Relationship Between Location of Cell Transplantation and Recovery for Intracerebral Stem Cell Transplantation for Chronic Traumatic Brain Injury: <i>Post-hoc</i> Analysis of STEMTRA Trial

Traumatic brain injury is a world-leading cause of disability. Current treatments are not sufficient to promote neurological recovery. Intracerebral transplantation of allogeneic mesenchymal stem cells, specifically SB623, has shown promise in achieving better neurological recovery compared with a sham surgery group in the STEMTRA trial. However, the optimal location for cell transplantation remains unclear, as transplanted lesions vary between patients. This study aimed to explore the relationship between functional recovery and the location of transplanted lesions. This study included all Japanese subjects from the STEMTRA trial who were assigned to the cell transplantation group. Functional recovery was assessed by the difference in Fugl-Meyer Motor Scale (FMMS) scores between the screening period and 24 or 48 weeks post-transplantation. An FMMS score improvement of >8 was defined as an improved group. Lesions responsible for motor deficits were categorized into three groups: motor cortex (Cortex), deep white matter (DWM), or both (Cortex and DWM). Data on the 15 transplanted sites per patient were obtained from surgical navigation software, and the distance from the damaged area to the transplanted sites was calculated. Twelve patients were included in this <i>post-hoc</i> analysis. No patients in the 2.5 × 10⁶ cells group showed improvement and were therefore excluded from further analysis. Five patients were categorized into the Cortex group and four into the DWM group. The distance between the transplanted site and the injury point ranged from 0 to 39 mm. A moderate to strong trend of correlations was observed, suggesting that a shorter distance is preferable for the motor cortex group, while a greater distance is preferable for the DWM group. The optimal site for stem cell transplantation may be different from the damaged site of the patient; however, a further large number cohort is necessary to elucidate this hypothesis.