Conference Presentation

Biogen to unveil first CELIA data on tau-targeting BIIB080 at AAIC

The Phase 2 CELIA study tests whether reducing tau production with an antisense drug moves CDR-SB in early Alzheimer's, a mechanism with no approved precedent.

By AppliedXLJuly 14, 2026Trial NCT05399888

Executive Summary

Biogen will lay out the clinical, biomarker, and safety detail behind a tau-lowering therapy in early Alzheimer's disease for the first time, building on a topline announcement made months earlier.
The approach targets tau production directly rather than amyloid plaques, testing a mechanism that has not yet produced an approved therapy in this disease.
Only one other clinical-stage program shares this exact target, so the data will be read as a proof point for tau reduction as a therapeutic strategy generally, not just for this drug.
Biogen has signaled it intends to advance the program into a larger trial, so the depth and consistency of the clinical and biomarker findings will shape how that next study gets designed.

The presentation

Biogen said it will present topline results from CELIA, an 18-month Phase 2 study evaluating diranersen, an antisense oligonucleotide designed to reduce tau RNA production, in patients with early Alzheimer's disease, during a Developing Topics session at AAIC on July 14, 2026. The company said the session will include initial clinical, biomarker, and safety results that build on the topline announcement it made in May 2026. Priya Singhal, Biogen's Executive Vice President and Head of Development, said the topline results "reinforce the potential of tau reduction as a therapeutic approach in early Alzheimer's disease". Biogen

Probability of Success

Endpoint Met1%

Completes42%

Clinical Significance76%

Regulatory53%

The trial

CELIA (NCT05399888) is a randomized, placebo-controlled Phase 2 study that enrolled 416 participants aged 50 to 80 with mild cognitive impairment or mild dementia due to Alzheimer's disease, confirmed by amyloid PET or CSF testing. Participants receive intrathecal (spinal injection) diranersen or placebo every 12 or 24 weeks for 76 weeks. The primary endpoint is dose response in change from baseline to week 76 on the Clinical Dementia Rating-Sum of Boxes (CDR-SB), a standard measure of cognitive and functional decline, with seven secondary endpoints spanning cognition (ADAS-Cog13, MMSE), function (ADCS-ADL-MCI), and safety (treatment-emergent and serious adverse events). The trial is not registrational. NCT05399888

Timeline and enrollment

The registry primary completion date moved from December 2026 to November 2027 in December 2023, then pulled forward to May 2026 and finally to March 11, 2026 as the trial progressed. Enrollment was revised from 735 to 364 in August 2024, then raised back to 416 by November 2024, where it has held since. The trial's overall completion date, covering a long-term extension period, remains June 2028. The AAIC presentation follows the primary completion date by about four months, consistent with data cleaning and analysis on a study of this size. NCT05399888

The mechanism and field

Diranersen targets MAPT RNA to lower tau production at its source, a mechanism Biogen describes as distinct from clearing tau protein after it accumulates. Tau-focused programs remain sparse in Alzheimer's disease: the nearest direct comparator sharing the MAPT target is Merck's MK-2214, also in Phase 2, while the broader indication is dominated by amyloid-targeting antibodies such as lecanemab and donanemab, which work through a different mechanism. No tau-lowering ASO has reached an approved or late-stage validated outcome in this disease, so the CELIA data will be read as an early test of whether reducing tau production translates into a measurable clinical or biomarker effect. Biogen

Regulatory context

The FDA granted diranersen Fast Track designation for Alzheimer's disease in 2025, a status that allows more frequent FDA interaction and rolling review but does not itself signal a particular approval outcome. Biogen has said the program is advancing toward Phase 3 development, positioning the AAIC data as an input into that next trial's design rather than a standalone regulatory event. Biogen

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