Preserved C-peptide 30 months after GAD-alum treatment of children and adolescents with recent-onset type 1 diabetes, and its relation to immune markers

• Glutamic acid decarboxylase 65 kDa isoform (GAD65) is a major autoantigen in type 1 diabetes (T1D). Although alum-formulated GAD65 (GAD-alum) induced preservation of residual insulin secretion in a previous clinical Phase II trial, recent Phase II and Phase III trials failed to reach their primary end-points. The European Phase III trial was therefore closed after 15 months, and the 30 months follow-up period was completed only for a minority of the patients. This study aimed to assess whether GAD-alum preserved β-cell function in those recent-onset T1D patients who completed their 30 months visit in the European Phase III trial, and to characterize their GAD65-induced cytokine secretion and proliferation. Peripheral blood mononuclear cells (PBMC) were isolated at baseline and after 1, 3, 9, 15 and 21 months from the 148 Swedish subjects included in the Phase III GAD-alum trial, and also at 30 months from 45 patients who had reached the final visit before the trial was closed. Patients had been randomly assigned into three arms: 4 doses of GAD-alum (4D), 2 doses of GAD-alum followed by two doses of placebo (2D), or 4 doses of placebo. Cytokine secretion was detected in cell culture supernatants by Luminex, after 7 days of in vitro culture. Cell proliferation was determined by 3H thymidine incorporation assay. Fasting and stimulated C-peptide was analysed in serum. Patients treated with 2 doses of GAD-alum had less decline of both fasting (p=0.040) and stimulated C-peptide (p=0.012) after 30 months, and a larger proportion of these patients preserved >25% of their initial stimulated C-peptide AUC compared to placebo (p=0.012). Both 2D and 4D patients showed increased PBMC proliferation to GAD65 and a cytokine profile that tended to switch towards a more predominant Th2 associated profile over time. The results support the concept of GAD-alum treatment, but no specific immune markers have been identified.

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