Despite the notion that human CD8+ T cells are the final mediators of autoimmune ?- cell destruction in type 1 diabetes (T1D), none of their target epitopes has been demonstrated to be naturally processed and presented by ? cells. The inventors therefore performed an epitope discovery study combining HLA Class I peptidomics and transcriptomics strategies.rnInflammatory cytokines increased ?-cell peptide presentation in vitro, paralleling upregulation of HLA Class I expression. Peptide sources included known ?-cell antigens and several insulin granule proteins. Urocortin 3 was identified as a novel ?-cell antigen, which was processed into HLA-A2- and HLA-A3-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 urocortin-3 and uses thereof for the diagnosis and treatment of T1D.