DR-18 for the Treatment of Relapsed or Persistent Acute Myeloid Leukemia or Myelodysplastic Syndrome After Hematopoietic Cell Transplantation, the DR. DREAM Trial

Inclusion Criteria: * ≥ 18 years of age (no upper age limit) * Documented persistent or recurrent AML or MDS after HCT (including measurable residual disease \[MRD\] or overt leukemia). Note: MRD (\< 5% malignant blasts) must be detected with flow cytometry testing at University of Washington Medical Center (UWMC)/Fred Hutchinson Cancer Center (Fred Hutch) clinical laboratory * No Food and Drug Administration (FDA)-approved targeted therapy for the subject's AML or MDS is available, or if such therapy is available, that class of drugs previously failed for the subject or the subject was intolerant of the therapy * No history of grade 3 or 4 acute GvHD after the most recent HCT * No history of moderate or severe chronic GvHD after the most recent HCT * No active acute or chronic GvHD or other immunologic phenomenon (e.g., immune cytopenias, cryptogenic immunologic pneumonia) in last month requiring systemic therapy (Hydrocortisone or prednisone for adrenal insufficiency at ≤ 10 mg/day prednisone-equivalent is permitted.) * Stable or reducing immune suppression in the preceding 4 weeks without GvHD flares * The most recent HCT was from a 10/10 human leukocyte antigen (HLA)-matched related or unrelated donor (assessed at HLA-A, B, C, DR, DQ) * Evidence of blood count recovery at any time post-HCT defined as absolute neutrophil count (ANC) ≥ 0.5 x 10\^9/L for ≥ 3 consecutive days and platelets ≥ 30 x 10\^9/L (independent of granulocyte colony-stimulating factor \[G-CSF\] or plat…