Delayed grafting of fetal CNS tissue into chronic compression lesions of the adult cat spinal cord

This review summarizes a series of experiments involving transplants of embryonic feline CNS tissue into chronic compression lesions of the adult cat spinal cord. Fetal spinal cord (FSC), caudal brainstem (BSt), neocortex (NCx) or a combination of either FSC/NCx or FSC/BSt was transplanted as solid pieces or as a suspension of dissociated cells into the developed cystic cavities produced by static-load compression trauma 2–10 weeks prior to grafting. All cats were immunosuppressed with cyclosporin A and their locomotor function was assessed for 6–30 weeks. Following the period of evaluation, all recipients were perfused with fixative and tissue specimens, taken at the transplantation site, were processed for general histological and/or immunocytochemical analysis. Viable graft tissue was found in all animals with the exception of two cats which showed active rejection of their transplants. All of the viable intraspinal grafts were extensively vascularized and did not show any signs of imminent or on-going tissue rejection. Fetal cat CNS grafts showed an extended maturational phase in that features of immature neural tissue (e.g. a paucity of myelination) were still seen even 6–9 weeks after transplantation. By 20–30 weeks, FSC and BSt grafts had attained a more advanced stage of maturation. Transplants in these chronic lesions were extensively blended with both the gray and white matter of the host spinal cord and could be visualized by magnetic resonance imaging (MRI). MRI could also detect regions of cavitation at the graft–host interface, as well as within some transplants. While preliminary evidence from behavioral studies suggest that the FSC and BSt grafts may improve or spare locomotor function in some recipients, a more rigorous analysis of post-grafting locomotor function is required to determine conclusively the functionality of these transplants.