In vitro effect of rGM-CSF on proliferation and maturation of leukemic cells from patients with acute myelogenous leukemia.

We investigated the effect of rGM-CSF on the proliferation/differentiation balance of the leukemic cells maintained in liquid cultures during 7 days, from 16 patients with acute myelogenous leukemia (AML). Cell proliferation was measured by tritiated thymidine (3HT) incorporation, and by the plating efficiency (PE) observed after 7 days of culture. Differentiation was measured by the ability of cells to reduce nitroblue tetrazolium (NBT) and by the percentage of immature myeloid cells. After 7 days of culture without rGM-CSF, an increase of 3HT incorporation (p = 0.01 compared to control) was observed in 8 cases. In these patients, an absence of PE was noted in only one case. Among the 8 patients with decreased 3HT incorporation (p = 0.01 compared to control), 6 exhibited functional maturation (increase of % of NBT + cells, p = 0.01), and 4 showed no PE. Seven days exposure to 50 ng/ml rGM-CSF increased the leukemic cell proliferation in 9 cases, induced complete functional differentiation in 4, and enhanced the CFU-L recovery in 6 cases. These effects were mainly observed in the "proliferative" group, where 7 of the cases had an increase of 3H-T. However, two of the "non proliferative" cases were also stimulated by GM-CSF. An absence of proliferation was generally accompanied by functional maturation.