Abstract 1767: Feasibility of In Vivo Cardiac Stem Cell Tracking, by SPECT and PET Imaging, Using the Sodium-iodide Symporter as Reporter Gene
Background. Stem cells offer the promise of cardiac repair. Stem cell labeling is a prerequisite to tracking cell fate in vivo.
Aim. To develop a reporter gene that permits in vivo stem cell labeling. We examined the sodium-iodide symporter (NIS), a protein that is not expressed in the heart, but promotes cellular uptake of 99mTc or 124I, thus permitting cell tracking by SPECT or PET imaging, respectively.
Methods. The human NIS gene (hNIS) was expressed in rat cardiac derived stem cells (rCDCs) using lentivirus driven by the CAG or CMV promoter. NIS function in transduced cells was confirmed by in vitro 99mTc uptake. Eleven rats were injected with 1 or 2 million rCDCs intramyocardially immediately after LAD ligation; 6 with CMV-NIS and 5 with CAG-NIS cells. Dual isotope SPECT imaging was performed on a small animal SPECT/CT system, using 99mTc for cell detection and 201Tl for myocardial delineation, 24 hrs after cell injection. PET was performed on a small animal PET scanner using 124I for cell tracking and 13NH3 for myocardial delineation, 48hrs after cell injection. Contrast Ratio (CR) was defined as [(signal in the cells)-(signal in blood pool)]/signal in blood pool. High resolution ex vivo SPECT scans of explanted hearts (n=3) were obtained to confirm that in vivo signal was derived from the cell injection site. The presence of hNIS mRNA was confirmed in injected hearts after animal sacrifice (n=2), by real-time RT-PCR.
Results. NIS expression in rCDCs did not affect cell viability/proliferation (p=0.718, ctr vs NIS). In vitro 99mTc uptake was 6.0±0.9% vs 0.07±0.05, without and with perchlorate (specific NIS blocker), respectively. NIS-transduced rCDCs were easily visualized as spots of 99mTc or 124I uptake within a perfusion deficit in the SPECT and PET images. CR was considerably higher when cells were transduced by the CMV-NIS virus in comparison to the CAG-NIS virus (70±40% vs 28±29%, p=0.085). Ex vivo small animal SPECT imaging confirmed that in vivo 99mTc signals were localized to the injection sites. PCR confirmed the presence of hNIS mRNA in injected hearts.
Conclusion. NIS expression allows non invasive in vivo stem cell tracking in the myocardium, using both SPECT and PET. This reporter gene has great potential for translation in future clinical applications.