This axis is composed of nine members, including five receptors, namely DNAM-1 (CD226, activator), TACTILE (CD96, activator), TIGIT (inhibitor), PVRIG (CD112R, inhibitor), and KIR2DL5A (CD158f, inhibitor), all expressed on cytotoxic cells (CD8+ T cells, Natural killer (NK) cells, and γδ T cells), and four ligands, namely NECTIN-1 (PVRL1/CD111), NECTIN-2 (PVRL2/CD112), NECTIN-3 (PVRL3/CD113), and PVR (CD155), which can be expressed on antigen-presenting cells or tumor cells [21]. Here, CD8A is linked to neoplasm.