IS-free Treg HaploHCT

Inclusion Criteria: * Cohort A: Histologically confirmed disease in the prior 4 weeks, despite at least 1 prior line of therapy (e.g., 3+7 chemotherapy, HMA therapy): Rel/ref AML (de novo or secondary) with ≥5% blasts in BM (or extramedullary sites); MDS EB-2 (BM ≥10% blasts, PB 5-19% blasts). * Cohort B: Ultra high-risk AML or MDS that meets definition of 'Myeloid Neoplasms with mutated TP53' per 2022 International Consensus Classification (Appendix L) regardless of response * Cohort C: Ultra high-risk AML or MDS that meets definition of 'Myeloid Neoplasms with multi-hit or complex karyotype (CK+) mutated TP53' per 2022 International Consensus Classification (Appendix L) with response: AML (de novo or secondary) with \<5% blasts in BM; MDS with \<10% blasts in BM or PB. * Available haploidentical HLA-matched (-A, -B, -C, -DRB1) related donor aged 18-65 years. * Age ≥18 to 65 years for Cohort A and B. Age ≥18 to 75 years for Cohort C. Because no dosing or adverse event data are currently available on the use of IS-free haploHCT in participants \<18 years of age, children are excluded from this study but will be eligible for future pediatric trials. * ECOG performance status ≤2 (Karnofsky ≥60, see Appendix A). * Adequate organ and marrow function as defined below: * Pulmonary Function: FEV1, FVC and DLCO ≥ 60% of predicted (corrected for hemoglobin) * Cardiac Ejection Fraction ≥ 45%, and no evidence of pulmonary hypertension * Hepatic: Total bilirubin within normal ins…