argenx Gains FDA Priority Review for VYVGART in Seronegative gMG with May 2026 Decision
argenx received FDA Priority Review for its supplemental Biologics License Application for VYVGART in AChR-Ab seronegative generalized myasthenia gravis, with a PDUFA target action date of May 10, 2026. The Phase III ADAPT SERON trial met the primary endpoint (p=0.0068) with a 3.35-point MG-ADL improvement and no new safety concerns.
1. FDA Accepts sBLA for VYVGART in AChR-Ab Seronegative gMG
On January 13, 2026, argenx announced that the U.S. Food and Drug Administration has accepted for Priority Review its supplemental Biologics License Application for VYVGART (efgartigimod alfa-fcab) in adults with acetylcholine receptor antibody seronegative generalized myasthenia gravis. The FDA has assigned a Prescription Drug User Fee Act target action date of May 10, 2026. This designation underscores the agency’s recognition of the significant unmet need for effective therapies in the approximately 20% of gMG patients without detectable anti-AChR antibodies.
2. Phase 3 ADAPT SERON Study Demonstrates Statistically Significant Efficacy
The sBLA submission was supported by data from the multinational ADAPT SERON trial, which enrolled 119 AChR-Ab seronegative gMG patients across North America, Europe, China and the Middle East. In the randomized, double-blind Part A, four once-weekly infusions of VYVGART achieved a mean improvement of 3.35 points in Myasthenia Gravis Activities of Daily Living (MG-ADL) total score at Week 4 versus placebo (p=0.0068). Benefits were maintained across MuSK-positive, LRP4-positive and triple seronegative subgroups, with consistent improvements in Quantitative Myasthenia Gravis scores over subsequent cycles.
3. Well-Characterized Safety Profile and Extension Phase Underway
VYVGART was generally well tolerated, exhibiting a safety profile in seronegative patients consistent with prior studies in AChR-Ab seropositive populations. No new safety signals emerged. Part B of ADAPT SERON is now in an open-label extension phase, offering up to two fixed cycles of four weekly infusions followed by additional cycles based on clinical response. This design will provide longer-term safety and durability data ahead of the PDUFA decision.
4. Potential to Expand Treatment Paradigm for Refractory gMG
If approved, VYVGART would become the first therapy indicated for seronegative gMG, addressing a high-burden segment historically excluded from clinical trials. argenx forecasts that this label extension could significantly broaden patient access, complementing its existing indication in AChR-Ab seropositive gMG and reinforcing its position in the FcRn inhibition class. The company plans to finalize commercial readiness activities in anticipation of a positive FDA decision in May 2026.