Obexelimab Cuts IgG4-Related Disease Flares by 56% in Phase 3 INDIGO Trial, Published in NEJM
Zenas BioPharma's obexelimab met its primary endpoint and all four key secondary endpoints in the Phase 3 INDIGO trial, with results published in NEJM and presented at EULAR 2026.
Overview
Zenas BioPharma reported on June 2, 2026 that its investigational antibody obexelimab produced a 56% reduction in the risk of disease flare compared with placebo in the registrational Phase 3 INDIGO trial of patients with immunoglobulin G4-related disease (IgG4-RD). The primary endpoint result carried a hazard ratio of 0.44 (95% CI 0.277-0.711; p=0.0005). The data were simultaneously presented at the EULAR 2026 Congress and published in the New England Journal of Medicine.
IgG4-RD is a multi-organ, fibro-inflammatory condition that can produce tumor-like lesions across the body. The most commonly involved organs are the pancreas, kidneys, orbital adnexal structures, salivary glands, and retroperitoneum, and corticosteroids are the mainstay of treatment — an approach that controls disease but carries cumulative toxicity and leaves relapse rates between 10% and 53% after steroid treatment.
What We Know
Trial design. INDIGO randomized 194 IgG4-RD patients with newly diagnosed or recurrent disease 1:1 to receive 250 mg of obexelimab or placebo subcutaneously weekly for 52 weeks. According to Zenas, obexelimab is a bifunctional monoclonal antibody designed to bind both CD19 and FcγRIIb, markers broadly present across B cell lineage. By engaging both targets, the antibody is intended to inhibit B-cell activity without depleting those cells.
Primary endpoint. Beyond the 56% relative reduction in flare risk, 73.2% of obexelimab patients remained flare-free through Week 52, compared to 45.4% of placebo-treated patients.
Secondary endpoints. The trial met all four key secondary endpoints. Time to first investigator-determined flare showed a 59% risk reduction (HR 0.41; 95% CI 0.26-0.66; p=0.0001), and the annualized adjudicated flare rate was 52% lower (HR 0.48; 95% CI 0.32-0.74; p=0.0008). 37.1% of patients receiving obexelimab achieved complete remission compared to 19.6% of patients who received placebo (p=0.0049).
Steroid sparing. Mean cumulative glucocorticoid rescue therapy use was 329.5 mg across all obexelimab-treated patients and 929.8 mg for placebo-treated patients — a 65% reduction.
Safety. Zenas said the safety profile of obexelimab was comparable to placebo. The rate of grade ≥3 treatment-emergent adverse events was lower with obexelimab (11.3%) compared to placebo (23.7%), and serious adverse events were 10.3% versus 18.6%.
Commentary. Lisa von Moltke, M.D., Head of Research and Development and Chief Medical Officer, said “INDIGO is the largest clinical trial ever conducted in IgG4-RD and represents the most extensive dataset to support the clinical activity of any advanced therapy for this disease.” Emanuel Della Torre, M.D., Ph.D., Associate Professor of Medicine at Vita-Salute San Raffaele University in Milan, Italy, said the data “indicate obexelimab could offer a novel, highly active, self-administered therapy for people living with IgG4-RD.”
Regulatory path. Zenas said a Biologics License Application for obexelimab in IgG4-RD was submitted to the FDA in May 2026.
What We Don’t Know
The public disclosures are topline and conference-level summaries; the full peer-reviewed analysis appears in the New England Journal of Medicine (DOI 10.1056/NEJMoa2601337), where subgroup breakdowns, durability beyond 52 weeks, and detailed adverse-event tables would be assessed. The company has not disclosed an FDA action date, pricing, or how obexelimab would be positioned relative to corticosteroids and off-label B-cell-depleting agents. Long-term data on whether sustained flare control translates into prevention of irreversible organ fibrosis were not part of the reported endpoints.
Analysis
IgG4-RD has historically been managed with corticosteroids despite their toxicity, and no targeted therapy has been approved specifically for the condition. A randomized, placebo-controlled Phase 3 readout at this scale — paired with simultaneous NEJM publication and a EULAR 2026 presentation in London on June 4, 2026 — marks an unusually well-documented evidence base for a rare immune-mediated disease. The steroid-sparing signal, with cumulative glucocorticoid exposure cut roughly two-thirds, is clinically meaningful given the long-term harms of chronic steroid use, though regulators will weigh the full safety dataset before any decision on the pending BLA.