Objective: Strategies to overcome the problem of extensive early stem cell loss following transplantation requires a method to quantitatively assess their efficacy. This study compared the ability of sodium/iodide symporter (NIS) and enhanced green fluorescent protein (EGFP) imaging to monitor the effectiveness of treatments to enhance early stem cell survival.
Methods: Human adipose-derived stem cells (ADSCs) transduced with an adenoviral vector to express both NIS and EGFP were mixed with culture media (control), matrigel (matrigel group) or pro-survival cocktail
(PSC group), and 5×106 cells were injected into thigh muscles of C57BL/6 mice. Animals underwent serial optical imaging and 99mTcO4 - scintigraphy. Image-based EGFP fluorescence and 99mTcO4 - uptake was measured by region-of-interest analysis, and extracted tissues were measured for 99mTc activity. Fluorescent intensity measured from homogenized muscle tissue was used as reference for actual amount of viable ADSCs.
Results: ADSCs were efficiently transduced to express EGFP and NIS without affecting proliferative capacity. The absence of significant apoptosis was confirmed by annexin V FACS analysis and Western blots for activated caspase-3. Both fluorescence optical imaging and 99mTcO4 - scintigraphy visualized implanted cells in living mice for up to 5days. However, optical imaging displayed large variations in fluorescence intensity, and thus failed to detect difference in cell survival between groups or its change over time. In comparison, 99mTcO4 -scintigraphy provided more reliable assessment of within-in group donor cell content as well as its temporal change. As a result, NIS imaging was able to discern beneficial effects of matrigel and pro-survival cocktail treatment on early ADSC survival, and provided quantitative measurements that correlated to actual donor cell content within implanted tissue.
Conclusion: NIS reporter imaging may be useful for noninvasively assessing the efficacies of strategies designed to improve early survival of transplanted stem cell