Programmed death protein-1 (PD-1) and cytotoxic T lymphocyte antigen 4 (CTLA4) are the most well-known immune checkpoints, promoting immune tolerance by binding to their ligands PD-L1 and B7 family molecules respectively, and therapeutic antibodies targeting them have greatly changed cancer immunotherapy in the past [190]. The gene discussed is CTLA4; the disease is cancer.