Research into exosome signaling has grown in recent years. Arguably the bulk of signaling between cells is transported via varieties of extracellular vesicle, collections of molecules packaged within a membrane. Exosomes are one such type of vesicle. An originating cell generates exosomes, releasing them to the environment, and other cells accept them as they arrive. The contents of an accepted exosome then go on to influence cell machinery and activities. The beneficial effects of most stem cell therapies are mediated by signaling rather than by any other actions of the transplanted cells, and thus in principle it should be possible to do away with the cells and base a therapy on the signals alone. In the near term that might be accomplished by harvesting exosomes from cell cultures, while in the long term manufacturing and delivering specific desired signal molecules directly will probably emerge as the dominant approach.

The research noted here is carried out in cell cultures only, but it is an interesting example of the degree of influence over cell behavior that might be obtained through delivery of exosomes. If cells in many tissue types can be encouraged to greater regeneration and greater resilience to adversity through exosomes harvested from stem cells, then this is enough, no doubt, to support a wide range of potential therapies. Juvena Therapeutics is one example of a company that is mining this sort of cell signaling to pull out therapeutics. In the years ahead a great many other similar ventures will arise.

At this point, even given two decades of experimentation with stem cell therapies, it remains something of an open question as how great of a benefit can be provided by regenerative therapies that work around underlying damage. "Putting cells back to work" might be the motto, but this happens without any deliberate attempt to repair the accumulation of damage that is present old tissues. How much of that damage will be fixed by telling cells to work harder? Certainly issues caused by too few active cells seem amenable to treatment via simple therapies that override cell instructions, but we know that at least some forms of molecular damage at the root of aging, such as persistent cross-links and a few varieties of metabolic waste, cannot be effectively repaired even by youthful and active cells.

Exosomes Derived from Human Induced Pluripotent Stem Cells Ameliorate the Aging of Skin Fibroblasts