With so many unknowns, Biogen is carefully eyeing its next-gen Alzheimer’s treatment diranersen as a high-risk, high-reward project with the potential for a major payout around 2030.
Biogen CEO Chris Viehbacher is not betting the whole house on the upcoming Alzheimer’s disease treatment diranersen. But the rewards, if the tau-targeting therapy is successful, could be extraordinary.
Earlier this month, Biogen revealed early data from the Phase 2 CELIA trial that appeared to validate the theory that lowering tau can improve cognition in Alzheimer’s. Tau has long been seen as a key biomarker for addressing the underlying cause of the disease but has confounded researchers. The Alzheimer’s space is littered with high-profile failures—including Biogen’s own Aduhelm, which was ultimately withdrawn from the market after a controversial FDA nod in 2021. The therapy was the first approved to address an underlying cause of the disease, but the high price and questions around efficacy stymied the launch.
That saga predates Viehbacher. But the lessons for Biogen have remained, with the CEO taking a more cautious—but not completely risk averse—approach to resting the company’s entire fortunes on the intractable neurodegenerative disease.
“Up until now, tau has been a theory—it’s been a favorite theory, but it’s still a theory—and this is the first time anybody’s shown any data on this,” Viehbacher said during a second quarter earnings call on Wednesday.
Diranersen, previously known as BIIB080, is an antisense oligonucleotide that targets microtubule-associated protein tau mRNA to reduce production of the protein. The drug goes beyond previous approaches to target intracellular and extracellular tau, with the goal of spurring a more meaningful reduction of the protein. Diranersen was licensed from Ionis Pharmaceuticals in 2019.
Viehbacher credits Head of Development Priya Singhal for booking a number of additional analyses from outside experts for the CELIA data before releasing it to the public. Singhal was around through the days of Aduhelm, stepping up to lead R&D in the wake of the controversy in 2022. She arranged for an independent biostatistician and other outside experts to review the data.
Biogen reported that while diranersen missed the CELIA trial’s primary endpoint , the therapy led to a 26% slowing of disease severity, as well as a slowing of cognitive decline. On the main goal, the drug performed better than placebo, the company pointed out.
“One of the very strong feedbacks is the signal is real. This is not due to chance,” Viehbacher said.
Tau is still not fully understood, the CEO acknowledged. While the data appear to show an impact on cognition, scientists—including those at Biogen—are still trying to parse out the correct level that would lead to the best outcome for patients. The company is working with the neurology community to find these answers, and the FDA on the regulatory side of this new class of medicines.
“It’s very clear that tau is important to neurotransmission,” Viehbacher said. “And so while too much is not good, maybe too little is also not good. We just don’t know.”
While Biogen now has conviction in diranersen thanks to the CELIA data, and Viehbacher appears confident that it will someday go on to FDA approval, he isn’t about to bet Biogen’s entire future on the asset.
“This is the issue of being in breakthrough. It’s very exciting, but it’s also one of the reasons we decided not to build the company on this type of product,” Viehbacher said, however adding, “We’re confident in the signal, and it could be an exciting option.”
A long-term extension of CELIA is currently underway as well as a Phase 3 trial. Meanwhile, Biogen will count more on its upcoming lupus portfolio for growth.
“Alzheimer’s is certainly going to be a core part of the portfolio of Biogen, particularly now that there’s a very good chance that diranersen ultimately makes it to market,” Viehbacher said.
The key to Biogen’s Alzheimer’s work is improving cognition, which is what patients and physicians have been clamoring for. If approved, diranersen would join Biogen’s Eisai-partnered Leqembi and Eli Lilly’s Kisunla, which have been noted to slow disease progression and improve cognition.
Asked about whether Biogen is looking at so-called “brain shuttle” technology as the next generation of treatments for the disease, Singhal confirmed that the company is indeed examining the modality. The technology uses iron to “shuttle” the medicine into the brain, allowing for lower doses than previously needed for Leqembi or Kisunla. This could, in turn, avoid major side effects known to the monoclonal antibody class, such as brain swelling or bleeding.
In December 2025, rival Roche revealed early results for trontinemab, which uses the Swiss pharma’s proprietary Brainshuttle technology, showing a reduction in amyloid plaques. The results marked a return to the Alzheimer’s space for Roche’s Genentech, which fell behind Lilly and Biogen, but also generated significant excitement again for the field.
Buoyed by the potential, Big Pharmas like Novartis and Lilly have been signing deals with small biotechs for better brain delivery tech.
The approval of Denali Therapeutics’ rare disease drug Avlayah earlier this year also bolstered interest in blood-brain barrier technology.
Others, like UCB and Johnson & Johnson, have been burned by the drive into tau. Biogen’s Leqembi partner Eisai is working on a tau agent, as are Merck and Bristol Myers Squibb.
Beyond blood-brain barrier technology, Viehbacher said the Biogen team is also looking at combination therapies. One option could be combining an anti-tau agent with an A-beta, with a patient perhaps taking a few injections of the former before switching to the latter.
“All of those things are kind of what we’re wargaming,” Viehbacher said. “If we’re going to be in Alzheimer’s, we are certainly looking to have a portfolio, and clearly, brain shuttles would be the next generation of products to pursue.”
Meanwhile, Leqembi is continuing its slow move into the market. The drug took in $184 million for the second quarter, a 15% year-over-year increase, or 9% quarter over quarter. This was mostly due to the rollout of Leqembi IQLIK, which allows for at-home subcutaneous initiation of treatment.
This new formulation helped put Biogen once again at the forefront of the market over Lilly’s Kisunla, which is dosed once a month in a care setting. Treatment can also now be opened to more patients in rural settings, who previously would not have been offered care if they could not reach their doctors routinely. Patients are also more likely to remain on treatment longer if they can do so at home.
“The benefit that the competitor has with once monthly dosing now seems to be much less when you’ve got a home and home subcutaneous option for them,” Viehbacher said.
