The US Food and Drug administration has approved a new drug to treat the autoimmune condition myasthenia gravis. Vyvgart (efgartigimod alfa-fcab) is a human IgG1 antibody fragment developed by argenx, a global biotech headquartered in the Netherlands. The myasthenia gravis treatment is designed to reduce the pathogenic circulating antibodies that drive the disease. It does so by blocking the neonatal Fc receptor (FcRn) and is the first agent to tackle this pathway. In myasthenia gravis, antibodies against the acetylcholine receptor (AChR) bind to the postsynaptic membrane at the neuromuscular junction. This causes fluctuating muscle weakness — ocular, bulbar, limb and respiratory — as the main clinical manifestations of the disease. Argenx’s Vyvgart blocks FcRn, involved in rescuing IgG antibodies from degradation, an intervention that lowers pathogenic antibodies in plasma.
In the phase 3 ADAPT trial, 68% of patients with generalized myasthenia gravis who were positive for antibodies to AChR responded when treated with Vyvgart, as measured on the Myasthenia Gravis Activities of Daily Living (MG-ADL) score, compared with 30% of patients on placebo. The first reports from this trial were published in July 2021. The drug is indicated for adult patients with generalized myasthenia gravis who are AChR antibody positive (85% of the patient population). Brussels-based UCB is also developing an FcRn-targeting treatment for myasthenia gravis; its antibody rozanolixizumab is in phase 3 trials. The company revealed in October that, in a phase 3 study testing the antibody in adults with generalized myasthenia gravis, the trial met its primary endpoint. Soliris (eculizumab), developed by Alexion, was the first approved myasthenia gravis drug in US and European Union markets. This monoclonal antibody targets the C5 complement cascade and has been available since 2017 for patients with AChR antibodies. Standard treatments for myasthenia gravis involve anticholinesterase agents, thymectomy and immunosuppression.
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