JJP Biologics Announces Positive Interim Phase 1b Data for Nebaprubart (JJP-1212), an Anti-CD89 Antagonist, in Linear IgA Disease (LAD)

• Favorable safety and tolerability profile, with rapid onset of clinical activity and therapeutic effects observed in patients with LAD
• Data support the start of a Phase 1b clinical trial in rheumatoid arthritis, anticipated in Q3 2026

Warsaw, Poland – June 03, 2026 – JJP Biologics, ("JJPBio" or the "Company") a clinical-stage, immune-focused biotech that engineers precision antibodies to correct derailed immune pathways that drive autoimmune diseases and cancer, today announces positive interim data from its ongoing Phase 1b trial evaluating nebaprubart, also known as JJP-1212, its investigational potential first-in-class anti-CD89 antagonist, in patients diagnosed with Linear IgA Disease (LAD), a rare autoantibody-mediated skin disease.

The interim results demonstrate encouraging safety and tolerability alongside early evidence of rapid and sustained clinical benefit, including the potential to reduce or eliminate reliance on chronically-administered immunosuppressive therapy.

Interim data demonstrates:

• Favorable safety and tolerability profile observed to date, consistent with Phase I outcomes in healthy volunteers.
• Clinical activity with therapeutic effects observed within one week of dosing.
• Preliminary evidence of therapeutic activity, characterized by reductions in blister formation and pruritus, together with progressive healing of ulcerative lesions.
• Continued tapering of dapsone-based treatment after first dose of JJP-1212, with a sustained response after complete tapering.

LAD currently has no approved therapies in the European Union. It was the first autoimmune-disease selected by JJPBio because the deposits of IgA autoantibodies in the skin are known to activate neutrophils via CD89 leading to tissue damage and widespread skin blistering that can progress to open sores affecting the mucous membranes. These visible manifestations demonstrate nebaprubart’s mechanism of action in IgA-mediated inflammation. By blocking the CD89 receptor present on neutrophils, nebaprubart interrupts this pathway at its source, restoring tissue integrity and preventing blister formation.

Paweł Szczepański, Chief Executive Officer of JJP Biologics, said: “The interim Phase 1b results in LAD, together with our previously reported Phase I data in healthy volunteers, provide early validation of our approach targeting the IgA/CD89 axis. LAD is our proof-of-mechanism showcase, and these positive interim data demonstrate the potential of nebaprubart to deliver rapid, durable responses while reducing dependence on traditionally-administered immunosuppressive agents withknown toxicities. This positions nebaprubart as a potentially transformative therapy across a broad range of IgA-mediated diseases, and we look forward to commencing a Phase 1b trial of nebaprubart for rheumatoid arthritis in Q3 2026 and a Phase 2a basket study in IgA nephropathy in Q4 2026.”

Given its well-defined pathophysiology and clinically overt reflection of a visual response to treatment within days, LAD provides a clear path to clinical validation, enabling expansion into other IgA-driven diseases.

Sohail Ahmed, MD, MBA, Chief Medical Officer of JJP Biologics, added: “The consistency between the safety profile observed in healthy volunteers and the early efficacy and tolerability signals seen in LAD patients is very encouraging. Our Phase Ib trial showed predictable pharmacology and no dose-limiting toxicities, reducing clinical development risk. In LAD, the tapering or elimination of other treatments that are difficult for some patients to tolerate is highly meaningful for this patient population.”

The Phase 1b study (registered in the EU Clinical Trials Information System (CTIS) under EU Trial Number 2023-508661-33-00) is an open-label trial designed to evaluate safety and tolerability along with pharmacokinetic, immunogenicity, and exploratory efficacy measures including disease activity, blister formation, and quality of life.

The interim results in LAD follows the positive top-line Phase I trial results of nebaprubart in healthy volunteers which were announced in January 2026.

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For further information from JJP Biologics, please contact:

JJP Biologics Paweł Szczepanski, Chief Executive Officer / Chairman of the Management Board info@jjpbiologics.com

Media enquiries

ICR Healthcare
Namrata Taak, Chris Welsh, Jonathan Edwards
JJPBiologics@icrhealthcare.com

About JJP Biologics (JJPBio)

JJP Biologics is a clinical-stage biotech that leverages its in-depth understanding of immune pathway science in autoimmune diseases and cancer. Starting from deep mechanistic insights, JJPBio engineers antibodies that are built-to-order, designed to restore immune balance and deliver better disease control for patients with significant unmet need, because we believe that we can do better for patients.

JJPBio is the first company to generate clinical validation of the IgA/CD89 axis, establishing first-mover advantage in a disease area with broad implications across autoimmune conditions including IgA nephropathy, rheumatoid arthritis, lupus, and celiac disease. Our immuno-oncology program targets the CD270/HVEM checkpoint pathway in cancer.

Backed by the long-term, socially responsible capital of the Starak family and the Polpharma Group, JJPBio operates with the scientific freedom and financial stability to pursue mechanisms others simply cannot.

JJP Biologics: We restore. We don't deplete. We work smarter.

About nebaprubart (JJP-1212)

Nebaprubart is a first-in-class IgG4-κ CD89 antagonist that is being developed to treat a wide range of autoimmune, inflammatory, and fibrotic diseases where IgA antibodies are known to have significant pathogenic involvement (e.g., rheumatoid arthritis, systemic lupus erythematosus, idiopathic pulmonary fibrosis, dermatitis herpetiformis, inflammatory bowel disease, IgA nephropathy, and IgA vasculitis). Nebaprubart was designated an Orphan Medicinal Product in October 2022 by the European Commission for the treatment of Linear IgA Disease. An open-label trial with nebaprubart for this indication is ongoing.