Biogen's stock sank 8% in mid-May, after one of its experimental drugs for Alzheimer's disease missed a Phase 2 study's primary endpoint.

On Tuesday, the biotech firm will show the first detailed data from the study. The presentation at the Alzheimer's Association International Conference in London will show why Biogen thinks the drug diranersen really works, and why it is forging ahead with a Phase 3 trial.

The presentation could give a shot in the arm to shares of Biogen, and those of its development partner Ionis Pharmaceuticals. Ionis could use a boost after last Thursday's surprising study failure of a heart drug it developed with AstraZeneca.

Biogen's May 14 announcement said diranersen had reduced levels of rogue proteins called tau, whose tangled fibers clog brain cells of Alzheimer's patients along with plaques of sticky substance called amyloid. The drug infusions also slowed the patients' cognitive decline over the 18 months. But those cognitive benefits didn't increase with higher doses of the drug -- and an expected dose-response had been the study's main endpoint.

The strongest cognitive benefit actually appeared at the lowest dose. That may make sense, wrote H.C. Wainwright analyst Andrew Fein in a May note. Side effects did increase with dosing, which makes Fein suspect that high doses of the gene-silencing drug may block cell production of normal tau protein.

Fein will be listening Tuesday to learn the magnitude of the drug's cognitive benefit. He's looking for something better than a 0.3 percentage point improvement versus the placebo, on the CDR-SB scale used in the Phase 2 study. That would be comparable to the benefit from Biogen's Leqembi, its marketed treatment that reduces amyloid plaque in Alzheimer's patients. Amyloid treatment can cause brain-swelling side effects, which a tau therapy would avoid.

Persuasive data on diranersen will also give a boost to other companies that are targeting tau. Those include Denali Therapeutics, Arrowhead Pharmaceuticals, and Voyager Therapeutics.

Write to Bill Alpert at william.alpert@barrons.com

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July 13, 2026 02:00 ET (06:00 GMT)

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