Biogen detailed Phase 2 CELIA data showing its lowest BIIB080 dose slowed early Alzheimer’s decline by 26% on CDR-SB over 18 months, a result close to Leqembi’s 27% in its pivotal study.
The tau-targeting drug technically failed CELIA’s main goal because benefit did not rise with higher doses, yet Biogen said cognitive gains and tau reductions justified moving into Phase 3.
Several other measures in the low-dose arm declined 23% to 50% more slowly than placebo, though Biogen said most of those endpoints had only nominal statistical significance.
Safety appeared manageable: most adverse events were mild to moderate, more than 90% of core-trial completers entered an extension phase, but confusional states in some patients still need explanation.
The readout could revive the long-struggling tau field and sharpen debate over whether BIIB080 merits a roughly $580 million Phase 3 investment despite analysts’ concerns about its odds of success.
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Biogen’s Diranersen Shows Robust Tau Reduction and Cognitive Gains in Phase 2 Alzheimer’s Trial, Advancing to Registrational Development
Overview
Biogen recently announced promising Phase 2 results for diranersen at the 2026 AAIC, marking a significant step forward in early Alzheimer’s disease treatment. The CELIA study showed that diranersen led to meaningful clinical improvements and a strong reduction in tau protein over 18 months. This dual impact on both symptoms and a key disease biomarker is encouraging for patients and researchers. The unprecedented combination of clinical and biomarker benefits has given Biogen the confidence to move diranersen into registrational development, with plans to work closely with regulators and the Alzheimer’s community on next steps.