Immunochemotherapy and AlloSCT in Patients With High Risk CD33+ AML/MDS

Inclusion Criteria: * Disease Status: * History of AML Induction/Reinduction Failure * AML 1st Complete Remission (CR) with poor cytogenetics * AML 2nd CR with minimal residual disease (MRD) * AML 3rd CR * AML in refractory relapse but ≤25% bone marrow leukemia blasts * MDS with \>6% bone marrow blasts at diagnosis * Secondary MDS with ≤5% bone marrow myeloblasts at diagnosis Disease Immunophenotype: • Disease must express a minimum of \>/= 10% CD33+ for patients with AML Organ Function: • Adequate renal function, adequate liver function, adequate cardiac function, adequate pulmonary function Age: ≤25 years of age Donor: matched family donor, unrelated cord blood donor, unrelated adult donor Exclusion Criteria: * Patients with active central nervous system (CNS) AML/MDS disease at time of conditioning therapy * Female patients who are pregnant * Karnofsky \<50% or Lansky \<50% if 10 years or less * Age \>25 years * Has received gemtuzumab in the previous 30 days or has not recovered from prior gemtuzumab therapy.