Do Very Small Embryonic-Like Stem Cells in Fact Exist in Adult Tissues?

In recent years a number of research groups have proposed that there exist populations of pluripotent stem cells in adult tissues, capable of forming any of the hundreds of different types of cell in the body. Different groups have different names for the cells they have found, but "very small embryonic-like stem cells" or VSELs is the name given by one of the more active researchers in this area. Greater confirmation or refutation of the existence of VSELs should also bias us one way or another for the various other researchers and their proposed pluripotent cell populations.

Why does this research matter? It is a matter of economics: if there is an easily accessible population of stem cells in every patient's skin that can be used to generate any type of cell in the body, then that will make a big difference to the pace at which regenerative therapies can be developed and deployed to the clinic, as well as making those therapies cheaper and faster. If, on the other hand, it turns out that adult tissues do not retain any sort of pluripotent stem cells, then it will require cell reprogramming to come to maturity in order to reach the same goals. All the other known and categorized stem cell populations in the adult body can be made to produce at best a couple of different types of cell, depending on their location and lineage.

Here, then, is a skeptical view on VSELs from researchers who have concluded that no such thing exists. Whenever you have a small number of researchers with differing opinions, the only thing to do is wait for more scientists to join in and produce further data:

A Wild Stem Cell Chase

The existence of very small embryonic-like stem cells (VSELs) has been hotly debated by scientists since they were first reported in mouse bone marrow in 2005. The cells were later identified in human blood and bone marrow as well, and have been proposed as a viable alternative to mouse and human embryonic stem cells (ESCs) in research and medicine. But a study published today [has] called the very existence of VSELs in question, with the senior author deeming them a "distraction."

Irving Weissman of Stanford University School of Medicine and his team set out to replicate the original finding of VSELs in mouse bone marrow, using the most rigorous protocols yet. They focused on identifying candidate VSELs by using the characteristics of size, phenotype, and pluripotency markers, but failed to find any cells that fit previous VSEL descriptions. The researchers found that the vast majority of events matching the estimated size of VSELs actually appeared to be artifacts, such as dead cells and debris. The team tested the remaining "exceedingly rare population" of cells that matched the VSEL profile for pluripotency markers without luck. "The claims about VSELs were not yet replicated by independent scientists. We redid the experiments as they have been described and could not confirm what was claimed."

Meanwhile, researchers continue to make progress on reprogramming of cells, but years lie between here and widespread use of therapies based on these technologies. The first early stage clinical trials using reprogrammed cells are only just starting now in Japan:

In the seven years since their discovery, induced pluripotent stem (iPS) cells have transformed basic research and won a Nobel prize. Now, a Japanese study is about to test the medical potential of these cells for the first time. Made by reprogramming adult cells into an embryo-like state that can form any cell type in the body, the cells will be transplanted into patients who have a debilitating eye disease. Masayo Takahashi, an ophthalmologist at the RIKEN Center for Developmental Biology in Kobe, Japan, plans to submit her application for the study to the Japanese health ministry next month, and could be recruiting patients as early as September.