Antigen‐specific Apheresis of Pathogenic Autoantibodies from Myasthenia Gravis Sera

Abstract

Myasthenia gravis (MG) is usually caused by autoantibodies against muscle nicotinic acetylcholine receptor (AChR), which is composed of five subunits (alpha(2)betagammadelta or alpha(2)betaepsilondelta). Current treatments, including plasmapheresis, are nonspecific, causing several side effects. We aim to develop an antigen-specific alternative to plasmapheresis, since the latter removes indispensable plasma components in addition to anti-AChR antibodies. We are developing a method for the selective depletion of the anti-AChR autoantibodies from patients' plasma through the construction of "immunoadsorbent" columns carrying AChR domains. We have expressed the extracellular domains (ECDs, amino acids approximately 1-210/220) of all human muscle AChR subunits in Pichia pastoris and, in preliminary experiments, in E. coli. The ECDs were immobilized (individually or mixed) on Sepharose beads, producing Sepharose-ECD columns, which were tested for their immunoadsorbing capacity on MG sera and shown to specifically eliminate major autoantibody fractions from several MG sera. The immobilized ECDs remained stable and did not dissociate from their matrix after incubation with serum, whereas the procedure was neither toxic nor immunogenic in two experimental rabbits. Testing the intact or antibody-depleted MG sera and the affinity purified autoantibodies showed that both the intact sera and the purified autoantibodies, but not the antibody-depleted sera, could induce AChR loss in cell cultures and experimental MG in rats. This preliminary study suggests that the myasthenic potency of MG sera is entirely due to their anti-AChR antibodies and therefore their depletion should be of therapeutic value. We conclude that ECD-mediated immunoadsorption can be used as an efficient, antigen-specific therapy for MG.

Expression of extracellular domains of muscle specific kinase (MuSK) and use as immunoadsorbents for the development of an antigen-specific therapy

“…In this report, we are applying our extensive expertise on AChRimmunoadsorption for the development of a specific extracorporeal treatment (Psaridi-Linardaki et al, 2005;Tzartos et al, 2008;Zisimopoulou et al, 2008a;Zisimopoulou et al, 2008b;Lazaridis et al, 2012) in order to follow a similar approach for MuSK-MG. Specifically, we aimed to deplete MuSK antibodies from patients' sera using the immobilized MuSK-ECDs as immunoadsorbents.…”

Acute Myocarditis – A Trigger of Cardiac Autoimmunity? Expected Insights from the Etiology, Titre-Course, and Effect on Survival of Cardiac Autoantibodies (ETiCS) Study

“…Their relevance in human heart disease and failure, however, still need to be substantiated Fu, M., 2008) although preliminary clinical data suggest that the presence of certain cardiac aabs clearly worsens the prognosis of patients with idiopathic DCM (Störk et al, 2006). Therapeutic strategies known from other autoimmune disorders, such as application of peptide-ligands (for multiple sclerosis (Warren et al, 2006)) or immunoadsorption of disease-causing aabs (for myasthenia gravis (Tzartos et al, 2008)) might thus also offer treatment options for a variety of human cardiac disorders. In this regard, recent in vitro experiments with functionally active receptor-aabs isolated from a smaller number of DCM-patients indicate, that aab-induced adrenoceptor activation might be abrogated by incubation with epitope-mimicking peptides (Nikolaev et al, 2007;Jahns et al 2010).…”

Development of novel therapies for MG: Studies in animal models

“…Such a removal is achieved by "immunoadsorbent" columns consisting of the ECDs of all human muscle AChR subunits. They showed that the antibody-depleted sera lost the ability to passively induce EAMG in rats suggesting that ECD-mediated immunoadsorption could be used as an efficient, antigen-specific treatment for MG [49].…”