Zenas BioPharma’s Obexelimab Cuts New MS Lesions by 95% in Phase 2 Trial
Obexelimab achieved a 95% relative reduction in new gadolinium-enhancing T1 lesions versus placebo over weeks 8 and 12 in the Phase 2 MoonStone trial (p=0.0009), with 97.2% of treated patients lesion-free. Durable response persisted through week 24 with lesion counts dropping to 0.04 and a 40% serum NfL decrease.
1. Phase 2 MoonStone Trial Efficacy
Obexelimab met the primary endpoint with a 95% reduction in cumulative new gadolinium-enhancing T1 lesions over weeks 8 and 12 compared to placebo (p=0.0009), delivering an adjusted mean of 0.01 lesions per scan versus 0.23 and leaving 97.2% of treated patients free from new lesions.
2. Durable Response through Week 24
Lesion suppression was maintained through week 24, with mean gadolinium-enhancing T1 lesion counts falling from 0.87 at baseline to 0.04, while serum neurofilament light levels declined 40% from 15.28 pg/mL to 9.2 pg/mL, indicating sustained neuroaxonal protection.
3. Safety and Tolerability
Obexelimab was well tolerated with no new safety signals; reported adverse events were primarily mild injection site reactions and infections, and mean B cell counts remained within normal ranges, consistent with its targeted inhibitory mechanism.
4. Next Clinical and Regulatory Milestones
The open-label extension of MoonStone is ongoing, and Zenas BioPharma plans to submit marketing applications for Immunoglobulin G4-related disease to U.S. and European regulators, present topline Phase 2 SunStone results for lupus later this year, and initiate global Phase 3 trials of orelabrutinib in progressive MS.