CAMBRIDGE, Mass., May 14, 2026
Biogen Inc. has announced promising topline results from its Phase 2 CELIA study evaluating diranersen (BIIB080), an investigational antisense oligonucleotide (ASO) therapy targeting tau protein in patients with early Alzheimer’s disease. The study marks the first randomized Phase 2 trial to demonstrate both a reduction in tau pathology and measurable cognitive benefit from a tau-directed therapy, potentially opening a major new pathway in Alzheimer’s disease treatment development.
First Tau-Targeting Therapy to Show Cognitive Benefit
Biogen reported that pre-specified analyses of cognitive endpoints showed slowing of clinical decline across all tested doses, with the strongest impact observed in patients receiving the lowest 60 mg dose administered every 24 weeks. Researchers also observed robust reductions in cerebrospinal fluid (CSF) tau biomarkers and significant decreases in tau pathology measured using positron emission tomography (PET) imaging across all dosing groups. These findings reinforce the growing scientific understanding that reducing tau accumulation may directly influence disease progression in Alzheimer’s patients.
Although the CELIA trial did not meet its primary endpoint assessing dose response on the Clinical Dementia Rating–Sum of Boxes (CDR-SB) at Week 76, Biogen stated that the overall biomarker and efficacy profile was compelling enough to support advancement into registrational development. The company plans to engage regulators regarding the next stages of clinical development for diranersen.
Priya Singhal, Executive Vice President and Head of Development at Biogen, described the data as an unprecedented combination of biomarker improvement and clinical efficacy from a tau-directed agent in early Alzheimer’s disease. The company emphasized that the findings could represent a major scientific advancement for neurodegenerative disease therapeutics.
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Innovative ASO Technology Targets Tau at Its Source
Diranersen is designed as a first-in-class antisense oligonucleotide therapy that targets microtubule-associated protein tau (MAPT) mRNA to reduce production of tau protein directly at its source. Unlike many experimental Alzheimer’s therapies focused primarily on extracellular tau, diranersen aims to reduce both intracellular and extracellular tau accumulation, which are strongly associated with neurodegeneration and cognitive decline.
The CELIA study enrolled 416 participants with mild cognitive impairment due to Alzheimer’s disease or mild Alzheimer’s dementia who had not previously received anti-amyloid therapies. The randomized, double-blind, placebo-controlled trial evaluated three intrathecal dosing regimens over a 76-week treatment period, including 60 mg every 24 weeks, 115 mg every 24 weeks, and 115 mg every 12 weeks.
Importantly, the safety and tolerability profile of diranersen was generally consistent with earlier Phase 1b data. Biogen reported that adverse event rates were comparable across dose groups, although a higher rate of serious adverse events was observed at the highest dose tested.
Alzheimer’s Research Gains Momentum
The topline findings arrive at a critical time for the Alzheimer’s disease field, where researchers continue searching for therapies capable of slowing neurodegeneration beyond amyloid-focused mechanisms. Experts believe tau pathology is closely linked to disease severity and cognitive decline, making tau reduction an increasingly important therapeutic target.
Dr. Jeff Cummings, Professor of Brain Sciences at the University of Nevada, Las Vegas, stated that the CELIA results provide the first evidence that reducing tau may meaningfully impact disease progression in Alzheimer’s disease. He described the data as meaningful progress toward shaping the next generation of Alzheimer’s treatments.
Biogen also confirmed that an ongoing long-term extension study will continue evaluating the long-term durability, safety, and tolerability of diranersen in early Alzheimer’s disease patients. Additionally, the U.S. FDA granted Fast Track designation to diranersen in 2025, highlighting the therapy’s potential importance in addressing a major unmet medical need.
Source: Biogen press release
