Expression of the EGFP/amiRNA cassette from the tetracycline repressor-controlled CMV promoter is inhibited in adenovirus packaging cells in the absence of doxycycline. A. T-REx-293 cells were transfected with the plasmid vector, pTO-TK-mi-, in which the expression of the EGFP/negative control amiRNA expression cassette from the CMV promoter is under control of the tetracycline repressor. The plasmid vector, pcDNA6.2-GW/EmGFP-miR-neg (abbreviated as pmiRE), in which the same cassette is expressed from a constitutive CMV promoter, was used as a control. The cells were incubated with or without doxycycline and, 24 h later, they were analyzed for EGFP expression by FACS analysis. Mean fluorescence intensities (MFIs) of a representative experiment performed in triplicate (mean ± SD; n = 3) are shown; ***p < 0.001. B. Setup and data acquisition as in (A), except that cells were transduced with the adenoviral versions of the vectors that allow either constitutive expression of the EGFP/amiRNA cassette (Ad-mi-) or tetracycline repressor-controlled expression (AdTO-TK-mi-). **p < 0.01.