Photoreceptor transplantation in inherited and environmentally induced retinal degeneration: anatomy, immunohistochemistry and function.

In conclusion, we have shown that photoreceptors can be transplanted to retina in which the host's photoreceptors are lost by environmental (constant light) or inherited deficits. Furthermore transplanted photoreceptor cells maintain basic characteristics of normal photoreceptor cells by producing opsin and maintaining an intercellular organization and apposition to the host retina that is similar to that seen in the normal outer nuclear layer. To accomplish this we have devised a method to isolate the intact photoreceptor layer. This is significant because it will be necessary to maintain tight matrix organization if coherent vision is to be restored to the retina compromised by the loss of photoreceptors. We have further developed a surgical approach which minimizes trauma to the eye and allows controlled positioning of sheets of transplanted photoreceptors to their homotopic location within the eye. In addition these methods for transplantation and isolation of photoreceptors could be utilized to prepare and transplant other retinal layers so that selected populations of retinal cells can be used in other neurobiological investigations. Photoreceptors can be transplanted when developing or when mature. Not only can mature rat photoreceptors can be transplanted, but we have shown that mature photoreceptors from human donors can be transplanted as well. This is significantly different from neurons which must be immature in order to be transplanted. At present the reason for this difference is not known but has obvious importance for retinal and neural transplantation research in general. Finally, we have shown that transplanted photoreceptors activate the host's dystrophic retina in a light dependent manner that closely resembles the activation pattern seen in normal retina. This finding taken together with our results showing that human photoreceptors can be transplanted presents the possibility that some forms of human blindness might eventually be ameliorated by photoreceptor transplantation. The authors are grateful to A. I. Cohen, and N. W. Daw for helpful discussions; to C. Barnstable for gifts of antibody; and to J. Lett for excellent technical assistance. This work was supported by grants from NIH, National Retinitis Pigmentosa Foundation, the Monsanto Company; and an Alfred P. Sloan Fellowship to MSS.