β‐Globin‐Expressing Definitive Erythroid Progenitor Cells Generated from Embryonic and Induced Pluripotent Stem Cell‐Derived Sacs

Human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells represent a potential alternative source for red blood cell transfusion. However, when using traditional methods with embryoid bodies, ES cell‐derived erythroid cells predominantly express embryonic type ɛ‐globin, with lesser fetal type γ‐globin and very little adult type β‐globin. Furthermore, no β‐globin expression is detected in iPS cell‐derived erythroid cells. ES cell‐derived sacs (ES sacs) have been recently used to generate functional platelets. Due to its unique structure, we hypothesized that ES sacs serve as hemangioblast‐like progenitors capable to generate definitive erythroid cells that express β‐globin. With our ES sac‐derived erythroid differentiation protocol, we obtained ∼120 erythroid cells per single ES cell. Both primitive (ɛ‐globin expressing) and definitive (γ‐ and β‐globin expressing) erythroid cells were generated from not only ES cells but also iPS cells. Primitive erythropoiesis is gradually switched to definitive erythropoiesis during prolonged ES sac maturation, concurrent with the emergence of hematopoietic progenitor cells. Primitive and definitive erythroid progenitor cells were selected on the basis of glycophorin A or CD34 expression from cells within the ES sacs before erythroid differentiation. This selection and differentiation strategy represents an important step toward the development of in vitro erythroid cell production systems from pluripotent stem cells. Further optimization to improve expansion should be required for clinical application. S tem C ells 2016;34:1541–1552