Nantes, France - OSE Immunotherapeutics SA (ISIN: FR0012127173; Mnemo: OSE) announced that promising data from dose escalation Phase 1 of selective SIRP? inhibitor BI 765063 in patients with advanced solid tumors (ePoster 983P) will be presented(1) at the 2021 European Society for Medical Oncology (ESMO) Virtual Conference to be held on September 16 - 21, 2021.

This Phase 1 clinical trial aims to evaluate the safety and efficacy of BI 765063 as monotherapy and in combination with ezabenlimab (BI 754091; anti-PD-1 mAb) in patients with advanced solid tumours. The dose escalation part (Step 1) of the Phase 1 trial has enrolled SIRP? V1/V1 homozygous or V1/V2 heterozygous patients with advanced solid tumours who failed or were not eligible for standard therapies. Two dose levels of BI 765063 (18 and 24 mg/kg IV every 3 weeks) were evaluated in combination with BI 754091 (240 mg IV every 3 weeks). As of April 2021, a total of 12 patients had received at least one or more doses of each therapy. The combination BI 765063 + BI 754091 has shown a good safety profile and demonstrated clinical activity in two patients, including a tumor shrinkage in a patient with colonic adenocarcinoma and a confirmed partial response in a patient with endometrial carcinoma. Both patients were Micro Satellite Stable (MSS) and PD-1 treatment naive. Micro Satellite Instable (MSI) biomarkers are recognized as effective for immunotherapy by checkpoint inhibitor alone. The majority of colorectal and endometrial cancers are MSS and achieve limited benefit from immune checkpoint inhibitor monotherapy (2) . Updated data of June 2021 on this dose escalation part of Phase 1 will be featured in an ePoster presentation at the upcoming 2021 ESMO meeting. The Phase 1 clinical study of BI 765063 is being conducted by OSE Immunotherapeutics as part of a collaboration and license agreement under which Boehringer Ingelheim obtained exclusive rights to the product.

Contact:

OSE Immunotherapeutics

Sylvie Detry

E: sylvie.detry@ose-immuno.com

T: +33 153 198 757

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 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 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 15 April 2021, including the annual financial report for the fiscal year 2020, 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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