Abstract 5216: Peripheral T cell receptor repertoire diversity is associated with outcome in bladder cancer

Abstract Bladder cancer is the sixth most common cancer overall, and treatment often involves removal of the bladder, which comes with a significant reduction in quality of life. Within this cancer type, an easily applicable prognostic biomarker may have clinical utility, potentially stratifying patients into bladder-sparing treatments. Expansion of T cell populations targeting cancer-specific neoantigens is an early response to malignancy. To investigate if the T cell receptor (TCR) repertoire could serve as a biomarker for cancer progression, we analyzed the TCR landscape in a cohort of 119 patients with muscle-invasive bladder cancer, treated with neoadjuvant chemotherapy before undergoing radical cystectomy. Peripheral and tumor TCR repertoires were produced using amplicon-based sequencing of the TCR beta chain. Additionally, T cell fraction was determined from whole exome sequencing data using TcellExTRECT, and latent viral DNA was investigated in plasma whole genome sequencing data using Kraken2. Antigen targets were estimated using GLIPH2. To explore the T cell repertoire subtypes, single-cell sequencing was performed on four fresh blood samples. In pre-treatment peripheral blood, low-diversity TCR repertoires were associated with worse survival (HR=2. 3, p=0. 024). Particularly poor outcome was observed in a subset of patients with both low TCR diversity and low fraction of circulating T cells (HR=4. 7, p=5e-4). Low-diversity repertoires were dominated by expanded T cell clones. TCR target annotation revealed that expanded T cell clones disproportionately targeted latent viral infections (p=2e-13), and cytomegalovirus DNA detection was strongly associated with decreased TCR diversity (p=5e-5). Additionally, tumor TCR sequencing revealed that expanded clones were rarely found in the tumor. Single-cell sequencing of peripheral blood found that most expanded clones consisted of cytotoxic T cells, while non-expanded clones mostly consisted of naive T cells. This indicates that low TCR diversity may represent a contraction of the naive T cell compartment, resulting in reduced immune competence. Finally, analysis of patient-matched longitudinal samples revealed that chemotherapy and cystectomy reduced TCR diversity in patients with high pre-treatment diversity (p=0. 001), indicating that treatment negatively affected the immune system in the most immune-competent patients. Our results suggest that both low TCR diversity and low T cell fraction represent decreased immune competency. This could be associated with an elevated risk of progression due to a reduced ability to control cancer growth and limit systemic cancer cell dissemination. These findings underline that immune health is an important factor during malignant disease, even when patients are not treated with immunotherapies. Therefore, improving immune health could be a potential future goal for cancer treatment and prevention. Citation Format: Asbjørn Kjær, Nanna Kristjánsdóttir, Iver Nordentoft, Randi Istrup Juul, Karin Birkenkamp-Demtröder, Johanne Ahrenfeldt, Darren Hodgson, Christopher Abbosh, Hugo JWL Aerts, Mads Agerbæk, Jørgen Bjerggaard Jensen, Nicolai J Birkbak, Lars Dyrskjøt. Peripheral T cell receptor repertoire diversity is associated with outcome in bladder cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 5216.