Preventing type 1 diabetes in late-stage pre-diabetic NOD mice with insulin: A central role for alum as adjuvant

Restoration of immune tolerance to disease-relevant antigens is an appealing approach to prevent or arrest an organ-specific autoimmune disease like type 1 diabetes (T1D). Numerous studies have identified insulin as a key antigen of interest to use in such strategies, but to date, the success of these interventions in humans has been inconsistent. The efficacy of antigen-specific immunotherapy may be enhanced by optimising the dose, timing, and route of administration, and perhaps by the inclusion of adjuvants like alum. The

An InsB:8-24 peptide vaccine prevented the onset of T1D in late-stage pre-diabetic NOD mice, but only when formulated in alum. These findings support the use of alum as adjuvant to optimise the efficacy of antigen-specific immunotherapy in future trials.

Starting at 10 weeks of age, female NOD mice received four weekly subcutaneous injections of an insulin B:8-24 (InsB:8-24) peptide with (Ins+alum) or without Imject® alum (Ins) as adjuvant. Diabetes incidence was assessed for up to 30 weeks of age. Insulin autoantibodies and C-peptide concentrations were measured in plasma and flow cytometric analysis was performed on pancreatic-draining lymph nodes (PLN) and pancreas using an InsB:12-20-reactive tetramer.

InsB:8-24 peptide formulated in alum reduced diabetes incidence (39%), compared to mice receiving the InsB:8-24 peptide without alum (71%, P < 0.05), mice receiving alum alone (76%, P < 0.01), or mice left untreated (70%, P < 0.01). This was accompanied by reduced insulitis severity, and preservation of C-peptide. Ins+alum was associated with reduced frequencies of pathogenic effector memory CD4+ and CD8+ T cells in the pancreas and increased frequencies of insulin-reactive FoxP3+ Tregs in the PLN. Of interest, insulin-reactive Tregs were enriched amongst populations of Tregs expressing markers indicative of stable FoxP3 expression and enhanced suppressive function.