Pre-clinical development of a tolerogenic peptide from glutamate decarboxylase as a candidate for antigen-specific immunotherapy in type 1 diabetes

Dysregulation and loss of immune tolerance towards pancreatic β-cell autoantigens are features of type 1 diabetes (T1D). Until recently, life-long insulin injection was the only approved treatment for T1D, and this does not address the underlying disease pathology. Antigen-specific immunotherapy (ASI) seeks to restore tolerance and holds potential as a new therapeutic strategy for treating autoimmune diseases with well characterised antigens. Peptide ASI using processing independent CD4+ T-cell epitopes (PIPs) shows promising results in several autoimmune diseases. Here we successfully applied the principles of PIP design to the T1D autoantigen glutamate decarboxylase 65 (GAD65). Peptides spanning GAD65 predicted to be pan-HLA-DR binding were selected. Peptide P10 displayed enriched responses in peripheral blood mononuclear cells from people with T1D. The minimal epitope of the P10 peptide was fine mapped using T-cell hybridomas generated from HLA-DRB1*04:01 transgenic mice. This minimal epitope, P10Sol, was demonstrated to induce tolerance to the parent peptide in HLA-DRB1*04:01 transgenic mice using a novel activation-induced marker assay. Finally, we show that GAD65 P10Sol PIP is recognised by CD4+ T-cells from people with T1D who possess a range of HLA-DR alleles and can, therefore, be defined as a pan-DR binding peptide with therapeutic potential.