Inebilizumab treatment in Japanese patients with IgG4-related disease: a subgroup analysis of a randomized, double-blind, placebo-controlled, phase 3 trial (MITIGATE)

Objectives This subgroup analysis of the MITIGATE study aimed to evaluate whether the efficacy and safety of inebilizumab in Japanese patients with IgG4-related disease are consistent with those observed in the overall trial population. Methods MITIGATE was a randomized, double-blind, placebo-controlled, phase 3 study conducted in 22 countries, and this subgroup analysis included Japanese patients enrolled in that trial. Results In total, 27 Japanese patients (inebilizumab, N = 20; placebo, N = 7) were included in this subgroup analysis. The organs most frequently affected were the submandibular gland (66.7%), lacrimal gland (59.3%), and pancreas (51.9%). Despite the discontinuation of glucocorticoids within 8 weeks of study initiation, there were no adjudication committee-determined flares requiring treatment in the inebilizumab group. Flares were observed in four patients (57.1%) in the placebo group, with a median time to first flare of 246.0 days. Inebilizumab reduced annualized flare rate, increased flare-free complete remission, and lowered glucocorticoid use. Safety profiles were similar between treatment groups; most treatment-emergent adverse events were non-serious. Conclusions Inebilizumab reduced flare risk and glucocorticoid exposure and was well tolerated in Japanese patients with IgG4-related disease, consistent with overall MITIGATE results. Trial registration NCT04540497.