FDA Grants Priority Review to Efgartigimod, First Potential Therapy for Seronegative Myasthenia Gravis

The United States (US) Food and Drug Administration (FDA) has accepted argenx’s supplemental Biologics License Application (sBLA) for intravenous efgartigimod alfa-fcab (Vyvgart) for the treatment of adults with acetylcholine receptor antibody (AChR-Ab) seronegative generalized myasthenia gravis (gMG), with a Prescription Drug User Fee Act (PDUFA) target action date of May 10, 2026.¹

“Patients living with seronegative gMG continue to face limited treatment options and there remains a significant need to meaningfully improve their lives. The FDA’s acceptance of our sBLA with Priority Review status reflects the potential of VYVGART to address this need,” Luc Truyen, MD, PhD, Chief Medical Officer, argenx, said in a statement.¹ “This development brings us closer to expanding the use of VYVGART in a broad spectrum of patients with MG. We look forward to continuing our dialogue with the FDA as they review our application.”

Efgartigimod was approved by the FDA in 2021 for people with AChR-Ab seropositive gMG. The therapy is an antibody fragment that binds to the neonatal Fc receptor (FcRn), preventing FcRn from recycling immunoglobulin G (IgG) back into the blood and reducing overall levels of IgG.²

The sBLA acceptance is based off data from the Phase 3 ADAPT SERON study, a randomized, double-blind, placebo-controlled study that included 119 patients across numerous continents randomized to receive 4 once-weekly IV infusions of efgartigimod or placebo, followed by a 5-week follow-up and primary analysis. The study met its primary end point, with efgartigimod leading to statistically significant (P = .0068) impacts on Myasthenia Gravis Activities of Daily Living (MG-ADL) total score after 29 days in Part A of the study.³

"The results of the ADAPT SERON study, the largest study to date of AChR-Ab seronegative gMG, confirm that VYVGART now has the potential to be a targeted, effective, safe, and necessary treatment for patients living with gMG, regardless of autoantibody status," principal investigator James F. Howard, MD, professor of neurology, The University of North Carolina at Chapel Hill School of Medicine, said in a statement.³

The study is continuing in its open-label extension, Part B, in which participants receive 2 fixed cycles of 4 once-weekly efgartigimod infusions, with a 4-week interval between cycles. From cycle 3 onward, additional cycles could be started ≥1 week after the last administration of the previous cycle, based on clinical status. Other end points assessed in the study include Quantitative MG score, Myasthenia Gravis Quality of Life 15-item revised scale, MG.¹

ADAPT SERON enrolled participants with a confirmed MG diagnosis (by an independent panel of experts), and an MG-ADL total score of 5 or greater, who had AChR-Ab seronegative disease, including MuSK-Ab seropositive, LRP4-Ab seropositive, or triple seronegative. Prior to randomization, participants were on a stable dose of at least one gMG treatment, including acetylcholinesterase inhibitors, corticosteroids or nonsteroidal immunosuppressive drugs.¹

"The ADAPT SERON study represents our longstanding commitment to the MG community and our ambition to help all MG patients address this debilitating condition and reach as many MG patients as we can," Truyen said in a statement about the data.³ "The positive outcome of the ADAPT SERON study clearly shows VYVGART’s ability to provide meaningful benefit across all AChR-ab seronegative gMG subtypes."

References

1. argenx Announces FDA Acceptance of Supplemental Biologics License Application with Priority Review for VYVGART in AChR-Ab Seronegative gMG. News release. argenx. January 13, 2026. https://argenx.com/news/2026/press-release-3217457

2. FDA Approves New Treatment for Myasthenia Gravis. News release. FDA. December 17, 2021. https://www.fda.gov/news-events/press-announcements/fda-approves-new-treatment-myasthenia-gravis

3. argenx Announces Positive Topline Results from ADAPT SERON Study of VYVGART in Patients with AChR-Ab Seronegative gMG. Argenx. August 25, 2025. Accessed August 25, 2025. https://argenx.com/news/2024/argenx-announces-positive-topline-results-from-adapt-seron-study