Abstract: Objective To observe the clinical efficacy and safety of umbilical cord mesenchymal stem cells (UC-MSCs) in treating spinal cord injury (SCI) by intrathecal injection. Methods From January 2008 to October 2013, 35 admitted patients with SCI were given UC-MSCs by intrathecal injection for 46 courses, at a dose of 1×106 cells/kg body weight once a week, 4 times as a course. American Spinal Injury Association (ASIA) standard and International Association of Neurorestoratology SCI Functional Rating Scale (IANR-SCIFRS) were used to evaluate SCI patient's neural function and ability of daily living. Results Among 35 cases, 22 cases were effective. Compared with the scale before therapy, effective patients'algaesthesis, tactile sensation, motion, activity of daily living scale were obviously increased one month after therapy (P<0.01). Nine effective patients received 2 to 3 courses of treatment, the effects of 7 cases were further enhanced. The effective rate of 25 cases with incomplete SCI was 88.46%, whereas all of 10 cases with complete SCI had no response. After therapy, there were headache, lumbago or fever in individual patients and disappeared within 1-3 days. All patients were followed up for 45 months to 114 months (average 84 months), no treatment-related adverse events happened. The effect was stable in effective patients. Conclusion UC-MSCs therapy by intrathecal injection is safe, and can ameliorate most of incomplete SCI patient's neurological function, multiple courses of treatment is likely to further improve the efficacy of patients.

Key words: Umbilical cord mesenchymal stem cells, Spinal cord injury, Intrathecal injection