In vivo trafficking and targeted delivery of magnetically labeled stem cells.

Targeted delivery of intravenously administered genetically altered cells or stem cells is still in an early stage of investigation. We developed a method of delivering iron oxide (ferumoxide)-labeled mesenchymal stem cells (MSCs) to a targeted area in an animal model by applying an external magnet. Rats with or without an external magnet placed over the liver were injected intravenously with ferumoxide-labeled MSCs and magnetic resonance imaging (MRI) signal intensity (SI) changes, iron concentration, and concentration of MSCs in the liver were monitored at different time points. SI decreased in the liver after injection of MSCs and returned gradually to that of control rat livers at approximately day 29. SI decreases were greater in rats with external magnets. Higher iron concentration and increased labeled cell numbers were detected in rat livers with external magnets. The external magnets influenced the movement of labeled MSCs such that the cells were retained in the region of interest. These results potentially open a new area of investigation for delivering stem cells or genetically altered cells.