Magnetic Resonance Imaging and Fluorescence Labeling of Clinical-Grade Mesenchymal Stem Cells Without Impacting Their Phenotype: Study in a Rat Model of Stroke

Human mesenchymal stem cells (hMSCs) have strong potential for cell therapy after stroke. Tracking stem cells in vivo following a graft can provide insight into many issues regarding optimal route and/or dosing. hMSCs were labeled for magnetic resonance imaging (MRI) and histology with micrometer-sized superparamagnetic iron oxides (M-SPIOs) that contained a fluorophore. We assessed whether M-SPIO labeling obtained without the use of a transfection agent induced any cell damage in clinical-grade hMSCs and whether it may be useful for in vivo MRI studies after stroke. M-SPIOs provided efficient intracellular hMSC labeling and did not modify cell viability, phenotype, or in vitro differentiation capacity. Following grafting in a rat model of stroke, labeled hMSCs could be detected using both in vivo MRI and fluorescent microscopy until 4 weeks following transplantation. However, whereas good label stability and unaffected hMSC viability were observed in vitro, grafted hMSCs may die and release iron particles in vivo. STEM CELLS TRANSLATIONAL MEDICINE 2012;1:333-340