Low-Dose or High-Dose Conditioning Followed by Peripheral Blood Stem Cell Transplant in Treating Patients With Myelodysplastic Syndrome or Acute Myelogenous Leukemia

Inclusion Criteria: * Myelodysplastic syndrome (MDS) or transformed acute myelogenous leukemia (transformed from MDS) * De novo acute myelogenous leukemia (AML) beyond first remission * Intermediate or high risk de novo AML in first complete response (at FHCRC unrelated donor recipients only) * Chemotherapy required prior to HCT for all patients: * A) Interval between start of a cycle of cytoreductive chemotherapy and infusion of donor stem cells must be at least 30 days; chemotherapy received for disease maintenance will be allowed during this time period * B) All patients must have \< 5% myeloblasts based on marrow morphology performed within 21 days prior to start of conditioning regimen and at least 3-4 weeks after the start of pre-transplant cytoreductive chemotherapy * C) All patients must have no circulating peripheral blood myeloblasts present based on morphologic analysis * Age 65 years or under for patients with related donors; age 60 years or under for patients with unrelated donors * HCT-Specific Comorbidity Index Score (HCT-CI) \< 3 * Related donor (age \> 12 years, nonsyngeneic) or unrelated donor, HLA phenotypically or genotypically identical at the allele level at A,B,C,DRQ1, and CBQ1 * DONOR: Related or unrelated donors who are genotypically or phenotypically matched by high resolution HLA typing (HLA-A, B, C, DRB1, and DQB1); class 1 single allele mismatch allowed * DONOR: Patient and donor pairs homozygous at a mismatched allele in the graft rejection vect…