Long-Term Transplant Effects of iPSC-RPE Monolayer in Immunodeficient RCS Rats

Abstract

Retinal pigment epithelium (RPE) replacement therapy is evolving as a feasible approach to treat age-related macular degeneration (AMD). In many preclinical studies, RPE cells are transplanted as a cell suspension into immunosuppressed animal eyes and transplant effects have been monitored only short-term. We investigated the long-term effects of human Induced pluripotent stem-cell-derived RPE (iPSC-RPE) transplants in an immunodeficient Royal College of Surgeons (RCS) rat model, in which RPE dysfunction led to photoreceptor degeneration. iPSC-RPE cultured as a polarized monolayer on a nanoengineered ultrathin parylene C scaffold was transplanted into the subretinal space of 28-day-old immunodeficient RCS rat pups and evaluated after 1, 4, and 11 months. Assessment at early time points showed good iPSC-RPE survival. The transplants remained as a monolayer, expressed RPE-specific markers, performed phagocytic function, and contributed to vision preservation. At 11-months post-implantation, RPE survival was observed in only 50% of the eyes that were concomitant with vision preservation. Loss of RPE monolayer characteristics at the 11-month time point was associated with peri-membrane fibrosis, immune reaction through the activation of macrophages (CD 68 expression), and the transition of cell fate (expression of mesenchymal markers). The overall study outcome supports the therapeutic potential of RPE grafts despite the loss of some transplant benefits during long-term observations.

Advances in the study of tissue-engineered retinal pigment epithelial cell sheets

“…Conversely, results in rhesus monkeys indicated immune rejection of hiPSC-RPE cell slices, which was not observed in the autologous iPSC-RPE cell slice transplantation group. Additionally, iPSC-RPE cell sheets prepared on hydrogels [ 30 ], silk fibroin membranes [ 31 ], polydimethylsiloxane (PDMS) scaffolds [ 32 ] and nanoengineered ultrathin parylene C scaffolds [ 33 ] successfully exhibited morphology, gene expression, and protein expression resembling that of natural RPE. Moreover, they achieved improved visual function in animal models.…”

“…Neither formation of tumors nor ectopic tissue was observed, and this condition persisted for at least 12 months. In RCS rats, Parylene-iPSC-RPE monolayer grafts demonstrated the ability to survive under their retinas and contribute to vision preservation [ 33 ]. Although RPE survival was observed in only half of the eyes with preserved vision at 11 months postoperatively, the potential of poly-paraxylene as a support for RPE transplantation cannot be disregarded.…”

Biomaterials used for tissue engineering of barrier-forming cell monolayers in the eye

“…Poly (chloro-para-xylylene) (parylene C) is a FDA approved class IV biocompatible polymer, that is, widely adopted for biomedical applications and drug delivery thanks to its mechanical strength, flexibility, transparency, chemical inertness, conformability, and good encapsulation efficiency ( Golda-Cepa et al, 2020 ; Coelho et al, 2023 ). In a long-term study, Rajendran Nair et al (2021b) transplanted human iPSC-RPE cultured on an ultrathin parylene C membrane into the subretinal space of immunodeficient RCS rat models. They assessed iPSC-RPE survival, RPE-specific marker expression, phagocytosis function, and vision restoration after 1, 4, and 11 months.…”

Recent Progress in Retinal Pigment Epithelium Cell-Based Therapy for Retinal Disease

“…Occasionally, cells were present on the underside of the parylene scaffold, a phenomenon that had been observed in preclinical studies. 44 RPE cells stained positively for RPE65, a visual cycle protein involved in the conversion of all- trans -retinyl ester to 11- cis -retinol. The cells also stained positive for Na-K ATPase in a distribution that was largely but not entirely apical.…”

“…The immunodeficient RCS rat is T-cell-deficient, but these animals possess bone marrow-dependent B cells and NK cells. Rajendran Nair et al, 44 for example, performed iPSC-RPE transplants in immunodeficient RCS rats. The RPE were derived from healthy adult human fibroblasts, and the cells were transplanted as a monoIayer on parylene sheets.…”