FIG. 4.

Tumor-selective transgene expression. (A) Selective E1a gene transcription in WI-38-VA13 cells. WI-38 and WI-38-VA13 cells were infected with adenoviruses E2F/hGM/ΔE3 and E2F/hGM/E3b at 1,000 particles per cell. Real-time PCR was performed on the infected cells at the 4-h time point to determine E1a RNA levels. To correct for differences in initial transduction efficiency, E1a RNA levels were normalized to hexon DNA copy number 4 h postinfection, ± standard deviation. (B) Selective transgene expression in WI-38-VA13 cells. Human GM-CSF levels secreted by WI-38 and WI-38-VA13 cells were determined by ELISA. Human GM-CSF was analyzed at 24 h after infection, using the quantitative human GM-CSF sandwich enzyme immunoassay kits from R&D Systems. The concentrations of human GM-CSF in the samples were calculated from the standard curve based on the optical density at 490 nm and normalized to adenoviral genome copy number determined 4 h following infection.