Zenas Biopharma's MS Drug Shows Promising Results in Phase 2 Trial

Zenas Biopharma has reported encouraging results from a phase 2 clinical trial of its lead autoimmune drug, obexelimab, in patients with relapsing multiple sclerosis (MS). The study, known as MoonStone, demonstrated a significant reduction in brain lesions, a key marker of MS disease progression.

Impressive Efficacy in Lesion Reduction

The MoonStone trial, which enrolled 116 patients with relapsing MS, evaluated the efficacy of obexelimab against placebo. Participants received either 250 mg of the bifunctional monoclonal antibody or a placebo via subcutaneous injection.

The primary endpoint of the study was met, with obexelimab showing a remarkable 95% reduction in the cumulative number of new Gd-enhancing T1 hyperintense lesions at Week 8 and Week 12, as measured by brain MRIs. This reduction was described by Zenas as "highly statistically significant."

Dr. Lisa von Moltke, Chief Medical Officer at Zenas, highlighted the importance of these findings: "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."

Safety Profile and Future Developments

The safety profile of obexelimab in the MoonStone study was reported to be consistent with observations from previous trials. The company noted that cases of infections and hypersensitivity were reported, though specific details were not provided in the initial release.

Zenas is looking ahead to reporting 24-week data from the MoonStone trial in the first quarter of 2026. This extended data set will include additional secondary and exploratory endpoints, which may provide insights into obexelimab's potential impact on disability progression in MS patients.

The company is also conducting trials of obexelimab in other autoimmune conditions. A phase 3 study in IgG4-related disease is expected to yield results around the end of this year, while a phase 2 study in systemic lupus erythematosus is anticipated to read out in mid-2026.

Market Response and Financial Implications

The positive phase 2 results have been well-received by investors, with Zenas's stock price surging 20% in premarket trading following the announcement. This uptick reflects growing confidence in obexelimab's potential as a treatment for MS and other autoimmune diseases.

The success of the MoonStone trial also validates a recent deal with Royalty Pharma, which provided Zenas with $75 million in exchange for future royalties on obexelimab sales, should the drug reach the market. This agreement, announced last month, includes the potential for additional funding, underscoring the pharmaceutical industry's interest in Zenas's lead candidate.