By Connor Hart

Dianthus Therapeutics' stock whipsawed Monday after the biotech company reported data from a mid-stage trial of its treatment for generalized myasthenia gravis, an autoimmune disease.

Shares surged in premarket trading as the drug, claseprubart, demonstrated strong efficacy in the Phase 2 trial, but they reversed course after investors zeroed in on potential safety concerns during a call with executives.

Analysts said shares have since rebounded as investors digested the totality of the data. They were recently trading 18% higher at $31.20, extending their 34% gain year-to-date.

Dianthus said before the bell that claseprubart met all primary and secondary endpoints in the trial, showing statistically significant and clinically meaningful improvements compared with placebo. The benefits are comparable to AstraZeneca's blockbuster drugs Ultomiris and Soliris, which together generate more than $2 billion annually as treatments for generalized myasthenia gravis, analysts said.

However, management on a conference call highlighted a link between the high-dose arm and anti-nuclear antibodies, which in some contexts can be tied to autoimmune disorders such as lupus.

"That's what investors were debating: How good is the efficacy data versus how bad is the safety signal, really, and trying to come to grips with whether this is actually going to be a blockbuster therapy," William Blair analyst Myles Minter said.

Minter said he believes the concerns are overblown. "What isn't in question is the efficacy of this program," he added, noting that claseprubart didn't show risks that have led to black-box safety warnings on AstraZeneca's competing medicines.

Dianthus also has convenience on its side, analysts said, as claseprubart is deliverable at home through a self-administered injection. Moving forward, the company plans to bring the data to regulators and launch a large Phase 3 study next year.

Write to Connor Hart at connor.hart@wsj.com

(END) Dow Jones Newswires

September 08, 2025 11:58 ET (15:58 GMT)

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