UPDATE ON THE TERMS OF THE SHAREHOLDERS GENERAL MEETING

Nantes, June 9th, 2025, 8 a.m. - OSE Immunotherapeutics SA (ISIN: FR0012127173; Mnemo: OSE) informs its shareholders and the market of the update on the terms of the Combined General Meeting scheduled for 25 June 2025 (the “General Meeting”).

In preparation of the General Meeting, OSE Immunotherapeutics has formally submitted to the President of the Nantes Commercial Court a request to extend the date of the General Meeting.

The purpose of this approach is to ensure that the General Meeting is held in a regular and transparent manner and that shareholders are properly informed. It is in response to requests made by some of the Company's shareholders, in a context marked by the filing, by a group of shareholders acting in concert, of several resolutions aimed at substantially changing the composition of the Board of Directors.

Furthermore, the communication of these resolutions to the market did not occur in a timely manner nor under conditions ensuring, at this stage, that shareholders are fully and fairly informed or that the General Meeting is properly or regularly held.

In this respect, the resolutions presented by the group of shareholders acting in concert and which have not been approved by the Board of directors are not identified clearly enough on the voting form posted on the Company's website on June 4^th, 2025.

The Company indicates that the resolutions of this group of shareholders, on which the Board of Directors recommends voting against, are renumbered A to K (instead of resolutions n°35 to 44). Apart from this renumbering, all the resolutions remain unchanged.

An amended convening notice will be published in the official legal bulletin.

The voting form along with the preparatory documents for the General meeting required by Article R. 22-10-23 of the French Commercial Code, as amended to include this renumbering, are available on the Company's website: https://www.ose-immuno.com/assemblees-generales/.

OSE Immunotherapeutics considers that the current situation as described above and in the press release dated June 4^th, 2025 raises significant legal uncertainties, which justify referring to the judge to extend the date of the General Meeting in order to secure the voting process and ensure that shareholders are consulted in an orderly fashion.

OSE Immunotherapeutics affirms its determination to protect the interests of all its shareholders and to defend the transparency and integrity of its governance, in compliance with the legal and regulatory framework.

OSE Immunotherapeutics will communicate in due course on the progress of this procedure.

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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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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