Transcriptome Profiling Identifies TIGIT as a Marker of T-Cell Exhaustion in Liver Cancer.

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.

CD4 and CD8 T lymphocyte interplay in controlling tumor growth.

The outstanding clinical success of immune checkpoint blockade has revived the interest in underlying mechanisms of the immune system that are capable of eliminating tumors even in advanced stages. In this scenario, CD4 and CD8 T cell responses are part of the cancer immune cycle and both populations significantly influence the clinical outcome. In general, the immune system has evolved several mechanisms to protect the host against cancer. Each of them has to be undermined or evaded during cancer development to enable tumor outgrowth. In this review, we give an overview of T lymphocyte-driven control of tumor growth and discuss the involved tumor-suppressive mechanisms of the immune system, such as senescence surveillance, cancer immunosurveillance, and cancer immunoediting with respect to recent clinical developments of immunotherapies. The main focus is on the currently existing knowledge about the CD4 and CD8 T lymphocyte interplay that mediates the control of tumor growth.

Recombinant LCMV Vectors Induce Protective Immunity following Homologous and Heterologous Vaccinations.

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.

CD40 Signaling Drives Potent Cellular Immune Responses in Heterologous Cancer Vaccinations.

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.

Administration of Gemcitabine After Pancreatic Tumor Resection in Mice Induces an Antitumor Immune Response Mediated by Natural Killer Cells.

BACKGROUND & AIMS: Even after potentially curative R0 resection, patients with pancreatic ductal adenocarcinoma (PDAC) have a poor prognosis owing to high rates of local recurrence and metastasis to distant organs. However, we have no suitable transgenic animal models for surgical interventions. METHODS: To induce formation of pancreatic tumor foci, we electroporated oncogenic plasmids into pancreata of LSL-KrasG12D × p53fl/fl mice; mutant Kras was expressed in p53fl/fl mice using a sleeping beauty transposon. We co-delivered a transposon encoding a constitutively active form of Akt2 (myrAkt2). Carcinogenesis and histopathologic features of tumors were examined. Metastasis was monitored by bioluminescence imaging. Tumors were resected and mice were given gemcitabine, and tumor recurrence patterns and survival were determined. Immune cells were collected from resection sites and analyzed by flow cytometry and in depletion experiments. RESULTS: After electroporation of oncogenic plasmids, mice developed a single pancreatic tumor nodule with histopathologic features of human PDAC. Pancreatic tumors that expressed myrAkt2 infiltrated the surrounding pancreatic tissue and neurons and became widely metastatic, reflecting the aggressive clinical features of PDAC in patients. Despite early tumor resection, mice died from locally recurring and distant tumors, but adjuvant administration of gemcitabine after tumor resection prolonged survival. In mice given adjuvant gemcitabine or vehicle, gemcitabine significantly inhibited local recurrence of tumors, but not metastasis to distant organs, similar to observations in clinical trials. Gemcitabine inhibited accumulation of CD11b+Gr1intF4/80int myeloid-derived suppressor cells at the resection margin and increased the number of natural killer (NK) cells at this location. NK cells but not T cells were required for gemcitabine-mediated antitumor responses. CONCLUSIONS: Gemcitabine administration after resection of pancreatic tumors in mice activates NK cell-mediated antitumor responses and inhibits local recurrence of tumors, consistent with observations from patients with PDAC. Transgenic mice with resectable pancreatic tumors might be promising tools to study adjuvant therapy strategies for patients.

Microsphere priming facilitates induction of potent therapeutic T-cell immune responses against autochthonous liver cancers.

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.