Effects of human yolk sac endothelial cells on supporting expansion of hematopoietic stem/progenitor cells from cord blood

In order to investigate the effects of human yolk sac-derived endothelial cells (hYSECs) on the expansion of human hematopoietic stem/progenitor cells (HS/PCs) from umbilical cord blood (UCB) in vitro, we purified hYSEC-like cells from 4-5 week human yolk sacs, which were morphologically similar to endothelial cells and expressed CD31, CD144 and vWF characteristics of endothelial cells. Then we isolated CD34+ cells from UCB in culture under three different conditions: with hematopoietic cytokines (CKs), contact-coculture or noncontact-coculture with hYSECs supplemented with CKs, and found that the contact-coculture system had the strongest expansion efficiency in the total cells' (TCs) ability to form HPP-CFCs. Erythroid burst-forming units (BFU-E) increased 52.35-fold, 20.26-fold and 27.77-fold, respectively, compared with pre-expansion. We detected that the mRNA of Notch ligands such as Jagged1, Delta1 and Delta4 could express in hYSECs after contacted culture with UCB-CD34+ cells but not the noncontacted cells by RT-PCR analysis. Therefore, we concluded that the contact-coculture system supplemented with CKs could support the expansion of UCB-HS/PCs in vitro, especially high potential proliferative colony-forming cells (HPP-CFC) and BFU-E, perhaps owing to Notch signal pathway.