Preclinical Development of a Tolerogenic Peptide From Glutamate Decarboxylase as a Candidate for Antigen-Specific...

Dysregulation and loss of immune tolerance toward pancreatic β-cell autoantigens are features of type 1 diabetes (T1D). Until recently, life-long insulin injection was the only approved treatment for T1D, but it does not address the underlying disease pathology. The aim for antigen-specific immunotherapy (ASI) is to restore tolerance. ASI holds potential as a new therapeutic strategy for treating autoimmune diseases with well-characterized 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 10 (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, using a novel activation-induced marker assay, to induce tolerance to the parent peptide in the transgenic mice. Finally, we show that GAD65 P10Sol PIP is recognized by CD4+ T cells from people with T1D who possess a range of HLA-DR alleles and, therefore, can be defined as a pan-DR-binding peptide with therapeutic potential.

There are currently no approved antigen-specific immunotherapies (ASIs) for people with type 1 diabetes (T1D). We aimed to develop a peptide for ASI for T1D based on the T1D-associated auto-antigen glutamate decarboxylase 65 (GAD65). A minimal and soluble peptide derived from GAD65 was demonstrated to induce tolerance in an HLA transgenic mouse. Our data suggest this peptide derived from the GAD65 islet protein should be tested for therapeutic potential in people with T1D who have residual β-cell function.