Allogeneic neonatal neuronal retina grafts display partial immune privilege in the subcapsular space of the kidney

Transplantation of immature retinal tissues may offer a solution for restoring sight to individuals afflicted with degenerative retinal diseases. Promising results have recently demonstrated that neonatal retinal grafts placed in the eye can survive, differentiate into photoreceptor cells, and respond to evoked electrical stimuli. These transplants, however, were performed in immunologically immature recipients. Since it is important to know whether neonatal neuronal retina (NNR) tissue is immunogenic in immune-competent recipients, and whether this tissue displays inherent immune privilege, we have examined the fate of such grafts placed in a non-immune-privileged site of adult recipient mice. We found that typical, photoreceptor-dominated rosettes formed in differentiating NNR grafts, and that these allografts survived beyond 12 days, whereas genetically identical skin grafts were rejected earlier. Class II MHC-bearing cells of recipient origin were observed along the edge of NNR allografts as early as day 5. Donor-specific delayed hypersensitivity was not detected at 12 days, but did emerge on day 20, coincident with rejection of NNR allografts. Lymph nodes, but not spleens, of mice bearing NNR grafts at 12 days contained regulatory lymphoid cells that suppressed delayed hypersensitivity in naive recipients. We conclude that NNR grafts accommodate and even differentiate in the non-immune-privileged space beneath the kidney capsule. Survival beneath the kidney capsule of NNR allografts, but not skin allografts, at 12 days and beyond implies that NNR tissue possesses inherent immune privilege. The vulnerability of these grafts to rejection by 20 days reveals this privilege to be partial and temporary.