Zenas BioPharma Announces the Presentation of New Obexelimab Data in IgG4-Related Disease at the 6th International Symposium on IgG4-Related Disease

Obexelimab shows strong 12-month flare protection and steroid-sparing potential in IgG4-RD.

What the company is saying

Zenas BioPharma is highlighting new clinical data for obexelimab in IgG4-related disease, emphasizing long-term flare protection, reduced steroid use, and vaccine response preservation. The company frames obexelimab as a potential long-term disease management option, with CEO Lonnie Moulder stating it may help patients remain flare-free and reduce steroid exposure. The announcement stresses the high probability of remaining flare-free over 12 months and a significant reduction in glucocorticoid toxicity versus placebo. Zenas also notes the preservation of vaccine-induced immunity during a treatment-free window and the absence of disease flares during this period. Manufacturing partners WuXi Biologics and InnoCare, both in China, are named, reflecting the company's global operational footprint. The tone is confident, focusing on quantitative clinical outcomes and the potential for broader application in autoimmune diseases.

What the data suggests

The 12-month probability of remaining flare-free on obexelimab was 0.93 (investigator- and adjudication committee-confirmed) and 0.87 (investigator-determined), with five patients pending adjudication. Median cumulative glucocorticoid rescue dose was 0 mg, and the mean was 105 mg, indicating minimal steroid use. Obexelimab reduced glucocorticoid toxicity at week 52, with a GTI Cumulative Worsening Score difference of -11.4 (p=0.021) versus placebo. Seroimmunity to influenza was achieved in 86% (6 of 7) and to COVID-19 in 100% (4 of 4) of participants during the treatment-free vaccination window, which averaged 34.6 days with no disease flares observed. After long-term obexelimab, 71% maintained pre-existing influenza immunity and 50% maintained COVID-19 immunity (n=7). Obexelimab has been tested in nine clinical trials with 667 subjects. The data support claims of flare protection, steroid-sparing, and preserved vaccine response, but lack detailed adverse event rates and granular patient-level toxicity data.

Analysis

The announcement is focused on realised clinical data from the Phase 3 INDIGO open-label extension, with specific, numerically supported outcomes for flare protection, glucocorticoid toxicity, and vaccine response. Nearly all key claims are realised and substantiated by disclosed figures, with only one forward-looking statement regarding upcoming Phase 2 SLE trial results. There is no exaggerated language or overstatement of future potential; the tone is positive but proportionate to the evidence. The only capital-related disclosure is a qualitative note about the need for additional financing, but no large capital outlay or long-dated benefit is claimed in this release. The absence of financial metrics is not a deficiency for a clinical-stage biotech update. Overall, the narrative closely matches the disclosed evidence, with no hype or inflation detected.

Risk flags

• ●The company discloses a need for substantial additional financing to achieve its goals, which could lead to dilution or delays if capital is not secured.
• ●Manufacturing for obexelimab is dependent on WuXi Biologics and InnoCare, both located in China, exposing Zenas to geopolitical, supply chain, and regulatory risks tied to US-China relations.
• ●While clinical efficacy and steroid-sparing effects are supported by disclosed data, the absence of detailed adverse event rates and full patient-level toxicity data limits independent assessment of long-term safety.
• ●The vaccine sub-study sample sizes are small (n=7 for influenza, n=4 for COVID-19), reducing the statistical power and generalizability of the immunogenicity findings.

Bottom line

Zenas BioPharma's new data show obexelimab delivers a high probability of 12-month flare protection and significant steroid-sparing in IgG4-RD, with 0.93 and 0.87 flare-free rates depending on adjudication method. The drug also appears to preserve vaccine-induced immunity during a treatment-free window, with no flares observed over an average of 34.6 days. These results are clinically meaningful for a rare disease affecting 25,000 people in the US, but the small sample sizes in immunogenicity sub-studies and limited safety detail temper the strength of the evidence. The company's reliance on Chinese manufacturing partners and its stated need for substantial additional financing introduce material operational and financial risks. Investors should focus on the upcoming Phase 2 SunStone SLE results in Q4 2026 as the next major catalyst. The most important takeaway is that obexelimab is demonstrating credible, quantifiable benefits in long-term IgG4-RD management, but commercial and financial execution risks remain.

Announcement summary

(NASDAQ:ZBIO) Zenas BioPharma, Inc. announced new data for obexelimab in immunoglobulin G4-related disease (IgG4-RD) presented at the 6th International Symposium on IgG4-Related Disease, held October 8-10, 2026, in Cambridge, Massachusetts. The presentations included longer-term flare protection and safety data from the Phase 3 INDIGO open-label extension, initial findings from a vaccine response sub-study, and an analysis of glucocorticoid-associated toxicity from the randomized, controlled period of INDIGO. Participants who completed the 52-week randomized, controlled period of the Phase 3 INDIGO study could enter the open-label extension and receive 250 mg obexelimab subcutaneously once weekly. The 12-month probability of remaining flare-free was 0.93 based on investigator- and adjudication committee-confirmed flares requiring rescue therapy, and 0.87 based on investigator-determined flares requiring rescue therapy, with five patients pending adjudication at the time of the data cutoff. The median and mean cumulative glucocorticoid rescue doses were 0 mg and 105 mg, respectively. Adverse event rates were comparable to or lower than those observed during the randomized, controlled period. A sub-analysis of the Phase 3 INDIGO trial evaluated glucocorticoid-associated toxicity using the Glucocorticoid Toxicity Index (GTI), showing that obexelimab significantly reduced cumulative glucocorticoid toxicity versus placebo at week 52 (GTI Cumulative Worsening Score difference: -11.4; p=0.021). Fewer patients receiving obexelimab reached clinical thresholds for cumulative glucocorticoid toxicity compared to placebo. Initial analyses from the ongoing vaccine sub-study assessed immune responses to vaccination during a planned treatment-free window, with seroimmunity to influenza achieved in 6 of 7 (86%) participants and seroimmunity to COVID-19 in 4 of 4 (100%) participants. No disease flares were observed during the treatment-free vaccination window, which lasted an average of 34.6 days. Participants (n=7) maintained pre-existing markers of immunity following long-term obexelimab treatment (71% for influenza and 50% for COVID-19). Obexelimab is a bifunctional monoclonal antibody designed to bind both CD19 and FcγRIIb, inhibiting B cell activity implicated in autoimmune diseases without depleting them. Obexelimab has been evaluated in nine clinical trials in a total of 667 subjects, including INDIGO, and was well tolerated with demonstrated clinical activity. Topline results from the Phase 2 SunStone trial in Systemic Lupus Erythematosus (SLE) are expected in 4Q 2026. An estimated 25,000 people in the United States have been diagnosed with IgG4-RD. Zenas BioPharma is advancing two late-stage molecules, obexelimab and orelabrutinib, and has earlier stage programs including ZB021, ZB022, and ZB014. WuXi Biologics (Hong Kong) Limited and InnoCare, both located in China, are named as the current sole contract manufacturing organization and partner, respectively, for obexelimab.

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