CTLA4 and cancer: The Food and Drug Administration (FDA) has approved a number of ICIs targeting programmed cell death protein 1 (PD-1), cytotoxic T lymphocyte antigen-4 (CTLA-4), and lymphocyte activation gene-3 (LAG-3) for the treatment of various cancers, such as non-small cell lung cancer (NSCLC), melanoma, carcinoma of the head and neck, and hematological malignancies [1, 5–9].