AbstractWe have studied the effect of recombinant human Stem Cell Factor (SCF) on the growth of human peripheral blood, bone marrow, and cord blood progenitor cells in semisolid medium. While SCF alone had little colony‐stimulating activity under fetal bovine serum (FBS)‐deprived culture conditions, SCF synergized with erythropoietin (Epo), granulocyte/macrophage colony‐stimulating factor (GM‐CSF), and interleukin 3 (IL‐3) to stimulate colony growth. Colony morphology was determined by the late‐acting growth factor added along with SCF. Of all the combinations of growth factors, SCF plus IL‐3 and Epo resulted in the largest number of mixed‐cell colonies‐ a larger number than observed with IL‐3 and Epo alone even in FBS‐supplemented cultures. These results suggest that SCF is a growth factor that more specifically targets early progenitor cells (mixed‐cell colony‐forming cells) and has the capacity to synergize with a wide variety of other hematopoietic growth factors to cause the proliferation and differentiation of committed progenitor cells. Our studies indicate that SCF may be the earliest acting growth
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