Phase 3 Trial Investigating Impact of Intravenous Efgartigimod in Anti-Acetylcholine Receptor Antibody Negative Generalized Myasthenia Gravis (P7-11.032)

Objective: 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). Background: 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. Design/Methods: 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. Results: 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. Conclusions: This Phase 3 trial will provide important data on the efficacy and safety of efgartigimod IV in the treatment of AChR-Ab− gMG. Disclaimer: Abstracts were not reviewed by Neurology® and do not reflect the views of Neurology® editors or staff. Disclosure: Dr. Howard has received personal compensation in the range of $10,000-$49,999 for serving on a Scientific Advisory or Data Safety Monitoring board for arenx . Dr. Howard has received personal compensation in the range of $5,000-$9,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Regeneron Pharmaceuticals. Dr. Howard has received personal compensation in the range of $10,000-$49,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Alexion Pharmaceuticals. Dr. Howard has received personal compensation in the range of $5,000-$9,999 for serving on a Scientific Advisory or Data Safety Monitoring board for AMGEN (Horizon Therapeutics). Dr. Howard has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Sanofi US. Dr. Howard has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Novartis. Dr. Howard has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Biohaven Ltd. Dr. Howard has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for CorEvitas. Dr. Howard has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Merck EMD Serono. Dr. Howard has received personal compensation in the range of $10,000-$49,999 for serving on a Speakers Bureau for Academic CME. Dr. Howard has received personal compensation in the range of $10,000-$49,999 for serving on a Speakers Bureau for PeerView CME. Dr. Howard has received personal compensation in the range of $10,000-$49,999 for serving on a Speakers Bureau for Platform Q CME. Dr. Howard has received personal compensation in the range of $5,000-$9,999 for serving on a Speakers Bureau for Zai Laboratories. Dr. Howard has received personal compensation in the range of $10,000-$49,999 for serving on a Speakers Bureau for Medscape CME. Dr. Howard has received personal compensation in the range of $5,000-$9,999 for serving on a Speakers Bureau for MJH LifeSci. Dr. Howard has stock in General Electric dividends. Dr. Howard has stock in Johnson & Johnson dividends. Dr. Howard has stock in Pfizer dividends. An immediate family member of Dr. Howard has stock in GlaxoSmithKline dividends. An immediate family member of Dr. Howard has stock in GE Healthcare dividends. Dr. Howard has stock in Viatris. The institution of Dr. Howard has received research support from Alexion Pharmaceuticals. The institution of Dr. Howard has received research support from argenx . The institution of Dr. Howard has received research support from UCB Biosciences. The institution of Dr. Howard has received research support from NIH. The institution of Dr. Howard has received research support from Centers for Disease Control/Research Triangle Institute. The institution of Dr. Howard has received research support from Duke University (DCRI). The institution of Dr. Howard has received research support from Cartestian Therapeutics. The institution of Dr. Howard has received research support from NMD Pharma. The institution of Dr. Howard has received research support from Ad Scientiam. Dr. Howard has a non-compensated relationship as a Scientific Advisiory Board member, Committee member with Myasthenia Gravis Foundation of America that is relevant to AAN interests or activities. Dr. Howard has a non-compensated relationship as a Committee member with American Assoc Neuromuscular and Electrodiagnostic Medicine that is relevant to AAN interests or activities. Dr. Guptill has received personal compensation for serving as an employee of argenx. Dr. Guptill has stock in argenx. Dr. Jimenez has nothing to disclose. Mrs. Gistelinck has nothing to disclose. Sophie Steeland has received personal compensation for serving as an employee of argenx. Sophie Steeland has stock in argenx.