There's a shake-up happening today in the world of stem cell research. Very small embryonic-like stem cells, or VSEL cells, have been proposed by some researchers as an alternative to human embryonic stem cells. Because they're said to exist in the bone marrow of adult humans and mice, they could obviate the ethical issues surrounding the use of human embryos.
The research has sounded promising enough that a New York-based company, NeoStem, was awarded a grant from the National Institute of Dental and Craniofacial Research to investigate the use of the cells to stimulate bone growth after tooth extraction.
“It has become important to know to what extent and where these VSEL cells exist to understand how they may affect the field of stem cell research,” said Weissman, who directs Stanford’s Institute for Stem Cell Biology and Regenerative Medicine and the Ludwig Center for Cancer Stem Cell Research and Medicine at Stanford. “We tried as hard as we could to replicate the original published results using the methods described and were unable to detect these cells in either the bone marrow or the blood of laboratory mice.”
Although other groups have seemingly confirmed the existence of these cells as defined by size and the expression of key cell-surface molecules, Weissman’s study is the first to evaluate the biological potency of the cells.
An article in today's Nature magazine summarizes the controversy surrounding the cells, and calls Weissman's study a "major blow to the field." Alison Abbott writes:
Led by Irving Weissman, a prominent stem-cell researcher at Stanford University in California, the study is the fourth to refute the cells’ existence — and the most thorough yet.
“Weissman’s evidence is a clincher — it is the end of the road for VSELs,” believes Rüdiger Alt, head of research at Vita 34, a private bank for umbilical cord blood in Leipzig, Germany, who last year published the first failure to replicate claims for the cells2.
Robin Smith, chief executive at Neostem, disagrees. She compares the attacks on VSELs to those suffered by Charles Darwin and Nicolaus Copernicus when they proposed their world-changing scientific theories.
It will likely take some time for the controversy to end. In the meantime, Weissman and his colleagues have concluded that “the existence of adult mouse VSELs in the bone marrow remains dubious.”