Human embryonic stem cell-derived hematoendothelial progenitors engraft chicken embryos

Objective: To investigate whether human embryonic stem cells (hESC) committed in culture into hematopoietic/endothelial cell progenitors can be further developed into mature blood and vascular cells following transplantation into chicken embryos. Materials and Methods: The yolk sac of 42- to 44-hour chicken embryos received yolk sac injections of unfractionated human embryoid body (hEB) cells, CD34-positive hEB cells, or CD34⁺CD45⁺ granulocyte colony-stimulating factor-mobilized human peripheral blood hematopoietic stem-progenitor cells. Human cells in the host were detected by flow cytometry and immunohistochemistry. Results: All injected cell populations engrafted chicken hematopoietic organs, as assessed by detection of CD45⁺ cells in the spleen, bursa of Fabricius, and thymus. CD34⁺ day -10 hEB cells showed the highest efficiency for producing human CD45⁺ cells in the hosts and yielded human glycophorin A⁺ erythroid, CD13⁺ myeloid, and CD19⁺ lymphoid cells in the spleen and bursa of Fabricius. Spleen cells from chimeric embryos also contained human colony-forming units-granulocyte macrophage, as assessed in methylcellulose colony-forming assays. Human endothelial cells expressing vascular endothelial-cadherin, von Willebrand factor, CD31, and the receptor for the Ulex europaeus lectin were also observed in the yolk sac vasculature following injection of either unfractionated or CD34⁺ day -10 hEB cells. Conclusion: Primitive angiohematopoietic stem cells (total and CD34⁺ day -10 hEB cells) as well as adult hematopoietic stem cells could home to intraembryonic blood-forming organs following injection into the yolk sac. These observations demonstrate the utility of the avian embryo as a convenient and reliable host to model the angiohematopoietic development of human embryonic, or other early stem cells.