Analysts, investors and scientists are eager for Biogen’s 2026 BIIB080 readout. Even if successful, executives warn that there are many more steps before the Alzheimer’s therapy could reach the market.
A major proof-of-concept readout for Biogen’s next big Alzheimer’s disease bet could unlock a major piece of the treatment puzzle for the intractable neurodegenerative disease. But even if—and it’s a big if—the Phase 2 trial is a runaway success, Biogen will only be at the beginning of answering the questions the scientific community has been asking for decades about the tau mechanism.
“What I can tell you is that the neurology community is going to be also looking at these data very closely,” Biogen CEO Chris Viehbacher said on the company’s fourth quarter earnings call on Friday. Scientists have long believed that there are two key targets in Alzheimer’s: amyloid beta and tau. Treatment of the first was opened up with the approval of Biogen and Eisai’s Leqembi and later Eli Lilly’s Kisunla.
Biogen is on the leading edge of companies hoping to bring a tau-targeting option to the market. Working together, both types of medicines may finally show real clinical improvements on cognition. A mid-stage readout of an anti-tau therapy from Johnson & Johnson was unsuccessful in November 2025, putting the pressure on Biogen to prove the theory is still valid.
The company is expecting results for BIIB080, a tau-targeting antisense oligonucleotide, from the Phase 2 CELIA program. On Friday, Biogen narrowed down the timeline for the readout to sometime in the second or third quarter, having previously advised sometime in 2026, William Blair said on Friday.
“Every Alzheimer’s expert I talked to really think tau is an important target. And if you look at the severity of Alzheimer’s, that’s really related to the level of tau,” Viehbacher said.
If the results are positive, Jefferies analysts expect that Biogen’s stock could move 5–15%, according to a Friday note. The trial is testing three doses out to week 76 with the primary endpoint assessing cognition.
Competitors are watching closely too. H.C. Wainright wrote on Friday that Biogen’s results “could validate tau knockdown as a therapeutic strategy even if the study is positioned as signal-finding rather than statistically definitive.”
Changing the Paradigm
Tau may be an important target, but in terms of how a tau-targeting treatment like BIIB080 could change treatment, Viehbacher doesn’t know yet. Biogen, with partner Eisai, already markets Leqembi, which became the first disease-modifying treatment for Alzheimer’s in 2023. While the drug can clear the amyloid beta plaques in the brain, the effects on the hallmark symptoms of Alzheimer’s, like cognition, are more subtle. Adding a tau agent to the mix could finally create meaningful impact for patients.
“With BIIB080, we know we can actually reduce tau. The question will be, How long do you have to reduce the tau to move the needle on cognition?” Viehbacher wondered.
Viehbacher pointed to the unsuccessful readout for Novo Nordisk’s semaglutide in Alzheimer’s, which failed to slow the disease in a pair of Phase 3 clinical trials that read out in November 2025. “It’s quite hard to move that level of cognition,” Viehbacher said.
Neurologists have long suggested that combination therapies could be the key to unlocking more disease modification and symptom alleviation in Alzheimer’s. BIIB080 could be that key, Viehbacher said, perhaps paired with one of the amyloid-targeting antibodies like Leqembi or Kisunla. But the sequence of those treatments is an open question, the CEO noted: Would you tackle tau first or amyloid beta, or would you dose them at the same time?
H.C. Wainright suggested the order would be amyloid first, with tau agents layered on top after to further slow progression. That means that success for one asset is helpful for others, “rather than direct competitive threats,” the firm wrote, specifically flagging Voyager Therapeutics’ programs.
Safety First
Biogen is also keenly interested in the side effect profile of BIIB080. Leqembi and Eli Lilly’s rival medicine Kisunla both have a known side effect called amyloid-related imaging abnormalities (ARIA), small blips on imaging results that can suggest bleeding or swelling in the brain. Several patient deaths have resulted from the adverse event and the FDA now recommends earlier MRI monitoring for patients taking Leqembi.
“There is a belief that we’re not going to have anything like ARIA” with BIIB080, Viehbacher said. But again, his team needs data to confirm. “This is Phase 2 data that is really breakthrough science. Nobody knows. Nobody has been able to move the needle so far.”
Priya Singhal, head of development, also emphasized the importance of looking at different subgroups of patients who may respond best to BIIB080. Biogen will be looking for nuance in high vs low tau burden, fluid biomarkers and other trends.
Viehbacher knows that, if the study is positive, the neurology community will be excited. But he warned those watching the results not put the cart before the horse.
“I would also remind everybody that we would then have to go into a Phase 3 program, and anything in Alzheimer’s doesn’t happen on a very quick basis, so this would take several years again to be able to do that Phase 3 and launch the product.”
Analysts are keenly awaiting the data. Jefferies said that tau reduction over 50% in the mid-stage test would instill confidence in that future Phase 3 readout. The therapy achieved 50% to 60% reduction in an earlier Phase 1b trial, plus a cognition benefit. These results were encouraging for Jefferies and Stifel.
“This program demonstrated meaningful and never-seen-before levels of tau PET reductions in the ph1,” Stifel said in a Friday note. “Tau continues to be a target that we and KOLs [key opinion leaders] really like given the pathology is more closely correlated with cognitive decline.”
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