ADJOURNMENT OF THE GENERAL MEETING INITALLY CONVENED ON JUNE 25, 2025

NANTES, France, June 11, 6:30 PM – OSE Immunotherapeutics SA (ISIN: FR0012127173; Mnemo: OSE), announces the cancellation of the convening of the mixed General Meeting initially scheduled for June 25, 2025 (the (( General Meeting ))) to clarify the situation. The Board of Directors will convene a new General Meeting within the allotted time frame.

Following the publication on June 3, 2025, of a concerted declaration on the website of the Autorité des Marchés Financiers and as indicated in the press release of June 9, 2025¹, OSE Immunotherapeutics requested the President of the Nantes Commercial Court to extend the legal deadline for holding the General Meeting. The President of the Court granted an extension of this deadline until September 30, 2025, by order issued on June 10, 2025.

The Board of Directors of OSE Immunotherapeutics has acknowledged this judicial decision and has taken all necessary consequences. It will convene the General Meeting within the now allotted time frame. This period will allow for verifying the regularity and transparency of the General Meeting and ensuring shareholders are well informed.

Proxy forms already received become void, and all information regarding the new convocation, agenda, resolution texts, and participation and voting procedures will be communicated in due course.

The Board of Directors of OSE Immunotherapeutics, chaired by Didier Hoch , states:“Dear shareholders, we wish to inform you of the postponement of our General Meeting. We will communicate the new date to you shortly. This situation calls for everyone's responsibility. It is my duty to ensure that each of you arrives at this meeting with all the necessary and useful information to vote in an informed and enlightened manner. Together, you will decide on the future of the Company. Our Company is dynamic and sustainable, with innovative research programs and significant clinical trials underway. I sincerely hope that we can, together, provide the OSE teams with the means to continue this momentum in the service of patients. The Board of Directors of OSE will continue to pursue this objective in a spirit of responsibility and openness to dialogue.”

OSE Immunotherapeutics reaffirms its commitment to rigorous governance and transparent communication and pledges to keep its shareholders informed of the outcomes of this decision.

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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