Zenas Biopharma's Obexelimab Shows Promise in Phase 2 Multiple Sclerosis Study

Zenas Biopharma has reported significant positive results from its phase 2 MoonStone study of obexelimab, a bifunctional monoclonal antibody, in patients with relapsing multiple sclerosis (MS). The trial demonstrated a 95% reduction in new brain lesions, marking a potentially important development in MS treatment.

Impressive Efficacy in Reducing MS Lesions

The MoonStone study, involving 116 patients with relapsing MS, evaluated the efficacy of obexelimab against placebo. Patients received either 250 mg of obexelimab or placebo via subcutaneous injection. The primary endpoint focused on reducing the cumulative number of new Gd-enhancing T1 hyperintense lesions at Weeks 8 and 12, as measured by brain MRIs.

Results showed a statistically significant 95% reduction in these lesions among patients treated with obexelimab. Notably, the study observed "near-complete suppression" of lesions in the treatment group by Week 8, which was maintained through Week 12.

Dr. Lisa von Moltke, Chief Medical Officer at Zenas, emphasized the significance 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 Outlook

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

Zenas Biopharma 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, potentially shedding light on obexelimab's impact on disability progression in MS patients.

Beyond MS, Zenas is actively exploring obexelimab's potential in other autoimmune conditions. A phase 3 study in IgG4-related disease is expected to yield results by 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 announcement of the phase 2 results had an immediate positive impact on Zenas Biopharma's stock, which saw a 20% increase in premarket trading, rising from $23.90 to $28.75.

The promising data also validates the recent investment by Royalty Pharma, which provided Zenas with $75 million last month in exchange for future royalties on obexelimab sales, should the drug reach the market. This deal, potentially worth up to $300 million, underscores the growing confidence in obexelimab's market potential.

Obexelimab, acquired by Zenas from Xencor in 2021 for up to $480 million, represents the company's most advanced clinical asset. With these positive phase 2 results, Zenas Biopharma has positioned itself as a notable player in the competitive landscape of autoimmune disease therapeutics.