A Phase 2 trial called CELIA tested diranersen, a drug designed to reduce tau — a protein that builds up harmfully in Alzheimer's disease. The study enrolled 416 people with early Alzheimer's who had never received amyloid-targeting treatment. Results showed the drug significantly reduced tau in spinal fluid and brain scans across all doses tested. Importantly, patients showed slowed cognitive decline, particularly at the lowest dose. While the trial missed its primary statistical endpoint measuring dose-response on a standard dementia rating scale, Biogen considers the cognitive and biomarker data strong enough to move into larger registrational trials. This is the first randomized Phase 2 evidence that targeting tau can produce both measurable brain changes and real cognitive benefit.
