Recombinant human IL-3 and G-CSF act synergistically in stimulating the growth of acute myeloid leukemia cells.

The effects of combinations of recombinant human growth factors (colony-stimulating factor (CSF], interleukin 3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and granulocyte colony stimulating factor (G-CSF) for inducing proliferation of leukemic cells were compared in 27 acute myeloid leukemias (AMLs). While functional heterogeneity of AML was clearly shown, we further demonstrated that optimal growth may be obtained with combinations of CSF. The most striking feature was that, in both suspension and semisolid cultures, IL-3 and G-CSF acted synergistically in supporting AML cell proliferation except in cases for which G-CSF was found to be an inhibitory factor. In the majority of cases, the proliferative effects of the IL-3 and GM-CSF combination were significantly higher than the most potent of either factor present alone in the cultures. Finally, preincubation with IL-3 greatly potentiated the responsiveness of AML cells to subsequent addition of either GM-CSF or G-CSF. These results indicate that AML cells respond to growth factor in the same way as normal hemopoietic cells and that stimulation by a second late-acting growth factor such as G-CSF is also required to yield optimal growth.