211At-BC8-B10 Followed by Donor Stem Cell Transplant in Treating Patients With Relapsed or Refractory High-Risk Acute Leukemia or Myelodysplastic Syndrome

This trial is testing a specialized radioactive treatment (211At-BC8-B10) that targets cancer cells, followed by a donor stem cell transplant, for patients with leukemia or a high-risk bone marrow disorder (MDS) that is hard to treat with standard approaches. **You may be eligible if...** - You have been diagnosed with acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), high-risk MDS, or a mixed type of leukemia (MPAL) - You are in first remission but still have traces of cancer detectable by testing, OR - Your cancer has relapsed (come back) or is hard to treat, OR - You have relapsed after a previous stem cell transplant - You have a matched donor (related or unrelated) available for stem cell transplant - You are in adequate health to undergo transplant **You may NOT be eligible if...** - You have cancer involving the brain or spinal fluid (central nervous system disease) - You have serious organ problems (heart, liver, kidney, or lungs) - You are pregnant or breastfeeding - You have active, uncontrolled infection - You have had prior radiation to levels that make further treatment unsafe Talk to your doctor to see if this trial is right for you.