Peptides derived from insulin granule proteins are targeted by CD8+ T cells across MHC Class I restrictions in humans and NOD mice
figureposted on 14.09.2020 by Ada Admin, Marie Eliane Azoury, Mahmoud Tarayrah, Georgia Afonso, Aurore Pais, Maikel L. Colli, Claire Maillard, Cassandra Lavaud, Laure Alexandre-Heymann, Sergio Gonzalez-Duque, Yann Verdier, Joelle Vinh, Sheena Pinto, Soren Buus, Danièle Dubois-Laforgue, Etienne Larger, Jean-Paul Beressi, Graziella Bruno, Decio L. Eizirik, Sylvaine You, Roberto Mallone
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The antigenic peptides processed by β cells and presented through surface HLA Class I molecules are poorly characterized. Each HLA variant, e.g. the most common HLA-A2 and HLA-A3, carries some peptide-binding specificity. Hence, features that, despite these specificities, remain shared across variants may reveal factors favoring β-cell immunogenicity. Building on our previous description of the HLA-A2/A3 peptidome of β cells, we analyzed the HLA-A3-restricted peptides targeted by circulating CD8+ T cells. Several peptides were recognized by CD8+ T cells within a narrow frequency (1-50/106), which was similar in donors with and without type 1 diabetes and harbored variable effector/memory fractions. These epitopes could be classified as conventional peptides or neo-epitopes, generated either via peptide cis-splicing or mRNA splicing, e.g. secretogranin-5 (SCG5)-009. As reported for HLA-A2-restricted peptides, several epitopes originated from β-cell granule proteins, e.g. SCG3, SCG5 and urocortin-3. Similarly, H-2Kd-restricted CD8+ T cells recognizing the murine orthologues of SCG5, urocortin-3, and proconvertase-2 infiltrated the islets of NOD mice and transferred diabetes into NOD/scid recipients. The finding of granule proteins targeted in both humans and NOD mice supports their disease relevance and identifies the insulin granule as a rich source of epitopes, possibly reflecting its impaired processing in type 1 diabetes.