https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(12)60028-2.pdf

Embryonic stem cell trials for macular degeneration: a preliminary report

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736%2814%2961376-3.pdf

Human embryonic stem cell-derived retinal pigment epithelium in patients with age-related macular degeneration and Stargardt's macular dystrophy: follow-up of two open-label phase 1/2 studies

Age-related macular degeneration: etiology, pathogenesis, and therapeutic strategies.

Age-related macular degeneration (AMD) causes severe visual impairment due in part to age-dependent impairment of retinal pigment epithelium (RPE). It has been suggested that autologous human induced pluripotent stem cells (hiPSCs) may represent a useful cell source for the generation of graft RPE. We generated hiPSC-derived RPE (hiPSC-RPE) cell sheets optimized to meet clinical use requirements, including quality, quantity, consistency, and safety. These cell sheets are generated as a monolayer of cells without any artificial scaffolds, express typical RPE markers, form tight junctions that exhibit polarized secretion of growth factors, and show phagocytotic ability and gene-expression patterns similar to those of native RPE. Additionally, upon transplantation, autologous nonhuman primate iPSC-RPE cell sheets showed no immune rejection or tumor formation. These results suggest that autologous hiPSC-RPE cell sheets may serve as a useful form of graft for use in tissue replacement therapy for AMD.

https://www.cell.com/stem-cell-reports/pdf/S2213-6711(13)00175-6.pdf

Characterization of Human Induced Pluripotent Stem Cell-Derived Retinal Pigment Epithelium Cell Sheets Aiming for Clinical Application

This study was designed to investigate the in vitro degradation of thin poly(DL-lactic-co-glycolic acid) (PLGA) films for applications in retinal pigment epithelium transplantation and guided tissue regeneration. PLGA films of copolymer ratios of 75:25 and 50:50 were manufactured with thickness levels of 10 microm (thin) and 100 microm (thick). Degradation of the films occurred during sample processing, and thin films with a higher surface area to volume ratio degraded faster. Sample weight loss, molecular weight loss, dimensional, and morphological changes were analyzed over a 10-week period of degradation in 0.2 M of phosphate-buffered saline (PBS), pH 7.4, at 37 degrees C. All PLGA films degraded by heterogeneous bulk degradation. Sample weights remained relatively constant for the first several weeks and then decreased dramatically. The molecular weights of PLGA films decreased immediately upon placement in PBS and continued to decrease throughout the time course. PLGA 50:50 films degraded faster than 75:25 films due to their higher content of hydrophilic glycolic units. The results also demonstrated that thick films degrade faster than corresponding thin films with the same composition. This was attributed to the greater extent of the autocatalytic effect, which further was confirmed by heterogeneous gel permeation chromatograms. These studies suggest that the degradation rate of thin films can be engineered by varying film thicknesses.

In vitro degradation of thin poly(DL-lactic-co-glycolic acid) films.

Background: Age-related macular degeneration (ARMD) is caused by abnormal retinal pigment epithelium (RPE) and may be complicated by choroidal neovascularization. The object of treatment would be to replace the diseased RPE with normal human RPE. • Method: Five patients with ARMD (preoperative visual acuity 0.08–0.2) underwent removal of subretinal fibrovascular membranes using pars plana vitrectomy techniques. Human fetal RPE (15–17 weeks gestational age) was cultured and transplanted as a monolayer patch into the subretinal space. Transplants were followed by funduscopy and fluorescein angiography. Macular function was assessed using scanning laser ophthalmoscopic (SLO) microperimetry. • Results: Three RPE transplants were placed in the fovea; two were placed parafoveally. All transplants have survived for 3 months. They have grown and increased in size covering part of the epithelial defect caused by removal of the fibrovascular membrane. SLO microperimetry indicated that visual function was present in four of the transplants at 1 month but in only two at 3 months after surgery. Function over the transplants, especially those in the fovea, was compromised by cystoidlike macular edema. • Conclusions: Human fetal RPE transplants survive well in the macula for as long as 3 months. They are capable of growing to cover epithelial defects caused by removal of subretinal neovascular membranes. The causes for development of macular edema in transplants directly in the fovea warrant further evaluation.

Transplantation of fetal retinal pigment epithelium in age-related macular degeneration with subfoveal neovascularization.

• A study was carried out to investigate whether human RPE allografts are tolerated or rejected in the subretinal space and to determine the feasibility of RPE transplantation in subjects with age-related macular degeneration (AMD). • Methods: Patches of human fetal RPE (13–20 weeks of gestational age) were transplanted into the subretinal space of five patients after surgical removal of subfoveal fibrovascular membranes, and to four subjects with dry geographic atrophy. Suspensions of RPE cells were transplanted to four other patients with nonexudative AMD. Results were evaluated with clinical ophthalmological examination, SLO microperimetry and fluorescein angiography over 8–20 months. • Results: In disciform lesions, RPE transplants developed macular edema and fluorescein leakage concomitant with gradual reduction of visual acuity, implying host-graft rejection, over 1–6 months. In geographic atrophy, three of four transplants showed little change in shape and size after 12 months (one transplant was slowly rejected). In non-exudative AMD, RPE suspension transplants showed no evidence of rejection and were associated with the disappearance of drusen; visual acuity remained stable and SLO microperimetry confirmed retinal function over the transplanted area. • Conclusion: Human RPE allografts are not invariably rejected in the subretinal space without immunosuppression. The rejection rate is lower in nonexudative than in neovascular AMD. An intact blood-retinal barrier is likely to protect against rejection. It is technically feasible to transplant human RPE into the submacular space without adversely affecting visual function in nonexudative AMD over relatively long periods of time

Transplantation of RPE in age-related macular degeneration: Observations in disciform lesions and dry RPE atrophy

Purpose To transplant human fetal retinal pigment epithelium (RPE) into the subretinal space of rabbits and monkeys as an organized monolayer without artificial support. Methods The method involves dissecting small patches of cultured RPE monolayers in sheets (1 to 5 mm2), sucking them into a glass pipette and injecting them into the subretinal space after producing a bleb detachment of the neural retina. Results These patches unfold and survive as a quasi-monolayer under the reattached neural retina intimately associated with the host photoreceptors and phagocytizing host outer segment material. Graft rejection is observed in most rabbits at 1 month but not in monkeys at 3 months after transplantation. Conclusions Monolayer patches of cultured human fetal RPE can be transplanted to the subretinal space, where they survive in contiguity with healthy host outer segments. In primates, but not in rabbits, host-graft rejection does not occur for at least 2 to 3 months.

Patch transplants of human fetal retinal pigment epithelium in rabbit and monkey retina.

• Background: RPE transplantation offers the possibility of treating certain forms of retinal degeneration. Understanding how to optimize the surgical technique for performing RPE transplantation, especially in primates, is therefore of considerable interest. • Methods: Fifteen patch RPE transplants were performed in six monkeys. The transplant sites were examined at follow-up by ophthalmoscopy, biomicroscopy, fluorescein angiography and histology. Foveal and peripheral retinal transplants were compared. • Results: Human fetal RPE xenografts can survive without rejection for at least 6 months after transplantation in monkey retina. Such grafts form a basal lamina and make intimate contacts with the outer segments of the host. Both rods and cones retain a normal appearance when in contact with unrejected transplants. Rejection occurred in only 30% (3/10) of the peripheral but in 60% (3/5) of the foveal transplants. • Conclusions: Cultured human fetal RPE patch transplants can survive and maintain local photoreceptor integrity for relatively long periods of time in monkey subretinal space without immunosuppression. Rejection, when it occurs, is more frequent near the fovea.

Tolerance of human fetal retinal pigment epithelium xenografts in monkey retina

Human retinal pigmented epithelium (RPE) can be cultured by removing small patches of this layer from the choroid of the fetal eye. Such RPE patches give rise to healthy, epithelioid monolayers in vitro within 1–2 weeks without contamination from retinal or choroidal cells. The viability and proliferative capacity of these cultures is independent of the initial polarity of the patch. These RPE monolayers develop apical/basal polarity and a basal lamina and rest on a field of collagen fibers; they are capable of phagocytizing outer segments. A patch can be lifted off a confluent monolayer and transferred to another culture dish without risking the viability of either the old or the new culture. This provides a means of transplanting an organized, polarized patch of human RPE from one place to another.

Y Sheng

Papers

Transplantation of fetal retinal pigment epithelium in age-related macular degeneration with subfoveal neovascularization.

Transplantation of RPE in age-related macular degeneration: Observations in disciform lesions and dry RPE atrophy

Patch transplants of human fetal retinal pigment epithelium in rabbit and monkey retina.

Tolerance of human fetal retinal pigment epithelium xenografts in monkey retina

Patch culturing and transfer of human fetal retinal epithelium.