Biogen decided to advance diranersen (BIIB-080) into registrational development for early Alzheimer’s disease even after missing a phase 2 primary endpoint. In the Celia trial, low-dose diranersen outperformed higher doses on cognition measures while the primary dose-response goal on Clinical Dementia Rating–Sum of Boxes at week 76 was not met. Biogen reported reductions in cerebrospinal fluid tau and tau pathology alongside cognitive slowing signals, and the company characterized biomarker and efficacy data as supportive of moving into phase 3. Analysts cited uncertainty around the dose-response pattern, underscoring the need for clearer regimens in late-stage studies.