In vitro labeling and MRI of mesenchymal stem cells from human umbilical cord blood

ObjectiveThe aim of this study was to label human umbilical cord blood mesenchymal stem cells (MSCs) with poly-l-lysine (PLL)-conjugated superparamagnetic iron oxide particles and to obtain magnetic resonance (MR) images of the labeled MSCs' suspension at 1.5 T.Material and MethodsPLL was conjugated with iron oxide to form superparamagnetic particles called Fe2O3-PLL. Human umbilical cord blood MSCs were isolated, purified, expanded and incubated with Fe2O3-PLL. Prussian blue stain was performed to show intracellular iron; spectrometry was used to quantify iron uptake within cells. Tetrazolium salt (MTT) assay was applied to evaluate toxicity and proliferation of MSCs labeled with various concentrations of Fe2O3-PLL. The cell apoptosis rate was determined by annexin V/propichium iodide (PI) double staining method. Vials containing cells underwent MR imaging (MRI) with T1, T2 and T2* weighted MRI.ResultsIron-containing intracytoplasmatic vesicles could be observed clearly with Prussian blue staining in all samples except the unlabeled control. The iron content per cell determined by spectrometry was 64.51±10.32 pg. Among MSCs with and without labeling of various concentrations of Fe2O3-PLL, MTT values of light absorption had no statistically significant difference (Kruskal–Wallis test, χ2=10.35, P=.17). A concentration at 20 μg/ml of iron appeared most suitable for incubating cells. Of labeled and unlabeled MSCs, the early [annexin V-fluorescein isothiocyanate (FITC)-positive/PI-negative] and late (annexin V-FITC-positive/PI-positive) apoptotic cells were 10.34±0.43%/11.36±1.30% and 4.01±1.76%/2.98±1.37%, respectively, and there were no significant differences between them (P>.05). T2 weighted image (WI) and T2*WI demonstrated significant decrease of signal intensity (SI) in vials containing 1×106 (1 day), 1×106 (8 days) and 5×105 labeled cells, in comparison with unlabeled cells (P<.05). The percentage change of SI (ΔSI) was significantly higher in 106 labeled cells after 1-day culture than that in the same number of labeled cells after 8-day culture and that in 5×105 labeled cells, particularly on T2*WI (P<.05). Among pulse sequences, T2*WI demonstrated the highest ΔSI (P<.05).ConclusionThe human umbilical cord blood MSCs can be labeled with Fe2O3-PLL without significant change in viability and apoptosis. The suspension of labeled MSCs can be imaged with standard 1.5-T MR equipment.