Intact sheets of fetal retina transplanted to restore damaged rat retinas.

PURPOSE The aim of this study was to establish a model for morphologic retinal reconstruction after destruction of photoreceptors. METHODS Rat embryos were prelabeled by injection of bromodeoxyuridine (BrdU) into timed pregnant rats on 2 to 6 consecutive days. Pieces of fetal retinas (embryonic day [E] 17 to E22) were embedded in growth factor-reduced matrigel for protection and stored in medium on ice. With the use of a custom-mnade implantation tool, trimmed embedded pieces were placed into the subretinal space of albino rats whose photoreceptors had been damaged by continuous exposure to blue light for 3 to 4 days. RESULTS Donor cells were unequivocally identified by the BrdU label. Approximately 25% of transplants in the subretinal space developed parallel layers, with photoreceptor outer segments facing the host pigment epithelium. Transplants developed rosettes if host pigment epithelium had been damaged, if trauma to the donor tissue occurred during preparation or transplantation, and if the donor tissue was misplaced into the choroid or into the epiretinal space on top of the host retina. If the surgery was performed more than 4 weeks after the light damage, continued degeneration of the host retina caused secondary pigment epithelium damage, and transplants did not develop parallel layers of photoreceptor outer segments. CONCLUSIONS After transplantation to the subretinal space of a degenerated retina, gel-protected fetal retina can develop parallel layers and photoreceptor outer segments in contact with host pigment epithelium. Transplants can develop good fusion with the inner retina of a photoreceptor-deficient recipient.