Impact of in vivo administration of interleukin 3 on proliferation, differentiation, and chemosensitivity of acute myeloid leukemia.

Early clinical trials of growth factor augmentation of induction chemotherapy for acute myeloid leukemia have yielded variable results. To test the hypothesis that this heterogeneity is a consequence of the pleiotropic effects of growth factors on leukemic cell biology, we measured the effects of in vivo interleukin 3 (IL-3) administration on leukemic cell proliferation and drug sensitivity. Thirty-four patients with acute myeloid leukemia with high-risk features or advanced myelodysplasia received IL-3 as a continuous infusion beginning 3 days prior to chemotherapy and continuing for the duration of intensive induction therapy. Bone marrow cells were studied prior to and after 3 days of IL-3 administration to assess changes in overall and leukemic progenitor cell [leukemia colony-forming unit (CFU-L)] proliferation, and progenitor cell sensitivity to 1-betad-arabinofuranosylcytosine. The median fold increase in overall leukemic cell proliferation in response to IL-3, assessed as expression of the nuclear antigen Ki67 in 28 patients, was 1.2. The median fold increase in percentage of cells in S phase (assessed in 29 patients) was 1.3. Despite the increase in overall cell proliferation in 70% of cases, CFU-L number increased in only 4 of 20 patients successfully studied (median day 4:day 1 ratio of CFU-L number, 0.6). While this suggests possible terminal differentiation of leukemic progenitor cells, expression of CD34, HLA-DR, c-kit, CD15, and CD14 were not consistently affected by the cytokine. 1-betad-Arabinofuranosylcytosine sensitivity of CFU-L increased significantly in 30% of cases, decreased in 30%, and was unchanged in 40%. Changes in overall cell proliferation (Ki67 expression) and CFU-L were independent predictors of change in 1-beta-d-arabinofuranosylcytosine sensitivity; increase in percentage of cells in S phase in response to IL-3 was correlated with attainment of complete remission. While these findings support the concept of cell cycle recruitment, IL-3 has marked pleiotropic effects on proliferation, differentiation, and survival of leukemic progenitors which make the clinical impact of in vivo cytokine administration for individual patients difficult to predict.