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Introduction: CD39 plays an important role in the immunoregulation and inhibition of effector cells. It is expressed on immune cells, including Tregs, and on extracellular vesicles (EVs) budding from the plasma membrane. Platelet transfusion may induce alloimmunization against HLA-I antigens, leading to refractoriness to platelet transfusion with severe consequences for patients. Tregs may play a key role in determining whether alloimmunization occurs in patients with hematologic disorders. We hypothesized that CD39 + EVs might play an immunoregulatory role, particularly in the context of platelet transfusions in patients with hematologic disorders. Such alloimmunization leads to the production of alloantibodies and is sensitive to the regulatory action of CD39., Methods: We characterized CD39 + EVs in platelet concentrates by flow cytometry. The absolute numbers and cellular origins of CD39 + EVs were evaluated. We also performed functional tests to evaluate interactions with immune cells and their functions., Results: We found that CD39 + EVs from platelet concentrates had an inhibitory phenotype that could be transferred to the immune cells with which they interacted: CD4 + and CD8 + T lymphocytes (TLs), dendritic cells, monocytes, and B lymphocytes (BLs). Moreover, the concentration of CD39 + EVs in platelet concentrates varied and was very high in 10% of concentrates. The number of these EVs present was determinant for EV-cell interactions. Finally, functional interactions were observed with BLs, CD4 + TLs and CD39 + EVs for immunoglobulin production and lymphoproliferation, with potential implications for the immunological management of patients., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Delorme, Laguide, Tamagne, Pinheiro, Cagnet, Neyrinck-Leglantier, Khelfa, Cleophax, Pirenne and Vingert.)

Introduction: Aplasia and hematological malignancies are treated with platelet transfusions, which can have major immunomodulatory effects. Platelet concentrates (PCs) contain many immunomodulatory elements, including the platelets themselves, residual leukocytes, extracellular vesicles, such as microparticles (MPs), cytokines and other soluble elements. Two of these components, MPs and a soluble form of CD27 (sCD27), have been shown to play a particularly important role in immune system modulation. The loss of CD27 expression is an irreversible marker of terminal effector CD3 + T-lymphocyte (TL) differentiation, and the CD27 + MPs present in PCs may maintain CD27 expression on the surface of TLs, and, thus, the activation of these cells., Methods: In this study, we phenotyped the CD27-expressing MPs present in PCs by microscale flow cytometry and investigated the interaction of these particles with CD4 + TLs. We cocultured MPs and PBMCs and determined the origin of the CD27 expressed on the surface of CD4 + TLs with the aid of two fluorochromes (BV510 for CD27 originating from MPs and BV786 for cellular CD27)., Results: We showed that the binding of CD27- expressing MPs involved the CD70 molecule, which was also present on these MPs. Finally, the maintenance of CD27 expression on the surface of TLs by sorted CD27 + MPs led to activation levels lower than those observed with other types of MPs., Discussion: These results for CD27-expressing MPs and their CD70-mediated targeting open up new possibilities for immunotherapy based on the use of MPs to maintain a phenotype or to target immune cells, for example. Moreover, decreasing the levels of CD27-expressing MPs in transfused platelets might also increase the chances of success for anti-CD27 monoclonal immunotherapy., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Cagnet, Neyrinck-Leglantier, Tamagne, Berradhia, Khelfa, Cleophax, Pirenne and Vingert.)