An Interferon-γ/FLT3 Axis Positively Regulates Hematopoietic Progenitor Cell Expansion from Human Pluripotent Stem Cells.

Since it became possible to differentiate human pluripotent stem cells (hPSCs) into hematopoietic cells in vitro, great efforts have been made to obtain highly potent hematopoietic stem/progenitor cells (HSPCs) from hPSCs. Immunophenotypical HSPCs can be obtained from hPSCs, but their repopulating potential in vivo is low. Here, we developed a novel hematopoietic differentiation method for human-induced pluripotent stem cells (hiPSCs) to determine why the existing hPSC differentiation systems are inadequate. hiPSC-derived CD45+CD34+ cells in our system were mostly CD38- immunophenotypical HSPCs. The vast majority of human CD45+CD34+ cells in umbilical cord blood, fetal liver, and bone marrow are CD38+ hematopoietic progenitor cells (HPCs); therefore, the poor production of CD38+ HPCs was indicative of a systematic problem. hiPSC-derived CD45+CD34+ cells did not express FLT3, a receptor tyrosine kinase. Exogenous FLT3 activity significantly enhanced the production of CD38+ HPCs from hiPSCs. Thus, poor production of CD38+ HPCs was due to a lack of FLT3 expression. Interferon-γ upregulated expression of FLT3 and increased the number of CD38+ HPCs among hiPSC-derived CD45+CD34+ cells. These results suggest that the poor production of CD38+ HPCs with hPSC differentiation systems is due to a lack of FLT3 expression, and that the addition of interferon-γ can solve this problem.