Zenas Biopharma’s autoimmune drug candidate has been tied to a 95% reduction in a type of brain lesions over 12 weeks in a phase 2 multiple sclerosis (MS) study.
The midstage MoonStone study saw 116 patients with relapsing MS receive either 250 mg of the bifunctional monoclonal antibody obexelimab or placebo by subcutaneous injection. The trial hit its primary endpoint of reducing the cumulative number of new Gd-enhancing T1 hyperintense lesions—markers of MS disease progression—at Week 8 and Week 12 as measured by brain MRIs.
Specifically, obexelimab demonstrated what Zenas described as a “highly statistically significant” 95% reduction in lesions. “Near-complete suppression” of lesions was observed among the obexelimab cohort by Week 8 and was sustained through to Week 12, the company explained in an Oct. 27 release.
The drug's safety profile was "consistent" with what had been observed in prior trials, according to the biotech, with cases of infections and hypersensitivity reported.
The readout got a warm reception from investors, who sent Zenas’ stock up 20% to $28.75 in premarket trading Monday from a Friday closing price of $23.90.
The phase 2 win validates the interest shown in obexelimab by Royalty Pharma, which handed $75 million to Zenas last month—with more potentially to follow—in return for royalties on sales should the drug make it to market.
Looking ahead, data from a phase 3 study of obexelimab in IgG4-related disease are expected around the end of the year, while a phase 2 study in systemic lupus erythematosus is likely to read out in mid-2026.
“The observed clinical activity in the MoonStone trial, combined with obexelimab’s unique inhibitory mechanism of action, subcutaneous self-administration and tolerability profile, position obexelimab as a potential option to broadly address the pathogenic role of B cells in autoimmune diseases,” Zenas Chief Medical Officer Lisa von Moltke, M.D., said in this morning’s release.
“With these highly statistically significant data, we look forward to reporting 24-week data in the first quarter of 2026, which will include additional secondary and exploratory endpoints that may inform obexelimab’s potential impact on disability progression and help us determine next steps for future development of obexelimab in relapsing MS,” von Moltke added.
Zenas bought exclusive global rights to the candidate in 2021 from Xencor in a deal worth as much as $480 million. Besides obexelimab, the company earlier this month licensed the BTK inhibitor orelabrutinib from China's InnoCare in a deal that could be worth up to $2 billion. The newly licensed asset is already in a phase 3 trial in primary progressive multiple sclerosis, and Zenas expects to start another late-stage study in secondary progressive multiple sclerosis in the first quarter of next year. The biotech has several other preclinical programs in its pipeline, as well.
Editor's note: This story was updated with information from Zenas' recent deal with InnoCare.