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Background CAR T cell therapy has revolutionized treatment outcomes for numerous B cell malignancies, yet disease progression remains common. A major ongoing challenge is the rapid terminal differentiation and exhaustion of CAR T cells, leading to poor expansion, limited persistence, and suboptimal clinical efficacy in patients. PRDM1, encoding the transcriptional repressor BLIMP1, has emerged as a crucial regulator of T cell differentiation and function. We evaluated the impact of PRDM1 deletion on CAR T cell anti-tumor activity and uncovered a unique role of PRDM1 in mediating mitochondrial fitness. Leveraging these mechanistic insights, we developed a novel pharmacological strategy to boost CAR T cell performance, offering substantial translational advantages over genetic modification approaches.Methods PRDM1 was deleted via CRISPR/Cas9 technique in human CD19-directed CAR T cells incorporating either 4-1BB (BB) or CD28 costimulatory domains, representative of clinical constructs. Functional impacts were evaluated through in vitro repeated stimulation using OCI-Ly8 human B-cell lymphoma cells and xenograft models. To validate mechanistic findings, PGC1α was knocked down using shRNA-based system.Results Genetic ablation of PRDM1 in BB or CD28-based CAR T cells significantly enhanced proliferative capacity, enriched early memory-like subsets, and improved survival outcomes in lymphoma-xenograft mice. (figure 1). Mechanistically, PRDM1 deletion derepressed PGC1α, a transcriptional co-activator that promotes mitochondrial biogenesis and cellular antioxidant defense. Indeed, PRDM1 knockout (KO) CAR T cells demonstrated increased tolerance to oxidative stress, together with enhanced mitochondrial content and membrane potential. Seahorse assays further confirmed their superior metabolic efficiency via both aerobic and anaerobic pathways (figure 1). Notably, knockdown of PGC1α completely abrogated the enhanced efficacy observed in PRDM1 KO CAR T cells (figure 2). Translationally, we explored the synergistic effects of a clinically approved PGC1α agonist, bezafibrate, in combination with CAR T cell therapy. This dual treatment drove robust CAR T cell expansion and anti-tumor responses without adverse events. Importantly, bezafibrate alone lacked intrinsic tumoricidal activity, indicating its action through CAR T cell modulation. Moreover, recognizing potential oncogenic concerns with systemic PGC1α activation, we validated that transient bezafibrate exposure during ex vivo manufacturing could markedly enhance metabolic activity and prolong the therapeutic effects of CAR T cells (figure 2).Conclusions Increased PGC1α activity contributes significantly to the improved memory differentiation and functionality of PRDM1-deleted CAR T cells. Impressively, bezafibrate co-treatment and preconditioning strategies amplified these favorable metabolic and therapeutic outcomes, highlighting its translational potential for generalizing application of CAR T cell therapy.Abstract 289 Figure 1Impact of PRDM1 deletion on CAR T cell efficacy and mitochondrial fitnessAbstract 289 Figure 2Dependency of PRDM1 KO CAR T cells on PGC1α activity and the therapeutic potential of PGC1α agonist