“…HSC and other nonhematopoietic stem cells are actively chemoattracted by factors secreted by BM stroma cells and osteoblasts (e.g., stromal derived factor-1 [SDF-1] and hepatocyte growth factor [HGF]) and colonize marrow by the end of the second and the beginning of the third trimester of gestation (Kmiecik et al, 1992;Ma et al, 1998;Nagasawa, 2000;Taichman et al, 2001). Accumulating evidence suggests that these nonhematopoietic stem cells residing in the BM play some role in the homeostasis/turnover of peripheral tissues and if needed could be released/mobilized from the BM into circulation during tissue injury and stress, thus facilitating the regeneration of damaged organs (LaBarge and Blau, 2002;Kale et al, 2003;Kollet et al, 2003;Abbott et al, 2004;Kucia et al, 2004Kucia et al, , 2006cWojakowski et al, 2004;Long et al, 2005;Gomperts et al, 2006). It is also possible that, in steady state conditions, they shuttle at very low level between BM and stem cell niches in peripheral organs/tissues.…”