Protective Effects of Human iPS-Derived Retinal Pigment Epithelium Cell Transplantation in the Retinal Dystrophic Rat

Abstract

Transformation of somatic cells with a set of embryonic transcription factors produces cells with the pluripotent properties of embryonic stem cells (ESCs). These induced pluripotent stem (iPS) cells have the potential to differentiate into any cell type, making them a potential source from which to produce cells as a therapeutic platform for the treatment of a wide range of diseases. In many forms of human retinal disease, including age-related macular degeneration (AMD), the underlying pathogenesis resides within the support cells of the retina, the retinal pigment epithelium (RPE). As a monolayer of cells critical to photoreceptor function and survival, the RPE is an ideally accessible target for cellular therapy. Here we report the differentiation of human iPS cells into RPE. We found that differentiated iPS-RPE cells were morphologically similar to, and expressed numerous markers of developing and mature RPE cells. iPS-RPE are capable of phagocytosing photoreceptor material, in vitro and in vivo following transplantation into the Royal College of Surgeons (RCS) dystrophic rat. Our results demonstrate that iPS cells can be differentiated into functional iPS-RPE and that transplantation of these cells can facilitate the short-term maintenance of photoreceptors through phagocytosis of photoreceptor outer segments. Long-term visual function is maintained in this model of retinal disease even though the xenografted cells are eventually lost, suggesting a secondary protective host cellular response. These findings have identified an alternative source of replacement tissue for use in human retinal cellular therapies, and provide a new in vitro cellular model system in which to study RPE diseases affecting human patients.

Retinal Pigmented Epithelial Cells Obtained from Human Induced Pluripotent Stem Cells Possess Functional Visual Cycle Enzymes in Vitro and in Vivo

“…Expression of Visual Cycle Molecules in RPE Cells-Differentiation of RPE cells from ES and iPS cells has been reported (8,9), and some RPE functions have been characterized in these cells. These include the expression of RPE-specific molecules such as BEST1, MERTK, RPE65, and CRALBP along with the capability to carry out phagocytosis, form adherence junctions, and produce cytokines (10,11).…”

“…Several research groups have reported that human ES and iPS cells can be differentiated into RPE cells which display some degree of RPE functionality, including phagocytosis and growth factor secretion (8,9). However, the visual (retinoid) cycle in hiPS-derived RPE (hiPS-RPE) cells has not been rigorously examined.…”

Stem Cells for Retinal Replacement Therapy

“…Although the process for deriving pure populations of retinal precursors from iPSCs is less efficient than for ESCs, culture protocols to differentiate iPSC-RSCs into photoreceptor cell precursors are sufficiently developed so that such progeny integrate into mouse retina and differentiate into both rod and cone photoreceptor cells [71]. Transplantation of iPSCs differentiated into functional iPS-RPE into the RCS rat retina resulted in the maintenance of longterm visual function, even after the xenografted cells were eventually lost to immune rejection, raising the possibility that a secondary protective host cellular response rescued photoreceptor cells [73]. iPSC are a promising source for retinal replacement therapy, although with significant remaining challenges to their clinical use.…”

Induced Pluripotent Stem Cell Therapies for Degenerative Disease of the Outer Retina: Disease Modeling and Cell Replacement

“…Production of RPE cells from ESC and iPSC has been established by a number of different laboratories that have developed protocols for generation of homogeneous polarized RPE monolayer cultures. 12,45,46,47 iPSC-derived RPE cells can be isolated, expanded, differentiated, reseeded, and monitored both for morphology and functionality. 48 Also highly significant has been the discovery that iPSC/ ESC are able to self-assemble into three-dimensional (3D) optic cup structures, which then form stratified neural retinal tissues.…”