Abstract Relapse is the most important cause of mortality after allogeneic hematopoietic cell transplant (allo-HCT), but little research progress has been made in several decades. Chimeric antigen receptors targeting CD19 (CD19 CARs) redirect T cell effector functions to eliminate CD19-expressing leukemia and lymphoma cells. However, many patients still relapse. The candidate has preclinical data indicating the feasibility of using genome editing to delete the endogenous T cell receptor (TCR) to reduce the alloreactivity of donor CD19 CAR T cells, but it is unknown how these TCR knockout (KO) cells will function in vivo as anti-tumor agents, to what extent graft- versus-host-disease (GVHD) will result, or how engineering impacts T cell metabolism. This knowledge is essential for progress toward creating readily available “off-the-shelf” CAR T cells for patients with hematologic malignancies. The overall objectives of the proposed research are to determine how donor and third-party TCR KO CD19 CAR T cells impact immune reconstitution, GVHD, and graft rejection in preclinical models, as well as to understand how removing the TCR impacts the immunometabolism of these cells. The central hypothesis is that potent anti-tumor effects as well as negligible GVHD and graft rejection can be demonstrated preclinically by using TCR KO CD19 CAR T cells (either donor or third-party) following allo-HCT, to produce superior outcomes to conventional CD19 CAR T cells following allo-HCT. This hypothesis will be tested in the proposed Specific Aims. This work will provide ideal training for the candidate as she prepares for her long-term career goal to lead an independent laboratory studying cellular therapeutics and allo-HCT. Memorial Sloan Kettering Cancer Center has a renowned immunology program, and Dr. Marcel van den Brink, the candidate’s primary mentor, is a leader in immunotherapy research. Her co-mentor and advisory committee members have diverse and complementary expertise, and all have strong track records of mentoring independent scientists. The candidate and her mentoring team have developed a rigorous training plan designed to increase her knowledge base in: 1) development of next-generation CAR T cells; 2) bioinformatics and programming; 3) cellular metabolism, metabolic flux, mitochondrial function, and metabolic analyses in CAR T cells; and 4) professional development skills. The candidate will undertake training in these areas through coursework, workshops, and mentorship. This research project and training will provide the foundation to establish her future career as an independent physician-scientist. The proposed studies are expected to generate findings that will guide future genome engineering of CAR T cells. The candidate’s aim is to launch an independent research program designing “off- the-shelf” CAR T cells, which are expected to provide much improved therapeutic options for a range of hematologic malignancies.