The Effect of Transient Local Anti-inflammatory Treatment on the Survival of Pig Retinal Progenitor Cell Allotransplants

Purpose: The development of photoreceptor replacement therapy for retinal degenerative disorders requires the identification of the optimal cell source and immunosuppressive regimen in a large animal model. Allotransplants are not acutely rejected in swine subretinal space, although it is not known if survival can be improved with immunosuppression. Here we investigated the survival and integration of expanded pig retinal progenitor cells (pRPCs) in normal recipients with and without transient anti-inflammatory suppression. Methods: pRPCs were derived from the neural retina of E60 GFP transgenic pigs, expanded for six passages, characterized, and transplanted into the subretinal space of 12 pigs. Six recipients received a single intravitreal injection of rapamycin and dexamethasone. Results: pRPCs expressed the photoreceptor development genes Sox2, Pax6, Lhx2, Crx, Nrl, and Recoverin in vitro. Transplanted cells were identified in 9 out of 12 recipients 4 weeks after the injection. pRPCs integrated primarily into the photoreceptor inner segment layer and outer nuclear layer with single cells present in the inner nuclear layer. Donor cells remained recoverin-positive and acquired rhodopsin. We did not observe any signs of graft proliferation. The immunosuppression did not affect the survival or distribution of grafts. No macrophage infiltration or loss of retinal structure was observed in either group. Conclusions: Local immunosuppression with rapamycin and dexamethasone does not improve the outcome of pRPC allotransplantation into the subretinal space. Translational Relevance: Survival and integration of pRPC together with the lack of graft proliferation suggests that allogeneic RPC transplantation without transient immunosuppression is a favorable approach for photoreceptor cell replacement.