Abstract 2257: Activation and clonotypic expansion of the native T cell repertoire identifies durable response to CD19 CAR T cell therapy

Background: Axicabtagene ciloleucel (Axi-cel), a CD19 directed CAR T cell therapy, results in durable response in a subset of patients with relapsed/refractory large B cell lymphoma (LBCL) in the absence of persistent circulating CAR T cells. Aim: We postulated that long-term efficacy of CAR T therapy depends on the downstream triggering of native T cell immunity. We performed single-cell transcriptomics of longitudinal peripheral blood (PB) samples and RNAseq of tumor samples from patients of the ZUMA 1 Axi-cel study. Methods: Single cell immunoprofiling (5’ expression + V(D)J, 10x Genomics) was performed on PB mononuclear cell samples from ZUMA-1 patients (N=32), collected at leukapheresis, 4 weeks, 6 and 12 months post Axi-cel infusion. RNAseq was performed on FFPE lymphoma samples (N=17). Patients were divided into 3 groups: non-responders, relapsed within 1 year from CAR T infusion, and long-term responders. A total of 405,775 cells passed quality check, capturing 73 cellular populations. Results: Long-term responders presented a distinct T cell landscape with increased CD8 T cells and CD8/CD4 ratios prior to CAR T therapy, compared to the other groups, with similar trends observed across time points. They also presented an increased abundance of 3 distinct CD8 T cell populations: (a) cells expressing cytotoxic and NK cell markers, (b) CD8 T effector memory cells characterized by CXCR4, TGFB1, and BCL3, and (c) proinflammatory CD8 T cells. In contrast, patients with early relapse showed increased levels of regulatory T cells pre-/post-CAR T infusion and lower abundance of CD4 cytotoxic T cells.Comparisons of the TCR repertoire pre-/post-CAR T demonstrated a greater clonal expansion of cytotoxic CD4 and CD8 T cell populations in the long-term responders, with high similarity of expanded clones post CAR T. Shared PB T cell clones and tumor antigen sequences derived from the RNAseq samples suggest an antigen-specific response driven by common epitopes. In contrast to the lack of expansion of T reg clones in responders, relapsed patients demonstrated high T reg-clonal expansion 6 months post treatment.Monocyte and NK cells were less prevalent in responders before treatment, driven by differences in phagocytic monocyte and inhibitory NK cell abundance. Modeling the interaction between monocyte and effector cell populations based on ligand receptor expression was suggestive of negative immunoregulatory impact on the T cell populations. Conclusion: The application of single-cell immunoprofiling on longitudinal samples from ZUMA-1 patients demonstrated distinct cellular and clonal profiles among long-term responders. These findings confirm our hypothesis of an important role for the native immune cell repertoire in response to CAR T therapeutics and can be utilized to further our understanding but also to potentially inform patient stratification, management, and treatment. Citation Format: Dimitra Karagkouni, Giulia Cheloni, Yered Pita-Juarez, Daniela Torres, Eleni Kanata, Zachary Avigan, Jessica Liegel, Dina Stroopinsky, Brodie Miles, Gayatri Tiwari, Jenny Kim, Mike Mattie, Jacalyn Rosenblatt, David Avigan, Ioannis Vlachos. Activation and clonotypic expansion of the native T cell repertoire identifies durable response to CD19 CAR T cell therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2257.