Evidence that very small embryonic-like stem cells are mobilized into peripheral blood.

Recently, we identified in murine adult tissues, including bone marrow, a population of very small embryonic-like (VSEL) stem cells. Here, we provide further evidence that under steady-state conditions these cells circulate at very low levels in peripheral blood (PB) ( approximately 100-200 cells/ml) and could be additionally mobilized during pharmacological granulocyte-colony-stimulating factor-induced or stress-related mobilization, as demonstrated in a model of toxic liver or skeletal muscle damage induced by injection of carbon tetrachloride or cardiotoxin, respectively. The number of circulating VSEL stem cells under steady-state conditions in PB of 2-month-old animals was five times higher than that in 1-year-old mice. In conclusion, this study supports a hypothesis that VSEL stem cells are a mobile pool of primitive stem cells that could be released from the stem cell niches into PB. Further studies are needed, however, to see whether the level of these cells circulating in PB could become a prognostic indicator to assess the regenerative potential of an adult organism and/or clinical outcome from an injury. Disclosure of potential conflicts of interest is found at the end of this article.