Iris Pigment Epithelium (IPE) Transplantation

Fort Lauderdale, FL. 12 May 1998

by Dr Dan-Ning Hu


The symposium " IPE Transplantation: Theoretical and Practical Considerations" was held in the Fort Lauderdale Convention Center, (Florida, USA) on May 12, 1998 during the 1998 Annual Meeting of The Association for Research in Vision and Ophthalmology. This meeting was organized by the Ocular/Extracutaneous Pigmentation Expert Group of the International Federation of Pigment Cell Societies. This symposium was composed of 2 sessions, which included 7 presentations. More than 150 ophthalmologists and basic scientists from all over the world joined this meeting. Dr. Uri Shabto of The New York Eye & Ear Infirmary (USA) gave the introduction, "Why IPE transplantation?". He mentioned that subretinal neovascular membranes associated with age-related macular degeneration are a major cause of legal blindness. Surgical excision of these membranes always leaves a retinal pigment epithelium (RPE) defect, which may lead to further damage to the neural retina and the visual function. RPE transplantation usually fails because of rejection of the RPE allograft. It is easy to obtain autologous IPE from iridectomy specimens. Therefore, it is worthy to study subretinal IPE transplantation as a substitute for RPE in various retinal degeneration diseases related to RPE defects. The first session, "Comparison of physiology and cell biology of IPE and RPE" was chaired by Dr. Dean Bok of University of California Los Angeles (USA). Dr. Ulrich Schraermeyer of the University of Cologne (Germany) presented on "Phagocytosis of photoreceptor outer segments by IPE". They found that the IPE possess phagocytic capacity in vivo and in vitro, which is one of the important function of the RPE. Dr. Dan-Ning Hu of The New York Eye & Ear Infirmary (USA), presented "Comparison of IPE and RPE in vitro". He showed that adult human IPE and RPE contain melanin that is similar in amount and nature. Both do not demonstrate any melanogenesis in vitro. Both cells reduced exogenous NO in the culture medium, and each responded similarly to various growth factors and cytokines and produced similar growth factors and neurotrophic factors. Drs. Dean Bok of UCLA and Ron P. Gallemore of Duke University (USA) presented "Retinoid metabolism of RPE" and "Water and ion transport by RPE", respectively. They discussed these two important functions of RPE, which have not yet been studied thoroughly on the IPE. The second session "Animal models and clinical experience" was chaired by Dr. Jason S. Slakter of Columbia University (USA). Dr. Kouros A. Rezai of Chicago University (USA) presented "IPE transplantation". He reported the studies on IPE transplantation in vitro and in vivo and documented that IPE have phagocytic activity and can form a blood-retinal barrier. Dr. Schraermeyer presented "IPE transplantation in rabbits and RCS rats". He reported that transplanted IPE could survive in subretinal space in both rats and rabbits. They took up photoreceptor outer segments and had a beneficial influence on photoreceptors of RCS rats. Dr. Amparo Navea of the University of LA FE (Spain) presented "Autologous transplantation of IPE into the subretinal space in humans". She reported 6 cases of IPE transplantation in age-related macular degeneration patients. IPE transplantation seems to be well tolerated. Three cases showed improvement of vision.

Based on this meeting, it is clear that much work has been done in the study on IPE transplantation, both in vitro and in experimental animals; preliminary clinical experiences have obtained encouraging results. However, many problems still exist and require further investigation in this exciting, nascent field.