Nantes, October 3, 2025, 8:00 a.m. CET – OSE Immunotherapeutics (ISIN: FR0012127173; Mnemonic: OSE) announces the termination of the position as chief executive officer of Mr. Nicolas Poirier and the appointment of Mr. Marc Le Bozec as interim CEO, as decided yesterday by the Board of Directors.

The Board of Directors has commenced a formal search for a new permanent Chief Executive Officer.

The Board of Directors has empowered Marc Le Bozec to lead a strategic evaluation of OSE's business, with a focus on maximizing value across partnerships, finances, and clinical development programs.

Nicolas Poirier will retain his position as Chief Scientific Officer at OSE.

The termination of Mr. Nicolas Poirier's duties as Chief Executive Officer will not result in the payment of any compensation or indemnity, given that Mr. Nicolas Poirier is remunerated exclusively under his employment contract with the Company.

The compensation of the new Chief Executive Officer will be reviewed by the Nomination and Compensation Committee and submitted to a vote at the next shareholders' general meeting, given the absence of a compensation policy for the Chief Executive Officer.

Regarding the appointment of Marc Le Bozec, Dr. Markus Cappel, Chairman of the Board of Directors, stated:

“I am delighted to work with Marc during this crucial transition for OSE. Our Board of Directors is committed to securing a bright future for the company. To achieve this, we need to gain a clearer understanding of our current position, realign our strategy, and accelerate our progress.

I am convinced that Marc is the ideal person for this task. His extensive experience in the French and international biotech sector, combined with his expertise in corporate governance and investment fund management, will be invaluable. He will bring much-needed stability, re-engage all our stakeholders, and help us develop a strategy that will allow OSE to realize its full potential and value.”

Marc Le Bozec added:“I thank the Board of Directors for their confidence. OSE is a success story, but it is also at a turning point. A comprehensive review is a priority today, and we owe it to our shareholders. Reassuring the teams, whose talent we know well, giving them a clear direction, while keeping the mission of therapeutic innovation at the heart of the company, is my other major priority. I am undertaking this interim CEO role with confidence and determination.”

Some biographical details about Marc Le Bozec :

Marc Le Bozec currently advises numerous biotech companies as a consultant, board member, and investor. He has extensive experience in interim management.

Between 2015 and 2023, he created and managed two biotech investment funds at Financière Arbevel. He made 11 investments and facilitated two exits: TransCure bioServices, sold to Cathay Capital in early 2022, and Imactis, sold to GE Healthcare in early 2023. Previously, he was CFO of Cellectis, where he raised €120 million and prepared the company for its Nasdaq listing. He also led and successfully restructured CYTOO.

A graduate of HEC Paris (1992), Marc Le Bozec began his career in organizational consulting (Bossard Consultants), then in strategy consulting (Arthur D. Little). He founded his first biotech company, BioProtein Technologies, in 1998.

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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Forward-looking statements

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.

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