Abstract: In vitro production of clinically useful quantities of single species of mature, differentiated human blood cells is carried out by a method in which human pluripotent hematopoietic stem cells, preferably from a universal donor, are incubated in a bioreactor in a growth medium also containing specific combinations of recombinant human growth and maturation promoting polypeptide factors that expand stem cell cultures and promote the maturation and differentiation of stem cells into single species of erythroid, thrombocytic or granulocytic human blood cells, and harvesting the mature cells. The growth and maturation promoting polypeptides employed include SCGF, Interleukins 1,3,4,5,6, and 11, GM-CSF, M-CSF, G-CSF and EPO. Stem cells may be preliminarily genetically modified so as to remove histocompatibility or blood group antigens with which a recipient may be incompatible, or the stem cells may be genetically altered by transfection with appropriate DNA-containing vectors, prior to addition to the bioreactor.