Survival and functionality of iPSC-RPE cultured as a polarized monolayer on ultrathin parylene assessed in a new immunodeficient RCS rat model

Abstract

Purpose : RPE replacement therapy is now evolved as a feasible approach to treat human retinal degeneration diseases like Age-related Macular Degeneration (AMD). This study is aimed to evaluate the survival and functionality of induced pluripotent stem cell derived retinal pigment epithelium (iPSC-RPE) cultured as a polarized monolayer on parylene substrate and transplanted into the subretinal space of a new immunodeficient Royal College of Surgeon (RCS) rat disease model.

Methods : Polarized iPSC-RPE (passage two cells generated from healthy adult human fibroblast cells) was cultured for 2 weeks on rectangular pieces of ultrathin parylene (0.4mm x 0.9mm). After the cells developed into a confluent monolayer, the implants were surgically placed into the subretinal (SR) space of postnatal day (P) 28 RCS rat pups (n=10). Histological assessments were performed using H&E and immunostaining techniques. Visual function was tested using an optokinetic (OKN) head-tracking apparatus and by electrophysiological mapping of the superior colliculus (SC).

Results : iPSC-RPE cultured on ultrathin parylene substrate appeared as a confluent monolayer and expressed RPE 65 and ZO1. In vitro characterization data demonstrated that this iPSC-RPE shows good similarity to fetal RPE (compared to hESC-RPE). Based on histological evaluation at 1 month and 2 month post-implantation, the iPSC-RPE survived and maintained its monolayer structure in all implanted rats. The transplanted RPE expressed RPE 65, iRBP and performed phagocytosis of shed photoreceptor outer segments. Visual functional improvement in immunodeficient dystrophic RCS rats following iPSC-RPE transplantation was demonstrated by SC luminance threshold mapping data (iPSC-RPE implanted rats -3.1±1.7 log cd/m² vs non-transplanted rats -0.6±0.3 log cd/m²). Based on OKN visual behavioral test, good preservation of visual activity was observed in the iPSC-RPE implanted eyes whereas no such responses were observed in the non-implanted eyes.

Conclusions : iPSC-RPE cells implanted as a polarized monolayer into the SR space of immunodeficient RCS rats can survive as a monolayer and contribute to visual functional benefits. The results support the use of such implants for therapeutic approaches aimed at slowing the progression of outer retinal degeneration diseases.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.