Intravenous Transplantation of Mesenchymal Progenitors Distribute Solely to the Lungs and Improve Outcomes in Cervical Spinal Cord Injury.

Cellular transplantation strategies utilizing intraspinal injection of mesenchymal progenitor cells (MPCs) have been reported as beneficial for spinal cord injuries. However, intraspinal injection is not only technically challenging, but requires invasive surgical procedures for patients. Therefore, we investigated the feasibility and potential benefits of noninvasive intravenous injection of MPCs in two models of cervical spinal cord injury, unilateral C5 contusion and complete unilateral C5 hemisection. MPCs isolated from green fluorescence protein (GFP)-luciferase transgenic mice compact bone (1 × 10(6) cells), or vehicle Hank's Buffered Saline Solution (HBSS), were intravenously injected via the tail vein at D1, D3, D7, D10, or D14. Transplanted MPCs were tracked via bioluminescence imaging. Live in vivo imaging data showed that intravenously injected MPCs accumulate in the lungs, confirmed by postmortem bioluminescence signal-irrespective of the time of injection or injury model. The results showed a rapid, positive modulation of the inflammatory response providing protection to the injured spinal cord tissue. Histological processing of the lungs showed GFP(+) cells evenly distributed around the alveoli. We propose that injected cells can act as cellular target decoys to an immune system primed by injury, thereby lessening the inflammatory response at the injury site. We also propose that intravenous injected MPCs modulate the immune system via the lungs through secreted immune mediators or contact interaction with peripheral organs. In conclusion, the timing of intravenous injection of MPCs is key to the success for improving function and tissue preservation following cervical spinal cord injury. Stem Cells 2016;34:1812-1825.