Long-term outcome of RPE allografts to the subretinal space of rabbits

Purpose: To determine the long-term RPE allograft survival in the subretina l space using suspensions of RPE cells and atraumatic transplantation surge ry. Methods: Nineteen albino rabbits were transplanted with suspensions of pigm ented RPE cells from brown rabbits. Following pars plana vitrectomy, the RP E cell suspension was injected through a small retinotomy using a glass mic ropipette into the subretinal space under microscopic control. No immunosup pression was used. The eyes were monitored by biomicroscopy, color fundus p hotography, and fluorescein angiography. Rabbits were sacrificed at 1, 3 an d 6 months, respectively, and the eyes processed for light and electron mic roscopy, using monoclonal antibodies for identifying macrophages, Results: Transplanted RPE cells were present in the subretinal space in all eyes at 6 months. There was no fluorescein leakage. Generally, the RPE all ograft formed a monolayer, but focal fragmentation and disruption with disp ersion of melanin pigment occurred. Foci of multilayers of cells in the sub retinal space, containing large macrophages, were associated with adjacent photoreceptor damage. There was no infiltration of lymphocytes but macropha ges and glial cells were contiguous to the transplant. Cells harboring intr acytoplasmatic melanin pigment were observed in the neural retina. Conclusion: Transplantation of RPE cell suspensions to the subretinal space generally forms a monolayer that persists at 6 months. However, in areas o f multilayers of RPE cells and macrophages, graft failure occurs in combina tion with adjacent photoreceptor damage. Graft failure is not associated wi th the infiltration of lymphocytes, but other mechanisms seem to occur.