P.044 Efficacy, safety, and tolerability of efgartigimod in AChR-Ab– patients with Generalized Myasthenia Gravis: interim analysis of ADAPT/ADAPT+

Background: Efgartigimod, a human IgG1 antibody Fc-fragment, reduces IgG levels through neonatal Fc receptor blockade. Patients with anti-acetylcholine antibody–negative (AChR-Ab–) generalized myasthenia gravis (gMG) comprise 15%-20% of the gMG population and have limited approved treatment options. We evaluated long-term safety efficacy efgartigimod in AChR-Ab– patients from ADAPT/ADAPT+ (open-label extension). Methods: ADAPT versus placebo AChR-Ab+ (n=129) Ab– (n=38) gMG. This integrated analysis includes 37 who received ≥1 dose October 2020 (median[range] follow-up: 453[85-721] days). Responder status was defined as ≥2-point (MG-ADL) ≥3-point (QMG) improvement for ≥4 consecutive weeks (with first 1 week after last infusion). Results: Among (cycle 1), 68.4% (13/19) efgartigimod-treated were MG-ADL responders (placebo, 63.2% [12/19]), 52.6% (10/19) QMG 36.8% [7/19]). In improved baseline MG-ADL/QMG scores, consistent improvements across multiple subsequent cycles. No clinically meaningful differences or outcomes between occurred. Conclusions: Long-term (median >1 year) well tolerated associated scores patients.