JJP Biologics Doses First Patients in RA Clinical Trial for Nebaprubart

Warsaw, Poland, October 19, 2026, JJP Biologics has announced that the first patients have been dosed in a Phase 1b clinical trial of nebaprubart (JJP-1212) for the treatment of seropositive rheumatoid arthritis (RA). This expansion of nebaprubart into RA follows positive interim data from its ongoing Phase 1b trial in linear IgA dermatosis (LAD), marking the second indication for the company’s lead asset and expanding clinical validation of the IgA/CD89 pathway.

Rheumatoid arthritis is a chronic autoimmune disorder affecting approximately 18 million people worldwide. Characterized by persistent joint inflammation, pain, and stiffness, RA can lead to severe and irreversible structural damage and functional impairment if left untreated. Biological disease-modifying antirheumatic drugs (DMARDs) are widely used, but a substantial proportion of patients do not respond adequately, lose response over time, or experience treatment-limiting side effects.

A growing body of evidence indicates that IgA autoantibodies contribute directly to RA pathogenesis and correlate with a more severe phenotype and poorer clinical outcomes via activation of the CD89 receptor on effector cells. However, current biologic therapies primarily target downstream inflammatory cytokines or IgG-driven pathways, leaving the IgA/CD89 axis largely unaddressed despite its important mechanistic role in pathology and disease progression.

Nebaprubart is an investigational monoclonal antibody designed to selectively block CD89, the primary receptor on myeloid cells that is activated during binding to IgA. The Phase 1b open-label trial will evaluate the safety and tolerability of nebaprubart, as well as pharmacokinetic and immunogenicity profiles in patients with rheumatoid arthritis, while exploring potential impact on disease activity and patient-reported outcomes.

By preventing pathogenic IgA signaling through CD89, nebaprubart is intended to inhibit immune complex-driven activation of neutrophils and other myeloid effector cells that drive synovial inflammation, cartilage degradation, and progressive articular destruction in rheumatoid arthritis. At the same time, it preserves the physiological functions of IgA that are important for mucosal homeostasis, protection, and immunity. Unlike approaches based on immune-cell depletion or immunoglobulin depletion, CD89 antagonism is fully reversible and does not reduce circulating IgA levels.

The first patient dosing in RA follows positive interim Phase 1b data in patients diagnosed with LAD, a rare autoantibody-mediated skin disease, which were announced in June 2026. Nebaprubart was designated an Orphan Medicinal Product in October 2022 by the European Commission for the treatment of Linear IgA Disease. An open-label Phase 1b trial with nebaprubart for this indication is ongoing.

Further details of the Phase 1b trial can be found on the EU Clinical Trials Information System (CTIS) under EU Trial Number 2023-508661-33-00.