Challenges facing in vivo tracking of mesenchymal stem cells used for tissue regeneration.

Bone marrow-derived mesenchymal stem cells (MSCs) are increasingly being investigated in the field of regenerative medicine. In vivo monitoring of MSCs can be performed with MRI, which is a non-invasive, non-toxic and clinically acceptable modality. In order to track these MSCs, cells must be labeled with detectable magnetic nanoparticles. However, they 'leak' from labeled cells, limiting their surveillance to a 3-week period. Li et al. developed a rodent model in order to evaluate MRI monitoring of intramuscularly injected aminopropyltriethoxysilane iron oxide-labeled MSCs. Both in vivo tracking and histological analysis were undertaken. Seeded MSCs demonstrated increased MRI signal in the labeled test group over 3 weeks compared with the unlabeled controls. Histological Prussian blue staining of posttermination tissues confirmed these findings. The authors conclude that successful labeling of MSCs is possible with aminopropyltriethoxysilane - magnetic nanoparticles and that these cells can be monitored in vivo. They offer this form of labeling as an alternative to more common dextran-coated magnetic nanoparticles.