The primary aim of this study is to confirm the age-appropriate dose of efgartigimod coformulated with recombinant hyaluronidase (efgartigimod PH20 SC).

Efgartigimod is a human IgG1 antibody Fc-fragment that blocks neonatal Fc receptor (FcRn), thereby reducing pathogenic IgG autoantibody levels. Previous phase 3 trials have demonstrated that both efgartigimod IV (ADAPT/ADAPT+) and efgartigimod PH20 SC (ADAPT-SC/ADAPT-SC+) is efficacious and well tolerated in adults with generalized myasthenia gravis (gMG). The incidence of juvenile gMG (1-5:1,000,000) is considerably lower than adult gMG and there remains an unmet need for effective and safe treatments in this population. A clinical trial assessing efgartigimod IV in juvenile gMG (NCT04833894) is currently underway. Here, we present the study design evaluating efgartigimod PH20 SC in patients with juvenile gMG (NCT06392386).

This study will recruit ≥12 patients, aged 2-17 years, and has a staggered design starting with the older age group (12-17 years). Patients must have a confirmed diagnosis of MGFA class II, III, or IVa, seropositivity for anti-AChR autoantibodies, and be on a stable dose of MG therapy. The study will consist of a 2-week screening period, 4-week treatment period, and 8-week follow-up period. During the treatment period, patients will receive 4 once-weekly injections of efgartigimod PH20 SC.

Pharmacokinetics (PK), pharmacodynamics (PD), safety, tolerability, immunogenicity, and clinical effect of efgartigimod PH20 SC will be assessed, along with evaluation of antibody responses to vaccines during efgartigimod treatment. Assessments include MG-ADL, QMG, EQ-5D-Y, Quality of Life in Neurological Disorders Pediatric Fatigue Score, and Clinical Global Impression of Improvement. Age-appropriate adaptations to assessments will be made during the study.

This study will use PK/PD modeling to confirm the appropriate efgartigimod PH20 SC dose and evaluate efficacy and safety for pediatric patients with gMG. Efgartigimod PH20 SC may provide additional flexibility for the treatment of pediatric patients with gMG.