Efgartigimod FDA Expansion Bridges Treatment Gap for All gMG Serotypes

For decades, roughly 20% of patients with generalized myasthenia gravis (gMG) — those without detectable anti-acetylcholine receptor antibodies (anti-AChR-Ab). That changed on May 8, 2026, when the FDA expanded the indications for efgartigimod alfa (Vyvgart) and efgartigimod alfa and hyaluronidase-qvfc (Vyvgart Hytrulo) to cover all adult patients with gMG regardless of serotype, including anti-muscle-specific kinase (anti-MuSK) antibody–positive, anti-LRP4 antibody–positive, and triple seronegative patients.

RheumatologyLive sat down with James F. Howard Jr, MD, Distinguished Professor of Neurology (Neuromuscular Disorders), Medicine, and Allied Health at the University of North Carolina at Chapel Hill School of Medicine and director of the Myasthenia Gravis Clinical Trials and Translational Research Unit, to learn more about the historic approval. Howard served as a global lead investigator on the ADAPT SERON trial that supported the approval.

The phase 3, randomized, double-blind, placebo-controlled, multicenter study enrolled 119 adults with anti-AChR-Ab–negative gMG across North America, Europe, China, and the Middle East — the largest dedicated trial in this population conducted to date. Part A randomized participants 1:1 to four once-weekly infusions of efgartigimod IV or placebo, followed by a 5-week observation period. Enrolled patients had confirmed gMG diagnosis by independent expert panel review, a baseline MG-ADL total score of at least 5, and a stable background gMG regimen.

The primary endpoint — change in MG-ADL total score from baseline to day 29 — was met with statistical significance (P = .0068). Patients receiving efgartigimod IV achieved a mean 3.35-point improvement in MG-ADL total score at week 4 across all three seronegative serotypes studied. Clinically meaningful improvements in both MG-ADL and Quantitative Myasthenia Gravis (QMG) scores were observed across subsequent treatment cycles and individual serotypes. Safety was consistent with efgartigimod's established profile from the original ADAPT trial in AChR-Ab–positive gMG, with no new safety signals identified; the most common adverse events included respiratory tract infection, headache, and urinary tract infection.

Howard noted that the response kinetics in ADAPT SERON differed from what was observed in ADAPT and ADAPT+, the pivotal studies in AChR-Ab–positive gMG, with some patients in the seronegative population demonstrating a slower initial response. He emphasized that this should not prompt premature discontinuation.

"While many physicians may give one or two courses of therapy, we urge folks not to abandon the drug — it may take 2 or 3 cycles of therapy before we see a meaningful response," Howard said. "Stick with it for a period of time, and the majority of these individuals will ultimately have a meaningful response."

He acknowledged that the mechanistic explanation for the slower onset in seronegative serotypes remains under investigation, with the predominating pathogenic mechanism at any given time likely contributing to the variable response trajectory.

Efgartigimod blocks the neonatal Fc receptor (FcRn), accelerating IgG catabolism and thereby reducing circulating pathogenic autoantibodies across IgG subtypes — a mechanism that extends logically to non-AChR–mediated gMG even though most early clinical development was concentrated in AChR-Ab–positive disease.

Howard situated the approval within a broader evolution of the FcRn inhibitor class, noting that the field is now actively debating whether to continue targeting disease downstream with rapid-acting agents like FcRn blockers or to shift toward upstream immune modulation for more durable remission.

He expressed confidence that FcRn inhibitors, given their speed of action and manageable adverse event profile relative to conventional immunosuppressants, will be increasingly incorporated into treatment programs across the expanding range of gMG serotypes.

Additional clinical development for efgartigimod is ongoing: the ADAPT OCULUS study has reported positive topline results in ocular MG, and the ADAPT Jr study is enrolling pediatric gMG patients, signaling further label expansion possibilities.

Howard’s disclosures include Alexion/AstraZeneca Rare Disease, Amgen, argenx, Biohaven Ltd, Cartesian Therapeutics, CorEvitas, Curie.Bio, Kyverna Therapeutics, Merck EMD Serono, MGFA, Novartis, Regeneron Pharmaceuticals, Seismic Therapeutics, Toleranzia AB, UCB, and Vor Biopharma.

References

1. argenx. argenx announces U.S. FDA approval expanding Vyvgart and Vyvgart Hytrulo for use in all adult patients living with gMG. Press release. May 8, 2026. https://argenx.com/news/2026/press-release-3291372

2. Nteve G, Dalagiorgou G, Alexopoulos H, Dalakas MC. Efgartigimod for generalized myasthenia gravis and beyond: a narrative review of its pharmacological profile, clinical utility, and expanding applications. Biomedicines. 2025;13(12):2975. doi:10.3390/biomedicines13122975