argenx Reports Positive Phase 3 Results for Vyvgart in Seronegative gMG

argenx Reports Positive Phase 3 Results for Vyvgart in Seronegative gMG

By, Admin 27 August 2025

argenx SE, a global immunology company, announced positive topline results from the pivotal ADAPT SERON study of Vyvgart (efgartigimod alfa-fcab, IV).

The phase 3 trial met its primary endpoint (p=0.0068). Patients with acetylcholine receptor antibody–negative (AChR-Ab seronegative) generalized myasthenia gravis (gMG) showed statistically significant and clinically meaningful improvement in MG-ADL total score versus placebo.

Regulatory Pathway Ahead

Based on these findings, argenx plans to file a supplemental Biologics License Application (sBLA) with the FDA.

  • Goal: expand Vyvgart’s label to adult AChR-Ab seronegative gMG patients across all three subtypes—MuSK+, LRP4+, and triple seronegative.
  • Detailed trial data will be shared at an upcoming medical meeting.

Safety Profile

Vyvgart was well tolerated across AChR-Ab seronegative subtypes.

  • Safety results were consistent with previous studies in AChR-Ab seropositive gMG and other indications.
  • No new safety concerns were reported.

Expert Commentary

“The ADAPT SERON study, the largest in AChR-Ab seronegative gMG, confirms Vyvgart’s potential as a targeted, safe, and effective therapy,”

  • Dr. James F. Howard Jr., principal investigator, University of North Carolina.

“These data show pathogenic IgGs drive gMG across patient subtypes. This is a critical step for patients with limited treatment options,” he added.

argenx CMO Dr. Luc Truyen noted: “This study underscores our commitment to the MG community. We aim to reach all patients living with this debilitating condition.”

Study Design

  • Type: Randomized, double-blind, placebo-controlled, multi-center.
  • Participants: 119 adults with confirmed seronegative gMG, across North America, Europe, China, and the Middle East.
  • Part A: Patients received 4 once-weekly infusions of Vyvgart or placebo, followed by a 5-week follow-up.
  • Part B: Open-label extension. Patients received 2 fixed treatment cycles, then additional cycles as needed.
  • Primary Endpoint: MG-ADL total score change from baseline to day 29.

Participants were required to have:

  • MG-ADL score ≥5 at baseline.
  • A confirmed gMG diagnosis by an independent panel.
  • Stable dosing of at least one gMG therapy, including acetylcholinesterase inhibitors, corticosteroids, or nonsteroidal immunosuppressants.

Disease Context

gMG is a rare autoimmune neuromuscular disease. Pathogenic IgGs disrupt neuromuscular transmission, leading to muscle weakness and fatigue.

  • 80% of patients are AChR-Ab seropositive.
  • ~20% are seronegative, including:
    - MuSK-Ab positive (1–10%).
    - LRP4-Ab positive (1–5%).
    - Triple seronegative (~10%), historically excluded from trials and facing higher disease burden.
  • Currently, no approved therapies exist for LRP4+ or triple seronegative patients.

About Vyvgart

Vyvgart is a human IgG1 antibody fragment that binds the neonatal Fc receptor (FcRn), lowering circulating IgG autoantibodies.

  • First approved FcRn blocker in the US, EU, China, and Canada for AChR-Ab positive gMG.
  • Approved in Japan for adults with gMG unresponsive to steroids or immunosuppressants.

About argenx

argenx is a global immunology company developing antibody-based medicines for severe autoimmune diseases. Its Immunology Innovation Program (IIP) connects academic research with drug development to build a world-class portfolio.

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