CAMBRIDGE, Mass., July 14, 2026
Biogen announced positive Phase 2 CELIA study results demonstrating that investigational antisense oligonucleotide therapy diranersen (BIIB080) achieved meaningful clinical benefits alongside robust reductions in tau biomarkers in patients with early Alzheimer’s disease. Presented at the Alzheimer’s Association International Conference (AAIC) 2026, the findings provide proof-of-concept for targeting tau pathology through MAPT mRNA suppression and support Biogen’s decision to advance diranersen into Phase 3 clinical development.
Phase 2 CELIA Trial Demonstrates Consistent Clinical Benefit
The global Phase 2 CELIA trial evaluated diranersen across three dose regimens in 416 patients with early Alzheimer’s disease over an 18-month placebo-controlled period. The investigational therapy demonstrated efficacy across all studied doses on multiple prespecified clinical endpoints, including Clinical Dementia Rating Sum of Boxes (CDR-SB), ADAS-Cog13, MMSE, modified iADRS, and ADCOMS. The 60 mg dose administered every six months produced the strongest clinical response, slowing cognitive decline by 42% on ADAS-Cog13, 50% on MMSE, and 26% on CDR-SB compared with placebo. Although the study did not meet its primary endpoint evaluating dose-response, the consistent benefit observed across multiple clinical measures supports continued development.
Diranersen Achieves Robust Tau Reduction Across Biomarkers
Diranersen became the first tau-directed therapy to demonstrate substantial reductions in both cerebrospinal fluid (CSF) total tau and brain tau pathology in a Phase 2 Alzheimer’s study. Across all dose groups, patients experienced 50% to 65% reductions in CSF total tau, while tau PET imaging showed decreases in tau pathology across multiple brain regions. Unlike therapies targeting extracellular tau alone, diranersen reduces production of all tau isoforms by targeting MAPT mRNA, lowering both intracellular and extracellular tau proteins and addressing a key pathological driver of Alzheimer’s disease.
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Favorable Safety Profile Supports Phase 3 Advancement
The investigational therapy was generally well tolerated, with most adverse events classified as mild or moderate and primarily related to lumbar puncture procedures. No amyloid-related imaging abnormalities (ARIA) were observed, consistent with diranersen’s tau-targeted mechanism of action. More than 90% of participants completing the placebo-controlled phase elected to continue into the ongoing long-term extension study. Based on the combined clinical efficacy, biomarker improvements, and safety profile demonstrated in the Phase 2 CELIA trial, Biogen plans to advance diranersen into confirmatory Phase 3 development as a potential disease-modifying therapy for early Alzheimer’s disease.
Source: Biogen, press release
