Myasthenia gravis (MG) is caused by T cell-dependent antibodies reactive with acetylcholine receptors. These autoreactive antibodies cause muscle weakness by interfering with neuromuscular transmission via removal of acetylcholine receptors from the neuromuscular junction as well as changing the architecture of the junction itself. Consequently, muscle fatigue is a debilitating aspect of MG often leading to more general feelings of tiredness not directly due to muscle weakness. We have previously described two peptides that are mimetics of antigen receptors on certain autoreactive T and B cells that are involved in MG. When used as vaccines in the rat model of MG, these peptides prevented and ameliorated disease and muscle fatigue by blunting acetylcholine receptor antibody responses. Such disease protection resulted from vaccine-induced anergizing antibodies against acetylcholine receptor-specific T and B cell antigen receptors. The present study prospectively evaluated the efficacy of these two vaccines in spontaneous acquired MG in pet dogs. When compared to historical controls that were prospectively studied, the vaccines increased the proportion of remitted dogs from 17 to 75%. In comparison to retrospectively studied historical controls that spontaneously remitted from MG, the vaccines accelerated the rate of decline in acetylcholine receptor antibody titers which resulted in a 3-fold decrease in the mean time to remission. These results are suggestive of a new type of targeted therapy that can drive autoimmune responses into long-term remission and possibly afford a means of determining whether correction of a physical cause of muscle weakness also corrects the perception of chronic, generalized fatigue. © 2006 Elsevier Inc. All rights reserved.