CTLA4 and cancer: ICIs were developed against programmed cell death ligand 1 (PD-L1) on cancer cells, such as atezolizumab, and the immune suppressive receptors programmed cell death 1 (PD-1), such as nivolumab and pembrolizumab, and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), such as ipilimumab, being present on cytotoxic T cells (2).