Surgical Technique for Subretinal Gene Therapy in Humans with Inherited Retinal Degeneration

Longitudinal Imaging of the Parafoveal Cone Mosaic in Congenital Achromatopsia

Purpose

To assess longitudinal changes in parafoveal cone density in individuals with congenital achromatopsia (ACHM).

Design

Retrospective longitudinal study.

Participants

Nineteen individuals (7 women and 12 men) with genetically confirmed ACHM. To be eligible, each had adaptive optics scanning light ophthalmoscope (AOSLO) images of the photoreceptor mosaic from ≥2 time points.

Methods

For each individual, follow-up AOSLO montages were aligned to their baseline montage. Notably, 100 × 100 μm regions of interest (ROIs) were extracted from the split-detection modality at locations 1°, 5°, and 10° temporal (T) from the peak cone density in each montage. All ROIs from follow-up visits were then manually aligned to their respective baseline ROI for that location. Cones were identified in each ROI by one observer, reviewed by a second observer, and confirmed together in a masked fashion. Cone density was calculated, and a linear mixed model was used to assess changes in density over time. A Wald test was performed to determine if the cone density changes were statistically significant.

Main Outcome Measures

Parafoveal cone spacing (at 1°, 5°, and 10° T) as a function of time.

Results

The mean (± standard deviation [SD]) age at baseline was 21.6 ± 10.7 years and the mean (±SD) follow-up period was 3.83 ± 2.93 years (range, 0.46-8.66 years). At 1° T, we observed a significant decrease of 352 cones/mm2 per year (P = 0.0003). At 5° T, the linear mixed model showed a nonstatistically significant decrease of 58 cones/mm2 per year (P = 0.504). At 10° T, we observed a significant decrease of 139 cones/mm2 per year (P = 0.0188). For a 100 × 100 μm ROI, these density changes correspond to a reduction of between about 0.5 and 4 cones per year, depending on the location.

Conclusions

Parafoveal cone density estimates in ACHM show a small decrease over time. These observed changes are within the previously reported longitudinal repeatability values for normal retinas, suggesting the observed average cone loss may not be clinically meaningful. Further studies with longer follow-up times and more genetically heterogeneous and age-diverse populations are needed to better understand factors contributing to changes in foveal and parafoveal cone structure in ACHM over time.

Financial Disclosures

Proprietary or commercial disclosures may be found in the Footnotes and Disclosures at the end of this article.

The 1-Step Versus 2-Step Subretinal Injection Trial (1,2-SIT)-A Randomized Controlled Trial to Compare Drug Reflux Following Subretinal Injection

PURPOSE

To estimate in humans, in vivo, drug retention in the subretinal space following either 1- or 2-step subretinal injection (SRI).

DESIGN

A single-masked, randomized, controlled trial.

METHODS

Patients presenting with submacular hemorrhage secondary to age-related macular degeneration were randomly allocated to receive subretinal tissue plasminogen activator (50 µg in 0.1 mL) with sodium fluorescein (10 µg in 0.1 mL) as an optical label either as a 1-step (n = 6) procedure, in which the drug defines the subretinal space, or as a 2-step (n = 6) procedure, in which balanced salt solution is first used to define the subretinal space, following pars plana vitrectomy. All patients underwent air-for-fluid exchange at the completion of surgery with subsequent 20% sulfahexafluoride gas and bevacizumab injection. Reflux of subretinally injected drug was calculated by performing fluorophotometry on the fluid collected at the end of air-for-fluid exchange. Patients received intravitreal anti-VEGF at 4-weekly intervals to the final follow-up at 12 weeks. The primary outcome measure was the proportion of drug reflux. Secondary outcomes included duration of surgery, change in visual acuity (VA), final VA, final foveal thickness, and change in foveal thickness. To determine our fluorophotometric technique's applicability to gene and cell therapy, real-time quantitative polymerase chain reaction was employed to determine adeno-associated viral (AAV) yields following exposure to 0.1 mg/mL sodium fluorescein and its effects on retinal progenitor cells (RPCs) was assessed using a cell viability assay.

RESULTS

Mean reflux was 4.8% ± 3.1% (mean ± SEM, range 0.4%-19.5%) for 1-step SRI and 3.9% ± 0.9% (range 1.7%-5.3%) for 2-step SRI (no significant difference in means; P = .0155 for the difference in variance). There was no significant difference in the duration of surgery (26.8 ± 1.2 minutes vs 30 ± 2.7 minutes), final VA (1.1 ± 0.26 [Snellen 20/252] vs 1.1 ± 0.32 [Snellen 20/252] logMAR), change in BCVA (-0.45 ± 0.27 vs -0.27 ± 0.23 logMAR) or foveal thickness (139.2 ± 33.2 µm vs 129.8 ± 21.1 µm). Quantitative polymerase chain reaction confirmed that AAV titers are not affected by 0.1 mg/mL sodium fluorescein in vitro, and viability assays suggest that it does not adversely affect RPC viability.

CONCLUSIONS

This study demonstrates that drug loss following SRI ranged from 0.4% to 19.8% (mean 4.3%). There is no significant difference between 1-step and 2-step SRI in the mean proportion of drug reflux, duration of surgery, change in neural retinal thickness, or change in BCVA. However, there is a significantly greater variability in reflux for 1-step injection compared to 2-step injection. AAV yields are not affected by 0.1 mg/mL sodium fluorescein, nor is RPC viability. These data suggest that sodium fluorescein may be an appropriate means of tracking subretinal AAV gene therapy and retinal cell therapy quantitatively and that the 2-step SRI approach is preferable to 1-step SRI to ensure consistency in drug delivery.

Optical coherence tomography for noninvasive monitoring of drug delivery

Optical Coherence Tomography (OCT) has revolutionized various medical imaging and diagnostics fields, offering unprecedented insights into the microstructural compositions of biological tissues. In recent years, OCT applications have been extended to noninvasive drug delivery monitoring, which is a critical aspect of many therapeutic procedures and pharmacokinetic studies. Such an extension is strongly enhanced by the inherent combination with 3D anatomical images provided by OCT. This review presents an overview of the principles of OCT technology, its functional extensions for drug delivery systems, and its advancements in monitoring therapeutic interventions. We discuss its advantages over traditional imaging modalities in terms of spatial resolution, depth penetration, and real-time capabilities. The paper highlights significant studies that have utilized OCT for the visualization and quantification of drug delivery processes, including the diffusion of injectable formulations in ocular tissues and the permeation of topical drugs through the skin. In the review, we focused on the latest OCT applications, including OCT-guided drug injection, topical drug delivery monitoring, application of OCT in inhaled drug delivery systems, and the integration of OCT with other imaging modalities.

Gene Therapy-Associated Uveitis (GTAU): Understanding and mitigating the adverse immune response in retinal gene therapy

Retinal gene therapy using adeno-associated viral (AAV) vectors has been a groundbreaking step-change in the treatment of inherited retinal diseases (IRDs) and could also be used to treat more common retinal diseases such as age-related macular degeneration and diabetic retinopathy. The delivery and expression of therapeutic transgenes in the eye is limited by innate and adaptive immune responses against components of the vector product, which has been termed gene therapy-associated uveitis (GTAU). This is clinically important as intraocular inflammation could lead to irreversible loss of retinal cells, deterioration of visual function and reduced durability of treatment effect associated with a costly one-off treatment. For retinal gene therapy to achieve an improved efficacy and safety profile for treating additional IRDs and more common diseases, the risk of GTAU must be minimised. We have collated insights from pre-clinical research, clinical trials, and the real-world implementation of AAV-mediated retinal gene therapy to help understand the risk factors for GTAU. We draw attention to an emerging framework, which includes patient demographics, vector construct, vector dose, route of administration, and choice of immunosuppression regime. Importantly, we consider efforts to date and potential future strategies to mitigate the adverse immune response across each of these domains. We advocate for more targeted immunomodulatory approaches to the prevention and treatment of GTAU based on better understanding of the underlying immune response.

Techniques for subretinal injections in animals

Subretinal injections are not commonly performed during clinical treatment of animals but are frequently used in laboratory animal models to assess therapeutic efficacy and safety of gene and cell therapy products. Veterinary ophthalmologists are often employed to perform the injections in the laboratory animal setting, due to knowledge of comparative ocular anatomy between species and familiarity with operating on non-human eyes. Understanding the different approaches used for subretinal injection in each species and potential complications that may be encountered is vital to achieving successful and reproducible results. This manuscript provides a summary of different approaches to subretinal injections in the most common animal model species, along with information from published literature and experience of the authors to educate novice or experienced surgeons tasked with performing these injections for the first time.

The Perspective of Using Optical Coherence Tomography in Ophthalmology: Present and Future Applications

Optical coherence tomography (OCT) imaging plays a major role in the field of diagnosing, monitoring, and treating ophthalmological diseases. Since its introduction in the early 1990s, OCT technology has continued to advance both in the direction of acquisition quality and technique. In this manuscript, we concentrate on actual and future applications of OCT in the ophthalmology field, reviewing multiple types of OCT techniques and systems, such as visible-light OCT, adaptative optics OCT, intraoperative OCT, wide-field OCT, and more. All of them allow better monitoring of ocular diseases, earlier and broader diagnosis, and a more suitable treatment. Furthermore, overviewing all these technologies could play a pivotal role in research, leading to an advance in understanding the pathophysiology of targeted diseases. Finally, the aim of the present review was to evaluate the technical advances in OCT and their actual and potential clinical applications.

Evaluation of subretinally delivered Cas9 ribonucleoproteins in murine and porcine animal models highlights key considerations for therapeutic translation of genetic medicines

Genetic medicines, including CRISPR/Cas technologies, extend tremendous promise for addressing unmet medical need in inherited retinal disorders and other indications; however, there remain challenges for the development of therapeutics. Herein, we evaluate genome editing by engineered Cas9 ribonucleoproteins (eRNP) in vivo via subretinal administration using mouse and pig animal models. Subretinal administration of adenine base editor and double strand break-inducing Cas9 nuclease eRNPs mediate genome editing in both species. Editing occurs in retinal pigmented epithelium (RPE) and photoreceptor cells, with favorable tolerability in both species. Using transgenic reporter strains, we determine that editing primarily occurs close to the site of administration, within the bleb region associated with subretinal injection. Our results show that subretinal administration of eRNPs in mice mediates base editing of up to 12% of the total neural retina, with an average rate of 7% observed at the highest dose tested. In contrast, a substantially lower editing efficiency was observed in minipigs; even with direct quantification of only the treated region, a maximum base editing rate of 1.5%, with an average rate of <1%, was observed. Our data highlight the importance of species consideration in translational studies for genetic medicines targeting the eye and provide an example of a lack of translation between small and larger animal models in the context of subretinal administration of Cas9 eRNPs.

Novel Therapies for Inherited Retinal Dystrophies

With the approval of the first retinal gene therapy, voretigene neparvovec [...].

Development of a novel SupraChoroidal-to-Optic-NervE (SCONE) drug delivery system

PURPOSE

Targeted drug delivery to the optic nerve head may be useful in the preclinical study and later clinical management of optic neuropathies, however, there are no FDA-approved drug delivery systems to achieve this. The purpose of this work was to develop an optic nerve head drug delivery technique.

METHODS

Different strategies to approach the optic nerve head were investigated, including standard intravitreal and retroorbital injections. A novel SupraChoroidal-to-Optic-NervE (SCONE) delivery was optimized by creating a sclerotomy and introducing a catheter into the suprachoroidal space. Under direct visualization, the catheter was guided to the optic nerve head. India ink was injected. The suprachoroidal approach was performed in New Zealand White rabbit eyes in vivo (25 animals total). Parameters, including microneedle size and design, catheter design, and catheter tip angle, were optimized ex vivo and in vivo.

RESULTS

Out of the candidate optic nerve head approaches, intravitreal, retroorbital, and suprachoroidal approaches were able to localize India ink to within 2 mm of the optic nerve. The suprachoroidal approach was further investigated, and after optimization, was able to deposit India ink directly within the optic nerve head in up to 80% of attempts. In eyes with successful SCONE delivery, latency and amplitude of visual evoked potentials was not different than the naïve untreated eye.

CONCLUSIONS

SCONE delivery can be used for targeted drug delivery to the optic nerve head of rabbits without measurable toxicity measured anatomically or functionally. Successful development of this system may yield novel opportunities to study optic nerve head-specific drug delivery in animal models, and paradigm-shifting management strategies for treating optic neuropathies.

TRANSLATIONAL RELEVANCE

Here we demonstrate data on a new method for targeted delivery to the optic nerve head, addressing a significant unmet need in therapeutics for optic neuropathies.

Intraoperative OCT-Guided Volumetric Measurements of Subretinal Therapy Delivery in Humans

Purpose: To evaluate a recently developed technique using intraoperative optical coherence tomography (OCT) to measure subretinal tissue plasminogen activator (tPA) volumes in patients with submacular hemorrhage secondary to exudative age-related macular degeneration (AMD). Methods: Three patients (72 to 83 years old) had 25-gauge pars plana vitrectomy, subretinal tPA, and a partial gas fill. An investigational intraoperative OCT system with a modified widefield noncontact indirect viewing apparatus was used to image subretinal tPA blebs. Using the recently developed technique, the volume and surface area in the segmented region of interest were determined. Results: In each case, the delivered tPA volume measured from the syringe differed from the intraoperative OCT-measured subretinal tPA volume: Patient 1, 130 µL from syringe, 118 µL based on intraoperative OCT, 9% difference; Patient 2, 140 µL, 50 µL, 64%; Patient 3, 110 µL, 122 µL, 11%. The total bleb surface area was 129 mm2 in Patient 1, 55 mm2 in Patient 2, and 106 mm2 in Patient 3. Conclusions: This was the first human study to implement and evaluate intraoperative OCT image-based methods to obtain volumetric bleb measurements in patients receiving subretinal tPA for exudative AMD. This proof-of-concept study showed that intraoperative OCT-obtained bleb volume differed from intraoperative recordings, which could be explained by tPA delivery into the vitreous, efflux through the retinotomy, or human error. Intraoperative OCT can provide visualization and quantification of subretinal tPA bleb volume and surface area, which has implications for improved safety, efficacy, and analysis of the effects of subretinal drug delivery.

Objective Outcomes to Evaluate Voretigene Neparvovec Treatment Effects in Clinical Practice

PURPOSE

To assess the efficacy of voretigene neparvovec (VN) treatment by objective fixation stability and chromatic pupillometry testing in clinical practice.

DESIGN

Retrospective cohort study with longitudinal follow-up.

SUBJECTS

Twelve patients (aged 7-34 years) with RPE65-related inherited retinal dystrophies were treated at the same center with VN in both eyes.

METHODS

Patients treated at the same center with VN were evaluated over a 12-month posttreatment follow-up by subjective and objective tests. Furthermore, patients treated with VN who developed atrophy were compared with those who did not.

MAIN OUTCOME MEASURES

Best-corrected visual acuity (BCVA), full-field stimulus threshold test (FST), semiautomated kinetic visual field (SKVF), microperimetry, and chromatic pupillometry over a 12-month follow-up.

RESULTS

Significant improvements of BCVA (P < 0.001), SKVF (P < 0.05), and FST (P < 0.001) were already observed 45 days after treatment and were maintained at the 12-month timepoint. Fixation stability, assessed by microperimetry, improved significantly (P < 0.05) after treatment. Chromatic pupillometry showed significant improvements (P < 0.05) at the 6- and 12-month timepoints. The increase in maximum pupillary constriction significantly (P < 0.001) correlated with higher retinal sensitivity in FST. Four patients developed multifocal retinal atrophy in both eyes, detected at the 6-month timepoint, but this atrophy was not generally associated with worse visual function outcomes.

CONCLUSIONS

This study explores objective outcomes in order to demonstrate the efficacy of VN treatment in addition to the tests normally performed in clinical practice. Our findings show a significant improvement of retinal function both in subjective assessments, such as BCVA, SKVF, and FST, and in objective measurements of fixation stability and maximum pupillary constriction. Moreover, the significant correlation between maximum pupillary constriction and light sensitivity thresholds corroborates the introduction of chromatic pupillometry as an objective test to better assess treatment outcomes in patients with inherited retinal dystrophies.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references in the Footnotes and Disclosures at the end of this article.

Artificial Intelligence, Digital Imaging, and Robotics Technologies for Surgical Vitreoretinal Diseases

OBJECTIVE

To review recent technological advancement in imaging, surgical visualization, robotics technology, and the use of artificial intelligence in surgical vitreoretinal (VR) diseases.

BACKGROUND

Technological advancements in imaging enhance both preoperative and intraoperative management of surgical VR diseases. Widefield imaging in fundal photography and OCT can improve assessment of peripheral retinal disorders such as retinal detachments, degeneration, and tumors. OCT angiography provides a rapid and noninvasive imaging of the retinal and choroidal vasculature. Surgical visualization has also improved with intraoperative OCT providing a detailed real-time assessment of retinal layers to guide surgical decisions. Heads-up display and head-mounted display utilize 3-dimensional technology to provide surgeons with enhanced visual guidance and improved ergonomics during surgery. Intraocular robotics technology allows for greater surgical precision and is shown to be useful in retinal vein cannulation and subretinal drug delivery. In addition, deep learning techniques leverage on diverse data including widefield retinal photography and OCT for better predictive accuracy in classification, segmentation, and prognostication of many surgical VR diseases.

CONCLUSION

This review article summarized the latest updates in these areas and highlights the importance of continuous innovation and improvement in technology within the field. These advancements have the potential to reshape management of surgical VR diseases in the very near future and to ultimately improve patient care.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Sharper vision, steady hands: can robots improve subretinal drug delivery? Systematic review

Subretinal injection (SI) is a novel drug delivery method, directly to retina for treatment of various eye disease. However, manual injection requires surgical experience and precision due to physiological factors. Robots offer solution to this issue, by reducing hand tremor and increased accuracy. This systematic review analyzes current status on robot-assisted SI compared to conventional techniques. Systematic search across 5 databases was conducted to identify studies comparing manual and robot-assisted SI procedures. Extracted data included robotic systems, complications, and success rates. Four studies, including one human trial, two ex vivo porcine eye studies, and one artificial eye model study were included in the synthesis. The findings show early advantages of robot-assisted SI. Compared to traditional interventions, robot procedures result in reduced tremor, what potentially lowers the risk of complications, including retinal tears and reflux. The first in-human randomized trial showed encouraging results, with no significant differences in surgical times or complications between robot-assisted and manual SI. However, major limitation of robot-assisted procedures is longer procedure time. Robot-assisted SI holds promise by offering increased precision and stability, reducing human error and potentially improving clinical outcomes. Challenges include cost, availability, and learning curve. Overall, early stage of robot-assisted SI suggests advantages in precision, complication reduction, and potentially improved drug delivery. Further research in human randomized trials is needed to fully assess its full-scale clinical application.

Prevalence and optical coherence tomography analyses of outer retinal tubulations in Chinese population with inherited retinal diseases

BACKGROUND

To investigate the prevalence of outer retinal tubulation (ORT) and its correlations with optical coherence tomography (OCT) parameters in Chinese population with inherited retinal diseases (IRDs).

METHODS

This retrospective study enrolled consecutive patients identified with IRDs and referred for genetic testing between February 2016 and April 2021. Clinical characteristics from medical records and features of cross-sectional B-scans were reviewed and analysed. The associations of patient-specific and ocular features with the presence of ORT were evaluated using univariate and multivariate analyses.

RESULTS

Two hundred and three patients (401 eyes) with a mean age of 49.7 ± 16.7 years were enrolled. ORT was observed in 41 eyes (10.2%), including 26 of 28 eyes (92.9%) with Bietti crystalline corneoretinal dystrophy (BCD), 14 of 338 eyes (4.1%) with retinitis pigmentosa (RP), and 1 of 26 eyes (3.8%) in eyes with cone-rod dystrophy. Eyes with ORT showed significantly worse visual acuity than those without ORT (P = 0.002). Multivariate analysis indicated that the presence of ORT was positively correlated with choroidal atrophy and inner nuclear layer (INL) cysts (P < 0.01). ORTs were detected more frequently in eyes with BCD than RP (P = 0.024), most of which located exclusively within the extrafoveal area. Large choroidal vessels were detected underneath the corresponding ORTs in both patients with BCD and RP.

CONCLUSIONS

The prevalence of ORT varies among different IRDs phenotypes, with the highest prevalence in BCD. The presence of choroidal atrophy and INL cysts may be associated with an increased risk of ORT formation in patients with IRD.

iOCT-guided simulated subretinal injections: a comparison between manual and robot-assisted techniques in an ex-vivo porcine model

The purpose of this study is to compare robot-assisted and manual subretinal injections in terms of successful subretinal blistering, reflux incidences and damage of the retinal pigment epithelium (RPE). Subretinal injection was simulated on 84 ex-vivo porcine eyes with half of the interventions being carried out manually and the other half by controlling a custom-built robot in a master-slave fashion. After pars plana vitrectomy (PPV), the retinal target spot was determined under a LUMERA 700 microscope with microscope-integrated intraoperative optical coherence tomography (iOCT) RESCAN 700 (Carl Zeiss Meditec, Germany). For injection, a 1 ml syringe filled with perfluorocarbon liquid (PFCL) was tipped with a 40-gauge metal cannula (Incyto Co., Ltd., South Korea). In one set of trials, the needle was attached to the robot's end joint and maneuvered robotically to the retinal target site. In another set of trials, approaching the retina was performed manually. Intraretinal cannula-tip depth was monitored continuously via iOCT. At sufficient depth, PFCL was injected into the subretinal space. iOCT images and fundus video recordings were used to evaluate the surgical outcome. Robotic injections showed more often successful subretinal blistering (73.7% vs. 61.8%, p > 0.05) and a significantly lower incidence of reflux (23.7% vs. 58.8%, p < 0.01). Although larger tip depths were achieved in successful manual trials, RPE penetration occurred in 10.5% of robotic but in 26.5% of manual cases (p > 0.05). In conclusion, significantly less reflux incidences were achieved with the use of a robot. Furthermore, RPE penetrations occurred less and successful blistering more frequently when performing robotic surgery.

The State of Intraoperative OCT in Vitreoretinal Surgery: Recent Advances and Future Challenges

Since its first introduction more than 30 years ago, optical coherence tomography (OCT) has revolutionized ophthalmology practice, providing a non-invasive in vivo cross-sectional view of the structures of the eye. Mostly employed in the clinical setting due to its tabletop configuration requiring an upright patient positioning, the recent advent of microscope-integrated systems now allows ophthalmologists to perform real-time intraoperative OCT (iOCT) during vitreoretinal surgical procedures. Numerous studies described various applications of this tool, such as offering surgeons feedback on tissue-instrument interactions in membrane peeling, providing structural images in macular hole repair, and showing residual subretinal fluid or perfluorocarbon in retinal detachment surgery. This narrative review aims at describing the state of the art of iOCT in vitreoretinal procedures, highlighting its modern role and applications in posterior segment surgery, its current limitations, and the future perspectives that may improve the widespread adoption of this technology.

X-Linked Retinoschisis

X-linked retinoschisis (XLRS) is an inherited vitreoretinal dystrophy causing visual impairment in males starting at a young age with an estimated prevalence of 1:5000 to 1:25,000. The condition was first observed in two affected brothers by Josef Haas in 1898 and is clinically diagnosed by characteristic intraretinal cysts arranged in a petaloid "spoke-wheel" pattern centered in the macula. When clinical electroretinogram (ERG) testing began in the 1960s, XLRS was noted to have a characteristic reduction of the dark-adapted b-wave amplitude despite normal or usually nearly normal a-wave amplitudes, which became known as the "electronegative ERG response" of XLRS disease. The causative gene, RS1, was identified on the X-chromosome in 1997 and led to understanding the molecular and cellular basis of the condition, discerning the structure and function of the retinoschisin protein, and generating XLRS murine models. Along with parallel development of gene delivery vectors suitable for targeting retinal diseases, successful gene augmentation therapy was demonstrated by rescuing the XLRS phenotype in mouse. Two human phase I/II therapeutic XLRS gene augmentation studies were initiated; and although these did not yield definitive improvement in visual function, they gave significant new knowledge and experience, which positions the field for further near-term clinical testing with enhanced, next-generation gene therapy for XLRS patients.

Surgical Observations From the First 120 Cases of Subretinal Gene Therapy for Inherited Retinal Diseases

PURPOSE

To report surgical observations formulated during the first 120 cases of subretinal gene therapy in patients with inherited retinal degenerations (IRDs).

METHODS

A two-surgeon team compiled surgical observations and formulated surgical pearls based on the consecutive cases of subretinal viral vector injection in patients enrolled in clinical trials focusing on choroideremia, achromatopsia, and RP GTPase regulator associated retinitis pigmentosa, as well as patients with retinal pigment epithelium-specific-65-kDa (RPE65) associated Leber congenital amaurosis receiving Food and Drug Administration-approved voretigene neparvovec-rzyl therapy.

RESULTS

One hundred twenty subretinal surgeries were performed by a two-surgeon team. Key anatomical features pertinent to surgical management were noted and are described in this article. Surgical decision making for successful subretinal administration of viral vectors and management of potential surgical challenges were formulated.

CONCLUSION

Lessons learned during subretinal gene therapy cases may be helpful to other surgeons entering clinical trials or performing postapproval gene therapy administration. Surgical pearls outlined in this article may also be helpful for other targeted subretinal therapies, such as cellular transplantation or retinal prosthesis implantation.

The Role of Subretinal Injection in Ophthalmic Surgery: Therapeutic Agent Delivery and Other Indications

Subretinal injection is performed in vitreoretinal surgery with two main aims, namely, the subretinal delivery of therapeutic agents and subretinal injection of fluid to induce a controlled and localized macular detachment. The growing interest in this technique is mainly related to its suitability to deliver gene therapy in direct contact with target tissues. However, subretinal injection has been also used for the surgical management of submacular hemorrhage through the subretinal delivery of tissue plasminogen activator, and for the repair of full-thickness macular holes, in particular refractory ones. In the light of the increasing importance of this maneuver in vitreoretinal surgery as well as of the lack of a standardized surgical approach, we conducted a comprehensive overview on the current indications for subretinal injection, surgical technique with the available variations, and the potential complications.

How to Set Up Genetic Counselling for Inherited Macular Dystrophies: Focus on Genetic Characterization

Inherited macular dystrophies refer to a group of degenerative conditions that predominantly affect the macula in the spectrum of inherited retinal dystrophies. Recent trends indicate a clear need for genetic assessment services in tertiary referral hospitals. However, establishing such a service can be a complex task due to the diverse skills required and multiple professionals involved. This review aims to provide comprehensive guidelines to enhance the genetic characterization of patients and improve counselling efficacy by combining updated literature with our own experiences. Through this review, we hope to contribute to the establishment of state-of-the-art genetic counselling services for inherited macular dystrophies.

Prime Editing for Human Gene Therapy: Where Are We Now?

Gene therapy holds tremendous potential in the treatment of inherited diseases. Unlike traditional medicines, which only treat the symptoms, gene therapy has the potential to cure the disease by addressing the root of the problem: genetic mutations. The discovery of CRISPR/Cas9 in 2012 paved the way for the development of those therapies. Improvement of this system led to the recent development of an outstanding technology called prime editing. This system can introduce targeted insertions, deletions, and all 12 possible base-to-base conversions in the human genome. Since the first publication on prime editing in 2019, groups all around the world have worked on this promising technology to develop a treatment for genetic diseases. To date, prime editing has been attempted in preclinical studies for liver, eye, skin, muscular, and neurodegenerative hereditary diseases, in addition to cystic fibrosis, beta-thalassemia, X-linked severe combined immunodeficiency, and cancer. In this review, we portrayed where we are now on prime editing for human gene therapy and outlined the best strategies for correcting pathogenic mutations by prime editing.

Nanoparticles-mediated CRISPR-Cas9 gene therapy in inherited retinal diseases: applications, challenges, and emerging opportunities

Inherited Retinal Diseases (IRDs) are considered one of the leading causes of blindness worldwide. However, the majority of them still lack a safe and effective treatment due to their complexity and genetic heterogeneity. Recently, gene therapy is gaining importance as an efficient strategy to address IRDs which were previously considered incurable. The development of the clustered regularly-interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) system has strongly empowered the field of gene therapy. However, successful gene modifications rely on the efficient delivery of CRISPR-Cas9 components into the complex three-dimensional (3D) architecture of the human retinal tissue. Intriguing findings in the field of nanoparticles (NPs) meet all the criteria required for CRISPR-Cas9 delivery and have made a great contribution toward its therapeutic applications. In addition, exploiting induced pluripotent stem cell (iPSC) technology and in vitro 3D retinal organoids paved the way for prospective clinical trials of the CRISPR-Cas9 system in treating IRDs. This review highlights important advances in NP-based gene therapy, the CRISPR-Cas9 system, and iPSC-derived retinal organoids with a focus on IRDs. Collectively, these studies establish a multidisciplinary approach by integrating nanomedicine and stem cell technologies and demonstrate the utility of retina organoids in developing effective therapies for IRDs.

OCT-guided Robotic Subretinal Needle Injections: A Deep Learning-Based Registration Approach

Subretinal injection (SI) is an ophthalmic surgical procedure that allows for the direct injection of therapeutic substances into the subretinal space to treat vitreoretinal disorders. Although this treatment has grown in popularity, various factors contribute to its difficulty. These include the retina's fragile, nonregenerative tissue, as well as hand tremor and poor visual depth perception. In this context, the usage of robotic devices may reduce hand tremors and facilitate gradual and controlled SI. For the robot to successfully move to the target area, it needs to understand the spatial relationship between the attached needle and the tissue. The development of optical coherence tomography (OCT) imaging has resulted in a substantial advancement in visualizing retinal structures at micron resolution. This paper introduces a novel foundation for an OCT-guided robotic steering framework that enables a surgeon to plan and select targets within the OCT volume. At the same time, the robot automatically executes the trajectories necessary to achieve the selected targets. Our contribution consists of a novel combination of existing methods, creating an intraoperative OCT-Robot registration pipeline. We combined straightforward affine transformation computations with robot kinematics and a deep neural network-determined tool-tip location in OCT. We evaluate our framework's capability in a cadaveric pig eye open-sky procedure and using an aluminum target board. Targeting the subretinal space of the pig eye produced encouraging results with a mean Euclidean error of 23.8μm.

Injection pressure levels for creating blebs during subretinal gene therapy

Retinal damage has been associated with increased injection pressure during subretinal gene therapy delivery in various animal models, yet there are no human clinical data regarding the pressures required to initiate and propagate subretinal blebs. This study characterized the intraoperative pressure levels for subretinal gene therapy delivery across eight retinal conditions. A total of 116 patients with retinal degenerative diseases have been treated with subretinal gene therapy at OHSU-Casey Eye Institute as of June 2020; seventy patients (60.3%) were treated using a pneumatic-assisted subretinal delivery system. All retinal blebs were performed using a 41-gauge injection cannula, and use of a balanced salt solution (BSS) "pre-bleb" prior to gene therapy delivery was performed at the discretion of the surgeon. Patient age and intraoperative data for BSS and vector injections were analyzed in a masked fashion for all patients who received pneumatic-assisted subretinal gene therapy. The median age of the patients was 35 years (range 4-70). No significant differences in injection pressures were found across the eight retinal conditions. In this study, patient age was shown to affect maximum injection pressures required for bleb propagation, and the relationship between age and pressure varied based on retinal condition. These data have important implications in optimizing surgical protocols for subretinal injections.

Subretinal Therapy: Technological Solutions to Surgical and Immunological Challenges

Recent advances in ocular gene and cellular therapy rely on precisely controlled subretinal delivery. Due to its inherent limitations, manual delivery can lead to iatrogenic damage to the retina, the retinal pigment epithelium, favor reflux into the vitreous cavity. In addition, it suffers from lack of standardization, variability in delivery and the need to maintain proficiency. With or without surgical damage, an eye challenged with an exogenous viral vector or transplanted cells will illicit an immune response. Understanding how such a response manifests itself and to what extent immune privilege protects the eye from a reaction can help in anticipating short- and long-term consequences. Avoidance of spillover from areas of immune privilege to areas which either lack or have less protection should be part of any mitigation strategy. In that regard, robotic technology can provide reproducible, standardized delivery which is not dependent on speed of injection. The advantages of microprecision medical robotic technology for precise targeted deliveries are discussed.

Lipid Nanoparticles for the Posterior Eye Segment

This review highlights the application of lipid nanoparticles (Solid Lipid Nanoparticles, Nanostructured Lipid Carriers, or Lipid Drug Conjugates) as effective drug carriers for pathologies affecting the posterior ocular segment. Eye anatomy and the most relevant diseases affecting the posterior segment will be summarized. Moreover, preparation methods and different types and subtypes of lipid nanoparticles will also be reviewed. Lipid nanoparticles used as carriers to deliver drugs to the posterior eye segment as well as their administration routes, pharmaceutical forms and ocular distribution will be discussed emphasizing the different targeting strategies most recently employed for ocular drug delivery.

Gene-Based Therapeutics for Acquired Retinal Disease: Opportunities and Progress

Acquired retinal diseases such as age-related macular degeneration and diabetic retinopathy rank among the leading causes of blindness and visual loss worldwide. Effective treatments for these conditions are available, but often have a high treatment burden, and poor compliance can lead to disappointing real-world outcomes. Development of new treatment strategies that provide more durable treatment effects could help to address some of these unmet needs. Gene-based therapeutics, pioneered for the treatment of monogenic inherited retinal disease, are being actively investigated as new treatments for acquired retinal disease. There are significant advantages to the application of gene-based therapeutics in acquired retinal disease, including the presence of established therapeutic targets and common pathophysiologic pathways between diseases, the lack of genotype-specificity required, and the larger potential treatment population per therapy. Different gene-based therapeutic strategies have been attempted, including gene augmentation therapy to induce in vivo expression of therapeutic molecules, and gene editing to knock down genes encoding specific mediators in disease pathways. We highlight the opportunities and unmet clinical needs in acquired retinal disease, review the progress made thus far with current therapeutic strategies and surgical delivery techniques, and discuss limitations and future directions in the field.

Two-step versus 1-step subretinal injection to compare subretinal drug delivery: a randomised study protocol

INTRODUCTION

There is increasing interest in subretinal injections as a surgical procedure, largely as a result of emerging treatments for ocular diseases which necessitate this manoeuvre. However, surgical variables in the efficacy of such treatments have to date been largely overlooked and the proportion of drug which reaches the intended compartment of the subretinal space remains unknown. Our aims are twofold: first, to determine the proportion of subretinally injected medication retained following surgical delivery and second, to compare two different techniques of injection ('1-step' vs '2-step').

METHODS

We outline a randomised controlled trial of subretinal injection of alteplase following vitrectomy for the management of submacular haemorrhage secondary to age-related macular degeneration. Patients will be randomised to receive either 1-step injection, where the therapeutic solution simultaneously defines the surgical plane or 2-step injection, where the surgical plane is first identified with balanced salt solution prior to injection of subretinal alteplase, as outlined below. Sodium fluorescein will be used as an optical label to track drug reflux into the vitreous cavity using quantitative protocols established in our laboratory. All patients will undergo fluid air exchange at the completion of surgery, with injection of bevacizumab 1.25 mg and 20% sulfahexafluoride gas as the vitreous substitute (both of which may help improve outcomes). Alteplase, sodium fluorescein and bevacizumab will all be used for off-label indications in the trial.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the South Eastern Sydney Local Health District's Human Research Ethics Committee (HREC 17/092). The results of this trial will be disseminated in peer-reviewed proceedings (associated with conference presentation) and in scholarly journals.

TRIAL REGISTRATION NUMBER

ACTRN12619001121156.

Visual Acuity, Retinal Morphology, and Patients' Perceptions after Voretigene Neparvovec-rzyl for RPE65-Associated Retinal Disease

OBJECTIVE

To explore the effect of patient's age, baseline visual acuity, and intraoperative foveal detachment on outcomes of subretinal voretigene neparvovec-rzyl (VN, Luxturna®) therapy and to assess patients' perceptions of the treatment effect.

DESIGN

Multicenter, retrospective, consecutive case series and cross-sectional prospective survey.

SUBJECTS

All 41 consecutive patients treated with VN after FDA approval at three institutions between January 2018 and May 2020.

METHODS

Retrospective chart review of operative reports, clinical notes, ancillary testing and complications, comparing data at baseline and 1, 2-3, 6-9, and 10-15 months after subretinal surgery. A survey was administered to adult patients and parents of pediatric patients.

MAIN OUTCOME MEASURES

Changes in BCVA and retinal morphology, and patients' perceptions.

RESULTS

77 eyes of 41 patients (16 adults and 25 children, range 2-44 years, mean follow-up 10 months, range 1 week to 18.5 months) were analyzed. There was no statistically significant vision change for the adults, whereas there was a trend of improvement for children that reached statistical significance for some time points but not all. At the last follow-up, 14/48 (29%) pediatric and 3/26 (12%) adult eyes improved ≥2 lines (p=0.15). Baseline VA did not have an effect on post-therapy VA (p=0.23). Central foveal thickness decreased mildly in both children and adults, without significant difference between the populations. The fovea was detached by VN in 62 eyes (81%). Inner segment-outer segment junction remained unchanged in 91% of 54 eyes with gradable OCTs, with or without foveal detachment. Thirty-two patients (78%) were reached for the survey an average of 1.15±0.50 years (range 0.31 to 2.31) after surgery in the first eye. Improvement in night, day, and/or color vision was reported by 23 (72%), 22 (69%), and 18 (56%) patients respectively.

CONCLUSIONS

This study is limited by large variability in follow-up time. There were no persistent statistical significant vision changes. A decrease in foveal thickness was noted in most eyes. The long-term significance of this remains to be determined.

The safety and efficacy of gene therapy treatment for monogenic retinal and optic nerve diseases: A systematic review

PURPOSE

This study aimed to systematically review and summarize gene therapy treatment for monogenic retinal and optic nerve diseases.

METHODS

This review was prospectively registered (CRD42021229812). A comprehensive literature search was performed in Ovid MEDLINE, Ovid Embase, Cochrane Central, and clinical trial registries (February 2021). Clinical studies describing DNA-based gene therapy treatments for monogenic posterior ocular diseases were eligible for inclusion. Risk of bias evaluation was performed. Data synthesis was undertaken applying Synthesis Without Meta-analysis guidelines.

RESULTS

This study identified 47 full-text publications, 50 conference abstracts, and 54 clinical trial registry entries describing DNA-based ocular gene therapy treatments for 16 different genetic variants. Study summaries and visual representations of safety and efficacy outcomes are presented for 20 unique full-text publications in RPE65-mediated retinal dystrophies, choroideremia, Leber hereditary optic neuropathy, rod-cone dystrophy, achromatopsia, and X-linked retinoschisis. The most common adverse events were related to lid/ocular surface/cornea abnormalities in subretinal gene therapy trials and anterior uveitis in intravitreal gene therapy trials.

CONCLUSION

There is a high degree of variability in ocular monogenic gene therapy trials with respect to study design, statistical methodology, and reporting of safety and efficacy outcomes. This review improves the accessibility and transparency in interpreting gene therapy trials to date.

Current trends in gene therapy for retinal diseases (Review)

The eye is considered an effective target for genetic therapy, as it has a privileged immune status, it is easily accessed for medication delivery and it is affected by a number of inherited disorders. In particular, the retina is considered for gene therapy due to the fact that it can be visualized with ease, it does not have lymphatic vessels, nor a direct blood network for the outer layers and its cells do not divide after birth, and thus transgene expression is not affected. As gene therapy is currently on a continuously progressive development trend, this emerging field of gene manipulation techniques has yielded promising results. This involves the development of treatments for a number of debilitating and blinding diseases, which were to date considered intractable. However, numerous unanswered questions remain as regards the long-term efficacy and safety profile of these treatments. The present review article discusses the current research status regarding genetic manipulation techniques aimed at addressing visual impairment related to retinal disorders, both inherited and degenerative.

A Modified Surgical Technique for Submacular Injection

BACKGROUND AND OBJECTIVE

To describe a modified simple surgical technique for submacular injection.

PATIENTS AND METHODS

The technique involves pars plana vitrectomy, a viscous fluid control (VFC) system for semi-automatic subretinal injection of tissue plasminogen activator (tPA), bevacizumab, and air and intravitreal gas injection for submacular hemorrhage (SMH), or subretinal balanced salt solution (BSS) for submacular perfluorocarbon (PFC) bubbles or persistent macular holes.

RESULTS

This technique was successfully performed for SMH (five patients), a subfoveal PFC bubble (two patients), and persistent full-thickness macular hole (FTMH) (one patient). The single surgical complication was an FTMH in a PFC bubble. Four SMH patients had postoperative displacement of the hemorrhage. The FTMH was partially closed.

CONCLUSIONS

Semi-automatic subretinal injection of tPA, bevacizumab, and air with the VFC system promoted displacement and clearance of SMH without complications. A subretinal BSS injection is effective for removing subfoveal PFC bubbles and for closing persistent FTMH. [Ophthalmic Surg Lasers Imaging Retina. 2021;52:551-555.].

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.

[Diagnostics of inherited retinal degenerations by gene therapy]

The article presents recent worldwide achievements in the area of diagnosis and treatment of inherited retinal degenerations (IRDs) from the standpoint of ophthalmic genetics. Clinical studies conducted in patients with Leber congenital amaurosis and retinitis pigmentosa caused by biallelic mutations in the RPE65 gene have provided the basis for future genes studies associated with IRDs. The conducted studies highlight the importance of fundamental understanding of function of the gene, timely diagnosis and study of natural history of the disease. Currently, surgical techniques are being improved for the efficient delivery of gene preparations to target cells, as well as the criteria for evaluating treatment outcomes.

Microscope-Integrated OCT-Guided Volumetric Measurements of Subretinal Blebs Created by a Suprachoroidal Approach

Purpose

To investigate the use of imaging modalities in the volumetric measurement of the subretinal space and examine the volume of subretinal blebs created by a subretinal drug delivery device utilizing microscope-integrated optical coherence tomography (MIOCT).

Methods

An MIOCT image-based volume measurement method was developed and assessed for accuracy and reproducibility by imaging ceramic spheres of known size that were surgically implanted into ex vivo porcine eyes. This method was then used to measure subretinal blebs created in 10 porcine eyes by injection of balanced salt solution utilizing a subretinal delivery device via a suprachoroidal cannula. Bleb volumes obtained from MIOCT were compared to the intended injection volume.

Results

Validation of image-based volume measurements of ceramic spheres showed accuracy to ±0.029 µL (5.6%) for objects imaged over the posterior pole and ±0.025 µL (4.8%) over peripheral retina. The mean expected injection volume from extraocular tests of the suprachoroidal cannula was 66.44 µL (σ = 2.4 µL). The mean injection volume as measured by the MIOCT imaging method was 54.8 µL (σ = 12.3 µL), or 82.48% of expected injection volume.

Conclusions

MIOCT can measure the volume of subretinal blebs with accuracy and precision. The novel suprachoroidal approach using a subretinal delivery device was able to deliver greater than 80% of expected injection volume into the subretinal space, as assessed by MIOCT.

Translational Relevance

MIOCT provides a method for visualization, and analysis of images enables surgeons to quantify and evaluate the success of subretinal drug delivery via a suprachoroidal approach.

Advantages of robotic assistance over a manual approach in simulated subretinal injections and its relevance for gene therapy

Subretinal injection is a method for gene delivery to treat genetic diseases of the photoreceptors and retinal pigment epithelium. A reflux-free subretinal injection is important to allow effective, safe, and cost-effective gene therapy to the retina. We report on a comparison between manual and robotic assistance in simulated subretinal injections using an artificial retina model. Nine surgeons carried out the procedure with and without the Preceyes Surgical System, using an OPMI Lumera 700 Zeiss surgical microscope equipped with intra-operative optical coherence tomography. Success in creating a bleb without reflux, injection duration, drift, tremor, and increase in the diameter of the puncture hole were analyzed. Robotic assistance improved drift (median 16 vs 212 µm), tremor (median 1 vs 18 µm), enlargement of the retinal hole, and allowed for prolonged injection times (median 52 vs 29 sec). Robotic assistance allowed higher rate of bleb formation (8/9 vs 4/9 attempts) with a moderate reduction in reflux (7/9 vs 8/9 attempts) in this artificial model. Robotic assistance can significantly contribute to subretinal injections and provide quantifiable parameters in assessing surgical and clinical success of novel retinal gene therapies.

Gene therapy for inherited retinal diseases: progress and possibilities

Inherited retinal diseases (IRDs) comprise a heterogeneous group of genetic disorders affecting the retina. Caused by mutations in over 300 genes, IRDs result in visual impairment due to dysfunction and degeneration of photoreceptors, retinal pigment epithelium, or the choroid. Important photoreceptor IRDs include retinitis pigmentosa and Leber congenital amaurosis. Macular dystrophies include Stargardt and Best disease. Currently, IRDs are largely incurable but the landscape of treatment options is rapidly changing for these diseases which, untreated, result in severe visual impairment and blindness.Advances in DNA delivery to the retina and improved genetic diagnosis of IRDs have led to a new era of research into gene therapy for these vision-threatening disorders. Gene therapy is a compelling approach due to the monogenic nature of most IRDs, with the retina being a favourable target for administering genetic vectors due to its immunoprivileged environment, direct visibility, and multiple methods to assess sensitivity and function. Generally, retinal gene therapy involves a subretinal or intravitreal injection of a viral vector, which infects target cells to deliver a therapeutic gene, or transgene. A gene augmentation strategy introduces a functioning copy of a gene to restore expression of a mutated gene, whereas a gene-editing strategy aims to directly edit and correct the mutation. Common delivery vectors include adeno-associated virus (AAV) and lentivirus.Voretigene neparvovec-rzyl (Luxturna) became the first FDA-approved direct gene therapy in December 2017, and the Australian TGA followed suit in August 2020. More are projected to follow, with clinical trials underway for many other IRDs.This review provides an overview of gene therapy for IRDs, including current progress and challenges. A companion article in this issue details target patient populations for IRD gene therapy, and how optometrists can assist in assessing individuals who may be eligible for current and future therapies.

Surgical Aspects in Gene Therapy for Inherited Retinal Diseases

Inherited retinal dystrophies (IRD) have been studied since their recognition by Franz Donders and Albrecht von Graefe. It nevertheless took 100 years for a causal therapy to take shape in the form of gene therapy: The approval of Voretigen Neparvovec (VN) for the treatment of hereditary retinal dystrophies due to RPE65 mutations was thus a significant milestone - for the era of personalised medicine in general and ophthalmology in particular. The clinical management around gene therapy applications is complex and requires the cooperation of various experts as a multidisciplinary team. This article describes the requirements, challenges, approaches, and open questions regarding the surgical aspects of gene therapy for retinal dystrophies. The first part outlines the standard surgical treatment. Based on this standard, alternative approaches are indicated for each individual step and their value discussed. Knowledge gaps are defined and in the outlook we speculate on future developments.

Clinical Perspective: Treating RPE65-Associated Retinal Dystrophy

Until recently, there was no approved treatment for a retinal degenerative disease. Subretinal injection of a recombinant adeno-associated virus (AAV) delivering the normal copy of the human RPE65 cDNA led to reversal of blindness first in animal models and then in humans. This led to the first US Food and Drug Administration (FDA)-approved gene therapy product for a genetic disease, voretigene neparvovec-rzyl (Luxturna). Luxturna was then approved by the European Medicines Association and is now available in the US through Spark Therapeutics and worldwide through Novartis. Not only has treatment with Luxturna changed the lives of people previously destined to live a life of blindness, but it has fueled interest in developing additional gene therapy reagents targeting numerous other genetic forms of inherited retinal disease. This review describes many of the considerations for administration of Luxturna and describes how lessons from experience with Luxturna could lead to additional gene-based treatments of blindness.

Hints for Gentle Submacular Injection in Non-Human Primates Based on Intraoperative OCT Guidance

Purpose

Delivery of Advanced Therapy Medicinal Products to the submacular space is increasingly evolving into a therapeutic modality. Cell replacement for age-related macular degeneration (AMD) and gene therapy for RPE65 are recent successful examples. Herein, a nonhuman primate (NHP) model was used to investigate surgical means to detach the macula.

Methods

Sixteen eyes of 13 healthy macaques underwent a 25-gauge vitrectomy and subretinal injection of balanced salt solution monitored by microscope-integrated intraoperative optical coherence tomography (miOCT). The animals were followed with OCT and histology.

Results

The miOCT monitoring allowed a more precise definition of surgical trauma ranging from an initial full-thickness foveal tear, or induction of a cystoid macular edema (CME), until no foveal defect was discernible, as the technique improved. However, as the subretinal fluid wave detached the fovea, the aforementioned lesions formed, whereas persistent retinal adhesion reproducibly proved to remain in the distal parafoveal semi-annulus. Measures to reduce foveal trauma during submacular fluid injection included reducing intraocular pressure, injection volume, and velocity, as well as the retinal location for bleb initiation, use of a vitreous tamponade, and a dual-bore subretinal cannula.

Conclusions

A stable very low intraocular pressure and careful subretinal injection may avoid tangential macular stretching or mechanical CME formation, while vitreous tamponade may facilitate a more lamellar subretinal flow, all thereby reducing foveal trauma during submacular injection in NHP.

Translational Relevance

These results can be relevant to any submacular surgery procedure used today, as they synergistically reduce the risk of compromising foveal integrity.

Creating an Ocular Biofactory: Surgical Approaches in Gene Therapy for Acquired Retinal Diseases

ABSTRACT

Gene therapy offers the potential to treat inherited retinal disorders and deliver sustained therapy for acquired retinal diseases. In the latter case, host cells can be harnessed to produce non-native proteins that have beneficial properties, such as antivascular endothelial growth factor activity, transforming the eye into an ocular "biofactory." Several gene therapy programs have entered clinical testing for delivery to the vitreous, subretinal, and suprachoroidal space. Improved viral vectors and refined surgical techniques are critical to successful delivery of therapeutic products to the target tissue. In this review, we discuss the development of gene therapy products aimed at acquired retinal diseases and the surgical techniques utilized to achieve targeted delivery.

Current Clinical Applications of In Vivo Gene Therapy with AAVs

Hereditary diseases are caused by mutations in genes, and more than 7,000 rare diseases affect over 30 million Americans. For more than 30 years, hundreds of researchers have maintained that genetic modifications would provide effective treatments for many inherited human diseases, offering durable and possibly curative clinical benefit with a single treatment. This review is limited to gene therapy using adeno-associated virus (AAV) because the gene delivered by this vector does not integrate into the patient genome and has a low immunogenicity. There are now five treatments approved for commercialization and currently available, i.e., Luxturna, Zolgensma, the two chimeric antigen receptor T cell (CAR-T) therapies (Yescarta and Kymriah), and Strimvelis (the gammaretrovirus approved for adenosine deaminase-severe combined immunodeficiency [ADA-SCID] in Europe). Dozens of other treatments are under clinical trials. The review article presents a broad overview of the field of therapy by in vivo gene transfer. We review gene therapy for neuromuscular disorders (spinal muscular atrophy [SMA]; Duchenne muscular dystrophy [DMD]; X-linked myotubular myopathy [XLMTM]; and diseases of the central nervous system, including Alzheimer’s disease, Parkinson’s disease, Canavan disease, aromatic l-amino acid decarboxylase [AADC] deficiency, and giant axonal neuropathy), ocular disorders (Leber congenital amaurosis, age-related macular degeneration [AMD], choroideremia, achromatopsia, retinitis pigmentosa, and X-linked retinoschisis), the bleeding disorder hemophilia, and lysosomal storage disorders.

Treatment-Emergent Adverse Events in Gene Therapy Trials for Inherited Retinal Diseases: A Narrative Review

Patient safety is a primary priority in the conduction of retinal gene therapy trials. An understanding of risk factors and mitigation strategies for post-procedure complications is crucial for the optimization of gene therapy clinical trial protocols. In this review, we synthesize the literature on ocular delivery methods, vector platforms, and treatment-emergent adverse effects in recent gene therapy clinical trials for inherited retinal diseases.

The new landscape of retinal gene therapy

Novel therapeutics for inherited retinal dystrophies (IRDs) have rapidly evolved since groundbreaking clinical trials for LCA due to RPE65 mutations led to the first FDA-approved in vivo gene therapy. Since then, advancements in viral vectors have led to more efficient AAV transduction and developed other viral vectors for gene augmentation therapy of large gene targets. Furthermore, significant developments in gene editing and RNA modulation technologies have introduced novel capabilities for treatment of autosomal dominant diseases, intronic mutations, and/or large genes otherwise unable to be treated with current viral vectors. We highlight strategies currently being evaluated in gene therapy clinical trials and promising preclinical developments for IRDs.

Intraoperative optical coherence tomographic findings in patients undergoing subretinal gene therapy surgery

BACKGROUND

To analyze intraoperative OCT (iOCT) findings during subretinal gene therapy.

METHODS

A single-center, retrospective, observational, case series study of twenty one eyes submitted to subretinal gene therapy. Intrasurgical high definition videos were included for analyzes. Cases with absence of iOCT video or unsuccessful bleb creation were excluded. Sharp needle tip (SNT) or blunted needle tip (BNT) and their interaction with neurosensory retina were evaluated. Presence of subretinal air bubbles, visible opened retinotomy, and medication reflux were also correlated and analyzed.

RESULTS

Nineteen of twenty-one eyes were included. Of the two excluded eyes, subretinal bleb creation was unsuccessful in one and technical issues prevented OCT image acquisition in the other. Immediately before subretinal injection, needle indention/penetration of the neurosensory retina with temporary indentation of the RPE/choroid was evident in 16 (84%) of the 19 eyes. Complete RPE/choroid indentation was needed with BNT use compared to SNT (p = 0.0114). An open retinotomy was identified in 14 (74%) of 19 eyes at the conclusion of bleb injection and was more commonly associated with SNT (p = 0.0108).

CONCLUSIONS

iOCT provides valuable real-time feedback of cross-sectional retinal anatomy during subretinal gene therapy surgeries. The type of needle tip and its use during the gene therapy procedure seems to influence in the bleb creation and presence of visible open retinotomy. Further studies of iOCT findings during gene therapy delivery procedures are likely to help refine the surgical technique.