Hemogenic Endothelial Progenitors Cells Isolated from Human Umbilical Cord Blood

¹ Vascular Biology Program and Department of Surgery, Children's Hospital Boston
² Stem Cell Program and Division of Hematology, Department of Medicine, Children's Hospital Boston and
³ Stem Cell Program and Division of Hematology, Department of Medicine, Children's Hospital Boston and Departments of Pediatrics and Surgery, Harvard Medical School, Boston, MA 02115
⁴ Vascular Biology Program and Department of Surgery, Children's Hospital Boston Surgery, Harvard Medical School, Boston, MA 02115

^* To whom correspondence should be addressed. E-mail: joyce.bischoff{at}childrens.harvard.edu.

	Abstract

Hemogenic endothelium has been identified in embryonic dorsal aorta and in tissues generated from mouse embryonic stem cells, but to date there is no evidence for such bi-potential cells in post-natal tissues or blood. Here we identify a cell population from human umbilical cord blood that gives rise to both endothelial cells and hematopoietic progenitors in vitro. Cord blood CD34+/CD133+ cells plated at high density in an endothelial basal medium formed an endothelial monolayer and a non-adherent cell population after 14-21 days. AML-1, a factor required for definitive hematopoiesis, was detected at low levels in adherent cells and at high levels in non-adherent cells. Non-adherent cells co-expressed the endothelial marker VE-cadherin and the hematopoietic marker CD45 while adherent cells were composed primarily of VE-cadherin+/CD45- cells and a smaller fraction of VE-cadherin+/CD45+ cells. Both non-adherent and adherent cells produced hematopoietic colonies in methylcellulose, with the adherent cells yielding more CFU-GEMM compared to the non-adherent cells. To determine if the adherent endothelial cells were producing hematopoietic progenitors, single cells from the adherent population were expanded in 96 well dishes for 14 days. The clonal populations expressed VE-cadherin and a subset expressed AML-1, -globin and -globin. Three out of 17 clonal cell populations gave rise to early CFU-GEMM hematopoietic progenitors and BFU-E erythroid progenitors. These results provide evidence for hemogenic endothelial cells in human umbilical cord blood.