HLA‐DA monoclonal antibodies inhibit the proliferation of normal and chronic granulocytic leukaemia myeloid progenitor cell

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Abstract
The capacity of murine monoclonal antibodies with HLA-DR specificity to inhibit the proliferation in vitro of erythroid burst-forming units (BFU-E) and erythroid colony-forming units (CFU-E) and granulocyte-macrophage (CFU-GM) progenitor cells was studied in normal bone marrow and the blood of patients with chronic granulocytic leukemia (CGL). Two IgG2 antibodies (CA 2.06 and L243) inhibited the proliferation of normal BFU-E and CFU-GM at relatively high dilution: a 3rd antibody, DA2, had no effect on either progenitor cell. A complement-fixing monoclonal antibody with T-cell activity (OKT3) produced only minor reduction in progenitor cell proliferation. Further studies with L243 showed that BFU-E and CFU-GM from the blood of patients with CGL were inhibited to the same degree as normal marrow progenitor cells. The inhibition of progenitor cell proliferation by a given antibody was always complement dependent and was therefore presumed to be due to a direct cytotoxic effect. The inhibitory effect of monoclonal antibodies is a valuable approach to the characterization of antigenic determinants on myeloid progenitor cells and the differential cytotoxicity of selected monoclonal antibodies might be exploitable for therapy.