Animal experiments and clinical application of olfactory ensheathing cell transplantation for treatment of spinal cord injury★

BACKGROUND: The olfactory epithelium can still generate new neurons after arresting its growth and development in the human body. Axons can still be generated and pass through peripheral tissue to reach the olfactory bulb. Thus, olfactory cells have been widely used in the repair of spinal cord injury. OBJECTIVE: Using animal experiments in conjunction with a clinical study of olfactory ensheathing cells, this paper was designed to clarify the function and application prospects of olfactory ensheathing cells, as well as the existing problems with their application. RETRIEVAL STRATEGY: Using the terms “olfactory ensheathing cells, spinal cord injury”, we retrieved manuscripts published from January 1990 to June 2007. The languages were limited to English and Chinese. Inclusion criteria: studies addressing the characteristics, basic study, clinical application and prospects of olfactory ensheathing cells; studies that were recently published or were published in high-impact journals. Exclusion criteria: repetitive studies. LITERATURE EVALUATION: The included 29 manuscripts were primarily clinical or basic experimental studies. DATA SYNTHESIS: Following spinal cord injury, spinal neurons die, neurotrophic factors are lacking, and the existing glial scar and cavities hinder axonal growth. One method to repair spinal cord injury is to interfere with the above-mentioned factors based on animal experiments. Myelination and axonal regeneration are the keys to spinal cord injury therapy. Olfactory ensheathing cells can secrete several neurotrophic factors, inhibit horizontal cell reactions, have noticeable neuroprotective effects, and possess a very strong reproductive activity, so they have many advantages in the fields of cell transplantation and gene therapy. However, there still exist many questions and uncertainties, such as the best time window and dose, as well as complications of olfactory ensheathing cell transplantation; precise mechanism of action after olfactory ensheathing cell transplantation; the number and length of growing axons as well as whether axonal growth is consistent with spinal cord recovery after olfactory ensheathing cell transplantation; and the long-term curative effect of olfactory ensheathing cells transplanted into spinal cord injury patients. CONCLUSION: Both animal experiments and clinical application have demonstrated that olfactory ensheathing cell transplantation helps spinal neurofunctional recovery, but the mechanism of action requires further investigation.