Possible therapeutic vaccines for canine myasthenia gravis: implications for the human disease and associated fatigue

Abstract

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.

Figures

Figure 1

Time course of AChR Ab levels in myasthenic dogs showing a monophasic decline (A, n=40) or fluctuating AChR Ab titers (B, n=7). Each line represents an individual animal and month 0 refers to the time of confirmed diagnosis.

Figure 2

A: Effect of T and B cell ARM vaccines on AChR Ab levels (mean ± SEM) in vaccinated dogs with canine MG (n=5) as compared to nonvaccinated historical controls (n=40) showing a monophasic decline in AChR Ab titers. The horizontal line represents the upper limit (

Figure 3

Time course of AChR Ab levels in myasthenic nonvaccinated historical control dogs (A, n=7) as compared to vaccinated myasthenic dogs (B, n=5). Each line represents an individual animal and month 0 is the time of confirmed diagnosis. C: Mean time (month ± SEM) to first remission and long-term remission for myasthenic nonvaccinated historical control and vaccinated dogs from A and B, respectively. First remission refers to the first time post confirmed diagnosis that an animal had a transient or sustained level of AChR Ab below 0.6 nM. Long-term remission refers to the time post confirmed diagnosis that an animal had a sustained level of AChR Ab below 0.6 nM. *, p=0.04. D: The effect of T and B cell ARM vaccines on the mean number of episodes (± SEM) of transient remissions per dog in vaccinated myasthenic animals (n=5) compared to nonvaccinated historical controls (n=7). An episode of transient remission refers to a transient level of AChR Ab below 0.6 nM at any 3 month interval after confirmed diagnosis and before long-term remission (i.e., sustained AChR Ab levels below 0.6 nM). The mean number of episodes/dog is calculated from the total number of episodes for all dogs in a group divided by the total number of dogs/group. *, p

Figure 4

A: Correlation between the time relative to confirmed diagnosis (0 time) of the administration of a particular dose of T and/or B cell ARM vaccine and the first transient remission postdiagnosis. Remission refers to the first measurement of a transient AChR Ab level below 0.6 nM. B: Correlation between AChR Ab levels (nM ± SEM) in blood samples drawn immediately before administration of a dose of T and/or B cell ARM vaccine with the AChR Ab level at the first sampling thereafter (2 to 4 weeks).

Figure 5

A: Comparison of the mean time (month ± SEM) to remission post confirmed diagnosis for myasthenic dogs immunized with sequential doses of T and B cell ARM vaccines (T → B) (n=7) or combined doses (T + B) of the two vaccines (n=3). Remission refers to the first transient or sustained AChR Ab level below 0.6 nM. B: Comparison of the mean time (month ± SEM) to remission per dose of vaccine administered for myasthenic dogs immunized with sequential doses of T and B ARM vaccines (T → B) or combined doses (T + B) of the two vaccines. Remission refers to the first transient or sustained AChR Ab level below 0.6 nM. *, p=0.0167.