CTLA4 and cancer: However, monoclonal antibodies for immune checkpoints, such as targeting programmed cell death protein 1 (PD-1), programmed death-ligand 1 (PD-L1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), have displayed heterogeneous and variable response rates and clinical outcomes in a large proportion of cancers [2–4].