Checkpoint inhibitors, including PD-1 inhibitors (e.g., nivolumab, pembrolizumab) and PD-L1 inhibitors (e.g., atezolizumab, durvalumab), restore immune surveillance by blocking the PD-1/PD-L1 interaction, thereby enhancing T-cell cytotoxicity and promoting anti-tumour responses. The gene discussed is PDCD1; the disease is neoplasm.