Zenas BioPharma (Nasdaq: ZBIO), based in Waltham, Massachusetts, has submitted a Biologics License Application (BLA) to the US FDA for obexelimab, an investigational bifunctional monoclonal antibody, seeking approval for the treatment of adults with Immunoglobulin G4-Related Disease (IgG4-RD). The filing marks the first BLA submission for obexelimab and would, if approved, position it as the second drug to receive regulatory authorization in this rare fibro-inflammatory condition.
The submission is supported by results from the Phase III INDIGO registrational trial (NCT05662241), a multicenter, randomized, double-blind, placebo-controlled study evaluating obexelimab in patients with active IgG4-RD over a 52-week primary treatment period. The company said the filing seeks approval for obexelimab administered via subcutaneous self-injection. No priority review designation or PDUFA date has been disclosed in the filing announcement.
In INDIGO, obexelimab met its primary endpoint, demonstrating a 56% reduction in the risk of IgG4-RD flare compared to placebo over the 52-week randomized period (Hazard Ratio 0.44; 95% CI 0.277–0.711; p=0.0005). The trial also met all four pre-specified key secondary endpoints, including time to first investigator-determined flare requiring rescue therapy (p=0.0001), number of flares requiring rescue therapy (p=0.0008), proportion of patients achieving complete remission (p=0.0049), and cumulative glucocorticoid rescue therapy use (p=0.0042). The company said obexelimab was generally well tolerated across the trial. Full data from INDIGO are scheduled for presentation at the European Alliance of Associations for Rheumatology (EULAR) 2026 Congress in London on June 4, 2026. A three-year open-label extension period continues to enroll participants, which the company said will further build on the clinical dataset in IgG4-RD.
Competitive and scientific context
Obexelimab enters a nascent but increasingly active treatment landscape. Uplizna (inebilizumab-cdon), developed by Amgen (Nasdaq: AMGN), became the first US FDA-approved therapy specifically for IgG4-RD in April 2025, following positive results from the Phase III MITIGATE trial. Inebilizumab targets CD19 and deploys an antibody-dependent cytotoxicity mechanism to deplete B cells, including plasmablasts, which are central to IgG4-RD pathogenesis.
Obexelimab shares the CD19 target but operates through a mechanistically distinct approach. The molecule is engineered to co-engage both CD19 and FcγRIIb — an inhibitory Fc gamma receptor broadly expressed across B-cell lineages — driving inhibitory intracellular signaling without depleting B cells. This non-depleting mechanism, combined with subcutaneous self-administration, differentiates obexelimab from inebilizumab, which requires intravenous infusion in a clinical setting. Whether the inhibitory rather than depleting approach translates into a meaningfully different safety or tolerability profile in IgG4-RD patients will require head-to-head or longer-term comparative data.