Evaluation of genome edited Islet-1^-/- retinal organoid sheets after transplantation in non-human primate models of retinal macular degeneration

Abstract

Purpose : We previously reported that human Islet-1^-/- retinal organoid (RO) sheets developed reduced number of ON bipolar cells thereby enhancing the host-graft synapse formation and increased light responses in host retinal ganglion cells (RGCs) compared to the wild type (WT) RO sheets in the end-stage retinal degeneration model rats. In this study, we transplanted human Wild type and Islet-1^-/- RO sheets into monkey eyes with focal para- and peri-foveal degeneration model and compared graft integration between WT and Islet-1^-/- grafts.

Methods : We generated RO sheets from WT and Islet-1^-/- Crx::Venus reporter human embryonic stem cell lines (KhES-1). We transplanted six RO sheets of WT or Islet-1^-/- RO in the eye of 2 monkeys with localized laser-induced retinal degeneration models at para- and peri-foveal region. After 1-year follow-up, the eyes were sampled for histology and the ratio of CRX::Venus (GFP labeled) area in the total graft area (STEM121 labeled) was compared between WT and Islet-1^-/-. We also compared the host-graft contact score between graft photoreceptors and host bipolar cells (good: direct contact, fair: no contact but synapse formation, poor: no contact) Host-graft synapses were also studied by immunohistochemistry (IHC) with Islet-1^-/- grafts.

Results : WT and Islet-1^-/- RO sheets survived and matured after 1 year of transplantation. Rod bipolar cells were absent in the Islet-1^-/- RO grafts. The area ratio of CRX::Venus in Islet-1^-/- grafts were higher than that in WT grafts. (61±14% vs 41±9%, p=2.427e-05) Photoreceptor cells in Islet-1^-/- grafts had better contact with host bipolar cells compared to WT. (WT: good 62.5%, fair 4.2%, poor: 33.3% ; Islet-1^-/-: good 91.7%, fair 4.2%, poor 4.2% ; p =0.023, n=24 rosettes) We observed synaptic markers between graft photoreceptors and host diffuse bipolar 1 cells (SCGN) and host rod bipolar cells(PKCα) with Islet-1^-/- RO sheets.

Conclusions : Genome edited Islet-1^-/- RO sheets may generate good graft-host synapse formation in non-human primate models of retinal degeneration.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.