Growth of CD34+ acute myeloblastic-leukemia colony-forming cells in response to recombinant hematopoietic growth-factors

In order to minimize the interactions of clonogenic cells with accessory cells and characterize the direct effect of recombinant hematopoietic growth factors (HGF) on acute myelogenous leukemia colony-forming cells (AML-CFU), the response of CD34+ AML-CFU to individual or combined recombinant HGF, i.e., interleukin-1 (IL-1), interleukin-3 (IL-3), interleukin-6 (IL-6), granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF), and macrophage colony-stimulating factor (M-CSF), was studied in 10 patients and compared with the growth response obtained from unfractionated marrow cells. IL-3 and GM-CSF had a similar stimulating activity on AML-CFU growth. G-CSF resulted the most efficient stimulus for colony formation and was additive or synergistic with IL-3 and GM-CSF. M-CSF, used alone, had a negligible stimulating activity. When CD34+ cells were used, IL-1 by itself had a low stimulating activity and displayed little or no synergy with IL-3, GM-CSF, and G-CSF. On the contrary, when unfractionated cells were used, IL-1 was very effective in inducing AML-CFU formation and was markedly synergistic with IL-3 and GM-CSF. These results show that IL-1-induced leukemic colony formation is prevalently mediated by accessory cells. IL-6 supported AML-CFU growth in seven of 10 cases, thus showing a direct effect on CD34+ leukemic cells, and enhanced the growth of IL-3-(+47 to + 167%) and GM-CSF-dependent (+ 60 to + 110%) AML-CFU. Recloning studies of single colonies demonstrated that primary CD34+ AML-CFU, stimulated by IL-3 and GM-CSF, generated secondary and tertiary colonies, whereas primary AML-CFU stimulated by G-CSF and IL-6 failed to give rise to secondary colonies, thus indicating a complete suppression of self-renewal. Sequential recloning of colonies grown in the presence of IL-3 + IL-6 demonstrated that addition of IL-6 and IL-3-containing plates resulted in a nearly complete suppression of self-renewal. In conclusion, these results demonstrate the heterogeneity of the CD34+ leukemic cell fraction and indicate the existence of complex regulatory events at the level of CD34+ leukemic cells. Data obtained from recloning experiments are of therapeutic interest in view of the clinical application of HGFs in the treatment of myeloid leukemias