About 400 patients with mild cognitive impairment or mild Alzheimer’s showed slower worsening on five of six cognitive tests after Biogen’s diranersen, with the lowest dose producing a 26% decline reduction in one measure.
The antisense drug works by reducing production of tau — a protein linked to Alzheimer’s symptoms — rather than clearing amyloid, the target of approved drugs lecanemab and donanemab.
Biogen’s phase 2 study missed its preset goal because higher doses did not outperform lower ones, but researchers said the twice-yearly spinal injection still delivered encouraging tau-lowering and clinical signals.
Side effects included injection-site pain and about a week of temporary confusion after dosing, while no brain inflammation was seen — a notable safety issue with some anti-amyloid treatments.
The findings, presented in London, add momentum to broader tau-focused efforts including an NIH-backed UCSF platform trial and other experimental approaches aimed at Alzheimer’s, which affects more than 7 million Americans.
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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.