansion of inflammatory cells in mouse SCI, which is associated with improved functional recovery (211). Detrimental signaling pathways in astrocytes are known to be activated by cytokines, sphingolipids and neurotrophins (200). As an example, IL-17 is a key pro-inflammatory cytokine produced by effector T cells that can bind to IL-17R on the astrocyte surface (200). Activation of IL-17R results in the activation of NF-B, which enhances expression of pro-inflammatory mediators, activation of oxidative pathways and exacerbation of neuroinflammation (200, 212). This evidence shows the significance of astrocytes in the inflammatory processes following SCI and other neuroinflammatory diseases of the CNS.

Neutrophils infiltrate the spinal cord from the bloodstream within the first few hours after injury (213). Their population increases acutely in the injured spinal cord tissue and reaches a peak within 24 h post-injury (214). The presence of neutrophils is mostly limited to the acute phase of SCI as they are rarely found sub-acutely in the injured spinal cord (214). The role of neutrophils in SCI pathophysiology is controversial. Evidence shows that neutrophils contribute to phagocytosis and clearance of tissue debris (48). They release inflammatory cytokines, proteases and free radicals that degrade ECM, activate astrocytes and microglia and initiate neuroinflammation (48). Although neutrophils have been conventionally associated with tissue damage (48, 215), their elimination compromises the healing process and impedes functional recovery (216).

To elucidate the role of neutrophils in SCI, Stirling and colleagues used a specific antibody to reduce circulating LyG6/Gr1+ neutrophils in a mouse model of thoracic contusive SCI (216). This approach significantly reduced neutrophil infiltration in the injured spinal cord by 90% at 24 and 48 h after SCI (216). Surprisingly, neutrophil depletion aggravated the neurological and structural outcomes in the injured animals suggesting a beneficial role for neutrophils in the acute phase of injury (216). It is shown that simulated neutrophils release IL-1 receptor antagonist that can exert neuroprotective effects following SCI (217). Moreover, ablation of neutrophils results in altered expression of cytokines and chemokines and downregulation of growth factors such as fibroblast growth factors (FGFs), vascular endothelial growth factors (VEGFs) and bone morphogenetic proteins (BMPs) in the injured spinal cord that seemingly disrupt the normal healing process (216). Altogether, neutrophils play important roles in regulating neuroinflammation at the early stage of SCI that shapes the immune response and repair processes at later stages. While neutrophils were originally viewed as being detrimental in SCI, emerging evidence shows their critical role in the repair process. Further investigations are required to elucidate the role of neutrophils in SCI pathophysiology.

Following neutrophil invasion, microglia/macrophages populate the injured spinal cord within 23 days post-SCI. Macrophage population is derived from invading blood-borne monocytes or originate from the CNS resident macrophages that reside in the perivascular regions within meninges and subarachnoid space (218, 219). The population of microglia/macrophages reaches its peak at 710 days post-injury in mouse SCI, followed by a decline in the subacute and chronic phases (20, 220). While macrophages and microglia share many functions and immunological markers, they have different origins. Microglia are resident immune cells of the CNS that originate from yolk sac during the embryonic period (221). Macrophages are derived from blood monocytes, which originate from myeloid progeny in the bone marrow (222, 223). Upon injury, acute disruption of brain-spinal cord barrier (BSB) enables monocytes, to infiltrate the spinal cord tissue and transform into macrophages (222). Macrophages populate the injury epicenter, while resident microglia are mainly located in the perilesional area (222). Once activated, macrophages, and microglia are morphologically and immunohistologically indistinguishable (224). Macrophages and microglia play a beneficial role in CNS regeneration. They promote the repair process by expression of growth promoting factors such as nerve growth factor (NGF), neurotrophin-3 (NT-3) and thrombospondin (225, 226). Macrophages and microglia are important for wound healing process following SCI due to their ability for phagocytosis and scavenging damaged cells and myelin debris following SCI (222, 227).

Based on microenvironmental signals, macrophages/microglia can be polarized to either pro-inflammatory (M1-like) or anti-inflammatory pro-regenerative (M2-like) phenotype, and accordingly contribute to injury or repair processes following SCI (191, 224, 228230). Whether both microglia and macrophages possess the ability to polarize or it is mainly the property of monocyte derived macrophages is still a matter of debate and needs further elucidation (231233). Some evidence show that Proinflammatory M1-like microglia/macrophages can be induced by exposure to Th1 specific cytokine, interferon (IFN)- (224, 230). Moreover, the SCI microenvironment appears to drive M1 polarization of activated macrophages (231). SCI studies have revealed that increased level of the proinflammatory cytokine, TNF-, and intracellular accumulation of iron drives an M1-like proinflammatory phenotype in macrophages after injury (231). Importantly, following SCI, activated M1-like microglia/macrophages highly express MHCII and present antigens to T cells and contribute to the activation and regulation of innate and adaptive immune response () (224, 228). Studies on acute and subacute SCI and experimental autoimmune encephalomyelitis (EAE) models have shown that M1-like macrophages are associated with higher expression of chondroitin sulfate proteoglycans (CSPGs) and increased EAE severity and tissue damage (234237). In vitro, addition of activated M1-like macrophages to dorsal root ganglion (DRG) neuron cultures leads to axonal retraction and failure of regeneration as the expression of CSPGs is much higher in M1-like compared to M2-like macrophages (237, 238). M1-like macrophages also produce other repulsive factors such as repulsive guidance molecule A (RGMA) that is shown to induce axonal retraction following SCI (239, 240). Interestingly, recent evidence shows that IFN- and TNF polarized M1 microglia show reduced capacity for phagocytosis (241), a process that is critical for tissue repair after SCI.

Pro-regenerative M2-like microglia/macrophages, are polarized by Th2 cytokines, IL-4 and IL-13 and exhibit a high level of IL-10, TGF-, and arginase-1 with reduced NF-B pathway activity (224). IL-10 is a potent immunoregulatory cytokine with positive roles in repair and regeneration following CNS injury (242244). IL-10 knock-out mice show higher production of pro-inflammatory and oxidative stress mediators after SCI (245). Lack of IL-10 is also correlated with upregulated levels of pro-apoptotic factors such as Bax and reduced expression of anti-apoptotic factors such as Bcl-2 (245). SCI mice that lacked IL-10 exhibited poorer recovery of function compared to wild-type mice (245). Our recent studies show that IL-10 polarized M2 microglia show enhanced capacity for phagocytosis (241). We have also found that M2 polarized microglia enhance the ability of neural precursor cells for oligodendrocyte differentiation through IL-10 mediated mechanisms (241). In addition to immune modulation, M2-like microglia/macrophages promote axonal regeneration (224). However, similar to the detrimental effects of prolonged M1 macrophage response, excessive M2-like activity promotes fibrotic scar formation through the release of factors such as TGF-, PDGF, VEGF, IGF-1, and Galectin-3 (224, 246248). Hence, a balance between proinflammatory M1 and pro-regenerative M2 macrophage/microglia response is beneficial for the repair of SCI (249).

T and B lymphocytes play pivotal role in the adaptive immune response after SCI (194). Lymphocytes infiltrate the injured spinal cord acutely during the first week of injury and remain chronically in mouse and rat SCI (47, 193, 194, 196). In contrast to the innate immune response that can be activated directly by foreign antigens, the adaptive immune response requires a complex signaling process in T cells elicited by antigen presenting cells (250). Similar to other immune cells, T and B lymphocytes adopt different phenotypes and contribute to both injury and repair processes in response to microenvironmental signals (194, 251). SCI elicits a CNS-specific autoimmune response in T and B cells, which remains active chronically (196). Autoreactive T cells can exert direct toxic effects on neurons and glial cells (194, 252). Moreover, T cells can indirectly affect neural cell function and survival through pro-inflammatory cytokine and chemokine production (e.g. IL-1, TNF-, IL-12, CCL2, CCL5, and CXCL10) (194, 252). Genetic elimination of T cells (in athymic nude rats) or pharmacological inhibition of T cells (using cyclosporine A and tacrolimus) leads to improved tissue preservation and functional recovery after SCI (194, 253) signifying the impact of T cells in SCI pathophysiology and repair.

Under normal circumstances, systemic autoreactive effector CD4+ helper T cells (Teff) are suppressed by CD4+FoxP3+ regulatory T cells (Treg) () (194, 254). This inhibition is regulated through various mechanisms such as release of anti-inflammatory cytokines IL-10 and TGF- by the Treg cells () (194). Moreover, it is known that Treg mediated inhibition of antigen presentation by dendritic cells (DCs) prevent Teff cell activation (194). Following SCI, this Treg -Teff regulation is disrupted. Increased activity of autoreactive Teff cells contributes to tissue damage through production of pro-inflammatory cytokines and chemokines, promoting M1-like macrophage phenotype and induction of Fas mediated neuronal and oligodendroglial apoptosis () (173). Moreover, autoreactive Teff cells promote activation and differentiation of antigen specific B cells to autoantibody producing plasma cells that contribute to tissue damage after SCI (255). In SCI and MS patients, myelin specific proteins such as myelin basic protein (MBP) significantly increase the population of circulating T cells (256, 257). Moreover, serological assessment of SCI patients has shown high levels of CNS reactive IgM and IgG isotypes confirming SCI-induced autoimmune activity of T and B cells () (196, 258, 259). In animal models of SCI, serum IgM level increases acutely followed by an elevation in the levels of IgG1 and IgG2a at later time-points (196). In addition to autoantibody production, autoreactive B cells contribute to CNS injury through pro-inflammatory cytokines that stimulate and maintain the activation states of Teff cells (194, 260). B cell knockout mice (BCKO) that have no mature B cell but with normal T cells, show a reduction in lesion volume, lower antibody levels in the cerebrospinal fluid and improved recovery of function following SCI compared to wild-type counterparts (255). Of note, antibody mediated injury is regulated through complement activation as well as macrophages/microglia that express immunoglobulin receptors (193, 255).

The effect of SCI on systemic B cell response is controversial. Evidence shows that SCI can suppress B cell activation and antibody production (261). Studies in murine SCI have shown that B cell function seems to be influenced by the level of injury (262). While injury to upper thoracic spinal cord (T3) suppresses the antibody production, a mid-thoracic (T9) injury has no effect on B cell antibody production (262). An increase in the level of corticosterone in serum together with elevation of splenic norepinephrine found to be responsible for the suppression of B cell function acutely following SCI (261). Elevated corticosterone and norepinephrine leads to upregulation of lymphocyte beta-2 adrenergic receptors eliciting lymphocyte apoptosis (194). This suggests a critical role for sympathetic innervation of peripheral lymphoid tissues in regulating B cell response following CNS injury (261). Despite their negative roles, B cells also contribute to spinal cord repair following injury through their immunomodulatory Breg phenotype () (263). Breg cells control antigen-specific T cell autoimmune response through IL-10 production (264).

Detrimental effects of SCI-induced autoimmunity are not limited to the spinal cord. Autoreactive immune cells contribute to the exacerbation of post-SCI sequelae such as cardiovascular, renal and reproductive dysfunctions (194). For example, presence of an autoantibody against platelet prostacyclin receptor has been associated with a higher incidence of coronary artery disease in SCI patients (265). Collectively, evidence shows the critical role of adaptive immune system in SCI pathophysiology and repair. Thus, treatments that harness the pro-regenerative properties of the adaptive immune system can be utilized to reduce immune mediated tissue damage, improve neural tissue preservation and facilitate repair following SCI.

Traumatic SCI triggers the formation of a glial scar tissue around the injury epicenter (266, 267). The glial scar is a multifactorial phenomenon that is contributed f several populations in the injured spinal cord including activated astrocytes, NG2+ oligodendrocyte precursor cells (OPCs), microglia, fibroblasts, and pericytes (268271). The heterogeneous scar forming cells and associated ECM provides a cellular and biochemical zone within and around the lesion () (272). Resident and infiltrating inflammatory cells contribute to the process of glial activation and scar formation by producing cytokines (e.g., IL-1 and IL-6) chemokines and enzymes that activate glial cells or disrupt BSB (267). Activated microglia/macrophages produce proteolytic enzymes such as matrix metalloproteinases (MMPs) that increase vascular permeability and further disruption of the BSB (273). Inhibition of MMPs improves neural preservation and functional recovery in animal models of SCI (273275). In addition to glial and immune cells, fibroblasts, pericytes and ependymal cells also contribute to the structure of the glial scar (267). In penetrating injuries where meninges are compromised, meningeal fibroblasts infiltrate the lesion epicenter (276). Fibroblasts contribute to the production of fibronectin, collagen, and laminin in the ECM of the inured spinal cord (267) and are a source of axon-repulsing molecules such as semaphorins that influence axonal regeneration following SCI (277). Fibroblasts have also been found in contusive injuries where meninges are intact (268, 270). Studies using genetic fate mapping in these injuries have unraveled that perivascular pericytes and fibroblasts migrate to the injury site and form a fibrotic core in the scar which matures within 2 weeks post-injury (268, 270). SCI also triggers proliferation and migration of the stem/progenitor cell pool of the spinal cord parenchyma and ependyma. These cells can give rise to new scar forming astrocytes and OPCs (278280). In a mature glial scar, activated microglia/macrophages occupy the innermost portion closer to the injury epicenter surrounded by NG2+ OPCs () (267), while reactive astrocytes reside in the injury penumbra and form a cellular barrier (267). Of note, in human SCI, the glial scar begins to form within the first hours after the SCI and remains chronically in the spinal cord tissue (281). The glial scar has been found within the injured human spinal cord up to 42 years after the injury (267).

Activated astrocytes play a leading role in the formation of the glial scar (267). Following injury, astrocytes increase their expression of intermediate filaments, GFAP, nestin and vimentin, and become hypertrophied (282, 283). Reactive astrocytes proliferate and mobilize to the site of injury and form a mesh like structure of intermingled filamentous processes around the injury epicenter (284, 285). The astrocytic glial scar has been shown to serve as a protective barrier that prevents the spread of infiltrating immune cells into the adjacent segments (267, 284, 286). Attenuating astrocyte reactivity and scar formation by blockade of STAT3 activation results in poorer outcomes in SCI (211, 286). Reactive astrogliosis is also essential for reconstruction of the BBB, and blocking this process leads to exacerbated leukocyte infiltration, cell death, myelin damage, and reduced functional recovery (211, 285, 286). Despite the protective role of the astrocytic glial scar in acute SCI, its evolution and persistence in the sub-acute and chronic stages of injury has been considered as a potent inhibitor for spinal cord repair and regeneration (267, 287). A number of inhibitory molecules have been associated with activated astrocytes and their secreted products such as proteoglycans and Tenascin-C (288). Thus, manipulation of the astrocytic scar has been pursued as a promising treatment strategy for SCI (267, 289).

Chondroitin sulfate proteoglycans (CSPGs) are well-known for their contribution to the inhibitory role of the glial scar in axonal regeneration (290295), sprouting (296299), conduction (300302), and remyelination (241, 303307). In normal condition, basal levels of CSPGs are expressed in the CNS that play critical roles in neuronal guidance and synapse stabilization (90, 308). Following injury, CSPGs (neurocan, versican, brevican, and phosphacan) are robustly upregulated and reach their peak of expression at 2 weeks post-SCI and remain upregulated chronically (309, 310). Mechanistically, disruption of BSB and hemorrhage following traumatic SCI triggers upregulation of CSPGs in the glial scar by exposing the scar forming cells to factors in plasma such as fibrinogen (311). Studies in cortical injury have shown that fibrinogen induces CSPG expression in astrocytes through TGF/Smad2 signaling pathway (311). The authors show that intracellular Smad2 translocation is essential for Smad2 signal transduction process and its inhibition reduces scar formation (312). In contrast, another study has identified that TGF induces CSPGs production in astrocytes through a SMAD independent pathway (313). This study showed a significant upregulation of CSPGs in SMAD2 and SMAD4 knockdown astrocytes. Interestingly, CSPG upregulation was found to be mediated by the activation of the phosphoinositide 3-kinase (PI3K)/Akt and mTOR axis (313). Further studies are required to confirm these findings.

Extensive research in the past few decades has demonstrated the inhibitory effect of CSPGs on axon regeneration (314, 315). The first successful attempt on improving axon outgrowth and/or sprouting by enzymatic degradation of CSPGs using chondroitinase ABC (ChABC) in a rat SCI model was published in 2002 by Bradbury and colleagues (291). This study showed significant improvement in recovery of locomotor and proprioceptive functions following intrathecal delivery of ChABC in a rat model of dorsal column injury (291). This observation was followed by several other studies demonstrating the promise of CSPGs degradation in improvement of axon regeneration and sprouting of the serotonergic (295, 297, 299, 303), sensory (293, 298, 316), corticospinal (291, 297, 303, 317), and rubrospinal fibers (318) in animal models of CNS injury. Additionally, ChABC treatment is shown to be neuroprotective by preventing CSPG induced axonal dieback and degeneration (303, 319, 320). Studies by our group also showed that degradation of CSPGs using ChABC attenuates axonal dieback in corticospinal fibers in chronic SCI model in the rat (303). ChABC also blocks macrophage-mediated axonal degeneration in neural cultures and after SCI (238).

The inhibitory effects of astrocytic glial scar on axonal regeneration has been recently challenged after SCI (321). Using various transgenic mouse models, a study by Sofroniew's and colleagues has shown that spontaneous axon regrowth failed to happen following the ablation or prevention of astrocytic scar in acute and chronic SCI. They demonstrated that when the intrinsic ability of dorsal root ganglion (DRG) neurons for growth was enhanced by pre-conditioning injury as well as local delivery of a combination of axon growth promoting factors into the SCI lesion, the axons grew to the wall of the glial scar and CSPGs within the lesion. However, when astrocyte scarring was attenuated, the pre-conditioned/growth factor stimulated DRG neurons showed a reduced ability for axon growth (321). From these observations, the authors suggested a positive role for the astrocytic scar in axonal regeneration following SCI (321). Overall, this study points to the importance of reactive and scar forming astrocytes and their pivotal role in the repair process following SCI (322). This is indeed in agreement with previous studies by the same group that showed a beneficial role for activated astrocytes in functional recovery after SCI by limiting the speared of infiltrated inflammatory cells and tissue damage in SCI (285). It is also noteworthy that the glial scar is contributed by various cell populations and not exclusively by astrocytes (269, 271). Therefore, the outcomes of this study need to be interpreted in the context of astrocytes and astrocytic scar. Moreover, the reduced capacity of the injured spinal cord for regeneration is not solely driven by the glial scar as other factors including inflammation and damaged myelin play important inhibitory role in axon regeneration (323, 324). Taken together, further investigation is needed to delineate the mechanisms of the glial scar including the contribution of astrocyte-derived factors on axon regeneration in SCI.

While CSPGs were originally identified as an inhibitor of axon growth and plasticity within the glial scar, emerging evidence has also identified them as an important regulator of endogenous cell response. Emerging evidence has identified CSPGs as an inhibitor of oligodendrocytes (241, 272, 306). Replacement of oligodendrocytes is an important repair process in SCI and other demyelinating conditions such as MS (90). SCI and MS triggers activation of endogenous OPCs and their mobilization to the site of injury (143, 162, 306, 325). In vitro and in vivo evidence shows that CSPGs limit the recruitment of NPCs and OPCs to the lesion and inhibit oligodendrocyte survival, differentiation and maturation (145, 272, 305, 306, 326). Our group and others have shown that targeting CSPGs by ChABC administration or xyloside, or through inhibition of their signaling receptors enhances the capacity of NPCs and OPCs for proliferation, oligodendrocyte differentiation and remyelination following SCI and MS-like lesions (145, 303, 304, 306).

Mechanistically, the inhibitory effects of CSPGs on axon growth and endogenous cell differentiation is mainly governed by signaling through receptor protein tyrosine phosphatase sigma (RPTP) and leukocyte common antigen-related phosphatase receptor (LAR) (327). RPTP is the main receptor mediating the inhibition of axon growth by CSPGs (327, 328). Improved neuronal regeneration has been demonstrated in RPTP/ mice model of SCI and peripheral nerve injury (328, 329). Blockade of RPTP and LAR by intracellular sigma peptide (ISP) and intracellular LAR peptide (ILP), facilitates axon regeneration following SCI (327, 330). Inhibition of RPTP results in significant improvement in locomotion and bladder function associated with serotonergic re-innervation below the level of injury in rat SCI (327). Our group has also shown that CSPGs induce caspase-3 mediated apoptosis in NPCs and OPCs in vitro and in oligodendrocytes in the injured spinal cord that is mediated by both RPTP and LAR (241). Inhibition of LAR and RPTP sufficiently attenuates CSPG-mediated inhibition of oligodendrocyte maturation and myelination in vitro and attenuated oligodendrocyte cell death after SCI (241).

CSPGs have been implicated in regulating immune response in CNS injury and disease. Interestingly, our recent studies indicated that CSPGs signaling appears to restrict endogenous repair by promoting a pro-inflammatory immune response in SCI (241, 331). Inhibition of LAR and RPTP enhanced an anti-inflammatory environment after SCI by promoting the populations of pro-regenerative M2-like microglia/macrophages and regulatory T cells (241) that are known to promote repair process (224). These findings are also in agreement with recent studies in animal models of MS that unraveled a pro-inflammatory role for CSPGs in autoimmune demyelinating conditions (332). In MS and EAE, studies by Stephenson and colleagues have shown that CSPGs are abundant within the leucocyte-containing perivascular cuff, the entry point of inflammatory cells to the CNS tissue (332). Presence of CSPGs in these perivascular cuffs promotes trafficking of immune cells to induce a pro-inflammatory response in MS condition. In contrast to these new findings, early studies in SCI described that preventing CSPG formation with xyloside treatment at the time of injury results in poor functional outcome, while manipulation of CSPGs at 2 days after SCI was beneficial for functional recovery (333). These differential outcomes were associated with the modulatory role of CSPGs in regulating the response of macrophages/microglia. Disruption in CSPG formation immediately after injury promoted an M1 pro-inflammatory phenotype in macrophages/microglia, whereas delayed manipulation of CSPGs resulted in a pro-regenerative M2 phenotype (333). In EAE, by products of CSPG degradation also improve the outcomes by attenuating T cell infiltration and their expression of pro-inflammatory cytokines IFN- and TNF (334).

These emerging findings suggest an important immunomodulatory role for CSPGs in CNS injury and disease; further investigations are needed to elucidate CSPG mechanisms in regulating neuroinflammation. Altogether, current evidence has identified a multifaceted inhibitory role for CSPGs in regulating endogenous repair mechanisms after SCI, suggesting that targeting CSPGs may present a promising treatment strategy for SCI.

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Traumatic Spinal Cord Injury: An Overview of ...

Stem Cell Therapy Market Research Report by Cell Source (Adipose tissue-derived MSCs (mesenchymal stem cells),, Bone marrow-derived MSCs,, and Placental/umbilical cord-derived MSCs), by Type (Allogeneic Stem Cell Therapy and Autologous Stem Cell Therapy), by Therapeutic Application, by End-User, by Region (Americas, Asia-Pacific, and Europe, Middle East & Africa) - Global Forecast to 2026 - Cumulative Impact of COVID-19

New York, Oct. 13, 2021 (GLOBE NEWSWIRE) -- Reportlinker.com announces the release of the report "Stem Cell Therapy Market Research Report by Cell Source, by Type, by Therapeutic Application, by End-User, by Region - Global Forecast to 2026 - Cumulative Impact of COVID-19" - https://www.reportlinker.com/p06175517/?utm_source=GNW

The Global Stem Cell Therapy Market size was estimated at USD 202.87 million in 2020 and expected to reach USD 240.88 million in 2021, at a CAGR 19.07% to reach USD 578.27 million by 2026.

Market Statistics:The report provides market sizing and forecast across five major currencies - USD, EUR GBP, JPY, and AUD. It helps organization leaders make better decisions when currency exchange data is readily available. In this report, the years 2018 and 2019 are considered historical years, 2020 as the base year, 2021 as the estimated year, and years from 2022 to 2026 are considered the forecast period.

Market Segmentation & Coverage:This research report categorizes the Stem Cell Therapy to forecast the revenues and analyze the trends in each of the following sub-markets:

Based on Cell Source, the market was studied across Adipose tissue-derived MSCs (mesenchymal stem cells),, Bone marrow-derived MSCs,, and Placental/umbilical cord-derived MSCs.

Based on Type, the market was studied across Allogeneic Stem Cell Therapy and Autologous Stem Cell Therapy.

Based on Therapeutic Application, the market was studied across Cardiovascular Diseases Surgeries, Inflammatory & Autoimmune Diseases, Musculoskeletal Disorders, Neurological Disorders, Other Therapeutic Applications, and Wounds & Injuries.

Based on End-User, the market was studied across Academic and Research Centers, Ambulatory Surgical Centers (ASCs), and Hospitals & Clinics.

Based on Region, the market was studied across Americas, Asia-Pacific, and Europe, Middle East & Africa. The Americas is further studied across Argentina, Brazil, Canada, Mexico, and United States. The United States is further studied across California, Florida, Illinois, New York, Ohio, Pennsylvania, and Texas. The Asia-Pacific is further studied across Australia, China, India, Indonesia, Japan, Malaysia, Philippines, Singapore, South Korea, Taiwan, and Thailand. The Europe, Middle East & Africa is further studied across France, Germany, Italy, Netherlands, Qatar, Russia, Saudi Arabia, South Africa, Spain, United Arab Emirates, and United Kingdom.

Cumulative Impact of COVID-19:COVID-19 is an incomparable global public health emergency that has affected almost every industry, and the long-term effects are projected to impact the industry growth during the forecast period. Our ongoing research amplifies our research framework to ensure the inclusion of underlying COVID-19 issues and potential paths forward. The report delivers insights on COVID-19 considering the changes in consumer behavior and demand, purchasing patterns, re-routing of the supply chain, dynamics of current market forces, and the significant interventions of governments. The updated study provides insights, analysis, estimations, and forecasts, considering the COVID-19 impact on the market.

Competitive Strategic Window:The Competitive Strategic Window analyses the competitive landscape in terms of markets, applications, and geographies to help the vendor define an alignment or fit between their capabilities and opportunities for future growth prospects. It describes the optimal or favorable fit for the vendors to adopt successive merger and acquisition strategies, geography expansion, research & development, and new product introduction strategies to execute further business expansion and growth during a forecast period.

FPNV Positioning Matrix:The FPNV Positioning Matrix evaluates and categorizes the vendors in the Stem Cell Therapy Market based on Business Strategy (Business Growth, Industry Coverage, Financial Viability, and Channel Support) and Product Satisfaction (Value for Money, Ease of Use, Product Features, and Customer Support) that aids businesses in better decision making and understanding the competitive landscape.

Market Share Analysis:The Market Share Analysis offers the analysis of vendors considering their contribution to the overall market. It provides the idea of its revenue generation into the overall market compared to other vendors in the space. It provides insights into how vendors are performing in terms of revenue generation and customer base compared to others. Knowing market share offers an idea of the size and competitiveness of the vendors for the base year. It reveals the market characteristics in terms of accumulation, fragmentation, dominance, and amalgamation traits.

Competitive Scenario:The Competitive Scenario provides an outlook analysis of the various business growth strategies adopted by the vendors. The news covered in this section deliver valuable thoughts at the different stage while keeping up-to-date with the business and engage stakeholders in the economic debate. The competitive scenario represents press releases or news of the companies categorized into Merger & Acquisition, Agreement, Collaboration, & Partnership, New Product Launch & Enhancement, Investment & Funding, and Award, Recognition, & Expansion. All the news collected help vendor to understand the gaps in the marketplace and competitors strength and weakness thereby, providing insights to enhance product and service.

Company Usability Profiles:The report profoundly explores the recent significant developments by the leading vendors and innovation profiles in the Global Stem Cell Therapy Market, including Advanced Cell Technology, Inc., AlloSource, Inc., Anterogen Co., Ltd., Bioheart Inc., BioTime, Inc., BrainStorm Cell Therapeutics Inc., Celgene Corporation, Cellartis AB, CellGenix GmbH, Cellular Engineering Technologies Inc., Gamida Cell Ltd, Gilead Sciences, Inc., Holostem Terapie Avanzate Srl, JCR Pharmaceuticals Co., Ltd., Lonza Group AG, Medipost Co., Ltd., Nuvasive, Inc., Osiris Therapeutics, Inc., Pharmicell Co., Ltd., Pluristem Therapeutics Inc., PromoCell GmbH, RTI Surgical, Inc., STEMCELL Technologies, Inc., Takeda Pharmaceutical Company Limited, Vericel Corporation, and VistaGen Therapeutics, Inc..

The report provides insights on the following pointers:1. Market Penetration: Provides comprehensive information on the market offered by the key players2. Market Development: Provides in-depth information about lucrative emerging markets and analyze penetration across mature segments of the markets3. Market Diversification: Provides detailed information about new product launches, untapped geographies, recent developments, and investments4. Competitive Assessment & Intelligence: Provides an exhaustive assessment of market shares, strategies, products, certification, regulatory approvals, patent landscape, and manufacturing capabilities of the leading players5. Product Development & Innovation: Provides intelligent insights on future technologies, R&D activities, and breakthrough product developments

The report answers questions such as:1. What is the market size and forecast of the Global Stem Cell Therapy Market?2. What are the inhibiting factors and impact of COVID-19 shaping the Global Stem Cell Therapy Market during the forecast period?3. Which are the products/segments/applications/areas to invest in over the forecast period in the Global Stem Cell Therapy Market?4. What is the competitive strategic window for opportunities in the Global Stem Cell Therapy Market?5. What are the technology trends and regulatory frameworks in the Global Stem Cell Therapy Market?6. What is the market share of the leading vendors in the Global Stem Cell Therapy Market?7. What modes and strategic moves are considered suitable for entering the Global Stem Cell Therapy Market?Read the full report: https://www.reportlinker.com/p06175517/?utm_source=GNW

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Stem Cell Therapy Market Research Report by Cell Source, by Type, by Therapeutic Application, by End-User, by Region - Global Forecast to 2026 -...

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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Therapy and Prevention Strategies for Myocardial Infarction | IJN - Dove Medical Press