Those of a “severe” nature (grade 3 or above according to common terminology criteria for adverse events, CTCAE) [2], occur in around 55% of people treated with anti-PD1/CTLA-4 combination therapy [3], including colitis (20%), skin rash (10%), hepatitis (15%), endocrine dysfunction (5%), pneumonitis (4%), and inflammatory arthritis (6%); up to 20% of those treated with single agent anti-PD1/PDL1 are similarly affected. Here, PDCD1 is linked to hepatitis A virus infection.