At 211 MAb BC8-B10

This phase I/II trial studies the side effects and best dose of a radioactive agent linked to an antibody (211At-BC8-B10) followed by donor stem cell transplant in treating patients with high-risk acute leukemia or myelodysplastic syndrome that has come back (recurrent) or isn't responding to treatment (refractory). 211At-BC8-B10 is a monoclonal antibody that may interfere with the ability of cancer cells to grow and spread. Giving chemotherapy and total body irradiation before a stem cell transplant helps stop the growth of cells in the bone marrow, including normal blood-forming cells (stem cells) and cancer cells. When the healthy stem cells from a donor are infused into the patient, they may help the patient's bone marrow make stem cells, red blood cells, white blood cells, and platelets. Sometimes the transplanted cells from a donor can attack the body's normal cells, called graft versus host disease. Giving cyclophosphamide, mycophenolate mofetil, and tacrolimus after a transplant may stop this from happening.