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.

During their development and progression tumors acquire numerous mutations that, when translated into proteins give rise to neoantigens that can be recognized by T cells. Initially, neoantigens were not recognized as preferred targets for cancer immunotherapy due to their enormous diversity and the therefore limited options to develop “one fits all” pharmacologic solutions. In recent years, the experience obtained in clinical trials demonstrating a predictive role of neoantigens in checkpoint inhibition has changed our view on the clinical potential of neoantigens in cancer immunotherapy. Technological advances such as sequencing of whole cancer genomes, the development of reliable algorithms for epitope prediction, and an increasing number of immunotherapeutic options now facilitate the development of personalized tumor therapies directly targeting a patient’s neoantigenic burden. Preclinical studies in mice that support the excellent therapeutic potential of neoantigen-directed immunotherapies have provided blueprints on how this methodology can be translated into clinical applications in humans. Consistently, very recent clinical studies on personalized vaccinations targeting in silico predicted neoepitopes shed a first light on the therapeutic potential of personalized, neoantigen-directed immunotherapies. In our review, we discuss the various subtypes of tumor antigens with a focus on neoantigens and their potential in cancer immunotherapy. We will describe the current methods and techniques of detection as well as the structural requirements for neoantigens that are needed for their recognition by T cells and for tumor destruction. To assess the clinical potential of neoantigens, we will discuss their occurrence and functional relevance in spontaneous and hereditary cancers and their prognostic and predictive value. We will present in detail the existing immunotherapeutic options that exploit the neoantigen burden of tumors encompassing both preclinical efforts that provided convincing technological proof-of-concept and the current clinical studies confirming the potential of neoantigen-directed immunotherapies.

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. Cancer Res; 77(8); 1918–26. ©2017 AACR.

The scope of therapeutic options for the treatment of hepatocellular carcinoma (HCC) has recently been expanded by immunotherapeutic regimens. T cell-based therapies, especially in combination with other treatments have achieved far better outcomes compared to conventional treatments alone. However, there is an emerging body of evidence that eliciting T cell responses in immunotherapeutic approaches is insufficient for favorable outcomes. Immune responses in HCC are frequently attenuated in the tumor microenvironment (TME) or may even support tumor progress. Hence, therapies with immune checkpoint inhibitors or adoptive cell therapies appear to necessitate additional modification of the TME to unlock their full potential. In this review, we focus on immunotherapeutic strategies, underlying molecular mechanisms of CD8 T cell immunity, and causes of treatment failure in HCC of viral and non-viral origin. Furthermore, we provide an overview of TME features in underlying etiologies of HCC patients that mediate therapy resistance to checkpoint inhibition and discuss strategies from the literature concerning current approaches to these challenges.

Immunotherapy of solid tumors is often hampered by the low frequency of tumor‐specific T cells elicited by current vaccination strategies. Here, we describe a prime‐boost vaccination protocol based on the administration of antigen conjugated to poly‐lactic‐co‐glycolic acid (PLGA) microspheres followed by booster vaccination with Listeria monocytogenes vectors, which rapidly generates potent immune responses within two weeks. Compared with conventional vaccination with antigen‐pulsed dendritic cells, the use of PLGA microspheres resulted in immune responses of significantly higher magnitude, which could be further enhanced via coinjection of TLR 3 agonists. In an immunocompetent model of subcutaneous hepatocellular carcinoma, PLGA/Listeria vaccination resulted in complete remission of established tumors and prolonged survival. To further test the efficacy of the novel vaccination for the treatment of solid tumors, we developed an orthotopic liver cancer model based on the injection of transposon‐flanked plasmids expressing oncogenes and model antigens. In this transgenic mouse model of liver cancer, PLGA/Listeria vaccination resulted in eradication of liver tumors, long‐term survival of animals and establishment of stable cancer‐specific memory CD8⁺ T‐cell populations. Therefore, combined PLGA/Listeria vaccination holds promise as a novel immunotherapeutic option for the treatment of solid cancers and as a means to boost the therapeutic efficacy of established cancer vaccines.