Rodent Neural Progenitor Cells Support Functional Recovery after Cervical Spinal Cord Contusion.

Previously, we and others have shown that rodent neural progenitor cells (NPCs) can support functional recovery after cervical and thoracic transection injuries. To extend these observations to a more clinically relevant model of spinal cord injury, we performed unilateral midcervical contusion injuries in Fischer 344 rats. Two-weeks later, E14-derived syngeneic spinal cord-derived multi-potent NPCs were implanted into the lesion cavity. Control animals received either no grafts or fibroblast grafts. The NPCs differentiated into all three neural lineages (neurons, astrocytes, oligodendrocytes) and robustly extended axons into the host spinal cord caudal and rostral to the lesion. Graft-derived axons grew into host gray matter and expressed synaptic proteins in juxtaposition with host neurons. Animals that received NPC grafts exhibited significant recovery of forelimb motor function compared with the two control groups (analysis of variance p < 0.05). Thus, NPC grafts improve forelimb motor outcomes after clinically relevant cervical contusion injury. These benefits are observed when grafts are placed two weeks after injury, a time point that is more clinically practical than acute interventions, allowing time for patients to stabilize medically, simplifying enrollment in clinical trials, and enhancing predictability of spontaneous improvement in control groups.

Prolonged human neural stem cell maturation supports recovery in injured rodent CNS.

Neural stem cells (NSCs) differentiate into both neurons and glia, and strategies using human NSCs have the potential to restore function following spinal cord injury (SCI). However, the time period of maturation for human NSCs in adult injured CNS is not well defined, posing fundamental questions about the design and implementation of NSC-based therapies. This work assessed human H9 NSCs that were implanted into sites of SCI in immunodeficient rats over a period of 1.5 years. Notably, grafts showed evidence of continued maturation over the entire assessment period. Markers of neuronal maturity were first expressed 3 months after grafting. However, neurogenesis, neuronal pruning, and neuronal enlargement continued over the next year, while total graft size remained stable over time. Axons emerged early from grafts in very high numbers, and half of these projections persisted by 1.5 years. Mature astrocyte markers first appeared after 6 months, while more mature oligodendrocyte markers were not present until 1 year after grafting. Astrocytes slowly migrated from grafts. Notably, functional recovery began more than 1 year after grafting. Thus, human NSCs retain an intrinsic human rate of maturation, despite implantation into the injured rodent spinal cord, yet they support delayed functional recovery, a finding of great importance in planning human clinical trials.

Bone Marrow Stromal Cell Intraspinal Transplants Fail to Improve Motor Outcomes in a Severe Model of Spinal Cord Injury.

Bone marrow stromal cells (BMSCs) have been reported to exert potential neuroprotective properties in models of neurotrauma, although precise mechanisms underlying their benefits are poorly understood. Despite this lack of knowledge, several clinical trials have been initiated using these cells. To determine whether local mechanisms mediate BMSC neuroprotective actions, we grafted allogeneic BMSCs to sites of severe, compressive spinal cord injury (SCI) in Sprague-Dawley rats. Cells were administered 48 h after the original injury. Additional animals received allogeneic MSCs that were genetically modified to secrete brain-derived neurotrophic factor (BDNF) to further determine whether a locally administered neurotrophic factor provides or extends neuroprotection. When assessed 2 months post-injury in a clinically relevant model of severe SCI, BMSC grafts with or without BDNF secretion failed to improve motor outcomes. Thus, allogeneic grafts of BMSCs do not appear to act through local mechanisms, and future clinical trials that acutely deliver BMSCs to actual sites of injury within days are unlikely to be beneficial. Additional studies should address whether systemic administration of BMSCs alter outcomes from neurotrauma.