Efgartigimod Shows Sustained Efficacy in Myasthenia Gravis Subtypes

Intravenous efgartigimod (Vyvgart) continued to demonstrate efficacy and safety in patients with generalized myasthenia gravis who did not have detectable anti-acetylcholine receptor (AChR) antibodies, data from the open-label period of the ADAPT SERON trial showed.

Patients maintained a mean improvement of approximately 5 points in Myasthenia Gravis Activities of Daily Living (MG-ADL) scores through week 52, reported James Howard, MD, of the University of North Carolina at Chapel Hill, at the 2026 American Association of Neuromuscular and Electrodiagnostic Medicine in Orlando. MG-ADL scores can range from 0-24, with higher values indicating more impairment.

The safety profile in the 1-year period aligned with data from previous efgartigimod trials, with no new or unexpected safety concerns, he added.

Efgartigimod is a human immunoglobulin G1 (IgG1) antibody fragment that binds to the neonatal Fc receptor (FcRn), leading to a reduction in circulating IgG autoantibodies. In 2021, it was approved to treat generalized myasthenia gravis with anti-AChR antibodies.

Approximately 20% of patients with generalized myasthenia gravis do not have detectable serum antibodies directed against AChR. Some of these patients have autoantibodies targeting other neuromuscular junction proteins including muscle-specific tyrosine kinase (MuSK), low-density lipoprotein receptor-related protein 4 (LRP4), or others.

Approximately 1% to 10% of myasthenia gravis patients have anti-MuSK antibodies and 1% to 5% have anti-LRP4 antibodies. About 10% of patients are considered triple negative and do not have any detectable autoantibodies against AChR, MuSK, or LRP4.

In the double-blind placebo-controlled ADAPT SERON trial, efgartigimod demonstrated improvements in myasthenia gravis patients with anti-MuSK, anti-LRP4, or triple seronegative subtypes. Based on these findings, the FDA expanded efgartigimod’s indication in May 2026 to include all people with generalized myasthenia gravis.

In the first 4 weeks of the ADAPT SERON study, MG-ADL scores dropped by an average of 3.35 points from baseline in the efgartigimod group, 1.46 points better than the drop in the placebo group (P=0.007).

Benefits continued in the open-label period, Howard said. Additional improvements were seen with subsequent cycles of treatment, he pointed out.

“This is borne out when we look at the accumulating degree of ADL improvement — those who had at least or greater than 2-, greater than 3-, greater than 4-point changes with subsequent cycles over time. More treatment gives you an improved response,” he stated.

“I think that becomes important as we determine is this a go or no-go for my patient? With the AChR population, we said two, three cycles … if they don’t respond, one might abandon it,” Howard added. “I’m not sure we can apply the same metric here. When we look at the achievement of minimal symptom expression — an ADL score of 0 or 1 — one sees improving, increasing percentages across the number of cycles received.”

The results suggest that pathogenic IgGs may be an underlying driver of generalized myasthenia gravis across patient subtypes regardless of autoantibody status, he noted.

ADAPT SERON included 119 participants with a confirmed diagnosis of generalized myasthenia gravis without anti-AChR antibodies. Enrolled participants had an MG-ADL total score of 5 or more.

Nearly half (58 participants) were randomized to efgartigimod. Of this group, 32 were triple seronegative, 20 had anti-MuSK antibodies, and six had anti-LRP4 antibodies. About a quarter (14 participants) had a prior thymectomy. The efgartigimod group had a mean MG-ADL score of 9.9 at baseline and an average age of 50.6 years; 75.9% were women.

Efgartigimod treatment was administered as once-weekly infusions every 4 weeks. As of June 2026, 80.5% of participants remained in the open-label phase of the study.