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

Extension findings included flare protection, while randomized trial analyses showed lower cumulative steroid toxicity versus placebo.

Rhea-AI Summary

Zenas BioPharma (Nasdaq: ZBIO) presented new obexelimab findings in IgG4-related disease from the Phase 3 INDIGO trial and its extension. The data were presented at the October 8–10, 2026 international symposium in Cambridge, Massachusetts.

In the open-label extension, where participants knew their treatment, the 12-month probability of remaining flare-free was 0.93 using investigator- and committee-confirmed flares requiring rescue therapy, versus 0.87 using investigator-determined flares requiring rescue therapy; five patients awaited adjudication. At week 52, cumulative steroid toxicity was lower versus placebo, with a score difference of -11.4; p=0.021. Initial vaccine sub-study findings showed blood markers of immunity to influenza in 6 of 7 participants and COVID-19 in 4 of 4 following vaccination during a treatment-free window.

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Positive

• Moderate pointTwelve-month flare-free probability was 0.93 using investigator- and committee-confirmed flares requiring rescue therapy; 0.87 using investigator-determined flares.
• Moderate pointCumulative steroid toxicity fell versus placebo at week 52: score difference -11.4; p=0.021.
• Minor pointPatients receiving obexelimab reached clinical steroid-toxicity thresholds less often than placebo recipients.
• Minor pointCumulative steroid rescue doses had a 0 mg median and 105 mg mean in the extension.
• Minor pointExtension adverse event rates were comparable to or lower than those during the randomized, controlled period.

3 minor points

• Minor pointInitial vaccination findings showed influenza immunity in 6 of 7 (86%) and COVID-19 immunity in 4 of 4 (100%).
• Minor pointDisease flares were not observed during the treatment-free vaccination window, averaging 34.6 days.
• Minor pointPre-existing immunity markers persisted after long-term treatment among participants (n=7): 71% for influenza and 50% for COVID-19.

Negative

• Minor pointFlare adjudication remained pending for five patients at the extension data cutoff.
• Minor pointVaccine response findings remain initial analyses from an ongoing sub-study.

Key Figures

12-month flare-free probability: 0.93 12-month flare-free probability: 0.87 GTI cumulative worsening score difference: -11.4; p=0.021 +5 more

12-month flare-free probability

0.93

Investigator- and adjudication committee-confirmed flares requiring rescue therapy

12-month flare-free probability

0.87

Investigator-determined flares requiring rescue therapy

GTI cumulative worsening score difference

-11.4; p=0.021

Obexelimab versus placebo at week 52

Median cumulative glucocorticoid rescue dose

0 mg

INDIGO open-label extension

Mean cumulative glucocorticoid rescue dose

105 mg

INDIGO open-label extension

Influenza vaccine seroimmunity

6 of 7 participants (86%)

Vaccination during the treatment-free window

COVID-19 vaccine seroimmunity

4 of 4 participants (100%)

Vaccination during the treatment-free window

Participants maintaining pre-existing immunity markers

71% for influenza; 50% for COVID-19

Following long-term obexelimab treatment; n=7

Key Terms

open-label extension, glucocorticoid toxicity index, seroimmunity, subcutaneously

4 terms

open-label extension medical

"Phase 3 INDIGO open-label extension findings demonstrated sustained clinical activity"

An open-label extension is a continuation of a clinical trial where all participants and researchers know which treatment is being given, often after an initial blinded phase. It allows further study of a drug's long-term safety and effectiveness. For investors, it can indicate ongoing interest and confidence in a product's potential, influencing perceptions of its future value.

glucocorticoid toxicity index medical

"using the Glucocorticoid Toxicity Index (GTI)"

A clinical scoring tool used to quantify and track the adverse effects caused by systemic glucocorticoid (steroid) treatment. The index combines measurements across multiple domains—such as weight/BMI, blood sugar control, blood pressure, bone health, eye problems, infections, mood or cognitive changes and skin effects—into a weighted numeric score that reflects the presence and severity of steroid-related toxicity and its change over time. It is a measurement instrument for clinical care and trials (to compare treatments or monitor patients) rather than a diagnostic test for a particular disease; different versions or scoring rules exist, so the specific items and weights used should be checked when comparing scores.

seroimmunity medical

"resulted in seroimmunity to influenza in 6 of 7"

Presence of specific antibodies in a person’s blood serum that indicates prior exposure to a pathogen or vaccination and suggests some level of immune protection; it is detected by serology tests that measure antibody types and quantities (titers). Seroimmunity describes what the blood test shows — antibodies detectable above a chosen threshold — rather than a precise guarantee of protection, because antibody levels can fall over time and do not measure other immune defenses such as T‑cells.

subcutaneously medical

"receive 250 mg obexelimab subcutaneously once weekly"

Given or delivered beneath the skin into the fatty layer just under the surface, usually by injection or a small device. For investors, whether a medicine is given subcutaneously affects how easy it is for patients to use, how often doses are needed, and the cost and complexity of manufacturing and regulation—think of it like placing a slow-release patch under a carpet instead of pouring medicine on top of it, which changes convenience and ongoing demand.

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– Phase 3 INDIGO open-label extension findings demonstrated sustained clinical activity of obexelimab –

– Additional analyses of secondary endpoints showed that significantly fewer patients experienced clinically meaningful cumulative glucocorticoid toxicity at week 52 –

– Initial open-label extension sub-study findings demonstrated vaccine responses following a treatment-free window –

– These new findings add to the clinical evidence supporting obexelimab’s investigational role as a reversible, steroid-sparing, B-cell inhibitor for the treatment of IgG4-RD –

WALTHAM, Mass., Oct. 12, 2026 (GLOBE NEWSWIRE) -- Zenas BioPharma, Inc. (“Zenas” or the “Company”) (Nasdaq: ZBIO), a clinical-stage global biopharmaceutical company advancing therapies for patients living with autoimmune and inflammatory diseases, today announced new obexelimab data 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 an associated vaccine response sub-study, and an analysis of glucocorticoid-associated toxicity from the randomized, controlled period of INDIGO.

“IgG4-RD is a chronic disease that may require ongoing management, even after an acute flare is controlled,” said Lonnie Moulder, Founder and Chief Executive Officer of Zenas. “Together, these new findings reinforce the potential role of obexelimab in long-term disease management, including helping patients remain flare-free, reducing steroid exposure, and potentially supporting vaccine responses following a treatment-free window.”

Phase 3 INDIGO Open-Label Extension Data
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 open-label extension evaluated longer-term flare protection and safety of continued obexelimab treatment in patients with IgG4-RD.

• The 12-month probability of remaining flare-free was 0.93 based upon investigator- and adjudication committee-confirmed flares requiring rescue therapy, and 0.87 based upon 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.
  

Glucocorticoid-Associated Toxicity Results
This Phase 3 INDIGO trial sub-analysis evaluated glucocorticoid-associated toxicity in patients with IgG4-RD using the Glucocorticoid Toxicity Index (GTI).

• 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 versus placebo.

Influenza and COVID-19 Vaccine Sub-Study Results
Initial analyses from the ongoing sub-study of the INDIGO open-label extension assessed immune responses to vaccination during a planned treatment-free window. In addition, the preservation of pre-existing influenza and SARS-COV-2 immunity following long-term obexelimab exposure was evaluated.

• Vaccination during the treatment-free window resulted in seroimmunity to influenza 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, lasting 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).
  

About Obexelimab
Obexelimab is a bifunctional monoclonal antibody designed to bind both CD19 and FcγRIIb, which are broadly present across B cell lineage, to inhibit the activity of cells that are implicated in many autoimmune diseases without depleting them. This unique inhibitory mechanism of action and self-administered, subcutaneous injection regimen may broadly and effectively modulate the pathogenic role of the B cell lineage in chronic autoimmune disease.

Obexelimab has been evaluated in nine clinical trials in a total of 667 subjects, including INDIGO. Obexelimab was well tolerated and demonstrated clinical activity across these clinical trials.

Phase 2 SunStone trial in Systemic Lupus Erythematosus (SLE) topline results expected in 4Q 2026.

About IgG4-RD
IgG4-related disease (IgG4-RD) is a rare, chronic immune-mediated disease characterized by inflammation and fibrosis that can affect multiple organs throughout the body. Patients experience periods of remission and unpredictable disease flares, with the potential for progressive and irreversible organ damage. Given its chronic and relapsing nature, IgG4-RD may require ongoing disease management. An estimated 25,000 people in the United States have been diagnosed with IgG4-RD.

About Zenas BioPharma
Zenas is a clinical-stage global biopharmaceutical company focused on the development and commercialization of therapies for autoimmune diseases and inflammatory conditions. Zenas combines our experienced leadership team with a disciplined global product candidate acquisition approach to identify, acquire and develop product candidates with the potential to deliver clinically meaningful benefits to patients. Zenas is advancing two late-stage, potential franchise molecules, obexelimab and orelabrutinib. Obexelimab, Zenas’ lead product candidate, is a bifunctional monoclonal antibody designed to bind CD19 and FcγRIIb to inhibit the activity of B cells implicated in many autoimmune diseases without depleting them. Zenas believes that the unique mechanism of action of obexelimab and its self-administered, subcutaneous injection regimen may enable sustained control across multiple chronic autoimmune diseases. Orelabrutinib is a potentially best-in-class, highly selective CNS-penetrant, oral, small molecule BTK inhibitor. Orelabrutinib’s mechanism of action targets pathogenic B cells not only in the periphery but also within the CNS. Additionally, it directly modulates macrophages and microglial cells in the CNS, with the potential to address compartmentalized inflammation and disease progression in MS. Zenas’ earlier stage programs include ZB021, a novel, potentially best-in-class, oral, IL-17AA/AF inhibitor, ZB022, a preclinical, potentially best-in-class, oral, brain-penetrant, TYK2 inhibitor, and ZB014, a preclinical, half-life extended anti-CD19 and FcγRIIb monoclonal antibody. For more information about Zenas BioPharma, please visit https://zenasbio.com/ and follow us on LinkedIn.

Forward-Looking Statements
This press release contains “forward-looking statements.” In some cases, forward-looking statements can be identified by terms such as “may,” “will,” “should,” “expect,” “plan,” “anticipate,” “could,” “intend,” “target,” “project,” “contemplate,” “believe,” “estimate,” “predict,” “potential” or “continue” or the negative of these terms or other similar expressions, although not all forward-looking statements contain these words. Forward-looking statements are neither historical facts nor assurances of future performance. Instead, they are based on our current beliefs, expectations, and assumptions. All statements other than statements of historical facts contained in this press release are forward-looking statements. Forward looking statements include, but are not limited to, the anticipated timing or likelihood of regulatory submissions and approvals, and the outcome of interactions with regulatory authorities; the therapeutic potential of the Company’s product candidates, including, the potential for obexelimab to provide long term flare protection, the potential to pause obexelimab for vaccinations or management of illness, the potential for obexelimab to be a steroid-sparing therapy and the potential for sustained control across multiple chronic autoimmune diseases; the Company’s expectations regarding the potential commercialization, estimated market size and market opportunities of its product candidates; and the timing of reporting the topline results of obexelimab in SLE. The forward-looking statements in this press release speak only as of the date of this press release and are subject to a number of known and unknown risks, uncertainties and assumptions that could cause the Company’s actual results, performance or achievements to differ materially from those anticipated in the forward-looking statements. These risks and uncertainties include, but are not limited to: the Company’s limited operating history, incurrence of substantial losses since the Company’s inception and anticipation of incurring substantial and increasing losses for the foreseeable future; the Company’s need for substantial additional financing to achieve the Company’s goals; the uncertainty of clinical development; potential competition, including from large and specialty pharmaceutical and biotechnology companies; the Company’s ability to realize the benefits of the Company’s current or future collaborations or licensing arrangements; the Company’s ability to obtain regulatory approval to commercialize its product candidates; risks related to the manufacturing of the Company’s product candidates and the risk that the Company’s third-party manufacturers may encounter difficulties in production; the Company’s ability to obtain and maintain sufficient intellectual property protection for the Company’s product candidates; the Company’s reliance on third parties to conduct the Company’s preclinical studies and clinical trials; the Company’s compliance with the its license obligations; significant political, trade, and regulatory developments, including changes in relations between the U.S. and China; risks related to the operations of the Company’s suppliers, many of which are located outside of the United States, including the Company’s current sole contract manufacturing organization for obexelimab drug substance and drug product, WuXi Biologics (Hong Kong) Limited, and our partner, InnoCare, both of which are located in China; the risk that the Company’s indebtedness could adversely affect the Company’s financial condition or restrict the Company’s future operations; and other risks and uncertainties described in the section “Risk Factors” in the Company’s Annual Report on Form 10-K for the year ended December 31, 2025, as supplemented from time to time by our subsequent filings with the Securities and Exchange Commission (the “SEC”), as well as other information we file with the SEC. The forward-looking statements in this press release are based upon information available to the Company as of the date of this press release and while the Company believes such information forms a reasonable basis for such statements, such information may be limited or incomplete. Because forward-looking statements are inherently subject to risks and uncertainties, these forward-looking statements should not be relied upon as guarantees of future events. Moreover, the Company operates in an evolving environment. New risks and uncertainties may emerge from time to time, and management cannot predict all risks and uncertainties. Except as required by applicable law, the Company does not undertake to publicly update or revise any forward-looking statements contained herein, whether as a result of any new information, future events, changed circumstances or otherwise.

The Zenas BioPharma word mark, logo mark, and the “lightning bolt” design are trademarks of Zenas BioPharma, Inc. or its affiliated companies. All rights reserved.

Contacts:

Investors:
Argot Partners
Zenas@argotpartners.com

Media:
Kristin Ainsworth
SVP, U.S. Commercial Strategy & Corporate Affairs
612.839.6748

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What did Zenas BioPharma's INDIGO analysis show about steroid toxicity?

Obexelimab significantly reduced cumulative steroid toxicity versus placebo at week 52. The Glucocorticoid Toxicity Index Cumulative Worsening Score difference was -11.4; p=0.021. Fewer obexelimab recipients reached clinical thresholds for cumulative toxicity than placebo recipients.

Who could enter Zenas BioPharma's INDIGO extension, and what treatment did they receive?

Participants who completed the 52-week randomized, controlled period could enter the open-label extension. They could receive 250 mg obexelimab by injection under the skin once weekly. The extension evaluated longer-term flare protection and safety.

What steroid rescue doses and safety findings did Zenas BioPharma report in the INDIGO extension?

The median cumulative steroid rescue dose was 0 mg, and the mean was 105 mg. Adverse event rates were comparable to or lower than those observed during the randomized, controlled period.

Did patients flare during the vaccine treatment-free window in Zenas BioPharma's INDIGO sub-study?

No disease flares were observed during the treatment-free vaccination window, which lasted an average of 34.6 days. These findings came from initial analyses of the ongoing extension sub-study.

Did pre-existing immunity persist after long-term obexelimab treatment in Zenas BioPharma's vaccine sub-study?

Participants (n=7) maintained pre-existing markers of immunity following long-term obexelimab treatment: 71% for influenza and 50% for COVID-19. This analysis evaluated existing immunity separately from responses to vaccination during the treatment-free window.