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Age-related macular degeneration (AMD) is one of the leading causes of irreversible blindness in the developed world. Antivascular endothelial growth factor therapy has transformed the management and outcome of neovascular AMD (nAMD), although the need for repeated intravitreal injections—even lifelong—and the related complications, high drug costs, frequent clinic visits and repeated imaging have resulted in an enormous burden both to healthcare systems and patients. The application of gene therapy approaches for sustained delivery of a range of antiangiogenic proteins has the promise of helping to address these aforementioned challenges. A number of early phase clinical trials of gene therapy in nAMD have provided encouraging results, with many more ongoing or anticipated. There remain significant areas of controversy, including regarding the optimal treatment targets, routes of administration and potential safety concerns. In this review we aim to provide an update of the current status of gene therapy for nAMD and briefly discuss future prospects.

Opticin is an endogenous vitreous glycoprotein that may have therapeutic potential as it has been shown that supranormal concentrations suppress preretinal neovascularization. Herein we investigated the pharmacokinetics of opticin following intravitreal injection in rabbits. To measure simultaneously concentrations of human and rabbit opticin, a selected reaction monitoring mass spectrometry assay was developed. The mean concentration of endogenous rabbit opticin in 7 uninjected eyes was measured and found to be 19.2 nM or 0.62 μg/mL. When the vitreous was separated by centrifugation into a supernatant and collagen-containing pellet, 94% of the rabbit opticin was in the supernatant. Intravitreal injection of human opticin (40 μg) into both eyes of rabbits was followed by enucleation at 5, 24, and 72 h and 7, 14, and 28 days postinjection (n= 6 at each time point) and measurement of vitreous human and rabbit opticin concentrations in the supernatant and collagen-containing pellet following centrifugation. The volume of distribution of human opticin was calculated to be 3.31 mL, and the vitreous half-life was 4.2 days. Assuming that rabbit and human opticin are cleared from rabbit vitreous at the same rate, opticin is secreted into the vitreous at a rate of 0.14 μg/day. We conclude that intravitreally injected opticin has a vitreous half-life that is similar to currently available antiangiogenic therapeutics. While opticin was first identified bound to vitreous collagen fibrils, here we demonstrate that >90% of endogenous opticin is not bound to collagen. Endogenous opticin is secreted by the nonpigmented ciliary epithelium into the rabbit vitreous at a remarkably high rate, and the turnover in vitreous is approximately 15% per day.

IMPORTANCE: The value of facedown positioning following surgery for large full-thickness macular holes is unknown. OBJECTIVE: To determine whether advice to position facedown postoperatively improves the outcome for large macular holes. DESIGN, SETTING, AND PARTICIPANTS: This randomized, parallel group superiority trial with 1:1 randomization stratified by site with 3 months’ follow-up was conducted at 9 sites across the United Kingdom and included participants with an idiopathic full-thickness macular hole of at least 400 μm minimum linear diameter and a duration of fewer than 12 months. All participants had vitrectomy surgery with peeling of the internal limiting membrane and injection of perfluoropropane (14%) gas, with or without simultaneous surgery for cataract. INTERVENTIONS: Following surgery, participants were randomly advised to position either facedown or face forward for 8 hours daily for 5 days. MAIN OUTCOMES AND MEASURES: The primary outcome was closure of the macular hole determined 3 months following surgery by masked optical coherence tomography evaluation. Secondary outcome measures at 3 months were visual acuity, participant-reported experience of positioning, and quality of life measured by the National Eye Institute Visual Function Questionnaire 25. RESULTS: A total of 185 participants (45 men [24.3%]; 156 white [84.3%]; 9 black [4.9%]; 10 Asian [5.4%]; median age, 69 years [interquartile range, 64-73 years]) were randomized. Macular hole closure was observed in 90 (85.6%) who were advised to position face forward and 88 (95.5%) advised to position facedown (adjusted odds ratio, 3.15; 95% CI, 0.87-11.41; P = .08). The mean (SD) improvement in best-corrected visual acuity at 3 months was 0.34 (0.69) logMAR (equivalent to 1 Snellen line) in the face-forward group and 0.57 (0.42) logMAR (equivalent to 3 Snellen lines) in the facedown group (adjusted mean difference, 0.22 [95 % CI, 0.05-0.38]; equivalent to 2 Snellen lines); 95% CI, 0.05-0.38; P = .01). The median National Eye Institute Visual Function Questionnaire 25 score was 89 (interquartile range, 76-94) in the facedown group and 87 (interquartile range, 73-93) in the face-forward group (mean [SD] change on a logistic scale, 0.08 [0.26] face forward and 0.11 [0.25] facedown; adjusted mean [SD] difference on a logistic scale, 0.02; 95% CI, −0.03 to 0.07; P = .41). CONCLUSIONS AND RELEVANCE: The results do not prove that facedown positioning following surgery is more likely to close large macular holes compared with facing forward but do support the possibility that visual acuity outcomes may be superior. TRIAL REGISTRATION: Isrctn.org Identifier: 12410596

We have developed a method to label and image myeloid cells infiltrating the mouse retina and choroid in vivo, using a single depot injection of indocyanine green dye (ICG). This was demonstrated using the following ocular models of inflammation and angiogenesis: endotoxin-induced uveitis, experimental autoimmune uveoretinitis and laser-induced choroidal neovascularization model. A near-infrared scanning ophthalmoscope was used for in vivo imaging of the eye, and flow cytometry was used on blood and spleen to assess the number and phenotype of labelled cells. ICG was administered 72 h before the induction of inflammation to ensure clearance from the systemic circulation. We found that in vivo intravenous administration failed to label any leukocytes, whereas depot injection, either intraperitoneal or subcutaneous, was successful in labelling leukocytes infiltrating into the retina. Progression of inflammation in the retina could be traced over a period of 14 days following a single depot injection of ICG. Additionally, bright-field microscopy, spectrophotometry and flow cytometric analysis suggest that the predominant population of cells stained by ICG are circulating myeloid cells. The translation of this approach into clinical practice would enable visualization of immune cells in situ. This will not only provide a greater understanding of pathogenesis, monitoring and assessment of therapy in many human ocular diseases but might also open the ability to image immunity live for neurodegenerative disorders, cardiovascular disease and systemic immune-mediated disorders.

Loss of photoreceptors due to retinal degeneration is a major cause of untreatable blindness. Cell replacement therapy, using pluripotent stem cell‐derived photoreceptor cells, may be a feasible future treatment. Achieving safe and effective cell replacement is critically dependent on the stringent selection and purification of optimal cells for transplantation. Previously, we demonstrated effective transplantation of post‐mitotic photoreceptor precursor cells labelled by fluorescent reporter genes. As genetically labelled cells are not desirable for therapy, here we developed a surface biomarker cell selection strategy for application to complex pluripotent stem cell differentiation cultures. We show that a five cell surface biomarker panel CD73(+)CD24(+)CD133(+)CD47(+)CD15(−) facilitates the isolation of photoreceptor precursors from three‐dimensional self‐forming retina differentiated from mouse embryonic stem cells. Importantly, stem cell‐derived cells isolated using the biomarker panel successfully integrate and mature into new rod photoreceptors in the adult mouse retinae after subretinal transplantation. Conversely, unsorted or negatively selected cells do not give rise to newly integrated rods after transplantation. The biomarker panel also removes detrimental proliferating cells prior to transplantation. Notably, we demonstrate how expression of the biomarker panel is conserved in the human retina and propose that a similar selection strategy will facilitate isolation of human transplantation‐competent cells for therapeutic application. StemCells2015;33:2469—2482

Ocular neovascularization is a central feature of diabetic retinopathy and age-related macular degeneration. These conditions are the major causes of blindness in the developed world. Current treatments are of limited efficacy and associated with significant adverse effects. Characterization of the molecular and cellular events involved in angiogenesis has led to the identification of a number of angiostatic molecules with potential therapeutic value. The systemic administration of small molecule angiostatic proteins risks significant systemic adverse effects and the effect of their intraocular injection is short-lived. Local gene transfer, however, offers the possibility of targeted, sustained and regulatable delivery of angiostatic proteins to the retina after a single procedure to introduce a vector to an intraocular site. The effect of intra-ocular delivery of recombinant viruses carrying genes encoding angiostatic proteins has been demonstrated in rodent models of ocular neovascularization. Recombinant adeno-associated virus-mediated local gene transfer of a vascular endothelial growth factor inhibitor controls both retinal and choroidal neovascularization. The clinical application of this approach may require the means to regulate gene expression in order to minimize the potential for adverse effects. Regulation of transgene expression by means of a hypoxia-responsive promoter offers an attractive strategy for the targeted and regulated delivery of angiostatic proteins to the retina in the management of ischaemia-induced ocular neovascularization. Preclinical studies of gene transfer in a large animal model following subretinal delivery of a recombinant adeno-associated virus vector have demonstrated efficient sustained reporter gene expression in cells of the outer retina. Recent progress has enabled the planning of clinical trials of gene therapy for ocular neovascular disorders.