A panel of murine and human monoclonal antibodies reactive with human leukemic myeloblasts will be prepared and characterized. The specificity of these antibodies will be determined by quantitative binding assays. Antibodies to leukemia cell surface antigens expressed either uniquely or quantitatively greater will be sought. Heterogeneity within and among leukemia cell populations will be determined by cytofluorography. These data will be used to subclassify cases of myelogenous leukemia and then correlated with standard classification methods. The ability of monoclonal antibodies to mediate selective leukemia cell lysis will be studied. Particular emphasis will be placed on abrogating leukemia cell escape from antibody-mediated cytolysis through a variety of mechanisms. A panel of antibodies that collectively, in combination, can mediate 100% leukemia cell lysis will be developed. The effect of these antibodies on normal stem cells will also be determined in order to prepare for their use in treating autologous bone marrow from patients with leukemia. Partial characterization of leukemia cell surface antigens expressed uniquely or quantitatively greater than on other cell types will be performed. Antigen expression on myeloid leukemia cell lines, fresh leukemia cells, and normal myeloid colonies undergoing differentiation will be studied using monoclonal antibodies. A potential clinical application of these monoclonal antibodies would be their use in the technique of autologous bone marrow transplantation for patients with leukemia in remission. Bone marrow could be treated in vitro with cytotoxic antibodies and then reinfused with less chance of recurrent leukemia caused by residual leukemic cells. These studies will hopefully contribute to a rational approach to such therapy with monoclonal antibodies.