Zenas BioPharma, Inc. (ZBIO), a clinical-stage global biopharmaceutical company, announced that its lead drug candidate Obexelimab met the primary endpoint of the Phase 2 MoonStone trial in Relapsing Multiple Sclerosis or RMS, along with durable activity based key findings at 24 weeks.
The data were presented in a late-breaking oral session at the Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS) Forum 2026, held from February 5 and 7, 2026, in San Diego, California.
Multiple Sclerosis (MS) is a chronic, autoimmune-mediated disorder of the Central Nervous System (CNS). Approximately 2.9 million people worldwide are currently living with MS, according to the Multiple Sclerosis International Federation.
RMS is characterised by distinct episodes of new or worsening neurological symptoms, followed by partial or complete remission. Approximately 85% of patients are initially diagnosed with RMS, in which 20%-30% transition to transition to Secondary Progressive Multiple Sclerosis SPMS.
Orelabrutinib is a selective central nervous system (CNS)-penetrant, oral, small molecule Bruton's Tyrosine Kinase (BTK) inhibitor.
The Phase 2 MoonStone trial and Key Findings
The Phase 2 MoonStone trial is a randomised, double-blind, placebo-controlled trial which evaluated the efficacy and safety of obexelimab in patients with Relapsing Multiple Sclerosis.
The trial enrolled 116 patients, who were randomised 2:1 to receive either 250 mg of obexelimab or placebo via subcutaneous injection once weekly over a 12-week double-blinded treatment period.
The primary endpoint is the cumulative number of new Gd-enhancing T1 hyperintense lesions over week 8 and week 12 as measured by brain MRI.
Obexelimab met the primary endpoint, demonstrating a highly statistically significant 95% relative reduction in the cumulative number of new gadolinium (Gd)-enhancing (GdE) T1 hyperintense lesions over week 8 and week 12 compared with placebo.
Near-complete suppression of new GdE T1 hyperintense lesions, markers of active inflammation, was observed with obexelimab by 8 weeks of treatment and was sustained through week 12. Additionally, during weeks 8 and 12, only two new GdE T1 lesions were observed in obexelimab-treated patients, compared with 19 in placebo-treated patients; 97.2% of obexelimab-treated patients remained free of T1 lesions during this period.
After the double-blind phase, all patients entered a 12-week open-label period where those on placebo switched to obexelimab and those already on obexelimab continued treatment, with secondary and exploratory outcomes assessed through week 24. After this, participants could join a 52-week open-label extension for continued Obexelimab and long-term outcome evaluation.
24 Week Data and Key Findings
In Parallel, the 24-week data showed significant reductions in total GdE T1 lesions observed with obexelimab over weeks 8 and 12 were maintained through week 24 with unadjusted means of 0.87 at baseline at 8 weeks, 0.08 at week 12 and 0.04 at week 24 for obexelimab indicating a 95% reduction.
Also, Obexelimab meaningfully reduced serum Neurofilament Light (NfL) by 40% through week 24; 15.28 pg/mL at baseline, declining to 12.7 pg/mL at week 12 and 9.2 pg/mL at week 24.
At week 24, New and/or enlarging T2 lesions were also lower in the obexelimab arm and the Expanded Disability Status Scale (EDSS) scores were stable, representing control over physical disability.
No new safety signals were observed at week 24.
Obexelimab For Other Indications
Obexelimab is evaluated in eight clinical trials, including the registrational Phase 3 INDIGO trial for Immunoglobulin G4-Related Disease (IgG4-RD) in which Obexelimab met both primary and secondary endpoints.
Zenas is currently on track to submit a Biologics License Application (BLA) to the U.S. Food and Drug Administration (FDA) in the second quarter of 2026 and a Marketing Authorisation Application (MAA) to the European Medicines Agency (EMA) in the second half of 2026. Also, Obexelimab is also being evaluated in a Phase 2 trial for Systemic Lupus Erythematosus, which is ongoing, and Zenas expects to report topline results, including biomarker data, in the fourth quarter of 2026.
The other indications under evaluation for Obexelimab include Primary Progressive Multiple Sclerosis and non-active Secondary Progressive Multiple Sclerosis.
Cash and Funding
On November 12, 2025, the company reported that its existing cash, cash equivalents and investments expected to be $301.6 million as of September 30,2025, together with the $120.0 million of gross proceeds from the Private Investment in Public Equity received in October 2025, will be sufficient to fund its operating and capital expenditures into the fourth quarter of 2026.
However, it also noted that it will not be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months from the reported date.
ZBIO has traded between $6.11 and $44.60 from April 2025 till current date. The stock closed Monday's trade at $22.48, up 3.12%.
In the overnight trading, ZBIO is down 2.67% at $21.88.
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May 22, 2026 14:46 ET Minutes of the latest Fed policy session was the highlight of the week along with survey data on the U.S. housing market. In Europe, survey data signaled the trends in the euro area private sector. Further, consumer price inflation data from the U.K. was in focus. In Asia, various economic indicators from China drew attention to the health of the economy.