Leukemia is well suited for monoclonal antibody therapy due to the acc
essible, differentiation antigens that characterize stages of maturati
on. 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 sur
vival 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 with
out an immunogenic response.