Monoclonal antibodies to myeloid differentiation antigens: in vivo studies of three patients with acute myelogenous leukemia

Three patients with acute myelogenous leukemia (AML) in relapse were treated with intravenous infusions of one or more purified murine monoclonal antibodies (MoAbs) specific for differentiation antigens on normal and malignant myeloid cells. Three of the MoAbs used were IgM immunoglobulins that react with glycolipids, while the fourth, an IgG2b, reacts with a protein antigen. Peripheral blood leukemia cell counts decreased significantly, but transiently, during treatment. Evidence of in vivo binding of each MoAb to leukemia cells was obtained, although two of the four MoAbs could not be detected in the plasma following infusion, perhaps due to circulating blocking factors. Antigenic modulation was not encountered in these studies. However, the induction of human antibody to murine MoAb was observed in one patient who was treated over a 70-day period. Toxicities encountered were minimal and included fever (3 patients), back pain (1 patient), and arthralgias and myalgias (1 patient). This is the first reported clinical trial of (1) IgM MoAbs, (2) MoAb therapy in patients with AML, (3) combinations of MoAbs directed toward different myeloid differentiation antigens, and (4) MoAbs directed to glycolipids. The relative lack of toxicity and the positive effects of MoAb treatment in the reduction of leukemia cell counts permit the continued study of more innovative approaches to the treatment of AML with MoAbs.