C. del Cerro

Intraretinal xenografts of differentiated human retinoblastoma cells integrate with the host retina

We report on the successful use of chemically modified Y79 human retinoblastoma cells for intraretinal xenografting into damaged adult mammalian eyes. Y79 cells were exposed in vitro to retinoic acid/butyrate to induce differentiation. Using a multisite transplantation method, the suspension was injected into the subretinal space of Fischer 344 rats. The survival, integration, and differentiation potential of these cells was studied, following their return to the intraocular milieu from which the progenitor cells originated. The grafted cells survived and differentiated into immature photoreceptor elements in the subretinal and intraretinal locations, as multiple clusters of rosette-forming cells intimately attached to the host neuroretina. The differentiation process included development of synaptic connectivity of the ribbon type with the surrounding neuropil. No signs of renewed cell division were found within grafts performed on 42 rat eyes, and there was no indication of cell-mediated host reaction against the transplants. This study indicates that tumorigenicity can be suppressed in mitotically arrested Y79 cells, and that these cells are capable of undergoing differentiation in vivo. This provides evidence of the remarkable differentiation properties of human retinoblastomas while indicating that Y79 cells may ultimately be able to substitute for fetal cells in experimental retinal transplantation.

Retinal transplants into the anterior chamber of the rat eye

Developing retinas from 13-18-day fetuses and 2-day neonatal Long-Evans rats transplanted into the anterior chamber of adult eyes of the same or different strain (Lewis) survive and differentiate. Light and electron microscopic studies show that the transplants undergo histogenetic differentiation, resulting in the development of neurons and Müller glial cells and formation of nuclear and plexiform layers. Vascular connections develop between the host iris and the retinal transplant. Vessels and nerves, presumably of iridal origin, were seen on the surface of some transplants. Possible manifestations of graft rejection were monitored; signs of tissue rejection in transplants performed in the Long-Evans rats, an outbred strain, were rare and if present they were mild, at least during the survival periods of up to 91 days allowed in these experiments. Transplants into the eyes of Lewis rats were also well tolerated during the survival period. These observations indicate that retinal transplantation to the adult eye of a genetically different host can be successfully achieved and that both embryonic and perinatal retinas are suitable as donor tissue for ocular transplants. The procedure offers ample opportunities for the study of problems related to retinal plasticity.

Cyclosporine Treatment Promotes Survival of Human Fetal Neural Retina Transplanted to the Subretinal Space of the Light-damaged Fischer 344 Rat.

We have reported that xenografts of human fetal neural retina survive in the subretinal space of cyclosporine-immunosuppressed rats. In view of the current controversy regarding the role of cyclosporine, we wished to determine if cyclosporine immunosuppression was an absolute requirement for retinal xenograft survival. Neural retinas from human fetal eyes obtained within 1 h of termination of pregnancy were stored in Optisol medium (Chiron Vision, Irvine, CA) at 4 degrees C for 2 and 7 days. Retinas were then transplanted to the subretinal space of either cyclosporine-treated (10 mg/kg/day) light-damaged Fischer 344 rat eyes (17 animals, 28 eyes) or to the subretinal space of light-damaged Fischer 344 rat eyes (9 animals, 15 eyes) receiving no cyclosporine treatment. Grafted eyes were observed clinically at 10, 20, and 30 days posttransplantation. At 30 days, the animals were sacrificed and the grafts observed histologically. Human fetal retina xenografted to the subretinal space of immunosuppressed rats survived (9/17 animals, 12/28 eyes), showed good integration with the host retina and initial photoreceptor differentiation. Tissue xenografted to the subretinal space of non-cyclosporine-treated rats was not observed to survive (0/9 animals, 0/15 eyes). A low level cellular reaction was seen around three of the injection sites within the nonimmunosuppressed rats. We conclude that immunosuppression is necessary for the survival of human fetal neural retina xenografted to the subretinal space.