BACKGROUND: Macular holes are breaks in the retinal tissue at the center of the macula, affecting central vision. The standard treatment involves vitrectomy with membrane peeling and gas tamponade. However, for larger or chronic holes, alternative techniques like autologous retinal graft have emerged. This meta-analysis evaluates the efficacy and safety of retinal transplantation in managing large macular holes.
METHODS: We conducted a systematic review and meta-analysis following PRISMA guidelines. The study was prospectively registered in PROSPERO (CRD42024504801). We searched PubMed, Web of Science, Cochrane, and Embase databases for observational studies including individuals with large macular holes with or without retinal detachments and retinal transplantation as the main therapy. We used a random-effects model to compute the mean difference with 95% confidence intervals and performed statistical analysis using R software.
RESULTS: We conducted a comprehensive analysis of 19 studies involving 322 patients diagnosed with various types of macular holes (MHs). These included cohorts with refractory MH, high myopia associated with MH, primary MH, and MH with retinal detachment (RD). The findings were promising, revealing an overall closure rate of 94% of cases (95% CI 88-98, I2 = 20%). Moreover, there was a significant improvement in postoperative visual acuity across all subgroups, averaging 0.45 (95% CI 0.33-0.58 ; I2 = 72%; p < 0.01) overall. However, complications occurred with an overall incidence rate of 15% (95% CI 7-25; I2 = 59%).
CONCLUSIONS: ART for large MH shows promising results, including significant improvements in visual acuity and a high rate of MH closure with low complication risks overall and for subgroups.

Retinal pigment epithelium (RPE) replacement therapy is evolving as a feasible approach to treat age-related macular degeneration (AMD). In many preclinical studies, RPE cells are transplanted as a cell suspension into immunosuppressed animal eyes and transplant effects have been monitored only short-term. We investigated the long-term effects of human Induced pluripotent stem-cell-derived RPE (iPSC-RPE) transplants in an immunodeficient Royal College of Surgeons (RCS) rat model, in which RPE dysfunction led to photoreceptor degeneration. iPSC-RPE cultured as a polarized monolayer on a nanoengineered ultrathin parylene C scaffold was transplanted into the subretinal space of 28-day-old immunodeficient RCS rat pups and evaluated after 1, 4, and 11 months. Assessment at early time points showed good iPSC-RPE survival. The transplants remained as a monolayer, expressed RPE-specific markers, performed phagocytic function, and contributed to vision preservation. At 11-months post-implantation, RPE survival was observed in only 50% of the eyes that were concomitant with vision preservation. Loss of RPE monolayer characteristics at the 11-month time point was associated with peri-membrane fibrosis, immune reaction through the activation of macrophages (CD 68 expression), and the transition of cell fate (expression of mesenchymal markers). The overall study outcome supports the therapeutic potential of RPE grafts despite the loss of some transplant benefits during long-term observations.

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.

Retinal progenitor cells (RPCs) have a potential role in the treatment of retinal degenerative diseases. This study is to investigate in vitro and in vivo characteristics and retinal transplantation of RPCs cultured in media with or without serum. Progenitor cells obtained from the neural retina of human eyes at 6-16 weeks gestation were cultured in serum-free media (SF-hRPCs) or in media containing 10% fetal bovine serum (FBS) (S-hRPCs). The differences were characterized between the cells cultured in vitro and transplanted (retinal transplantation) into Royal College of Surgeons (RCS) rats. The functional status of the rats was examined by flash-electroretinogram recordings. The result was that S-hRPCs exhibited higher proliferative dynamics in vitro. On the basis of outer nuclear layer thickness and flash-electroretinograms, S-hRPCs were more efficacious in slowing the progression of retinal degeneration following transplantation compared with SF-hRPCs. Moreover, retinal mesenchymal-like stem cells were isolated and identified from the S-hRPCs cultures. Our study demonstrated the potential of retinal MSCs for the treatment of retinal degeneration.

Retinal multielectrode array (MEA) recording allows us to examine the action potentials of retinal ganglion cells and field potentials of photoreceptors and bipolar cells. In addition to studying the retinal circuitry, it has become one of the standard examination tools for the characterization of stem cell-derived retinal transplantation in degenerated retinas. Besides the detection of responses to simple light stimulation, it is also necessary to consider the spatial correlation of the graft and the electrodes, in order to unbiasedly reveal the locally reconstructed retinal circuitry after transplantation. Here, we introduce our newly developed protocol of MEA recording and analysis that may serve as a standard for evaluating transplanted retinas.

Cell replacement therapies are often enhanced by utilizing polymer scaffolds to improve retention or direct cell orientation and migration. Obstacles to refinement of such polymer scaffolds often include challenges in controlling the microstructure of biocompatible molecules in three dimensions at cellular scales. Two-photon polymerization of acrylated poly(caprolactone) (PCL) could offer a means of achieving precise microstructural control of a material in a biocompatible platform. In this work, we studied the effect of various formulation and two-photon polymerization parameters on minimum laser power needed to achieve polymerization, resolution, and fidelity to a target 3D model designed to be used for retinal cell replacement. Overall, we found that increasing the concentration of crosslink-able groups decreased polymerization threshold and the size of resolvable features while increasing fidelity of the scaffold to the 3D model. In general, this improvement was achieved by increasing the number of acrylate groups per prepolymer molecule, increasing the acrylated PCL concentration, or decreasing its molecular weight. Resulting two-photon polymerized PCL scaffolds successfully supported human iPSC derived retinal progenitor cells in vitro. Sub-retinal implantation of cell free scaffolds in a porcine model of retinitis pigmentosa did not cause inflammation, infection or local or systemic toxicity after one month. In addition, comprehensive ISO 10993 testing of photopolymerized scaffolds revealed a favorable biocompatibility profile. These results represent an important step towards understanding how two-photon polymerization can be applied to a wide range of biologically compatible chemistries for various biomedical applications. STATEMENT OF SIGNIFICANCE: Inherited retinal degenerative blindness results from the death of light sensing photoreceptor cells. To restore high-acuity vision a photoreceptor cell replacement strategy will likely be necessary. Unfortunately, single cell injection typically results in poor cell survival and integration post-transplantation. Polymeric biomaterial cell delivery scaffolds can be used to promote donor cell viability, control cellular polarity and increase packing density. A challenge faced in this endeavor has been developing methods suitable for generating scaffolds that can be used to deliver stem cell derived photoreceptors in an ordered columnar orientation (i.e., similar to that of the native retina). In this study we combined the biomaterial poly(caprolactone) with two-photon lithography to generate a biocompatible, clinically relevant scaffold suitable for retina cell delivery.

OBJECTIVE: To create new immunodeficient Royal College of Surgeons (RCS) rats by introducing the defective MerTK gene into athymic nude rats.
METHODS: Female homozygous RCS (RCS-p+/RCS-p+) and male nude rats (Hsd:RH-Foxn1mu, mutation in the foxn1 gene; no T cells) were crossed to produce heterozygous F1 progeny. Double homozygous F2 progeny obtained by crossing the F1 heterozygotes was identified phenotypically (hair loss) and genotypically (RCS-p+ gene determined by PCR). Retinal degenerative status was confirmed by optical coherence tomography (OCT) imaging, electroretinography (ERG), optokinetic (OKN) testing, superior colliculus (SC) electrophysiology, and by histology. The effect of xenografts was assessed by transplantation of human embryonic stem cell-derived retinal pigment epithelium (hESC-RPE) and human-induced pluripotent stem cell-derived RPE (iPS-RPE) into the eye. Morphological analysis was conducted based on hematoxylin and eosin (H&E) and immunostaining. Age-matched pigmented athymic nude rats were used as control.
RESULTS: Approximately 6% of the F2 pups (11/172) were homozygous for RCS-p+ gene and Foxn1mu gene. Homozygous males crossed with heterozygous females resulted in 50% homozygous progeny for experimentation. OCT imaging demonstrated significant loss of retinal thickness in homozygous rats. H&E staining showed photoreceptor thickness reduced to 1-3 layers at 12 weeks of age. Progressive loss of visual function was evidenced by OKN testing, ERG, and SC electrophysiology. Transplantation experiments demonstrated survival of human-derived cells and absence of apparent immune rejection.
CONCLUSIONS: This new rat animal model developed by crossing RCS rats and athymic nude rats is suitable for conducting retinal transplantation experiments involving xenografts.

Loss of photoreceptors and other retinal cells is a common endpoint in retinal degenerate (RD) diseases that cause blindness. Retinal transplantation is a potential therapy to replace damaged retinal cells and improve vision. In this study, we examined the development of human fetal retinal sheets with or without their retinal pigment epithelium (RPE) transplanted to immunodeficient retinal degenerate rho S334ter-3 rats. Sheets were dissected from fetal human eyes (11-15.7 weeks gestation) and then transplanted to the subretinal space of 24-31 d old RD nude rats. Every month post surgery, eyes were imaged by high-resolution spectral-domain optical coherence tomography (SD-OCT). SD-OCT showed that transplants were placed into the subretinal space and developed laminated areas or rosettes, with clear development of plexiform layers first seen in OCT at 3 months post surgery. Several months later, as could be expected by the much slower development of human cells compared to rat cells, transplant photoreceptors developed inner and later outer segments. Retinal sections were analyzed by immunohistochemistry for human and retinal markers and confirmed the formation of several retinal subtypes within the retinal layers. Transplant cells extended processes and a lot of the cells could also be seen migrating into the host retina. At 5.8-8.6 months post surgery, selected rats were exposed to light flashes and recorded for visual responses in superior colliculus, (visual center in midbrain). Four of seven rats with transplants showed responses to flashes of light in a limited area of superior colliculus. No response with the same dim light intensity was found in age-matched RD controls (non-surgery or sham surgery). In summary, our data showed that human fetal retinal sheets transplanted to the severely disturbed subretinal space of RD nude rats develop mature photoreceptors and other retinal cells, integrate with the host and induce vision improvement.

N-methyl-N-nitrosourea (MNU) has been reported to induce photoreceptor-specific degeneration with minimal inner retinal impact in small animals in vivo. Pending its use within a retinal transplantation paradigm, we here explore the effects of MNU on outer and inner retinal neurons and glia in an in vitro large animal model of retinal degeneration. The previously described degenerative culture explant model of adult porcine retina was used and compared with explants receiving 10 or 100 μg/ml MNU (MNU10 and MNU100) supplementation. All explants were kept for 5 days in vitro, and examined for morphology as well as for glial and neuronal immunohistochemical markers. Rhodopsin-labeled photoreceptors were present in all explants. The number of cone photoreceptors (transducin), rod bipolar cells (PKC) and horizontal cells (calbindin) was significantly lower in MNU treated explants (p < 0.001). Gliosis was attenuated in MNU10 treated explants, with expression of vimentin, glial fibrillary protein (GFAP), glutamine synthetase (GS), and bFGF comparable to in vivo controls. In corresponding MNU100 counterparts, the expression of Müller cell proteins was almost extinguished. We here show that MNU causes degeneration of outer and inner retinal neurons and glia in the adult porcine retina in vitro. MNU10 explants display attenuation of gliosis, despite decreased neuronal survival compared with untreated controls. Our results have impact on the use of MNU as a large animal photoreceptor degeneration model, on tissue engineering related to retinal transplantation, and on our understanding of gliosis related neuronal degenerative cell death.

OBJECTIVE: We followed cone and rod development in the pig and we correlated development with the potential for cone and rod precursor integration and differentiation following subretinal transplantation.
METHODS: Rod and cone precursors were identified during development by their position in the outer retina and by immunostaining for markers of differentiation. Embryonic retinal cells from green fluorescent protein (GFP)(+) transgenic pigs at different developmental stages were transplanted into adult retinas and integration and differentiation was followed and quantified by immunostaining for markers of cone and rod differentiation.
RESULTS: Pig cones and rods are spatially segregated, allowing us to follow rod and cone development in situ. Gestation in the pig is 114 days. By embryonic day (E) 50, postmitotic cone progenitors had formed the outer two rows of the retina. These cone progenitors are marked by expression of Islet1 (ISL1) and Recoverin (RCVRN) (at this embryonic stage, RCVRN exclusively marks these cone precursors). By contrast, postmitotic neural retina leucine zipper (NRL)(+) rod precursors, located interior to the cone precursors, did not appear until E65. At E50, before NRL(+) rod precursors are evident, transplanted cells gave rise almost exclusively to cones. At, E57, transplanted cells gave rise to equal numbers of rods and cones, but by E65, transplanted cells gave rise almost exclusively to rods. Transplantation of cells at E85 or E105, as precursors initiate opsin expression, led to few integrated cells.
CONCLUSIONS: Consistent with their sequential appearances in embryonic retina, these results demonstrate sequential and surprisingly narrow developmental windows for integration/differentiation of cone and rod precursors following transplantation.