ERAP1 and melanoma: To investigate the changes in the immunopeptidome of cancer cells due to ERAP1 inhibition, we compared MHC-I peptide repertoires in A375 melanoma cells under three conditions: untreated, treated for 6 days with 10 μM of an allosteric ERAP1 inhibitor (compound 3, targeting the B3P site (24), Supplemental Fig. S3), and an ERAP1-deficient clone (19).