CD274 and neoplasm: However, untamable tumor cells can frequently raise the expression of regulatory proteins on the cell surface, including cytotoxic T lymphocyte antigen 4 (CTLA-4), Fas-L, programmed cell death-ligand 1 (PD-L1), lymphocyte activation gene-3 (LAG-3) and T cell immunoglobulin and ITIM domain (TIGIT), so triggering T cell apoptosis [52].