CD28 and B-cell chronic lymphocytic leukemia: To investigate a potential EV-mediated communication between CLL-cells and T-cells, we co-cultured PKH26-labeled CLL cell lines (that also secrete PKH26+ EVs, data not shown) together with HD-derived T-cells in the absence/presence of a T-cell stimulatory signal (via anti-CD2/CD3/CD28-coated beads).