CTLA4 and cancer: The application of immune checkpoint blockade (ICB) therapy has had a great impact on the treatment of cancer.1–3 In US Food and Drug Administration-approved clinical trials, three different ICB antibodies targeting cytotoxic T-lymphocyte-associated antigen 4, programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) produced favourable clinical outcomes.4–7 Clinical trials using these antibodies revealed that immune checkpoints have critical roles in tumour surveillance, and that antibody-based ICB therapies are a promising approach for cancer.