OSE Immunotherapeutics Presents a Poster on OSE-Cytomask®, a Novel “Cis-Demasking” Cytokine Technology to Increase Therapeutic Index of Immunocytokines

OSE Immunotherapeutics Presents a Poster on OSE-Cytomask®, a Novel

“Cis-Demasking” Cytokine Technology to Increase

Therapeutic Index of Immunocytokines

NANTES, France, November 7, 2025 – 6:00pm CET - OSE Immunotherapeutics SA (ISIN: FR0012127173; Mnemo: OSE), a clinical-stage biotechnology company developing immunotherapies for cancer and autoimmune diseases, presents a poster   on its novel OSE-Cytomask® Cis-Demasking¹ immunocytokine technology at the Society for Immunotherapy of Cancer (SITC) 2025 Annual Meeting, taking place November 5–9, in National Harbor, Maryland.

OSE-Cytomask® platform is an innovative proprietary non-cleavable linker technology to create a new class of regulated and targeted cytokine therapeutics that enables precise cytokine activation on the appropriate T cell population, thereby improving the therapeutic index of immunocytokines. This innovative technology addresses a current unmet need in immunocytokine therapy by enabling the safe and targeted delivery of cytokines to tumor-specific T cell populations.

The poster presented highlighted how OSE-Cytomask® keeps cytokines inactive until they reach the right immune cells, specifically those expressing PD-1. This targeted activation helps avoid unwanted activation in healthy tissues and reduces side effects. Unlike other systems that rely on other biological agents to activate the cytokine, OSE-Cytomask® works independently of the tumor environment, offering enhanced stability and adaptability.

Aurore Morello, Head of Research and Director of R&D Programs, OSE Immunotherapeutics, said: “We are happy to present our novel OSE-Cytomask® technology at this leading scientific conference. This highly innovative technology promises to unleash the full potential of cytokines in oncology by dramatically increasing the therapeutic index of this class of drugs. This approach helps avoid unwanted activation in healthy tissues and improves safety compared to conventional cytokine-based therapies.

We've successfully tested this technology with several antibodies and cytokines, including IL-15, IL-2, and IL-10. By enabling precise immune activation and optimizing it through PD1 targeting, the OSE-Cytomask® technology could enhance existing therapies and lead to safer and more effective immunotherapies for patients with hard-to-treat solid tumors.”

Immunocytokines are a new way to help the immune system fight cancer by sending special proteins (called interleukins) directly to tumors. When these proteins are combined with anti-PD-1 antibodies, they can activate the right immune cells—but sometimes they also affect the wrong ones, which can cause side effects and reduce their effectiveness. To solve this problem, OSE Immunotherapeutics created the OSE-Cytomask® platform. It uses a special design that keeps the protein inactive until it reaches the tumor, helping it work only where it's needed and making the treatment safer and more effective.

ABOUT OSE IMMUNOTHERAPEUTICS

OSE Immunotherapeutics is a biotech company dedicated to developing first-in-class assets in immuno-oncology (IO) and immuno-inflammation (I&I) that address the unmet patient needs of today and tomorrow. We partner with leading academic institutions and biopharmaceutical companies in our efforts to develop and bring to the market transformative medicines for people with serious diseases. OSE Immunotherapeutics is based between Nantes and Paris and is quoted on Euronext.

Additional information about OSE Immunotherapeutics assets is available on the Company’s website: . Follow us on LinkedIn.

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This press release contains express or implied information and statements that might be deemed forward-looking information and statements in respect of OSE Immunotherapeutics. They do not constitute historical facts. These information and statements include financial projections that are based upon certain assumptions and assessments made by OSE Immunotherapeutics’ management considering its experience and its perception of historical trends, current economic and industry conditions, expected future developments and other factors they believe to be appropriate.

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1 Cis-Demasking: Bispecific antibodies ^(*) have the capability to target cells either in a Cis- targeting (on the same cell) or in a Trans-binding orientation (between two different cells). Cis-Demasking bispecific technology targets two antigens expressed on the same cell, with one masked modality (eg. Cytokine) and enabling conditional activity of the cytokine on the desired immune cell types upon antibody binding.

^(*) Segués A. et al. International Review of Cell and Molecular Biology 2022.

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