Effect of recombinant and purified hematopoietic growth factors on human megakaryocyte colony formation.

The effect of a number of purified or recombinant hematopoietic growth factors, including recombinant erythropoietin (rEpo), thrombocytopoiesis stimulating factor (TSF), recombinant interleukin 1 alpha (rIL-1 alpha), recombinant granulocyte colony-stimulating factor (rG-CSF), macrophage colony-stimulating factor (CSF-1), recombinant interleukin 3 (rIL-3), and recombinant granulocyte-macrophage colony-stimulating factor (rGM-CSF), on megakaryocyte (MK) colony formation by normal human marrow cells in a serum-depleted assay system was determined. Neither rEpo, TSF, CSF-1, rIL-1 alpha, nor rG-CSF alone augmented MK colony formation. Both rGM-CSF and rIL-3 at optimal doses increased MK colony formation eightfold and tenfold, respectively, above baseline values. Addition of increasing amounts of either rGM-CSF or rIL-3 led to progressively greater numbers of MK colonies formed until plateau levels were reached. Both rGM-CSF and rIL-3 also led to a dose-related increase in the number of cells per MK colony formed in culture. These molecules were equivalent stimulators of MK colony formation when their effects at optimal concentrations were compared. The effects of rGM-CSF and rIL-3 were additive at suboptimal concentrations of rIL-3 in that colony formation by a combination of the two growth factors approximated the sum of colony formation by each growth factor alone. These data suggest that rGM-CSF and rIL-3 alone and in combination are important regulators of in vitro megakaryocytopoiesis at the progenitor cell level.