Regeneron announced positive results from a phase 3 study in generalized myasthenia gravis (gMG), strengthening its case to seek FDA approval for its siRNA therapy in a very crowded neuromuscular field.
The trial enrolled 190 adults with symptomatic gMG and anti-AChR antibodies, assigning them to one of three groups. Roughly a third received cemdisiran alone, an siRNA that blocks production of C5 in the liver, given every 12 weeks. Another third received cemdisiran plus pozelimab, a C5-targeting antibody, dosed every four weeks, while the rest were treated with placebo.
By Week 24, patients on cemdisiran showed a 2.3-point reduction on the MG-ADL scale of gMG symptoms compared with placebo. The combination arm registered a 1.74-point decline. Both results were statistically significant, allowing the study to meet its primary endpoint. Regeneron added that cemdisiran, either alone or paired with pozelimab, also succeeded on key secondary measures.
The main endpoint for cemdisiran aligned with expectations set earlier in the year. Speaking at a TD Cowen conference in March, Ryan Crowe, Regeneron’s SVP of investor relations and strategic insights, had remarked that a result “in the 2s” would be encouraging.
Regeneron placed its findings in context by pointing to studies of currently authorized C5 inhibitors, which showed placebo-adjusted MG-ADL improvements ranging from -1.6 to -2.1 over 12 to 26 weeks. Another benchmark in the space is Argenx’s FcRn blocker Vyvgart, which earned FDA clearance in gMG after demonstrating that nearly 70% of patients achieved at least a two-point drop on MG-ADL during the initial treatment cycle.
The success of Vyvgart has heightened competition for AstraZeneca’s Ultomiris, a C5 inhibitor. In response, AstraZeneca advanced a self-administered subcutaneous nanobody version that recently cleared a phase 3 trial. Unlike these therapies, Regeneron’s cemdisiran applies a distinct action mechanism, offering potential differentiation from both approved and late-stage rivals.
During a March appearance, Crowe highlighted Regeneron’s rationale for pairing cemdisiran and pozelimab, describing the former as a tool to suppress C5 production at the source and the latter as a way to clear circulating C5. However, in the phase 3 trial, cemdisiran alone delivered stronger numerical outcomes on both primary and secondary measures compared with the dual regimen. Regeneron now intends to pursue U.S. approval of cemdisiran as a standalone therapy in the first quarter of 2026.
TD Cowen analyst Tyler Van Buren noted that the study results, combined with the option for patients to self-administer treatment at home, enhance the therapy’s appeal. He contrasted this with the burden of current weekly intravenous treatments, which must be given under a doctor’s supervision, making Regeneron’s candidate the more convenient alternative.
The siRNA medicine traces back to Alnylam, from whom Regeneron secured rights by amending an existing deal in 2024. That update provided Alnylam with $10 million upfront plus a potential regulatory milestone for monotherapy approval and up to $325 million tied to sales of a combination version.
