Abstract LB024: CAR-adapted PIK3CD base editing enhances T cell anti-tumor potency

Abstract Chimeric antigen receptor (CAR) T cell therapy has demonstrated promising outcomes in patients with certain refractory hematological malignancies. However, insufficient functional T cell persistence impedes therapeutic success of CAR therapies in a significant number of patients. Here, we performed a CAR-adapted screen of base-edited PIK3CD alleles to optimally calibrate PI3K/AKT signaling in T cells given its critical role in T cell function, metabolism, and fate. Our screen comprised both, prototypic 4-1BBz and CD28z CAR T cells to account for the distinct effector and memory functions imparted to T cells through incorporation of different costimulatory domains in CARs. We identified individual point mutations that induce beneficial CAR T cell profiles through precise balancing of endogenous PI3Kδ signaling strength in 4-1BBz and CD28z CAR T cells, respectively. Remarkably, point mutations with differing effects on PI3Kδ signaling activity were advantageous within the distinct CAR contexts: While 28z CAR T cells profited from attenuated signaling, the PI3Kδ-activating mutation E81K enhanced proliferative capacity, metabolic fitness and effector function in 4-1BBz but not in 28z CAR T cells. E81K-modified BBz CARs ameliorated long-term functional T cell persistence and enhanced therapeutic efficacy in established in vivo models of hematological and solid tumors without evidence of malignant transformation. Together, these data illustrate the importance of tailoring intrinsic T cell signaling capacities to the specific requirements of different CAR designs and demonstrate the potential of base editing to precisely optimize T cell function for bespoke cellular therapies. Citation Format: Josef Leibold, Philip Bucher, Judith Feucht, Nadine Brückner, Jule Kortendieck, Melanie Grimm, Karlotta Bartels, Steffen Hardy, Hannah Wurzer, Meike Thiemann, Celina May, Julia Quach, Nayan Jain, Letizia Quintanilla de Fend, Yu-Jui Ho, Francisco J. Sanchez-Rivera, Jie Sun, Bettina Weigelin, Martina Rausch, Mara Mitstorfer, Irene Gonzalez-Menendez, Michel Sadelain. CAR-adapted PIK3CD base editing enhances T cell anti-tumor potency [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB024.