To evaluate long-term safety and efficacy of efgartigimod PH20 SC in participants with generalized myasthenia gravis (gMG) enrolled in the ADAPT-SC+ open-label extension (OLE).

Efgartigimod is a human immunoglobulin G1 (IgG1) antibody Fc-fragment that reduces IgG levels (including pathogenic autoantibodies) through neonatal Fc receptor blockade. In the ADAPT-SC study, subcutaneous (SC) efgartigimod PH20 (coformulated with recombinant human hyaluronidase PH20) was shown to have noninferior total IgG reduction to efgartigimod IV in participants with gMG. Participants completing ADAPT-SC or enrolled in ADAPT+ (efgartigimod IV OLE) were eligible for the ADAPT-SC+ OLE.

Efgartigimod PH20 SC 1000 mg was administered in cycles of 4 once-weekly injections. Subsequent cycles were initiated based on clinical evaluation. Myasthenia Gravis Activities of Daily Living (MG-ADL) score assessed clinical efficacy. 

As of December 2022, 179 participants received ≥1 dose of efgartigimod PH20 SC, with a mean (SD) study duration of 413 (105) days. Adverse events were predominantly mild/moderate. Injection-site reactions were mild/moderate, did not lead to treatment discontinuation, and decreased in incidence with subsequent cycles. Improvement from cycle baseline (mean [SE]) in MG-ADL total score was observed in Week 4 of cycle 1 (-4.1 [0.27]) in anti-acetylcholine receptor antibody positive participants, with consistent/repeatable improvements seen through cycle 9. Similar results were seen on quality-of-life measures. The proportion of participants achieving minimal symptom expression (MG-ADL score, 0-1) at any time through 9 cycles was 54.6%. Clinical improvements were similar to those seen with efgartigimod IV during ADAPT/ADAPT+. Updated data analysis will be presented at the congress.

Treatment with multiple cycles of efgartigimod PH20 SC was well tolerated and efficacious.