Delivery of Autologous Neurotrophin-producing Fibroblasts Promotes Locomotion in the Chronic Spinal Cat

Adult cats show limited locomotor capabilities following spinal transection. With body-weight support training, the animals recover stepping ability with weight-bearing plantar foot placement. We previously found that delivery of neurotrophins via xenografts of genetically modified rat fibroblasts promotes a similar motor recovery without training. Similar results were obtained in rodents using direct injection of viruses into the cord. Viral delivery raises clinical concerns regarding recombinant genetics, and xeno/allografts require immunosuppression that increases cancer risks. Furthermore, none of these studies has investigated the effects of delayed onset of neurotrophin delivery on recovery. Our study utilized autologous fibroblasts modified to express the neurotrophins BDNF and NT-3 grafted into the spinal cord following a complete transection at the T11-T12 vertebral level. Fibroblasts were grafted at the time of injury, 2 weeks after injury, or 6 weeks after injury. Recovery of bipedal stepping on a treadmill was evaluated before and after injury and grafting. Kinematic evaluation indicated that grafting promoted recovery of treadmill stepping in the experimental groups. While control cats could only perform limited stepping at low (<= 0.4m/s) speeds, grafted cats recovered stepping at all speeds up to 0.8m/s. Recovery was seen in many grafted cats as early as 3 weeks after injury, and all but one grafted cat were capable of stepping at all speeds tested by 5 weeks after grafting. This recovery remained 12 weeks after grafting. Histological evaluation showed no regeneration through the lesion. We also began preliminary evaluation of lumbar puncture (LP) as a delivery method for autologous grafts. Kinematic evaluation showed that delivery of cells via LP (n = 1) resulted in recovery of stepping to higher levels than seen in acute graft cats. We conclude that neurotrophin-producing autografts are effective at promoting stepping even when delivered in a chronic spinal cord injury model.