Regeneron's cemdisiran achieves Phase 3 win, confirming siRNA’s potential in treating myasthenia gravis

Regeneron's siRNA therapy, cemdisiran, met its primary endpoint in a phase 3 trial for generalized myasthenia gravis (gMG), outperforming placebo and positioning the company for an FDA filing in early 2026.

Why it matters: This success puts Regeneron in the race for a growing gMG market, potentially offering a differentiated treatment option with a novel mechanism targeting C5 production. Cemdisiran’s performance has been shown to be competitive with current C5 inhibitors like AstraZeneca’s Ultomiris.

Backstory: Regeneron licensed cemdisiran from Alnylam last year amid other modifications of their RNA partnership. Under this deal, Regeneron paid $10m upfront and may owe up to $325M in milestones if the drug is sold as a combination therapy, but will seek monotherapy approval first.

Zoom in: The phase 3 trial tested cemdisiran alone, in combination with pozelimab, and against placebo in 190 patients. Cemdisiran as a monotherapy achieved a 2.3 point drop in MG-ADL scores, meeting Regeneron’s goal and beating expectations.

Big picture: gMG is becoming a hotbed for innovation, with multiple C5 and FcRn-targeted therapies already on the market or in late-stage trials. Regeneron's siRNA approach sets it apart mechanistically, potentially improving long-term control and reducing treatment burden, in comparison to competition like Argenx´s Vyvgart, an FcRn blocker.

On that note: Argenx announced yesterday Vyvgart met its primary endpoint in the phase 3 ADAPT SERON trial, demonstrating safety and efficacy in seronegative gMG patients, who lack detectable acetylcholine receptor antibodies. Currently approved for seropositive gMG, Argenx now plans to seek FDA approval by year-end to expand Vyvgart's label across all seronegative gMG subtypes, potentially adding 11,000 U.S. patients. If approved, Vyvgart would hold the broadest label among FcRn antagonists in the gMG treatment landscape.