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The present studies investigated the effects of the recently cloned flt3 ligand (FL) on the in vitro growth and differentiation of primitive and committed subsets of human CD34+ bone marrow (BM) progenitor cells. FL alone was a weak growth stimulator of CD34+ BM cells, but synergistically and directly enhanced colony formation in combination with interleukin (IL) 3, granulocyte colony-stimulating factor (G-CSF), CSF-1, granulocyte macrophage (GM) CSF stem cell factor (SCF), and IL-6. FL and SCF were equally effective in stimulating colony formation in combination with IL-3. However, the tri-factor combination of FL + IL-3 + SCF stimulated 2.3-fold and 2.5-fold more colonies than FL + IL-3 and SCF + IL-3, respectively. These additional recruited progenitors appeared to be predominantly located in a primitive (CD71-) subset of the CD34+ progenitors, as 4.5-fold more colonies were formed by CD34+CD71- cells in response to FL + IL-3 + SCF than to FL + IL-3 or SCF + IL-3. Similar findings were observed in serum-containing and serum-deprived cultures. Whereas FL did not enhance burst-forming unit-erythroid (BFU-E) colony formation of CD34+ BM cells in the presence of serum, a low number of BFU-E colonies were formed in response to FL plus erythropoietin (Epo) under serum-deprived conditions. In addition, FL both in serum-containing and serum-deprived cultures stimulated colony formation of more committed myeloid progenitors in CD34+CD71+ BM cells. Thus, FL potently stimulates the growth of primitive and more committed human BM progenitor cells.


Journal article



Publication Date





1317 - 1325


Adult, Antigens, CD, Antigens, CD34, Antigens, Differentiation, B-Lymphocyte, Bone Marrow Cells, Cell Differentiation, Cell Division, Cells, Cultured, Growth Substances, Hematopoiesis, Hematopoietic Stem Cells, Humans, Interleukin-3, Membrane Proteins, Receptors, Transferrin, Stem Cell Factor