• Biogen and Ionis reported topline Phase 2 CELIA data for diranersen in early Alzheimer's disease, showing robust biomarker and cognitive effects.
• The antisense therapy targets tau, and the trial offers the first randomized Phase 2 evidence that this approach can pair biomarker reductions with clinical benefit.
• Biogen plans to move diranersen into registrational studies, positioning Ionis's tau program for potential late stage development.

For investors tracking Ionis Pharmaceuticals (NasdaqGS:IONS), the CELIA readout comes with the stock at $73.84 and a 1 year return of 114.2%. Over 3 and 5 years, returns of 74.6% and 109.3% highlight how central neurology programs like diranersen have become to the Ionis story.

This new data helps clarify why Ionis is increasingly viewed as a key antisense partner in large disease areas such as Alzheimer's. As registrational plans take shape, the focus now shifts to trial design, regulatory interactions, and how Ionis and Biogen frame the opportunity in a market where disease modifying therapies remain limited.

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For Ionis, the CELIA outcome moves diranersen from an early proof of concept asset into a program with randomized Phase 2 data that links tau reduction to cognitive benefit in early Alzheimer’s disease. Biogen’s decision to move straight into registrational development signals that, despite the primary endpoint miss on dose response, the totality of biomarker and clinical data is viewed as strong enough to justify late stage investment. If registrational trials are successful and lead to approval, Ionis could see royalty or milestone upside from a large, high profile indication where current disease modifying options are still limited, alongside players such as Eli Lilly and Eisai. At the same time, the higher rate of serious adverse events at the top dose and the need to confirm cognitive effects in larger, longer studies keep clinical and regulatory risk firmly on the table.

How This Fits Into The Ionis Pharmaceuticals Narrative

• The CELIA results support the idea in the narrative that Ionis’s antisense platform can supply late stage assets, adding a potential Alzheimer’s royalty stream on top of launches like TRYNGOLZA and DAWNZERA.
• The trial’s failure to meet the primary dose response endpoint highlights the narrative risk around heavy reliance on a concentrated set of late stage programs where any setback can affect revenue and margins.
• The tau opportunity in early Alzheimer’s through diranersen, including the FDA Fast Track status and registrational plans, is not fully reflected in the rare disease and cardiometabolic focus that dominates the existing narrative.

Knowing what a company is worth starts with understanding its story. Check out one of the top narratives in the Simply Wall St Community for Ionis Pharmaceuticals to help decide what it's worth to you.

The Risks and Rewards Investors Should Consider

• ⚠️ Registrational Alzheimer’s trials are lengthy and expensive, and any weaker than expected cognitive or safety data could limit or delay potential royalty income from diranersen.
• ⚠️ Competition from larger Alzheimer’s players such as Eli Lilly, Roche and others may intensify, which could affect pricing, uptake and how regulators and payors view additional therapies.
• 🎁 Positive CELIA data provides Ionis with a differentiated tau targeting approach that addresses both intracellular and extracellular tau, potentially broadening its neurology footprint beyond rare diseases.
• 🎁 If registrational development progresses smoothly, diranersen could add another high profile Biogen partnered asset to Ionis’s growing mix of royalties, alongside TRYNGOLZA, DAWNZERA and other late stage programs.

What To Watch Going Forward

From here, watch how Biogen and Ionis structure the registrational program, including dosing choices after the lower dose signal in CELIA, and any feedback from regulators on required endpoints. The presentation of full CELIA data at AAIC 2026 will be important for assessing durability of tau reductions, consistency of cognitive benefit and the safety profile across doses. Investors should also track how diranersen is discussed alongside Ionis’s broader neurology pipeline and commercial products, as this will shape expectations for how meaningful Alzheimer’s related economics could become within the overall story.

To stay informed on how the latest news affects the investment narrative for Ionis Pharmaceuticals, visit the community page for Ionis Pharmaceuticals for ongoing updates on the top community narratives.

This article by Simply Wall St is general in nature. We provide commentary based on historical data and analyst forecasts only using an unbiased methodology and our articles are not intended to be financial advice. It does not constitute a recommendation to buy or sell any stock, and does not take account of your objectives, or your financial situation. We aim to bring you long-term focused analysis driven by fundamental data. Note that our analysis may not factor in the latest price-sensitive company announcements or qualitative material. Simply Wall St has no position in any stocks mentioned.