Intraparenchymal stem cell transplantation for spinal cord injury: a review of clinical trials

Traumatic spinal cord injury (SCI) results in severe and often permanent motor, sensory, and autonomic impairment, and current treatments offer limited restorative benefit. Stem-cell based approaches have been investigated to promote neural repair, but peripheral delivery is limited by poor cell localization and engraftment. Intraparenchymal (IP) transplantation, which delivers cells directly into injured spinal cord, is intended to improve local retention, survival, and integration. This review synthesizes early-phase clinical trials from the United States, Canada, Europe, and Australia, evaluating five major cell platforms: autologous olfactory-ensheathing-cells (OECs), fetal-derived neural stem cells (HuCNS-SC), embryonic stem cell derived oligodendrocyte progenitors (OPC1), fetal spinal cord derived neural progenitor cells (NSI-566), and autologous Schwann cells (ahSCs). IP delivery demonstrates convergent early-phase safety, with no recurrent cell-related severe toxicity, tumor formation, or progressive neurological deterioration attributable to the delivery platform. Functional outcomes remain heterogeneous and modest. Large, reproducible neurological recovery has not been observed, although some studies report limited sensory improvements, isolated motor gains, or electrophysiologic evidence of conduction across or below the injury. These findings support biological activity but insufficient functional efficacy under current trial designs. Future progress will require controlled efficacy studies with standardized endpoints, optimized timing and dosing, and rehabilitation or neuromodulatory integration.