CD8+ regulatory T cells are responsible for GAD-IgG gene-transferred tolerance induction in NOD mice

Our previous studies demonstrated that lipopolysaccharide (LPS)-stimulated splenocytes, retrovirally transduced with a glutamate decarboxylate 65 (GAD) and immunoglobulin G (IgG) fusion construct, can protect non-obese diabetic (NOD) mice from diabetes by inducing GAD-specific tolerance, and also that there are increased numbers of CD4(+) regulatory T cells (Tregs) in GAD-IgG-treated NOD mice. However, little is known about the role of CD8(+) Tregs in GAD-IgG gene-transferred tolerance induction in NOD mice. Here, we found that GAD-IgG-transduced splenocytes induced an increase in the number of CD8(+) Foxp3(+) Tregs in vitro. Using a T-cell depletion assay, we found that, compared with undepleted groups, NOD recipients transfused with CD8(-) or CD8(-) CD25(-) GAD-IgG-transduced splenocytes showed a decrease in the percentage of CD8(+) Foxp3(+) T cells, a high incidence of diabetes, serious insulitis, GAD-specific hyperresponsiveness at both the cellular and humoral levels, and changes in cytokine expression. These results indicate that CD8(+) Tregs, which were induced in vitro by GAD-IgG-transduced splenocytes, were also responsible for GAD-IgG gene-transferred tolerance induction in NOD mice.