Targeting co‐stimulatory receptors with agonistic antibodies is a promising cancer immunotherapy option. We aimed to investigate co‐stimulatory receptor expression, particularly 4‐1BB (CD137 or TNFRSF9), on tumor‐infiltrating CD8+ T cells (CD8+ TILs) and its association with distinct T‐cell activation features among exhausted CD8+ TILs in hepatocellular carcinoma (HCC). Tumor tissues, adjacent non‐tumor tissues and peripheral blood were collected from HCC patients undergoing surgical resection (n=79). Lymphocytes were isolated and used for multi‐color flow cytometry, RNA‐sequencing and in vitro functional restoration assays. Among the examined co‐stimulatory receptors, 4‐1BB was most prominently expressed on CD8+ TILs. 4‐1BB expression was almost exclusively detected on CD8+ T cells in the tumor—especially on PD‐1high cells and not PD‐1int and PD‐1neg cells. Compared to PD‐1int and PD‐1high 4‐1BBneg CD8+ TILs, 4‐1BBpos PD‐1high CD8+ TILs exhibited higher levels of tumor reactivity and T‐cell activation markers and significant enrichment for T‐cell activation gene signatures. Per‐patient analysis revealed positive correlations between percentages of 4‐1BBpos cells among CD8+ TILs and levels of parameters of tumor reactivity and T‐cell activation. Among highly exhausted PD‐1high CD8+ TILs, 4‐1BBpos cells harbored higher proportions of cells with proliferative and reinvigoration potential. Our new 4‐1BB‐related gene signature predicted survival outcomes of HCC patients in the The Cancer Genome Atlas cohort. 4‐1BB agonistic antibodies enhanced the function of CD8+ TILs and further enhanced the anti‐PD‐1‐mediated reinvigoration of CD8+ TILs, especially in cases showing high levels of T‐cell activation. Conclusion: 4‐1BB expression on CD8+ TILs represents a distinct activation state among highly exhausted CD8+ T cells in HCC. 4‐1BB co‐stimulation with agonistic antibodies may be a promising strategy for treating HCCs exhibiting prominent T‐cell activation.
Keywords : Liver cancer, CD137, TNFRSF9, Tumor‐infiltrating lymphocytes