Long-term safety and clinical outcomes from a single-site phase 1 study of neural stem cell transplantation for chronic cervical spinal cord injury

Neural stem cell transplantation offers a promising avenue for spinal cord injury (SCI) repair, but demonstrating safety and feasibility in human populations remains a critical step. In this phase 1 trial, we investigate the long-term outcomes of cervical spinal cord implantation of NSI-566, a human spinal cord-derived neural stem cell line. With prospective data collection over 60 months, we assess adverse events, functional outcomes, and neurophysiological measures in a small cohort (N = 3) of chronic AIS-A SCI patients. We report a favorable safety profile with no evidence of tumorigenicity or procedure-related complications. Subclinical neurophysiological changes and limited functional gains were observed, although interpretation is constrained by the absence of a control group and the confounding effects of post-operative rehabilitation. These findings support the feasibility of intraparenchymal stem cell delivery for chronic SCI and underscore the need for larger, controlled trials to clarify efficacy and optimize therapeutic parameters.