PDCD1 and cancer: ICI targeting cytotoxic T-lymphocyte-antigen 4 (CTLA-4), programmed cell death 1 (PD-1) and more recently lymphocyte activation gene-3 (LAG-3) have entered the clinic as monotherapies but work even more potently in combination, transforming outcomes for cancer patients, especially for those whose tumours carry a high mutational burden and are T-cell-inflamed [1–4].