Ocular gene therapies in clinical practice: viral vectors and nonviral alternatives

A photothermal surface modified with polyelectrolyte multilayers for gene transfection and cell harvest

Gene transfection, which involves introducing nucleic acids into cells, is a pivotal technology in the life sciences and medical fields, particularly in gene therapy. Surface-mediated transfection, primarily targeting cells adhering to surfaces, shows promise for enhancing cell transfection by localizing and presenting surface-bound nucleic acids directly to the cells. However, optimizing endocytosis for efficient delivery remains a persistent challenge. Additionally, ensuring efficient and non-traumatic cell harvest capability is crucial for applications such as ex vivo cell-based therapy. To address these challenges, we developed a photothermal platform with enzymatic degradation capability for efficient gene transfection and cell harvest. This platform is based on carbon nanotubes (CNTs) doped with poly(dimethylsiloxane) and modified with polyelectrolyte multilayers (PEMs) containing hyaluronic acid and quaternized chitosan, allowing for substantial loading of poly(ethyleneimine)/plasmid DNA (pDNA) complexes through electrostatic interactions. Upon irradiation of near-infrared laser, the photothermal properties of CNTs enable high transfection efficiency by delivering pDNA into attached cells via a membrane disruption mechanism. The engineered cells can be harvested by treating with a non-toxic hyaluronidase solution to degrade PEMs, thus maintaining good viability for further applications. This platform has demonstrated remarkable efficacy across various cell lines (including Hep-G2 cells, Ramos cells and primary T cells), achieving a transfection efficiency exceeding 95 %, cell viability exceeding 90 %, and release efficiency surpassing 95 %, highlighting its potential for engineering living cells.

How Advanced are Nanocarriers for Effective Subretinal Injection?

Subretinal injection (SR injection) is a commonly used method of ocular drug delivery and has been mainly applied for the treatment of neovascular age-associated macular degeneration (nAMD) and sub-macular hemorrhage (SMH) caused by nAMD, as well as various types of hereditary retinopathies (IRD) such as Stargardt's disease (STGD), retinitis pigmentosa (RP), and a series of fundus diseases such as Leber's congenital dark haze (LCA), choroidal defects, etc. The commonly used carriers of SR injection are mainly divided into viral and non-viral vectors. Leber's congenital amaurosis (LCA), choroidal agenesis, and a series of other fundus diseases are also commonly treated using SR injection. The commonly used vectors for SR injection are divided into two categories: viral vectors and non-viral vectors. Viral vectors are a traditional class of SR injection drug carriers that have been extensively studied in clinical treatment, but they still have many limitations that cannot be ignored, such as poor reproduction efficiency, small loading genes, and triggering of immune reactions. With the rapid development of nanotechnology in the treatment of ocular diseases, nanovectors have become a research hotspot in the field of non-viral vectors. Nanocarriers have numerous attractive properties such as low immunogenicity, robust loading capacity, stable structure, and easy modification. These valuable features imply greater safety, improved therapeutic efficacy, longer duration, and more flexible indications. In recent years, there has been a growing interest in nanocarriers, which has led to significant advancements in the treatment of ocular diseases. Nanocarriers have not only successfully addressed clinical problems that viral vectors have failed to overcome but have also introduced new therapeutic possibilities for certain classical disease types. Nanocarriers offer undeniable advantages over viral vectors. This review discusses the advantages of subretinal (SR) injection, the current status of research, and the research hotspots of gene therapy with viral vectors. It focuses on the latest progress of nanocarriers in SR injection and enumerates the limitations and future perspectives of nanocarriers in the treatment of fundus lesions. Furthermore, this review also covers the research progress of nanocarriers in the field of subretinal injection and highlights the value of nanocarrier-mediated SR injection in the treatment of fundus disorders. Overall, it provides a theoretical basis for the application of nanocarriers in SR injection.

Current developments of gene therapy in human diseases

Gene therapy has witnessed substantial advancements in recent years, becoming a constructive tactic for treating various human diseases. This review presents a comprehensive overview of these developments, with a focus on their diverse applications in different disease contexts. It explores the evolution of gene delivery systems, encompassing viral (like adeno-associated virus; AAV) and nonviral approaches, and evaluates their inherent strengths and limitations. Moreover, the review delves into the progress made in targeting specific tissues and cell types, spanning the eye, liver, muscles, and central nervous system, among others, using these gene technologies. This targeted approach is crucial in addressing a broad spectrum of genetic disorders, such as inherited lysosomal storage diseases, neurodegenerative disorders, and cardiovascular diseases. Recent clinical trials and successful outcomes in gene therapy, particularly those involving AAV and the clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated proteins, are highlighted, illuminating the transformative potentials of this approach in disease treatment. The review summarizes the current status of gene therapy, its prospects, and its capacity to significantly ameliorate patient outcomes and quality of life. By offering comprehensive analysis, this review provides invaluable insights for researchers, clinicians, and stakeholders, enriching the ongoing discourse on the trajectory of disease treatment.

A Photothermal Polymeric Platform for Efficient and Safe Gene Transfection: When Polyethylenimine Collaborates with Indocyanine Green

Gene transfection, defined by the delivery of nucleic acids into cellular compartments, stands as a crucial procedure in gene therapy. While branched polyethylenimine (PEI) is widely regarded as the "gold standard" for nonviral vectors, its cationic nature presents several issues, including nonspecific protein adsorption and notable cytotoxicity. Additionally, it often fails to achieve high transfection efficiency, particularly with hard-to-transfect cell types. To overcome these challenges associated with PEI as a vector for plasmid DNA (pDNA), the photothermal agent indocyanine green (ICG) is integrated with PEI and pDNA to form the PEI/ICG/pDNA (PI/pDNA) complex for more efficient and safer gene transfection. The negatively charged ICG serves a dual purpose: neutralizing PEI's excessive positive charges to reduce cytotoxicity and, under near-infrared irradiation, inducing local heating that enhances cell membrane permeability, thus facilitating the uptake of PI/pDNA complexes to boost transfection efficiency. Using pDNA encoding vascular endothelial growth factor as a model, our system shows enhanced transfection efficiency in vitro for hard-to-transfect endothelial cells, leading to improved cell proliferation and migration. Furthermore, in vivo studies reveal the therapeutic potential of this system in accelerating the healing of infected wounds by promoting angiogenesis and reducing inflammation. This approach offers a straightforward and effective method for gene transfection, showing potentials for tissue engineering and cell-based therapies.

Optogenetics and Targeted Gene Therapy for Retinal Diseases: Unravelling the Fundamentals, Applications, and Future Perspectives

With a common aim of restoring physiological function of defective cells, optogenetics and targeted gene therapies have shown great clinical potential and novelty in the branch of personalized medicine and inherited retinal diseases (IRDs). The basis of optogenetics aims to bypass defective photoreceptors by introducing opsins with light-sensing capabilities. In contrast, targeted gene therapies, such as methods based on CRISPR-Cas9 and RNA interference with noncoding RNAs (i.e., microRNA, small interfering RNA, short hairpin RNA), consists of inducing normal gene or protein expression into affected cells. Having partially leveraged the challenges limiting their prompt introduction into the clinical practice (i.e., engineering, cell or tissue delivery capabilities), it is crucial to deepen the fields of knowledge applied to optogenetics and targeted gene therapy. The aim of this in-depth and novel literature review is to explain the fundamentals and applications of optogenetics and targeted gene therapies, while providing decision-making arguments for ophthalmologists. First, we review the biomolecular principles and engineering steps involved in optogenetics and the targeted gene therapies mentioned above by bringing a focus on the specific vectors and molecules for cell signalization. The importance of vector choice and engineering methods are discussed. Second, we summarize the ongoing clinical trials and most recent discoveries for optogenetics and targeted gene therapies for IRDs. Finally, we then discuss the limits and current challenges of each novel therapy. We aim to provide for the first time scientific-based explanations for clinicians to justify the specificity of each therapy for one disease, which can help improve clinical decision-making tasks.

Treatment avenues for age-related macular degeneration: Breakthroughs and bottlenecks

Age-related macular degeneration (AMD) is a significant factor contributing to serious vision loss in adults above 50. The presence of posterior segment barriers serves as chief roadblocks in the delivery of drugs to treat AMD. The conventional treatment strategies use is limited due to its off-targeted distribution in the eye, shorter drug residence, poor penetration and bioavailability, fatal side effects, etc. The above-mentioned downside necessitates drug delivery using some cutting-edge technology including diverse nanoparticulate systems and microneedles (MNs) which provide the best therapeutic delivery alternative to treat AMD efficiently. Furthermore, cutting-edge treatment modalities including gene therapy and stem cell therapy can control AMD effectively by reducing the boundaries of conventional therapies with a single dose. This review discusses AMD overview, conventional therapies for AMD and their restrictions, repurposed therapeutics and their anti-AMD activity through different mechanisms, and diverse barriers in drug delivery for AMD. Various nanoparticulate-based approaches including polymeric NPs, lipidic NPs, exosomes, active targeted NPs, stimuli-sensitive NPs, cell membrane-coated NPs, inorganic NPs, and MNs are explained. Gene therapy, stem cell therapy, and therapies in clinical trials to treat AMD are also discussed. Further, bottlenecks of cutting-edge (nanoparticulate) technology-based drug delivery are briefed. In a nutshell, cutting-edge technology-based therapies can be an effective way to treat AMD.

Durable transgene expression and efficient re-administration after rAAV2.5T-mediated fCFTRΔR gene delivery to adult ferret lungs

The dosing interval for effective recombinant adeno-associated virus (rAAV)-mediated gene therapy of cystic fibrosis lung disease remains unknown. Here, we assessed the durability of rAAV2.5T-fCFTRΔR-mediated transgene expression and neutralizing antibody (NAb) responses in lungs of adult wild-type ferrets. Within the first 3 months following rAAV2.5T-fCFTRΔR delivery to the lung, CFTRΔR transgene expression declined ∼5.6-fold and then remained stable to 5 months at ∼26% the level of endogenous CFTR. rAAV NAbs in the plasma and bronchoalveolar lavage fluid (BALF) peaked at 21 days, coinciding with peak ELISpot T cell responses to AAV capsid peptides, after which both responses declined and remained stable at 4-5 months post dosing. Administration of reporter vector rAAV2.5T-gLuc (gaussia luciferase) at 5 months following rAAV2.5T-fCFTRΔR dosing gave rise to similar levels of gLuc expression in the BALF as observed in age-matched reporter-only controls, demonstrating that residual BALF NAbs were functionally insignificant. Notably, the second vector administration led to a 2.6-fold greater ELISpot T cell response and ∼2.3-fold decline in fCFTRΔR mRNA and vector genomes derived from the initial rAAV2.5T-fCFTRΔR administration, suggesting selective destruction of transduced cells from the first vector dose. These findings provide insights into humoral and cellular immune response to rAAV that may be useful for optimizing gene therapy to the cystic fibrosis lung.

Fostering the unleashing potential of nanocarriers-mediated delivery of ocular therapeutics

Ocular delivery is the most challenging aspect in the field of pharmaceutical research. The major hurdle for the controlled delivery of drugs to the eye includes the physiological static barriers such as the complex layers of the cornea, sclera and retina which restrict the drug from permeating into the anterior and posterior segments of the eye. Recent years have witnessed inventions in the field of conventional and nanocarrier drug delivery which have shown considerable enhancement in delivering small to large molecules across the eye. The dynamic challenges associated with conventional systems include limited drug contact time and inadequate ocular bioavailability resulting from solution drainage, tear turnover, and dilution or lacrimation. To this end, various bioactive-based nanosized carriers including liposomes, ethosomes, niosomes, dendrimer, nanogel, nanofibers, contact lenses, nanoprobes, selenium nanobells, nanosponge, polymeric micelles, silver nanoparticles, and gold nanoparticles among others have been developed to circumvent the limitations associated with the conventional dosage forms. These nanocarriers have been shown to achieve enhanced drug permeation or retention and prolong drug release in the ocular tissue due to their better tissue adherence. The surface charge and the size of nanocarriers (10-1000 nm) are the important key factors to overcome ocular barriers. Various nanocarriers have been shown to deliver active therapeutic molecules including timolol maleate, ampicillin, natamycin, voriconazole, cyclosporine A, dexamethasone, moxifloxacin, and fluconazole among others for the treatment of anterior and posterior eye diseases. Taken together, in a nutshell, this extensive review provides a comprehensive perspective on the numerous facets of ocular drug delivery with a special focus on bioactive nanocarrier-based approaches, including the difficulties and constraints involved in the fabrication of nanocarriers. This also provides the detailed invention, applications, biodistribution and safety-toxicity of nanocarriers-based therapeutcis for the ophthalmic delivery.

Effective AAV-mediated gene replacement therapy in retinal organoids modeling AIPL1-associated LCA4

Biallelic variations in the aryl hydrocarbon receptor interacting protein-like 1 (AIPL1) gene cause Leber congenital amaurosis subtype 4 (LCA4), an autosomal recessive early-onset severe retinal dystrophy that leads to the rapid degeneration of retinal photoreceptors and the severe impairment of sight within the first few years of life. Currently, there is no treatment or cure for AIPL1-associated LCA4. In this study, we investigated the potential of adeno-associated virus-mediated AIPL1 gene replacement therapy in two previously validated human retinal organoid (RO) models of LCA4. We report here that photoreceptor-specific AIPL1 gene replacement therapy, currently being tested in a first-in-human application, effectively rescued molecular features of AIPL1-associated LCA4 in these models. Notably, the loss of retinal phosphodiesterase 6 was rescued and elevated cyclic guanosine monophosphate (cGMP) levels were reduced following treatment. Transcriptomic analysis of untreated and AAV-transduced ROs revealed transcriptomic changes in response to elevated cGMP levels and viral infection, respectively. Overall, this study supports AIPL1 gene therapy as a promising therapeutic intervention for LCA4.

Gene-edited cells: novel allogeneic gene/cell therapy for epidermolysis bullosa

Epidermolysis bullosa (EB) is a group of rare genetic skin fragility disorders, which are hereditary. These disorders are associated with mutations in at least 16 genes that encode components of the epidermal adhesion complex. Currently, there are no effective treatments for this disorder. All current treatment approaches focus on topical treatments to prevent complications and infections. In recent years, significant progress has been achieved in the treatment of the severe genetic skin blistering condition known as EB through preclinical and clinical advancements. Promising developments have emerged in the areas of protein and cell therapies, such as allogeneic stem cell transplantation; in addition, RNA-based therapies and gene therapy approaches have also become a reality. Stem cells obtained from embryonic or adult tissues, including the skin, are undifferentiated cells with the ability to generate, maintain, and replace fully developed cells and tissues. Recent advancements in preclinical and clinical research have significantly enhanced stem cell therapy, presenting a promising treatment option for various diseases that are not effectively addressed by current medical treatments. Different types of stem cells such as primarily hematopoietic and mesenchymal, obtained from the patient or from a donor, have been utilized to treat severe forms of diseases, each with some beneficial effects. In addition, extensive research has shown that gene transfer methods targeting allogeneic and autologous epidermal stem cells to replace or correct the defective gene are promising. These methods can regenerate and restore the adhesion of primary keratinocytes in EB patients. The long-term treatment of skin lesions in a small number of patients has shown promising results through the transplantation of skin grafts produced from gene-corrected autologous epidermal stem cells. This article attempts to summarize the current situation, potential development prospects, and some of the challenges related to the cell therapy approach for EB treatment.

Nucleic acid delivery to retinal cells using lipopeptides as a potential tool towards ocular gene therapies

We evaluated the use of lipopeptides capable to bind to nucleic acids towards plasmid DNA (pDNA) delivery. The investigations were particularly focused on arising retinal pigment epithelial cells (ARPE-19) as motivated by the considerable number of ocular disorders linked to gene aberrations. The lipopeptides comprised the artificial oligoamino acid succinyl-tetraethylene pentamine (Stp) as well as incorporated lysines, histidines, cysteines, fatty acids, and tyrosine trimers. Regardless of the structural differences, the lipopeptides demonstrated to efficiently condense pDNA at nitrogen-to-phosphate molar ratio (N/P) ≥ 6. Spheric nanoparticles were observed by cryo-TEM and dynamic light scattering determined hydrodynamic sizes ranging from 50 to 130 nm. The biological assays evidenced highly efficient pDNA delivery with a lower degree of cytotoxicity compared to the well-known transfecting agent linear polyethylenimine (LPEI). Although more efficient than LPEI, cysteine-containing carriers were demonstrated to be less efficient than the other counterparts possibly due to exceeding polyplex stabilization via disulfide cross links, which could hamper pDNA unpacking at the target site. Therefore, clearly a balance between complex stability and cargo release should be taken into account to optimize the transfection efficiency of the non-viral vectors. The gene transfer activity in ARPE-19 cells suggests the applicability of this kind of carrier for ocular treatments based on retinal gene delivery.

AAV-Based Strategies for Treatment of Retinal and Choroidal Vascular Diseases: Advances in Age-Related Macular Degeneration and Diabetic Retinopathy Therapies

Age-related macular degeneration (AMD) and diabetic retinopathy (DR) are vascular diseases with high prevalence, ranking among the leading causes of blindness and vision loss worldwide. Despite being effective, current treatments for AMD and DR are burdensome for patients and clinicians, resulting in suboptimal compliance and real risk of vision loss. Thus, there is an unmet need for long-lasting alternatives with improved safety and efficacy. Adeno-associated virus (AAV) is the leading vector for ocular gene delivery, given its ability to enable long-term expression while eliciting relatively mild immune responses. Progress has been made in AAV-based gene therapies for not only inherited retinal diseases but also acquired conditions with preclinical and clinical studies of AMD and DR showing promising results. These studies have explored several pathways involved in the disease pathogenesis, as well as different strategies to optimise gene delivery. These include engineered capsids with enhanced tropism to particular cell types, and expression cassettes incorporating elements for a targeted and controlled expression. Multiple-acting constructs have also been investigated, in addition to gene silencing and editing. Here, we provide an overview of strategies employing AAV-mediated gene delivery to treat AMD and DR. We discuss preclinical efficacy studies and present the latest data from clinical trials for both diseases.

The concept of gene therapy for glaucoma: the dream that has not come true yet

Gene therapies, despite of being a relatively new therapeutic approach, have a potential to become an important alternative to current treatment strategies in glaucoma. Since glaucoma is not considered a single gene disease, the identified goals of gene therapy would be rather to provide neuroprotection of retinal ganglion cells, especially, in intraocular-pressure-independent manner. The most commonly reported type of vector for gene delivery in glaucoma studies is adeno-associated virus serotype 2 that has a high tropism to retinal ganglion cells, resulting in long-term expression and low immunogenic profile. The gene therapy studies recruit inducible and genetic animal models of optic neuropathy, like DBA/2J mice model of high-tension glaucoma and the optic nerve crush-model. Reported gene therapy-based neuroprotection of retinal ganglion cells is targeting specific genes translating to growth factors (i.e., brain derived neurotrophic factor, and its receptor TrkB), regulation of apoptosis and neurodegeneration (i.e., Bcl-xl, Xiap, FAS system, nicotinamide mononucleotide adenylyl transferase 2, Digit3 and Sarm1), immunomodulation (i.e., Crry, C3 complement), modulation of neuroinflammation (i.e., erythropoietin), reduction of excitotoxicity (i.e., CamKIIα) and transcription regulation (i.e., Max, Nrf2). On the other hand, some of gene therapy studies focus on lowering intraocular pressure, by impacting genes involved in both, decreasing aqueous humor production (i.e., aquaporin 1), and increasing outflow facility (i.e., COX2, prostaglandin F2α receptor, RhoA/RhoA kinase signaling pathway, MMP1, Myocilin). The goal of this review is to summarize the current state-of-art and the direction of development of gene therapy strategies for glaucomatous neuropathy.

Prospective approaches to gene therapy computational modeling - spotlight on viral gene therapy

Clinical studies have found there still exists a lack of gene therapy dose-toxicity and dose-efficacy data that causes gene therapy dose selection to remain elusive. Model informed drug development (MIDD) has become a standard tool implemented throughout the discovery, development, and approval of pharmaceutical therapies, and has the potential to inform dose-toxicity and dose-efficacy relationships to support gene therapy dose selection. Despite this potential, MIDD approaches for gene therapy remain immature and require standardization to be useful for gene therapy clinical programs. With the goal to advance MIDD approaches for gene therapy, in this review we first provide an overview of gene therapy types and how they differ from a bioanalytical, formulation, route of administration, and regulatory standpoint. With this biological and regulatory background, we propose how MIDD can be advanced for AAV-based gene therapies by utilizing physiological based pharmacokinetic modeling and quantitative systems pharmacology to holistically inform AAV and target protein dynamics following dosing. We discuss how this proposed model, allowing for in-depth exploration of AAV pharmacology, could be the key the field needs to treat these unmet disease populations.

An optimized HEK293T cell expansion protocol using a hollow-fiber bioreactor system

Viral vectors are commonly used to introduce genetic material into cells to modify cell function for a variety of purposes. Manufacture of those modified viruses may use a variety of cell types to generate high titers of viral particles; one of the most common being HEK293 cells. These cells have been modified into different lines aimed at satisfying specific use cases. HEK293T cells, for example, have been modified to include the SV40 large T antigen. Efficient viral particle production by HEK293T cells requires the maintenance of favorable cell culture conditions during expansion and transfection. This protocol describes the use of the Quantum® hollow-fiber bioreactor (HFB) system for the automated expansion of HEK293T cells, and the results derived using the protocol described herein were not compared with those from tissue culture flasks or other expansion platforms, as the parameters described are unique to Quantum's hollow fiber cell expansion environment. The purpose of this protocol is to help users of Quantum to focus on relevant parameters of expansion in the HFB milieu and to provide guidelines for a successful expansion of HEK293T cells in the Quantum system. The steps provided have been optimized to reliably control environmental factors related to glucose, lactate, and pH. Data reflecting this consistency are provided along with procedural time points reflected in text and figure formats.

A new era in posterior segment ocular drug delivery: Translation of systemic, cell-targeted, dendrimer-based therapies

Vision impairment and loss due to posterior segment ocular disorders, including age-related macular degeneration and diabetic retinopathy, are a rapidly growing cause of disability globally. Current treatments consist primarily of intravitreal injections aimed at preventing disease progression and characterized by high cost and repeated clinic visits. Nanotechnology provides a promising platform for drug delivery to the eye, with potential to overcome anatomical and physiological barriers to provide safe, effective, and sustained treatment modalities. However, there are few nanomedicines approved for posterior segment disorders, and fewer that target specific cells or that are compatible with systemic administration. Targeting cell types that mediate these disorders via systemic administration may unlock transformative opportunities for nanomedicine and significantly improve patient access, acceptability, and outcomes. We highlight the development of hydroxyl polyamidoamine dendrimer-based therapeutics that demonstrate ligand-free cell targeting via systemic administration and are under clinical investigation for treatment of wet age-related macular degeneration.

Emerging Gene Therapy Technologies for Retinal Ganglion Cell Neuroprotection

ABSTRACT

Optic neuropathies encompass a breadth of diseases that ultimately result in dysfunction and/or loss of retinal ganglion cells (RGCs). Although visual impairment from optic neuropathies is common, there is a lack of effective clinical treatments. Addressing a critical need for novel interventions, preclinical studies have been generating a growing body of evidence that identify promising new drug-based and cell-based therapies. Gene therapy is another emerging therapeutic field that offers the potential of specifically and robustly increasing long-term RGC survival in optic neuropathies. Gene therapy offers additional benefits of driving improvements following a single treatment administration, and it can be designed to target a variety of pathways that may be involved in individual optic neuropathies or across multiple etiologies. This review explores the history of gene therapy, the fundamentals of its application, and the emerging development of gene therapy technology as it relates to treatment of optic neuropathies.

Future directions in managing aniridia-associated keratopathy

Congenital aniridia is a panocular disorder that is typically characterized by iris hypoplasia and aniridia-associated keratopathy (AAK). AAK results in the progressive loss of corneal transparency and thereby loss of vision. Currently, there is no approved therapy to delay or prevent its progression, and clinical management is challenging because of phenotypic variability and high risk of complications after interventions; however, new insights into the molecular pathogenesis of AAK may help improve its management. Here, we review the current understanding about the pathogenesis and management of AAK. We highlight the biological mechanisms involved in AAK development with the aim to develop future treatment options, including surgical, pharmacological, cell therapies, and gene therapies.

Insights into adeno-associated virus-based ocular gene therapy: A bibliometric and visual analysis

BACKGROUND

Adeno-associated virus (AAV) plays a vital role in ocular gene therapy and has been widely studied since 1996. This study summarizes and explores the publication outputs and future research trends of AAV-based ocular gene therapy.

METHODS

Publications and data about AAV-based ocular gene therapy were downloaded from the Web of Science Core Collection or ClinicalTrials.gov database. The publications and data were analyzed by Microsoft Excel, CiteSpace, VOS viewer, and a free online platform (http://bibliometric.com).

RESULTS

Totally 832 publications from the Web of Science Core Collection relevant to AAV-based ocular gene therapy were published from 1996 to 2022. These publications were contributed by research institutes from 42 countries or regions. The US contributed the most publications among these countries or regions, notably the University of Florida. Hauswirth WW was the most productive author. "Efficacy" and "safety" are the main focus areas for future research according to the references and keywords analysis. Eighty clinical trials examined AAV-based ocular gene therapy were registered on ClinicalTrials.Gov. Institutes from the US and European did the dominant number or the large proportion of the trials.

CONCLUSIONS

The research focus of the AAV-based ocular gene therapy has transitioned from the study in biological theory to clinical trialing. The AAV-based gene therapy is not limited to inherited retinal diseases but various ocular diseases.

Liposome-polyethylenimine complexes for the effective delivery of HuR siRNA in the treatment of diabetic retinopathy

Diabetic retinopathy (DR) is a vision-impairing complication of diabetes, damaging the retinal microcirculatory system. Overexpression of VEGF (vascular endothelial growth factor) is implicated in the pathogenesis of DR. Human antigen R (HuR) is an RNA-binding protein that favorably regulates VEGF protein expression by binding to VEGF-encoding mRNA. Downregulating HuR via RNA interference strategies using small interfering RNAs (siRNAs) may constitute a novel therapeutic method for preventing VEGF protein overexpression in DR. Delivery of siRNAs to the cellular cytoplasm can be facilitated by cationic peptides or polymers and lipids. In this study, a cationic polymer (polyethylenimine (PEI)) and lipid nanoparticles (liposomes) were co-formulated with siRNA to form lipopolyplexes (LPPs) for the delivery of HuR siRNA. LPPs-siRNA were analyzed for size, zeta potential, serum stability, RNase stability, heparin stability, toxicity, and siRNA encapsulation efficiency. Cellular uptake, downregulation of the target HuR (mRNA and protein), and associated VEGF protein were used to demonstrate the biological efficacy of the LPPs-HuR siRNA, in vitro (human ARPE-19 cells), and in vivo (Wistar rats). In vivo efficacy study was performed by injecting LPPs-HuR siRNA formulations into the eye of streptozotocin (STZ)-induced diabetic rats after the development of retinopathy. Our findings demonstrated that high retinal HuR and VEGF levels observed in the eyes of untreated STZ rats were lowered after LPPs-HuR siRNA administration. Our observations indicate that intravitreal treatment with HuR siRNA is a promising option for DR using LPPs as delivery agents.

Enhanced Biosafety of the Sleeping Beauty Transposon System by Using mRNA as Source of Transposase to Efficiently and Stably Transfect Retinal Pigment Epithelial Cells

Neovascular age-related macular degeneration (nvAMD) is characterized by choroidal neovascularization (CNV), which leads to retinal pigment epithelial (RPE) cell and photoreceptor degeneration and blindness if untreated. Since blood vessel growth is mediated by endothelial cell growth factors, including vascular endothelial growth factor (VEGF), treatment consists of repeated, often monthly, intravitreal injections of anti-angiogenic biopharmaceuticals. Frequent injections are costly and present logistic difficulties; therefore, our laboratories are developing a cell-based gene therapy based on autologous RPE cells transfected ex vivo with the pigment epithelium derived factor (PEDF), which is the most potent natural antagonist of VEGF. Gene delivery and long-term expression of the transgene are enabled by the use of the non-viral Sleeping Beauty (SB100X) transposon system that is introduced into the cells by electroporation. The transposase may have a cytotoxic effect and a low risk of remobilization of the transposon if supplied in the form of DNA. Here, we investigated the use of the SB100X transposase delivered as mRNA and showed that ARPE-19 cells as well as primary human RPE cells were successfully transfected with the Venus or the PEDF gene, followed by stable transgene expression. In human RPE cells, secretion of recombinant PEDF could be detected in cell culture up to one year. Non-viral ex vivo transfection using SB100X-mRNA in combination with electroporation increases the biosafety of our gene therapeutic approach to treat nvAMD while ensuring high transfection efficiency and long-term transgene expression in RPE cells.

Retinal Organoids from an AIPL1 CRISPR/Cas9 Knockout Cell Line Successfully Recapitulate the Molecular Features of LCA4 Disease

Aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1) is expressed in photoreceptors where it facilitates the assembly of phosphodiesterase 6 (PDE6) which hydrolyses cGMP within the phototransduction cascade. Genetic variations in AIPL1 cause type 4 Leber congenital amaurosis (LCA4), which presents as rapid loss of vision in early childhood. Limited in vitro LCA4 models are available, and these rely on patient-derived cells harbouring patient-specific AIPL1 mutations. While valuable, the use and scalability of individual patient-derived LCA4 models may be limited by ethical considerations, access to patient samples and prohibitive costs. To model the functional consequences of patient-independent AIPL1 mutations, CRISPR/Cas9 was implemented to produce an isogenic induced pluripotent stem cell line harbouring a frameshift mutation in the first exon of AIPL1. Retinal organoids were generated using these cells, which retained AIPL1 gene transcription, but AIPL1 protein was undetectable. AIPL1 knockout resulted in a decrease in rod photoreceptor-specific PDE6α and β, and increased cGMP levels, suggesting downstream dysregulation of the phototransduction cascade. The retinal model described here provides a novel platform to assess functional consequences of AIPL1 silencing and measure the rescue of molecular features by potential therapeutic approaches targeting mutation-independent pathogenesis.

Potential therapeutic strategies for photoreceptor degeneration: the path to restore vision

Photoreceptors (PRs), as the most abundant and light-sensing cells of the neuroretina, are responsible for converting light into electrical signals that can be interpreted by the brain. PR degeneration, including morphological and functional impairment of these cells, causes significant diminution of the retina's ability to detect light, with consequent loss of vision. Recent findings in ocular regenerative medicine have opened promising avenues to apply neuroprotective therapy, gene therapy, cell replacement therapy, and visual prostheses to the challenge of restoring vision. However, successful visual restoration in the clinical setting requires application of these therapeutic approaches at the appropriate stage of the retinal degeneration. In this review, firstly, we discuss the mechanisms of PR degeneration by focusing on the molecular mechanisms underlying cell death. Subsequently, innovations, recent developments, and promising treatments based on the stage of disorder progression are further explored. Then, the challenges to be addressed before implementation of these therapies in clinical practice are considered. Finally, potential solutions to overcome the current limitations of this growing research area are suggested. Overall, the majority of current treatment modalities are still at an early stage of development and require extensive additional studies, both pre-clinical and clinical, before full restoration of visual function in PR degeneration diseases can be realized.

Formulation and Evaluation of Polymer-Based Nanoparticles for Intravitreal Gene-Delivery Applications

The advent of the first-ever retinal gene therapy product, involving subretinal administration of a virus-based gene delivery platform, has garnered hope that this state-of-the-art therapeutic modality may benefit a broad spectrum of patients with diverse retinal disorders. On the other hand, clinical studies have revealed limitations of the applied delivery strategy that may restrict its universal use. To this end, intravitreal administration of synthetic gene-delivery platforms, such as polymer-based nanoparticles (PNPs), has emerged as an attractive alternative to the current mainstay. To achieve success, however, it is imperative that synthetic platforms overcome key biological barriers in human eyes encountered following intravitreal administration, including the vitreous gel and inner limiting membrane (ILM). Here, we introduce a series of experiments, from the fabrication of PNPs to a comprehensive evaluation in relevant experimental models, to determine whether PNPs overcome these barriers and efficiently deliver therapeutic gene payloads to retinal cells. We conclude the article by discussing a few important considerations for successful implementation of the strategy. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Preparation and characterization of PNPs Basic Protocol 2: Evaluation of in vitro transfection efficacy Basic Protocol 3: Evaluation of PNP diffusion in vitreous gel Basic Protocol 4: Ex vivo assessment of PNP penetration within vitreoretinal explant culture Basic Protocol 5: Assessment of in vivo transgene expression mediated by intravitreally administered PNPs.

AAV2/9-mediated gene transfer into murine lacrimal gland leads to a long-term targeted tear film modification

Corneal blindness is the fourth leading cause of blindness worldwide. Since corneal epithelium is constantly renewed, non-integrative gene transfer cannot be used to treat corneal diseases. In many of these diseases, the tear film is defective. Tears are a complex biological fluid secreted by the lacrimal apparatus. Their composition is modulated according to the context. After a corneal wound, the lacrimal gland secretes reflex tears, which contain growth factors supporting the wound healing process. In various pathological contexts, the tear composition can support neither corneal homeostasis nor wound healing. Here, we propose to use the lacrimal gland as bioreactor to produce and secrete specific factors supporting corneal physiology. In this study, we use an AAV2/9-mediated gene transfer to supplement the tear film. First, we demonstrate that a single injection of AAV2/9 is sufficient to transduce all epithelial cell types of the lacrimal gland efficiently and widely. Second, we detect no adverse effect after AAV2/9-mediated nerve growth factor expression in the lacrimal gland. Only a transitory increase in tear flow is measured. Remarkably, AAV2/9 induces an important and long-lasting secretion of this growth factor in the tear film. Altogether, our findings provide a new clinically applicable approach to tackle corneal blindness.

Nanomedicine and drug delivery to the retina: current status and implications for gene therapy

Blindness affects more than 60 million people worldwide. Retinal disorders, including age-related macular degeneration (AMD), diabetic retinopathy (DR), and glaucoma, are the leading causes of blindness. Finding means to optimize local and sustained delivery of drugs or genes to the eye and retina is one goal to advance the development of new therapeutics. Despite the ease of accessibility of delivering drugs via the ocular surface, the delivery of drugs to the retina is still challenging due to anatomic and physiologic barriers. Designing a suitable delivery platform to overcome these barriers should enhance drug bioavailability and provide a safe, controlled, and sustained release. Current inventions for posterior segment treatments include intravitreal implants and subretinal viral gene delivery that satisfy these criteria. Several other novel drug delivery technologies, including nanoparticles, micelles, dendrimers, microneedles, liposomes, and nanowires, are now being widely studied for posterior segment drug delivery, and extensive research on gene delivery using siRNA, mRNA, or aptamers is also on the rise. This review discusses the current state of retinal drug/gene delivery and highlights future therapeutic opportunities.

Emerging gene therapy products for RPGR-associated X-linked retinitis pigmentosa

INTRODUCTION

Mutations in the RPGR gene are responsible for one of the most prevalent and severe types of retinitis pigmentosa. Gene therapy has shown great promise to treat inherited retinal diseases, and currently, four RPGR gene therapy vectors are being evaluated in clinical trials.

AREAS COVERED

This manuscript reviews the gene therapy products that are in development for X-linked retinitis pigmentosa caused by mutations in RPGR, and the challenges that scientists and clinicians have faced.

EXPERT OPINION

The development of a gene therapy product for RPGR-associated retinal degeneration has been a great challenge due to the incomplete understanding of the underlying genetics and mechanism of action of RPGR, and on the other hand, due to the instability of the RPGR gene. Three of the four gene therapy vectors currently in clinical trials include a codon-optimized version of the human RPGR sequence, and the other vector contains a shortened version of the human RPGR. To date, the only Phase I/II results published in a peer-reviewed journal demonstrate a good safety profile and an improvement in the visual field using a codon optimized version of RPGRORF15.

Therapeutic Approaches for Age-Related Macular Degeneration

Damage to the retinal pigment epithelium, Bruch's membrane and/or tissues underlying macula is known to increase the risk of age-related macular degeneration (AMD). AMD is commonly categorized in two distinct types, namely, the nonexudative (dry form) and the exudative (wet form). Currently, there is no ideal treatment available for AMD. Recommended standard treatments are based on the use of vascular endothelial growth factor (VEGF), with the disadvantage of requiring repeated intravitreal injections which hinder patient's compliance to the therapy. In recent years, several synthetic and natural active compounds have been proposed as innovative therapeutic strategies against this disease. There is a growing interest in the development of formulations based on nanotechnology because of its important role in the management of posterior eye segment disorders, without the use of intravitreal injections, and furthermore, with the potential to prolong drug release and thus reduce adverse effects. In the same way, 3D bioprinting constitutes an alternative to regeneration therapies for the human retina to restore its functions. The application of 3D bioprinting may change the current and future perspectives of the treatment of patients with AMD, especially those who do not respond to conventional treatment. To monitor the progress of AMD treatment and disease, retinal images are used. In this work, we revised the recent challenges encountered in the treatment of different forms of AMD, innovative nanoformulations, 3D bioprinting, and techniques to monitor the progress.

Minicircle Delivery to the Neural Retina as a Gene Therapy Approach

Non-viral gene therapy has the potential to overcome several shortcomings in viral vector-based therapeutics. Methods of in vivo plasmid delivery have developed over recent years to increase the efficiency of non-viral gene transfer, yet further improvements still need to be made to improve their translational capacity. Gene therapy advances for inherited retinal disease have been particularly prominent over the recent decade but overcoming physical and physiological barriers present in the eye remains a key obstacle in the field of non-viral ocular drug delivery. Minicircles are circular double-stranded DNA vectors that contain expression cassettes devoid of bacterial DNA, thereby limiting the risks of innate immune responses induced by such elements. To date, they have not been extensively used in pre-clinical studies yet remain a viable vector option for the treatment of inherited retinal disease. Here, we explore the potential of minicircle DNA delivery to the neural retina as a gene therapy approach. We consider the advantages of minicircles as gene therapy vectors as well as review the challenges involved in optimising their delivery to the neural retina.

Advancing precision medicines for ocular disorders: Diagnostic genomics to tailored therapies

Successful sequencing of the human genome and evolving functional knowledge of gene products has taken genomic medicine to the forefront, soon combining broadly with traditional diagnostics, therapeutics, and prognostics in patients. Recent years have witnessed an extraordinary leap in our understanding of ocular diseases and their respective genetic underpinnings. As we are entering the age of genomic medicine, rapid advances in genome sequencing, gene delivery, genome surgery, and computational genomics enable an ever-increasing capacity to provide a precise and robust diagnosis of diseases and the development of targeted treatment strategies. Inherited retinal diseases are a major source of blindness around the world where a large number of causative genes have been identified, paving the way for personalized diagnostics in the clinic. Developments in functional genetics and gene transfer techniques has also led to the first FDA approval of gene therapy for LCA, a childhood blindness. Many such retinal diseases are the focus of various clinical trials, making clinical diagnoses of retinal diseases, their underlying genetics and the studies of natural history important. Here, we review methodologies for identifying new genes and variants associated with various ocular disorders and the complexities associated with them. Thereafter we discuss briefly, various retinal diseases and the application of genomic technologies in their diagnosis. We also discuss the strategies, challenges, and potential of gene therapy for the treatment of inherited and acquired retinal diseases. Additionally, we discuss the translational aspects of gene therapy, the important vector types and considerations for human trials that may help advance personalized therapeutics in ophthalmology. Retinal disease research has led the application of precision diagnostics and precision therapies; therefore, this review provides a general understanding of the current status of precision medicine in ophthalmology.

Emerging Gene Manipulation Strategies for the Treatment of Monogenic Eye Disease

Genetic eye diseases, representing a wide spectrum of simple and complex conditions, are one of the leading causes of visual loss in children and working adults, and progress in the field has led to changes in disease investigation, diagnosis, and management. The past 15 years have seen the emergence of novel therapies for these previously untreatable conditions to the extent that we now have a licensed therapy for one form of genetic eye disease and many more in clinical trial. This is a systematic review of published and ongoing clinical trials of gene therapies for monogenic eye diseases. Databases of clinical trials and the published literature were searched for interventional studies of gene therapies for eye diseases. Standard methodological procedures were used to assess the relevance of search results. A total of 59 registered clinical trials are referenced, showing the significant level of interest in the potential for translation of these therapies from bench to bedside. The breadth of therapy design is encouraging, providing multiple possible therapeutic mechanisms. Some fundamental questions regarding gene therapy for genetic eye diseases remain, such as optimal dosing, the relative benefits of adeno-associated virus (AAV)-packaging and the potential for a significant inflammatory response to the therapy itself. As a result, despite the promise of the eye as a target, it has proven difficult to deliver clinically effective gene therapies to the eye. Despite setbacks, the licensing of Luxturna (voretigene neparvovec, Novartis) for the treatment of RPE65-mediated Leber congenital amaurosis (LCA) is a major advance in efforts to treat these rare, but devastating, causes of visual loss.

Pigment epithelium-derived factor engineered to increase glycosaminoglycan affinity while maintaining bioactivity

Pigment epithelium-derived factor (PEDF) is a secreted protein that is essential in tissue homeostasis and is involved in multiple functions in the eye, such as antiangiogenesis and neuroprotection. However, short retention in the retinal microenvironment can limit its therapeutic effects. In this study, we modified the amino acid sequence of PEDF to increase its affinity for heparin and hyaluronic acid (HA), which are negatively charged extracellular matrix (ECM) molecules. HA is the major component of the vitreous humor. We selectively converted neutral or anionic residues into cationic residues to obtain engineered PEDF (ePEDF). Using in vitro binding assays, we demonstrate that ePEDF had higher affinity for heparin and HA than wild-type PEDF (wtPEDF). ePEDF exhibited antiangiogenic and retinal survival bioactivities. It inhibited endothelial cell proliferation and tube formation in vitro. In an ex vivo model mimicking retinal degeneration, ePEDF protected photoreceptors from cell death. The findings suggest that protein engineering is an approach to develop active PEDF with higher ECM affinity to potentially improve its retention in the retina microenvironment and in turn make it a more efficient therapeutic drug for retinal diseases.

Ocular Barriers and Their Influence on Gene Therapy Products Delivery

The eye is formed by tissues and cavities that contain liquids whose compositions are highly regulated to ensure their optical properties and their immune and metabolic functions. The integrity of the ocular barriers, composed of different elements that work in a coordinated fashion, is essential to maintain the ocular homeostasis. Specialized junctions between the cells of different tissues have specific features which guarantee sealing properties and selectively control the passage of drugs from the circulation or the outside into the tissues and within the different ocular compartments. Tissues structure also constitute selective obstacles and pathways for various molecules. Specific transporters control the passage of water, ions, and macromolecules, whilst efflux pumps reject and eliminate toxins, metabolites, or drugs. Ocular barriers, thus, limit the bioavailability of gene therapy products in ocular tissues and cells depending on the route chosen for their administration. On the other hand, ocular barriers allow a real local treatment, with limited systemic side-effects. Understanding the different barriers that limit the accessibility of different types of gene therapy products to the different target cells is a prerequisite for the development of efficient gene delivery systems. This review summarizes actual knowledge on the different ocular barriers that limit the penetration and distribution of gene therapy products using different routes of administration, and it provides a general overview of various methods used to bypass the ocular barriers.

Novel and investigational therapies for wet and dry age-related macular degeneration

Age-related macular degeneration (AMD) is a macular degenerative eye disease, the major cause of irreversible loss of central vision. In this review, we highlight current progress and future perspectives of novel and investigational therapeutic strategies in the drug pipeline, including anti-vascular endothelial growth factor (VEGF) agents, bispecific antibodies, biosimilars, small molecules, gene therapy, and long-acting drug delivery strategies for both dry and wet AMD. We anticipate that biologics with dual functionalities and combined therapies with long-acting capabilities will lead the wet AMD pipeline. Sustained-release platforms also show potential. However, significant breakthroughs are yet to be made for dry AMD. The personalized approach might be well suited in the scenario of diverse genetic variations in both conditions. Teaser: AMD is the leading cause of global blindness in the developed world. This article highlights investigational therapeutics, such as antibodies, Bi-specifics, small molecules, biosimilars, gene therapy and long-acting strategies (Port Delivery System), for this condition.

Strategies for improving the safety and RNAi efficacy of noncovalent peptide/siRNA nanocomplexes

In the past decades, the striking development of cationic polypeptides and cell-penetrating peptides (CPPs) tailored for small interfering RNA (siRNA) delivery has been fuelled by the conception of nuclear acid therapy and precision medicine. Owing to their amino acid compositions, inherent secondary structures as well as diverse geometrical shapes, peptides or peptide-containing polymers exhibit good biodegradability, high flexibility, and bio-functional diversity as nonviral siRNA vectors. Also, a variety of noncovalent nanocomplexes could be built via self-assembling and electrostatic interactions between cationic peptides and siRNAs. Although the peptide/siRNA nanocomplex-based RNAi therapies, STP705 and MIR-19, are under clinical trials, a guideline addressing the current bottlenecks of peptide/siRNA nanocomplex delivery is in high demand for future research and development. In this review, we present strategies for improving the safety and RNAi efficacy of noncovalent peptide/siRNA nanocomplexes in the treatment of genetic disorders. Through thorough analysis of those RNAi formulations using different delivery strategies, we seek to shed light on the rationale of peptide design and modification in constructing robust siRNA delivery systems, including targeted and co-delivery systems. Based on this, we provide a timely and comprehensive understanding of how to engineer biocompatible and efficient peptide-based siRNA vectors.

Challenges to Gene Editing Approaches in the Retina

Retinal gene therapy has recently been at the cutting edge of clinical development in the diverse field of genetic therapies. The retina is an attractive target for genetic therapies such as gene editing due to the distinctive anatomical and immunological features of the eye, known as immune privilege, so that inherited retinal diseases (IRDs) have been studied in several clinical studies. Thus, rapid strides are being made toward developing targeted treatments for IRDs. Gene editing in the retina faces a group of heterogenous challenges, including editing efficiencies, off-target effects, the anatomy of the target organ, immune responses, inactivation, and identifying optimal application methods. As clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated nuclease (Cas) based technologies are at the forefront of current gene editing advances, their specific editing efficiency challenges and potential off-target effects were assessed. The immune privilege of the eye reduces the likelihood of systemic immune responses following retinal gene therapy, but possible immune responses must not be discounted. Immune responses to gene editing in the retina may be humoral or cell mediated, with immunologically active cells, including microglia, implicated in facilitating possible immune responses to gene editing. Immunogenicity of gene therapeutics may also lead to the inactivation of edited cells, reducing potential therapeutic benefits. This review outlines the broad spectrum of potential challenges currently facing retinal gene editing, with the goal of facilitating further advances in the safety and efficacy of gene editing therapies.

Neovascular Age-Related Macular Degeneration (nAMD): A Review of Emerging Treatment Options

Neovascular age-related macular degeneration (nAMD) is a common world-wide cause of visual loss. Intravitreal anti-vascular endothelial growth factor (anti-VEGF) agents are an effective means to treat nAMD and reduce its impact on vision compared to either sham treatment or photodynamic therapy. Currently, the approved anti-VEGF drugs include ranibizumab, aflibercept and brolucizumab. In addition, bevacizumab, used as an off-label drug, and has been shown to be effective in treating nAMD. While anti-VEGF agents are effective, its limitations include the requirement for frequent, often monthly injections, and the need for long-term treatment of nAMD. These present significant burdens on the healthcare system and on the patients. In addition, reviews of patients with nAMD treated with anti-VEGF have reported deterioration of vision over time with progression of geographic atrophy. These limitations are partly addressed by exploring different treatment regimens that reduce the frequency of treatments. Newer anti-VEGF drugs have been shown in Phase III clinical trials to have injection intervals as long as 12 or even 16 weeks for a proportion of patients. There is research on newer drugs that affect other pathways, such as the angiopoietin pathway, which may impact nAMD by extending the treatment interval and reducing the burden of treatment. Other measures include the use of sustained-release implants that release the drug regularly over a period of time, and can be refilled periodically, as well as hydrogel platforms that serve to release the drug. The use of biosimilars will also serve to reduce the cost of treatment for nAMD. A new frontier of gene therapy, primarily targeting genes involved in the transduction of retinal cells to produce anti-VEGF proteins intraocularly, also opens a new avenue of therapeutic approaches that can be used for treatment. This review paper will discuss both current treatment options and the newer treatments under development.

A Photothermal Nanoplatform with Sugar-Triggered Cleaning Ability for High-Efficiency Intracellular Delivery

Intracellular delivery of functional molecules is of great importance in various biomedical and biotechnology applications. Recently, nanoparticle-based photothermal poration has attracted increasing attention because it provided a facile and efficient method to permeabilize cells transiently, facilitating the entry of exogenous molecules into cells. However, this method still has some safety concerns associated with the nanoparticles that bind to the cell membranes or enter the cells. Herein, a nanoplatform with both photothermal property and sugar-triggered cleaning ability for intracellular delivery is developed based on phenylboronic acid (PBA) functionalized porous magnetic nanoparticles (named as M-PBA). The M-PBA particles could bind to the target cells effectively through the specific interactions between PBA groups and the cis-diol containing components on the cell membrane. During a short-term near-infrared irradiation, the bound particles convert absorbed light energy to heat, enabling high-efficiency delivery of various exogenous molecules into the target cells via a photothermal poration mechanism. After delivery, the bound particles could be easily "cleaned" from the cell surface via mild sugar-treatment and collected by a magnet, avoiding the possible side effects caused by the entrance of particles or their fragments. The delivery and cleaning process is short and effective without compromising the viability and proliferation ability of the cells with delivered molecules, suggesting that the M-PBA particles could be used as promising intracellular delivery agents with a unique combination of efficiency, safety, and flexibility.

Novel therapies for proliferative retinopathies

Proliferative retinopathies, such as neovascular age–related macular degeneration and proliferative diabetic retinopathy, are a special health issue due to their contribution to irreversible blindness. Although the promoting conditions and physiopathology of proliferative retinopathies are different, these feature a highly detrimental angiogenesis driven by the overproduction of vascular endothelial growth factor (VEGF). This article describes the mechanism of action of ocular antiangiogenic therapies currently found in clinical development. Systems classify accordingly as (a) novel anti-VEGF systems, (b) molecules targeting non-VEGF pathways, and (c) gene therapies. Whereas most therapies are designed to neutralize VEGF, there is a significant set of products with diverse complexity and mechanism of action. Anti-VEGF therapies are still the most studied approach to tackle angiogenesis. Therapies targeting non-VEGF pathways, however, are highlighted because they could be an option for patients nonresponsive to anti-VEGF therapies. Finally, gene therapy is a promissory technology platform but still is subject to demonstrate safety and efficacy.

Co-grafts of Human Embryonic Stem Cell Derived Retina Organoids and Retinal Pigment Epithelium for Retinal Reconstruction in Immunodeficient Retinal Degenerate Royal College of Surgeons Rats

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.

Molecular Therapy for Choroideremia: Pre-clinical and Clinical Progress to Date

Choroideremia is an inherited retinal disease characterised by a degeneration of the light-sensing photoreceptors, supporting retinal pigment epithelium and underlying choroid. Patients present with the same symptoms as those with classic rod-cone dystrophy: (1) night blindness early in life; (2) progressive peripheral visual field loss, and (3) central vision decline with a slow progression to legal blindness. Choroideremia is monogenic and caused by mutations in CHM. Eight clinical trials (three phase 1/2, four phase 2, and one phase 3) have started (four of which are already finished) to evaluate the therapeutic efficacy of gene supplementation mediated by subretinal delivery of an adeno-associated virus serotype 2 (AAV2/2) vector expressing CHM. Furthermore, one phase 1 clinical trial has been initiated to evaluate the efficiency of a novel AAV variant to deliver CHM to the outer retina following intravitreal delivery. Lastly, a non-viral-mediated CHM replacement strategy is currently under development, which could lead to a future clinical trial. Here, we summarise the rationale behind these various studies, as well as any results published to date. The diversity of these trials currently places choroideremia at the forefront of the retinal gene therapy field. As a consequence, the trial outcomes, regardless of the results, have the potential to change the landscape of gene supplementation for inherited retinal diseases.

Visualizing spatial differences in corneal electroretinogram potentials using a three-dimensional surface spline

Objective. The spatial distribution of activity at the retina determines the spatial distribution of electroretinogram potentials at the cornea. Here a three-dimensional surface spline method is evaluated for interpolating corneal potentials between measurement points in multi-electrode electroretinography (meERG) data sets.Approach. 25-channel meERG responses were obtained from rat eyes before and after treatment to create local lesions. A 3rd order surface spline was used to interpolate meERG values resulting in smooth color-coded maps of corneal potentials. Potential maps were normalized using standard score values. Pre- and post-treatment responses were characterized by spatial standard deviation and by difference-from-normal plots.Main results. The spatial standard deviation for eyes with local lesions were significantly higher than for healthy eyes. The 3rd order spline resulted in well-behaved corneal potential maps that maintained low error rate when up to 30% of recording channels were excluded from analysis. Post-normalization, responses could be combined within experimental groups, and individual eyes with lesions were clearly distinguished from the healthy-eye mean response. A 3rd order surface spline is an acceptable means of interpolating meERG potentials to create corneal potential maps. The spatial standard deviation is more sensitive to local dysfunction than absolute amplitudes.Significance. This work demonstrates solutions to key challenges in the recording and analysis of meERG responses: visualization, normalization, channel loss, and identification of abnormal responses. Continued development of the meERG technique is relevant to research and clinical applications, especially where local dysfunction (early progressive disease) or local therapeutic effect (subretinal injection) is of interest.

An Optimized Treatment Protocol for Subretinal Injections Limits Intravitreal Vector Distribution

Purpose

Subretinal injections (SRis) are commonly used in retinal gene therapy procedures to deliver adeno-associated virus (AAV) to photoreceptors and retinal pigment epithelial cells. We present an optimized surgical protocol to minimize off-target application of AAV in the vitreous, which in turn reduces the risk of extensive biodistribution and inflammation, ultimately leading to enhanced safety of the therapy.

Design

Experimental animal research study.

Participants

Eight cynomolgus monkeys (Macaca fascicularis).

Methods

Subretinal injections with an AAV2/8 vector were performed. The animals were allocated to 2 different vector dose groups (1×10^ˆ11 and 5×10^ˆ11 viral genomes [vg]). Samples of intravitreal fluid were taken at the end of the SRi procedure and again after a 3-minute lavage (wash-out) with balanced salt solution (BSS).

Main Outcome Measures

Intravitreal vector genome copies were analyzed with quantitative polymerase chain reaction and compared between groups.

Results

Even uneventful SRi leads to dissemination of millions of AAV particles (0.1–0.7% of viral vector loading dose) into the vitreous cavity. Three minutes of lavage led to a substantial decrease (on average 96%) of intravitreal vector load.

Conclusions

Multiple studies have shown that the intravitreal space is not as immune privileged as the subretinal space. Intravitreal AAV particles disseminate into the bloodstream, lead to increased biodistribution into lymphatic tissue, and help to stage an immune response with implications for both safety and efficacy. Therefore, minimizing off-target vector application after reflux of vector from the subretinal space is of significant interest. We show that a simple lavage of intravitreal fluid efficiently decreases the intravitreal vector load. Such a step should be considered when performing subretinal gene therapy.

The future of retinal gene therapy: evolving from subretinal to intravitreal vector delivery

Inherited retinal degenerations are a leading and untreatbale cause of blindness, and as such they are targets for gene therapy. Numerous gene therapy treatments have progressed from laboratory research to clinical trails, and a pioneering gene therapy received the first ever FDA approval for treating patients. However, currently retinal gene therapy mostly involves subretinal injection of the therapeutic agent, which treats a limited area, entails retinal detachment and other potential complications, and requires general anesthesia with consequent risks, costs and prolonged recovery. Therefore there is great impetus to develop safer, less invasive and cheapter methods of gene delivery. A promising method is intravitreal injection, that does not cause retinal detachment, can lead to pan-retinal transduction and can be performed under local anesthesia in out-patient clinics. Intravitreally-injected vectors face several obstacles. First, the vector is diluted by the vitreous and has to overcome a long diffusion distance to the target cells. Second, the vector is exposed to the host's immune response, risking neutralization by pre-existing antibodies and triggering a stronger immune response to the injection. Third, the vector has to cross the inner limiting membrane which is both a physical and a biological barrier as it contains binding sites that could cause the vector's sequestration. Finally, in the target cell the vector is prone to proteasome degradation before delivering the transgene to the nucleus. Strategies to overcome these obstacles include modifications of the viral capsid, through rational design or directed evolution, which allow resistance to the immune system, enhancement of penetration through the inner limiting membrane or reduced degradation by intracellular proteasomes. Furthermore, physical and chemical manipulations of the inner limiting membrane and vitreous aim to improve vector penetration. Finally, compact non-viral vectors that can overcome the immunological, physical and anatomical and barriers have been developed. This paper reviews ongoing efforts to develop novel, safe and efficacious methods for intravitreal delivery of therapeutic genes for inherited retinal degenerations. To date, the most promising results are achieved in rodents with robust, pan-retinal transduction following intravitreal delivery. Trials in larger animal models demonstrate transduction mostly of inner retinal layers. Despite ongoing efforts, currently no intravitreally-injected vector has demonstrated outer retinal transduction efficacy comparable to that of subretinal delivery. Further work is warranted to test promising new viral and non-viral vectors on large animal models of inherited retinal degenerations. Positive results will pave the way to development of the next generation of treatments for inherited retinal degeneration.

Complement Inhibitors in Age-Related Macular Degeneration: A Potential Therapeutic Option

Age-related macular degeneration (AMD) is a multifactorial disease, which can culminate in irreversible vision loss and blindness in elderly. Nowadays, there is a big gap between dry AMD and wet AMD on treatment. Accounting for nearly 90% of AMD, dry AMD still lacks effective treatment. Numerous genetic and molecular researches have confirmed the significant role of the complement system in the pathogenesis of AMD, leading to a deeper exploration of complement inhibitors in the treatment of AMD. To date, at least 14 different complement inhibitors have been or are being explored in AMD in almost 40 clinical trials. While most complement inhibitors fail to treat AMD successfully, two of them are effective in inhibiting the rate of GA progression in phase II clinical trials, and both of them successfully entered phase III trials. Furthermore, recently emerging complement gene therapy and combination therapy also offer new opportunities to treat AMD in the future. In this review, we aim to introduce genetic and molecular associations between the complement system and AMD, provide the updated progress in complement inhibitors in AMD on clinical trials, and discuss the challenges and prospects of complement therapeutic strategies in AMD.