GAD-specific T cells are induced by GAD-alum treatment in Type-1 diabetes patients

Mikael Pihl, Hugo Barcenilla, Stina Axelsson, Mikael Chéramy, Linda Åkerman, Ingela Johansson, Johnny Ludvigsson, Rosaura Casas

Administration of Glutamic Acid Decarboxylase (GAD)65 formulated in aluminium hydroxide preserved insulin secretion in a phase II trial in recent onset Type 1 Diabetes. A subsequent European phase III trial was closed at 15months after failing to reach primary endpoint, but the majority of the Swedish patients completed the 21months follow-up. We studied the frequencies and phenotype of T cells, suppressive capacity of Tregs, GAD65-induced proliferation, and frequencies of T cells with a GAD65-specific TCR in Swedes participating in the trial. Stimulation with GAD65 induced activated T cells and also cells with a suppressive phenotype. Activated GAD65-specific effector T cells were detected by tetramer staining while the frequency of GAD65-specific Treg was not affected by the treatment. Additional doses of GAD-alum increased frequencies of CD25(+)CD127(+), but had no effect on CD25(hi)CD127(lo). Our findings indicate that GAD-alum treatment primarily induced activated T cells. GAD65-specific cells were mainly of activated phenotype.