Tu131 - Hybrid Insulin Peptides Activate Autoreactive T Cells Restricted by a Non-risk HLA Haplotype

Perrin Guyer – Benaroya Research Institute; Rocky Baker – Department of Immunology and Microbiology – University of Colorado School of Medicine; Katie Haskins – Department of Immunology and Microbiology – University of Colorado School of Medicine; Eddie James – Benaroya Research Institute

Abstract Text: Hybrid insulin peptides (HIPs) formed through covalent cross-linking of proinsulin fragments to other secretory granule peptides have been detected within murine and human islets. HIPs were shown to be recognized by pancreas infiltrating T cells from nonobese diabetic mice and human pancreatic organ donors with type 1 diabetes (T1D). A recent study probed T cell reactivity in new onset patients, documenting HIP-specific responses in most subjects and isolating several unique HIP-responsive T cell clones. Surprisingly, one T cell clone responded vigorously to a C-peptide/WE14 HIP (HIP9, the human equivalent of murine 2.5HIP) in the context of DRB1*11:03 (DR11). Since DR11 is a non-risk haplotype, we reasoned that T cell responses with this HLA restriction could play either pathogenic or protective roles. Therefore, we recruited subjects with T1D and healthy controls with DR11 haplotypes and utilized an HLA class II tetramer to characterize HIP9-reactive CD4+ T cells. HLA class II tetramer staining revealed higher frequencies of HIP9-reactive T cells in subjects with T1D than the HLA-matched control subjects. Furthermore, in DR11+ subjects who had heterozygous haplotypes that carry the disease-associated DRB4 allele, HIP9-reactive T cell frequencies were higher than those observed for an immunodominant proinsulin epitope (PPI 9-28). Finally, phenotypic analysis indicated that a subset of HIP9-reactive T cells exhibit a Th1-like phenotype. These results provide the first direct evidence that a HIP containing a ChgA sequence is relevant in human disease and suggest a mechanism that may contribute to the rising incidence of T1D among individuals with non-risk HLA haplotypes.