TIGIT and PD1 Co-blockade Restores ex vivo Functions of Human Tumor-Infiltrating CD8(+) T Cells in Hepatocellular Carcinoma

BACKGROUND & AIMS: TIGIT is a co-inhibitory receptor, and its suitability as a target for cancer immunotherapy in HCC is unknown. PD1 blockade is clinically effective in about 20% of advanced HCC patients. Here we aim to determine whether co-blockade of TIGIT/PD1 has added value to restore functionality of HCC tumor-infiltrating T cells (TILs). METHODS: Mononuclear leukocytes were isolated from tumors, paired tumor-free liver tissues (TFL) and peripheral blood of HCC patients, and used for flow cytometric phenotyping and functional assays. CD3/CD28 T-cell stimulation and antigen-specific assays were used to study the ex vivo effects of TIGIT/PD1 single or dual blockade on T-cell functions. RESULTS: TIGIT was enriched, whereas its co-stimulatory counterpart CD226 was down-regulated on PD1(high) CD8(+) TILs. PD1(high) TIGIT(+) CD8(+) TILs co-expressed exhaustion markers TIM3 and LAG3 and demonstrated higher TOX expression. Furthermore, this subset showed decreased capacity to produce IFN-γ and TNF-α. Expression of TIGIT-ligand CD155 was up-regulated on tumor cells compared with hepatocytes in TFL. Whereas single PD1 blockade preferentially enhanced ex vivo functions of CD8(+) TILs from tumors with PD1(high) CD8(+) TILs (high PD1 expressers), co-blockade of TIGIT and PD1 improved proliferation and cytokine production of CD8(+) TILs from tumors enriched for PD1(int) CD8(+) TILs (low PD1 expressers). Importantly, ex vivo co-blockade of TIGIT/PD1 improved proliferation, cytokine production, and cytotoxicity of CD8(+) TILs compared with single PD1 blockade. CONCLUSIONS: Ex vivo, co-blockade of TIGIT/PD1 improves functionality of CD8(+) TILs that do not respond to single PD1 blockade. Therefore co-blockade of TIGIT/PD1 could be a promising immune therapeutic strategy for HCC patients.