TIGIT and neoplasm: Tumor-infiltrating T cells can become exhausted, a condition characterized by low effector function and persistently high levels of IC receptors [75,76], including PD-1, cytotoxic T lymphocyte antigen 4 (CTLA-4), TIM-3, lymphocyte activation gene 3 (LAG-3), T-cell immune-receptor with Ig and ITIM domains (TIGIT), along with others [77].