After incubation for 1 min, 1.6 mL of staining buffer (Partec) was added to the mixture. The mixture was filtered through a 30 m nylon mesh disposable filter (CellTrics®, Partec) and collected in a 3.5 mm×55 mm×12 mm Rohren-Tube (Sarstedt, Nümbrecht,Germany) and stored on ice.