Apoptosis in the retina following subretinal injection of human fetal retinal pigment epithelial cells

Abstract

Purpose. To determine if apoptotic cell death occurs in the retina following subretinal transplantation of human fetal retinal pigment epithelial cells (HFRPE). Methods. Following a standard vitrectomy, 15 μl of cultured HFRPE suspensions were injected transvitreally into the subretinal space of the eyes of pigmented rabbits. 2, 7, and 30 days after the xenogenic transplantation, the animals were euthanized and their eyes enucleated. A second group of rabbits received subretinal injections of 15 μl of PBS and served as controls. The retinas were analyzed for nicked-nuclear DNA in situ by TdT-mediated biotin-dUTP nick-end-labeling (TUNEL) and visualized by fluorescent microscopy. Results. TUNEL-positive photoreceptor cells were observed in both HFRPE-transplanted and control retinas. 2 days after the transplantation, intense and extensive labeling was noted in the outer nuclear layer. The labeled photoreceptor cells were distributed predominantly along the areas of injection. Scattered TUNEL-positive photoreceptor cells were seen in the 7 day group and only occasional labeling was noted in the 30-day group. In addition, the transplanted retinas exhibited more labeling than those of the control group. Conclusions. This study demonstrated that apoptotic photoreceptor cell death occurred following HFRPE transplantation. The retinal detachment created by the subretinal injections may account partly for this observation in both the transplant and control groups. In addition, the more extensive labeling observed in the transplant group may be secondary to an additional insult that resulted from the introduction of foreign cells to the subretinal space.