Development of Hematopoietic, Endothelial and Perivascular Cells from Human Embryonic and Fetal Stem Cells

Studies of hemangioblasts (a common progenitor of hematopoietic and endothelial cells) during human development are difficult due to limited access to early human embryos. To overcome this obstacle, the in vitro approach of using human embryonic stem cells (hESC) and the embryoid body (hEB) system has been invaluable to investigate the earliest events of hematopoietic and endothelial cell formation. Herein, firstly, optimal culture conditions of hEB were determined for differentiation of hESC toward hematopoietic and endothelial cell lineages and then different developmental stages of hEB were characterized for angio-hematopoietic cell markers expression. Day-8 to day-10 hEB included the highest numbers of hematopoietic and endothelial progenitor cells, and CD34+ CD45- day-10 hEB cells were sorted to evaluate their hemangioblastic cell potential. Next, we established an in vivo chick embryo system that allowed sorted candidate hemangioblast populations to proliferate, migrate, and differentiate. Different stages of hEB cells, day-10 hEB cells purified for expression of CD34, and human peripheral blood hematopoietic stem/progenitor cells were examined for their engraftment capacity in chick embryos. Meanwhile, we examined the multi-lineage differentiation potentiality of CD146+ CD34- differentiating hESC. Recently, our group characterized pericytes/perivascular cells, that displayed positive expression of CD146 (and a lack of mature endothelial cell markers) in a variety of human organisms. Differentiating hESC include a CD146+ population that concomitantly expresses endothelial progenitor cell markers (CD31, CD34, CD133, and BB9). CD146+ pericyte-like hESC were tested for their hematopoietic, myogenic, and neurogenic potential. Finally, perivascular cells were obtained from human fetal placenta villi in order to evaluate their myogenic differentiation, migration ability, and mesenchymal stem cell phenotype. Placental villi are exceptionally rich in fetal microvessels; these might prove to be a beneficial source for stem cells that reside within blood vessel walls. Both CD146+ pericytes isolated from freshly dissociated placenta and purified blood vessel vasculature of placenta were observed for their myogenic potential. In summary, this project provided approaches to understand the early events of hematopoiesis using hESC and a chick embryo model, and allowed for observation of the mesenchymal lineage potential of perivascular cells derived from hESC and human fetal placenta