Given that ERAP1-trimmed peptides modulate the adaptiveimmuneresponse, controlling ERAP1 activity is an attractive strategy forcancer immunotherapy, autoimmune diseases and increasing immune responsesagainst pathogens.4 There is evidence ofupregulation of ERAP1 in cancerous cells,4 where peptides can be “overtrimmed” and thus cannotbe presented in a complex with MHC-I, which has strict length requirements.5 This effectively hides the cancerous cells fromthe immune system. Here, ERAP1 is linked to autoimmune disease.