TIGIT (T cell Immunoreceptor with Ig and ITIM domains), also known as Vstm3, Vsig9, WUCAM, is a newly discovered immunosuppressive co stimulator molecule with a molecular weight of 30-34kD. It is expressed on T cells and NK cells and has immunoglobulin like domains, transmembrane domains, and immunoglobulin tyrosine inhibitory motifs (ITIMs), hence the name TIGIT. TIGIT is a type I transmembrane protein and belongs to the Ig superfamily CD28 member. Human TIGIT has 244 amino acids, including a 21aa signal peptide, a 120aa extracellular domain (containing V-type immunoglobulin like domains and two potential N-terminal glycosylation sites), a 21aa transmembrane region, and an 82aa cytoplasmic region carrying ITIM motifs. TIGIT is an emerging inhibitory receptor shared by NK and T cells, with high affinity for the highly expressed PVR (CD155) in tumor cells. It directly inhibits the killing effect of NK and T cells on tumor cells through the ITIM region of TIGIT, similar to the inhibitory effect of CTLA-4 on T cells.