Single-cell transcriptomics reveals maturation of transplanted stem cell-derived retinal pigment epithelial cells toward native state.

Transplantation of stem cell-derived retinal pigment epithelial (RPE) cells is considered a viable therapeutic option for age-related macular degeneration (AMD). Several landmark Phase I/II clinical trials have demonstrated safety and tolerability of RPE transplants in AMD patients, albeit with limited efficacy. Currently, there is limited understanding of how the recipient retina regulates the survival, maturation, and fate specification of transplanted RPE cells. To address this, we transplanted stem cell-derived RPE into the subretinal space of immunocompetent rabbits for 1 mo and conducted single-cell RNA sequencing analyses on the explanted RPE monolayers, compared to their age-matched in vitro counterparts. We observed an unequivocal retention of RPE identity, and a trajectory-inferred survival of all in vitro RPE populations after transplantation. Furthermore, there was a unidirectional maturation toward the native adult human RPE state in all transplanted RPE, regardless of stem cell resource. Gene regulatory network analysis suggests that tripartite transcription factors (FOS, JUND, and MAFF) may be specifically activated in posttransplanted RPE cells, to regulate canonical RPE signature gene expression crucial for supporting host photoreceptor function, and to regulate prosurvival genes required for transplanted RPE's adaptation to the host subretinal microenvironment. These findings shed insights into the transcriptional landscape of RPE cells after subretinal transplantation, with important implications for cell-based therapy for AMD.

A novel model of persistent retinal neovascularization for the development of sustained anti-VEGF therapies.

Anti-vascular endothelial growth factor (VEGF) therapies lead to a major breakthrough in treatment of neovascular retinal diseases such as age-related macular degeneration or diabetic retinopathy. Current management of these conditions require regular and frequent intravitreal injections to prevent disease recurrence once the effect of the injected drug wears off. This has led to a pressing clinical need of developing sustained release formulations or therapies with longer duration. A major drawback in developing such therapies is that the currently available animal models show spontaneous regression of vascular leakage. They therefore not only fail to recapitulate retinal vascular disease in humans, but also prevent to discern if regression is due to prolonged therapeutic effect or simply reflects spontaneous healing. Here, we described the development of a novel rabbit model of persistent retinal neovascularization (PRNV). Retinal Müller glial are essential for maintaining the integrity of the blood-retinal barrier. Intravitreal injection of DL-alpha-aminoadipic acid (DL-AAA), a selective retinal glial (Müller) cell toxin, results in persistent vascular leakage for up to 48 weeks. We demonstrated that VEGF concentrations were significantly increased in vitreous suggesting VEGF plays a significant role in mediating the leakage observed. Intravitreal administration of anti-VEGF drugs (e.g. bevacizumab, ranibizumab and aflibercept) suppresses vascular leakage for 8-10 weeks, before recurrence of leakage to pre-treatment levels. All three anti-VEGF drugs are very effective in re-ducing angiographic leakage in PRNV model, and aflibercept demonstrated a longer duration of action compared with the others, reminiscent of what is observed with these drugs in human in the clinical setting. Therefore, this model provides a unique tool to evaluate novel anti-VEGF formulations and therapies with respect to their duration of action in comparison to the currently used drugs.

Antiangiogenic Nanomicelles for the Topical Delivery of Aflibercept to Treat Retinal Neovascular Disease.

The traditional intravitreal injection delivery of antivascular endothelial growth factor (anti-VEGF) to the posterior segment of the eye for treatment of retinal diseases is invasive and associated with sight-threatening complications. To avoid such complications, there has been significant interest in developing polymers for topical drug delivery to the retina. This study reports a nanomicelle drug delivery system made of a copolymer EPC (nEPCs), which is capable of delivering aflibercept to the posterior segment topically through corneal-scleral routes. EPC is composed of poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), and polycaprolactone (PCL) segments. In this study, aflibercept-loaded nEPCs (nEPCs + A) are capable of penetrating the cornea in ex vivo porcine eye models and deliver a clinically significant amount of aflibercept to the retina in laser-induced choroidal neovascularization (CNV) murine models, causing CNV regression. nEPCs + A also demonstrate biocompatibility in vitro and in vivo. Interestingly, this study also suggests that nEPCs have intrinsic antiangiogenic properties. The ability to deliver anti-VEGF drugs and the intrinsic antiangiogenic properties of nEPCs may result in synergistic effects, which can be harnessed for effective therapeutics. nEPCs may be a promising topical anti-VEGF delivery platform for the treatment of retinal diseases.

A bio-functional polymer that prevents retinal scarring through modulation of NRF2 signalling pathway.

One common cause of vision loss after retinal detachment surgery is the formation of proliferative and contractile fibrocellular membranes. This aberrant wound healing process is mediated by epithelial-mesenchymal transition (EMT) and hyper-proliferation of retinal pigment epithelial (RPE) cells. Current treatment relies primarily on surgical removal of these membranes. Here, we demonstrate that a bio-functional polymer by itself is able to prevent retinal scarring in an experimental rabbit model of proliferative vitreoretinopathy. This is mediated primarily via clathrin-dependent internalisation of polymeric micelles, downstream suppression of canonical EMT transcription factors, reduction of RPE cell hyper-proliferation and migration. Nuclear factor erythroid 2-related factor 2 signalling pathway was identified in a genome-wide transcriptomic profiling as a key sensor and effector. This study highlights the potential of using synthetic bio-functional polymer to modulate RPE cellular behaviour and offers a potential therapy for retinal scarring prevention.

Surgical Transplantation of Human RPE Stem Cell-Derived RPE Monolayers into Non-Human Primates with Immunosuppression.

Recent trials of retinal pigment epithelium (RPE) transplantation for the treatment of disorders such as age-related macular degeneration have been promising. However, limitations of existing strategies include the uncertain survival of RPE cells delivered by cell suspension and the inherent risk of uncontrolled cell proliferation in the vitreous cavity. Human RPE stem cell-derived RPE (hRPESC-RPE) transplantation can rescue vision in a rat model of retinal dystrophy and survive in the rabbit retina for at least 1 month. The present study placed hRPESC-RPE monolayers under the macula of a non-human primate model for 3 months. The transplant was able to recover in vivo and maintained healthy photoreceptors. Importantly, there was no evidence that subretinally transplanted monolayers underwent an epithelial-mesenchymal transition. Neither gliosis in adjacent retina nor epiretinal membranes were observed. These findings suggest that hRPESC-RPE monolayers are safe and may be a useful source for RPE cell replacement therapy.

cGMP-grade human iPSC-derived retinal photoreceptor precursor cells rescue cone photoreceptor damage in non-human primates.

BACKGROUND: Retinal regenerative therapies hold great promise for the treatment of inherited retinal degenerations (IRDs). Studies in preclinical lower mammal models of IRDs have suggested visual improvement following retinal photoreceptor precursors transplantation, but there is limited evidence on the ability of these transplants to rescue retinal damage in higher mammals. The purpose of this study was to evaluate the therapeutic potential of photoreceptor precursors derived from clinically compliant induced pluripotent stem cells (iPSCs). METHODS: Photoreceptor precursors were sub-retinally transplanted into non-human primates (Macaca fascicularis). The cells were transplanted both in naïve and cobalt chloride-induced retinal degeneration models who had been receiving systemic immunosuppression for one week prior to the procedure. Optical coherence tomography, fundus autofluorescence imaging, electroretinography, ex vivo histology and immunofluorescence staining were used to evaluate retinal structure, function and survival of transplanted cells. RESULTS: There were no adverse effects of iPSC-derived photoreceptor precursors on retinal structure or function in naïve NHP models, indicating good biocompatibility. In addition, photoreceptor precursors injected into cobalt chloride-induced retinal degeneration NHP models demonstrated an ability both to survive and to mature into cone photoreceptors at 3 months post-transplant. Optical coherence tomography showed restoration of retinal ellipsoid zone post-transplantation. CONCLUSIONS: These findings demonstrate the safety and therapeutic potential of clinically compliant iPSC-derived photoreceptor precursors as a cell replacement source for future clinical trials.

A Pilot Study on MicroRNA Profile in Tear Fluid to Predict Response to Anti-VEGF Treatments for Diabetic Macular Edema.

(1) Background: Intravitreal anti-vascular endothelial growth factor (anti-VEGF) is an established treatment for center-involving diabetic macular edema (ci-DME). However, the clinical response is heterogeneous. This study investigated miRNAs as a biomarker to predict treatment response to anti-VEGF in DME. (2) Methods: Tear fluid, aqueous, and blood were collected from patients with treatment-naïve DME for miRNA expression profiling with quantitative polymerase chain reaction. Differentially expressed miRNAs between good and poor responders were identified from tear fluid. Bioinformatics analysis with the miEAA tool, miRTarBase Annotations, Gene Ontology categories, KEGG, and miRWalk pathways identified interactions between enriched miRNAs and biological pathways. (3) Results: Of 24 participants, 28 eyes received bevacizumab (15 eyes) or aflibercept (13 eyes). Tear fluid had the most detectable miRNA species (N = 315), followed by serum (N = 309), then aqueous humor (N = 134). MiRNAs that correlated with change in macular thickness were miR-214-3p, miR-320d, and hsa-miR-874-3p in good responders; and miR-98-5p, miR-196b-5p, and miR-454-3p in poor responders. VEGF-related pathways and the angiogenin-PRI complex were enriched in good responders, while transforming growth factor-ß and insulin-like growth factor pathways were enriched in poor responders. (4) Conclusions: We reported a panel of novel miRNAs that provide insight into biological pathways in DME. Validation in larger independent cohorts is needed to determine the predictive performance of these miRNA candidate biomarkers.

Sustained delivery of anti-VEGFs from thermogel depots inhibits angiogenesis without the need for multiple injections.

Anti-vascular endothelial growth factor (anti-VEGF) proteins are the gold-standard treatment for posterior eye segment proliferative vascular diseases such as Age-Related Macular Degeneration (AMD) and Diabetic Retinopathy (DR). However, the standard of care requires inconvenient monthly intravitreal injections. This underlies an unmet clinical need to develop alternative solutions for sustained delivery of biologics. In this paper, we demonstrated that anti-VEGFs can be encapsulated by a simple mild process into our polyurethane thermogel depots. By changing the hydrophilic-hydrophobic balance in the copolymer, anti-VEGF release rates can be modulated. The antibody in the thermogel partitions into protein domains which vary in size corresponding to the hydrophilicity balance of the polymer. Anti-VEGFs can be released in a relatively linear manner from the thermogel for up to 40 days in vitro. The encapsulated anti-VEGFs demonstrate anti-angiogenic bioactivity by inhibiting vessel outgrowth in rat ex vivo choroidal explants, and reducing vascular leakage in a VEGF-driven neovascularization rabbit model. In conclusion, we show that these thermogels can be tuned in terms of hydrophilicity and used for sustained delivery of bioactive anti-VEGFs. Physically cross-linked polyurethane thermoresponsive hydrogels could be a promising platform for sustained delivery of biologically active therapeutic proteins.