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International audience; Background & AimMesenchymal stromal/stem cells (MSCs) are a heterogeneous population characterized by self-renewing and ability to differentiate into mesodermal cell origin. Wharton Jelly MSC (WJ-MSC) are a promising candidate for cell therapy due to their ease of isolation and their tissue regeneration capabilities. Moreover, they can regulate the immune response by secreting a set of soluble factors and by establishing direct interactions with the cells of immune system. These immunomodulation properties are used in the treatment of different pathologies such as graft versus host disease. In order to use WJ-MSCs for clinical applications, an in vitro expansion step is critical to obtain the sufficient dose. This step imposes several physicochemical and hydrodynamic constraints that can influence the quality and functional properties of cells.The objective of this work was to identify and validate predictive markers related to immunomodulatory properties of WJ-MSCs. For this purpose, CD119, CD200 and Notch1 were chosen and studied.Methods, Results & ConclusionAt first, markers distribution was studied by flow cytometry. Secondly, immunomodulatory potential of WJ-MSC was evaluated by a coculture of these cells with CD4, CD8 lymphocytes, followed by the study of lymphocytes proliferation by flow cytometry. These experimentss were performed under different conditions: WJ-MSCs cultivated in normoxia (N) and hypoxia (H), early passage and senescent cells, and under stimulation with gamma interferon (IFN-γ).Our results showed a heterogeneity of distribution of the markers studied. In addition, our study revealed that WJ-MSC cultivated in H was more immunosuppressive than those cultivated in N. Moreover, we showed that the cellular senescence induced a reduction of the immunosuppressive properties, and that IFN-γ stimulation increased WJ-MSC immunosuppression potential. Finally, our study highlighted a trend towards a correlation between the expression of CD119 and Notch1 by WJ-CSM and their immunomodulatory properties.To conclude, the culture conditions and cell senescence affect the immunomodulatory properties of WJ-CSM hence the interest of verifying these properties after the cell expansion procedures. Furthermore CD119 and Notch1 receptors may be predictive markers of the immunomodulatory properties of WJ -CSM to be checked during in vitro amplification.