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

• We expressed two different recombinant MuSK-ECDs and tested them as immunoadsorbents.
• MuSK-ECD immunoadsorbents remove almost all MuSK antibodies from patients' sera.
• The immunoadsorption procedure has no toxic effect in immunized rabbits.
• Passive transfer of purified MuSK antibodies in mice affect the NMJs of diaphragms.

Antibodies against MuSK seem to be the pathogenic factor in approximately 5–8% of myasthenia gravis (MG) patients. We aim to develop an antigen-specific therapy in which only MuSK antibodies will be removed from patients' plasma using MuSK extracellular domain (MuSK-ECD) as immunoadsorbent. We showed that two different immunoadsorbents, very efficiently and selectively depleted the MuSK antibodies from all tested sera, were stable during the procedure and were reusable. Furthermore, animal experiments showed that the treatment has no toxic effects to the animals. We conclude that the MuSK-ECD-mediated immunoadsorption can be used as an efficient antigen-specific therapy for MuSK-MG.