TIGIT, a co-inhibitory receptor belonging to the poliovirus receptor (PVR) family. TIGIT is expressed on activated and memory T cells, regulatory T cells (Tregs), and natural killer (NK) cells. It binds with high affinity to two ligands: CD155 (PVR) and CD112 (PVRL2, nectin-2), which are often overexpressed on tumor cells and antigen-presenting cells. The TIGIT-ligand interaction delivers an inhibitory signal that suppresses T cell and NK cell activation, proliferation, and cytotoxic function, contributing to immune evasion.