Patients with myasthenia gravis, a debilitating autoimmune disorder that causes loss of muscle function, have a new class of treatment to tackle their disease. Meanwhile, the green light sets the stage for the therapy’s developer, argenx, to make its commercial debut.
The FDA on Friday approved argenx’s Vyvgart, also known as efgartigimod, for adults with generalized myasthenia gravis (gMG) who test positive for the anti-acetylcholine receptor (AChR) antibody. The approval provides the first validation for a drug in the FcRn inhibitor class.
Argenx's Vyvgart is an antibody fragment designed to bind to neonatal Fc receptor (FcRn), driving down levels of antibodies implicated in multiple autoimmune diseases.
Some 65,000 people in the U.S. suffer from myasthenia gravis, and about 85% of those patients have the generalized form of the disease, meaning it affects multiple organ groups throughout the body, Tim Van Hauwermeiren, chief executive officer of argenx, said in an interview.
As with many autoimmune diseases, the current slate of treatment options is "sub-optimal," Van Hauwermeiren said. There's surgery: patients can have their thymus removed. Then there are the "unavoidable" high dose steroids, which patients hate with a passion, he added. There's chemotherapy to shut down a patient's immune system and, as a last resort, plasma exchange, Van Hauwermeiren explained.
The disease is caused by an autoantibody of the immunoglobulin G (IgG) type, which, for reasons that are largely unknown, attacks what is known as the neuromuscular junction. The autoantibody essentially "interferes" with the signal transmission between the nerves and the muscle cells. This prevents muscle cells from contracting, which leads to the weakness that characterizes the disease, Van Hauwermeiren said.
Up until Vyvgart's approval, doctors had to rely on the "sledgehammer" of surgery, steroids and chemotherapy to treat gMG, he said. With Vyvgart, however, physicians now have a "scalpel" to precisely remove the autoantibody of concern, according to the CEO.
Beyond gMG, argenx sees plenty of potential for the drug in various other autoimmune diseases. There are more than 100 IgG-mediated autoimmune diseases, and all of them can be addressed with an FcRn antagonist, he said.
Meanwhile, in gMG, argenx is "launch ready," Van Hauwermeiren said.
"We did everything we had to do," he noted. "If we were to get approval on December 17th, we can launch the day after," he told Fierce Pharma earlier this month.
The company's U.S. organization boasts about 250 employees, 146 of which are customer facing, including 70 sales reps, Van Hauwermeiren said. On the coverage side, argenx's market access team has now had multiple meetings with "most" of the U.S. national payers, plus regional payers. To get the word out, argenx thinks it needs to reach about 7,700 neurologists, Van Hauwermeiren added.
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The drug won approval thanks to data from the phase 3 Adapt trial. Earlier this year, the company reported that 67.7% of acetylcholine receptor (AChR)-antibody positive patients in the treatment arm met the criteria for a response to the drug, compared to 29.7% of people in the placebo cohort. The med also outperformed placebo in a clutch of secondary endpoints.
While argenx started development of the drug in three indications—MG, immune thrombocytopenia and pemphigus vulgaris—it's now running studies in six and the goal is to move into 15 indications by 2025, Van Hauwermeiren said.