A Phase 3 Trial of Inebilizumab in Generalized Myasthenia Gravis

BACKGROUND: Autoimmune generalized myasthenia gravis is a disease that manifests with fluctuating muscle weakness. Inebilizumab is a monoclonal antibody that depletes CD19+ B cells, which are central to disease pathogenesis.

METHODS: In this phase 3, double-blind, randomized, placebo-controlled trial, we enrolled participants with myasthenia gravis who had anti-acetylcholine receptor antibodies or anti-muscle-specific kinase antibodies. Participants were randomly assigned, in a 1:1 ratio, to receive intravenous inebilizumab (300 mg administered on days 1 and 15 for all, and additionally on day 183 for participants who were acetylcholine receptor antibody-positive) or matching placebo for 52 weeks (in participants who were acetylcholine receptor antibody-positive) or 26 weeks (in those who were muscle-specific kinase antibody-positive). Glucocorticoid therapy was tapered, starting at week 4, to a target of 5 mg per day by week 24. The primary end point was the change from baseline in the score on the Myasthenia Gravis Activities of Daily Living scale (MG-ADL; scores range from 0 to 24, with higher scores indicating greater disease activity) at week 26 in the combined acetylcholine receptor antibody-positive and muscle-specific kinase antibody-positive trial populations. A key secondary end point was the change from baseline in the score on the Quantitative Myasthenia Gravis scale (QMG; scores range from 0 to 39, with higher scores indicating greater disease activity) at week 26 in the combined population. Safety was assessed.

RESULTS: A total of 238 participants underwent randomization (119 per group). Participants who received inebilizumab had a greater reduction in the MG-ADL score than those who received placebo (least-squares mean change, -4.2 vs. -2.2; adjusted difference, -1.9; 95% confidence interval [CI], -2.9 to -1.0; P<0.001) at week 26. Participants who received inebilizumab had a greater reduction in the QMG score than those who received placebo (least-squares mean change, -4.8 vs. -2.3; adjusted difference, -2.5; 95% CI, -3.8 to -1.2; P<0.001). The most common adverse events with inebilizumab were headache, cough, nasopharyngitis, infusion-related reactions, and urinary tract infections. Inebilizumab was not associated with a higher incidence of serious adverse events.

CONCLUSIONS: In participants with acetylcholine receptor antibody-positive or muscle-specific kinase antibody-positive generalized myasthenia gravis, inebilizumab improved function and reduced disease severity. (Funded by Amgen; MINT ClinicalTrial.gov number, NCT04524273.).