Abstract IA005: Analysis of site-specific CAR T cell efficacy in LBCL and development of novel engineering strategies

Abstract Large B cell lymphomas (LBCLs) occupy diverse anatomic sites (nodal and extranodal), where physical barriers, cellular ecosystems, and inhibitory factors vary. This prompted us to investigate how CAR T cells behave across these distinct locations. We reviewed data from a locally conducted CD19 CAR T-cell clinical trial and observed differences in response rates by disease presentation, consistent with other clinical reports. To further explore this, we used an immunocompetent mouse model of lymphoma to interrogate CAR T cell engraftment and B cell clearance across multiple anatomic sites. Notably, the liver emerged as a site of both poor tumor clearance and frequent relapse. Ex vivo functional assays revealed impaired activity of CAR T cells retrieved from the liver compared to those from the spleen, supporting the concept of site-specific functional imprinting. Liver-derived CAR T cells also exhibited increased expression of inhibitory receptors, particularly CD39 and TIM-3. To identify strategies for enhancing CAR T cell efficacy at sites associated with relapse, we performed an in vivo CRISPR knockout screen using a transcription factor–targeting library. This approach identified perturbations (including both gene disruption and overexpression) that improved CAR T cell function in both tissue-agnostic and site-specific contexts. These candidates were further characterized in vitro and in vivo. Overall, the challenges faced by CAR T cells in LBCL appear to reflect the unique architecture and composition of the tissues in which tumour deposits reside. These findings highlight the importance of understanding site-specific mechanisms of resistance and designing next-generation CAR T cells tailored to overcome them. Citation Format: Gillian Savage, Zachary Morse, Pauline Loos, Kevin Bronischewski, Sherry Tan, Angela Wan, Kevin Hay, Natasha Kekre, Laura Evgin. Analysis of site-specific CAR T cell efficacy in LBCL and development of novel engineering strategies [abstract]. In: Proceedings of the Fifth AACR International Meeting on Advances in Malignant Lymphoma: From Discovery to Clinical Impact; 2026 Jun 24-27; Philadelphia, PA. Philadelphia (PA): AACR; Blood Cancer Discov 2026;7(3_Suppl):Abstract nr IA005.