Novel T Cell reactivities to Hybrid Insulin Peptides in Islet Autoantibody-Positive At-Risk Subjects

Type 1 Diabetes (T1D) is an autoimmune disease mediated by autoreactive T cells. Our studies indicate that CD4 T cells reactive to Hybrid Insulin Peptides (HIPs) play a critical role in T cell-mediated beta-cell destruction. We have shown that HIPs form in human islets between fragments of the C-peptide and cleavage products of secretory granule proteins. To identify T cell specificities contributing to T1D pathogenesis, we tested T cell reactivity from T1D patients or healthy control using an IFN-γ ELISPOT assay against a library of 240 C-peptide HIPs. We observed elevated T cell responses to peptide pools containing HIPs that form at the amino acid residues G15, A18 and L26 of C-peptide. In a second cohort of healthy controls, at-risk individuals, and T1D patients, T cell reactivity to HIPs forming at these three residues was monitored. Results indicate that, prior to clinical onset of T1D, there were significantly elevated responses to multiple pools of HIPs, and the magnitude of T cell reactivity to HIPs forming at residue A18 of the C-peptide was increased. Overall, our study identifies new T cell specificities in at-risk subjects and indicates that T cell reactivity to HIPs can be observed before T1D onset.