This is a renewal application to RFA-HL-24-010 to propose that the Division of Blood and Marrow Transplantation and Cellular Therapy (BMT-CT) at Stanford University continue as a Core Clinical Center for the BMT Clinical Trials Network (BMT CTN). Stanford’s Program will perform ~700 adult transplants/cellular therapies in 2023 including autologous and allogeneic transplants using cells from matched and mismatched related and unrelated donors, cord blood units, ex vivo manipulated cell products and genetically modified cells, as well as novel chimeric antigen receptor T cell products. Stanford’s BMT-CT Program participates in basic and clinical research as a single institution, and within regional, national and international consortia. The Division is supported by a NIH Program Project Grant with over 32 years of funding of basic scientific research and clinical translational trials that advance the field. The Program is strengthened by highly experienced biostatics and data management groups, and a cGMP-compliant, FACT and CLIA certified Cellular Therapy Facility for routine cell processing and the development of investigational cellular therapies. The Program is a high accrual BMT CTN center and has enrolled 579 patients to 25 CTN studies. In the past granting period, Stanford investigators served in leadership roles of both committees and clinical trial protocols. Additionally, Stanford faculty participated on several protocol development committees and on other steering committees and task forces. Stanford will continue to leverage the capabilities of its Program to support the research goals of the CTN. It is our collective mission to advance the field of BMT-CT for patients with rare and difficult to treat blood diseases through high quality multi-center clinical trials. The goal of the proposed protocol in the current application is to determine whether a novel strategy can prevent and reduce the risk of developing graft-versus-host disease (GVHD) in patients lacking HLA matched donors, and thereby improve upon traditional allogeneic BMT. We propose a phase 1/2 clinical trial to evaluate the safety and efficacy of Orca-T, an engineered donor graft in which a highly purified Treg product is administered the same day as hematopoietic stem and progenitor cells followed 2 days later by conventional CD3+ T cells. The target population is patients with ALL, MDS, or AML receiving myeloablative conditioning followed by HCT using HLA mismatched unrelated donors (MMURDs). This investigator-initiated study builds upon our prior preclinical and clinical work with the Orca-T graft engineering platform in the HLA matched donor setting. The primary outcome of the Phase 2 portion is efficacy, as defined by GVHD-relapse-free survival (GRFS) at one year following HCT. Based on aggregated data, we hypothesize that the Orca-T allograft in combination with dual-agent GVHD prophylaxis (tacrolimus plus ruxolitinib) will synergistically and significantly reduce ra...