Aims: Immunomodulation with autoantigens potentially constitutes a specific and safe treatment for type 1 diabetes (T1D). Studies with GAD-alum administrated subcutaneously have shown to be safe, but its efficacy has been inconclusive. Administration of GAD-alum into the lymph nodes, aimed to optimise antigen presentation, has shown promising results in an open-label clinical trial. Herein, we compared the immune response of the individuals included in the trial with a group who received GAD-alum subcutaneously in a previous study.

Materials and methods: Samples from T1D individuals collected 15 months after administration of either three doses 1 month apart of 4 mu g GAD-alum into lymph nodes (LN, n = 12) or two doses 1 month apart of 20 mu g subcutaneously (SC, n = 12) were studied. GADA, GADA subclasses, GAD(65)-induced cytokines, peripheral blood mononuclear cell proliferation, and T cells markers were analysed.

Results: Low doses of GAD-alum into the lymph nodes induced higher GADA levels than higher doses administrated subcutaneously. Immune response in the LN group was characterised by changes in GADA subclasses, with a relative reduction of IgG1 and enhanced IgG2, IgG3, and IgG4 proportion, higher GAD(65)-induced secretion of IL-5, IL-10, and TNF-alpha, and reduction of cell proliferation and CD8(+) T cells. These changes were not observed after subcutaneous (SC) injections of GAD-alum.

Conclusions: GAD-specific immune responses 15 months after lymph node injections of GAD-alum differed from the ones induced by SC administration of the same autoantigen.