Biogen and Ionis report first Phase 2 evidence that reducing tau protein may also help slow cognitive decline.
Alzheimer’s research may be entering its next chapter. Isn’t it that it’s been decades since Alzheimer’s drug development has chased the same amyloid plaques, the sticky protein clumps believed to build up in the brain long before symptoms appear? Billions of dollars and countless failed trials later, the field has started asking a more uncomfortable question: what if amyloid is only part of the story?
Now, new data from Biogen and Ionis Pharmaceuticals are helping push attention toward another suspect that researchers increasingly believe may be more directly tied to the disease people actually experience: tau.
The companies announced topline results from the Phase 2 CELIA study of diranersen (BIIB080), an investigational therapy designed to reduce tau protein in people with early Alzheimer’s disease [1]. The findings are drawing attention because they suggest something researchers have been trying to demonstrate for years: lowering tau may also slow cognitive decline.
Tau is deeply entangled (quite literally) with how Alzheimer’s progresses. If amyloid is often described as the match that starts the fire, many scientists now see tau as the flames spreading through the house.
Inside healthy brain cells, tau acts a bit like scaffolding, helping stabilize the internal transport systems neurons rely on to function. However, in Alzheimer’s disease, tau proteins can become abnormal, twist into tangles and spread through the brain. As those tangles accumulate, communication between neurons starts breaking down. Memory slips. Language becomes harder. Familiar routines suddenly feel unfamiliar.
Unlike many experimental Alzheimer’s therapies that attempt to clear tau after it accumulates, diranersen is designed to intervene earlier in the process by reducing the production of tau itself.
The therapy uses antisense technology – essentially short strands of synthetic genetic material designed to interrupt the instructions that tell cells to make tau protein. It is part of a growing class of RNA-based medicines that aim to stop disease processes closer to their biological source.
The CELIA study enrolled 416 people with early Alzheimer’s disease and followed them over 76 weeks. Participants received one of three dosing schedules or a placebo.
Technically, the study did not meet its primary endpoint, a measurement designed to assess dose response using a standard dementia rating scale. In many biotech announcements, that would be the headline.
Researchers still observed robust reductions in tau biomarkers across all doses studied. Brain imaging scans also showed reductions in tau pathology, suggesting the drug was affecting the biology of the disease itself rather than simply masking symptoms.
At the same time, pre-specified cognitive analyses showed slower clinical decline among treated participants, particularly among those receiving the lowest dose. In practical terms, patients appeared to lose cognitive function more slowly while the underlying tau buildup in the brain was also being reduced.
That dual signal – biological impact paired with cognitive benefit – is what has researchers paying attention.
“In CELIA, we believe we have seen an unprecedented and compelling confluence of efficacy and biomarkers results from a tau-directed agent in a randomized early Alzheimer’s disease study,” said Dr Priya Singhal, Executive Vice President and Head of Development at Biogen.
Biogen said the findings are strong enough to advance diranersen into registrational development, the stage typically intended to support eventual regulatory approval.
The excitement around tau is not just about one drug candidate. It reflects a larger transition happening across medicine and longevity research. Increasingly, aging-related diseases are being viewed less as isolated conditions and more as interconnected biological processes that may be modifiable earlier than once believed.
Alzheimer’s, in particular, has become central to that conversation because it represents one of the clearest examples of the gap between lifespan and healthspan. People are living longer than previous generations, but many still spend their later years battling cognitive decline, loss of independence and prolonged neurodegeneration. That is why therapies capable of slowing progression, even modestly, matter so much.
A few extra months of preserved memory may sound small in a clinical chart. In real life, it can mean recognizing a spouse’s face longer, holding onto conversations a little further into the disease or delaying full-time caregiving.
“We are highly encouraged by the topline results from CELIA, which underscore the potential of targeting tau to meaningfully impact patient outcomes in early Alzheimer’s disease,” said Dr Holly Kordasiewicz, executive vice president and chief development officer at Ionis.
There are still important caveats. Larger studies will ultimately determine whether the benefits hold up over time and translate into meaningful real-world outcomes. Safety also remains under close watch, particularly at higher doses where more serious adverse events were observed.
However, after years of disappointment in Alzheimer’s drug development, the CELIA results feel notable for another reason: they suggest the field may finally be broadening its playbook.
For a long time, Alzheimer’s research has operated with a kind of tunnel vision. The emerging focus on tau and on earlier biological intervention more broadly hints at a more sophisticated understanding of how neurodegeneration unfolds.
