Determination of bystander effect. A) Upper panel. DU145 cells stably transfected with a vector expressing the fluorescent protein Venus to identify DU145 cells in mixed cultures. Two populations are clearly distinguishable by Venus fluorescence in mixed cultures. Lower panels. PC3 and PNT2 cells were co-cultured with DU145-venus cells and treated with 50 U/ml scFv62-TRAIL in the presence of 5 μg/ml CHX for 18 h. Apoptosis induction was analyzed with Annexin/PI staining and flow cytometry. Venus-positive (DU145 cells) are depicted in orange; green represents PC3/PNT2 cells (bystander cells). B) Quantification of the change in apoptosis of bystander cells was calculated.