Cytotoxicity of monoclonal antibodies against individually immunophenotyped human leukemic cells

Peripheral blood and bone marrow mononuclear cells from 12 patients with acute myeloid leukemia (AML), 2 patients with acute lymphatic leukemia, and 1 patient with chronic myeloid leukemia in blastic crisis were taken at diagnosis or in relapse. Cells were immunophenotyped with a panel of monoclonal antibodies (Moab) (OKIa, Leu M1, Leu M2, Leu M3, Leu M4, B1, Okt 11, J5) and the same antibodies were used in an in vitro cytotoxicity test. Of the 14 patients, 10 had antibody-binding cells, and the percentage of lysed cells was almost equal to that of blasts. The other 4 patients had few binding cells and little lysis. Acute leukemia with and without preceding myelodysplastic features did not differ in immunophenotype. Mean spontaneous release of 51Cr was 12.7% and complement alone caused an additional average release of 11.8%. Four single antibodies together with complement showed a mean 51Cr release of 0.7-32.4% above that found with complement alone. Combinations of Moabs resulted in 51Cr release at least 10% above the single most efficient Moab in 8 out of 12 patients. Not all blast cells showed antibody binding, nor were all antibody-binding cells susceptible to cytotoxicity. Normal bone marrow growth in vitro seemed to be stimulated by factors in complement and in the Moab. When this stimulation was compensated for by adding fetal calf serum, cytotoxicity tests prior to CFUc assays resulted in a mean decrease of 46% of colonies and 25% of clusters in normal bone marrow. CFUc are thus sensitive to the cytotoxicity, although CFU may also be resistant.