211^At-BC8-B10 Before Donor Stem Cell Transplant in Treating Patients With High-Risk Acute Myeloid Leukemia, Acute Lymphoblastic Leukemia, Myelodysplastic Syndrome, or Mixed-Phenotype Acute Leukemia

OUTLINE: This is a dose-escalation study of 211\^At-BC8-B10. Patients receive 211\^At-BC8-B10 intravenously (IV) over 6-8 hours on day -7 and may receive 131\^I-BC8-B10 IV on day -7 and fludarabine phosphate IV over 30 minutes on days -4, -3 and -2. Patients undergo TBI and peripheral blood stem cell (PBSC) transplant on day 0. Patients also receive cyclosporine orally (PO) or IV every 12 hours on days -3 to 56 and then tapered to day 180 (for patients with related donors), or continuing to day 96 and then tapered to day 150 (for patients with unrelated donors). Patients receive mycophenolate mofetil PO or IV (first dose to occur 4-6 hours after PBSC infusion) every 12 hours on days 0-27 (for patients with related donors) or every 8 hours on day 0 and then reduced to every 12 hours on days 30-150 then tapered to day 180 (for patients with unrelated donors). Patients may undergo single photon emission computed tomography (SPECT), bone marrow aspirate sample and blood sample collection on study. After completion of study treatment, patients are followed up at 100 days and then at 6, 9, 12, 18 and 24 months.