Basic Research - Cancer(구연) (E-002) TOX-expressing terminally exhausted tumor-infiltrating CD8+ T cells are reinvigorated by co-blockade of PD-1 and TIGIT in bladder cancer ¹충북대학교 의과대학 비뇨기과학교실, ²내과학교실 Seok-Joong Yun¹, Hye Sook Han², Hee Kyung Kim², Kyeong Kim¹, Hee Youn Lee¹, Sung Pil Seo¹, Ho Won Kang¹, Won Tae Kim¹, Yong-June Kim¹, Sang-Cheol Lee¹, Wun-Jae Kim¹ Purpose: Exhausted T cells in the tumor microenvironment are heterogeneous and major targets of immunotherapies. We examined their distinct exhaustion status based on the level of programmed cell death-1 (PD-1) and thymocyte selection-associated high mobility group box protein (TOX) expression in CD8+ tumor-infiltrating lymphocytes (TILs) in patients with urothelial bladder cancer. Experimental Design: Peripheral blood mononuclear cells (PBMCs) and tumor single-cell suspensions were collected from 30 bladder cancer patients undergoing transurethral resection of the bladder tumor. We examined the expression of immune checkpoint receptors (ICRs), T-cell transcription factors, and tumor reactivity markers via flow cytometry and ex vivo functional restoration assays. Results: The expression levels of ICRs on CD8+ T cells were higher in TILs than PBMCs. PD-1highCD8+ TILs were more terminally exhausted than PD-1neg and PD-1int CD8+ TILs. TOX-expressing PD-1highCD8+ TILs had the highest expression of ICRs, the most terminally exhausted features, and the highest tumor antigen reactivity among PD-1+CD8+ TILs. Bladder cancer patients with a high percentage of PD-1highTOX+CD8+ TILs had more progressed T-cell exhaustion features and higher programmed death-ligand 1 expression in tumor tissues. TIGIT was the most frequent co-expressed ICR on PD-1+CD8+ TILs, and TIGIT blockade further enhanced the PD-1 blockade-mediated cytokine production by CD8+ TILs from bladder cancer patients. Conclusions: TOX-expressing PD-1highCD8+ TILs are the most terminally exhausted and tumor antigen reactive CD8+ TILs in bladder cancer. The co-blockade of PD-1 and TIGIT could be a strategy for enhancing the functional restoration of CD8+ TILs in bladder cancer patients. keywords : Bladder cancer, CD8+ T cell, PD-1, TIGIT, TOX