The β-cell plays a crucial role in the pathogenesis of type 1 diabetes, in part through the posttranslational modification of self-proteins by biochemical processes such as deamidation. These neoantigens are potential triggers for breaking immune tolerance. We report the detection by LC-MS/MS of 16 novel Gln and 27 novel Asn deamidations in 14 disease-related proteins within inflammatory cytokine–stressed human islets of Langerhans. T-cell clones responsive against one Gln- and three Asn-deamidated peptides could be isolated from peripheral blood of individuals with type 1 diabetes. Ex vivo HLA class II tetramer staining detected higher T-cell frequencies in individuals with the disease compared with control individuals. Furthermore, there was a positive correlation between the frequencies of T cells specific for deamidated peptides, insulin antibody levels at diagnosis, and duration of disease. These results highlight that stressed human islets are prone to enzymatic and biochemical deamidation and suggest that both Gln- and Asn-deamidated peptides can promote the activation and expansion of autoreactive CD4+ T cells. These findings add to the growing evidence that posttranslational modifications undermine tolerance and may open the road for the development of new diagnostic and therapeutic applications for individuals living with type 1 diabetes.

Article Highlights
  • Posttranslationally modified neoantigens are formed in β-cells under conditions of inflammation, but studies to date have focused on a limited number of antigens.

  • We sought to identify disease-relevant β-cell neoantigens through unbiased proteomic analysis and confirmation by antigen-specific T-cell assays.

  • We detected novel Gln and Asn deamidations within 14 type 1 diabetes–related proteins in cytokine-stressed human islets and verified disease-associated T-cell recognition for three corresponding epitopes.

  • These results demonstrate that both enzymatic and biochemical deamidation in cytokine-exposed islets undermine self-tolerance and lay a foundation for new diagnostic and therapeutic approaches for individuals living with type 1 diabetes.

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E.A.J. and L.O. share senior authorship.

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