Efficacy, Safety, and Tolerability of Efgartigimod in AChR-Ab– Patients With Generalized Myasthenia Gravis: Interim Analysis of ADAPT/ADAPT+ Studies

Topic:

Clinical Trials

Poster Number: 132

Author(s):

Deborah Gelinas, MD, argenx, Tuan Vu, MD, University of South Florida, Vera Bril, MD, Ellen & Martin Prosserman Centre for Neuromuscular Diseases, University Health Network, Chafic Karam, MD, Penn Neuroscience Center - Neurology, Hospital of the University of Pennsylvania, Stojan Peric, MD, PhD, University Clinical Center of Serbia - Belgrade, Jan De Bleecker, MD, PhD, Ghent University Hospital, Hiroyuki Murai, MD, PhD, School of Medicine, International University of Health and Welfare, Mamatha Pasnoor, MD, The University of Kansas, Francesco Saccà, MD, AOU Federico II, Andreas Meisel, MD, NeuroCure Clinical Research Center, Charité Universitätsmedizin Berlin, Caroline T’joen, MSc, argenx, Kimiaki Utsugisawa, MD, PhD, Hanamaki General Hospital, Renato Mantegazza, MD, Fondazione IRCCS Istituto Neurologico Carlo Besta, James Howard, MD, FAAN, The University of North Carolina at Chapel Hill, in collaboration with the ADAP in collaboration with the ADAPT Investigator Study, ADAPT Investigator Study Group

Background: Efgartigimod is a human IgG1 antibody Fc-fragment that reduces pathogenic autoantibody and total IgG levels through neonatal Fc receptor blockade. Patients with anti-acetylcholine receptor antibody–negative (AChR-Ab–) generalized myasthenia gravis (gMG) comprise 15%-20% of the gMG population and have limited approved treatment options owing to historical exclusion from clinical trials.

Objectives: To evaluate long-term safety and efficacy of efgartigimod in AChR-Ab– patients using data pooled from the phase 3 ADAPT study and ongoing long-term extension, ADAPT+.

Methods: ADAPT evaluated the safety and efficacy of efgartigimod versus placebo in AChR-Ab+ (n=129) and Ab– (n=38; 6 MuSK-Ab+) patients with gMG. This integrated analysis includes data from 37 AChR-Ab– patients (5 MuSK-Ab+) who received ≥1 dose of efgartigimod in ADAPT/ADAPT+ through October 2020 (median[range] follow-up: 453[85-721] days). Efficacy was assessed using Myasthenia Gravis Activities of Daily Living (MG-ADL) and Quantitative Myasthenia Gravis (QMG) scores. Responder status was defined as ≥2-point (MG-ADL) and ≥3-point (QMG) improvement for ≥4 consecutive weeks (with first improvement ≤1 week after last infusion).

Results: Among AChR-Ab– patients in ADAPT, 68.4% (13/19) of patients treated with efgartigimod were MG-ADL responders (placebo, 63.2% [12/19]), and 52.6% (10/19) were QMG responders (placebo, 36.8% [7/19]) in cycle 1. In cycle 1 of the integrated analysis, AChR-Ab– patients (including 18 placebo patients who received efgartigimod during ADAPT+) improved from cycle baseline in both MG-ADL (≥2- to ≥7-point improvements of 87.9%–35.1%, respectively) and QMG (≥3- to ≥9-point improvements of 86.5%–27.0%). Consistently similar improvements in both efficacy measures occurred through at least 7 cycles. Safety and efficacy outcomes in AChR-Ab– patients were similar to those observed in AChR-Ab+ patients.

Conclusion: Long-term treatment (median >1 year) with efgartigimod was associated with clinically meaningful improvements in MG-ADL/QMG scores in AChR-Ab– patients in ADAPT/ADAPT+.