Paracrine proangiopoietic effects of human umbilical cord blood-derived purified CD133+ cells--implications for stem cell therapies in regenerative medicine.

CD133+ cells purified from hematopoietic tissues are enriched mostly for hematopoietic stem/progenitor cells, but also contain some endothelial progenitor cells and very small embryonic-like stem cells. CD133+ cells, which are akin to CD34+ cells, are a potential source of stem cells in regenerative medicine. However, the lack of convincing donor-derived chimerism in the damaged organs of patients treated with these cells suggests that the improvement in function involves mechanisms other than a direct contribution to the damaged tissues. We hypothesized that CD133+ cells secrete several paracrine factors that play a major role in the positive effects observed after treatment and tested supernatants derived from these cells for the presence of such factors. We observed that CD133+ cells and CD133+ cell-derived microvesicles (MVs) express mRNAs for several antiapoptotic and proangiopoietic factors, including kit ligand, insulin growth factor-1, vascular endothelial growth factor, basic fibroblast growth factor, and interleukin-8. These factors were also detected in a CD133+ cell-derived conditioned medium (CM). More important, the CD133+ cell-derived CM and MVs chemoattracted endothelial cells and display proangiopoietic activity both in vitro and in vivo assays. This observation should be taken into consideration when evaluating clinical outcomes from purified CD133+ cell therapies in regenerative medicine.