Antigen-specific apheresis of human anti-acetylcholine receptor autoantibodies from myasthenia gravis patients' sera using Escherichia coli-expressed receptor domains

Myasthenia gravis (MG) is an autoimmune disease usually caused by autoantibodies against the muscle nicotinic acetylcholine receptor (nAChR), found at the neuromuscular junction. Current treatments for the disease, including plasmapheresis, are not antigen-specific, and thus often cause severe side effects. The development and implementation of new therapeutic approaches for the disease attain particular importance, since the number of diagnosed myasthenic patients has increased considerably. In order to develop an antigen-specific approach for the selective depletion of anti-nAChR autoantibodies from MG patients' sera, we have expressed the extracellular domains (ECDs) of all human muscle nAChR subunits in E. coli. These recombinant proteins were immobilized on CNBr-Sepharose and used in immunoadsorption assays with MG sera. We showed that, despite being purified from E. coli under denaturing conditions, these recombinant ECDs could be successfully used as immunoadsorbents with a comparable efficiency to the corresponding ECDs produced in water-soluble form in the yeast Pichia pastoris. The high yield of the ECDs, the stability of the constructed ECD resins and the high selectivity for anti-nAChR antibodies increase the therapeutic potential of the system.