SAN FRANCISCO — Interim results from an ongoing phase 2/3 trial suggested that intravenous efgartigimod (Vyvgart) significantly reduced disease activity in adolescents with acetylcholine receptor antibody-positive (AChR-Ab+) generalized myasthenia gravis (gMG), new research showed.

In the ADAPT JR trial, minimal symptom expression — defined as an Myasthenia Gravis Activities of Daily Living (MG-ADL) score of 0 or 1 — was achieved by eight of 11 (72.7%) female participants aged 12-17 years during the first treatment cycle and by four of five (80.0%) during the second cycle, said study investigator Abigail Schwaede, MD, of Lurie Children’s Hospital of Chicago, Chicago.

Reductions in total IgG and AChR-Ab, reported only in chart form without specific numbers, were similar to those reported in adults taking efgartigimod for gMG.

“We have very limited available products that are FDA approved [for pediatric gMG], and it can be a very debilitating disease for patients,” Schwaede said.

“It’s important to look at this study and understand there was reproducible decrease in MG-ADL, as well as reproducible decrease in the IgG and acetylcholine receptor antibody levels,” she added.

The findings were presented on October 29 at the American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM) 2025.

Extremely Rare Disease

Schwaede told Medscape Medical News that juvenile gMG is extremely rare, which is why recruitment for these trials is extremely difficult.

Treatment options are limited, she said, and similar to those in adults. “The standard of care would be a low-dose steroid, get them off that pretty quickly, and then do IVIG [intravenous immunoglobulin].”

However, she said, the effects of IVIG can fade over time and its impact is more limited in patients with severe or refractory disease and “it’s not really a good long-term treatment.”

Eculizumab (Soliris), a C5 inhibitor and one of two FDA-approved treatments, requires an extensive vaccine schedule prior to treatment, she said. In addition, she noted, children can’t go onto the drug immediately because of this requirement.

Enter efgartigimod, an human Fc receptor (FcRn) blocker which the FDA approved for gMG in certain adults in 2021.

For the study, researchers enrolled 11 adolescents with AChR-Ab+ gMG (Myasthenia Gravis Foundation of America [MGFA] class II, III, or IVa) who had unsatisfactory response to immunosuppressants, steroids, or AChEIs (mean age, 14.8 years; 100% female; 72.7% White, 18.2% other, and 9.1% Black; 18.2% Hispanic/Latino).

Participants received an initial single infusion, were observed for 8 weeks, underwent a cycle of four once-weekly injections, had a 4-week rest period, and then were treated with one cycle as needed.

All 11 participants had at least one treatment-emergent adverse event (TEAE), and two had at least one serious TEAE. No TEAE led to treatment discontinuation. Headache was the most common TEAE (63.6%), followed by oropharyngeal pain (27.3%), and lymphopenia, nausea, nasal congestion, and rhinorrhea (all 18.2%).

In the open-label extension trial, known as ADAPT JR+, four of six participants (66.7%) achieved MG-ADL score of 0 or 1 in cycle 3, the highest level out of nine cycles.

More pediatric data are expected by 2027, including information from a trial in younger children, Schwaede said.

Before puberty, the disease acts differently than in adolescents, with some escalating and others going into remission and remaining disease-free, she said.

A Welcome Option

Commenting on the trial’s results Katherine Ruzhansky, MD, MS, neurologist at the Medical University of South Carolina, Charleston, South Carolina, who wasn’t involved in the study, told Medscape Medical News that the findings appear valid and, although not ground-breaking, are in line with research into efgartigimod’s effects in adults with gMG.

In adolescents, “it’s fairly safe, and it seems to have some improvements.” Reaching a MG-ADL level of 0 can be “life-changing,” she noted.

Ruzhansky added that the small number of participants is to be expected considering the rarity of gMG in children.

She added that there are already two FDA-approved drugs for adolescent gMG — eculizumab and nipocalimab (Imaavy), which is an FcRn blocker like efgartigimod. Still, “the more options we have for patients, the better.”

As for cost, she said these types of drugs are expensive. While efgartigimod could be prescribed now on an off-label basis in kids, she said, insurers won’t cover it.

Argenx funded the study. Schwaede disclosed having relationships with Alexion, Argenx, NS Pharma, Johnson & Johnson, Sarepta, and Biogen. Ruzhansky disclosed having relationships with Alexion, Amylyx, Argenx, Immunovant, UCB, Janssen, MGNet, and MGFA.