Experimental Neuroretinal Transplantation

Embryonic full-thickness rabbit neuroretinal sheets were transplanted to the subretinal space of adult hosts. This was accomplished by using a new transplantation technique involving vitrectomy and retinotomy. The grafts were followed from 10 to 306 days after surgery, and were then examined by different histological techniques. In the light microscope, the transplants were seen to develop the normal retinal lamination and fused with the host retina, especially after long survival times. Ultrastructurally, normal photoreceptor outer segments, well integrated with the host retinal pigment epithelium were found. Growth cones were present in the zone of fusion between graft and host retina. Immunohistochemical labeling revealed many of the normal retinal components not previously found in retinal transplants, and graft-host connections between neurons in the rod pathway were seen. The morphology of vibratome sectioned neuroretinal sheets as well as adult full-thickness grafts was also examined. These transplantation types showed less of the normal morphology compared with embryonic full-thickness grafts. The immunogenicity of embryonic full-thickness and fragmented grafts was compared using Major Histocompatibility Complex (MHC) immunolabeling. Fragmented grafts elicited a response from the host immune system similar to a chronic transplant rejection. This reaction was absent in the full-thickness grafts which is in accordance with their good long-term survival.