Abstract
Continuing advances in Schwann cell (SC) cultivation methods, particularly of human SC, allow for large purified SC populations to be generated from small donor segments. This permits the reliable construction of autologously-derived SC transplants which may foster CNS regeneration following injury. The cells can be presented to the CNS within novel constructs, such as channels, which may concentrate SC-derived factors and exert other salutary effects. This thesis examines several aspects of the potential for purified and expanded human SCs to support meaningful regeneration of injured CNS neurons following a lower-thoracic spinal cord resection in the nude rat, a xenograft tolerant animal. Initially, the ability of human SC to survive within a distally closed PAN/PVC guidance channel apposed to the spinal cord was assessed. We recultured human SC from grafts 35 days following implantation and determined the cellular composition of initially homogeneous grafts following CNS integration.Using immunohistochemical and retrograde tracing methods we determined which injured axons have regenerated into human SC/Matrigel and nude rat SC/Matrigel grafts 35 days following implantation of distally closed-ended channels. These included propriospinal, sensory, motor, and also brainstem neurons known to be significant for locomotor function. The ability of such transplanted SC to form myelin in association with regenerating axons was demonstrated in these spinal cord grafts. Large numbers of axons and brainstem neurons regenerated into both human and nude rat SC grafts. In addition there appeared to be enhanced tissue preservation of the host spinal cord in the interface regions. The unique immunobiology of the nude rat may be responsible for this effect.The reentry of regenerating fibers from human SC grafts back into the host spinal cord was assessed using novel combinations of retrograde and anterograde tracing and analysis methods. Propriospinal and sensory neuronal processes which had regenerated back into the host spinal cord for 2--3 mm were visualized near host spinal cord neurons. This regeneration may be enhanced by the additional injury created by anterograde tracing procedures. Animals with openended human SC grafts exhibited locomotor improvements that were not seen in animals with distally-capped channel grafts.Improved graft/host integration was obtained by using a novel technique to place preformed grafts without channels. At the interfaces of such grafts we observed close morphologic similarity to transition zones and the deposition of potentially inhibitory proteoglycans.Finally, following placement of human SC grafts and guidance channels the injury environment was further modified in an attempt to improve the regeneration of injured axons, particularly those of the corticospinal (CST) tract. Injections of hybridoma culture supernatant containing an antibody to neutralize inhibitory epitopes on oligodendrocyte membranes were made into the intrathecal space; this lead to CST sprouting but not elongation of fibers into the grafts and did not enhance functional recovery. The placement of an acidic FGF fibrin-glue mixture at host cord/graft interfaces significantly reduced CST die-back and allowed some fibers to enter human SC grafts.Human Schwann cells that were expanded, purified and transplanted into continuity with nude rat spinal cords promoted the regeneration of several types of injured neurons into grafts. Some locomotor recovery occurred despite the absence of long distance regeneration of injured neurons beyond the grafts.