Search

OBJECTIVE Insulin in pancreatic β-cells is a target of autoimmunity in type 1 diabetes. In the NOD mouse model of type 1 diabetes, oral or nasal administration of insulin induces immune tolerance to insulin and protects against autoimmune diabetes. Evidence for tolerance to mucosally administered insulin or other autoantigens is poorly documented in humans. Adults with recent-onset type 1 diabetes in whom the disease process is subacute afford an opportunity to determine whether mucosal insulin induces tolerance to insulin subsequently injected for treatment. RESEARCH DESIGN AND METHODS We randomized 52 adults with recent-onset, noninsulin-requiring type 1 diabetes to nasal insulin or placebo for 12 months. Fasting blood glucose and serum C-peptide, glucagon-stimulated serum C-peptide, and serum antibodies to islet antigens were monitored three times monthly for 24 months. An enhanced ELISpot assay was used to measure the T-cell response to human proinsulin. RESULTS β-Cell function declined by 35% overall, and 23 of 52 participants (44%) progressed to insulin treatment. Metabolic parameters remained similar between nasal insulin and placebo groups, but the insulin antibody response to injected insulin was significantly blunted in a sustained manner in those who had received nasal insulin. In a small cohort, the interferon-γ response of blood T-cells to proinsulin was suppressed after nasal insulin. CONCLUSIONS Although nasal insulin did not retard loss of residual β-cell function in adults with established type 1 diabetes, evidence that it induced immune tolerance to insulin provides a rationale for its application to prevent diabetes in at-risk individuals.

Despite the understanding that type 1 diabetes pathogenesis is mediated by T-cells, detection of these rare lymphocytes remains largely elusive. Suitable T-cell assays are highly needed, since they could offer preclinical diagnoses and immune surrogate end points for clinical trials. Although CD4+ T-cell assays have met with limited success, CD8+ T-cells are increasingly recognized as key actors in the diabetes of the NOD mouse. CD8+ T-cells are likely to play a role also in humans and may provide new markers of β-cell autoimmunity. Taking advantage of a panel of HLA-A2–restricted β-cell epitopes derived from preproinsulin, GAD, and islet glucose-6-phosphatase catalytic subunit-related protein (IGRP), we have implemented an islet-specific CD8+ T-cell interferon-γ enzyme-linked immunospot (ISL8Spot) assay. The ISL8Spot assay is capable of detecting and quantifying β-cell–reactive CD8+ T-cells directly ex vivo, without any preliminary expansion, using either fresh or frozen samples. Positive ISL8Spot responses separate new-onset diabetic and healthy samples with high accuracy (86% sensitivity, 91% specificity), using as few as five immunodominant epitopes. Moreover, sensitivity reaches 100% when the ISL8Spot assay is complemented by antibody determinations. Combination of CD8+ T-cell measurements with immune intervention strategies may open new avenues toward type 1 diabetes prediction and prevention.