Description of the gating procedure of the viable epithelial cells. FSC-SSC dot-plot was used for the visualisation of the various cell populations in this sample of a colorectal cancer. The viable cells (which were negative for 7AAD and positive for calcein) were selected with R1 gate on FL2 (calcein fluorescence)-FL3 (7AAD signal) dot-plot. R1 was further analyzed for gating out viable epithelial cells with R2 on two parallel FL4-SSC dot-plots of isotype control (middle, left) and BerEP4 antibody binding (middle, right) upon high FL4-BerEP4-positivity. Lower tables show number of cells in each gate. Only cells within R1 and R2 gates were used for the determination of the functional activity of MDR1 and MRP1 transporters.