Do Pluripotent Stem Cells Exist in Adult Mice as Very Small Embryonic Stem Cells?

• We rigorously evaluated the mouse VSEL hypothesis
• Most CD45−/intLin−SCA-1+ events were neither “very small” nor diploid cells
• No pluripotency was detected in CD45−/intLin−SCA-1+ cells, regardless of their size
• Existence of adult mouse VSELs in the bone marrow remains dubious

SummaryVery small embryonic-like stem cells (VSELs) isolated from bone marrow (BM) have been reported to be pluripotent. Given their nonembryonic source, they could replace blastocyst-derived embryonic stem cells in research and medicine. However, their multiple-germ-layer potential has been incompletely studied. Here, we show that we cannot find VSELs in mouse BM with any of the reported stem cell potentials, specifically for hematopoiesis. We found that: (1) most events within the “VSEL” flow-cytometry gate had little DNA and the cells corresponding to these events (2) could not form spheres, (3) did not express Oct4, and (4) could not differentiate into blood cells. These results provide a failure to confirm the existence of pluripotent VSELs.