Biogen Presents Phase 2 CELIA Data at AAIC Demonstrating Meaningful Clinical Outcomes and Robust Tau Reduction with Diranersen in Early Alzheimer’s Disease
Rhea-AI Summary
Biogen (Nasdaq: BIIB) reported detailed Phase 2 CELIA results for diranersen, an investigational antisense oligonucleotide targeting tau, in early Alzheimer’s disease. At 18 months, all studied doses showed efficacy on multiple prespecified cognitive and composite endpoints versus placebo, with the 60 mg every six months dose showing the strongest effects.
According to Biogen, the 60 mg regimen slowed decline by 0.54 points (26%) on CDR-SB, 42% on ADAS-Cog13, 50% on MMSE, 30% on modified iADRS, and 23% on ADCOMS, with most differences nominally significant. Diranersen achieved robust target engagement, producing mean 50–65% reductions in CSF total tau and PET-detected brain tau decreases across regions. The primary endpoint of a dose response on CDR-SB was not met, and no separation from placebo was seen on ADCS-ADL-MCI at 18 months. Diranersen was generally well tolerated, without anticipated amyloid-related imaging abnormalities, and Biogen plans to advance it into confirmatory Phase 3 development.
AI-generated analysis. How Rhea-AI works. Not financial advice.
Positive
- CDR-SB decline slowed 26% (0.54 points) with 60 mg every six months versus placebo at 18 months
- Cognitive endpoints improved with 60 mg: 42% slowing on ADAS-Cog13 and 50% on MMSE versus placebo
- Robust tau reduction: mean 50–65% decreases in CSF total tau across all studied doses
- Brain tau pathology decreased on PET across evaluated regions for all diranersen doses in the substudy (n=131)
- High treatment continuity: over 90% of participants completing the placebo-controlled period entered the extension study
- Biogen plans Phase 3 development of diranersen based on Phase 1b and Phase 2 CELIA data
Negative
- Primary endpoint not met: no dose response on CDR-SB at 18 months, with higher doses not providing greater benefit
- No ADCS-ADL-MCI separation from placebo at 18 months across dose groups, despite effects in CDR-SB functional domains
- Confusional state events reported, typically occurring within days of dosing, though mostly resolving within a week
Market reaction: BIIB -8.84% on Phase 2 CELIA clinical data
On the day this news was published, BIIB declined 8.84%, reflecting a notable negative market reaction. Argus tracked a trough of -5.3% from its starting point during tracking. Our momentum scanner triggered 37 alerts that day, indicating elevated trading interest and price volatility. This price movement removed approximately $2.99B from the company's valuation, bringing the market cap to $30.86B at that time.
Data tracked by StockTitan Argus on the day of publication.
Key Figures
Previous Clinical trial Reports
| Date | Event | Sentiment | 24h Move | Catalyst |
|---|---|---|---|---|
| Jul 12 | Clinical data update | Positive | +5.0% | LEQEMBI subcutaneous autoinjector data showing bioequivalent exposure and similar safety to IV. |
| Jun 30 | Phase 3 enrollment | Positive | -0.3% | Completion of enrollment of 162 patients in Phase 3 EMPEROR Dravet syndrome study. |
| Jun 29 | Conference preview | Positive | +0.3% | AAIC 2026 preview highlighting CELIA data and multiple LEQEMBI presentations. |
| May 14 | Topline Phase 2 data | Negative | -6.4% | CELIA topline showing no dose‑response on CDR‑SB but decision to advance diranersen. |
| Mar 19 | Phase 2 data | Positive | +0.6% | Late‑breaking AMETHYST data and Breakthrough Therapy Designation for litifilimab in CLE. |
24h Move is the share-price change in the day after each event; other market factors may also have contributed.
Tag‑matched clinical‑trial headlines have mostly moved in the same direction as their news tone, with an average one‑day move of -0.17%, indicating generally modest price impact but occasional sharp reactions.
Key Terms
adas-cog13 medical
mmse medical
antisense oligonucleotide medical
pet medical
apoe4 medical
AI-generated analysis. How Rhea-AI works. Not financial advice.
- Clinical outcomes: Diranersen demonstrated efficacy across all studied doses at 18 months, with consistent results across multiple prespecified clinical endpoints; the 60 mg dose showed the strongest response with slowing of clinical decline on the cognitive endpoints—
42% on ADAS-Cog13 and50% on MMSE—alongside a26% slowing on CDR-SB - Biomarker response: Diranersen is the first tau-directed therapy to demonstrate robust reductions in both CSF total tau, with mean reductions of 50–
65% , and brain tau pathology, as measured by PET, across all studied doses in a Phase 2 study - Dose response: CDR-SB results favored diranersen versus placebo across all studied doses; higher doses were not associated with greater slowing of decline
- Mechanism of action: Distinct from other tau-lowering approaches, diranersen targets MAPT mRNA to reduce the production of all tau isoforms, lowering both intracellular and extracellular tau protein
CAMBRIDGE, Mass., July 14, 2026 (GLOBE NEWSWIRE) -- Biogen Inc. (Nasdaq: BIIB) today announced data from the Phase 2 CELIA study evaluating diranersen, an investigational antisense oligonucleotide (ASO) therapy targeting tau, in individuals with early Alzheimer’s disease. The data, presented at the Alzheimer’s Association International Conference (AAIC) 2026, expand upon previously reported topline results and demonstrate a combination of meaningful clinical efficacy and robust biomarker effects, providing Phase 2 proof of concept for diranersen’s tau-directed mechanism of action. Based on the growing and consistent body of evidence from the Phase 1b and Phase 2 studies, Biogen plans to advance diranersen into confirmatory Phase 3 development.1
“The CELIA data provide some of the clearest evidence that reducing tau pathology can translate into clinically meaningful benefit,” said Professor Cath Mummery, Professor of Clinical Neurology at the UCL Queen Square Institute of Neurology and Consultant Neurologist at University College London Hospitals NHS Foundation Trust. “The magnitude of tau reduction and cognitive benefit observed in CELIA is among the most compelling reported to date in Alzheimer’s disease drug development and supports advancing diranersen to Phase 3 development.”
“The CELIA clinical, biomarker, and safety data presented at AAIC provide proof of concept and important evidence of diranersen’s novel tau-reduction mechanism of action translating into clinical benefit. If confirmed in Phase 3, diranersen could represent an important new therapeutic approach targeting one of the core pathologies of Alzheimer's disease,” said Priya Singhal, M.D., M.P.H., Executive Vice President and Head of Development at Biogen. “Patients and families urgently need new approaches that address the complexity of Alzheimer’s disease. We look forward to working with health authorities and the broader Alzheimer’s community as diranersen advances to Phase 3.”
Diranersen demonstrated efficacy across all studied doses at 18 months, with consistent efficacy across multiple prespecified secondary endpoints, including the Clinical Dementia Rating Sum of Boxes (CDR-SB), a global measure of cognition and daily function; ADAS-Cog13 and MMSE, measures of cognition; modified iADRS and ADCOMS, composite measures of cognition, function, and disease progression; as well as the individual cognitive and functional domains of CDR-SB. Diranersen 60 mg administered intrathecally every six months (n=60) showed the strongest response at 18 months. Compared with placebo (n=115), diranersen 60 mg demonstrated slowing of clinical decline by 0.54 points (
Clinical effects were also observed in the other studied dose regimens. Compared with placebo, diranersen 115 mg administered intrathecally every six months (n=115) and diranersen 115 mg administered intrathecally every three months (n=116) demonstrated slowing of clinical decline by 0.28 and 0.18 points (
CELIA was designed with a primary endpoint of dose response on CDR-SB at 18 months to investigate whether higher doses of diranersen could provide greater clinical benefit. As previously disclosed, this was not observed, and the study did not meet its primary endpoint.
Diranersen demonstrated target engagement and robust reductions in cerebrospinal fluid (CSF) total tau across all studied doses, with mean reductions of 50–
Diranersen was generally well tolerated. During the placebo-controlled period, most participants who experienced adverse events had events that were mild or moderate in severity, non-serious, and did not result in treatment discontinuation or study withdrawal. The most frequent adverse events were procedural pain, post-lumbar puncture syndrome, and confusional state. Most adverse events of confusional state occurred within a few days of dosing and resolved within a week. Among participants who completed the placebo-controlled period, more than
The study enrolled a population representative of early Alzheimer’s disease, with baseline characteristics generally balanced across treatment groups. Participants had a mean age of 68 years,
Additional analyses and data from CELIA and the ongoing long-term extension study will be presented at future scientific conferences.
A Media Snippet accompanying this announcement is available by clicking on this link.
Educational Program on Tau in Alzheimer’s Disease
At AAIC, Biogen is hosting an interactive booth offering an immersive journey into the role of tau in Alzheimer’s disease, from pathology to clinical presentation. Biogen is also expanding its educational efforts with a new e-learning module on KnowTau.com, building on the resources already available.
For more information, please see the AAIC 2026 program and visit the Biogen AAIC booth.
About diranersen (BIIB080)
Diranersen (BIIB080) is an investigational antisense oligonucleotide (ASO) therapy designed to target microtubule-associated protein tau (MAPT) mRNA to reduce the production of tau protein. Unlike many investigational approaches that have focused on targeting extracellular tau, diranersen is designed to reduce both intracellular and extracellular tau.
Diranersen is being investigated as a potential treatment for early Alzheimer’s disease. In 2025, the U.S. Food and Drug Administration (FDA) granted Fast Track designation to diranersen for the treatment of Alzheimer’s disease.
In December 2019, Biogen exercised a license option with Ionis Pharmaceuticals and obtained a worldwide, exclusive, royalty-bearing license to develop and commercialize diranersen. Diranersen was discovered by Ionis.
About the CELIA Study
CELIA is a global Phase 2 randomized, double-blind, placebo-controlled, dose-ranging study evaluating the efficacy, safety, and tolerability of diranersen in individuals with early Alzheimer’s disease. The study enrolled 416 participants with mild cognitive impairment due to Alzheimer’s disease or mild Alzheimer’s disease dementia. All participants enrolled in CELIA had not previously received anti-amyloid therapy.
The study evaluated three doses of diranersen administered intrathecally over an 18-month placebo-controlled treatment period: 60 mg every six months, 115 mg every six months, and 115 mg every three months.
The primary endpoint of CELIA was assessment of dose response for change from baseline on the Clinical Dementia Rating–Sum of Boxes (CDR-SB) at Week 76. Secondary and exploratory endpoints included additional clinical, biomarker, and imaging measures, including cerebrospinal fluid tau biomarkers and tau positron emission tomography (PET). Additional information on the study design is available in the ClinicalTrials.gov listing for the CELIA study.
An ongoing long-term extension (LTE) study is continuing to evaluate the long-term safety, tolerability, and durability of diranersen’s clinical benefit in early Alzheimer’s disease.
About Biogen
Founded in 1978, Biogen is a leading biotechnology company that pioneers innovative science to deliver new medicines to transform patients’ lives and to create value for shareholders and our communities. We apply deep understanding of human biology and leverage different modalities to advance first-in-class treatments or therapies that deliver superior outcomes. Our approach is to take bold risks, balanced with return on investment to deliver long-term growth.
We routinely post information that may be important to investors on our website at www.biogen.com. Follow us on social media - Facebook, LinkedIn, X, YouTube.
Biogen Safe Harbor
This news release contains forward-looking statements, including, among others, relating to: the potential benefits, efficacy and safety of diranersen; the potential that, if confirmed in Phase 3, diranersen could represent a new therapeutic approach targeting one of the core pathologies of Alzheimer's disease; potential regulatory discussions, submissions, decisions and approvals and the timing thereof; the anticipated benefits, risks and potential of our collaboration arrangements; the potential of our commercial business and pipeline programs, including diranersen; and risks and uncertainties associated with drug development and commercialization. These forward-looking statements may be accompanied by such words as “aim,” “anticipate,” “assume,” “believe,” “contemplate,” “continue,” “could,” “estimate,” “expect,” “forecast,” “goal,” “guidance,” “hope,” “intend,” “may,” “objective,” “outlook,” “plan,” “possible,” “potential,” “predict,” “project,” “prospect,” “should,” “target,” “will,” “would” or the negative of these words or other words and terms of similar meaning. Drug development and commercialization involve a high degree of risk, and only a small number of research and development programs result in commercialization of a product. Results in early-stage clinical trials may not be indicative of full results or results from later stage or larger scale clinical trials and do not ensure regulatory approval. You should not place undue reliance on these statements. Given their forward-looking nature, these statements involve substantial risks and uncertainties that may be based on inaccurate assumptions and could cause actual results to differ materially from those reflected in such statements.
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Reference:
- Shulman M, Wu S, Ziogas N, et al. Exploratory analyses of clinical outcomes from the BIIB080 phase 1b study in mild Alzheimer’s disease. Nature Aging. 2026;6:445-453. https://doi.org/10.1038/s43587-025-01031-9. Accessed July 2026.
| MEDIA CONTACT: Madeleine Shin + 1 781 464 3260 public.affairs@biogen.com | INVESTOR CONTACT: Tim Power +1 781 464 2442 IR@biogen.com |
