Engineering Transplantation-suitable Retinal Pigment Epithelium Tissue Derived from Human Embryonic Stem Cells

Comparison of human amniotic membrane decellularisation approaches for hESC-derived RPE cells culture

Objective

Recent clinical studies have shown that the transplantation of functional retinal pigment epithelium (RPE) cells can prevent the onset of RPE degeneration in age-related macular degeneration. This study aimed to investigate the potential of human amniotic membrane (hAM) as a viable scaffold for the growth and proliferation of pluripotent-derived RPE cells.

Methods and analysis

Three enzymatic hAM de-epithelialisation methods (thermolysin, trypsin-EDTA and dispase II) were assessed by histological analysis and optical coherence tomography (OCT). We generated RPE cells from a human embryonic stem cell (hESC) line subjected to spontaneous differentiation in feeder-free conditions. The hESC-derived RPE cells were seeded over denuded hAM at a density of 2.0×10⁵ cells/cm² and maintained in culture for up to 4 weeks. Immnofluorescence was carried out to evaluate the development of a confluent monolayer of RPE cells on the top of the hAM. Conditioned medium was collected to measure pigment epithelium-derived factor (PEDF) concentration by ELISA.

Results

Laminin α5 and collagen IV staining confirmed the efficiency of the de-epithelialisation process. In particular, thermolysin showed good retention of tissue integrity on OCT images and greater preservation of the hAM basement membrane. The hESC-derived RPE cells formed patches of pigmented cells interspersed along the denuded hAM, but failed to form a regular sheet of RPE cells. These cells expressed typical RPE markers, such as PMEL17 and RPE65, but they secreted low levels of PEDF.

Conclusion

The biological variability of the hAM could influence the adhesion and the expansion of hESC-derived RPE cells. Further studies are required to verify whether a non-confluent monolayer might represent a limit to transplantation.

Stem cell transplantation as a progressing treatment for retinitis pigmentosa

Retinal degenerative diseases such as retinitis pigmentosa (RP) are of the major causes of vision loss in developed countries. Despite the unclear pathophysiology, treatment methods have been investigated vastly in the past decades. This review article mainly discusses the advances in application of stem cell and progenitor transplantation for retinitis pigmentosa. Stem cell sources such as mesenchymal stem cells, embryonic stem cells, induced pluripotent stem cells, neural stem cells, retinal progenitor cells, and olfactory ensheathing cells are discussed separately in addition to a brief description of two approaches for treatment of early-stage RP, including gene therapy and nutritional therapy.

Cell-Based Therapies for Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness worldwide. The pathogenesis of AMD involves dysfunction and loss of the retinal pigment epithelium (RPE), a monolayer of cells that provide nourishment and functional support for the overlying photoreceptors. RPE cells in mammals are not known to divide, renew or regenerate in vivo, and in advanced AMD, RPE loss leads to degeneration of the photoreceptors and impairment of vision. One possible therapeutic approach would be to support and replace the failing RPE cells of affected patients, and indeed moderate success of surgical procedures in which relatively healthy autologous RPE from the peripheral retina of the same eye was transplanted under the retina in the macular area suggested that RPE replacement could be a means to attenuate photoreceptor cell loss. This prompted exploration of the possibility to use pluripotent stem cells (PSCs) as a potential source for "healthy and young" RPE cells for such cell-based therapy of AMD. Various approaches ranging from the use of allogeneic embryonic stem cells to autologous induced pluripotent stem cells are now being tested within early clinical trials. Such PSC-derived RPE cells are either injected into the subretinal space as a suspension, or transplanted as a monolayer patch upon scaffold support. Although most of these approaches are at early clinical stages, safety of the RPE product has been demonstrated by several of these studies. Here, we review the concept of cell-based therapy of AMD and provide an update on current progress in the field of RPE transplantation.

Human pluripotent stem cells: A toolbox to understand and treat retinal degeneration

Age-related Macular Degeneration (AMD) and Retinitis Pigmentosa (RP) are retinal degenerative disorders that dramatically damage the retina. As there is no therapeutic option for the majority of patients, vision is progressively and irremediably lost. Owing to their unlimited renewal and potency to give rise to any cell type of the human adult body, human pluripotent stem cells (hPSCs) have been extensively studied in recent years to develop more physiologically relevant in vitro cellular models. Such models open new perspectives to investigate the pathological molecular mechanisms of AMD and RP but also in drug screening. Moreover, proof-of-concept of hPSC-derived retinal cell therapy in animal models have led to first clinical trials. This review outlines the recent advances in the use of hPSCs in pathological modeling of retinal degeneration and their use in regenerative medicine. We also address the associated limitations and challenges that need to be overcome when using hPSCs.