Pericytes (5×104) were cultured with GBM cells at 1:1 proportion in 6-well plates for 24-72 hours. After, pericytes and GBM cells were isolated by GFP or RFP sorting, respectively or only trypsinized to break cell interactions. GBM cells interacting with pericytes were defined as PCC-GB and pericytes interacting with GBM cells as GBC-PC. Both types of cells were counted using an inverted fluorescence microscope (Nikon, Tokyo, Japan). Cumulative population doubling level was calculated using the formula: “PD=(1Log102)xLog10(NtNo)” where No is the number of viable cells (as determined by trypan blue exclusion) at seeding, whereas Nt is the number of viable cells at harvest.