Background

Spinal cord injury (SCI) is a severe condition in which the spinal cord is damaged, typically due to trauma such as traffic accidents or falls, resulting in impaired motor and sensory function below the injury site. The central nervous system has very limited regenerative capacity, making the spontaneous recovery of damaged neural circuits virtually impossible. Current clinical practice involves surgical stabilization of the spine and administration of high-dose steroids to suppress acute inflammation, but these treatments are limited in scope. However, these approaches only prevent the progression of the injury and have significant limitations in restoring lost nerve cells and axons.

To overcome these limitations, research is being conducted to reconstruct damaged neural tissue using stem cells. In particular, induced pluripotent stem cells (iPSCs), which are derived from adult cells through reprogramming, are considered advantageous due to their potential for patient-specific therapy and large-scale production. However, there have been concerns that the direct transplantation of neural stem cells (NSCs) derived from iPSCs into humans may lead to the formation of teratomas or tumors. Therefore, before evaluating the efficacy of cell therapies, it has been emphasized that the safety of the transplanted cells, i.e., their long-term harmlessness in the human body, must be verified as the top priority.

Key Findings

This study, published in the international journal 'Nature Medicine,' presents the results of a Phase 1 clinical trial that comprehensively evaluated the safety of iPSC-derived neural stem cell transplantation in patients with subacute complete spinal cord injury. The researchers administered iPSC-derived neural stem cells directly to the injured spinal cord of patients in the subacute phase, i.e., within a few weeks after injury, and performed long-term follow-up observations for a minimum of 2 years and up to 4 years.

The clinical team used regular magnetic resonance imaging (MRI) to closely monitor structural changes and the presence of abnormal tissue growth at the transplantation site. In addition, they conducted neurological examinations, including the American Spinal Injury Association (ASIA) functional grading scale, and comprehensive functional assessments. The results showed that no cases of abnormal proliferation or tumor formation were observed in the transplanted stem cells. No serious adverse events (SAEs) directly related to the treatment were reported, and the researchers successfully met the primary endpoint of long-term safety. MRI analysis also showed no signs of cyst formation or worsening of nerve compression at the transplantation site, demonstrating the safety of the cell transplantation procedure.

Significance and Prospects

This clinical trial demonstrates that iPSC-derived neural cells can be safely delivered and integrated into the spinal cord, which has no regenerative capacity. By resolving the long-standing concern about the potential for long-term tumorigenicity with years of precise follow-up data, this study has paved the way for future research. Safety confirmation is a critical step that next-generation regenerative medicine therapies must take before entering Phase 2 and Phase 3 clinical trials.

However, this Phase 1 study is limited by the number of participants and its focus on safety as the primary outcome, so caution is needed in concluding about the actual nerve regeneration efficacy. Whether sensory and motor function is precisely restored in patients with complete paralysis needs to be demonstrated in a larger, placebo-controlled Phase 2 clinical trial. In addition, establishing a multidisciplinary treatment strategy that combines improved engraftment of the transplanted cells with optimal rehabilitation programs remains a key challenge for commercialization.