GM-CSF administered before immunization exerted a sustained suppressive effect against the induction of myasthenia gravis (MG). This suppression was associated with lowered serum autoantibody levels, reduced T cell proliferative responses to AChR, and an expansion in the population of FoxP3+ regulatory T cells. Manipulating DCs to expand regulatory T cells is useful for the control of autoimmune diseases such as myasthenia gravis MG.