Long-term full-thickness embryonic rabbit retinal transplants

PURPOSE. To establish the light and electron microscopic morphology of long -term full-thickness embryonic rabbit retinal transplants, with special att ention paid to graft-host integration. METHODS. Eighteen rabbits received a complete embryonic neuroretina 19 days after conception. The transplants were positioned under the host retina, f lat against the host retinal pigment epithelium with proper polarity, using a vitrectomy technique. After surviving 3 to 10 months, the transplants we re examined by light and electron microscopy. RESULTS. The outer retina of the host had degenerated in all specimens. In 16 of the 18 eyes, well-laminated transplants with correct polarity, measur ing up to 3.2 mm in length, were found. The transplants displayed long oute r segments facing the host retinal pigment epithelium, and they were lamina ted to the level of the inner plexiform layer in which fusion with the host was often evident. Fusion was more prominent in the oldest transplants. El ectron microscopy revealed bundles of neurites at different levels of matur ation in close contact with Muller cell fimbriae at regular intervals along the graft-host border. CONCLUSIONS. Full-thickness embryonic rabbit retinal transplants positioned with correct polarity develop into large laminated retinas and survive wit hout immunosuppression for at least 10 months, Host and graft adapt and alm ost reconstruct the normal retinal appearance. Ultrastructurally, well-deve loped photoreceptors and many normal synapse types are seen, and neuron spr outing is evident at the graft-host border.