IgG4-related disease is the rare fibroinflammatory condition that can quietly scar the pancreas, salivary glands, kidneys, or aorta — and for which glucocorticoids remain the default, despite their toxicity and the relapses that follow tapering. In the Phase 3 INDIGO trial, the investigational antibody obexelimab gave patients a different option, significantly delaying the next flare as they came off steroids.
The trial, published in The New England Journal of Medicine on June 2 and presented at EULAR 2026, randomized 194 adults with active IgG4-related disease 1:1 to subcutaneous obexelimab 250 mg or placebo once weekly for 52 weeks, with glucocorticoids tapered to discontinuation by week 8 in both groups. The primary endpoint was time to the first flare requiring rescue therapy, adjudicated by both the investigator and an independent committee.
On that endpoint, obexelimab reduced the risk of flare by 56% (hazard ratio 0.44; 95% CI, 0.28 to 0.71; P<0.001). Flares requiring rescue occurred in 26 of 97 patients (26.8%) on obexelimab versus 53 of 97 (54.6%) on placebo.
Weekly obexelimab led to a significantly lower risk of disease flare and significantly less glucocorticoid exposure than placebo.
The drug also met its key secondary endpoints. Complete remission at week 52 reached 37.1% with obexelimab versus 19.6% with placebo (P=0.005), and the cumulative dose of rescue glucocorticoid was 329.5 mg versus 929.8 mg (P=0.004) — roughly a two-thirds reduction in steroid exposure, the practical goal in a steroid-sparing disease.
Mechanism and safety
Unlike rituximab and other B-cell-depleting agents used off-label here, obexelimab is a bifunctional antibody that co-engages CD19 and the inhibitory receptor FcγRIIb to dampen B-cell activity without depleting the cells. Across the safety data, more obexelimab-treated than placebo-treated patients reported arthralgias (19.6% vs. 11.3%), hypersensitivity (16.5% vs. 11.3%), and diarrhea (11.3% vs. 6.2%); serious adverse events were less frequent on obexelimab, affecting 10.3% of obexelimab-treated patients versus 18.6% of placebo-treated patients.
Obexelimab remains investigational and is not approved for any use. Sponsor Zenas BioPharma says it submitted a Biologics License Application to the FDA in May; that claim comes from the company and has not been confirmed by the agency. A BLA submission begins the FDA’s review process — it is not an approval and does not make the drug available as standard care. No therapy is yet approved specifically for IgG4-related disease. The trial’s peer-reviewed protocol paper describes INDIGO, which enrolled 194 patients, as the largest Phase 3 trial in IgG4-related disease to date; it continues into a three-year open-label extension.