In polycythemia vera human interleukin 3 and granulocyte-macrophage colony-stimulating factor enhance erythroid colony growth in the absence of erythropoietin.

To further define the growth factors required for the in vitro proliferation of erythroid progenitors in polycythemia vera (PV), we have compared the ability of interleukin 3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF) to support the growth of erythropoietin (Epo)-dependent and -independent erythroid colony formation. By using nonadherent mononuclear cells from peripheral blood, Epo-dependent colony formation was enhanced by IL-3 and GM-CSF in PV patients. Comparable results were obtained with normal erythroid progenitors. Augmenting effects of IL-3 and GM-CSF were observed on spontaneous erythroid colony formation, i.e., erythroid colony formation in the absence of exogenous supplied Epo. This was not due to a small amount of Epo in the culture media because an anti-Epo antibody did not prevent endogenous colony formation, nor did it prevent the enhancing effects of IL-3. Finally it was observed that in contrast to IL-3, monocyte depletion was required for the enhancing effects of GM-CSF on erythroid colony formation. These results provide evidence that endogenous colony formation in PV is independent of Epo but can be augmented by IL-3 or GM-CSF.