WALTHAM, Mass., June 2, 2026
Zenas BioPharma, Inc. announced positive results from its registrational Phase 3 INDIGO trial evaluating obexelimab in patients with Immunoglobulin G4-Related Disease (IgG4-RD). The data, simultaneously presented at the EULAR 2026 Congress and published in the New England Journal of Medicine, demonstrated that obexelimab met its primary endpoint and all four key secondary endpoints with strong statistical significance. The company also confirmed that a Biologics License Application (BLA) for obexelimab in IgG4-RD was submitted to the U.S. Food and Drug Administration in May 2026.
IgG4-RD is a rare, chronic autoimmune disease that can affect multiple organs and often requires long-term corticosteroid therapy, which is associated with significant side effects. The Phase 3 INDIGO study enrolled 194 patients with newly diagnosed or recurrent disease who were randomized to receive either weekly subcutaneous obexelimab or placebo for 52 weeks. Results showed that obexelimab reduced the risk of disease flare by 56% compared with placebo, with 73.2% of treated patients remaining flare-free through one year compared with 45.4% in the placebo arm. The findings highlight the potential of obexelimab to provide durable disease control while reducing dependence on long-term steroid therapy.
Strong Efficacy Across Primary and Secondary Endpoints
The trial demonstrated highly significant improvements across all efficacy measures. Obexelimab reduced the risk of investigator-determined disease flare requiring rescue treatment by 59%, while the annualized flare rate was reduced by 52% compared with placebo. Complete remission at Week 52 was achieved in 37.1% of patients receiving obexelimab versus 19.6% of those receiving placebo. Importantly, patients treated with obexelimab required substantially less rescue glucocorticoid therapy, with cumulative steroid exposure reduced by approximately 65% compared with placebo. These results support the therapy’s potential as a steroid-sparing treatment option for patients with IgG4-RD.
Favorable Safety Profile and Reduced Steroid Toxicity
Advertisement
Beyond efficacy, obexelimab demonstrated a favorable safety and tolerability profile. The incidence of serious adverse events was lower in the obexelimab group than in the placebo group, and rates of severe treatment-emergent adverse events were also reduced. Infection rates were lower among obexelimab-treated patients, and there were no deaths reported in the treatment arm. Furthermore, patients receiving obexelimab experienced significantly lower levels of glucocorticoid-related toxicity, as measured by the Glucocorticoid Toxicity Index. The reductions in steroid exposure translated into meaningful improvements across multiple health domains, including metabolic, cardiovascular, and neuropsychiatric outcomes.
Obexelimab Positioned as Potential First-Line Therapy
According to Zenas BioPharma, the INDIGO trial represents the largest clinical study ever conducted in IgG4-RD and provides the most extensive dataset generated for an advanced therapy in this disease. Obexelimab’s unique mechanism of action targets both CD19 and FcγRIIb, inhibiting pathogenic B-cell activity without depleting B cells. Combined with its convenient self-administered subcutaneous dosing and favorable safety profile, the therapy has the potential to become a first-line treatment for long-term disease management. The company is also advancing obexelimab in additional autoimmune diseases, with topline Phase 2 results in systemic lupus erythematosus (SLE) expected later in 2026..
Source: Zenas BioPharma press release
