The success of human neural stem cell (NSC) implantation in spinal cord injury is time-dependent, according to a new study published in The Journal of Clinical Investigation. Researchers at the University of California examined markers of neuronal maturity and motor recovery in immunodeficient rats after NSC implantation. Human NSCs grafted into spinal cord injuries of adult rats differentiated, matured and integrated into the rodents' spinal cords after 12 months — a time frame typically associated with normal development of these cells in humans — and coincided with recovery of forelimb function. The results indicate that NSC implantation could offer therapeutic benefits following CNS injury, but the process might take some time. These finding could be of considerable importance for the design of future human trials.