Background
Efgartigimod, a human immunoglobulin G1 antibody Fc fragment, blocks the neonatal Fc receptor. Phase 3 ADAPT/ADAPT+ trials demonstrated that efgartigimod intravenous (IV) is efficacious and well tolerated in adults with generalized myasthenia gravis (gMG). There is an unmet need for safe and effective treatments in juvenile gMG, which is rarer than adult-onset gMG (incidence: 1-5 cases vs 30 cases per 1,000,000 people per year).
Objectives
To present interim results of ADAPT JR (NCT04833894), a Phase 2/3 trial assessing pharmacokinetics, pharmacodynamics, safety, and activity of IV efgartigimod in participants with acetylcholine receptor antibody–positive (AChR-Ab+) juvenile gMG to confirm an age-appropriate dose in this population.
Methods
Staggered enrollment in ADAPT JR began with an adolescent cohort (aged 12-17 years) and is continuing with a child cohort (aged 2-11 years). During dose-confirmatory Part A (8 weeks), participants received 1 efgartigimod infusion; pharmacokinetic, pharmacodynamic, and safety endpoints were monitored. During treatment response–confirmatory Part B (18 weeks), participants received 1 or 2 cycles of 4 once-weekly efgartigimod infusions; additional endpoints, including MG-ADL scores, were assessed.
Results
In the adolescent cohort, 6 participants enrolled in Part A and continued to Part B, and 5 participants enrolled directly in Part B (N=11; median [range] age, 15.0 [12-17] years). Efgartigimod treatment resulted in IgG and AChR-Ab decreases similar to those observed in previous studies of adults with gMG. Safety profile and MG-ADL improvements were also similar to previous observations.
Conclusions
Pharmacodynamics, safety, and efficacy of efgartigimod in adolescent participants were similar to previous studies in adults. ADAPT JR child cohort enrollment is ongoing.