Some regulatory mechanisms are planned in order to control the intensity and durationof the T cell response or to mantein self tolerance: co-inhibitory immune checkpointmolecules, such as cytotoxic T-lymphocyte-associated protein 4 (CTLA4), can beoverexpressed from lymphocytes to antagonize those costimulatory signals thatactivate lymphocytes; programmed death 1 (PD1) is another receptor expressed bylymphocytes that can lead them to exaustion when it recognizes its ligand; programmeddeath ligand (PDL)1 and PDL2 can be overexpressed by cancer cells. This evidence concerns the gene PDCD1 and cancer.