A meta-analysis of clinical trial data consisting of 3721 patients from 30 study arms showed a 27% rate of colitis (95% CI 19–34%) when anti-CTLA-4 ICIs were used (20 CTLA-4 therapy study arms, 10 combined PD-1/PD-L1 and CTLA-4 therapy study arms), and 58% (95% CI 41–76%) of these had colitis of grade 3–5 in severity. Here, PDCD1 is linked to colitis.