T-cell immunoglobulin and ITIM domain in cancer immunotherapy: A focus on tumor-infiltrating regulatory T cells.

T-cell immunoglobulin and ITIM domain (TIGIT) is a novel type of immune checkpoint. Importantly, immune checkpoint molecules promote cancer progression by various antitumor suppressive mechanisms. TIGIT is an inhibitory receptor expressed on T cells, natural killer cells, and regulatory T cells that was recently attracted attention as a major emerging target for cancer immunotherapy. Regulatory T cells (Tregs) play crucial roles in immune homeostasis. Specifically, tumor-infiltrating Tregs promote cancer progression by restricting antitumor immunity and supporting tumor immune escape. In this review, we summarized the current understanding on TIGIT and tumor-infiltrating Tregs. Here, we reviewed the latest advances in the understanding of mechanisms causing tumor-infiltrating Tregs abundance to optimize Tregs targeted therapy. Collectively, anti-TIGIT targeting Tregs hold great promise for potent cancer target therapy.