"Very small embryonic-like stem cells" is the name given by one research group to populations of stem cells that they believe sustain adult tissue throughout life, and which retain most of the desired characteristics needed for the first generation of cell-based regenerative therapies. They are thought to be pluripotent, able to give rise to any form of cell, unlike the more limited and better known forms of stem cell identified in adults and used in the development of regenerative therapies. Over at h+ Magazine, there's an interview with Mariusz Ratajczak, one of the researchers involved:
Very small embryonic like stem cells (VSELs) are purified from adult tissues and are potential sources of stem cells for application in regenerative medicine and stem cell therapies. ... A question that is important from the developmental point of view is why pluripotent stem cells, (PSCs) such as VSELs, would reside in adult organs? For many years, it had been accepted that adult tissues contain only tissue-committed stem cells (TCSCs) that have limited possibility of differentiation - for example, epidermal stem cells, hematopoietic stem cells, skeletal muscle stem cells.
Ratajczak has comments on longevity and regenerative medicine - it's always good to see noted researchers stepping up to support the goal of engineered longevity in public, given that it's only been a handful of years since that sort of freedom of opinion became possible for researchers who wished to retain their funding sources. One of the many necessary preconditions for widespread support of longevity science is that researchers must speak out in favor of rejuvenation biotechnology.
I am deeply convinced that regenerative medicine is our key to a better life and our key to extending lifespan. I believe that we will be able to employ [pluripotent stem cells] (e.g., VSELs), isolated from adult tissues, to harness stem cells to regenerate damaged organs. In combination with developing scaffold-technologies, we may be able to generate ex vivo organ fragments or even whole organs and replace organ transplantations with in vitro generated ones.
I should note that Ratajczak presented at the SENS5 conference last year, alongside other researchers bullish on the future of longevity and medical science. In his presentation, he theorizes a direct link between VSELs and aging:
We propose, based on our experimental data in animal models, that gradual decrease in the number of VSELs deposited in adult tissues, which occurs throughout life in an [insulin/insulin growth factor] signaling-dependent manner is an important mechanism of aging.
Which is much the view that the research community has on stem cells as a whole: stem cells and their capacity to maintain tissue decline with age, for reasons that are being explored in detail, and which may in the near future be addressed in a number of different ways.