ADAPT-SC+ evaluated long-term safety and efficacy of subcutaneous (SC) efgartigimod PH20 (coformulated with recombinant human hyaluronidase PH20) in participants with generalized myasthenia gravis (gMG).

Efgartigimod, a human immunoglobulin G1 (IgG1) Fc fragment, reduces IgG levels (including pathogenic autoantibodies) through neonatal Fc receptor blockade. During ADAPT-SC, efgartigimod PH20 SC demonstrated noninferior total IgG reduction to intravenous (IV) efgartigimod in participants with gMG. Participants completing ADAPT-SC or enrolled in ADAPT+ (efgartigimod IV open-label extension [OLE]) could enter the ADAPT-SC+ OLE study.

Efgartigimod PH20 SC 1000 mg was administered in cycles of 4 once-weekly injections. Subsequent cycles were initiated based on clinical evaluation (Year 1, ≥4 weeks between cycles; Year 2 and onward, ≥1 week between cycles following protocol amendment). Safety was assessed using incidence and severity of adverse events. Clinical efficacy was assessed using Myasthenia Gravis Activities of Daily Living (MG-ADL) scores. 

During ADAPT-SC+, 180 participants received ≥1 efgartigimod PH20 SC injection (mean [SD] study duration, 2.6 [0.9] years; 459.4 participant years of follow-up). Adverse events were predominantly mild/moderate. Injection site reactions were mild/moderate, did not lead to discontinuation, and decreased in incidence with subsequent cycles. Efgartigimod remained well tolerated in participants whose cycle intervals shortened after Year 1. MG-ADL total score improvements in anti-acetylcholine receptor antibody–positive (AChR-Ab+) participants were observed by Week 1 and sustained through Week 163. 59.2% of AChR-Ab+ participants achieved minimal symptom expression (MG-ADL score, 0-1) at any time. Sustained improvements in quality-of-life measures were observed.