www.landesbioscience.com Cell Cycle 859

The differentiation of human embryonic stem cells (hESCs) into hematopoietic stem cells (HSCs) that match the repopu-lation potential of bone marrow-derived correlates has tremendous clinical prom-ise, but this goal has eluded researchers despite 15 y of dogged effort. In vivo, HSCs have been shown to arise from specialized endothelial cells (ECs) with hemogenic potential, and endothelial to hematopoietic transition (EHT) has also been demonstrated in vitro using a mouse ESC platform (reviewed in ref. 1). Recently, we generated transgenic hESCs in which endothelial and early hematopoi