OSE Immunotherapeutics Announces Strategic Amendment To Abbvie's Partnership On ABBV-230 Development

Strategic Amendment Enhances OSE Immunotherapeutics' Role in ABBV-230 Development While Preserving AbbVie's Long-Term Commitment

NANTES, France, December 8 ^th , 2025 – 7:30am CET - OSE Immunotherapeutics SA (ISIN: FR0012127173; Mnemo: OSE) today announced an amendment to its partnership agreement with AbbVie regarding ABBV-230, a monoclonal antibody designed to resolve chronic and severe inflammation, currently in the pre-clinical development stage.

Under the revised agreement, OSE Immunotherapeutics regains control of the early-stage development of the ABBV-230, while AbbVie maintains its rights to control future development and commercialization following successful completion of Phase 1. The revised approach reflects both parties' continued enthusiasm for the potential of ABBV-230 and aligns development responsibilities with each company's core strengths.

Highlights of the Amended Agreement

• OSE Immunotherapeutics to Lead Early Development: OSE Immunotherapeutics will assume responsibility for the preclinical and Phase 1 development of ABBV-230, drawing on its deep immunology expertise. These activities will be fully financed by OSE Immunotherapeutics, contingent upon securing adequate funding, at its sole discretion.
• AbbVie Retains Future Rights: AbbVie remains the exclusive licensee and retains its rights to develop and commercialize following successful completion of Phase 1, continuing its leadership in immunology innovation.
• Commercial Terms Unchanged: All existing commercialization rights, including royalties on global net sales and sales-based milestone payments, remain unchanged. OSE Immunotherapeutics retains its full economic entitlements under the original agreement.
• Milestone Payment Adjustment: With the amendment, OSE Immunotherapeutics will no longer receive the previously anticipated milestone payment tied to the initiation of a Phase 1 clinical study. However, OSE Immunotherapeutics becomes eligible for milestone payments in the following stages of development, should AbbVie advance the candidate beyond Phase 1.

ChemR23 is a dual-function receptor involved in both the initiation and resolution of inflammation, depending on the ligand that binds to it. It plays a key role in multiple diseases by regulating immune cell recruitment and activity. Both companies remain committed to exploring its potential as a first-in-class therapy for inflammation resolution.

Marc Le Bozec, Chief Executive Officer of OSE Immunotherapeutics, commented:“The overall value of our collaboration with AbbVie for ABBV-230 remains unchanged. Assuming leadership of early-stage development enables OSE to accelerate progress on this innovative program while leveraging our core immunology expertise. The restructured agreement reflects the value we've built and our shared commitment to advancing transformative therapies for chronic inflammatory diseases.”

OSE Immunotherapeutics and AbbVie announced the strategic partnership to develop OSE-230, in February 2024 [Press Release ].

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: . 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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