Anti-CD33 monoclonal antibody M195 for the therapy of myeloid leukemia.

Leukemia is well suited for monoclonal antibody therapy due to the accessible, differentiation antigens that characterize stages of maturation. In this paper, we describe the use of radio-labeled M195, a murine IgG2a, anti-CD33 monoclonal antibody, that can be used to effectively cytoreduce AML cells in relapsed patients when tumor burden is high; or to eliminate minimal residual disease and lengthen disease-free survival in patients with APL in remission. To decrease the likelihood of immunogenicity, a humanized IgG1 version of M195 was constructed that demonstrated a higher avidity and improved effector function than the parent murine antibody. Preliminary results of the first trial in AML using a humanized antibody showed specific bone marrow targeting without an immunogenic response.