Abstract 3766: Low T cell diversity is associated with poor outcome in bladder cancer: A comprehensive longitudinal analysis of the T cell receptor repertoire

Abstract T cells are central to the endogenous antitumor response and can recognize cancer neoantigens through their receptors (TCRs). Studies in multiple cancer types have shown an association between the TCR repertoire and disease outcome, but the TCR repertoire remains underexplored for bladder cancer. We hypothesized that the TCR landscape offers insights into immune competency. We aimed to characterize the TCR repertoire and its dynamics in patients with bladder cancer and analyze correlations with disease outcomes to improve our understanding of the antitumor response.This study analyzed the TCR landscape in blood and tumor samples from 119 patients with muscle-invasive bladder cancer (MIBC) using ultradeep amplicon-based sequencing of the TCR-β chain. Additionally, T cell fractions were inferred from whole exome sequence data of blood DNA using TcellExTRECT. The T cell subtype composition was investigated in four patients using the Chromium Single Cell kit from 10X Genomics.Low pre-treatment peripheral TCR diversity was associated with poor outcomes in bladder cancer (HR = 2.3, p = 0.024, n = 119), particularly when combined with a low fraction of circulating T cells (HR = 4.7, p = 0.00049, n = 67)). We validated these findings in two independent cohorts of patients with MIBC (p = 0.01, n = 107; p = 0.042, n = 79). The low-diversity TCR repertoires were characterized by large, expanded T cell clones that persisted over time. Longitudinal analysis indicated a potential adverse impact of treatment, evidenced by a reduction in TCR diversity and lymphocyte counts over time in patients with initially high-diversity repertoires. We observed a notable disparity between tumor and peripheral blood TCR repertoires. Single-cell sequencing revealed a prevalence of regulatory T cells in the tumor, while a combination of cytotoxic and naïve T cells dominated the blood. Specifically, expanded clones in blood were commonly annotated as terminally differentiated cytotoxic T cells with effector memory phenotypes.We suggest that high TCR diversity and T cell fraction are markers of general immune competence, reflecting the ability to combat cancer and other diseases. Our findings demonstrate the immune system’s crucial role in determining disease outcomes and highlight the potential for targeting immune function as a promising approach for future treatment and prevention. To build on these findings, we are expanding the project with 191 patients with MIBC from a clinical trial (TOMBOLA: NCT04138628) receiving adjuvant immunotherapy guided by ctDNA detection. TCR- and single-cell sequencing has been performed on blood samples from the cohort, and the data is currently under analysis. Results will be presented at the AACR meeting, aiming to provide new insights into the TCR repertoire’s role in bladder cancer and enhance our understanding of immune dynamics across different treatments. Citation Format: Nanna Kristjansdottir, Asbjørn Kjær, Randi I. Juul, Iver Nordentoft, Karin Birkenkamp-Demtröder, Johanne Ahrenfeldt, Trine Strandgaard, Deema Radif, Darren Hodgson, Christopher Abbosh, Hugo J. Aerts, Mads Agerbæk, Jørgen Bjerggaard Jenssen, Nicolai Birkbak, Lars Dyrskjøt. Low T cell diversity is associated with poor outcome in bladder cancer: A comprehensive longitudinal analysis of the T cell receptor repertoire [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3766.