P.034 Minimal symptom expression following treatment with efgartigimod in patients with Generalized Myasthenia Gravis

Background: Efgartigimod is a human IgG1 antibody Fc-fragment that reduces IgG levels through FcRn blockade. A key efficacy indicator in the treatment of IgG autoantibody-mediated generalized myasthenia gravis (gMG) is improvement in MG-ADL score. Methods: The ADAPT phase 3 trial evaluated safety and efficacy of efgartigimod in patients with gMG, including reaching and maintaining of minimal symptom expression (MSE; defined as an MG-ADL total score of 0 or 1). Results: 167 patients (AChR-Ab+, n=129; AChR-Ab-, n=38) were randomized to receive treatment cycles of 4 weekly infusions of efgartigimod or placebo. Significantly more AChR-Ab+ efgartigimod-treated patients achieved MSE during cycle 1 compared to placebo-treated patients (40.0% [n=26/65] vs 11.1% [n=7/63; P <0.0001]). In cycle 2, 31.4% (n=16/51) of AChR-Ab+ patients in the efgartigimod cohort achieved MSE compared to none in the placebo cohort. MG-ADL score improved by ≥6 points in 56.9% of AChR-Ab+ efgartigimod-treated patients compared to 20.6% of placebo-treated patients in cycle 1. Most patients achieved MSE by week 4 of a cycle, paralleling early reduction in IgG levels, and MSE duration ranged from 1 to ≥10 weeks. Adverse events were predominantly mild to moderate. Conclusions: Efgartigimod treatment resulted in more patients with AChR-Ab+ gMG achieving both MSE and clinically meaningful MG-ADL improvements.