A blockbuster Argenx therapy now has an additional FDA approval as a treatment for a rare autoimmune disorder affecting nerves, marking the first new treatment for this condition in decades and a new blockbuster opportunity for this pipeline-in-a-product drug.
The disease, chronic inflammatory demyelinating polyneuropathy, or CIDP, develops as the immune system attacks myelin, the protective covering of nerve fibers. CIDP leads to weakness and impairment of motor function, numbness and tingling, and difficulty walking. In many cases, the loss of muscle function requires patients to rely on a wheelchair for mobility. The FDA’s late Friday approval of the Argenx product, Vyvgart Hytrulo, covers the treatment of adults diagnosed with CIDP.
Standard CIDP treatment is intravenous immunoglobulin, an infusion of antibodies sourced from the blood of human donors. This treatment is intended to modulate the immune response. Plasma exchange, a procedure in which harmful antibodies are removed from the blood, is also used to treat CIDP. Both procedures are invasive and must be done in a clinical setting. Corticosteroids may also be used to treat the condition, but chronic use of such anti-inflammatory agents comes with a wide range of complication risks. These currently available treatments do not work for all CIDP patients.
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With Vyvgart Hytrulo, Amsterdam-based Argenx aims to reduce levels of immunoglobulin G autoantibodies thought to be important in the progression of CIDP, Jeff Guptill, Argenx’s neuromuscular franchise lead, clinical development, explained during a briefing with journalists in advance of Friday’s regulatory decision. The drug is an antibody fragment designed to bind to the neonatal Fc receptor (FcRn), which is responsible for initiating the recycling of antibodies in the body, including autoantibodies that drive immune disorders. A recycled antibody stays in the blood’s circulation. Blocking antibodies from binding to FcRn means antibodies will instead go to cellular systems that degrade proteins.
“If we can remove these autoantibodies from circulation, this prevents them from damaging the nerves,” Guptill said.
The antibody fragment, efgartigimod (brand name Vyvgart), was initially developed as an intravenous infusion. Vyvgart was first approved in 2021 as a treatment for generalized myasthenia gravis, a rare disease in which autoantibodies interfere with communication between nerves and muscles. Vyvgart Hytrulo is a subcutaneously injectable version of the drug that pairs efgartigimod with an engineered enzyme from Halozyme that enables delivery of biologic drugs as injections. Vyvgart Hytrulo was approved for generalized myasthenia gravis a year ago.
The new approval of Vyvgart Hytrulo is based on the results of a placebo-controlled Phase 2 study that enrolled 322 adults, spanning those patients who have previously received a CIDP treatment as well as treatment-naïve patients. The main goal was to score patients according to a 10-point rating scale used to measure arm and leg function — the higher the score, the greater the impairment. Guptill said a one or two point change on this scale is clinically meaningful for a patient’s ability to move.
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“Going from a walker to using a simple cane, that’s a big improvement in how someone functions,” he said.
The trial results showed 69% of patients treated with the study drug demonstrated evidence of clinical improvement in measures of mobility, function, and strength. Vyvgart Hytrulo also demonstrated a 61% reduction in the risk of relapse versus a placebo. The most commonly reported side effects were respiratory tract infections, headaches, urinary tract infections, and injection site reactions.
Argenx pegs the U.S. population of CIDP patients at about 41,000. Of the approximately 24,000 CIDP-treated patients in the U.S., the company estimates 12,000 are not well-managed by currently available therapies. While Vyvgart Hytrulo’s expanded label does not restrict the drug’s use to CIDP patients who have not responded to earlier therapies, Argenx said its initial focus in the new indication will be on patients who need a different choice due to the treatment burden, lack of efficacy, or poor tolerability of currently available therapies. The company estimates the net price per CIDP patient will be $450,000 annually, which is in line with the drug’s price in generalized myasthenia gravis.
In an investor presentation, Argenx said commercialization in the new indication will initially focus on the 10,000 neurologists who share a 72% overlap in prescribing for both generalized myasthenia gravis and CIDP. Regulatory submissions of subcutaneously injected efgartigimod for CIDP are still under review in Japan and Europe. Zai Lab holds rights to the therapy in China, where a submission is also under review.
Efgartigimod, in all of its formulations, is Argenx’s only commercialized product. The company reported nearly $1.2 billion in product sales in 2023, up 197% from the prior year. In a note sent to investors on Monday, William Blair analysts Myles Minter and Matt Phipps described the product’s new approval as a “best-case scenario” for the company, avoiding potential label restrictions that could limit uptake of the drug. The new approval in CIDP represents another $1 billion-plus peak sales market opportunity in the U.S. alone, they said.
Argenx is not the only company pursuing CIDP and other indications with an FcRn inhibitor. UCB antibody drug Rystiggo, which won FDA-approval last June in generalized myasthenia gravis, failed a mid-stage CIDP test but is still in clinical development in several neurological indications. Argenx has touted its drug’s potential to address a wide range of autoimmune disorders. The next one could be Sjogren’s syndrome, a disease in which the immune system attacks moisture-producing glands in the eyes and mouth. A Phase 2 test is evaluating intravenous efgartigimod in Sjogren’s. William Blair expects an update on that program during Argenx’s R&D day, scheduled for July 16. The analysts are looking for data to show how the Argenx drug compares with nipocalimab, an FcRn-targeting antibody that Johnson & Johnson gained as part of a $6.5 billion acquisition. J&J’s pipeline lists nine different clinical programs for nipocalimab, including late-stage studies in both CIDP and generalized myasthenia gravis.
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