Survival of allografted pancreatic islets in the subretinal space in rats

The purpose of this study was to determine whether the subretinal space would provide immune privilege for pancreatic islet transplantation. Islets from outbred Sprague Dawley (SD) rats were isolated by collagenase digestion, and about 200 handpicked islets were transplanted into the subretinal space of SD rats. Similar grafts were transplanted into the subconjunctival space of SD rats as controls. Transplanted eyes were enucleated after 2 to 60 days, fixed and embedded in paraffin for immunoperoxidase staining of insulin, glucagon, and CD8+ lymphocytes. Clinical examination of rat eyes revealed minimal or no inflammation in the anterior chamber or vitreous at any time point. Fifteen of 19 subretinal allografts survived up to 60 days. Few CD8+ lymphocytes were present in the subretinal grafts and the endocrine cells stained intensely for insulin and glucagon at all time points. In contrast, CD8+ lymphocytes were present in subconjunctival grafts in rats by day 14 and all grafts were destroyed by day 21. These results suggest that the subretinal space provides immune privilege for islet allotransplantation by preventing massive lymphocyte infiltration.