Purpose: In this study we investigated the application of the human sodium iodide symporter (hNIS) as a reporter gene to noninvasively image in vivo gene transfer and expression in lung tissue in real time.
Methods: Human NIS-expressing adenoviruses (Ad-hNIS) or empty adenoviruses (Ad-Bgl II) were instilled into the lungs of Cotton rats via the nostrils. After 3, 10, and 17 days post infection, gamma camera scintigraphy with 99mTcO4- was performed to observe the distribution and duration of gene transfer. At 20 days after infection, reverse transcription polymerase chain reaction was performed to detect hNIS gene expression. Dual expressing vector Ad-hNIS-eGFP was used to detect transgene expression by fluorescence photomicroscopy in infected lung tissue. Positron emission tomography (PET) imaging of gene transfer to the lungs was performed using 124I- as tracer. Finally, hNIS transfer to a polarized human airway epithelial cell layer was evaluated by phosphorimaging.
Results: Lungs in animals infected with Ad-hNIS were clearly visible on scintigraphy and PET scans, while those infected with Ad-Bgl II were undetectable. Lungs in Ad-hNIS infected animals could still be visualized at 17 days but were no longer detectable at 20 days. Fluorescence microscopy showed that lung tissue infected with Ad-hNIS-eGFP had significantly higher GFP signal intensity than that infected with Ad-Bgl II.
Conclusion: It is feasible to use the hNIS gene as a reporter gene to monitor the location, magnitude, and timing of expression of genes delivered during pulmonary gene therapy. The ability to noninvasively visualize gene expression tomographically in real time has significant translational implications in human gene therapy.