Correction of a Material Error Relating to the Total Number of Voting Rights and Shares Comprising the Share Capital

Correction of a Material Error Relating to the Total Number of

Voting Rights and Shares Comprising the Share Capital

 Clarification in Response to Unfounded Accusations

NANTES, France – September 24, 2025, 8:00 a.m. CET – OSE Immunotherapeutics SA (ISIN: FR0012127173; Mnemo: OSE) corrects the information relating to the total number of shares and voting rights comprising its share capital. 

As part of the prepara,on for the General Mee,ng on September 30, 2025, OSE iden,fied a processing error related to the accelera,on - recorded between June and September 2025 by the Board of Directors - of the ves,ng period for 546,919 free shares.

This material error, which has no impact on the rights of the beneficiaries nor on votes already cast, was acknowledged and immediately corrected by the Board of Directors at its mee,ng on September 23. All necessary measures have been taken to inform the shareholders concerned.

The number of outstanding shares comprising the share capital is 22,463,262. The number of theore,cal^[1] vo,ng rights is 27,859,524.

Clarifica(on in Response to Unfounded Accusa(ons

OSE firmly refutes the unfounded and false allega,ons disseminated by the group of concerted minority shareholders, accusing the Execu,ve Management and the Board of Directors of “fraudulent manipula,on.” The iden,fied processing error does not in any way result from a deliberate act, let alone a fraudulent one. It stems from an inaccurate legal qualifica,on by one of the Company’s corporate advisors and was corrected by the Board of Directors as quickly as possible, without any impact on the rights of the beneficiaries or on votes already cast. The Company regrets the aggressive and defamatory communica,on strategy adopted by certain minority shareholders who have chosen to exploit this situa,on in a polemical manner just days before a General Mee,ng that is crucial for its future.

OSE remains firmly commiYed to maintaining an open and construc,ve dialogue with all its shareholders, in compliance with the law and in the interest of the Company.

Consequences on the Holding of the Block Formed by the Shareholders Who Signed a Shareholders’ Agreement

It is noted that 61 founding, historical, employee, and execu,ve shareholders of the Company (the “Shareholder Group”) entered into an agreement regarding the vo,ng of resolu,ons related to the composi,on of the Board of Directors at the General Mee,ng scheduled for September 30, 2025^[2].

Following the adjustment of the number of shares and vo,ng rights in circula,on, this Shareholder Group, ac,ng in concert, now holds—directly and indirectly—approximately 14.22% of the Company’s share capital and 19.05% of vo,ng rights.

In this context, the Company has been informed that an amended declara,on of threshold crossing and intent will be submiYed to the AMF.

As a reminder, this Shareholder Group has commiYed to vote at the General Mee,ng: 

•       FOR the resolu,ons proposed by the Board of Directors concerning its own composi,on (resolu,ons 5 to 8), and 

•       AGAINST the resolu,ons proposed by the group of concerted minority shareholders (resolu,ons A to K); it being specified that vo,ng rights may be exercised freely for the remaining resolu,ons.

Clarifica(on on the recommenda(ons of proxy advisory firms.

The Company also recalls that two interna,onal proxy advisory firms recommended vo,ng in favor of resolu,ons 5 to 8 proposed by the Board of Directors concerning its composi,on^[3]. OSE notes that these firms have issued differing opinions on certain other resolu,ons submiYed to the General Mee,ng by the Board (notably concerning execu,ve remunera,on, related-party agreements, or financial authoriza,ons). Shareholders are invited to form their own opinion by consul,ng the full recommenda,ons available under subscrip,on from these firms. 

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: http://ose-immuno.com. 

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Contacts

Fiona Olivier fiona.olivier@ose-immuno.com

Sylvie Détry sylvie.detry@ose-immuno.com French Media Contact 

FP2COM

Florence Portejoie fportejoie@fp2com.fr +33 6 07 768 283

U.S. Media Contact

Rooney Partners LLC Kate BarreFe kbarreFe@rooneypartners.com +1 212 223 0561

Forward-looking statements 

This press release contains express or implied information and statements that might be deemed forward-looking 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 can often be identified by the use of the conditional tense and by verbs such as “expect”, “anticipate”, “believe”, “target”, “plan”, or “estimate”, their declensions and conjugations as well as other similar terms. Although the management of 

OSE Immunotherapeutics believes that the forward-looking statements and information are reasonable, 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 within the AMF. Such forward-looking statements are not guarantees of future performance. This press release includes only summary information and should be read alongside 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 OSE Immunotherapeutics’ website. Other than as required by applicable laws, 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.