Full Breakdown
Biogen Moves Tau-Targeting Antisense Therapy to Phase 3 After Mixed Phase 2 Results
5/14/2026, 9:23:36 PM
Core Findings from the CELIA Phase 2 Trial
Biogen’s CELIA study enrolled 416 participants with mild cognitive impairment or mild Alzheimer’s dementia who had not received anti-amyloid therapy. Three intrathecal doses of diranersen (BIIB080)—60 mg every 24 weeks, 115 mg every 24 weeks, and 115 mg every 12 weeks—were tested over 76 weeks. The primary endpoint, a dose-response change on the Clinical Dementia Rating–Sum of Boxes (CDR-SB), was not met. Across all doses, cerebrospinal-fluid tau and tau-PET signals fell markedly, and a pre-specified cognitive analysis showed slower decline, most pronounced at the lowest dose. Safety was comparable across groups, with serious adverse events modestly higher at the highest dose.
Background & Context
Tau accumulation drives neurodegeneration in Alzheimer’s disease, complementing amyloid-centric approaches. Biogen’s earlier amyloid-targeting drugs, Aduhelm and Leqembi, remove amyloid plaques but have faced mixed reception. Diranersen, discovered by Ionis Pharmaceuticals, is an antisense oligonucleotide that reduces MAPT mRNA, lowering intracellular and extracellular tau. The U.S. FDA granted Fast Track designation for diranersen in 2025, reflecting regulatory interest in novel mechanisms.
Key Figures & Organizations
- Biogen Inc. – developer of diranersen.
- Priya Singhal, M.D., M.P.H. – Executive Vice President and Head of Development, Biogen.
- Diana Gallagher – Head of Clinical Development for MS, Immunology and Alzheimer’s Disease, Biogen.
- Jeff Cummings, Ph.D. – Professor of Brain Sciences, University of Nevada, Las Vegas, external expert.
- Ionis Pharmaceuticals – licensor of the antisense technology.
- U.S. Food and Drug Administration (FDA) – granted Fast Track status.
Data & Statistics
- Participants: 416 (early Alzheimer’s).
- Doses: 60 mg q24 wks; 115 mg q24 wks; 115 mg q12 wks.
- Primary endpoint: Dose-response on CDR-SB at week 76 – not achieved.
- Biomarker impact: Significant reductions in CSF tau and tau-PET across all doses.
- Cognitive signal: Slower decline across doses, strongest at 60 mg.
- Safety: Adverse-event rates similar across groups; serious events higher at 115 mg q12 wks.
Official Statements & Responses
Biogen said the trial “provides compelling evidence of tau reduction and cognitive benefit,” giving the company confidence to pursue registrational development. Executives emphasized a favorable safety profile and announced plans to engage regulators and present full data at the Alzheimer’s Association International Conference in July. The firm also highlighted an ongoing long-term extension study to assess durability of effect.
Criticism & Opposition
Analysts noted the absence of a dose-response and the lack of disclosed effect-size data, describing the results as “not a worst-case outcome, but leaves much to be desired.” Concerns were raised about the intrathecal administration route and the modest increase in serious adverse events at the highest dose. While some view any cognitive signal as encouraging, others urge caution until Phase 3 outcomes are available.
Conflicting Reports & Gaps
Biogen’s statements stress meaningful cognitive slowing, yet the company released no quantitative metrics, creating a gap between claimed benefit and measurable evidence. The primary efficacy goal was missed, while biomarker improvements were robust; the relationship between tau reduction magnitude and clinical impact remains unquantified.
Verbatim Quotes
- “In CELIA, we believe we have seen an unprecedented and compelling confluence of efficacy and biomarkers results from a tau-directed agent in a randomized early Alzheimer’s disease study,” — Priya Singhal, M.D., M.P.H., Executive Vice President and Head of Development, Biogen
- “The CELIA topline results represent an important advance for the field, providing the first evidence that reducing tau, a hallmark of Alzheimer’s disease closely associated with neurodegeneration and cognitive decline, may meaningfully impact disease progression,” — Dr. Jeff Cummings, Professor of Brain Sciences, University of Nevada, Las Vegas
- “not a worst-case outcome, but leaves much to ?be desired,” — Christian Moore, Analyst, Bernstein
- “We want to be a little cautious here until we see the full data,” — Stifel analyst
What’s Next
Biogen plans to launch a Phase 3 registrational trial of diranersen, with enrollment criteria mirroring CELIA’s early-Alzheimer’s cohort. Full CELIA data will be presented at the July Alzheimer’s Association International Conference, and the long-term extension study will continue monitoring safety and durability. Regulatory discussions are expected to follow the Phase 3 readout.
