Repetitive Intrathecal Catheter Delivery of Bone Marrow Mesenchymal Stromal Cells Improves Functional Recovery in a Rat Model of Contusive Spinal Cord Injury

Transplantation of bone marrow mesenchymal stromal cells (MSCs) has been shown to improve the functional recovery in various models of spinal cord injury (SCI). However, the issues of the optimal dose, timing, and route of MSC application are crucial factors in achieving beneficial therapeutic outcomes. The objective of this study was to standardize the intrathecal (IT) catheter delivery of rat MSCs after SCI in adult rats. MSCs labeled with PKH-67 were administered by IT delivery to rats at 3 or 7 days after SCI as one of the following treatment regimens: (1) a single injection (5 x 10(5) MSCs/rat), or (2) as three daily injections (5 x 10(5) MSCs/rat/d for a total of 1.5 x 10(6) MSCs/rat over 3 days, injected on days 3, 4, and 5, or days 7, 8, and 9 following SCI. The animals were behaviorally tested for 4 weeks using the Basso, Beattie, and Bresnahan (BBB) locomotor rating scale, and histologically assessed for MSC survival, distribution, and engraftment properties after 28 days. Rats treated with a single injection of MSCs at 3 or 7 days post-injury showed a modest, non-significant improvement in function and low survival of grafted MSCs, which were found attached to the pia mater or accumulated around the anterior spinal artery. In contrast, rats treated with three daily injections of MSCs at days 7, 8, and 9, but not on days 3, 4, and 5, showed significantly higher motor function recovery (BBB score 16.8 +/- 1.7) at 14-28 days post-injury. Transplanted PKH-67 MSCs were able to migrate and incorporate into the central lesion. However, only a limited number of surviving MSCs, ranging from 24,128 +/- 1170 to 116,258 +/- 8568 cells per graft, were observed within the damaged white matter. These results suggest that repetitive IT transplantation, which imposes a minimal burden on the animals, may improve behavioral function when the dose, timing, and targeted IT delivery of MSCs towards the lesion cavity are optimized.