Biogen's Tau-Targeting Diranersen Shows Promise in Phase 2 Alzheimer's Trial
Biogen's Phase 2 CELIA trial showed diranersen slowed Alzheimer's decline and cut tau biomarkers, but missed the dose-response goal. Leqembi sales data is expected next quarter.
On May 14, 2026, Biogen announced top-line results from the Phase II CELIA study evaluating diranersen (BIIB080), an investigational antisense oligonucleotide therapy targeting tau, in individuals with early Alzheimer’s disease. The trial demonstrated a slowing of clinical decline in Alzheimer’s patients, especially at the lowest dose of diranersen, 60 mg administered biannually, and is the first randomized Phase 2 trial to indicate a substantial impact on biomarkers and cognitive function through a tau-targeted approach. Treatment also showed significant reductions in tau levels in cerebrospinal fluid and tau-related pathology, as evidenced by positron emission tomography (PET) scans.
The study did not, however, achieve its primary goal of establishing a dose-response relationship by Week 76, and the safety profile of diranersen remained consistent with previous research.
In a related Alzheimer’s development, Leqembi, developed in partnership with Eisai, received full FDA approval in July 2023 and was widely expected to become a blockbuster treatment for early Alzheimer’s disease. The commercial ramp has been slower than many had anticipated, with challenges around patient identification, diagnostic infrastructure, and insurance reimbursement limiting near-term uptake. Biogen has been working with healthcare systems and insurance providers to broaden access, and the company has signalled that it expects uptake to accelerate as the infrastructure around amyloid testing and infusion administration matures. The next major catalyst will be updated Leqembi sales data in its upcoming quarterly earnings report.
Biogen Inc. is an established biopharmaceutical company focused on discovering, developing, manufacturing, and delivering therapies for neurological, rare, and autoimmune diseases. With a market capitalization of approximately $29.42 billion, the company’s largest revenue generator in 2025 was its multiple sclerosis franchise, which contributed 40% of total revenue. Legacy products including Tecfidera for multiple sclerosis and Spinraza for spinal muscular atrophy continue to generate revenue but face generic and biosimilar competition. The company has restructured its research pipeline to focus on neuroscience and rare diseases. Biogen’s stock has had a difficult period in 2025 and 2026, trading well below the peaks reached when Alzheimer’s drug approvals first generated investor excitement.