Regulatory applications for cemdisiran, a small interfering RNA (siRNA) therapeutic targeting complement factor C5, have been accepted for review by both the US FDA and the European Medicines Agency (EMA) for the treatment of adult patients with generalized myasthenia gravis (gMG) who are anti-acetylcholine receptor (AChR) antibody-positive. The filings represent what would be the first siRNA therapy approved in generalized myasthenia gravis and, if authorized, the only gMG treatment administered subcutaneously four times a year. Regeneron Pharmaceuticals (Nasdaq: REGN) is solely responsible for cemdisiran's development under a worldwide licensing agreement with Alnylam.
The US FDA is reviewing the New Drug Application (NDA) under Priority Review, following use of a Priority Review Voucher, with a target action date in November 2026, the company said. A decision from the European Commission is anticipated in the second half of 2027. Regeneron also plans to submit a regulatory filing in Japan in early 2027. The filing seeks approval in adults with symptomatic gMG who may be receiving standard of care immunosuppressants at investigator discretion, with cemdisiran dosed subcutaneously at 600 mg every 12 weeks.
The submissions are supported by data from the Phase III NIMBLE trial, described as one of the largest global interventional gMG trials conducted to date. Results, simultaneously published in The Lancet and presented at the American Academy of Neurology Annual Meeting in April 2026, demonstrated that cemdisiran met its primary endpoint at week 24, with a placebo-adjusted improvement of 2.3 points on the Myasthenia Gravis-Activities of Daily Living scale (p<0.001). The key secondary endpoint, the Quantitative Myasthenia Gravis score, showed a placebo-adjusted improvement of 2.8 points (p=0.002). Notably, 76.6% of cemdisiran-treated patients achieved a clinically meaningful threshold of at least a 3-point MG-ADL improvement versus 44.1% on placebo, with improvements detectable within two weeks of the first dose. No serious infections, meningococcal events, or deaths occurred during the double-blind period.
Cemdisiran is a GalNAc-conjugated siRNA that suppresses hepatic C5 synthesis at the mRNA level, reducing circulating complement factor C5 and thereby limiting complement-mediated neuromuscular junction damage. This upstream mechanism contrasts with approved protein-level C5 inhibitors such as eculizumab (Soliris) and ravulizumab (Ultomiris), and enables the quarterly subcutaneous dosing schedule. If approved, cemdisiran would become the first GalNAc-conjugated siRNA therapy available for generalized myasthenia gravis, extending the application of RNA interference therapeutics into another autoimmune indication.