Magnetic Resonance Tracking of Implanted Adult and Embryonic Stem Cells in Injured Brain and Spinal Cord

A bstract : Stem cells are a promising tool for treating brain and spinal cord injury. Magnetic resonance imaging (MRI) provides a noninvasive method to study the fate of transplanted cells in vivo . We studied implanted rat bone marrow stromal cells (MSCs) and mouse embryonic stem cells (ESCs) labeled with iron‐oxide nanoparticles (Endorem®) and human CD34 + cells labeled with magnetic MicroBeads (Miltenyi) in rats with a cortical or spinal cord lesion. Cells were grafted intracerebrally, contralaterally to a cortical photochemical lesion, or injected intravenously. During the first week post transplantation, transplanted cells migrated to the lesion. About 3% of MSCs and ESCs differentiated into neurons, while no MSCs, but 75% of ESCs differentiated into astrocytes. Labeled MSCs, ESCs, and CD34 + cells were visible in the lesion on MR images as a hypointensive signal, persisting for more than 50 days. In rats with a balloon‐induced spinal cord compression lesion, intravenously injected MSCs migrated to the lesion, leading to a hypointensive MRI signal. In plantar and Basso‐Beattie‐Bresnehan (BBB) tests, grafted animals scored better than lesioned animals injected with saline solution. Histologic studies confirmed a decrease in lesion size. We also used 3‐D polymer constructs seeded with MSCs to bridge a spinal cord lesion. Our studies demonstrate that grafted adult as well as embryonic stem cells labeled with iron‐oxide nanoparticles migrate into a lesion site in brain as well as in spinal cord.