Immunoregulatory extracellular vesicles in multiple myeloma patients' peripheral blood

Aim: Extracellular vesicles (EVs) mediate cell-to-cell communication and co-contribute in cancer progression and modulation of immune responses. The aim of this work was to characterize the phenotype and function of EVs isolated from the peripheral blood (PB) of multiple myeloma (MM) patients, with particular attention to adenosinergic ectoenzymes. Methods: EVs were isolated by centrifugation of PB plasma samples from newly diagnosed (ND) MM patients and healthy donors (HD). EVs were characterized by nanoparticle tracking analysis (NTA). Flow cytometry was used to assess the expression of CD138 (a tumor-associated antigen), nicotinamide phosphoribosyltransferase/pre-B cell colony enhancing factor (NAMPT/PBEF1), and adenosinergic ectoenzymes CD38, CD39, CD203a, and CD73. Functional studies were performed by assessing T-cell proliferation in vitro using carboxyfluorescein succinimidyl ester (CFSE) dilution and flow cytometry, with or without EVs to the culture. Results: The PB EVs size was comparable between MM patients and HDs, whereas EV concentration was significantly higher in MM patients. EVs from MM patients expressed higher levels of CD138, PBEF, CD38, and CD73 than those from HDs. In addition, CD138⁺ EVs from MM patients expressed higher levels of PBEF, CD38, CD39, and CD73 than CD138^- counterparts. Finally, MM-derived EVs inhibited T-cell proliferation in vitro. This inhibition correlated with the expression of CD138 and CD203a. Conclusion: This study provides the first phenotypic and functional characterization of EVs obtained from the PB of MM patients. The presence of functional adenosinergic molecules may represent a novel immune-escape mechanism operating at distant sites. Nonetheless, further studies are required to define specific contributions of adenosinergic ectoenzymes and other immune-regulatory mechanisms.