Biogen Inc. (NASDAQ:BIIB) traded higher after releasing encouraging Phase 2 data for its experimental Alzheimer’s treatment, diranersen, with results showing meaningful reductions in tau pathology alongside improvements across several measures of cognitive decline.
The findings, presented at the Alzheimer’s Association International Conference, support the company’s decision to advance the therapy into Phase 3 clinical development.
Study Shows Encouraging Cognitive Benefits
The Phase 2 CELIA trial demonstrated clinical benefits across all dose levels after 18 months of treatment.
The 60 mg dose delivered the strongest outcomes, slowing cognitive decline by 42% on the ADAS-Cog13 assessment and by 50% on the Mini-Mental State Examination (MMSE). The treatment also reduced disease progression by 26% on the Clinical Dementia Rating–Sum of Boxes (CDR-SB) scale.
Tau Biomarkers Decline Across All Doses
According to Biogen, diranersen is the first tau-targeting therapy to demonstrate reductions in both cerebrospinal fluid total tau and brain tau pathology in a Phase 2 Alzheimer’s study.
The treatment reduced total tau levels in cerebrospinal fluid by an average of 50% to 65%, while PET imaging also showed lower levels of tau accumulation in the brain across every dose evaluated.
Diranersen is an antisense oligonucleotide designed to target MAPT messenger RNA, reducing production of all forms of the tau protein associated with Alzheimer’s disease.
Phase 3 Programme Planned
Based on the latest findings, Biogen confirmed it intends to move diranersen into Phase 3 clinical trials.
The CELIA study enrolled 416 patients with early-stage Alzheimer’s disease, who received one of three intrathecal dose levels over an 18-month treatment period.
Although the study did not achieve its primary endpoint of demonstrating a dose-response effect on the CDR-SB scale at 18 months, the broader clinical and biomarker results supported continued development.
Safety Profile Remains Favourable
Biogen said diranersen was generally well tolerated throughout the study.
Most adverse events were classified as mild or moderate, with the most frequently reported events including procedural pain, post-lumbar puncture syndrome and episodes of confusional state.
More than 90% of participants who completed the placebo-controlled portion of the study chose to continue into the ongoing extension trial.
FDA Fast Track Status Supports Development
The U.S. Food and Drug Administration granted Fast Track designation to diranersen in 2025 for the treatment of Alzheimer’s disease, potentially helping to accelerate the programme’s regulatory pathway as development progresses.