Biogen said diranersen delivered Phase 2 evidence of both reduced tau pathology and slower cognitive decline in early Alzheimer’s disease, which it described as the first randomized study to show both effects for a tau-directed therapy.
The 18-month CELIA trial enrolled 416 patients and found benefits across all studied doses, with the strongest cognitive signal at 60 mg every 24 weeks and robust reductions in cerebrospinal fluid tau and PET-measured tau pathology.
CELIA still missed its primary endpoint, which tested dose response on CDR-SB change at Week 76, but Biogen said the overall biomarker and efficacy package was strong enough to move diranersen into registrational development.
Safety was generally in line with the earlier Phase 1b study, although serious adverse events were more frequent at the highest dose; the drug already holds FDA Fast Track designation, and longer-term extension follow-up is ongoing.
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Diranersen’s Phase 2 CELIA Results: Strong Tau Pathology Reduction, Unexpected Dose Response, and Implications for Alzheimer’s Drug Development
Overview
On May 14, 2026, Biogen announced topline results from its Phase 2 CELIA study of diranersen, showing robust reductions in tau pathology across all doses. These results are significant because they align with earlier Phase 1b findings, suggesting diranersen’s effect on tau is reproducible. However, the topline summary did not immediately share details about the primary endpoint, cognitive benefits—especially at the lowest dose—or the full safety profile. More information about Biogen’s next steps, including plans for Phase 3 development and regulatory engagement, is expected as detailed results become available.