Immunological problems of transplantation into the subretinal space

The objective of retinal transplantation is to substitute destroyed or dege nerated retina to improve visual function. Photoreceptors and retinal pigme nt epithelium cells of embryonic and nonembryonic origin have been transpla nted into the subretinal space in different animal models. Recently, retina l cells have also been used for transplantation in untreated or immunosuppr essed patients with retinitis pigmentosa and age-related macular degenerati on. Transplants performed in animals such as the RCS rat have maintained re tinal function at the transplantation site for long periods of time, althou gh such transplantations in humans have not proved conclusively, to date, w hether there is a real effect or not. One reason for this phenomenon seems to be an immune response to transplanted retinal cells at the transplantati on site. The detectable rejection process shows that the posterior part of the eye is not absolutely immunologically privileged and that rejection is a serious problem in human retinal transplantation. Many questions concerni ng transplantation technique, graft treatment and postoperative treatment w ill be answered through more intensive experiments and clinical trials rega rding the immunology. However, rejection of transplanted material is one of the main reasons why retinal transplantation has not yet proved successful .