Retinal transplantation: progress and problems in clinical application.

There is currently no real treatment for blinding disorders that stem from the degeneration of cells in the retina and affect at least 50 million individuals worldwide. The excitement that accompanied the first studies showing the potential of retinal cell transplantation to alleviate the progress of blindness in such diseases as retinitis pigmentosa and age-related macular degeneration has lost some of its momentum, as attempts to apply research to the clinic have failed so far to provide effective treatments. What these studies have shown, however, is not that the approach is flawed but rather that the steps that need to be taken to achieve a viable, clinical treatment are many. This review summarizes the course of retinal transplant studies and points to obstacles that still need to be overcome to improve graft survival and efficacy and to develop a protocol that is effective in a clinical setting. Emphasis is given particularly to the consequences of introducing transplants to sites that have been considered immunologically privileged and to the role of the major histocompatibility complex classes I and II molecules in graft survival and rejection.