AB Science announces the identification of a plasma biomarker that indicates the activity of masitinib in treating ALS

Page 1 of 2 PRESS RELEASE AB SCIENCE ANNOUNCES THE IDENTIFICATION OF A PLASMA BIOMARKER THAT IND ICATES THE ACTIVITY OF MASITINIB IN TREATING AMYOTROPHIC LATERAL SCLEROSIS, AND THAT IS CAPAB LE OF IDENTIFYING PATIENTS WITH PRO INFLAMATORY MICROGLIA, WHICH ARE TARGETED BY MASITINIB THIS BIOMARKER IS ALSO APPLICABLE TO PROGRESSIVE FORMS OF MULTIPLE SCLEROSIS AND ALZHEIMER DISEASE THIS BIOMARKER CAN BE STRATEGIC TO DETERMINE WHICH PATIENTS RES POND TO TREATMENT AND POTENTIALLY INCREASE CHANCE OF REGISTRATION IN NEURODEGENERATIVE DISEASES Paris, February 24, 2026, 6pm CET AB Science SA (Euronext - FR0010557264 - AB) announced the identification of a potential bi omarker for assessing the activity of masitinib in pathological microglial involvement in Amyotrophic Lateral Scler osis (ALS). The key characteristics of this newly identified biomarker are as follows: - It is a blood-based (plasmatic) biomarker, which has the advantages of being easy to collect and accurately evaluated using ELISA (enzyme-linked immunoassay). - It is produced by proinflammatory microglia. - It activates microglia and astrocytes and is therefore an activator contributi ng to a vicious neuroinflammation feedback loop. - It is also released by mast cells, establishing a link between mast cells and microglia, which are two major cellular targets of masitinib. - It is predictive of survival in ALS, potentially explaining why masitinib coul d extend survival in some specific patients. - In-house experiments showed that this biomarker was reduced by masitinib when mast cells and microglia were activated in vitro, underscoring the specific and potent activity of masitinib on mast cells and microglia. Professor Olivier Hermine, President of AB Science's Scientific Committee, member of the French Academy of Sciences and Head of the Hematology Department at Necker Hospital, commented: “ Interestingly, this biomarker could be used in ALS but also in other neurodegenerative diseases of interest, namely progressive forms of multiple sclerosis (MS) and Alzheimer’s disease. In multiple sclerosis, for instance, this biomarker has normal plasmatic levels in clinically isolated syndrome (CIS), is elevated in RRMS during relapse, and is high in progressive forms, consistent with what we know about the involvement of microglia in MS”. This biomarker will be introduced in the phase 3 program of masitinib in ALS, as well as in progressive MS and Alzheimer’s disease, to validate the mechanism of action of masitinib in humans and its clinical relevance. Once validated, it could facilitate registration by determining which patients respond best to treatment and serve as a surrogate endpoint of efficacy if necessary . Indeed, FDA Guidance on ALS states that “ FDA encourages sponsors to incorporate exploratory biomarkers in all phases of development of ALS drugs. In the Page 2 of 2 future, greater scientific understanding of ALS may provide opportunities for discuss ion of surrogate endpoints that are reasonably likely to predict clinical benefit and that might serve as a basis for accelerated approval.” This biomarker remains undisclosed for patent protection reasons. About AB Science Founded in 2001, AB Science is a pharmaceutical company specializing in the research, development, and commercialization of protein kinase inhibitors (PKIs), a class of targeted proteins whose action is key in signaling pathways within cells. Our programs target only diseases with high un met medical needs, which are often lethal with short-term survival or rare or refractory to previous lines of treatment. AB Science has developed a proprietary portfolio of molecules, and the Company’s lead compound, masitinib, has already been registered for veterinary medicine and is being develope d for human medicine in oncology, neurological diseases, inflammatory diseases, and viral diseases. The company is headquartered in Paris, France and is listed on Euronext Paris (ticker: AB). Further information is available on AB Science’s website: www.ab-science.com. Forward-looking Statements - AB Science This press release contains forward-looking statements. These sta tements are not historical facts. These statements include projections and estimates as well as the assumptions on which they are based, statements based on projects, objectives, intentions, and expectations regarding financial results, e vents, operations, future services, product development, and their potential or future performance. These forward-looking statements can often be identified by the words "expect", "anticipate", "believe", "intend", "estimate" or "plan" as well as other similar terms. While AB Science believes these forward-looking statements are reasonable, investors are cautioned that these forward-looking stateme nts are subject to numerous risks and uncertainties that are difficult to predict and generally beyond the control of AB Science, which may imply that results and actual events significantly differ from those expressed, induced, or anticipated in the forward-looking information and statements. These risks and uncertainties include uncertainties relat ed to the product development of the Company, which may not be successful, or to the marketing authorizations granted by competent authorities, or, more generally, any factors that may affect the marketing capacity of the products developed by AB Science, as well as those developed or identified in the public documents published by AB Science. AB Science disclaims any obligation or undertaking to update forward-looking information and statements, subject to the applicable regulations, in particular articles 223-1 et seq. of the AMF General Regulations. For additional information, please contact: AB Science Financial Communication & Media Relations [email protected]

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