Despite the notion that human CD8+ T cells are the final mediators of autoimmune β-cell destruction in type 1 diabetes (T1D), none of their target epitopes has been demonstrated to be naturally processed and presented by β cells. The inventors therefore performed an epitope discovery study combining HLA Class I peptidomics and transcriptomics strategies. Inflammatory cytokines increased β-cell peptide presentation in vitro, paralleling upregulation of HLA Class I expression. Peptide sources included known β-cell antigens and several insulin granule proteins. PCSK2 was identified as a novel β-cell antigen, which was processed into HLA-A2-restricted epitopes recognized by circulating naïve CD8+ T cells in type 1 diabetic and healthy donors. Accordingly, the present invention relates to antigenic peptides derived from PCSK2 and uses thereof for the diagnosis and treatment of T1D.