Hematologic response of four patients with smoldering acute myelogenous leukemia to partially pure gamma interferon

In vitro and in vivo studies were conducted to obtain basic information on the activity of gamma interferon (IFN-γ) in acute myelogenous leukemia (AML). In a selected case of AML, recombinant IFN-γ, but not IFN-α, induced differentiation of primary leukemic blasts in vitro. Similarly, IFN-γ inhibited leukemic colony formation in vitro. This contrasted with IFN-α which was inactive. In one case of AML (M2), partially purified IFN-γ given intravenously caused a shift of the WBC profile from immature blasts to maturing myeloid cells and neutrophil granulocytes. Intravenous IFN-γ treatment of another patient who had AML as a second malignancy resulted in a complete hematologic remission, normalization of marrow granulocyte-macrophage colony-forming cell in vitro growth, and conversion of marrow cytogenetics from 95% hyperdiploid clone with complex abnormalities into 100% diploid. The results indicate a potential use of IFN-γ in the treatment of selected patients with AML and the possibility of in vitro pretreatment evaluation of these patients' leukemic response to IFNs.