Guadecitabine and Donor Lymphocyte Infusion in Treating Patients With Acute Myeloid Leukemia or Myelodysplastic Syndrome Relapsing After Allogeneic Stem Cell Transplant

Inclusion Criteria: * Diagnosis of acute myeloid leukemia (AML) and myelodysplastic syndrome (including chronic myelomonocytic leukemia \[CMML\]) according to WHO classification that underwent first allogeneic hematopoietic cell transplant (HSCT) with either peripheral blood or bone marrow as the source of the hematopoietic stem cells * No more than 1 antigen mismatch at human leukocyte antigen (HLA)-A, B, C, DRB1 and DQB1 locus for either related or unrelated donor * High risk AML and MDS patients will be included * Cohort 1: morphological relapse after stem cell transplant: * MDS patients: re-appearance of dysplastic changes in the bone marrow, with or without increase in bone marrow last count, which is pathologically consistent with myelodysplastic syndrome; * AML patients: bone marrow blast count \>= 5% * Cohort 2: Persistence or reappearance of minimal residual disease by flow cytometry or cytogenetic or molecular testing while being in morphological remission after allogeneic stem cell transplantation * Cohort 3: High risk AML and MDS patients who are in complete remission morphologically with no evidence of minimal residual disease by flow cytometry or cytogenetic or molecular testing after allogeneic stem cell transplantation * MDS patients: * Cytogenetics consistent with poor or very poor risk group by 5-risk classification; * Cytogenetics consistent with monosomal karyotype * Bone marrow blast count \> 5% but less than 20% at any time during their dise…