Autoimmune specialist Zenas BioPharma has posted a win for its lead candidate, obexelimab, from a mid-stage study in relapsing multiple sclerosis (RMS).
During the Phase II MoonStone study (NCT06564311), obexelimab triggered a statistically significant 95% relative reduction in new gadolinium-enhancing T1 hyperintense (GdE T1) lesions at week eight and week 12 compared with placebo – meeting the trial’s primary endpoint. In MS, GdE T1 lesions are a common biomarker of active inflammation. They are believed to correspond with axonal loss and white matter destruction.
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The CD19/Fc gamma receptor IIb (FcγRIIb-b)-targeting drug also achieved near-complete suppression of new lesions at both weeks eight and 12, with two new GdE T1 lesions observed in patients treated with obexelimab compared with the 19 seen across the placebo cohort. Within the obexelimab arm, 97.2% of patients were free from new T1 lesions during the study period.
24-week data from the MoonStone study supports obexelimab’s durability in RMS, as the decrease in new GdE T1 lesions relative to placebo was maintained across the extension period. Patients treated with the bifunctional monoclonal antibody (mAb) also maintained stable expanded disability status scale (EDSS) scores at this timepoint.
The results of the Phase II MoonStone study were first presented during a late-breaking oral abstract at the 2026 Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS) Forum, which took place from 5 to 7 February in San Diego, California.
RMS market remains competitive
While obexelimab has demonstrated potential to improve outcomes in RMS, Zenas will face tough competition in the increasingly crowded RMS market if it gains approval for the drug.
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By GlobalDataRoche-owned Genentech’s Ocrevus (ocrelizumab) currently dominates the RMA market in terms of total sales. In fiscal year 2025 (FY25), the drug brought in SFr7bn ($9.14bn) for Roche – 9% more than the previous fiscal year.
Now, the Swiss pharma is looking to strengthen its footing in the MS field with its newest asset, fenebrutinib, which significantly reduced annualised RMS relapse rates over Sanofi’s commonly prescribed MS medication, Aubagio (teriflunomide), in the Phase III FENhance 2 (NCT04586023) study.
However, Christie Wong, managing neurology analyst at GlobalData, believes that obexelimab’s novel mechanism of action could differentiate it from approved therapies.
“Should obexelimab be able to replicate the positive findings from the MoonStone trial in larger Phase III studies and receive regulatory approval, it could become a high-efficacy therapy option for patients who cannot tolerate, or respond sub-optimally to anti-CD20 mAbs,” Wong said.
Obexelimab’s development journey
The follow-up data gathered from the MoonStone study succeeds the positive topline readout from October 2025, which was met with a warm reception from investors – as evidenced by Zenas’ stock value climbing 33% upon the news’ debut.
However, results from the Phase III INDIGO study (NCT05662241) of obexelimab in immunoglobulin G4-related disease (IgG4-RD) reversed this share value growth, sending the company’s stock value plummeting by over 50% after the drug failed to best standard of care (SoC) therapy, Uplizna (inebilizumab) in terms of efficacy. Despite this setback, Zenas plans to file for the drug’s approval in this indication in Q2 2026.
Zenas is also hoping for obexelimab’s success in systemic lupus erythematosus (SLE). The company is currently conducting the Phase II SunStone study (NCT06559163), which is expected to read out in 2026.
