BTLA and neoplasm: However, exhaustive T cells are a state of T cell function defects, often occurring in tumors and chronic infections, mainly manifested by the high expression of such IRs as PD-1, TIM-3, BTLA, CTLA-4, LAG-3, and TIGIT, and the gradual decline in the secretion of functional cytokines, including IL-2, IFN-γ, TNF-α, which can cause T cell dysfunction, induce T cell inactivation, and weaken the killing ability of T cells to tumor cells in the tumor microenvironment, leading to the occurrence of tumor immune escape.