Annual General Meeting on June 24, 2026

Procedures for obtaining preparatory documents for the General Meeting

NANTES, France, June 3, 2026 – 8:00pm CET - OSE Immunotherapeutics SA (ISIN: FR0012127173; Mnemo: OSE) (the "Company"), announced that it will hold its Annual General Meeting on June 24, 2026, at 10:00 am CET at Jones Day’s offices located 2 rue Saint Florentin, 75001 Paris, France.

The General Meeting will also be webcast live for shareholders on the Company’s website (www.ose-immuno.com).

The notice containing the agenda and draft resolutions was published in the French BALO on May 20, 2026. The notice confirming the time and place of the meeting will be published in the French BALO and in a legal gazette on June 8, 2026.

The preparatory documents for the General Meeting listed in Article R. 22-10-23 of the French Commercial Code are posted on the Company’s website (www.ose-immuno.com).

The preparatory documents for the General Meeting will also be made available to shareholders as of the convening of the meeting. It is specified that the full text of the documents intended to be presented to the Meeting, in accordance in particular with Articles L. 225-115 and R. 225-83 of the Commercial Code, are made available at the Company’s headquarters.

From the date of the convocation and until the fifth day inclusive before the meeting, any shareholder may ask the Company to send him the documents and information mentioned in Articles R. 225-81 and R. 22583 of the Commercial Code, preferably by email to the following address: investors@ose-immuno.com. Bearer shareholders must justify this status by sending an account registration certificate.

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 listed on Euronext. Additional information about OSE Immunotherapeutics assets is available on the Company’s website: www.ose-immuno.com. Follow us on LinkedIn.

Contacts

OSE Immunotherapeutics: investors@ose-immuno.com

FP2COM (Media Relations): Florence Portejoie: fportejoie@fp2com.fr I +33 6 07 768 283

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.