The concomitant expression of pTP-mi5 and HSV-TK results in an increased inhibitory effect on the generation of infectious virus progeny in the presence of GCV. A549 cells were transduced with the adenoviral HSV-TK/pTP-mi5 expression vector, AdTO-TK-pTP-mi5x6 (carrying 6 copies of pTP-mi5), or the respective control vector, AdTO-TK-mi-x6 (carrying 6 copies of a negative control amiRNA) at an MOI of 100 TCID50/cell. At 24 h post-transduction, cells were infected with wt Ad5 at an MOI of 0.01 TCID50/cell, and GCV was or was not added at concentrations of 0.15 μM (A), 0.3 μM (B), 0.6 μM (C), or 1.2 μM (D). The output of infectious virus progeny was determined by TCID50 assays. Data represent the means ± SD of 3 independent transduction/infection experiments each performed in triplicate. *p < 0.05, **p < 0.01.