Spatio-temporal dynamics, differentiation and viability of human neural stem cells after implantation into neonatal rat brain

Neural stem cells (NSCs) have attracted major research interest due to their potential use in cell replacement therapy. In patients, human cells are the preferred choice, one source of human NSCs being the brain of fetuses. The aims of the present study were to explore the long-term differentiation, mobility and viability of NSCs derived from the human fetal striatum in response to intracerebral implantation. To investigate long-term spatio-temporal and functional dynamics of grafts in vivo by magnetic resonance imaging, these cells were labeled with superparamagnetic iron oxide (SPIO) nanoparticles prior to implantation. SPIO-labeling of human NSCs left the quantitative profile of the proliferation, cell composition and differentiation capacity of the cells in vitro unaltered. Also after transplantation, the phenotypes after long-term cell differentiation were not significantly different from naive cells. Upon transplantation, we detected a hypointensity corresponding to the striatal graft location in all animals and persisting for at least 4 months. The hypointense signal appeared visually similar both in location and in volume over time. However, quantitative volumetric analysis showed that the detectable, apparent graft volume decreased significantly from 3 to 16 weeks. Finally, the human NSCs were not proliferating after implantation, indicating lack of tumor formation. These cells are thus a promising candidate for translationally relevant investigations for stem cell-based regenerative therapies.