STEM-CELL FACTOR RETARDS DIFFERENTIATION OF NORMAL HUMAN ERYTHROID PROGENITOR CELLS WHILE STIMULATING PROLIFERATION

Stem cell factor (SCF), the ligand for the c-kit tyrosine kinase recep tor, markedly stimulates the accumulation of erythroid progenitor cell s in vitro. We now report that SCF delays erythroid differentiation am ong the progeny of individual erythroid progenitors while greatly incr easing the proliferation of these progeny, These effects appear to be independent of an effect on maintenance of cell viability, Highly puri fied day-6 erythroid colony-forming cells (ECFC), consisting mainly of colony-forming units-erythroid (CFU-E), were generated from human per ipheral blood burst-forming units-erythroid (BFU-E). Addition of SCF t o the ECFC in serum-free liquid culture, together with erythropoietin (EP) and insulin-like growth factor 1 (IGF-1), resulted in a marked in crease in DNA synthesis, associated with a delayed peak in cellular be nzidine positivity and a delayed incorporation of Fe-59 into hemoglobi n compared with cultures without SCF. In the presence of SCF, the numb er of ECFC was greatly expanded during this culture period, and total production of benzidine-positive cells plus hemoglobin synthesis were ultimately increased, To determine the effect of SCF on individual ECF C, single-cell cultures were performed in both semisolid and liquid me dia. These cultures demonstrated that SCF, in the presence of EP and I GF-1, acted on single cells and their descendants to delay erythroid d ifferentiation while substantially stimulating cellular proliferation, without an enhancement of viability of the initial cells. This was al so evident when the effect of SCF was determined using clones of ECFC derived from single BFU-E. Our experiments demonstrate that SCF acts o n individual day-6 ECFC to retard erythroid differentiation while simu ltaneously providing enhanced proliferation by a process apparently in dependent of an effect on cell viability or programmed cell death. (C) 1995 by The American Society of Hematology.