Efgartigimod Gains FDA Approval as First Treatment for Seronegative Forms of Myasthenia Gravis

The FDA has approved a supplemental Biologics License Application (sBLA) for efgartigimod alfa-fcab (Vyvgart; argenx), expanding its indication to include adults with acetylcholine receptor antibody (AChR-Ab) seronegative generalized myasthenia gravis (gMG) who do not have detectable anti-acetylcholine receptor antibodies (AChR-Ab). The approval extends the anti–FcRn therapy beyond its prior use in AChR-Ab–positive patients becoming the first approved treatment for the newly included seronegative population, marking a broader biomarker-independent use of the FcRn inhibitor in gMG.¹

“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,” Luc Truyen, MD, PhD, chief medical officer at argenx, said in a statement.¹ "For clinicians, this simplifies treatment decisions, representing a major advancement in reaching as many patients living with gMG as possible.”

Efgartigimod’s approval stemmed largely from the results of phase 3 ADAPT SERON study (NCT06298552), a randomized, double-blind, placebo-controlled trial that featured 119 patients followed over a 5-week treatment period. The study is the largest study to date of patients with gMG who do not have detectable anti-acetylcholine receptor antibodies (AChR-Ab) across three serotypes. In the study, patients were randomly assigned to receive 4 once-weekly intravenous (IV) infusions of efgartigimod or placebo, with change in Myasthenia Gravis Activities of Daily Living (MG-ADL) as the primary end point, recorded at 29 days.

In the overall population, mean change from baseline in patients treated with efgartigimod was a clinically meaningful 3.35 point improvement in MG-ADL total score at week 4. Improvements in MG-ADL and Quantitative Myasthenia Gravis (QMG) scores were observed across subsequent treatment cycles in the overall population and in all patient subgroups, including MuSK+, LRP4+, and triple seronegative gMG.

Throughout the study, efgartigimod was well-tolerated with a safety profile consistent with the established profile of the treatment in patients with AChR-Ab seropositive gMG and other indications. Above all, no new safety concerns were identified.

“For too long, gMG patients who do not have detectable AChR-Ab have been left behind, feeling disengaged and excluded from receiving treatments that specifically treat their disease, which has led to patients experiencing a higher burden of suffering,” Allison Foss, executive director of the Myasthenia Gravis Association, said in a statement. “This approval validates that gMG patients without AChR-Ab can benefit from a targeted treatment, bringing a sense of hope to thousands in our community.”

As reported previously by NeurologyLive, the FDA first approved the first-in-class investigational antibody fragment for the treatment of gMG in 2021. At the time, the indication was for adults with gMG who test positive for the anti-acetylcholine AChR antibody.²

To date, the agency has granted the therapy both fast track and orphan drug designations. The biologics license application (BLA) submitted to the agency for its original approval was supported by data from the phase 3 ADAPT trial (NCT03669588).³ All told, 167 patients were randomized to an evaluation arm in the ADAPT trial, 84 who were randomized to the efgartigimod group and 83 to the placebo group. Of the full population, 77% (n = 129) were acetylcholine receptor-antibody positive (AChR-Ab+).

REFERENCES
1. Argenx Announces U.S. FDA Approval Expanding VYVGART and VYVGART Hytrulo for Use in All Adult Patients Living with gMG. Argenx. News Release. May 8, 2026. Accessed: May 8, 2026. https://argenx.com/news/2026/press-release-3291372
2. FDA Approves New Treatment for Myasthenia Gravis. News release. FDA. December 17, 2021. Accessed December 17, 2021. https://www.fda.gov/news-events/press-announcements/fda-approves-new-treatment-myasthenia-gravis
3. argenx Announces FDA Acceptance of BLA Filing for Efgartigimod for the Treatment of Generalized Myasthenia Gravis. News release. Argenx. March 2, 2021. Accessed December 17, 2021. https://www.argenx.com/news/argenx-announces-fda-acceptance-bla-filing-efgartigimod-treatment-generalized-myasthenia