CD14−/CD34+ is the founding population of umbilical cord blood-derived endothelial progenitor cells and angiogenin1 is an important factor promoting the colony formation

The origin of endothelial progenitor cells (EPCs) in umbilical cord blood (UCB) is unknown. In this study, we explored the origin of UCB-derived EPCs by culturing CD14+ or CD14− subpopulation separately and co-culturing these two subpopulations either with or without transwells. We found no colony formation with CD14+ or CD14− subpopulation alone, but there were EPC colonies observed in direct co-cultures of both subpopulations. Transwell culture system was used to further study the effect of cytokines on EPC colony formation. We observed the presence of EPC colonies derived from CD14− subpopulation in the presence of CD14+ subpopulation in the upper compartment whereas there was no colony generated from CD14+ subpopulation with CD14− subpopulation in the upper compartment. Therefore, CD14− subpopulation is likely to be the origin of EPCs and EPC colony derivation requires cytokines released from CD14+ subpopulation. We further characterized the founding population of UCB-derived EPCs by separating CD14− subpopulation into CD14−/CD34+ and CD14−/CD34− subpopulations. There were colonies observed only in co-cultures of CD14+ with CD14−/CD34+ subpopulation but not with CD14−/CD34− subpopulation either with or without transwells. We screened 42 cytokines involving in angiogenesis using an ELISA array in the supernatant collected from CD14+ compared to CD14− subpopulations. We found consistently the presence of angiogenin1 in the supernatant of CD14+ subpopulation but not in that of CD14− subpopulation. The addition of angiogenin1 in culture of CD14− subpopulation yielded EPC colonies. We conclude that UCB-derived EPCs are confined to CD14−/CD34+ subpopulation and angiogenin1 released from CD14+ subpopulation may be an important factor promoting the EPC colony formation.