Long-Term Safety, Tolerability, and Efficacy of Efgartigimod in Participants With Generalized Myasthenia Gravis: Concluding Analyses from ADAPT+


Clinical Trials

Poster Number: M266


Jamie Aldridge, PhD, MPAS, argenx US, INC, James Howard, MD, University of North Carolina, Chapel Hill, Mamatha Pasnoor, MD, University of Kansas Medical Center, Vera Bril, BSc, MD, FRCPC, University of Toronto, Chafic Karam, MD, University of Pennsylvania, Stojan Peric, MD, PhD, University of Belgrade, Jan De Bleecker, MD, PhD, Ghent University Hospital, Hiroyuki Murai, MD, PhD, International Univ of Health and Welfare, Andreas Meisel, Charité – Universitätsmedizin Berlin, Said Beydoun, MD, FAAN, Keck School of Medicine of USC, Tuan Vu, MD, University of South Florida, Peter Ulrichts, PhD, argenx, Benjamin Van Hoorick, MD, argenx, Caroline T’joen, MSc, argenx, Kimiaki Utsugisawa, MD, PhD, Hanamaki General Hospital (総合花巻病院), Renato Mantegazza, MD, Fondazione I.R.C.C.S. Istituto Neurologico Carlo Besta, ADAPT+ Study Group

Efgartigimod is a human IgG1 antibody Fc-fragment that reduces total immunoglobulin G (IgG) levels (including pathogenic autoantibodies) through neonatal Fc receptor blockade. ADAPT, a 26-week, global, randomized, controlled, phase 3 trial, evaluated efgartigimod in adult participants with generalized myasthenia gravis (gMG). Participants who completed ADAPT were eligible to enroll in the ADAPT+ open-label extension study.

Efgartigimod (10 mg/kg IV) was administered in cycles of once-weekly infusions for 4 weeks, with subsequent cycles initiated based on clinical evaluation. Primary objectives in ADAPT+ were to evaluate long-term safety and tolerability of efgartigimod in adult participants with gMG. Long-term efficacy was assessed using the Myasthenia Gravis Activities of Daily Living (MG-ADL) and Quantitative Myasthenia Gravis (QMG) scores.

Ninety percent of participants (151/167) from ADAPT entered ADAPT+, and 145 (111 anti-acetylcholine receptor antibody positive [AChR-Ab+]/34 anti-AChR-Ab-) received ≥1 cycle as of January 2022. With 229 participant-years of follow-up (mean duration per participant: 610 days), the most common adverse events were headache (25%), COVID-19 infection (16%), nasopharyngitis (14%), diarrhea (10%), and urinary tract infection (9%), which were mostly mild to moderate and did not increase in frequency in subsequent cycles. AChR-Ab+ participants with ≥1 year of follow-up across ADAPT/ADAPT+ (n=103) received a median (range) 5.2 (0.5-7.5) cycles per year. All anti-AChR-Ab+ participants (n=111), showed consistent and repeatable improvements in MG-ADL (mean [SE] change Week 3 of Cycle 1: -5.0 [0.33]; ≤19 cycles) and QMG (-4.7 [0.41]; ≤7 cycles) during each cycle, mirroring repeatable reductions in total IgG (mean[SE] reduction; ≤7 cycles: -55.9% [1.15]) and anti-AChR autoantibody levels (-56.1% [1.43]). Similar results were seen in AChR-Ab- participants.

These analyses suggest long-term efgartigimod treatment is well tolerated and results in consistent, repeatable improvements in clinical outcomes (MG-ADL and QMG) in adult participants with gMG.