Biogen advances diranersen after mixed phase 2 Alzheimer’s data

Biogen is advancing diranersen into registrational development after reporting topline results from the phase 2 CELIA study in early Alzheimer’s disease, even though the trial missed its primary endpoint. The company said the study failed on its planned dose-response analysis for change from baseline on CDR-SB at Week 76, but also reported pre-specified evidence of slower clinical decline across all dose groups, particularly with the lowest dose, and robust reductions in tau biomarkers. (globenewswire.com)

That makes CELIA a nuanced readout rather than a clean win or loss. Diranersen is an investigational antisense oligonucleotide designed to reduce production of tau protein by targeting MAPT mRNA. Tau has been a high-interest target in Alzheimer’s research because abnormal tau accumulation is closely linked to neurodegeneration and cognitive decline, but drug development in this area has lagged behind amyloid-focused programs. Biogen has been positioning BIIB080 as a potentially important pipeline asset for several years, and its 2025 annual report described it as a phase 2, proof-of-concept program. The FDA granted Fast Track designation to BIIB080 in April 2025. (globenewswire.com)

The CELIA study enrolled 416 participants with mild cognitive impairment due to Alzheimer’s disease or mild Alzheimer’s disease dementia. It was a global, randomized, double-blind, placebo-controlled, dose-ranging trial, with three intrathecal dosing regimens tested over a 76-week placebo-controlled period: 60 mg every 24 weeks, 115 mg every 24 weeks, and 115 mg every 12 weeks. According to Biogen, the study showed reductions in cerebrospinal fluid tau and tau PET measures across all doses, with the strongest clinical signal at the lowest dose. The company also said safety and tolerability were generally consistent with prior phase 1b findings, though serious adverse events were more common at the highest dose. (globenewswire.com)

Outside reaction has been cautiously constructive. The Alzheimer’s Association said the trial “did not hit its primary endpoint,” but called the readout important progress because of the reported slowing of clinical decline and reductions in tau in the brain. The group said people living with Alzheimer’s need more treatment options and pointed to the coming AAIC 2026 presentation for a fuller look at benefit and safety. In Biogen’s release, Jeff Cummings of the University of Nevada, Las Vegas, said the results offer the first evidence that reducing tau in a randomized phase 2 study may meaningfully affect disease progression. (alz.org)

The bigger industry takeaway is that Biogen appears to be betting regulators and investors will view CELIA as directionally positive despite the formal miss. That interpretation is supported by the company’s emphasis on pre-specified cognitive analyses, biomarker consistency across doses, and the possibility that lower exposure may be the more effective and safer path forward. That’s an inference from the topline framing, not a confirmed regulatory conclusion, and it will need fuller data to hold up. STAT characterized the results as mixed, underscoring the tension between the missed primary endpoint and the biomarker-plus-clinical signal Biogen is highlighting. (globenewswire.com)

Why it matters: For veterinary professionals, this story sits outside day-to-day companion animal practice, but it matters as a signal in comparative neuroscience and drug development. Tau biology is relevant across neurodegenerative research, and CELIA may influence how industry designs CNS trials when biomarker movement and clinical outcomes don’t align neatly with the original statistical plan. It’s also a reminder that late-stage decisions increasingly hinge on totality of evidence, not just a headline endpoint. For clinicians and industry watchers alike, the case will be whether regulators accept Biogen’s argument that the overall package justifies a registrational study. (globenewswire.com)

What to watch: The next key milestone is the full data presentation at AAIC in July 2026, where dosing effects, subgroup findings, and safety details should become clearer. After that, the main questions are how Biogen structures a phase 3 or other registrational program, whether it narrows to the 60 mg every-24-weeks regimen, and how diranersen might eventually fit alongside or after anti-amyloid therapies, given that CELIA enrolled participants who had not previously received them. (alz.org)