FDA Expands argenx's VYVGART to All Adult Myasthenia Gravis Serotypes, Reaching Seronegative Patients for the First Time
The May 8 sBLA approval extends efgartigimod's label to MuSK, LRP4 and triple-seronegative gMG patients after the 119-patient ADAPT SERON trial hit its MG-ADL endpoint with a 3.35-point improvement at week 4 (p=0.0068).
Overview
The U.S. Food and Drug Administration on May 8, 2026 approved a label expansion for argenx’s VYVGART (efgartigimod alfa-fcab) and VYVGART Hytrulo (efgartigimod alfa and hyaluronidase-qvfc), extending the antibody therapy to all adult patients living with generalized myasthenia gravis (gMG) regardless of antibody serotype, argenx announced. The decision, granted via a supplemental Biologics License Application, covers anti-AChR-Ab positive, anti-MuSK-Ab positive, anti-LRP4-Ab positive, and triple seronegative patients, the company said.
What We Know
The approval rests on the Phase 3 ADAPT SERON study, a randomized, double-blind, placebo-controlled, multi-center trial that enrolled 119 adults with anti-AChR antibody negative gMG across North America, Europe, China, and the Middle East, according to argenx’s press release. RTTNews described ADAPT SERON as “the largest to date in antibody-negative gMG”.
The primary endpoint was the change in Myasthenia Gravis Activities of Daily Living (MG-ADL) total score from baseline to week 4. Patients on VYVGART achieved a mean 3.35-point improvement at week 4 with a p-value of 0.0068, argenx reported. The trial showed improvements consistent across each of the three antibody-negative serotypes studied.
Approximately 20% of people with gMG are seronegative for AChR antibodies, the Muscular Dystrophy Association noted in welcoming the decision. That subgroup has historically been excluded from gMG trials. Tahseen Mozaffar, MD, Director of the UCI Health ALS & Neuromuscular Center, said in an MDA statement that “Patients with seronegative generalized myasthenia gravis have historically had limited treatment options, and many clinical trials have excluded them.”
Luc Truyen, M.D., Ph.D., Chief Medical Officer at argenx, said in the company announcement that “Today’s approval means that all adult gMG patients, regardless of serotype, can now benefit from VYVGART’s rapid onset, sustained disease control, and favorable safety profile.” James F. Howard Jr., M.D., Professor of Neurology (Neuromuscular Disease), Medicine and Allied Health, Department of Neurology, The University of North Carolina at Chapel Hill School of Medicine, added that “The expanded indication of efgartigimod for use in all adult gMG patients enables healthcare providers to prescribe this targeted treatment more readily upon clinical diagnosis.”
Angela Lek, PhD, Chief Research Officer at the Muscular Dystrophy Association, called the decision meaningful progress for the seronegative community, saying that “People living with seronegative generalized myasthenia gravis often face a longer, more complicated journey to diagnosis and treatment.”
Commercial Context
VYVGART was first approved by the FDA in December 2021 for adult AChR-Ab positive gMG, and VYVGART Hytrulo, the subcutaneous formulation, was cleared on June 20, 2023, according to RTTNews. The franchise generated $4.2 billion in full-year 2025 sales, with Q1 2026 global net sales of $1.3 billion versus $0.8 billion a year earlier, RTTNews reported. Argenx shares closed at $782.17 on May 8, 2026, and traded at $802.18 in pre-market following the announcement, per RTTNews.
What We Don’t Know
The published materials do not disclose adverse event rates from ADAPT SERON, long-term durability beyond the initial treatment cycle, or how payors will adjust reimbursement now that the indication covers patients without a confirmed autoantibody. argenx has not detailed how the approval will affect ongoing efgartigimod programs in other autoimmune indications.