We detected reactivity to several pools of peptides from the stressed islet immunopeptidomes predicted to bind to A*02:01 or DRB1*03:01, to individual peptides from two islet secretory hormones (SCG5, CHGB), and to two PTM neo-epitopes derived from CHGA, an islet prohormone and insulin packaging factor already known as a target of T cells in T1D. Here, CHGB is linked to type 1 diabetes mellitus.