Co-grafts of Human Embryonic Stem Cell Derived Retina Organoids and Retinal Pigment Epithelium for Retinal Reconstruction in Immunodeficient Retinal Degenerate Royal College of Surgeons Rats

Abstract

End-stage age-related macular degeneration (AMD) and retinitis pigmentosa (RP) are two major retinal degenerative (RD) conditions that result in irreversible vision loss. Permanent eye damage can also occur in battlefields or due to accidents. This suggests there is an unmet need for developing effective strategies for treating permanent retinal damages. In previous studies, co-grafted sheets of fetal retina with its retinal pigment epithelium (RPE) have demonstrated vision improvement in rat retinal disease models and in patients, but this has not yet been attempted with stem-cell derived tissue. Here we demonstrate a cellular therapy for irreversible retinal eye injuries using a “total retina patch” consisting of retinal photoreceptor progenitor sheets and healthy RPE cells on an artificial Bruch’s membrane (BM). For this, retina organoids (ROs) (cultured in suspension) and polarized RPE sheets (cultured on an ultrathin parylene substrate) were made into a co-graft using bio-adhesives [gelatin, growth factor-reduced matrigel, and medium viscosity (MVG) alginate]. In vivo transplantation experiments were conducted in immunodeficient Royal College of Surgeons (RCS) rats at advanced stages of retinal degeneration. Structural reconstruction of the severely damaged retina was observed based on histological assessments and optical coherence tomography (OCT) imaging. Visual functional assessments were conducted by optokinetic behavioral testing and superior colliculus electrophysiology. Long-term survival of the co-graft in the rat subretinal space and improvement in visual function were observed. Immunohistochemistry showed that co-grafts grew, generated new photoreceptors and developed neuronal processes that were integrated into the host retina. This novel approach can be considered as a new therapy for complete replacement of a degenerated retina.

The Prospects for Retinal Organoids in Treatment of Retinal Diseases

“…Lesions of the visual cortex had no effect on OKT, suggesting that OKT was driven by subcortical and contralateral pathways 126. Several studies have shown improvements in optokinetic responses after RO sheet transplantation 16,19,45…”

“…Another very sensitive technique is electrophysiological recording from the SC16,19,45 in the midbrain, which plays a central role in integrating multiple sensory inputs to motor behaviors such as eye and head movements 129. In this test, a microelectrode is directly placed on the surface of SC; under full-field retinal stimulation at specific light intensities, visual thresholds, and visual responses (spike counts) of specific retinotopic areas of the SC were recorded.…”

Transretinal migration of astrocytes and brain/spinal cord-like cells arising from transplanted human retinal organoids

“…The origin, heterogeneity, spatial distribution, and proliferative capacity of migratory donor cells have not been characterized. Migratory cells can arise from human retinal organoids 29,41,[43][44][45][46] and human fetal retina 42,57 , suggesting that migratory behavior is not unique to donor cells obtained through pluripotent stem cell culture. Migratory donor cells were observed in mouse, rat, cat, and nonhuman primate retinas, and in normal and degenerative retinas 29, 37-41, 58, 59 , suggesting that this phenomenon is common across recipient species and independent of retinal health.…”

“…A substantial body of data in multiple animal models supports the regenerative potential of nonmigratory donor photoreceptor precursor-derived cells that mature in the recipient subretinal space, spurring experiments in large animals 21,[26][27][28][29][30] en route to clinical studies [31][32][33][34][35][36] . Aside from the nonmigratory cells, migratory donor cells in the inner retinal layers overlying the graft have been observed [37][38][39][40][41][42][43][44][45][46] , which do not appear to be essential for the therapeutic mechanism. These observations raised concerns regarding long-range migration of donor cells beyond the graft margins that may incite immune exposure and invasive tissue damage.…”

Retinal Organoids Long-Term Functional Characterization Using Two-Photon Fluorescence Lifetime and Hyperspectral Microscopy

“…Human embryonic stem cells (hESCs) or induced pluripotent stem cells (iPSCs) derived retinal organoids (RtOgs) are self-organized tissues that recapitulate in vivo retinal development (Nakano et al, 2012;Zhong et al, 2014;Wahlin et al, 2017;Fligor et al, 2018). RtOgs exhibit similar structures and cell types as in vivo retina, and are used for many applications, including drug screening (Llonch et al, 2018), disease modeling, developmental biological research (Bell et al, 2020), and transplantation therapies (Shirai et al, 2016;McLelland et al, 2018;Lin et al, 2020;Thomas et al, 2021).…”