CD226 and neoplasm: The regulation of NK cells, and also of T cells, by DNAM-1, TIGIT, PVRIG and TACTILE receptors is achieved by complex interactions with their ligands in tumor cells that, depending on the number of inhibitory receptors involved and their binding affinity for CD155 and CD112 on the target cells, will counteract or not the activation signals mediated through the DNAM-1 receptor.