Imaging

In-vivo imaging can also be used to track the survival of injected MSCs. MSCs from transgenic mice that constitutively express luciferase or fluorescent proteins allow for long-term tracking of cells and estimations of survival in vivo [33]. For larger animal models, where MSCs cannot be imaged in vivo by bioluminescence, iron oxide-labeled MSCs have been tracked via magnetic resonance imaging (MRI) [54]. The disadvantage to labeling cells with iron oxide is that the signal will persist even after the MSCs have died or have been phagocytosed [55]. Labeling of cells with membrane dyes also allows for identifying remaining transplanted MSCs on histology, but the cells cannot be tracked over time [54]. Imaging alone cannot detect or assess immune responses, but when used with the other functional assays described above it can help determine the effects and kinetics of an immune response on MSC survival.