Magnetic Resonance Evaluation of Transplanted Mesenchymal Stem Cells After Myocardial Infarction in Swine

Introduction: Our objective was to trace and evaluate intracoronary transplanted mesenchymal stem cells (MSCs) labelled with superparamagnetic iron oxide (SPIO) by using magnetic resonance imaging (MRI) in a swine model of myocardial infarction (MI). Methods: MSCs were transfected with a lentiviral vector carrying the gene encoding green fluorescent protein (GFP) and labelled in vitro with SPIO. At 2 weeks after MI, swine were randomized to intracoronary transplantation of dual-labelled MSCs (n = 10), MSC-GFP (n = 10), and saline (n = 5). MRI examination was performed with a 1.5-T clinical scanner at 24 hours, 3 weeks, and 8 weeks after cell transplantation. Signal intensity changes, cardiac function, and MI size were measured by means of MRI. The correlation between MRI findings and histomorphologic findings was also investigated. Results: MSCs could be efficiently and safely labelled with SPIO and GFP, and multipotentiality was not affected, especially for cardiomyocyte-like cell differentiation. Signal intensity on T2*-weighted imaging decreased substantially in the interventricular septum 24 hours after injection of MSCs. The intensity of hypointense signals appeared to increase throughout the later time points. Both dual-labelled MSCs and MSC-GFP could dramatically reduce the size of MI and improve cardiac function. Histologic data revealed that cells positive for Prussian blue stain were found mainly in the border zone, which also showed green fluorescence. Conclusions: In vivo 8-week tracing of dual-labelled MSCs can be achieved by MRI. Intracoronary transplantation of dual-labelled MSCs can increase cardiac function and reduce the size of MI in a swine model.