PSC-RED and MNC-RED: Albumin-free and low-transferrin robust erythroid differentiation protocols to produce human enucleated red blood cells.

Many methods have been developed to produce cultured red blood cells (cRBCs) in vitro but translational applications have been hampered by high costs of production and by low rates of enucleation. We have developed R6 and IMIT, two chemically defined culture media and combined them into robust erythroid differentiation (RED) protocols to differentiate induced-pluripotent stem cells (iPSCs) and peripheral blood mononuclear cells (MNCs) into enucleated erythroid cells. The RED protocols do not require any albumin or animal components and require ten- to twentyfold less transferrin (Tf) than previously, because iron is provided to the differentiating erythroblasts by small amounts of recombinant Tf supplemented with FeIII-EDTA, an iron chelator that allows Tf recycling to take place in cell culture. Importantly, cRBCs produced by iPSC differentiation using the long PSC-RED protocol enucleate at much higher rates than with previous protocols, eliminating one of the impediments to the use of these cells to produce clinically useful cRBCs. The absence of albumin, the reduced amounts of Tf, the improved reproducibility associated with the elimination of all animal components, and the high yield on the RED protocols decrease the cost of production of cultured red blood cells. RED protocols should therefore help to make translational applications of cultured RBCs more economically realistic.