The Incorporation of Extracellular Vesicles from Mesenchymal Stromal Cells Into CD34⁺ Cells Increases Their Clonogenic Capacity and Bone Marrow Lodging Ability

Mesenchymal stromal cells (MSC) may exert their functions by the release of extracellular vesicles (EV). Our aim was to analyze changes induced in CD34⁺ cells after the incorporation of MSC-EV. MSC-EV were characterized by flow cytometry (FC), Western blot, electron microscopy, and nanoparticle tracking analysis. EV incorporation into CD34⁺ cells was confirmed by FC and confocal microscopy, and then reverse transcription polymerase chain reaction and arrays were performed in modified CD34⁺ cells. Apoptosis and cell cycle were also evaluated by FC, phosphorylation of signal activator of transcription 5 (STAT5) by WES Simple, and clonal growth by clonogenic assays. Human engraftment was analyzed 4 weeks after CD34⁺ cell transplantation in nonobese diabetic/severe combined immunodeficient mice. Our results showed that MSC-EV incorporation induced a downregulation of proapoptotic genes, an overexpression of genes involved in colony formation, and an activation of the Janus kinase (JAK)-STAT pathway in CD34⁺ cells. A significant decrease in apoptosis and an increased CD44 expression were confirmed by FC, and increased levels of phospho-STAT5 were confirmed by WES Simple in CD34⁺ cells with MSC-EV. In addition, these cells displayed a higher colony-forming unit granulocyte/macrophage clonogenic potential. Finally, the in vivo bone marrow lodging ability of human CD34⁺ cells with MSC-EV was significantly increased in the injected femurs. In summary, the incorporation of MSC-EV induces genomic and functional changes in CD34⁺ cells, increasing their clonogenic capacity and their bone marrow lodging ability. Stem Cells 2019;37:1357–1368.