Adeno-Associated Virus Mediated Gene Therapy for Corneal Diseases

A tissue-targeted prime/pull/keep therapeutic herpes simplex virus vaccine protects against recurrent ocular herpes infection and disease in HLA-A*0201 transgenic rabbits

Herpes simplex virus type 1 (HSV-1) continues to be one of the most prevalent viral infections globally, with approximately 3.72 billion individuals affected worldwide. A clinical herpes vaccine is still lacking. In the present study, a novel prime/pull/keep vaccine was tested in a human leukocyte antigen transgenic rabbit model of ocular herpes (HLA-A*0201 Tg rabbit). Ten asymptomatic (ASYMP) CD8+ T-cell peptide epitopes and 3 CD4+ T-cell epitopes were selected from the HSV-1 glycoproteins D and B (gD and gB), viral tegument proteins (VP11/12 and VP13/14), and the DNA replication-binding helicase (UL9), all preferentially recognized by CD8+ and CD4+ T cells from "naturally protected" HSV-1-seropositive healthy ASYMP individuals (who never had recurrent corneal herpetic disease). HLA Tg rabbits were ocularly infected with HSV-1, then during latency at day 30 post-infection, the rabbits were ocularly vaccinated with a recombinant neurotropic AAV8 vector (107GC/ eye) encoding for the 10 CD8+ T-cell peptide and 4 CD4+ T-cell peptide (prime), T-cell attracting CXCL-11 (pull), and T-cell keeping IL-2/IL-15 cytokines (keep). The rabbits were followed up for corneal disease and viral loads in tears for 28 days. The frequency, function, and protective efficacy of HSV-specific CD8+ T cells induced by the prime/pull/keep vaccine were assessed in the trigeminal ganglia (TG), cornea, spleen, and peripheral blood. Compared to the mock group (unvaccinated), the peptides/CXCL11/IL-2/IL-15 vaccine generated frequent resident CD8+ T cells that infiltrated the TG. In ocularly HSV-1-infected and prime/pull/keep vaccinated rabbits, CD8+ T cell mobilization and retention into TG were associated with a significant reduction in corneal herpes infection and disease. These findings draw attention to the novel prime/pull/keep therapeutic vaccine strategy to mobilize and retain antiviral T cells to tissues protecting them against herpetic infection and disease.

IMPORTANCE

There is an urgent need for a vaccine against widespread human herpes simplex virus infections. The present study demonstrates that immunization of humanized HLA-A*0201 transgenic rabbits with CD8+ and CD4+ T-cell epitope peptides (prime)/ CXCL11 (pull)/ IL-2/IL-15 (keep) AAV8-based vaccine triggered mobilization and retention of HSV-1-specific CD8+ T cells locally in the cornea and TG, the sites of acute and latent herpes infections. Mobilization and retention of antiviral CD8+ T cells into the cornea and TG of HSV-1-infected rabbits that received the prime/pull/keep vaccine was associated with protection against ocular herpes infection and disease. These results highlight the importance of the prime/pull/keep vaccine strategy to bolster the number and function of protective CD8+ T cells within infected tissues.

Latest trends & strategies in ocular drug delivery

Ocular drug delivery is one of the most challenging routes of administration, and this may be attributed to the complex interplay of ocular barriers and clearance mechanisms that restrict therapeutic payload residence. Most of the currently approved products that ameliorate ocular disease conditions are topical, i.e., delivering therapeutics to the outside anterior segment of the eye. This site of administration works well for certain conditions such as local infections but due to the presence of numerous ocular barriers, the permeation of therapeutics to the posterior segment of the eye is limited. Conditions such as age-related macular degeneration and diabetic retinopathy that contribute to an extreme deterioration of vision acuity require therapeutic interventions at the posterior segment of the eye. This necessitates development of intraocular delivery systems such as intravitreal injections, implants, and specialized devices that deliver therapeutics to the posterior segment of the eye. Frequent dosing regimens and high concentration formulations have been strategized and developed to achieve desired therapeutic outcomes by overcoming some of the challenges of drug clearance and efficacy. Correspondingly, development of suitable delivery platforms such as biodegradable and non-biodegradable implants, nano delivery systems, and implantable devices have been explored. This article provides an overview of the current trends in the development of suitable formulations & delivery systems for ocular drug delivery with an emphasis on late-stage clinical and approved product. Moreover, this work aims to summarize current challenges and highlights exciting pre-clinical developments, and future opportunities in cell and gene therapies that may be explored for effective ocular therapeutic outcomes.

Looking to the Future of Viral Vectors in Ocular Gene Therapy: Clinical Review

Eye diseases can significantly affect the quality of life of patients due to decreased visual acuity. Although modern ophthalmological diagnostic methods exist, some diseases of the visual system are asymptomatic in the early stages. Most patients seek advice from an ophthalmologist as a result of rapidly progressive manifestation of symptoms. A number of inherited and acquired eye diseases have only supportive treatment without eliminating the etiologic factor. A promising solution to this problem may be gene therapy, which has proven efficacy and safety shown in a number of clinical studies. By directly altering or replacing defective genes, this therapeutic approach will stop as well as reverse the progression of eye diseases. This review examines the concept of gene therapy and its application in the field of ocular pathologies, emphasizing the most recent scientific advances and their potential impacts on visual function status.

Ocular toxicity, distribution, and shedding of intravitreal AAV-eqIL-10 in horses

Non-infectious uveitis (NIU) is a painful recurrent disease affecting 2%-5% of horses. Current treatments require frequent administration with associated adverse events. In a previous study, intravitreal (IVT) adeno-associated virus (AAV) harboring equine interleukin-10 (eqIL-10) cDNA inhibited experimental uveitis in rats. The goal of this study was to evaluate the ocular tolerability, vector genome (vg) distribution, and vector shedding following an IVT injection of AAV8-eqIL-10 in normal horses with the hypothesis that it would be well tolerated in a dose-dependent manner in horses. Injections were well tolerated with mild transient signs of ocular inflammation; however, horses receiving the highest dose developed keratic precipitates. The vgs were not detected in the tears 3 days after injection, or in urine or feces at any time. Aqueous and vitreous humor eqIL-10 levels increased to higher than 1.5 ng/mL, more than 20 times higher than reported effective endogenous and induced levels. The vgs were detected in ocular tissues, and systemic distribution was identified only in the liver and kidney. No systemic effects were identified 86 days after dosing with IVT AAV-eqIL-10. Further investigation of lower doses of IVT AAV8-eqIL-10 therapy is an important next step toward a safe and effective single-dose treatment of equine uveitis with broader implications for treating NIU in humans.

Ocular Gene Therapy: An Overview of Viral Vectors, Immune Responses, and Future Directions

Ocular gene therapy has rapidly advanced from proof-of-concept studies to clinical trials by exploiting the unique advantages of the eye, including its easy accessibility, relative immune privilege, and the ability to use the contralateral eye as a control. An important step forward was achieved with the Food and Drug Administration (FDA) approval of voretigene neparvovec (Luxturna) for the treatment of biallelic RPE65-mutation-associated retinal dystrophies in 2017. Gene therapy is a promising field aimed at treating various inherited and acquired eye diseases. Viral vectors such as adeno-associated virus (AAV) are mainly used to efficiently deliver genes. Despite the immune-privileged status of the eye, viral vector-based therapies can induce immune responses, potentially leading to gene therapy-associated uveitis. Future directions include developing strategies to reduce immune responses while maintaining therapeutic efficacy, optimizing vector selection, and improving delivery techniques. Continued advances in the field of viral vectors, particularly AAV, are expanding the potential applications of gene therapy to treat a variety of ocular diseases. To fully realize the potential of ocular gene therapy, more research and clinical trials are needed to improve these methods, ensure safe and efficient treatments, and ultimately overcome existing obstacles.

Schlemm's canal-selective Tie2/TEK knockdown induces sustained ocular hypertension in adult mice

Deficient Angiopoietin-Tie2 signaling is linked to ocular hypertension in glaucoma. Receptor Tie2/TEK expression and signaling at Schlemm's canal (SC) is indispensable for canal integrity and homeostatic regulation of aqueous humor outflow (AHO) and intraocular pressure (IOP), as validated by conditional deletion of Tie2, its ligands (Angpt1, Angpt2 and Angpt3/4) or regulators (Tie1 and PTPRB/VE-PTP). However, these Tie2/TEK knockouts and conditional knockouts are global or endothelial, preventing separation of systemic and ocular vascular defects that impact retinal or renal integrity. To develop a more targeted model of ocular hypertension induced by selective knockdown of Tie2/TEK expressed in SC, we combined the use of viral vectors to target the canal, and two distinct gene-editing strategies to disrupt the Tie2 gene. Adeno-associated virus (AAV2) is known to transduce rodent SC when delivered into the anterior chamber by intracameral injection. First, delivery of Cre recombinase via AAV2.Cre into R26tdTomato/+ reporter mice confirmed preferential and stable transduction in SC endothelium. Next, to disrupt Tie2 expression in SC, we injected AAV2.Cre into homozygous floxed Tie2 (Tie2FL/FL) mice. This led to attenuated Tie2 protein expression along the SC inner wall, decreased SC area and reduced trabecular meshwork (TM) cellularity. Functionally, IOP was significantly and steadily elevated, whereas AHO facility was reduced. In contrast, hemizygous Tie2FL/+ mice responded to AAV2.Cre with inconsistent and low IOP elevation, corroborating the dose-dependency of ocular hypertension on Tie2 expression/activation. In a second model using CRISPR/SaCas9 genome editing, wild-type C57BL/6 J mice injected with AAV2.saCas9-sgTie2 showed similar selective SC transduction and comparable IOP elevation in course and magnitude to that induced by AAV2.Cre in Tie2FL/FL mice. Together, our findings, demonstrate that selective Tie2 knockdown in SC is a targeted strategy that reliably induces chronic ocular hypertension and reproduces glaucomatous damage to the conventional outflow pathway, providing novel models of SC-Tie2 signaling loss valuable for preclinical studies.

Temporal insights into molecular and cellular responses during rAAV production in HEK293T cells

The gene therapy field seeks cost-effective, large-scale production of recombinant adeno-associated virus (rAAV) vectors for high-dosage therapeutic applications. Although strategies like suspension cell culture and transfection optimization have shown moderate success, challenges persist for large-scale applications. To unravel molecular and cellular mechanisms influencing rAAV production, we conducted an SWATH-MS proteomic analysis of HEK293T cells transfected using standard, sub-optimal, and optimal conditions. Gene Ontology and pathway analysis revealed significant protein expression variations, particularly in processes related to cellular homeostasis, metabolic regulation, vesicular transport, ribosomal biogenesis, and cellular proliferation under optimal transfection conditions. This resulted in a 50% increase in rAAV titer compared with the standard protocol. Additionally, we identified modifications in host cell proteins crucial for AAV mRNA stability and gene translation, particularly regarding AAV capsid transcripts under optimal transfection conditions. Our study identified 124 host proteins associated with AAV replication and assembly, each exhibiting distinct expression pattern throughout rAAV production stages in optimal transfection condition. This investigation sheds light on the cellular mechanisms involved in rAAV production in HEK293T cells and proposes promising avenues for further enhancing rAAV titer during production.

Sustained and Efficient Delivery of Antivascular Endothelial Growth Factor by the Adeno-associated Virus for the Treatment of Corneal Neovascularization: An Outlook for Its Clinical Translation

Corneal diseases represent 5.1% of all eye defects and are the fourth leading cause of blindness globally. Corneal neovascularization can arise from all conditions of chronic irritation or hypoxia, which disrupts the immune-privileged state of the healthy cornea, increases the risk of rejection after keratoplasty, and leads to opacity. In the past decades, significant progress has been made for neovascular diseases of the retina and choroid, with plenty of drugs getting commercialized. In addition, to overcome the barriers of the short duration and inadequate penetration of conventional formulations of antivascular endothelial growth factor (VEGF), multiple novel drug delivery systems, including adeno-associated virus (AAV)-mediated transfer have gone through the full process of bench-to-bedside translation. Like retina neovascular diseases, corneal neovascularization also suffers from chronicity and a high risk of recurrence, necessitating sustained and efficient delivery across the epithelial barrier to reach deep layers of the corneal stroma. Among the explored methods, adeno-associated virus-mediated delivery of anti-VEGF to treat corneal neovascularization is the most extensively researched and most promising strategy for clinical translation although currently although, it remains predominantly at the preclinical stage. This review comprehensively examines the necessity, benefits, and risks of applying AAV vectors for anti-VEGF drug delivery in corneal vascularization, including its current progress and challenges in clinical translation.

Genetic therapies and potential therapeutic applications of CRISPR activators in the eye

Conventional gene therapy involving supplementation only treats loss-of-function diseases and is limited by viral packaging sizes, precluding therapy of large genes. The discovery of CRISPR/Cas has led to a paradigm shift in the field of genetic therapy, with the promise of precise gene editing, thus broadening the range of diseases that can be treated. The initial uses of CRISPR/Cas have focused mainly on gene editing or silencing of abnormal variants via utilising Cas endonuclease to trigger the target cell endogenous non-homologous end joining. Subsequently, the technology has evolved to modify the Cas enzyme and even its guide RNA, leading to more efficient editing tools in the form of base and prime editing. Further advancements of this CRISPR/Cas technology itself have expanded its functional repertoire from targeted editing to programmable transactivation, shifting the therapeutic focus to precise endogenous gene activation or upregulation with the potential for epigenetic modifications. In vivo experiments using this platform have demonstrated the potential of CRISPR-activators (CRISPRa) to treat various loss-of-function diseases, as well as in regenerative medicine, highlighting their versatility to overcome limitations associated with conventional strategies. This review summarises the molecular mechanisms of CRISPRa platforms, the current applications of this technology in vivo, and discusses potential solutions to translational hurdles for this therapy, with a focus on ophthalmic diseases.

Recent advancements and applications of ophthalmic gene therapy strategies: A breakthrough in ocular therapeutics

Over the past twenty years, ocular gene therapy has primarily focused on addressing diseases linked to various genetic factors. The eye is an ideal candidate for gene therapy due to its unique characteristics, such as easy accessibility and the ability to target both corneal and retinal conditions, including retinitis pigmentosa (RP), Leber congenital amaurosis (LCA), age-related macular degeneration (AMD), and Stargardt disease. Currently, literature documents 33 clinical trials in this field, with the most promising results emerging from trials focused on LCA. These successes have catalyzed further research into other ocular conditions such as glaucoma, AMD, RP, and choroideremia. The effectiveness of gene therapy relies on the efficient delivery of genetic material to specific cells, ensuring sustained and optimal gene expression over time. Viral vectors have been widely used for this purpose, although concerns about potential risks such as immune reactions and genetic mutations have led to the development of non-viral vector systems. Preliminary laboratory research and clinical investigations have shown a connection between vector dosage and the intensity of immune response and inflammation in the eye. The method of administration significantly influences these reactions, with subretinal delivery resulting in a milder humoral response compared to the intravitreal route. This review discusses various ophthalmic diseases, including both corneal and retinal conditions, and their underlying mechanisms, highlighting recent advances and applications in ocular gene therapies.

Adaptor protein 14-3-3zeta promotes corneal wound healing via regulating cell homeostasis, a potential novel therapy for corneal injury

Severe corneal injury can lead to blindness even after prompt treatment. 14-3-3zeta, a member of an adaptor protein family, contributes to tissue repair by enhancing cellular viability and inhibiting fibrosis and inflammation in renal disease or arthritis. However, its role in corneal regeneration is less studied. In this study, filter disc of 2-mm diameter soaked in sodium hydroxide with a concentration of 0.5 N was placed at the center of the cornea for 30 s to establish a mouse model of corneal alkali injury. We found that 14-3-3zeta, which is mainly expressed in the epithelial layer, was upregulated following injury. Overexpression of 14-3-3zeta in ocular tissues via adeno-associated virus-mediated subconjunctival delivery promoted corneal wound healing, showing improved corneal structure and transparency. In vitro studies on human corneal epithelial cells showed that 14-3-3zeta was critical for cell proliferation and migration. mRNA-sequencing in conjunction with KEGG analysis and validation experiments revealed that 14-3-3zeta regulated the mRNA levels of ITGB1, PIK3R1, FGF5, PRKAA1 and the phosphorylation level of Akt, suggesting the involvement of the PI3K-Akt pathway in 14-3-3zeta-mediated tissue repair. 14-3-3zeta is a potential novel therapeutic candidate for treating severe corneal injury.

Corneal fibrosis: From in vitro models to current and upcoming drug and gene medicines

Fibrotic diseases are characterised by myofibroblast differentiation, uncontrolled pathological extracellular matrix accumulation, tissue contraction, scar formation and, ultimately tissue / organ dysfunction. The cornea, the transparent tissue located on the anterior chamber of the eye, is extremely susceptible to fibrotic diseases, which cause loss of corneal transparency and are often associated with blindness. Although topical corticosteroids and antimetabolites are extensively used in the management of corneal fibrosis, they are associated with glaucoma, cataract formation, corneoscleral melting and infection, imposing the need of far more effective therapies. Herein, we summarise and discuss shortfalls and recent advances in in vitro models (e.g. transforming growth factor-β (TGF-β) / ascorbic acid / interleukin (IL) induced) and drug (e.g. TGF-β inhibitors, epigenetic modulators) and gene (e.g. gene editing, gene silencing) therapeutic strategies in the corneal fibrosis context. Emerging therapeutical agents (e.g. neutralising antibodies, ligand traps, receptor kinase inhibitors, antisense oligonucleotides) that have shown promise in clinical setting but have not yet assessed in corneal fibrosis context are also discussed.

Use of Biologics and Stem Cells in Equine Ophthalmology

Regenerative therapy and biologics have the promise to treat equine ocular surface diseases, including corneal ulceration or immune-mediated keratitis, or intraocular diseases such as uveitis. The use of blood-derived products such as serum or platelet-rich plasma, mesenchymal stem cells, or amniotic membrane grafts may be beneficial for the treatment of ulcerative and chronic keratitis in horses. Furthermore, the use of stem cells or gene therapy has promise for the treatment of Intraocular diseases such as equine recurrent uveitis by providing efficacious, practical, and long-term therapy for these blinding diseases.

Successful transduction of target gene mediated by adeno-associated virus 2 into lens epithelial cells in rats

The Adeno-Associated Virus (AAV) has emerged as a promising candidate for delivery of genetic material, exhibiting significant potential in various clinical applications. Although multiple AAV serotypes have been shown to transduce ocular tissues, there have been few studies of AAV transduction of lens epithelial cells (LECs) in the ocular. In this study, we compared the efficiency of intravitreal injection of six AAV serotypes (AAV2, AAV5, AAV6, AAV8, AAV9, and AAVDJ) to transduce lens and retina in rats, The expression and localization of the reporter gene ZsGreen in the lens and retina were examined using immunofluorescence staining, and the relative expression of ZsGreen mRNA was detected using RT-qPCR. Our results demonstrated that AAV2 had the highest efficiency in transducing LECs. All six AAV serotypes could transduce the retina. To validate this observation, we further constructed an AAV2 vector with exogenous gene senescence marker protein 30 (SMP30) and performed intravitreal injection to successfully overexpress SMP30 in LECs of rats. our results provide a basis for the use of AAV vector-mediated gene therapy for lens diseases.

NF-κB c-Rel Is a Potential Therapeutic Target for Acute Corneal Transplant Rejection

Purpose

The purpose of this study was to determine the role of nuclear factor kappa B (NF-κB) c-Rel during acute corneal transplant rejection and whether targeting c-Rel can reduce corneal transplant rejection.

Methods

Allogeneic corneal transplantation was performed in wild-type and c-Rel-deficient mice. Corneal graft survival rate, opacity, neovascularization, and edema were evaluated by slit-lamp microscopy. Adeno-associated virus 6 (AAV6) expressing c-Rel-specific small hairpin RNA (AAV6-shRel) and the small-molecule compound pentoxifylline (PTXF) were used to reduce c-Rel expression. Enzyme-linked immunosorbent assay was used to determine the expression of inflammatory cytokines. c-Rel expression was determined by quantitative RT-PCR and western blot. The effect of c-Rel inhibition on corneal transplant rejection was examined using a mouse model of acute allogeneic corneal transplantation. Tear production and corneal sensitivity were measured to determine the potential toxicity of AAV6-shRel and PTXF.

Results

The expression of c-Rel and its inflammatory targets was increased in both mice and patients with corneal transplant rejection. Loss of c-Rel reduced corneal transplant rejection in mouse. Both AAV6-shRel and PTXF were able to downregulate the expression of c-Rel and its inflammatory targets in vitro. Treatment with AAV6-shRel or PTXF reduced corneal transplant rejection in mouse and downregulated the expression of inflammatory cytokines in peripheral blood mononuclear cells from patients with corneal transplant rejection. Treatment with AAV6-shRel or PTXF displayed no side effects on tear production or corneal sensitivity.

Conclusions

Increased expression of c-Rel is a risk factor for acute corneal transplant rejection, and targeting c-Rel can efficiently reduce corneal transplant rejection.

Leverage of nuclease-deficient CasX for preventing pathological angiogenesis

Gene editing with a CRISPR/Cas system is a novel potential strategy for treating human diseases. Pharmacological inhibition of phosphoinositide 3-kinase (PI3K) δ suppresses retinal angiogenesis in a mouse model of oxygen-induced retinopathy. Here we show that an innovative system of adeno-associated virus (AAV)-mediated CRISPR/nuclease-deficient (d)CasX fused with the Krueppel-associated box (KRAB) domain is leveraged to block (81.2% ± 6.5%) in vitro expression of p110δ, the catalytic subunit of PI3Kδ, encoded by Pik3cd. This CRISPR/dCasX-KRAB (4, 269 bp) system is small enough to be fit into a single AAV vector. We then document that recombinant AAV serotype (rAAV)1 efficiently transduces vascular endothelial cells from pathologic retinal vessels, which show high expression of p110δ; furthermore, we demonstrate that blockade of retinal p110δ expression by intravitreally injected rAAV1-CRISPR/dCasX-KRAB targeting the Pik3cd promoter prevents (32.1% ± 5.3%) retinal p110δ expression as well as pathological retinal angiogenesis in a mouse model of oxygen-induced retinopathy. These data establish a strong foundation for treating pathological angiogenesis by AAV-mediated CRISPR interference with p110δ expression.

Nanotechnology-based ocular drug delivery systems: recent advances and future prospects

Ocular drug delivery has constantly challenged ophthalmologists and drug delivery scientists due to various anatomical and physiological barriers. Static and dynamic ocular barriers prevent the entry of exogenous substances and impede therapeutic agents' active absorption. This review elaborates on the anatomy of the eye and the associated constraints. Followed by an illustration of some common ocular diseases, including glaucoma and their current clinical therapies, emphasizing the significance of drug therapy in treating ocular diseases. Subsequently, advances in ocular drug delivery modalities, especially nanotechnology-based ocular drug delivery systems, are recommended, and some typical research is highlighted. Based on the related research, systematic and comprehensive characterizations of the nanocarriers are summarized, hoping to assist with future research. Besides, we summarize the nanotechnology-based ophthalmic drugs currently on the market or still in clinical trials and the recent patents of nanocarriers. Finally, inspired by current trends and therapeutic concepts, we provide an insight into the challenges faced by novel ocular drug delivery systems and further put forward directions for future research. We hope this review can provide inspiration and motivation for better design and development of novel ophthalmic formulations.

Corneal gene therapy: Structural and mechanistic understanding

Cornea, a dome-shaped and transparent front part of the eye, affords 2/3rd refraction and barrier functions. Globally, corneal diseases are the leading cause of vision impairment. Loss of corneal function including opacification involve the complex crosstalk and perturbation between a variety of cytokines, chemokines and growth factors generated by corneal keratocytes, epithelial cells, lacrimal tissues, nerves, and immune cells. Conventional small-molecule drugs can treat mild-to-moderate traumatic corneal pathology but requires frequent application and often fails to treat severe pathologies. The corneal transplant surgery is a standard of care to restore vision in patients. However, declining availability and rising demand of donor corneas are major concerns to maintain ophthalmic care. Thus, the development of efficient and safe nonsurgical methods to cure corneal disorders and restore vision in vivo is highly desired. Gene-based therapy has huge potential to cure corneal blindness. To achieve a nonimmunogenic, safe and sustained therapeutic response, the selection of a relevant genes, gene editing methods and suitable delivery vectors are vital. This article describes corneal structural and functional features, mechanistic understanding of gene therapy vectors, gene editing methods, gene delivery tools, and status of gene therapy for treating corneal disorders, diseases, and genetic dystrophies.

Corneal Regeneration Using Gene Therapy Approaches

One of the most remarkable advancements in medical treatments of corneal diseases in recent decades has been corneal transplantation. However, corneal transplants, including lamellar strategies, have their own set of challenges, such as graft rejection, delayed graft failure, shortage of donor corneas, repeated treatments, and post-surgical complications. Corneal defects and diseases are one of the leading causes of blindness globally; therefore, there is a need for gene-based interventions that may mitigate some of these challenges and help reduce the burden of blindness. Corneas being immune-advantaged, uniquely avascular, and transparent is ideal for gene therapy approaches. Well-established corneal surgical techniques as well as their ease of accessibility for examination and manipulation makes corneas suitable for in vivo and ex vivo gene therapy. In this review, we focus on the most recent advances in the area of corneal regeneration using gene therapy and on the strategies involved in the development of such therapies. We also discuss the challenges and potential of gene therapy for the treatment of corneal diseases. Additionally, we discuss the translational aspects of gene therapy, including different types of vectors, particularly focusing on recombinant AAV that may help advance targeted therapeutics for corneal defects and diseases.

The RNA m5C Methylase NSUN2 Modulates Corneal Epithelial Wound Healing

Purpose

The emerging epitranscriptomics offers insights into the physiopathological roles of various RNA modifications. The RNA methylase NOP2/Sun domain family member 2 (NSUN2) catalyzes 5-methylcytosine (m5C) modification of mRNAs. However, the role of NSUN2 in corneal epithelial wound healing (CEWH) remains unknown. Here we describe the functional mechanisms of NSUN2 in mediating CEWH.

Methods

RT-qPCR, Western blot, dot blot, and ELISA were used to determine the NSUN2 expression and overall RNA m5C level during CEWH. NSUN2 silencing or overexpression was performed to explore its involvement in CEWH both in vivo and in vitro. Multi-omics was integrated to reveal the downstream target of NSUN2. MeRIP-qPCR, RIP-qPCR, and luciferase assay, as well as in vivo and in vitro functional assays, clarified the molecular mechanism of NSUN2 in CEWH.

Results

The NSUN2 expression and RNA m5C level increased significantly during CEWH. NSUN2 knockdown significantly delayed CEWH in vivo and inhibited human corneal epithelial cells (HCEC) proliferation and migration in vitro, whereas NSUN2 overexpression prominently enhanced HCEC proliferation and migration. Mechanistically, we found that NSUN2 increased ubiquitin-like containing PHD and RING finger domains 1 (UHRF1) translation through the binding of RNA m5C reader Aly/REF export factor. Accordingly, UHRF1 knockdown significantly delayed CEWH in vivo and inhibited HCEC proliferation and migration in vitro. Furthermore, UHRF1 overexpression effectively rescued the inhibitory effect of NSUN2 silencing on HCEC proliferation and migration.

Conclusions

NSUN2-mediated m5C modification of UHRF1 mRNA modulates CEWH. This finding highlights the critical importance of this novel epitranscriptomic mechanism in control of CEWH.

In situ transduction of cells in human corneal limbus using adeno-associated viruses: an ex vivo study

This study aimed to evaluate the efficacy of in situ adeno-associated virus (AAV)-mediated gene delivery into the human corneal limbal region via targeted sub-limbal injection technique. Human cadaveric corneal tissues were fixed on an artificial anterior chamber. Feasibility of sub-limbal injection technique was tested using trypan blue and black India ink. An enhanced green fluorescent protein (eGFP) encoding AAV DJ was injected into sub-limbal region. After AAV injection, corneal tissues were incubated in air-lift culture and prepared for immunohistochemical analysis. Cell survivial and expression of eGFP, stem cell markers (p63α and cytokeratin 19 (KRT19)), and differentiation marker cytokeratin 3 (KRT3) were evaluated using confocal microscopy. Both trypan blue and black India ink stained and were retained sub-limbally establishing specificity of the injection technique. Immunohistochemical analysis of corneas injected with AAV DJ-eGFP indicated that AAV-transduced cells in the limbal region co-express eGFP, p63α, and KRT19 and that these transduced cells were capable of differentiating to KRT3 postitive corneal epithelial cells. Our sub-limbal injection technique can target cells in the human limbus in a reproducible and efficient manner. Thus, we demonstrate that in situ injection of corneal limbus may provide a feasible mode of genetic therapy for corneal disorders with an epithelial etiology.

Rapid characterization of adeno-associated virus (AAV) gene therapy vectors by mass photometry

Recombinant adeno-associated viruses (rAAV) are used extensively as gene delivery vectors in clinical studies, and several rAAV based treatments have already been approved. Significant progress has been made in rAAV manufacturing; however, better and more precise capsid characterization techniques are still needed to guarantee the purity and safety of rAAV preparations. Current analytical techniques used to characterize rAAV preparations are susceptible to background signals, have limited accuracy, or require a large amount of time and material. A recently developed single-molecule technique, mass photometry (MP), measures mass distributions of biomolecules with high-resolution and sensitivity. Here we explore applications of MP for the characterization of capsid fractions. We demonstrate that MP is able to resolve and quantify not only empty and full-genome containing capsid populations but also identify partially packaged capsid impurities. MP data accurately measures full and empty capsid ratios, and can be used to estimate the size of the encapsidated genome. MP distributions provide information on sample heterogeneity and on the presence of aggregates. Sub-picomole quantities of sample are sufficient for MP analysis, and data can be obtained and analyzed within minutes. This method provides a simple, robust, and effective tool to monitor the physical attributes of rAAV vectors.

Update on the Corneal Dystrophies-Genetic Testing and Therapy

ABSTRACT

One major purpose of the IC3D Corneal Dystrophy Nomenclature Revision was to include genetic information with a goal of facilitating investigation into the pathogenesis, treatment, and perhaps even prevention of the corneal dystrophies, an ambitious goal. Over a decade has passed since the first publication of the IC3D Corneal Dystrophy Nomenclature Revision. Gene therapy is available for an early-onset form of inherited retinal degeneration called Leber congenital amaurosis, but not yet for corneal degenerations. We review the current state of affairs regarding our original ambitious goal. We discuss genetic testing, gene therapy [RNA interference (RNAi) and genome editing], and ocular delivery of corneal gene therapy for the corneal dystrophies. Why have gene therapy techniques not yet been introduced for the corneal dystrophies?

Developing advanced therapeutics through the study of naturally occurring immune-mediated ocular disease in domestic animals

This review, which is part of the "Currents in One Health" series, describes the importance of the study of immune-mediated ocular disease in the development of innovative therapeutics, such as cell and gene therapy for the eye. Recent examples of cell and gene therapy studies from the author's laboratory are reviewed to emphasize the importance of One Health initiatives in developing innovative therapies for ocular diseases. Spontaneous immune-mediated corneal disease is common in horses, cats, dogs, and humans. Autologous bone marrow-derived mesenchymal stem cells (BM-MSCs) injected subconjunctivally resulted in the resolution of naturally occurring immune-mediated keratitis (IMMK) without adverse effects. These results support that autologous subconjunctival BM-MSC therapy may be a viable treatment alternative for IMMK. Furthermore, the use of subconjunctival MSCs may be an effective method to treat ocular surface immune-mediated diseases in humans and other species, including herpetic stromal keratitis and immunologic dry eye disease. Furthermore, the use of adeno-associated viral (AAV) vectors to deliver the immunosuppressive transgene cDNA of equine interleukin 10 (eqIL-10) or human leukocyte antigen G injected intravitreally was shown to be safe and inhibited the development of uveitis in the experimental autoimmune uveitis rat model. Efficacy and safety studies of ocular gene therapy in models will pave the way for clinical trials in animals with naturally occurring immune-mediated diseases, such as a therapeutic clinical trial for AAV-eqIL-10 in horses with equine recurrent uveitis.

Ocular Drug Delivery: Advancements and Innovations

Ocular drug delivery has been significantly advanced for not only pharmaceutical compounds, such as steroids, nonsteroidal anti-inflammatory drugs, immune modulators, antibiotics, and so forth, but also for the rapidly progressed gene therapy products. For conventional non-gene therapy drugs, appropriate surgical approaches and releasing systems are the main deliberation to achieve adequate treatment outcomes, whereas the scope of “drug delivery” for gene therapy drugs further expands to transgene construct optimization, vector selection, and vector engineering. The eye is the particularly well-suited organ as the gene therapy target, owing to multiple advantages. In this review, we will delve into three main aspects of ocular drug delivery for both conventional drugs and adeno-associated virus (AAV)-based gene therapy products: (1) the development of AAV vector systems for ocular gene therapy, (2) the innovative carriers of medication, and (3) administration routes progression.

New Frontier in the Management of Corneal Dystrophies: Basics, Development, and Challenges in Corneal Gene Therapy and Gene Editing

ABSTRACT

Corneal dystrophies represent a group of heterogeneous hereditary disorders causing progressive corneal opacification and blindness. Current corneal transplant management for corneal dystrophies faces the challenges of repeated treatments, complex surgical procedures, shortage of appropriate donor cornea, and, more importantly, graft rejection. Genetic medicine could be an alternative treatment regime to overcome such challenges. Cornea carries promising scope for a gene-based therapy involving gene supplementation, gene silencing, and gene editing in both ex vivo and in vivo platforms. In the cornea, ex vivo gene therapeutic strategies were attempted for corneal graft survival, and in vivo gene augmentation therapies aimed to prevent herpes stromal keratitis, neovascularization, corneal clouding, and wound healing. However, none of these studies followed a clinical trial-based successful outcome. CRISPR/Cas system offers a broad scope of gene editing and engineering to correct underlying genetic causes in corneal dystrophies. Corneal tissue--specific gene correction in vitro with minimal off-target effects and optimal gene correction efficiency followed by their successful surgical implantation, or in vivo CRISPR administration targeting pathogenic genes finds a way to explore therapeutic intervention for corneal dystrophies. However, there are many limitations associated with such CRISPR-based corneal treatment management. This review will look into the development of corneal gene therapy and CRISPR-based study in corneal dystrophies, associated challenges, potential approaches, and future directions.

Therapeutic Applications of Adeno-Associated Virus (AAV) Gene Transfer of HLA-G in the Eye

The purpose of this paper is to review human leukocyte antigen G (HLA-G) in the eye, its role in immune tolerance, and the potential therapeutic use of AAV gene transfer and expression of HLA-G in various ocular tissues. Several studies are reviewed that demonstrate efficacy in animal models of disease, including intracorneal delivery of AAV-HLA-G to treat corneal inflammation and prevent corneal graft rejection, subconjunctival injection of AAV-HLA-G for ocular graft vs. host disease and potentially dry eye disease, and intravitreal injection of AAV-HLA-G to inhibit uveitis. Furthermore, due to the anti-vascular function of HLA-G, AAV-HLA-G may be an effective therapy for posterior ocular diseases, such as neovascular age-related macular degeneration, diabetic retinopathy, and choroidal neovascularization. Therefore, AAV-mediated gene transfer of HLA-G may be an effective treatment for common immune-mediated, inflammatory, and neovascular diseases of the eye.

Rescue of the Congenital Hereditary Endothelial Dystrophy Mouse Model by Adeno-Associated Viruse-Mediated Slc4a11 Replacement

Purpose

Congenital hereditary endothelial dystrophy (CHED) is a rare condition that manifests at an early age showing corneal edema, increased oxidative stress, mitochondrial dysfunction, and eventually apoptosis of the endothelium due to loss of function of the membrane transport protein SLC4A11. This project tested whether replacing Slc4a11 into the Slc4a11 -/- CHED mouse model can reverse the disease-associated phenotypes.

Design

Experimental study.

Participants

Five-week-old or 11-week-old Slc4a11 -/- mice. Age- and gender-matched Slc4a11 +/+ animals were used as controls. A total of 124 animals (62 female, and 62 male) were used in this study. Fifty-three animals of the genotype Slc4a11 +/+ were used as age- and gender-matched noninjected controls. Seventy-one Slc4a11 -/- mice were administered anterior chamber injections of adeno-associated virus (AAV).

Methods

Anterior chambers of young (5 weeks old) or older (11 weeks old) Slc4a11 -/- mice were injected once with adeno-associated virus serotype 9 (AAV9) mouse Slc4a11 or AAV9-Null vectors. Corneal thickness was measured using OCT. End point analysis included corneal endothelial cell density, mitochondrial oxidative stress, and corneal lactate concentration.

Main Outcome Measures

Corneal thickness, endothelial cell loss, lactate levels, and mitochondrial oxidative stress.

Results

In the young animals, AAV9-Slc4a11 reversed corneal edema, endothelial cell loss, mitochondrial oxidative stress, lactate transporter expression, and corneal lactate concentration to the levels observed in wild-type animals. In the older animals, gene replacement did not reverse the phenotype but prevented progression.

Conclusions

Functional rescue of CHED phenotypes in the Slc4a11 -/- mouse is possible; however, early intervention is critical.

Efficacious, safe, and stable inhibition of corneal neovascularization by AAV-vectored anti-VEGF therapeutics

Corneal neovascularization (CoNV) leads to visual impairment, affecting over 1.4 million people in the United States per year. It is caused by a variety of pathologies, such as inflammation, hypoxia, and limbal barrier dysfunction. Injection of the anti-vascular endothelial growth factor (VEGF) drug KH902 (conbercept) can inhibit CoNV but requires repeated dosing that produces associated side effects, such as cornea scar. To explore more efficacious and long-lasting treatment of CoNV, we employed recombinant adeno-associated virus (rAAV)2 and rAAV8 vectors to mediate KH902 expression via a single intrastromal injection and investigated its anti-angiogenic effects and safety in both alkali-burn- and suture-induced CoNV mouse models. Our results showed that rAAV-mediated KH902 mRNA expression in the cornea was sustained for at least 3 months after a single intrastromal injection. Moreover, the expression level of rAAV8-KH902 far exceeded that of rAAV2-KH902. A single-dose rAAV8-KH902 treatment at 8 × 10⁸ genome copies (GCs) per cornea dramatically inhibited CoNV for an extended period of time in mouse CoNV models without adverse events, whereas the inhibition of CoNV by a single intrastromal administration of the conbercept drug lasted for only 10−14 days. Overall, our study demonstrated that the treatment of CoNV with a single dose of rAAV8-KH902 via intrastromal administration was safe, effective, and long lasting, representing a novel therapeutic strategy for CoNV.

Diabetic eye: associated diseases, drugs in clinic, and role of self-assembled carriers in topical treatment

Introduction: Diabetes is a pandemic disease that causes relevant ocular pathologies. Diabetic retinopathy, macular edema, cataracts, glaucoma, or keratopathy strongly impact the quality of life of the patients. In addition to glycemic control, intense research is devoted to finding more efficient ocular drugs and improved delivery systems that can overcome eye barriers. Areas covered: The aim of this review is to revisit first the role of diabetes in the development of chronic eye diseases. Then, commercially available drugs and new candidates in clinical trials are tackled together with the pros and cons of their administration routes. Subsequent sections deal with self-assembled drug carriers suitable for eye instillation combining patient-friendly administration with high ocular bioavailability. Performance of topically administered polymeric micelles, liposomes, and niosomes for the management of diabetic eye diseases is analyzed in the light of ex vivo and in vivo results and outcomes of clinical trials. Expert opinion: Self-assembled carriers are being shown useful for efficient delivery of not only a variety of small drugs but also macromolecules (e.g. antibodies) and genes. Successful design of drug carriers may offer alternatives to intraocular injections and improve the treatment of both anterior and posterior segments diabetic eye diseases.

Long-Term Safety and Tolerability of BMP7 and HGF Gene Overexpression in Rabbit Cornea

Purpose

Tissue-targeted localized BMP7+HGF genes delivered into the stroma via nanoparticle effectively treats corneal fibrosis and rehabilitates transparency in vivo without acute toxicity. This study evaluated the long-term safety and tolerability of BMP7+HGF nanomedicine for the eye in vivo.

Methods

One eye each of 36 rabbits received balanced salt solution (group 1, naïve; n = 12), naked vector with polyethylenimine-conjugated gold nanoparticles (PEI2-GNP; group 2, naked-vector; n = 12), or BMP7+HGF genes with PEI2-GNP (group 3, BMP7+HGF; n = 12) via a topical delivery technique. Safety and tolerability measurements were performed by clinical biomicroscopy in live rabbits at predetermined time intervals up to 7 months. Corneal tissues were collected at 2 months and 7 months after treatment and subjected to histology, immunofluorescence, and quantitative real-time PCR analyses.

Results

Clinical ophthalmic examinations and modified MacDonald-Shadduck scores showed no significant changes in corneal thickness (P = 0.3389), tear flow (P = 0.2121), intraocular pressure (P = 0.9958), epithelial abrasion, or ocular abnormality. Slit-lamp, stereo, confocal, and specular biomicroscopy showed no signs of blepharospasm chemosis, erythema, epiphora, abnormal ocular discharge, or changes in epithelium, stroma, and endothelium after BMP7+HGF therapy for up to 7 months, as compared with control groups. Throughout the 7-month period, no significant changes were recorded in endothelial density (P = 0.9581). Histological and molecular data were well corroborated with the subjective clinical analyses and showed no differences in the naïve, naked-vector, and BMP7+HGF groups.

Conclusions

Localized BMP7+HGF therapy is a safe, tolerable, and innovative modality for the treatment of corneal fibrosis.

Translational Relevance

Nanoparticle-mediated BMP7+HGF combination gene therapy has the potential to treat corneal fibrosis in vivo without short- or long-term toxicity.

Gene therapy in the anterior eye segment

This review provides comprehensive information about the advances in gene therapy in the anterior segment of the eye including cornea, conjunctiva, lacrimal gland, and trabecular meshwork. We discuss gene delivery systems including viral and non-viral vectors as well as gene editing techniques, mainly CRISPR-Cas9, and epigenetic treatments including antisense and siRNA therapeutics. We also provide a detailed analysis of various anterior segment diseases where gene therapy has been tested with corresponding outcomes. Disease conditions include corneal and conjunctival fibrosis and scarring, corneal epithelial wound healing, corneal graft survival, corneal neovascularization, genetic corneal dystrophies, herpetic keratitis, glaucoma, dry eye disease, and other ocular surface diseases. Although most of the analyzed results on the use and validity of gene therapy at the ocular surface have been obtained in vitro or using animal models, we also discuss the available human studies. Gene therapy approaches are currently considered very promising as emerging future treatments of various diseases, and this field is rapidly expanding.