Endothelial cell precursors are normal components of human umbilical cord blood

Endothelial cells are part of the normal bone marrow stroma. We have previously shown human umbilical cord blood (UCB) does not produce stroma in standard long-term cultures. Highly enriched (93-98%) UCB CD34(+) cells were cultured for 6 weeks with interleukin-2 and conditioned medium from the 5637 carcinoma cell line (n=4). The resulting 'fibroblast like' cells were shown to be endothelial by expression of von Willebrand factor (VWF), ICAM-1 (CD54), E-selectin (CD62(E)) and PECAM (CD31). Endothelial monolayers seeded with CD34(+) UCB cells supported expansion of colony forming cells and CD34(+) cells. We conclude that endothelial cell precursors circulate in UCB, and may be derived from the CD34(+) cell fraction.