The adenoviral vector containing both the pTP-mi5 and HSV-TK expression cassettes is heavily compromised in its replication rate in the presence of the E1 gene products. T-REx 293 cells that express the adenoviral E1 genes were transduced with AdTO-TK-pTP-mi5x6 at an MOI of 0.01 TCID50/cell. At the same time, amiRNA expression was or was not induced by the addition of 1 μg/ml doxycycline (dox) to the medium, and GCV was added at concentrations ranging between 0 and 1.2 μM. Vector copy numbers were determined at 48 h post-transduction by qPCR using a primer/probe set specific for the hexon gene present on AdTO-TK-pTP-mi5x6. Data represent the means ± SD of 3 independent transductions. Statistically significant differences between the individual samples and the -dox/0 μM GCV control sample are indicated. **p < 0.01; ns, not significant.