Tracking transplanted stem cell migration using bifunctional, contrast agent-enhanced, magnetic resonance imaging.

The ability to track stem cell transplants in the brain by in vivo neuroimaging will undoubtedly aid our understanding of how these cells mediate functional recovery after neural transplantation. One major challenge for the development and refinement of stem cell transplantation is to map the spatial distribution and rate of migration in situ. Here we report a method for tracking transplanted stem cells in the ischemia-damaged rat hippocampus by magnetic resonance imaging (MRI). Before transplantation, stem cells were labeled in vitro either with a novel bifunctional contrast agent, gadolinium rhodamine dextran (GRID), identifiable by both MRI and fluorescence microscopy, or with PKH26, visible exclusively under fluorescence microscopy. At different time points following engraftment, the brains were evaluated by both histology and ex vivo MR imaging. Transplanted stem cells were identified by MRI only if prelabeled with GRID, whereas fluorescence microscopy detected transplanted cells using either label. The distribution of GRID-labeled stem cells identified by MRI corresponded to those detected using fluorescence microscopy. These results demonstrate that GRID-enhanced MRI can reliably identify transplanted stem cells and their migration in the brain.