Bystander effect after GCV treatment oftk-transduced RPMI 8226 MM cells. RPMI 8226 MM cells (3 × 104/well) were transduced with Ad.CMV-βgal or Ad.CMV-tk (•) or with Ad.DF3-βgal or Ad.DF3-tk (○) at MOI = 0, 1, 5, 10, 50, and 100 for 2 hours. Cells were washed out for 10 hours, and tk-transduced tumor cells were then treated with GCV (50 μmol/L) for 36 hours. The bystander effect was determined by comparing the percentage of transduced cells after Ad.CMV-βgal and Ad.DF3-βgaltransduction, assessed by X-Gal staining, with the percentage of cells killed after GCV treatment of Ad.CMV-tk– and Ad.DF3-tk–transduced cells, assessed by trypan blue exclusion. HeLa cervical carcinoma cells (▴), known to demonstrate the bystander effect,34 were similarly transduced with Ad.CMV-βgal or Ad.CMV-tk and served as positive controls.
