However, tumors exploit self-expression of these molecules, such as CTLA-4 (cytotoxic T-lymphocyte-associated protein) and PD-1 (programmed cell death protein 1), to inhibit the response of tumor-infiltrating T lymphocytes (TILs), as they are two major negative regulators of the anti-tumor response. This evidence concerns the gene PDCD1 and neoplasm.