Abstract 6326: Targeting PRDM1 to enhance CAR T cell efficacy against diffuse large B cell lymphoma (DLBCL)
Authors: Wang Sidney , Xie Lishi , Chen Xiufen , Cooper Alan , Chorazeczewski Joanna , Kline Justin 
Published: March 2024

Abstract
CAR T cell therapy has shown remarkable success in treating patients with relapsed or refractory (r/r) DLBCL, but a majority (&gt;60%) will experience disease progression. A key failure mechanism is the rapid terminal differentiation and exhaustion of CAR T cells, driven by persistent antigen exposure in vitro during manufacturing and in vivo in the DLBCL environment, which culminates in poor persistence and short-term effector functions. Recent studies have identified the transcriptional repressor PR/SET domain 1 (PRDM1) as a key regulator that drives differentiation of T cells toward these unwanted fates. Further, single cell transcriptomic profiling of r/r DLBCL biopsies has revealed PRDM1 enrichment in a cluster of exhausted-like CD8+ CAR T cells. These observations indicate that targeting PRDM1 could prevent or delay terminal differentiation/exhaustion in CAR T cells, thereby enhancing their persistence for lasting anti-tumor activity. Using CRISPR/Cas9 targeting, we have demonstrated that PRDM1-deficient CAR T cells exhibit enhanced proliferative capacity, memory characteristics, and resilience against exhaustion upon repeated stimulation. Moreover, genetic ablation of PRDM1 also promoted the in vivo expansion and persistence of CAR T cells, which led to significantly improved survival of lymphoma-bearing mice. Mechanistically, loss of PRDM1 leads to de-repression of PPARGC1A (PGC1α), a master regulator of mitochondrial biogenesis and antioxidant activity. This confers elevated tolerance to oxidative damage in CAR T cells lacking PRDM1, which showed increased capacity to buffer oxidative stress induced by mitochondrial uncouplers and constant stimulation. These findings suggest that PRDM1 loss may improve CAR T cell fitness through PGC1α upregulation and mitochondrial activation. From a translational perspective, we assessed the potential synergistic effects of PGC1α agonist, bezafibrate, with CAR T cells. Dual therapy with bezafibrate and CAR T cells mediated more robust expansion and anti-tumor immunity of CAR T cells without causing discernible adverse events. Importantly, bezafibrate alone had no direct tumoricidal effects, which indicates that bezafibrate suppressed tumor growth through modulating CAR T cell functions. Moving forward, we will uncover the previously uncharted role of PRDM1 in orchestrating the mitochondrial and metabolic activity of CAR T cells. Building upon a correlation between PRDM1 expression and CAR T cell dysfunction, we aim to pioneer the use of PRDM1 and/or its target genes as novel biomarkers for predicting clinical responses of r/r DLBCL patients to CAR T cell therapy. Our endeavors will shed light on the long-standing conundrum of CAR T cell dysfunction and offer solutions that may be applicable for improving T cell-based therapy against cancer in general.
Citation Format: Sidney Wang, Lishi Xie, Xiufen Chen, Alan Cooper, Joanna Chorazeczewski, Justin Kline. Targeting PRDM1 to enhance CAR T cell efficacy against diffuse large B cell lymphoma (DLBCL) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6326.