OSE Immunotherapeutics

Legal Proceedings Report • Feb 15, 2023

OSE Immunotherapeutics Provides Regulatory Update on Tedopi®, a Cancer Vaccine at a Late-Stage Clinical Development in Lung Cancer After Failure to Immunotherapies

Nantes, France – February 15, 2023, 6:00 p.m. CET – OSE Immunotherapeutics SA (ISIN: FR0012127173; Mnemo: OSE) today provides a regulatory update on the clinical development plan of Tedopi®, an immunotherapy activating tumor specific T-cells, in phase 3 in monotherapy in advanced or metastatic non-small cell lung cancer (NSCLC) after checkpoint inhibitor failure (ICI).

Nicolas Poirier, Chief Executive Officer of OSE Immunotherapeutics, comments:

"We are pleased with the positive outcomes from the US Food & Drug Administration (FDA) Type C Meeting following the supportive European Medicines Agency (EMA) advice, as we are actively preparing a confirmatory phase 3 trial to support the regulatory registration of Tedopi®.

Leveraging on the positive data on efficacy, safety and quality of life from the initial phase 3 randomized trial in third line post-chemotherapy followed by an immune checkpoint inhibitor (ICI), we are committed in advancing the clinical development for Tedopi® as a potential new standard of care in monotherapy in second line for advanced or metastatic lung cancer patients in secondary resistance to ICI now used in first line. No therapeutic options have yet been approved to date in this patient population with high unmet medical needs."

Positive recommendations from the US Food and Drug Administration (FDA) "Type C" meeting following the European Medicines Agency (EMA) scientific advice for the confirmatory phase 3 trial in second line treatment

Both Agencies supported the continuation of the clinical development for Tedopi® through a new confirmatory phase 3 clinical trial versus standard of care in second line treatment for HLA-A2+ patients in advanced in non-small cell lung cancer (NSCLC).

OSE Immunotherapeutics is thus progressing on the protocol development for the next confirmatory phase 3 pivotal trial to support the regulatory registration of Tedopi® in second line. This upcoming phase 3 is planned for HLA-A2+ patients with secondary resistance to immunotherapy (IO) after a first line of chemo-IO followed by failure to maintenance IO of at least 12 weeks (defined as the threshold for secondary/acquired resistance by international expert consensus recommendations). The protocol design is developed with the support of the international NSCLC clinician experts' group which were already involved in the previous phase 3 ATALANTE trial.

Positive clinical data from the initial phase 3 trial ATALANTE in third line treatment

Tedopi® is the first cancer vaccine to show positive and clinically meaningful efficacy results associated with a better safety and quality of life profile in monotherapy versus active comparator

(chemotherapy-based standard of care) in third line with secondary resistance to ICI in advanced or metastatic NSCLC.

• Significant overall survival (primary endpoint) (p=0.017) with 44.4% overall survival rate at 1 year with Tedopi® versus 27.5% with chemotherapy;
• Significant better safety profile with less severe (Grade 3-5) adverse events (11% with Tedopi® versus 35% with chemotherapy, p<0.05);
• Significant better quality of life (Global health status: p=0.045; Role Functioning: p=0.025).

The results from the first phase 3 trial (ATALANTE) in a clearly defined target population are based on a strong biological rationale: increased specific T-cell responses induced by Tedopi®'s innovative mechanism of action correlated to the overall survival in HLA-A2+ NSCLC patients. The direct activation of tumor specific T-cells by Tedopi® differs from ICI releasing the break of immune response.

Ongoing compassionate use* programs in third line treatment in secondary resistance postsequential chemotherapy and immunotherapy

OSE Immunotherapeutics is committed to provide Tedopi® through cohort early access and nominative compassionate use programs across European countries to address patients' needs alongside physicians' engagement.

The French National Authority for Health issued a negative decision on the cohort early access program in third line treatment related to the COVID crisis which led to the suspension of patient inclusion in the previous phase 3 ATALANTE and the consecutive primary analysis on a population of interest with secondary resistance.

Patients can benefit from Tedopi® through compassionate use programs in third or further lines of treatment (post chemotherapy and immunotherapy) currently approved in France, Italy and Spain, confirming thereby the significant medical need for new therapeutic alternatives.

On-going combination studies of Tedopi®

Tedopi® is currently being evaluated in phase 2 combination trials in three indications:

• Non-Small Cell Lung Cancer: Tedopi® plus docetaxel or Tedopi® plus nivolumab or docetaxel alone, in second-line treatment in metastatic NSCLC, progressing after first-line chemo-immunotherapy (CombiTED study: NCT04884282, 105 patients planned, sponsor: FoRT);
• Pancreatic cancer: Tedopi® plus FOLFIRI vs FOLFIRI as maintenance treatment in patients with advanced or metastatic pancreatic adenocarcinoma with no progression after 8 cycles of FOLFIRINOX (TEDOPaM study: NCT03806309, 106 patients planned, sponsor: GERCOR);
• Ovarian cancer: Tedopi® alone or in combination with pembrolizumab vs best supportive care as maintenance treatment in platinum-sensitive recurrent ovarian cancer patients (TEDOVA study: NCT04713514, 180 patients planned, sponsor: ARCAGY-GINECO).

* Compassionate use is a treatment option that allows for the use of an unauthorized medicine. Under strict conditions, products in development can be made available to nominative patients who have a disease with no

satisfactory authorized therapies and who cannot enter clinical trials(https://www.ema.europa.eu/en/humanregulatory/research-development/compassionate-use).

ABOUT OSE Immunotherapeutics

OSE Immunotherapeutics is a biotech company dedicated to developing first-in-class assets in immuno-oncology and immuno-inflammation. The Company's current well-balanced first-in-class clinical pipeline includes:

• Tedopi® (immunotherapy activating tumor specific T-cells, off-the-shelf, neoepitope-based): this cancer vaccine is the Company's most advanced product; positive results from the Phase 3 trial (Atalante 1) in Non-Small Cell Lung Cancer patients in secondary resistance after checkpoint inhibitor failure. Other Phase 2 trials, sponsored by clinical oncology groups, of Tedopi® in combination are ongoing in solid tumors.
• OSE-279 (anti-PD1): ongoing Phase 1/2 in solid tumors or lymphomas (first patient included). OSE-279 is the backbone therapy of the BiCKI® platform.
• OSE-127/S95011 lusvertikimab (humanized monoclonal antibody antagonist of IL-7 receptor) developed in partnership with Servier; ongoing Phase 2 in ulcerative colitis (sponsor OSE Immunotherapeutics) and ongoing Phase 2a in Sjögren's syndrome (sponsor Servier); ongoing pre-clinical research in leukemia (OSE Immunotherapeutics).
• FR-104/VEL-101 (anti-CD28 monoclonal antibody): developed in partnership with Veloxis Pharmaceuticals, Inc. in transplantation; ongoing Phase 1/2 in renal transplant (sponsor Nantes University Hospital); Phase 1 ongoing in the US (sponsor Veloxis Pharmaceuticals, Inc.).
• OSE-172/BI 765063 (anti-SIRPα monoclonal antibody on CD47/SIRPα pathway) developed in partnership with Boehringer Ingelheim in advanced solid tumors; positive Phase 1 dose escalation results in monotherapy and in combination, in particular with anti-PD-1 antibody ezabenlimab; international Phase 1b ongoing clinical trial in combination with ezabenlimab alone or with other drugs in patients with recurrent/metastatic head and neck squamous cell carcinoma (HNSCC) and hepatocellular carcinoma (HCC).

OSE Immunotherapeutics expects to generate further significant value from its two proprietary drug discovery platforms, which are central to its ambitious goal to deliver next-generation first-in-class immunotherapeutics:

• BiCKI® platform focused on immuno-oncology (IO) is a bispecific fusion protein platform built on the key backbone component of anti-PD1 combined with a new immunotherapy target to increase anti-tumor efficacy. BiCKI-IL-7 is the most advanced BiCKI® candidate targeting anti-PD1xIL-7.
• Myeloid platform focused on optimizing the therapeutic potential of myeloid cells in IO and immuno-inflammation (I&I). OSE-230 (ChemR23 agonist mAb) is the most advanced candidate generated by the platform, with the potential to resolve chronic inflammation by driving affected tissues to tissue integrity.

Additional information about OSE Immunotherapeutics assets is available on the Company's website: www.ose-immuno.com Click and follow us on Twitter and LinkedIn

Contacts OSE Immunotherapeutics Sylvie Détry sylvie.detry@ose-immuno.com +33 1 53 198 757

Investor Relations

Thomas Guillot thomas.guillot@ose-immuno.com +33 6 07 380 431

Forward-looking statements

French Media: FP2COM Florence Portejoie fportejoie@fp2com.fr +33 6 07 768 283

International Media: MEDiSTRAVA Consulting Sylvie Berrebi OSEImmuno@medistrava.com +44 203 928 6900

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 in light of 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 forwardlooking 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 15 April 2022, including the annual financial report for the fiscal year 2021, 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 forwardlooking information or statements.