PDCD1 and cancer: Approaches in active anti-cancer immunotherapy include 1) the introduction of tumor-associated antigens or derivatives thereof as vaccines in an immunogenic context to break tumor tolerance; [31] 2) isolation of immune cells from cancer patients, followed by antigen pulsing and/or stimulation ex vivo before re-infusion into the patient [32] as well as 3) blocking immunosuppressive molecules like cytotoxic T lymphocyte-associated antigen 4 (CTLA4), and programmed cell death protein 1 (PD1) with monoclonal antibodies [33].