Abstract B031: TCR signal strength drives tumor-specific CD8 T cell differentiation

Abstract Immunotherapies, such as immune checkpoint blockade, demonstrate the potential power of CD8 T cells to eliminate cancer cells, however these strategies only work in a subset of patients and tumor types. To design predictably effective immunotherapies, we must elucidate the mechanisms controlling tumor-specific T cell dysfunction and therapeutic reprogramming. TOX is a key transcription factor driving T cell differentiation in progressing tumors and required for T cell persistence. T cell receptor (TCR) signal strength (determined by the affinity of TCR for peptide-bound major histocompatibility complex (pMHC)) is known to regulate T cell differentiation during infections. However, how TCR signal strength impacts TOX expression and differentiation in tumors is less clear. Here, we developed a novel autochthonous mouse cancer model in which we can vary TCR signal strength to span the range observed for human tumor-infiltrating T cells and track tumor-specific CD8 T cells over several months from tumor initiation until end-stage cancer progression: we cloned a Sleeping Beauty transposon/transposase-based vector (SB-Cre) encoding Cre-recombinase and a fluorescent reporter protein fused to a tumor model antigen (OVA) under the control of the liver-specific albumin promoter. Through single amino acid substitutions of the native OVA sequence, we generated altered peptide ligands that are recognized by OVA-specific CD8 T cells with varying TCR signal strength. SB-vectors were delivered via hydrodynamic tail vein injection into mice with inducible activating oncogenes and silencing of tumor suppressor genes, a highly-efficient method to induce liver tumors. Over the course of tumor development we phenotypically and functionally characterized tumor-specific CD8 T cells in tumor draining lymph nodes (tdLN) and progressing liver tumors. Our data reveal how TCR signal strength determines TOX-driven differentiation and dysfunction of tumor-specific T cells starting at the earliest stages of tumorigenesis in tdLN. Ongoing efforts aim to investigate the functional impact of TCR signal strength on T cell differentiation and anti-tumor responses, including responsiveness to immunotherapeutic interventions. Citation Format: Sandra Carson, Andrea Schietinger. TCR signal strength drives tumor-specific CD8 T cell differentiation [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr B031.