Effects of five recombinant hematopoietic growth factors on enriched human erythroid progenitors in serum-replaced cultures

Erythroid progenitors from normal human marrow were purified by a two-step immune panning method permitting both the enrichment of erythroid progenitors (plating efficiency up to 10%) and the separation of CFU-E from BFU-E. The purified erythroid progenitors were grown in serum-replaced conditions; in some experiments at an average of one cell per well. Human recombinant granulocyte-macrophage colony stimulating factor (GM-CSF), interleukin 3 (IL3), erythroid potentiating activity (EPA), and human erythropoietin (Epo) either recombinant or homogenous native were tested for their effect on CFU-E growth. Epo was an absolute requirement for CFU-E growth and was sufficient to obtain colony formation at the unicellular level whereas GM-CSF and IL3 did not further increase the plating efficiency. EPA potentiated the effect of Epo on this progenitor only in experiments performed at unicellular level. Human recombinant GM-CSF, IL3, Interleukin 1 alpha (IL1 alpha), and Epo were subsequently tested for their ability to promote BFU-E growth. GM-CSF and IL3 supported the growth of erythroid bursts in the presence of Epo, even at the unicellular level. However, IL3 promoted a higher number of bursts than GM-CSF under all conditions tested. These two growth factors have no or very small additive effects when tested in combination. IL1 alpha added to Epo alone had no effect on the growth of BFU-E whereas it potentiated the combined action of IL3 and GM-CSF on the primitive BFU-E. In conclusion, this study confirms at the unicellular level and under serum-free conditions that erythroid progenitors are regulated by multipotential growth factors in early phases of erythropoiesis and become sensitive only to Epo in later phases of differentiation.