Biogen Inc.

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Bullish +75

Topline Results from Phase 2 CELIA Study of Diranersen (BIIB080): First Study to Show Reduction in Tau Pathology and Cognitive Benefit in Patients with Early Alzheimer’s Disease

🧠 Biogen announced positive topline results from the Phase 2 CELIA study of diranersen (BIIB080), an investigational antisense oligonucleotide (ASO) targeting tau in early Alzheimer's disease.

📉 The trial showed robust reductions in cerebrospinal fluid tau and tau pathology on PET scans across all studied doses, maintaining throughout the treatment period.

🧠 Cognitive endpoints demonstrated a slowing of clinical decline across all doses, with the most pronounced effect observed at the lowest dose of 60 mg administered every 24 weeks.

⚠️ The study did not meet its primary endpoint, which assessed dose response for change from baseline on the Clinical Dementia Rating–Sum of Boxes (CDR-SB) at Week 76.

📅 CELIA is an 18-month, global Phase 2 randomized, double-blind, placebo-controlled study that enrolled 416 participants with mild cognitive impairment or mild Alzheimer's dementia.

💉 Participants received diranersen via intrathecal injection over a 76-week treatment period, evaluating three doses: 60 mg Q24W, 115 mg Q24W, and 115 mg Q12W.

🛡️ The safety profile was generally consistent with Phase 1b data, though a higher incidence of serious adverse events was observed at the highest dose studied (115 mg every 12 weeks).

💊 Diranersen is a first-in-class therapy designed to reduce both intracellular and extracellular tau protein production at its source in early Alzheimer's disease.

🏆 Biogen received FDA Fast Track designation for diranersen in 2025 following the discovery of the asset by Ionis Pharmaceuticals in 2019.

🎤 Priya Singhal, Executive VP of Development at Biogen, stated that these results provide confidence to advance diranersen to registrational development.

🗣️ Dr. Jeff Cummings from the University of Nevada, Las Vegas noted the data represents meaningful progress toward a new mechanism of action for Alzheimer's treatments.

📢 Data from the CELIA study will be presented at the Alzheimer's Association International Conference (AAIC) in 2026 and other upcoming scientific congresses.

🤝 An ongoing long-term extension (LTE) study is continuing to evaluate the long-term safety and efficacy of diranersen beyond the initial Phase 2 period.

Bullish Signals
  • Topline results from the Phase 2 CELIA study demonstrated robust reductions in tau pathology across all studied doses, with findings generally consistent with the positive Phase 1b study.
  • Pre-specified analyses of cognitive endpoints showed a slowing of clinical decline across all doses, particularly notable at the lowest dose of 60 mg administered every 24 weeks.
  • Diranersen achieved its first-ever randomized Phase 2 demonstration of both robust biomarker impact and cognitive benefit in patients with early Alzheimer's disease.
  • Biogen Executive Vice President Priya Singhal stated that these compelling results give the company confidence to advance diranersen to registrational development.
  • The safety and tolerability profile was generally consistent with prior Phase 1b data, indicating a favorable risk profile across the studied doses.
  • Diranersen (BIIB080) received Fast Track designation from the U.S. FDA in 2025 for the treatment of Alzheimer's disease.
  • The study enrolled 416 participants with mild cognitive impairment or mild Alzheimer's disease, and all had not previously received anti-amyloid therapy.
Risk Factors
  • The primary endpoint of the Phase 2 CELIA study was not met, as diranersen failed to demonstrate a statistically significant dose-response effect on the Clinical Dementia Rating–Sum of Boxes (CDR-SB) at Week 76.
  • While cognitive decline slowed across doses, the results for the primary efficacy metric fell short of regulatory approval thresholds required for registrational development.
  • Safety concerns arose in the highest dose group, which observed a higher incidence of serious adverse events (SAEs) compared to other groups and placebo.
  • The study failed to show consistent efficacy at all doses; specifically, the lowest dose of 60 mg showed particular promise, suggesting that lower dosing may be more effective than the higher doses tested.
  • No patients in the CELIA trial had prior exposure to anti-amyloid therapy, limiting the generalizability of results to the broader Alzheimer's disease population who are currently being treated with anti-amyloid agents.
Full Analysis
Biogen Inc. (BIIB) announced compelling topline results from the Phase 2 CELIA study on May 14, 2026, evaluating diranersen (BIIB080), a tau-targeting antisense oligonucleotide (ASO), in patients with early Alzheimer's disease. This trial marks the first randomized Phase 2 study of a tau-directed therapy to demonstrate both robust biomarker impact and cognitive benefit. The study enrolled 416 participants with mild cognitive impairment or mild dementia who had not previously received anti-amyloid therapy, with results expected to be presented at the Alzheimer's Association International Conference in 2026. Pre-specified analyses of cognitive endpoints showed a slowing of clinical decline across all studied doses, particularly at the lowest dose of 60 mg administered every 24 weeks. Additionally, diranersen demonstrated robust reductions in cerebrospinal fluid (CSF) tau and tau pathology as measured by PET across all dose groups, with reductions maintained throughout the dosing period. Despite these positive findings on secondary and exploratory measures, the study did not meet its primary endpoint, which was to assess dose response for change from baseline on the Clinical Dementia Rating–Sum of Boxes (CDR-SB) at Week 76. The safety profile was generally consistent with prior observations from Phase 1b, though a higher incidence of serious adverse events was noted at the highest dose studied compared to other groups. The drug has received Fast Track designation from the FDA for Alzheimer's disease since 2025 and is developed under an exclusive license obtained by Biogen from Ionis Pharmaceuticals in December 2019. These results suggest that reducing tau, a hallmark of Alzheimer's associated with neurodegeneration, may meaningfully impact disease progression, though registrational development will require further evidence following this Phase 2 data.