311 Treatment of Bullous Pemphigoid by Inhibiting Fcrn: Pre-registration Report of a Phase 2/3 Trial with Efgartigimod

Bullous pemphigoid (BP) is an autoimmune blistering disease, characterized by subepidermal blisters and mediated by IgG autoantibodies against BP180 (type XVII collagen) and BP230 structural proteins of the dermal-epidermal junction. Efgartigimod, an engineered Fc fragment, inhibits FcRn activity, thereby decreasing serum IgG and autoantibodies. This pre-registration report describes a Phase 2/3 randomized, double-blind, placebo-controlled trial of efgartigimod in patients with moderate to severe (by PDAI) BP. In Part A (proof of concept, phase 2), 40 participants will be recruited, while in Part B (confirmatory, phase 3) 120 participants will be recruited. Part A and B are identical in schedule, structure, assessments, and conduct. 2000 mg efgartigimod PH20 SC (as two 1000 mg injections) will be given on days 1 (baseline) and 8 (week 1), and 1000 mg efgartigimod PH20 SC will be administered weekly through week 35. The primary endpoint is the proportion of participants who have been in complete remission while receiving minimal oral corticosteroid therapy for ≥8 weeks at week 26.