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: www.ose-immuno.com. 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.

These forward-looking statements include statements typically using conditional and containing verbs such as “expect”, “anticipate”, “believe”, “target”, “plan”, or “estimate”, their declensions and conjugations and words of similar import. Although the OSE Immunotherapeutics management believes that the forward-looking statements and information are reasonable, the OSE Immunotherapeutics’ shareholders and other investors are cautioned that the completion of such expectations is by nature subject to various risks, known or not, and uncertainties which are difficult to predict and generally beyond the control of OSE Immunotherapeutics. These risks could cause actual results and developments to differ materially from those expressed in or implied or projected by the forward-looking statements. These risks include those discussed or identified in the public filings made by OSE Immunotherapeutics with the AMF. Such forward-looking statements are not guarantees of future performance. This press release includes only summary information and should be read with the OSE Immunotherapeutics Universal Registration Document filed with the AMF on April 30, 2025, including the annual financial report for the fiscal year 2024, available on the OSE Immunotherapeutics’ website. Other than as required by applicable law, OSE Immunotherapeutics issues this press release at the date hereof and does not undertake any obligation to update or revise the forward-looking information or statements.

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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