Abstract 3220: PD-1 antibody-bound progenitor-exhausted CD8+T cells in lymph nodes enhance PD-1 blockade anti-tumor immunity in gastrointestinal cancer

Abstract Introduction: Progenitor-exhausted T (Tpex) cells, marked by TCF1 and PD-1 expression, are essential for the efficacy of immune checkpoint inhibitors (ICIs) like anti-PD-1 antibodies. These cells serve as precursors to intratumoral exhausted T (Tex) cells and may play a pivotal role in maintaining immune responses during cancer therapy. While Tpex cells are recognized for their importance, the detailed mechanisms by which ICIs influence their activation, proliferation, and migration remain unclear. Specifically, the dynamics of ICI-bound Tpex cells across lymph nodes (LNs) and tumors have not been fully characterized. To address this point, we investigated the spatial and functional behavior of Tpex cells in gastrointestinal cancer patients, focusing on how ICIs reprogram these cells to exert anti-tumor immunity. Methods: We collected tumor, lymph node (LN), and blood samples from gastrointestinal cancer patients treated with or without anti-PD-1 antibodies. Purified lymphocytes were analyzed with flowcytometry and sequencing analysis. To identify ICI-binding T cells, we developed a method using IgG4 detection, which allowed us to detect cells directly bound by therapeutic anti-PD-1 antibodies. We further used combined sequencing technique including single-cell RNA sequencing, T cell receptor sequencing and CITE-sequencing for IgG4 detection (scRNA/TCR/CITE-seq) to profile 29, 388 T cells across tissue compartments, including LNs, tumors, and blood. Results: Our flowcytometry analysis revealed that CD8-Tpex cells were enriched in proximal LNs and exhibited significant proliferation following ICI treatment. Using IgG4 detection and sequencing, we confirmed that PD-1+ Tpex cells in LNs directly bound therapeutic anti-PD-1 antibodies and underwent clonal expansion. Notably, these ICI-bound Tpex cells shared TCR clonotypes with intratumoral Tex cells, suggesting that Tpex cells migrate from LNs to tumors after treatment. Conclusion: ICIs primarily target PD-1+ Tpex cells in proximal LNs, driving their proliferation and migration to tumors, where they differentiate into Tex cells and contribute to sustained tumor destruction. These results not only deepen our understanding of the mechanisms underlying ICI therapy but also provide a robust methodological framework for tracking ICI-binding T cells across tissues. Citation Format: Takuro Saito, Yohei Nose, Yoshiaki Yasumizu, Naganari Ohkura, Hisashi Wada, Hidetoshi Eguchi, Yuichiro Doki. PD-1 antibody-bound progenitor-exhausted CD8T cells in lymph nodes enhance PD-1 blockade anti-tumor immunity in gastrointestinal cancer [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 3220.