To determine the efficacy and safety of 10 mg/kg IV efgartigimod compared with placebo in participants with anti-acetylcholine receptor antibody negative (AChR-Ab-) generalized myasthenia gravis (gMG).

Approximately 15% of patients with gMG who do not have antibodies directed against AChR and are referred to as AChR-Ab-. Lack of approved treatment options for the AChR-Ab- gMG population represents an unmet need in the gMG treatment landscape. Efgartigimod is an immunoglobulin G (IgG)1 antibody Fc-fragment that selectively reduces IgG levels by blocking neonatal Fc receptor (FcRn)-mediated IgG recycling and is approved for the treatment of patients with AChR-Ab+ gMG. The Phase 3 ADAPT SERON Trial (NCT06298552) will investigate the efficacy and safety of efgartigimod in participants with AChR-Ab- gMG.

Adult participants with AChR-Ab- gMG who have a Myasthenia Gravis Activities of Daily Living (MG-ADL) total score of ≥5 (with >50% of the score due to nonocular symptoms) and are on a stable dose of ≥1 concomitant gMG treatment will be included. One-hundred-ten adjudicated participants will be randomized 1:1 to either receive 10 mg/kg IV efgartigimod or placebo. The study has 2 stages: the double-blinded placebo-controlled Part A, consisting of 4 once-weekly infusions and 5 weeks of follow-up, and the open-label extension Part B, consisting of varying number and frequency of cycles, and weekly infusions for ≤2 years.

The primary endpoint is the change in MG-ADL total score from study baseline to Day 29 in Part A. Additional efficacy outcomes (QMG, MG-QoL15r, EQ-5D-5L), safety/tolerability, and pharmacokinetic/pharmacodynamic effects are also being assessed.

This Phase 3 trial will provide important data on the efficacy and safety of efgartigimod IV in the treatment of AChR-Ab- gMG.