Development of Anti-human T Cell Immunoreceptor with Ig and ITIM Domains (TIGIT) Monoclonal Antibodies for Flow Cytometry

The release of negative regulators of immune activation (immune checkpoints) that limit antitumor responses has resulted in unprecedented rates of long-lasting tumor responses in patients with a variety of cancers. This can be achieved by antibodies blocking the cytotoxic T lymphocyte antigen-4 (CTLA-4) or the programmed death-1 (PD-1) pathway, either alone or in combination. The main premise for inducing an immune response is the pre-existence of antitumor T cells that were limited by specific immune checkpoints. Most patients who have tumor responses maintain long lasting disease control, yet one third of patients relapse. Mechanisms of acquired resistance are currently poorly understood, but evidence points to alterations that converge on the antigen presentation and interferon gamma signaling pathways. New generation combinatorial therapies may overcome resistance mechanisms to immune checkpoint therapy.

Here we have identified a surface protein, TIGIT, containing an immunoglobulin variable domain, a transmembrane domain and an immunoreceptor tyrosine-based inhibitory motif that was expressed on regulatory, memory and activated T cells. Poliovirus receptor, which is expressed on dendritic cells, bound TIGIT with high affinity. A TIGIT-Fc fusion protein inhibited T cell activation in vitro, and this was dependent on the presence of dendritic cells. The binding of poliovirus receptor to TIGIT on human dendritic cells enhanced the production of interleukin 10 and diminished the production of interleukin 12p40. Knockdown of TIGIT with small interfering RNA in human memory T cells did not affect T cell responses. TIGIT-Fc inhibited delayed-type hypersensitivity reactions in wild-type but not interleukin 10-deficient mice. Our data suggest that TIGIT exerts immunosuppressive effects by binding to poliovirus receptor and modulating cytokine production by dendritic cells.

Tumors constitute highly suppressive microenvironments in which infiltrating T cells are "exhausted" by inhibitory receptors such as PD-1. Here we identify TIGIT as a coinhibitory receptor that critically limits antitumor and other CD8(+) T cell-dependent chronic immune responses. TIGIT is highly expressed on human and murine tumor-infiltrating T cells, and, in models of both cancer and chronic viral infection, antibody coblockade of TIGIT and PD-L1 synergistically and specifically enhanced CD8(+) T cell effector function, resulting in significant tumor and viral clearance, respectively. This effect was abrogated by blockade of TIGIT's complementary costimulatory receptor, CD226, whose dimerization is disrupted upon direct interaction with TIGIT in cis. These results define a key role for TIGIT in inhibiting chronic CD8(+) T cell-dependent responses.