Abstract A017: Clonally expanded CD8+ T cells exhibit tissue-specific differentiation and variable antigen specificity in renal cell carcinoma

Abstract Unlike other solid tumors responsive to immune checkpoint blockade, high CD8+ T cell infiltration is not associated with improved clinical outcome in clear cell renal cell carcinoma (RCC). This suggests that T cell phenotype, specificity, and tissue localization may be critical. To dissect these factors, we performed scRNA/TCR-seq on T cells from paired tumor, blood, and draining lymph node (tdLN) tissues from two treatment-naïve RCC patients. We integrated this data with transcriptional signatures of antigen specificity and a complementary antigen-specific RCC mouse model. In patient 1, we identified expanded, computationally inferred, tumor-reactive CD8+ T cell clones with shared TCRs across tumor, blood, and tdLNs. Although each exhausted clonotype encompassed heterogeneous phenotypes, they displayed tissue-specific differentiation, with stem-like exhausted cells (TCF7+) enriched in tdLNs, effector exhausted cells (CX3CR1+) in blood, and terminally exhausted cells (PDCD1+/HAVCR2+) in the tumor. Notably, stem-like CD8+ T cells with shared clones in the tumor were present in two tdLNs, suggesting maintenance and trafficking across lymph nodes. This tissue-dependent differentiation pattern was recapitulated in a complementary antigen-specific mouse model of RCC. Patient 2 exhibited distinct transcriptional profiles within the tumor compared to patient 1. Viral-reactive (VR) signature scores were significantly increased in patient 2 (median = 0.034 vs. -0.0627; p<0.001), with a greater proportion of VR CD8+ T cells (57.9% vs. 42.0%, p<0.001). Conversely, patient 1 demonstrated a higher proportion of TR CD8+ T cells (44.8% vs. 34.2%, p<0.001), indicating interpatient heterogeneity in antigen specificity. We further identified FOXP3+ regulatory T cells and tolerogenic plasmacytoid dendritic cells enriched in the tdLN of patient 2, suggesting an immunosuppressive niche that may shape T cell priming, differentiation, and maintenance. Together, these findings demonstrate that while tissue-dependent differentiation of CD8+ T cells is conserved in RCC, antigen specificity varies substantially. Ongoing studies aim to distinguish TR from VR populations, define the migration and function of stem-like CD8+ T cells, and determine how the tdLN microenvironment regulates CD8+ T cell fate in RCC. Citation Format: Lena V. Wirth, Ethan C. Burns, Vivien Moritz, Fady Ghali, Michael Hurwitz, Adebowale Adeniran, Patrick Kenney, David A. Braun. Clonally expanded CD8+ T cells exhibit tissue-specific differentiation and variable antigen specificity in renal cell carcinoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Innovations in Kidney Cancer Research: From Molecular Insights to Therapeutic Breakthroughs; 2026 Mar 13-16; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2026;86(5_Suppl_2):Abstract nr A017.