Mylotarg is a novel immunoconjugate directed against the CD33 antigen found on most leukemia cells. This humanized murine IgG4 monoclonal antibody is tagged with the toxin, calicheamicin. In equal molar concentrations, calicheamicin is about 3200 times more potent than adriamycin. In a Phase I study involving adult patients with relapse AML, Mylotarg has been shown to have significant anti-leukemia activity with little toxicity. The most concerning side effects of Mylotarg were prolonged neutropenia and thrombocytopenia. Phase II studies have also demonstrated good efficacy with little toxicity.

The goal of this proposal is to include Mylotarg in a nonmyeloablative preparative regimen similar to FAI used at MD Anderson Cancer Center. The hypothesis is that Mylotarg will provide potent anti-leukemic effects without adding toxicity to the mini-allogeneic bone marrow transplant regimen. A more potent anti-leukemic response may increase the complete remission rates and induce a state of minimal residual disease (MRD). Therefore, the Graft vs. Leukemia (GVL) effect of allogeneic transplantation will have a better chance for success. In addition, the administration of donor cells after Mylotarg should ameliorate the cytopenias previously associated with Mylotarg. This medication likely will be well-tolerated.

Patients with high-risk hematopoietic malignancies that express CD33 (i.e. AML, ALL, CML and MDS) will be included. We will enroll older patients (>55 years old) or medically infirm patients who are unable to tolerate standard allogeneic bone marrow transplant. Patients will be evaluated at 28 days post-transplant for evidence of response. Those with residual disease may be eligible for additional Mylotarg given together with donor lymphocyte infusions. Additional courses of Mylotarg may improve overall survival in this poor prognosis group.