TIGIT (T cell immunoreceptor with Ig and ITIM domains) was recently characterized as an inhibitory receptor, which is expressed mainly on NK, Treg, CD8+ T, and CD4+ T cells. TIGIT harbors an immunoglobulin tail tyrosine (ITT)-like phosphorylation motif and an ITIM (immunoreceptor tyrosine-based inhibition motif) in its cytoplasmic tail. The poliovirus receptor (PVR or CD155) was identified as the physical ligand of TIGIT with high affinity, and PVRL2 (Nectin2 or CD112) also binds to TIGIT with a weaker binding capacity. TIGIT/PVR engagement suppresses T cell activation through IL-10 secretion mediated by dendritic cells. Furthermore, TIGIT also exerts an intrinsic inhibitory function to T cell activation.