OSE Immunotherapeutics Announces Presentation of TEDOVA Phase 2 Topline Results of Tedopi® in Ovarian Cancer at the ASCO 2026 Meeting

Nantes, France, April 23, 2026 – 7:30am CEST - OSE Immunotherapeutics SA (ISIN: FR0012127173; Mnemo: OSE), a clinical-stage biotech company dedicated to developing first-in-class therapies in immuno-oncology and immuno-inflammation, today announced that topline results from the TEDOVA Phase 2 international clinical trial of Tedopi® in Ovarian Cancer sponsored by ARCAGY-GINECO have been selected for an oral presentation at the 2026 Annual Meeting of the American Society of Clinical Oncology (ASCO) in Chicago, Illinois, United States (May 29 - June 2, 2026).

Alexandra Leary, MD, PhD, Deputy Head of the Department of Medical Oncology at Gustave Roussy (Paris, France), oncologist specialising in gynaecological cancers, Chair of the GINECO group and Lead Investigator of the TEDOVA Phase 2 clinical trial of Tedopi®, will present topline results from the TEDOVA trial evaluating Tedopi® as a maintenance treatment of ovarian cancer.

“The neo-epitope-based vaccine OSE-2101 with or without pembrolizumab versus best supportive care as maintenance in platinum-sensitive recurrent ovarian cancer patients with controlled disease after platinum-based chemotherapy: The academic randomized TEDOVA/GINECO-OV244b/ENGOT-ov58 trial”

• Rapid Oral Abstract
• Session: Gynecologic Cancer – Subtrack: Ovarian Cancer
• Abstract 5510
• Room: E450
• May 30, 2026, 8:06-8:12am CDT (3:06-3:12pm EST)

TEDOVA is a three-arm Phase 2 study evaluating Tedopi® as a maintenance treatment, alone or in combination with anti-PD1 immune checkpoint inhibitor Keytruda® (pembrolizumab), versus best supportive care in 185 patients in platinum-sensitive recurrent ovarian cancer with controlled disease after platinum-based chemotherapy who have already received both bevacizumab and a PARP (Poly ADP-Ribose Polymerase) inhibitor. The primary endpoint is the Progression Free Survival (PFS) of the maintenance of Tedopi®, with a PD1 inhibitor, after platinum-based chemotherapy in relapsed ovarian cancer.

NCT04713514.

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.

ABOUT ARCAGY-GINECO

ARCAGY-GINECO (Groupe d’Investigateurs National pour l’Étude des Cancers de l’Ovaire et du sein) is a cooperative group founded in 1993 and accredited by the French National Cancer Institute (INCa). It specializes in clinical and translational research in the field of women’s cancers (gynecologic cancers and metastatic breast cancer). Its mission is to help improve survival and quality of life for patients by initiating and coordinating clinical trials in France and internationally. ARCAGY-GINECO contributes to the validation of scientific hypotheses by defining new standards of treatment and disseminating these results worldwide. More information on www.arcagy.org and our LinkedIn page.

ABOUT ENGOT

ENGOT (European Network for Gynecological Oncological Trial groups) is a research network of the European Society of Gynecological Oncology (ESGO) and was founded in 2007. Currently, ENGOT includes 21 cooperative groups from 33 European countries. Visit ENGOT website https://engot.esgo.org/ of LinkedIn page.

Contacts

OSE Immunotherapeutics: investors@ose-immuno.com

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

LifeSci Advisors (Investor Relations): Guillaume van Renterghem: gvanrenterghem@lifesciadvisors.com I +41 76 735 01 31

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.