Type 1 diabetes results from autoimmune destruction of insulin producing pancreatic β-cells. We have shown that treatment with alum-formulated glutamic acid decarboxylase 65 (GAD-alum) preserved residual insulin secretion and induced antigen-specific responses in children with recent onset type 1 diabetes. The aim of this study was to further investigate the immunomodulatory effect of GAD-alum, focusing on CD4⁺CD25^high cells and their association to cytokine secretion. Samples obtained 21 and 30 months after the initial injection of GAD-alum or placebo were included in the present study. GAD₆₅-stimulation enhanced the percentage of CD4⁺CD25^highFOXP3⁺ cells, but reduced the percentage of CD4⁺CD25⁺ cells, in samples from the GAD-alum treated group. Further, the GAD₆₅-induced secretion of IL-5, -10, and -13 correlated with the expression of CD4⁺CD25^highFOXP3⁺ cells, but inversely with CD4⁺CD25⁺ cells. These new data suggest that GAD-alum treatment induced GAD₆₅-specific T cells with regulatory features.