TIGIT as an emerging immune checkpoint

Combined Anti-Cancer Strategies Based on Anti-Checkpoint Inhibitor Antibodies

Therapeutic monoclonal antibodies for the treatment of cancer came of age in 1997, with the approval of anti-CD20 Rituximab. Since then, a wide variety of antibodies have been developed with many different formats and mechanisms of action. Among these, antibodies blocking immune checkpoint inhibitors (ICI) have revolutionized the field, based on the novelty of their concept and their demonstrated efficacy in several types of cancer otherwise lacking effective immunotherapy approaches. ICI are expressed by tumor, stromal or immune cells infiltrating the tumor microenvironment, and negatively regulate anti-tumor immunity. Antibodies against the first discovered ICI, CTLA-4, PD-1 and PD-L1, have shown significant activity in phase III studies against melanoma and other solid cancers, alone or in combination with chemotherapy or radiotherapy. However, not all cancers and not all patients respond to these drugs. Therefore, novel antibodies targeting additional ICI are currently being developed. In addition, CTLA-4, PD-1 and PD-L1 blocking antibodies are being combined with each other or with other antibodies targeting novel ICI, immunostimulatory molecules, tumor antigens, angiogenic factors, complement receptors, or with T cell engaging bispecific antibodies (BsAb), with the aim of obtaining synergistic effects with minimal toxicity. In this review, we summarize the biological aspects behind such combinations and review some of the most important clinical data on ICI-specific antibodies.

Targeting the "PVR-TIGIT axis" with immune checkpoint therapies

Checkpoint inhibitors have become an efficient way to treat cancers. Indeed, anti-CTLA-4, anti-PD1, and anti-PDL-1 antibodies are now used as therapies for cancers. However, while these therapies are very efficient in certain tumors, they remain poorly efficient in others. This might be explained by the immune infiltrate, the expression of target molecules, and the influence of the tumor microenvironment. It is therefore critical to identify checkpoint antigens that represent alternative targets for immunotherapies. PVR-like molecules play regulatory roles in immune cell functions. These proteins are expressed by different cell types and have been shown to be upregulated in various malignancies. PVR and Nectin-2 are expressed by tumor cells as well as myeloid cells, while TIGIT, CD96, and DNAM-1 are expressed on effector lymphoid cells. PVR is able to bind DNAM-1, CD96, and TIGIT, which results in two distinct profiles of effector cell activation. Indeed, while binding to DNAM-1 induces the release of cytokines and cytotoxicity of cytotoxic effector cells, binding TIGIT induces an immunosuppressive and non-cytotoxic profile. PVR is also able to bind CD96, which induces an immunosuppressive response in murine models. Unfortunately, in humans, results remain contradictory, and this interaction might induce the activation or the suppression of the immune response. Similarly, Nectin-2 was shown to bind TIGIT and to induce regulatory profiles in effectors cells such as NK and T cells. Therefore, these data highlight the potential of each of the molecules of the “PVR–TIGIT axis” as a potential target for immune checkpoint therapy. However, many questions remain to be answered to fully understand the mechanisms of this synapse, in particular for human CD96 and Nectin-2, which are still understudied. Here, we review the recent advances in “PVR–TIGIT axis” research and discuss the potential of targeting this axis by checkpoint immunotherapies.

Challenges for Immunotherapy in Multiple Myeloma: Bone Marrow Microenvironment-Mediated Immune Suppression and Immune Resistance

The power of immunotherapy in the battle of Multiple Myeloma (MM) started with allogeneic stem cell transplantation, and was rediscovered with immunomodulatory drugs and extended with the outstanding results achieved with targeted antibodies. Today, next to powerful antibodies Elotuzumab and Daratumumab, several T-cell-based immunotherapeutic approaches, such as bispecific antibodies and chimeric antigen receptor-transduced T-cells (CAR T-cells) are making their successful entry in the immunotherapy arena with highly promising results in clinical trials. Nonetheless, similar to what is observed in chemotherapy, MM appears capable to escape from immunotherapy, especially through tight interactions with the cells of the bone marrow microenvironment (BM-ME). This review will outline our current understanding on how BM-ME protects MM-cells from immunotherapy through immunosuppression and through induction of intrinsic resistance against cytotoxic effector mechanisms of T- and NK-cells.

CD155: A Multi-Functional Molecule in Tumor Progression

CD155 is an adhesion molecule belonging to the Nectin/Nectin-like family often overexpressed on tumor cells and involved in many different processes such as cell adhesion, migration and proliferation. In contrast to these pro-tumorigenic functions, CD155 is also a ligand for the activating receptor DNAM-1 expressed on cytotoxic lymphocytes including Natural Killer (NK) cells and involved in anti-tumor immune response. However, during tumor progression inhibitory receptors for CD155 are up-regulated on the surface of effector cells, contributing to an impairment of their cytotoxic capacity. In this review we will focus on the roles of CD155 as a ligand for the activating receptor DNAM-1 regulating immune surveillance against cancer and as pro-oncogenic molecule favoring tumor proliferation, invasion and immune evasion. A deeper understanding of the multiple roles played by CD155 in cancer development contributes to improving anti-tumor strategies aimed to potentiate immune response against cancer.

Tumor microenvironmental influences on dendritic cell and T cell function: A focus on clinically relevant immunologic and metabolic checkpoints

Cancer immunotherapy is fast becoming one of the most promising means of treating malignant disease. Cancer vaccines, adoptive cell transfer therapies, and immune checkpoint blockade have all shown varying levels of success in the clinical management of several cancer types in recent years. However, despite the clinical benefits often achieved by these regimens, an ongoing problem for many patients is the inherent or acquired resistance of their cancer to immunotherapy. It is now appreciated that dendritic cells and T lymphocytes both play key roles in antitumor immune responses and that the tumor microenvironment presents a number of barriers to the function of these cells that can ultimately limit the success of immunotherapy. In particular, the engagement of several immunologic and metabolic checkpoints within the hostile tumor microenvironment can severely compromise the antitumor functions of these important immune populations. This review highlights work from both preclinical and clinical studies that has shaped our understanding of the tumor microenvironment and its influence on dendritic cell and T cell function. It focuses on clinically relevant targeted and immunotherapeutic strategies that have emerged from these studies in an effort to prevent or overcome immune subversion within the tumor microenvironment. Emphasis is also placed on the potential of next-generation combinatorial regimens that target metabolic and immunologic impediments to dendritic cell and T lymphocyte function as strategies to improve antitumor immune reactivity and the clinical outcome of cancer immunotherapy going forward.