Human mesenchymal stem cell (MSC) is known to have therapeutic effect in spinal cord injury (SCI), but the optimal therapeutic time window and survival pattern is not well known. The authors evaluated the treatment effect of MSC in the respect of injection time and survival rate in spinal cord injured rats.

In experiment I, SCI is performed by New York State University (NYU) Impactor in 30 rats. Human MSCs were injected intramedullarily with 5 groups. The animals were grouped with Group 1 (injury only), Group 2 (immediate MSC injection), Group 3 (injection after 3 days), Group 4 (injection after 1 week), Group 5 (injection after 2 weeks), and Group 6 (injection after 4 weeks). The Basso Beattie Bresnahan (BBB) locomotor scale was evaluated during 8 weeks after SCI in all the animals, and then the spinal cords were stained with H&E and antinucleic acid staining (Antinuclei®). In experiment II, MSC were injected at 1 week after SCI. After that, cord tissue were stained with antinucleic acid at 1 week (n=5), 2 weeks (n=5), and 3 weeks (n=5) after injection.

In experiment I, BBB score improvement at 8th week after SCI were statistically significant at Group 4, 5, 6 compared to Group 1. The cavity size were not significantly different in each group. In the antinucleic acid staining, the MSCs could not be observed within the cords. In experiment II, stained cell numbers at each group were significantly different.

In this study, the authors observed that neurological recovery after SCI in rats were improved by human MSCs which were injected intramedullarily at 1, 2, or 4 weeks after SCI and the injected cells could not survive over 4 weeks. Therefore, the neuroprotective effect by MSCs is supposed to be ocurred in the early period of injection time when the MSCs survive.