FL B cells produce EVs that are internalized by BM-MSCs and trigger their differentiation toward an FL-supportive stroma. (A) Transmission electron microscopy of EVs harvested by ultracentrifugation of conditioned medium from the RL B-cell line. Representative images of the data obtained with the different B-cell lines and primary FL B cells are shown. (B) Size analyze of EVs by TRPS. Data are represented as the mean ± SD from 6 (B-cell lines) or 4 (purified FL B cells) independent experiments. (C) Quantification of EVs by TRPS after 48 hours of culture of 10⁴ B cells. (D) Flow cytometry analysis of 1.5 µM CellTrace Far Red–dyed EV uptake by BM-MSCs after 6 hours in the presence or not of specific endocytosis inhibitors. Data are represented as the mean ± SD of 4 independent experiments compared with the control condition (CTRL) arbitrarily assigned at 100%. Statistical significance was evaluated before normalization using the Dunnett post hoc test. ***P < .001; *P < .5. (E) Purified primary FL B cells (n = 8) were cocultured (ratio 4:1) or not with BM-MSCs pretreated or not with FL-derived EVs for 3 days. After 2 days, the percentage of active caspase-3⁺ CD19/CD20⁺ apoptotic malignant B cells was evaluated and compared with that of malignant B cells cultured alone using a nonparametric Wilcoxon test. Each symbol represents a different FL patient. *P < .05.