Arterial Identity Of Hemogenic Endothelium: A Key To Unlock Definitive Hematopoietic Commitment In hPSC Cultures.

Human pluripotent stem cells (hPSCs) have been suggested as a potential source for the de novo production of blood cells for transfusion, immunotherapies and transplantation. However, even with advanced hematopoietic differentiation methods, the primitive and myeloid-restricted waves of hematopoiesis dominate in hPSC differentiation cultures while cell-surface markers to distinguish these waves of hematopoiesis from lympho-myeloid hematopoiesis remain unknown. In the embryo, hematopoietic stem cells (HSCs) arise from hemogenic endothelium (HE) lining arteries, but not veins. This observation led to a long-standing hypothesis that arterial specification is an essential prerequisite to initiate HSC program. It has also been established that lymphoid potential in yolk sac and extraembryonic vasculature is mostly confined to arteries, while myeloid-restricted hematopoiesis is not specific to arterial vessels. Here we review how the link between arterialization and subsequent definitive multilineage hematopoietic program can be exploited to identify hemogenic endothelium enriched in lymphoid progenitors and aid in in vitro approaches to enhance the production of lymphoid cells and potentially HSCs from hPSCs. We also discuss alternative models of hematopoietic specification at arterial sites and the recent advances in understanding hematopoietic development and producing engraftable hematopoietic cells from hPSCs.