Differentiation of Human Embryonic and Induced Pluripotent Stem Cells into Blood Cells in Coculture

The establishment of human embryonic stem cell (hESC) lines, as well as the recent induced pluripotent stem cells (hiPSC), has greatly expanded our knowledge about the early development in human ontogeny. In the past decade, hESCs and hiPSCs have been proven excellent tools in characterization of molecular and cellular mechanisms underlying the normal and diseased differentiation of hematopoietic progenitors and mature, functional blood cells. Most of the types of hematopoietic cells (HCs) derived from hESCs have recently been shown with functionally mature properties, including erythrocytes, neutrophils, platelets, megakaryocytes, eosinophils, monocytes, dendritic cells (DC), nature killer (NK) cells, mast cells (MCs), and B- and T-lineage lymphoid cells. Along with the advances in research, a clinical translation of hESC/hiPSC-derived HCs as novel therapies is foreseen in the near future. However, different efficiencies in blood cell production have been reported when using different culture systems. Because of the restriction to use living human embryos, most of the hematopoiesis-inducing cultures are based on murine stromal cells. In our laboratory, we established efficient blood cell-inducing systems by coculturing hESC/hiPSCs with murine fetal stromal cells derived from aorta-gonad-mesonephros (AGM) region and fetal livers. These fetal hematopoietic tissue-derived cells showed strong supporting effects on hESC/hiPSCs, gradually inducing them to terminally mature blood cells if given proper conditions. The murine fetal hematopoietic tissue-derived stromal cells, AGM stromal cells [Xu M et al. Blood 92:2032–2040, 1998], and mid-gestation fetal liver stromal cells [Ma F et al. Blood 97:3755–3762, 2001; Ma F et al. Proc Natl Acad Sci USA 105:13087–13092, 2008] are maintained in our laboratory and radiated right before coculture. When undifferentiated hESC/hiPSC colonies are plated on these stromal cells, they grow up and differentiate to, firstly, a mesoderm-like structure. On days 10–14 in cocultures, some floating cells free themselves from the adherent layer, and they are characterized as hematopoietic progenitor cells. In the second culture system, these hematopoietic progenitors are further induced along to a specific blood cell lineage, such as erythrocytes, MCs, eosinophils, etc. At certain time points, these hESC/hiPSC-derived blood cells are examined with maturity and function. In this chapter, we will describe a coculture protocol developed in our laboratory for differentiating hESC/hiPSCs into hematopoietic cells.