Targeting PRDM1 to Enhance CAR T Cell Therapy Against Diffuse Large B Cell Lymphoma (DLBCL)
Authors: Wang Sidney , Xie Lishi , Chen Xiufen , Cooper Alan J. , Chorazeczewski Joanna , Kline Justin 
Published: December 2024

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 activation in vitro during manufacturing and persistent antigen exposure 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, possibly facilitated by an increase in early memory-like cell subsets, which significantly extended the survival of lymphoma-xenografted mice. Mechanistically, loss of PRDM1 led to de-repression of PPARGC1A (PGC1α), a master regulator of mitochondrial biogenesis and antioxidant activity. This conferred elevated tolerance to oxidative damage in CAR T cells lacking PRDM1, empowering them to better buffer oxidative stress induced by mitochondrial uncouplers and constant stimulation. Further metabolic analysis revealed that deleting PRDM1 in CAR T cells boosted their respiratory capacity and energy production efficiency in both aerobic and anaerobic pathways. These results indicate that PRDM1-disrupted CAR T cells are better equipped for metabolic adaptation in order to meet the high energy demands required for rapid expansion and eradication of cancer cells. Collectively, 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 a 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, indicating that bezafibrate suppressed tumor growth through modulating CAR T cell functions. Moving forward, we will investigate if PRDM1 deletion differentially reprograms CAR T cells carrying distinct costimulatory domains, with a focus on the previously uncharted role of PRDM1 in orchestrating the mitochondrial and metabolic activity. 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 better elucidate the mechanisms by which PRDM1 determines the fates of clinical CAR T cell products and the translational potential of targeting PRDM1/PRDM1-mediated pathways to generalize the application of CAR T cell therapy against cancers.