BACKGROUND AND AIMS Programmed death 1 (PD‐1) checkpoint inhibition has shown promising results in patients with hepatocellular carcinoma, inducing objective responses in approximately 20% of treated patients. The roles of other coinhibitory molecules and their individual contributions to T‐cell dysfunction in liver cancer, however, remain largely elusive. APPROACH AND RESULTS We performed a comprehensive mRNA profiling of cluster of differentiation 8 (CD8) T cells in a murine model of autochthonous liver cancer by comparing the transcriptome of naive, functional effector, and exhausted, tumor‐specific CD8 T cells. Subsequently, we functionally validated the role of identified genes in T‐cell exhaustion. Our results reveal a unique transcriptome signature of exhausted T cells and demonstrate that up‐regulation of the inhibitory immune receptor T‐cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine‐based inhibitor motif domains (TIGIT) represents a hallmark in the process of T‐cell exhaustion in liver cancer. Compared to PD‐1, expression of TIGIT more reliably identified exhausted CD8 T cells at different stages of their differentiation. In combination with PD‐1 inhibition, targeting of TIGIT with antagonistic antibodies resulted in synergistic inhibition of liver cancer growth in immunocompetent mice. Finally, we demonstrate expression of TIGIT on tumor‐infiltrating CD8 T cells in tissue samples of patients with hepatocellular carcinoma and intrahepatic cholangiocarcinoma and identify two subsets of patients based on differential expression of TIGIT on tumor‐specific T cells. CONCLUSIONS Our transcriptome analysis provides a valuable resource for the identification of key pathways involved in T‐cell exhaustion in patients with liver cancer and identifies TIGIT as a potential target in checkpoint combination therapies.

Antagonistic antibodies targeting coinhibitory receptors have revolutionized the treatment of cancer by inducing durable immune responses and clinical remissions in patients. In contrast, success of agonistic costimulatory antibodies has thus far been limited because of the insufficient induction of adaptive immune responses. Here, we describe a novel vaccination method consisting of a primary dendritic cell (DC) immunization followed by a composite vaccination, including an agonistic CD40 antibody, soluble antigen, and a TLR3 agonist, referred to as CoAT. In mice, DC/CoAT prime-boost vaccinations targeting either MHC class I or II neoantigens or tumor-associated antigens rendered up to 60% of the total T-cell population specific for a single tumor epitope. DC/CoAT induced durable and complete remissions of large subcutaneous tumors without detectable side effects. Thus, booster vaccinations with agonistic costimulatory antibodies represent an ideal means to amplify DC vaccinations and induce robust T-cell immune responses while providing maximum flexibility regarding the choice of antigen. .

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Successful vaccination against cancer and infectious diseases relies on the induction of adaptive immune responses that induce high-titer antibodies or potent cytoxic T cell responses. In contrast to humoral vaccines, the amplification of cellular immune responses is often hampered by anti-vector immunity that either pre-exists or develops after repeated homologous vaccination. Replication-defective lymphocytic choriomeningitis virus (LCMV) vectors represent a novel generation of vaccination vectors that induce potent immune responses while escaping recognition by neutralizing antibodies. Here, we characterize the CD8 T cell immune response induced by replication-defective recombinant LCMV (rLCMV) vectors with regard to expansion kinetics, trafficking, phenotype, and function and we perform head-to-head comparisons of the novel rLCMV vectors with established vectors derived from adenovirus, vaccinia virus, or Listeria monocytogenes. Our results demonstrate that replication-deficient rLCMV vectors are safe and ideally suited for both homologous and heterologous vaccination regimens to achieve optimal amplification of CD8 T cell immune responses in vivo.

<div>Abstract<p>Antagonistic antibodies targeting coinhibitory receptors have revolutionized the treatment of cancer by inducing durable immune responses and clinical remissions in patients. In contrast, success of agonistic costimulatory antibodies has thus far been limited because of the insufficient induction of adaptive immune responses. Here, we describe a novel vaccination method consisting of a primary dendritic cell (DC) immunization followed by a composite vaccination, including an agonistic CD40 antibody, soluble antigen, and a TLR3 agonist, referred to as CoAT. In mice, DC/CoAT prime-boost vaccinations targeting either MHC class I or II neoantigens or tumor-associated antigens rendered up to 60% of the total T-cell population specific for a single tumor epitope. DC/CoAT induced durable and complete remissions of large subcutaneous tumors without detectable side effects. Thus, booster vaccinations with agonistic costimulatory antibodies represent an ideal means to amplify DC vaccinations and induce robust T-cell immune responses while providing maximum flexibility regarding the choice of antigen. <i>Cancer Res; 77(8); 1918–26. ©2017 AACR</i>.</p></div>