Abstract

Type 1 diabetes develops when the insulin-secreting beta cells, found in the pancreatic islets of Langerhans, are destroyed by infiltrating T cells. How human T cells recognize beta-cell derived antigens remains unclear. Genetic studies have shown that HLA and insulin alleles are the most strongly associated with risk of T1D. These long-standing observations implicate CD4⁺ T-cell responses against (pro)insulin in the pathogenesis of T1D. To dissect the autoimmune T-cell response against human beta cells we isolated and characterized 53 CD4⁺ T cell clones from within the residual pancreatic islets of a deceased organ donor who had T1D. These 53 clones expressed 47 unique clonotypes, 8 of these encoded proinsulin specific TCRs. On an individual clone basis, 14 of 53 (26%) CD4⁺ T-cell clones recognized six distinct, but overlapping, epitopes in the C-peptide of proinsulin These clones recognized C-peptide epitopes presented by HLA-DQ8 and, notably, HLA-DQ8 transdimers that form in HLA-DQ2/DQ8 heterozygous individuals. Responses to these epitopes were detected in the PBMC of some people with recent onset T1D, but not in HLA-matched control subjects. Hence, proinsulin specific, HLA-DQ8 and DQ8 transdimer restricted, CD4⁺ T cells are strongly implicated in the autoimmune pathogenesis of human T1D.