WALTHAM, Mass. — 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.
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