Prolonged Heat-Treated Mesenchymal Precursor Cells Induce Positive Outcomes Following Transplantation in Cervical Spinal Cord Injury

Cellular transplantation therapies have been extensively used in experimental spinal cord injury research. However, there is no consensus as to what the most effective cellular controls for the therapeutic cell of interest are. For this reason, we examined whether dead cells obtained through prolonged heat treatment can act as an appropriate cellular control for intravenously injected Sca-1+ mesenchymal precursor cells (MPCs) in C5 unilateral contusion cervical spinal cord injury. This was tested in single intravenous MPC injection alone or intravenous MPC plus intraspinal neural stem cell (NSC) combinatory transplantation studies. MPCs were isolated from the compact bone of FVB mice, while NSCs were isolated from the subventricular zone of luciferase-GFP transgenic FVB mice. Dead MPCs were obtained by heating at 72 °C for at least 12 h. In the MPC only transplant study, injured mice received an injection of 1 × 10⁶ dead or live MPCs D1 post-injury. Mice were then sacrificed at 8 weeks post-injury. In this study, intravenous injections of dead MPCs showed no statistical difference in injured paw usage compared to live MPCs, but behavior was improved compared to the media-vehicle-only control at D7 and D21. In the combinatory MPC plus NSC transplant study, injured mice received an intravenous injection of 1 × 10⁶ dead or live MPCs D1 post-injury followed by intraspinal injection of 100,000 NSCs at D3 or D7 post-injury. Another two cohorts of mice received only NSCs at D3 or D7 post-injury. Mice were then sacrificed at 6 weeks post-injury. In this study, there was no functional difference in any of the groups in the dual injection study. Morphologically, mice receiving IV injection of dead MPCs had a smaller lesion size compared to the vehicular control, but the lesion size was larger than that of the lesion size in mice receiving live MPC injection. Dead cells elicited functional and anatomical benefits for the spinal-cord-injured mice. In summary, dead cells obtained through prolonged heat treatment proved to be inconsistent and not optimal for use as cellular controls for cell transplantation studies in spinal cord injury but provide positive evidence for non-transplantation-based cell therapies.