Proinsulin-Specific, HLA-DQ8, and HLA-DQ8-Transdimer–Restricted CD4+ T Cells Infiltrate Islets in Type 1 Diabetes

Abstract

Type 1 diabetes (T1D) develops when insulin-secreting b-cells, found in the pancreatic islets of Langerhans, are destroyed by infiltrating T cells. How human T cells recognize b-cell-derived antigens remains unclear. Genetic studies have shown that HLA and insulin alleles are the most strongly associated with risk of T1D. These longstanding observations implicate CD4 + T-cell responses against (pro)insulin in the pathogenesis of T1D. To dissect the autoimmune T-cell response against human b-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 which encoded proinsulin-specific T-cell receptors. On an individual clone basis, 14 of 53 CD4 + T-cell clones (26%) recognized 6 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 peripheral blood mononuclear cells of some people with recent-onset T1D but not in HLAmatched control subjects. Hence, proinsulin-specific, HLA-DQ8, and HLA-DQ8-transdimer-restricted CD4 + T cells are strongly implicated in the autoimmune pathogenesis of human T1D.Type 1 diabetes (T1D) is an autoimmune disease caused by the CD4 + and CD8 + T-cell-mediated destruction of pancreatic insulin-producing b-cells (1). b-Cell destruction leads to primary insulin deficiency, which is treated by exogenous insulin therapy, and currently there is no cure. The pathogenesis of T1D has been well characterized using the NOD mouse model, but the immune basis of T1D in humans is less clear.Genetic association studies have provided powerful insights into the etiology of human T1D (2,3). The HLA class II region has the strongest impact on risk of T1D. Some HLA alleles-DQB1*06:02 for example-dominantly protect against T1D (4). In contrast, of all alleles, HLA-DQ2

Regulatory vs. inflammatory cytokine T-cell responses to mutated insulin peptides in healthy and type 1 diabetic subjects

“…For example, the work by Kent et al (28) identified CD4 T cells responding to DR4-presented epitopes from the insulin A-chain. Another recent study has described a series of CD4 T-cell clones isolated from the pancreas of a T1D patient that is reactive to C-peptide epitopes presented by DQ8 or DQ8/DQ2 heterodimers (29). Unfortunately, unlike in the case of NOD mouse, the tools are presently lacking to determine the relative importance of these different antiinsulin responses in the onset and progression of the disease in humans.…”

“…ELISPOT analyses were conducted as previously described using the human IFN-γ and IL-10 ELISPOT Kits (UCyTech Biosciences) (29). Details are discussed in SI Materials and Methods.…”

Discovery of a Selective Islet Peptidome Presented by the Highest-Risk HLA-DQ8trans Molecule

“…The islet epitopes presented by HLA-DQ8trans are largely unknown. Importantly, HLA-DQ8cis/trans-restricted CD4 T-cell clones have been isolated from human insulitis lesions, and T-cell autoreactivity was confirmed for several proinsulin peptides, underscoring the potential relevance of preproinsulin (PPI) peptides presented by HLA-DQ in diabetogenesis (10)(11)(12)(13). We contend that knowledge of the HLA-DQ8trans islet peptidome provides insight in the mechanism by which HLA-DQ2/8 heterozygosity imposes excessive risk for T1D.…”

“…1 and Table 1) were eluted with a mean peptide length of 14 amino acids (range [11][12][13][14][15][16][17][18][19]. All peptides are members of nested peptide sets covering three distinct core regions of the N-terminus of IA-2.…”

How to Make Mice Tell the Truth

“…NOD mice have also been informative about mechanisms that result in autoimmune diabetes, although it is unclear how these specifically contribute to disease pathogenesis in an individual human patient (1). Predisposing MHC genes, along with autoimmune reactions to insulin and its precursor proinsulin, are important in both mouse and human disease (2)(3)(4)(5)(6). Less clear is the value of animal models as part of the preclinical development of new treatments for disease.…”