Importance of GAD65 peptides and I-Ag7 in the development of insulitis in nonobese diabetic mice

 Insulin-dependent diabetes mellitus (IDDM) develops in nonobese diabetic (NOD) mice through the destruction of the B cells in pancreatic Langerhans islets by islet autoantigen-specific T cells. The islet autoantigen glutamic acid decarboxylase 65 (GAD65) is thought to be a major target autoantigen in IDDM. In the present report, we established GAD65-specific T-cell clones using overlapping peptides that cover the amino acid sequences of mouse GAD65. T-cell epitopes of GAD65 were characterized by proliferation and binding assays using various analogue peptides and wild-type or mutant I-A^g7 transfectants. The efficacy of the peptide vaccine in IDDM was determined by administering T-cell epitope peptides to NOD mice and evaluating the histopathology of their insulitis. We obtained two types of T-cell clone, one specific for peptide p316–335 and another specific for p531–545 of GAD65. The p531–545 site has already been identified, but we report the p316–335 site for the first time. T-cell clones recognized those peptides in the wild-type I-A^g7 but not in the mutant I-A^g7 in which the serine at position 57 of the β-chain was replaced by an aspartic acid. Both the p316–335 and p531–545 peptides bound weakly to I-A^g7. Some peptides with amino acid substitutions had antagonistic activity, and administration of a large amount of wild-type peptide reduced the severity of insulitis in NOD mice. Our results suggest that peptide vaccine therapy may be useful in autoimmune diseases, including IDDM. Received: 19 July 1999 / Revised: 4 January 2000