Long-term neuroretinal full-thickness transplants in a large animal model of severe retinitis pigmentosa

Background The purpose of this study was to explore neuroretinal transplantation in a large animal model of severe retinitis pigmentosa and to establish graft development, long-term survival, graft-host integration, and effects on the host retina. Methods Rhodopsin transgenic pigs, aged 6 months, received in one eye a fetal full-thickness neuroretinal sheet in the subretinal space by means of vitrectomy and retinotomy. Six months postoperatively, eyes were studied in the light microscope and with immunohistochemical markers. Full-field electroretinography (ERG) was performed at 4 and 6 months. Results Laminated grafts with well-organized photoreceptors, rod bipolar cells, and Muller cells were found in five of six eyes. Neuronal connections between graft and host retina were not seen. In the five eyes containing a graft, the number of surviving rods in the host retina was significantly higher compared with unoperated eyes. The ERG did not reveal any significant difference in b-wave amplitude between operated and control eyes, but the cone-derived response in operated eyes increased significantly from 4 to 6 months while the rod response in control eyes decreased significantly. Conclusions Fetal full-thickness neuroretina can be transplanted safely to an eye with severe retinal degeneration. In their major part, the transplants develop a normal laminated morphology and survive for at least 6 months. Graft and host retinal neurons do not form connections. Retinal function in the host is reduced initially by the surgical trauma, but the presence of a well-laminated graft counteracts this effect and rescues rods from degeneration.