Novel T-Cell Reactivities to Hybrid Insulin Peptides in Islet Autoantibody-Positive At-Risk Individuals

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 β-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 individuals using an IFN-γ enzyme-linked immunosorbent spot 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 control individuals, 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 individuals and indicates that T-cell reactivity to HIPs can be observed before T1D onset.

We identified a new region of the C-peptide that is targeted by hybrid insulin peptide (HIP)-reactive T cells in patients with type 1 diabetes and antibody-positive individuals. Antibody-positive individuals exhibited robust and broad T cell responses to HIPs. When compared to healthy control individuals, a significantly higher percentage of antibody-positive individuals who progressed to a higher stage of type 1 diabetes displayed responses to HIPs.