Biogen has delivered fresh evidence that an experimental medicine aimed at curbing tau protein production can slow cognitive slide in people with early Alzheimer’s disease. The findings, released this week, come as the field absorbs data from major meetings and weighs how best to build on two approved therapies that attack amyloid instead.
Diranersen, which Biogen developed with Ionis Pharmaceuticals, reduced cognitive decline by 26 percent on one key measure in a subset of roughly 400 participants who received the lowest dose every six months. Five of six brain imaging tests also pointed to slower worsening. And brain scans showed a clear drop in tau levels. The results surfaced at the Alzheimer’s Association International Conference and were covered by Fortune.
Researchers greeted the data with measured hope. “This is really quite promising if it were to hold up” in larger testing, said Jessica Langbaum of the Banner Alzheimer’s Institute. Others struck a similar tone. Dr. Reisa Sperling, a neurologist at Massachusetts General Hospital, observed that “this is early days” but added the approach could “reinvigorate interest” in therapies aimed at tau. And Dr. Cath Mummery of University College London explained the biology simply. “If you lower tau production, you are lowering the amount of the abnormal tau that needs to be cleared. So that enables the normal clearance mechanism to have more capacity to clear the tau.”
The study enrolled volunteers with mild cognitive impairment or mild Alzheimer’s. Participants received injections of diranersen directly into spinal fluid. That route differs sharply from the intravenous or subcutaneous infusions used for lecanemab and donanemab. Those two drugs, sold as Leqembi and Kisunla, clear amyloid plaques and have shown they can slow clinical decline by about 25 to 30 percent in similar patients. Yet many physicians say the benefit still leaves families wanting more.
Side effects of diranersen stayed mostly mild. Some patients reported pain at the injection site. Others experienced a temporary state of confusion that appeared a few days after the shot and lasted about a week. Scans revealed no signs of brain inflammation or swelling, a complication that has dogged several amyloid antibodies.
But. The trial was small. The effect appeared strongest at the lowest dose. And the company has already sketched plans for a bigger, longer study that will test whether those signals hold when more patients receive treatment over more months. Without that confirmation, enthusiasm could fade quickly.
Still, the tau reduction offers a concrete biological clue. Tau tangles spread as Alzheimer’s advances and track more closely with cognitive loss than amyloid alone. Lowering the production of new tau, the thinking goes, might give the brain’s cleanup systems a fighting chance. Several experts quoted in recent coverage called that idea biologically sound.
News outlets picked up the story almost immediately. A report from iHeartRadio’s WCJM The Bull on July 14 highlighted the same 26 percent slowing and the drop in tau. On the social platform X, users shared the findings within hours. One post from @PracticalNeuro noted parallel real-world data on subcutaneous Leqembi that appeared at the same conference, showing reduced treatment burden for patients. Another from @sprintome pointed to Biogen’s broader anti-tau work, including an oligonucleotide that also slowed decline in early results presented at AAIC.
Those conference presentations sit inside a much larger pipeline. A review published in May in Alzheimer’s & Dementia: Translational Research & Clinical Interventions counted 158 drugs in active development for Alzheimer’s this year. That number rose from 2025. More candidates now target inflammation, epigenetics, and proteostasis. Yet only a handful have reached late-stage testing. Eli Lilly’s remternetug, another anti-amyloid antibody, is expected to report Phase 3 data in early 2026. AriBio’s AR1001, an oral pill originally approved in South Korea for erectile dysfunction, will finish its large trial by the end of 2025.
Meanwhile, approved therapies continue to evolve. Just days before the diranersen data landed, the FDA cleared an at-home starting dose for Leqembi. Eisai and Biogen announced the approval, which builds on an earlier green light for once-weekly maintenance injections. Real-world studies presented at AAIC found that the subcutaneous version cut clinic visits and improved patient experience. A neurologist writing for Los Altos Neurology on July 11 reviewed the latest on Leqembi and Kisunla, noting that both remain limited to people with confirmed amyloid and mild symptoms.
Prevention trials are also gaining ground. Researchers at ADPD 2026 in March presented long-term data showing that structured lifestyle changes can cut Alzheimer’s risk even a decade later. And a new preventative candidate called trontinemab is selecting volunteers through blood tests for p-tau217, a marker that predicts future disease with high accuracy. Coverage in The Telegraph on July 14 drew wide attention on X, where users described it as a potential breakthrough.
Diagnostic tools are improving in step. Lilly told investors on July 9 that it would present new data on p-tau217 blood tests at AAIC, alongside long-term analyses of Kisunla. The company hopes such tests can identify patients earlier and monitor treatment response without repeated PET scans. A forecast from the BrightFocus Foundation in February predicted that easier diagnostics and at-home dosing would expand access dramatically over the next few years.
So the diranersen results arrive at a moment of genuine momentum. Two anti-amyloid drugs are on the market. Subcutaneous options are reaching patients. Blood tests are moving from research to clinic. And the tau hypothesis is getting a fresh look. Yet the gap between modest slowing and true disease modification remains wide. Families still watch loved ones slip away. Clinicians still lack tools to stop the process cold.
Biogen executives have said little publicly beyond confirming the next trial. Ionis, the antisense oligonucleotide specialist, brings decades of experience in lowering protein production. Their partnership already produced nusinersen for spinal muscular atrophy. That track record lends credibility. But Alzheimer’s has humbled many well-resourced companies before.
Experts caution against overinterpreting one dose in one small study. The 26 percent figure echoes the benefit seen with anti-amyloid antibodies. If the larger trial replicates it, and if safety holds, diranersen could join the handful of drugs that actually change the course of disease. If not, the field will move on to the next candidate in a pipeline that now numbers well over 150.
Either way, the conversation has shifted. Ten years ago, many scientists doubted whether any therapy could slow Alzheimer’s once symptoms appeared. Today they debate how to combine anti-amyloid, anti-tau, anti-inflammatory, and lifestyle approaches into regimens that deliver bigger gains. The diranersen data, however preliminary, adds one more piece to that puzzle. And physicians, patients, and investors are watching closely to see what happens next.
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