Over the past decade, scientists have learned that the molecules that mesenchymal stem cells release are every bit as important to regenerative medicine as the stem cells themselves. Stem cells release exosomes, which are tiny packets that contain countless molecules of microRNA, cytokines, and growth factors. These molecules are mainly what allows stem cells to help the body regrow and repair.
Dr. Vizoso and colleagues published a review article that describes the many benefits of the secretome, that is, stem cell exosomes and the substances they produce. They not only explain why exosomes are helpful in regenerative medicine but why stem cell exosomes bring a powerful enhancement to stem cells themselves.
Compared to exosomes, whole stem cells are rather big—one can safely inject far more exosomes than stem cells in each treatment. And, really, it seems that the stem cell exosomes are what is supplying most of the benefits.
Stem cells can be made to produce millions of exosomes. These stem cell exosomes can then be collected, stored, shipped, and infused with much less cost and aggravation than stem cells themselves. Exosomes have small molecules on their surfaces that allow them to seek out and find areas in the body where they are needed. Stem cells often need to be injected near the site of injury. Exosomes may work if simply infused into a vein.
Dr. Vizoso and coauthors make a persuasively strong argument about the potential benefits of infusing stem cell exosomes instead of stem cells themselves. They also point out the potential limitations of the process, given the current technology. For example, stem cells would need to be made “immortal” so that they can keep producing large amounts of the same sorts of exosomes over time. Fortunately, the techniques of cell immortalization have been around for at least 30 years. Thus, most of the barriers to widespread, large scale exosome use are things scientists already know how to overcome.
While there may still be benefits for direct stem cell infusions, the future of research is moving forward with stem cells and exosomes.
Reference: Vizoso, F., et al. (2017). Mesenchymal Stem Cell Secretome: Toward Cell-Free Therapeutic Strategies in Regenerative Medicine. International Journal of Molecular Sciences. 2017, 18(9), 1852.