Allogeneic Engineered Hematopoietic Stem Cell Transplant (HCT) Lacking the CD33 Protein, and Post-HCT Treatment With Mylotarg, for Patients With CD33+ AML or MDS

High risk acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) frequently relapses despite hematopoietic stem cell transplant (HCT). Post-HCT targeted therapy to reduce relapse is limited by toxicity to the engrafted cells. VOR33, an allogeneic CRISPR/Cas9 genome-edited hematopoietic stem and progenitor cell (HSPC) therapy product, lacking the CD33 protein, is being investigated for participants with CD33+ AML or MDS at high risk for relapse after HCT to allow post-HCT targeting of residual CD33+ acute AML cells using Mylotarg™ without toxicity to engrafted VOR33 cells. Participants will undergo a myeloablative HCT with matched related or unrelated donor CD34+-selected hematopoietic stem and progenitor cells (HSPCs) engineered to remove CD33 expression (VOR33 product). Mylotarg™ will be given after engraftment for up to 4 cycles. The primary endpoint assessing safety of VOR33 will be the incidence of successful engraftment at 28 days. Part 1 of this study will evaluate the safety of escalating Mylotarg™ dose levels to determine the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D). Part 2 will expand the number of participants to evaluate the Mylotarg™ RP2D.