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Hematopoietic stem cells (HSCs) are responsible for the life-long production of the blood system and are pivotal cells in hematologic transplantation therapies. During mouse and human development, the first HSCs are produced in the aorta-gonad-mesonephros region. Subsequent to this emergence, HSCs are found in other anatomical sites of the mouse conceptus. While the mouse placenta con- tains abundant HSCs at midgestation, little is known concerning whether HSCs or hematopoietic progenitors are present and supported in the human placenta during development. In this study we show, over a range of developmental times including term, that the human placenta contains hematopoietic progenitors and HSCs. Moreover, stromal cell lines generated from human placenta at several developmental time points are pericyte-like cells and support human hematopoiesis. Immunostaining of placenta sections during development localizes hematopoietic cells in close contact with pericytes/ perivascular cells. Thus, the human placenta is a potent hematopoietic niche throughout development. [ABSTRACT FROM AUTHOR]

In vivo hematopoietic generation occurs in waves of primitive and definitive cell emergence. Differentiation cultures of pluripotent embryonic stem cells (ESCs) offer an accessible source of hematopoietic cells for blood-related research and therapeutic strategies. However, despite many approaches, it remains a goal to robustly generate hematopoietic progenitor and stem cells (HP/SCs) in vitro from ESCs. This is partly due to the inability to efficiently promote, enrich, and/or molecularly direct hematopoietic emergence. Here, we use Gata2Venus (G2V) and Ly6a(SCA1)GFP (LG) reporter ESCs, derived from well-characterized mouse models of HP/SC emergence, to show that during in vitro differentiation they report emergent waves of primitive hematopoietic progenitor cells (HPCs), definitive HPCs, and B-lymphoid cell potential. These results, facilitated by enrichment of single and double reporter cells with HPC properties, demonstrate that in vitro ESC differentiation approximates the waves of hematopoietic cell generation found in vivo, thus raising possibilities for enrichment of rare ESC-derived HP/SCs., (Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.)