A Genetic modification that reduces ON-bipolar cells in hESC-derived retinas enhances functional integration after transplantation

Abstract

Summary Pluripotent stem cell (PSC)-derived retinal sheet transplanted in vivo can form structured photoreceptor layers, contact with host bipolar cells, and transmit light signals to host retinas. However, a major concern is the presence of graft bipolar cells that may impede host-graft interaction. In this study, we used human ESC-retinas with the deletion of Islet-1 ( ISL1 ) gene to achieve the reduced graft ON-bipolar cells after xenotransplantation into end-stage retinal degeneration model rats. Compared with wild-type graft, ISL1 −/− hESC-retinas showed better host-graft contact, with indication of host-graft synapse formation and significant restoration of light responsiveness in host ganglion cells. We further analyzed to find out that improved functional integration of ISL1 −/− hESC-retinas seemed attributed by a better host-graft contact and a better preservation of host inner retina. ISL1 −/− hESC-retinas are promising for the efficient reconstruction of a degenerated retinal network in future clinical application.

Transplanted human cones incorporate into the retina and function in a murine cone degeneration model

“…Single-cell suspension studies have often been criticized for the lack of structure of the resulting graft ( 38 ). Although, in theory, retinal sheet transplantation could provide preestablished structure, current studies have described extensive rosette formation in the graft and self-synapsing to graft second-order neurons ( 5 , 7 – 9 , 39 , 40 ), although a recent study provides evidence of improved synapse formation when organoid bipolar cell numbers are reduced ( 10 ). Sheet transplantations are surgically more challenging, particularly in the context of degenerative retinas, in which rupture of the tissue remains a potential risk.…”

“…Several recent studies have utilized human stem cell–derived retinal organoids as a source of either photoreceptors or retinal sheets for transplantation, particularly in end-stage degeneration models. While some improvements in vision have been reported through the use of retinal sheets ( 5 – 9 ), these grafted sheets were largely disorganized, with extensive rosette formation and the complication of donor photoreceptors mostly synapsing to donor second-order neurons rather than host cells, although synaptic connectivity has recently been improved through the reduction of bipolar cells within the organoid transplant ( 10 ). For human cone cell suspension transplantations, although functionality has recently been reported by 2 different research groups, grafts appeared disordered, with little evidence of cell polarization ( 11 ) (i.e., inner and outer segments oriented toward the retinal pigment epithelium [RPE]; axons extended toward second-order neurons), or showed some polarization but poor general transplant cell survival ( 12 , 13 ).…”

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

“…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.…”

“…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, 43-46 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.…”

“…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. Few migratory cells were reported to express GFAP 37, 58 , progenitor markers (e.g., PAX6, Nestin) 40, 58 or neuronal markers (e.g., MAP2, β-tublin3) 60 , but not mature photoreceptor markers 29, 39, 41, 43 - 46, 58, 61 . Gasparini et al ., in a study of the influence of the murine retinal environment on the morphological maturation of transplanted donor human cone photoreceptors, also observed migratory cells but did not molecularly characterize these cells 62 .…”