Flow cytometry assays were analysed on an Agilent NovoCyteflow cytometer (Agilent). GFP was analysed at 488 nm. Cells were washed three times with 100 μL of PBS, trypsinized with 30 μl of Trypsin-EDTA (Gibco) for 5 min at 37 ºC and, then 80 μL of supplemented medium with formalin (33% v/v) was added. Cells were detached by repeated pipetting and analysed.