Abstract
Purpose :
Localized inflammation response and immune rejection of transplanted RPE cells in human hasn’t been well understood. In this study, we aim to observe the long-term effect of xenotransplant of human RPE monolayers in subretinal space of naïve non-human primates without immune suppression.
Methods :
iPSC re-programmed from human skin fibroblast cells (HDFa and asF5) were differentiated into RPE cells. Cultured human RPE monolayers on polyethylene terephthalate (PET) transwells were trephined with a 1x2 mm bullet-shaped implant and transplanted into subretinal space of 10 eyes of 8 cynomolgus monkeys without systemic immunosuppression. Color fundus, fundus autofluorescence (FAF), fundus angiography (FA), optical coherence tomography (OCT), and full-field electroretinography (ffERG) was conducted monthly for up to 1 year. Histology was used to assess for graft survival and engraftment at different time points.
Results :
At 1 month, in all 10 eyes with skin iPSC-RPE xenografts (HDFa, n=5, and asF5, n=5), the outer nuclear layer, external limiting membrane, and ellipsoid zone were preserved by OCT, demonstrating tolerance until 1 month without immunosuppression. During the long-term observation, all grafts showed mild to severe localized inflammation and immune rejection signs from 2 to 6 months, including subretinal deposits, subretinal hyper-reflective materials, retinal scars, and choroidal edema. In addition, the xenografts showed gradual RPE pigmentation loss on the color fundus starting from 2 months. On FAF and FA images, the global retinal structure maintained normal except for localized changes at the graft’s site. Global retinal function assessed by ffERG demonstrated maintained amplitudes. On 8-month histology, the longest time point we have achieved so far, the pigmented RPE monolayers presented above the PET scaffold by H&E, followed by immunofluorescence staining of human cytoplasmic marker (SC121), which confirmed these cells were transplanted human cells.
Conclusions :
Human iPSC-RPE monolayers caused delayed localized inflammation and immune rejection under healthy monkeys’ retinas. Pigment RPE monolayers showed gradual pigmentation loss, but the xeno-transplanted cells could achieve long-term survival in the subretinal space. These findings can contribute to understanding the immune response of RPE cell therapy in clinical trials.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.