Circulating skeletal stem cells

We report the isolation of adherent, clonogenic, fibroblast-like cells with osteogenic and adipogenic potential from the blood of four mammalian speci es. These cells phenotypically resemble but are distinguishable from skelet al stem cells found in bone marrow (stromal stem cells,''mesenchymal stem c ells"), The osteogenic potential of the blood-borne cells was proven by an in vivo transplantation assay in which either polyclonal or single colony-d erived strains were trans-planted into the subcutis of immunocompromised mi ce, and the donor origin of the fully differentiated bone cells was proven using species-specific probes. This is the first definitive proof of the ex istence of circulating skeletal stem cells in mammals.