European immunology company argenx SE (EBR & NASDAQ: ARGX) said on Tuesday that the US Food and Drug Administration has accepted for priority review a supplemental Biologics License Application for VYVGART IV (efgartigimod alfa-fcab) to treat adults with acetylcholine receptor antibody seronegative generalised myasthenia gravis.

The submission is supported by data from the Phase 3 ADAPT SERON trial, which evaluated efficacy and safety in adults with seronegative generalised myasthenia gravis across MuSK-positive, LRP4-positive and triple seronegative subtypes. The study met its primary endpoint, showing a statistically significant improvement in Myasthenia Gravis Activities of Daily Living total score versus placebo at four weeks (p=0.0068).

Patients treated with VYVGART achieved a mean 3.35-point improvement in the MG-ADL score at week four, with improvements in MG-ADL and Quantitative Myasthenia Gravis scores observed across subsequent treatment cycles and all subgroups. VYVGART was well tolerated, with a safety profile consistent with its established use in acetylcholine receptor antibody seropositive generalised myasthenia gravis. No new safety concerns were identified.

The application carries a Prescription Drug User Fee Act target action date of 10 May 2026.