Sustained Disease Control in Adolescent Myasthenia Gravis With FcRn Blocker

SAVANNAH, Ga. — Investigational nipocalimab plus standard of care achieved sustained reductions in immunoglobulin G (IgG) and appeared to be safe for adolescent patients with generalized myasthenia gravis (gMG), the phase II/III Vibrance-MG study showed.

From baseline to week 24 of the active treatment phase, the mean percentage change in total serum IgG from baseline was -68.98% (95% CI -78.4 to -59.6%), reported Jonathan Strober, MD, of the UCSF Benioff Children’s Hospital in San Francisco.

The median pre-dose total serum IgG reduction from baseline to week 2 was -72%, Strober said. The median reduction to week 24 was -69.87%.

The findings, presented at the Myasthenia Gravis Foundation of America (MGFA) session of the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM) annual meeting, show the potential of this investigational therapy for patients, ages 12 to 17 years, with gMG, Strober noted.

“It is encouraging to see these positive results as there are currently no approved advanced treatment options for this adolescent population in the United States,” he said.

The prevalence of gMG increases with age, and few myasthenia gravis patients are children. Some research has suggested that a high percentage of juvenile gMG patients may require hospitalization in an ICU throughout the course of their disease.

Nipocalimab was designed to block the IgG binding site on the neonatal Fc receptor (FcRn) to reduce serum levels of circulating IgG, including pathogenic IgG autoantibodies in gMG. The treatment recently has been tested in a pivotal trial of adult gMG patients.

“These are the first clinical trial data reported with an FcRn blocker in adolescents,” Strober said.

The treatment was well tolerated in adolescents with gMG, he pointed out: there were no serious adverse events (AEs), no AEs leading to discontinuation, and no AEs of special interest through week 24. The most common AE was nasopharyngitis.

Vibrance-MG is an ongoing open-label study of nipocalimab plus standard of care in children and adolescents with gMG, with enrollment open to patients ages 2 years up to age 18.

All participants were diagnosed with gMG MGFA Classification IIa to IVb gMG, were seropositive for anti-acetylcholine receptor (anti-AChR) or muscle-specific kinase (anti-MuSK) autoantibodies, and had an insufficient clinical response to ongoing, stable standard-of-care therapy.

The results presented at AANEM included adolescents, ages 12 years to <18 years. The mean baseline age was 14 years; 85% were girls.

“Seven patients were screened. Five entered the active treatment at the time of this cutoff, where they received a nipocalimab 30 mg/kg loading dose, followed by 15 mg/kg every 2 weeks for 24 weeks,” Strober said. “After that, they all entered the long-term extension phase where they were able to get either the 15 mg/kg dose every 2 weeks or nipocalimab 30 mg/kg every 4 weeks.”

The primary outcome included total serum IgG, plus safety and tolerability at 24 weeks. Secondary endpoints included changes in Myasthenia Gravis Activities of Daily Living (MG-ADL) and Quantitative Myasthenia Gravis (QMG) scores. The MG-ADL ranges from 0 to 24 with higher scores indicating more severe symptoms; the QMG ranges from 0 to 39 with higher scores indicating more severe disease.

“The baseline mean MG-ADL was on the lower side — 4.29 — with a range of 2.5 to 9.5, and the mean QMG was 12.5,” Strober noted.

There was a clinically meaningful reduction in MG-ADL score at week 4, which was maintained through week 24, Strober said. At week 24, the mean MG-ADL score improved by -2.40 points.

“Four out of the five participants showed an MG-ADL score of 0 or 1 at week 24,” Strober noted.

Similarly, QMG scores fell at week 4, he observed. At week 24, the mean QMG score improved by -3.80 points.

Two other trials are evaluating FcRn blockers in small phase II/III studies of juvenile myasthenia gravis: one in rozanolixizumab (Rystiggo), and one is in efgartigimod (Vyvgart). The terminal complement C5 inhibitor eculizumab (Soliris) also has been tested and was approved last year in the European Union and Japan to treat children and adolescents with refractory gMG.

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