Obexelimab Achieves 95% Reduction in New Lesions in Phase 2 MoonStone Trial—A Game Changer for Relapsing MS?
Phase 2 Results: Obexelimab Nearly Eliminates New Brain Lesions
Zenas BioPharma made headlines this morning by announcing positive topline results from its Phase 2 MoonStone trial of obexelimab in relapsing multiple sclerosis (RMS). The key highlight? Obexelimab achieved a striking 95% relative reduction in the cumulative number of new gadolinium-enhancing T1 brain lesions compared to placebo over the 8- and 12-week endpoints—a highly statistically significant result (p=0.0009).
These findings indicate that obexelimab’s mechanism—suppressing B cell activity without depleting them—may deliver a new standard for efficacy and tolerability in MS therapies. The result was more than just a number; near-complete suppression of inflammation-associated lesions was observed by week 8 and sustained through week 12. Notably, the adjusted mean number of new GdE T1 lesions per scan was 0.01 in the obexelimab group (versus 0.23 in the placebo group), showing the therapy’s robust impact in a notoriously difficult-to-treat disease.
| Group | Mean New Lesions (8–12wks) | 95% Confidence Interval |
|---|---|---|
| Obexelimab | 0.01 | 0.00 – 0.06 |
| Placebo | 0.23 | 0.11 – 0.51 |
Sustained Efficacy, Solid Safety—Signals for Broad Autoimmune Application
Obexelimab also showed substantial reduction in cumulative new and/or enlarging T2 lesions—markers of disease burden and chronicity—adding further weight to its potential. Safety results from MoonStone were consistent with earlier trials, primarily mild injection site reactions and infections, with no major surprises.
This promising profile could make obexelimab a flexible option not just for RMS, but potentially for other autoimmune disorders. Zenas is already investigating the drug in late-stage studies for Immunoglobulin G4-Related Disease (Phase 3) and Systemic Lupus Erythematosus (Phase 2), with more pivotal readouts ahead.
What’s Next? Major Data Milestones and Broader Implications
Looking forward, investors and patients alike will be watching for several critical catalysts:
- 24-week MoonStone trial data (Q1 2026)—including additional endpoints on disability progression.
- Phase 3 INDIGO trial topline results in IgG4-Related Disease (late 2025).
- Phase 2 SunStone data in Systemic Lupus Erythematosus (mid-2026).
- New Phase 3 programs for orelabrutinib in progressive forms of MS beginning in early 2026.
Key Takeaways: Is Obexelimab Poised to Redefine RMS Treatment?
For a disease as unpredictable and disabling as MS, the nearly complete suppression of inflammatory lesions in just 12 weeks stands out. Add to this the manageable safety profile and the convenience of subcutaneous self-administration, and it’s no surprise Zenas BioPharma is moving quickly toward more expansive clinical programs.
Investors should keep their sights set on the upcoming 24-week MoonStone data for deeper insight into obexelimab’s ability to modify disease course and reduce disability. If the trend holds, the treatment landscape for relapsing MS—and possibly a spectrum of autoimmune diseases—could shift dramatically.
Quick Reference: MoonStone Trial Snapshot
| Metric | Value |
|---|---|
| Number of Patients | 116 |
| Treatment Regimen | 250mg obexelimab or placebo weekly for 12 weeks |
| Primary Endpoint | Cumulative new GdE T1 lesions (week 8/12) |
| Statistical Significance | p=0.0009 |
| Reduction in Lesions | 95% |
| Safety | Consistent with previous studies (mostly mild AEs) |
Zenas BioPharma (ZBIO) Stock as of 11:12 AM: $30.20
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