Hematopoietic Differentiation of Human Induced Pluripotent Stem Cells

Induced pluripotent stem cells (iPSCs) provide an unprecedented opportunity for modeling of human diseases in vitro as well as for developing novel approaches for regenerative therapy based on immunologically compatible cells. In the present study, we employed an OP9 differentiation system to characterize the hematopoietic differentiation potential of seven human iPSC lines obtained from human fetal, neonatal, and adult fibroblasts through reprogramming with POU5F1, SOX2, NANOG, and LIN28 and compared it with the differentiation potential of five human embryonic stem cell lines (hESC; H1, H7, H9, H13, and H14). Similar to hESCs, all iPSCs in coculture with OP9 generated all types of colony forming cells (CFCs) as well as CD34+ cells that can be separated into distinct subsets based on differential expression of CD43 and CD31. CD34+CD31+CD43− cells obtained from all iPSCs expressed molecules present on endothelial cells and readily formed a monolayer when placed in endothelial conditions, while hematopoietic CFC potential was restricted to CD43+ cells. iPSC-derived CD43+ cells could be separated into three major subsets based on differential expression of CD235a/CD41a and CD45: CD235a+CD41a+/− (erythro-megakaryocytic progenitors), and lin-CD34+CD43+CD45− (multipotent), and lin-CD34+CD43+CD45+ (myeloid-skewed) primitive hematopoietic cells. Both subsets of primitive hematopoietic cells expressed genes associated with myeloid and lymphoid development, although myeloid genes were upregulated in CD45+ cells, which are skewed toward myeloid differentiation. Cytogenetic analysis demonstrated that iPSCs and derived from them CD43+ cells maintained normal karyotype. In addition short tandem repeat analysis of CFCs generated from IMR90-1 cells has been performed to confirm that blood cells are in fact derived from reprogrammed IMR90 cells, and not from contaminating hESCs. While we observed some variations in the efficiency of hematopoietic differentiation between different iPSCs, the pattern of differentiation was very similar in all seven tested iPSC and five hESC lines. Using different cytokine combinations and culture conditions we were able to expand iPSC-derived myeloid progenitors and induce their differentiation toward red blood cells, neutrophils, eosinophils, macrophages, ostoeclasts, dendritic and Langerhans cells. Although several issues remain to be resolved before iPSC-derived blood cells can be administered to humans for therapeutic purposes, patient-specific iPSCs can already be used for characterization of mechanisms of blood diseases and to identify molecules that can correct affected genetic networks.