Cell therapy with pluripotent stem cells differentiated to retinal pigment epithelium and photoreceptor cells in a rat model of Retinitis Pigmentosa

Abstract

 

Purpose

 

At present, stem cell-based therapy is one of the most promising treatments for Retinitis Pigmentosa (RP). We produced retinal pigment epithelium (RPE) and photoreceptor cells from hESC (human Embryonic Stem Cells) and hiPSC (human induced Pluripotent Stem Cells) and transplanted RPE only or RPE in combination with photoreceptors into the subretinal space of the experimental RP rat model RCS. This model bears a mutation in the protein MERTK. When MERTK is unfunctional a progressive RPE degeneration takes place, eventually driving RPE and photoreceptors to undergo apoptosis. Thus, we aim to study how effective is and which are the benefits of these cell therapy approaches in restoring visual function in RCS rats.

 

Methods

 

We characterized RPE and photoreceptor cells by studying expression of proliferative and lineage-specific markers. Once pure differentiated cultures were obtained, cell morphology and apicobasal polarity were assessed by electron microscopy. RPE only or RPE together with photoreceptor cells were transplanted into the subretinal space of RP rats. After determining graft survival, we studied the functionality and integration of such transplants in the rat retina by in vivo and post-mortem analyses.

 

Results

 

RPE cells derived from human stem cells survive into the subretinal space. Importantly, they are not only able to survive but also to integrate into the host RPE and establish tight junctions with neighbor rat cells. Human RPE continues expressing CRALBP and is functional for rhodopsin phagocytosis. Remarkably, the fact that human cells preserve essential RPE features has an effect in other retina layers. For instance, more photoreceptor nuclei are found in regions close to the transplanted area versus areas far from the graft. There are less apoptotic photoreceptor cells in regions neighboring the graft and glial stress is diminished as well. In terms of electroretinographic activity, transplanted areas respond better to light stimuli. Recently, we differentiated photoreceptor cells from human pluripotent stem cells. We are currently evaluating the effects of the co-transplantation of RPE and photoreceptors in our RP model.

 

Conclusions

 

We have successfully differentiated RPE and photoreceptor cells from human pluripotent stem cells and demonstrated that human RPE transplants slow down photoreceptor degeneration in RCS rats.