The exosomes (or extracellular vesicles) released by stem cells may be the disruptive therapy for tackling age-related diseases doctors and patients have been waiting for. Despite over a decade and a half of hope and hype, stem cell therapy has failed to deliver on the promise.

Stem cell therapy once seemed beguilingly simple. As we age the number of stem cells in our bodies declines and degeneration increases.

The idea back in the early 2000s was that progenitor or adult stem cells (MSCs) could be given to patients as an unmatched (allogeneic) off-the-shelf drug and the administered cells would migrate to sites of damage or disease in the body.

Once there, it was thought, the cells would engraft and persist at these sites of injury and directly replace the patients own damaged cells. The administered cells treating cardiac disease would become a part of the patients heart tissue, for example.

It was thought that by injecting additional stem cells into the body, the new cells would transform the way that we treat certain conditions such as joint pain, stroke and cardiac degeneration. Animal studies and early human trials appeared to bear the idea out.

But nearly 20 years on, the general safety and efficacy of stem cell therapy has still not been proven, experts from the US Food and Drug Administration (FDA) recently concluded in the New England Journal of Medicine.1

Despite the earlier promise, cellular therapy for regenerative medicine is struggling to get approvals and to generate sales. Only a few allogeneic off-the-shelf cellular therapies have been approved for sale worldwide for regenerative medicine, despite huge investments2.

It turned out that a therapy based on transplanting living cells from donors into the patients body was anything but simple.

The first key issue with stem cell therapy is the question mark over safety. Introducing foreign living cells into a system as complex as the human body is challenging.

Predicting the cells behaviour once injected is a problem, FDA experts say.

A growing list of cautionary examples catalogue how things can go wrong when unproven stem cell therapies are used in the clinic; from a kidney failure patient who developed tumours following stem cell therapy, to patients with an age-related eye condition called macular degeneration, who were left blinded by their therapy given at a US clinic3.

In late 2018 and after infections linked to unapproved stem cell treatments sent 12 people to hospital, the FDA issued a stern warning about the cell products4.

Some autologous therapies using the patients own cells have also become notorious in certain countries and the subject of doubtful or dangerous medical tourism.

Today, the only stem cell therapy that has received FDA approval in the regenerative medicine field is the use of blood-forming stem cells for patients with specific blood production disorders.

Stem cells appear to be making little progress toward FDA-approved clinical use. Little wonder, then, that regenerative medicine researchers are increasingly turning to exosomes: packets of beneficial biomolecules released by stem cells.

We now know that the old working hypothesis for how stem cells exert their regenerative effects was wrong. The transplanted stem cells dont stick around long in the recipients body to replace damaged cells; most are cleared within a week.

As researchers from Oxford5 to Scripps6 have now concluded, its the exosomes stem cells release, rather than the cells themselves, that impart the regenerative benefit.

Exosomes are being described as the secret sauce of stem cells. Exosome therapy would avoid all the problems of a therapy based on live stem cells and yet harness a natural regenerative capability from stem cells.

Tellingly, some biotech stocks established back in the early 2000s as stem cell companies have shifted their focus to exosome research.

Exosome drugs could be harvested from stem cells housed in a bioreactor and then purified as a proper drug product to be administered by injection or infusion.

Exosomes should be a simpler, safer, lower cost, more easily stored and transported, alternative to stem cells.

Critically, exosomes are inherently less risky that live stem cell transplants. Exosomes cannot replicate; they cannot transform into malignant cells or other harmful cell types; they are less likely to trigger an immunogenic response; they cannot be infected with virus.

As a further demonstration of their safety, blood plasma contains high concentrations of unmatched exosomes, and blood transfusions have been carried out in hospitals for decades.

And exosomes should have an efficacy advantage, too. Being much smaller than whole cells, exosomes can circulate much more easily through the body to reach sites of injury or disease and trigger healing.

Early academic clinical studies are starting to prove exosomes potential. A recent placebo-controlled trial on 40 patients with advanced chronic kidney disease showed that the patients receiving exosomes saw enhanced kidney function at 12 months after treatment and no adverse events in the treatment group7.

Exosomes administered to patients could exert their regenerative effects in a number of ways giving treatment by exosomes multiple shots at goal.

Some degeneration, such as Parkinsons Disease, is due to a loss of specialised cells over time. Struggling cells that take up exosomes can be rescued from programmed cell death (apoptosis), and restored to health, thanks to the regenerative genetic material and the protein and lipid cellular building blocks that the exosome delivers.

Degeneration with age has also been associated with an increase in senescence cells. Senescent cells are like zombie cells that dont undergo normal clearance, yet cannot divide and proliferate to generate new tissue.

Recent research points to a benefit in animal models of human disease when the number of senescent cells is reduced. In 2019 researchers published that exosomes and vesicles from stem cells can alleviate cellular aging (senescence) in cells exposed to the exosomes/vesicles8.

Exosomes can also play a role in a recently discovered, previously unsuspected regenerative process in our bodies. Exosomes can trigger fully differentiated, specialised cells such as liver cells (hepatocytes) to a de-differentiate into a more stem cell-like state cell type9 and then maintain a pool of progenitor cells that can replenish the damaged liver with new cells10.

This same mechanism could be used to treat cardiac disease (e.g. cardiac ischemia where a lack of blood flow leads to cardiac muscle cell death). Normally a damaged heart fails to regenerate and becomes fibrotic with scar tissue.

Unfortunately, the scar tissue doesnt have the capacity to beat like cardiomyocytes, so increased fibrosis leads to progressive loss of heart pumping ejected volume and impairment or death. But using exosomes to reprogram the patients own heart muscle cells into cardiac progenitor stem cells offers a new way to treat cardiac damage and drive regeneration.

Exosomes from stem cells could be a better medicine than live stem cells a way to harness stem cells regenerative power without all the problems and disappointment.

But while stem cells secrete trillions of exosomes naturally, efficient separation and purification of exosomes has proven to be very difficult indeed11. Until now.

Exopharms proprietary LEAP technology is a robust and reliable method for producing a well-defined set of proprietary pharmaceutical-grade exosome product as a next-generation cell-free regenerative medicine.

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The Next Big Thing: Exosomes versus Stem Cells