Endoplasmic reticulumaminopeptidase 1 (ERAP1) cleaves the N-terminal aminoacids of peptides, which can then bindonto major histocompatibility class I (MHC-I) molecules for presentationonto the cell surface, driving the activation of adaptive immune responses.In cancer, overtrimming of mature antigenic peptides can reduce cytotoxicT-cell responses, and ERAP1 can generate self-antigenic peptides whichcontribute to autoimmune cellular responses. The gene discussed is ERAP1; the disease is cancer.