A new role of thrombopoietin enhancing ex vivo expansion of endothelial precursor cells derived from AC133-positive cells.

We previously reported that CD31(bright) cells, which were sorted from cultured AC133(+) cells of adult peripheral blood cells, differentiated more efficiently into endothelial cells than CD31(+) cells or CD31(-) cells, suggesting that CD31(bright) cells may be endothelial precursor cells. In this study, we found that CD31(bright) cells have a strong ability to release cytokines. The mixture of vascular endothelial growth factor (VEGF), thrombopoietin (TPO), and stem cell factor stimulated ex vivo expansion of the total cell number from cultured AC133(+) cells of adult peripheral blood cells and cord blood cells, resulting in incrementation of the adhesion cells, in which endothelial nitric oxide synthase and kinase insert domain-containing receptor were positive. Moreover, the mixture of VEGF and TPO increased the CD31(bright) cell population when compared with VEGF alone or the mixture of VEGF and stem cell factor. These data suggest that TPO is an important growth factor that can promote endothelial precursor cells expansion ex vivo.