Two-Year Results After AAV2-Mediated Gene Therapy for Choroideremia: The Alberta Experience

Long-term natural history of visual acuity in eyes with choroideremia: a systematic review and meta-analysis of data from 1004 individual eyes

BACKGROUND/AIMS

Best-corrected visual acuity (BCVA) is the most common primary endpoint in treatment trials for choroideremia (CHM) but the long-term natural history of BCVA is unclear.

METHODS

We searched in seven databases to identify studies that reported BCVA of untreated eyes with CHM. We sought individual-level data and performed segmented regression between BCVA and age. For eyes followed longitudinally, we introduced a horizontal translation factor to each dataset to account for different ages at onset of a rapid BCVA decline.

RESULTS

We included 1004 eyes from 23 studies. BCVA of the right and left eyes was moderately correlated (r=0.60). BCVA as a function of age followed a 2-phase decline (slow followed by rapid decline), with an estimated transition age of 39.1 years (95% CI 33.5 to 44.7). After the introduction of horizontal translation factors to longitudinal datasets, BCVA followed a 2-phase decline until it reached 0 letters (r²=0.90). The BCVA decline rate was 0.33 letters/year (95% CI -0.38 to 1.05) before 39 years, and 1.23 letters/year (95% CI 0.55 to 1.92) after 39 years (p=0.004).

CONCLUSION

BCVA in eyes with CHM follows a 2-phase linear decline with a transition age of approximately 39 years. Future trials enrolling young patients may not be able to use BCVA as a primary or sole endpoint, but rather, may need to employ additional disease biomarkers that change before age 39. BCVA may still have utility as a primary endpoint for patients older than 39 years who have measurable BCVA decline rates.

Retinal Dystrophies and the Road to Treatment: Clinical Requirements and Considerations

: Retinal dystrophies (RDs) comprise relatively rare but devastating causes of progressive vision loss. They represent a spectrum of diseases with marked genetic and clinical heterogeneity. Mutations in the same gene may lead to different diagnoses, for example, retinitis pigmentosa or cone dystrophy. Conversely, mutations in different genes may lead to the same phenotype. The age at symptom onset, and the rate and characteristics of peripheral and central vision decline, may vary widely per disease group and even within families. For most RD cases, no effective treatment is currently available. However, preclinical studies and phase I/II/III gene therapy trials are ongoing for several RD subtypes, and recently the first retinal gene therapy has been approved by the US Food and Drug Administration for RPE65-associated RDs: voretigene neparvovec-rzyl (Luxturna). With the rapid advances in gene therapy studies, insight into the phenotypic spectrum and long-term disease course is crucial information for several RD types. The vast clinical heterogeneity presents another important challenge in the evaluation of potential efficacy in future treatment trials, and in establishing treatment candidacy criteria. This perspective describes these challenges, providing detailed clinical descriptions of several forms of RD that are caused by genes of interest for ongoing and future gene or cell-based therapy trials. Several ongoing and future treatment options will be described.

Synonymous Variant in the CHM Gene Causes Aberrant Splicing in Choroideremia

Purpose

Choroideremia is an inherited retinal degeneration caused by 280 different pathogenic variants in the CHM gene. Only one silent/synonymous variant (c.1359C>T; p.(Ser453=)) has been reported and was classified as inconclusive based on in silico analysis. This study elucidates the pathogenicity of this variant also found in a Brazilian patient.

Methods

Ophthalmological examinations such as color fundus photography, spectral-domain optical coherence tomography, fundus autofluorescence, and macular integrity assessment microperimetry were performed. The subjects' total RNA was extracted from peripheral blood cells. cDNA was synthesized and the amplification between exon 10 and 14 of the CHM mRNA was performed. The amplification products were sequenced by Sanger sequencing and the results were aligned to the reference sequence.

Results

The synonymous variant c.1359C>T p.(Ser453=) in the CHM gene is associated with an error in mRNA processing, leading preferentially to production of an aberrant transcript without exon 11 (p.(Gln451Phefs*3)). This anomalous mRNA production is related to typical choroideremia phenotype.

Conclusions

These molecular findings reinforce the need for more detailed investigation of silent variants in patients with well-defined phenotype of retinal dystrophies. Molecular and clinical findings provided evidence that c.1359C>T (p.(Gln451Phefs*3)) in CHM should be considered a disease-causing variant.

Long-term Natural History of Atrophy in Eyes with Choroideremia-A Systematic Review and Meta-analysis of Individual-Level Data

PURPOSE

To conduct a systematic review and meta-analysis of the natural history of atrophy secondary to choroideremia (CHM).

CLINICAL RELEVANCE

A sensitive and reliable anatomic measure to monitor disease progression is needed in treatment trials for CHM. However, the long-term natural history of the residual retinal pigment epithelium (RPE) is unclear, with reported RPE area decline rates varying widely among patients.

METHODS

We searched in 7 literature databases up through July 17, 2019, to identify studies that assessed the residual RPE area in untreated eyes with CHM using fundus autofluorescence (FAF). We sought individual-eye data and investigated the RPE decline pattern using 3 models: the area linear model (ALM), radius linear model (RLM), and area exponential model (AEM), in which the area, radius, and log-transformed area of RPE change linearly with time, respectively. To account for different eyes' entry times into the studies, we added a horizontal translation factor to each dataset. The RPE decline rate was estimated using a 2-stage random-effects meta-analysis. We assessed the risk of bias using the Quality In Prognosis Studies tool.

RESULTS

Of 807 articles screened, we included 9 articles containing cross-sectional data (257 eyes) from 6 studies and longitudinal data (229 visits from 68 eyes) from 5 studies. The residual RPE area followed a trend of exponential decay as a function of patient age. After the introduction of horizontal translation factors to longitudinal datasets of individual eyes, the datasets fit along a straight line in the AEM over nearly 60 years (r² = 0.997). The decline rate of log-transformed RPE area was 0.050 (95% confidence interval, 0.046-0.055) log(mm²)/year and was independent of the baseline RPE area (r = -0.18; P = 0.15) and age (r = 0.06; P = 0.63). In contrast, the decline rates of the area and effective radius of residual RPE strongly correlated with the baseline RPE area (r = 0.90 and 0.61, respectively; P < 0.001).

CONCLUSIONS

The loss of residual RPE area in untreated eyes with CHM follows the AEM over approximately 60 years. Log-transformed residual RPE area measured by FAF can serve as an anatomic endpoint to monitor CHM.

Has retinal gene therapy come of age? From bench to bedside and back to bench

Retinal gene therapy has advanced considerably in the past three decades. Initial efforts have been devoted to comprehensively explore and optimize the transduction abilities of gene delivery vectors, define the appropriate intraocular administration routes and obtain evidence of efficacy in animal models of inherited retinal diseases (IRDs). Successful translation in clinical trials of the initial promising proof-of-concept studies led to the important milestone of the first approved product for retinal gene therapy in both US and Europe. The unprecedented clinical development observed during the last decade in the field is however highlighting new challenges that will need to be overcome to bring gene therapy to fruition to a larger patient population within and beyond the realm of IRDs.

Patient-reported outcome measures in inherited retinal degeneration gene therapy trials

Patient-reported outcome (PRO) measures have the potential to uniquely capture patient experience and serve as an outcome measure in inherited retinal degeneration (IRD) gene therapy trials. An IRD-specific patient-reported outcome measure may yield valuable information that has not been obtained from inherited retinal dystrophy gene therapy trials published to-date. Existing PRO measures have inherent limitations for use in IRD gene therapy trials. Developing an applicable patient-reported outcome measure for such trials needs to incorporate patient input from the target population, demonstrate sound psychometric properties, and be made in accordance with U.S. Food and Drug Administration (FDA) guidelines. This review will discuss the currently available PRO instruments, their limitations for IRD therapeutic trials, and suggestions for future PRO development in IRD populations. The PRO instruments highlighted were identified in PubMed search of English-language journals and previously published review articles.

Disease asymmetry and hyperautofluorescent ring shape in retinitis pigmentosa patients

Retinitis pigmentosa (RP) is described as a bilateral disease with inter-eye symmetry that presents on short-wavelength fundus autofluorescence (SW-AF) imaging with hyperautofluorescent (hyperAF) rings with an ellipsoid shape and regular borders. Nevertheless, both asymmetry and irregular ring morphologies are also observed. In this retrospective study of 168 RP patients, we characterize the degree of inter-eye asymmetry and frequency of irregular hyperAF ring morphologies according to mode of inheritance and disease-causing gene by using SW-AF imaging and spectral-domain optical coherence tomography (SD-OCT) scans. We observed that from 336 eyes, 290 (86%) presented with regular hyperAF rings and 46 (14%) presented with irregular shapes. From the 168 patients, 23 (14%) presented with asymmetric disease, with 16 (70%) of these patients also presenting with irregular ring shapes. Patients with autosomal dominant RP (adRP) had the highest proportion of irregular ring shapes (21%) and disease asymmetry (23%) in comparison to other modes of inheritance. Furthermore, both RP1 and RHO-adRP had the highest proportions of both disease asymmetry and irregular ring morphology. Our results suggest that in patients presenting with either irregular ring shapes or asymmetric disease, emphasis should be placed in targeted gene sequencing of genes known to cause adRP, such as RHO and RP1.

Perspectives on Gene Therapy: Choroideremia Represents a Challenging Model for the Treatment of Other Inherited Retinal Degenerations

Purpose

To report combined viewpoints on ocular gene therapy from a select group of clinician scientists and a patient advocacy group.

Methods

With the support of Randy Wheelock and Dr. Chris Moen from the Choroideremia Research Foundation (CRF), a special interest group at the 2019 Annual meeting of the Association for Research in Vision and Ophthalmology in Vancouver, Canada, shared their knowledge, experience, concepts, and ideas and provided a forum to discuss therapeutic strategies for the treatment of inherited retinal disorders, using experience in choroideremia (CHM) as a model.

Results

A member of the CRF presented the patient perspective and role in clinical trials. Five clinician scientists presented reasons for limited long-term visual improvement in many gene therapy trials, including challenges with dose, incomplete understanding of photoreceptor metabolism, vector delivery, inflammation, and identification of patients likely to benefit from treatment.

Conclusions

The shared experience of the five clinician scientists indicates that the results of ocular gene therapy for choroideremia have been less successful than for RPE65-related Leber congenital amaurosis. Improvement in vector delivery and developing a better understanding of gene expression in target tissues, treatment dose and side effects, and inflammation, as well as identifying patients who are most likely to benefit without suffering excessive risk, are necessary to advance the development of effective therapies for inherited retinal degenerations.

Translational Relevance

Additional long-term data are required to determine if ocular gene therapy will be sufficient to alter natural progression in choroideremia. Combination therapies may have to be considered, as well as alternative vectors that minimize risk.

Patterns and Intensities of Near-Infrared and Short-Wavelength Fundus Autofluorescence in Choroideremia Probands and Carriers

Purpose

To ascertain cellular constituents within islands of preserved retina in choroideremia (CHM) by multimodal imaging.

Methods

CHM probands (16) and female carriers (9) of CHM were studied. Near-infrared autofluorescence (NIR-AF; 787-nm excitation; emission, >830 nm), short-wavelength autofluorescence (SW-AF; 488-nm excitation, 500- to 680-nm emission), and spectral-domain optical coherence tomography (SD-OCT) images were acquired with a confocal scanning laser ophthalmoscope. SW-AF intensities were measured by quantitative fundus autofluorescence (qAF), and NIR-AF intensity profiles were analyzed. Retinal thicknesses and visual acuity were measured.

Results

In 19 of 31 eyes of affected males, islands of preserved NIR-AF signal were also visible as fluorescence signal in SW-AF images. Notable in 12 eyes were areas of speckled SW-AF that was hypoautofluorescent in the NIR-AF image. Islands of preserved NIR-AF and SW-AF signal were often associated with the presence of visible but thinned outer nuclear layer and discontinuous interdigitation zone, ellipsoid zone, and external limiting membrane. NIR-AF profiles revealed that even in areas of preserved retina, the NIR-AF signal from retinal pigment epithelium (RPE) melanin is greatly reduced. qAF was reduced overall. The fundus of carriers was characterized by a mosaicism in which patches of reduced NIR-AF colocalized with reduced SW-AF.

Conclusions

In CHM-affected males, the presence of RPE was indicated by an NIR-AF signal and the absence of hypertransmission of OCT signal into the choroid. RPE preservation was associated with better visual acuity. In carriers, patches of reduced SW-AF colocalized with decreased NIR-AF and qAF was severely reduced.

Inclusion of PF68 Surfactant Improves Stability of rAAV Titer when Passed through a Surgical Device Used in Retinal Gene Therapy

Recent advances in recombinant adeno-associated virus (rAAV) gene therapy for choroideremia show gene replacement to be a promising approach. It is, however, well known that contact of vector solution with plastic materials in the surgical device may result in non-specific adsorption with resulting loss of physical titer and/or level of protein expression and activity. Here we assessed the biocompatibility and stability of rAAV2-REP1 (Rab Escort Protein-1) before and following passage through the injection device over a period of time to mimic the clinical scenario. Three identical devices were screened using two concentrations of vector: high (1E+12 DNase-resistant particles [DRP]/mL) and low (1E+11 DRP/mL), to mimic high- and low-dose administrations of vector product. The low dose was prepared using either formulation buffer that contained 0.001% of a non-ionic surfactant (PF68) or balanced salt solution (BSS). We observed significant losses in the genomic titer of samples diluted with BSS for all time points. The addition of 0.001% PF68 did not, however, affect rAAV physical titer, or REP1 protein expression and biological activity. Hence we observed that neither the genomic titer nor the biological activity of a rAAV2-REP1-containing solution was affected following passage through the surgical device when PF68 was present as a surfactant and this was maintained over a period up to 10 h.

Spectrum of Disease Severity and Phenotype in Choroideremia Carriers

PURPOSE

To characterize and bring awareness to the disease spectrum of female choroideremia patients, as severity can vary from mild to severe disease, comparable to that observed in male patients.

DESIGN

Retrospective cohort study.

METHODS

Twelve female carriers of disease-causing variants in the CHM gene confirmed by molecular genetic sequencing were characterized clinically and imaged with short-wave fundus autofluorescence (SW-FAF), spectral-domain optical coherence tomography (OCT), and color fundus imaging.

RESULTS

Twelve unrelated female patients with a clinical and genetic diagnosis of choroideremia carriers were included in this study. Disease severity among these phenotypes ranged from mild to severe, resembling the typical presentation of choroideremia in male patients. Mild disease presented with retinal pigment epithelium mottling, a patchy pattern of hypoautofluorescent speckles on SW-FAF, and intact retinal layers on spectral-domain OCT. Severe disease presented with widespread chorioretinal atrophy as shown by SW-FAF and spectral-domain OCT. Each of the identified genetic variants in CHM was predicted to be disease-causing according to in silico prediction software. Disease progression analysis of 4 patients with follow-up showed a decline in visual acuity for 2 patients, with progression observed on spectral-domain OCT in 1 of the patients. No significant disease progression on SW-FAF was observed for any of the patients.

CONCLUSIONS

Female carriers of choroideremia can present with a wide range of clinical phenotypes and disease severity, from mild to severe disease, similar to male subjects. Symptomatic female subjects should be considered for current and upcoming gene replacement therapy clinical trials.

Efficacy and Safety of Retinal Gene Therapy Using Adeno-Associated Virus Vector for Patients With Choroideremia: A Randomized Clinical Trial

Importance

Choroideremia (CHM) is a rare, degenerative, genetic retinal disorder resulting from mutation of the CHM gene, leading to an absence of functional ras-associated binding escort protein 1 (REP1). There is currently no approved treatment for CHM.

Objective

To assess the safety and efficacy of retinal gene therapy with an adeno-associated virus vector (AAV2) designed to deliver a functional version of the CHM gene (AAV2-REP1) for treatment of patients with choroideremia.

Design, Setting, and Participants

Tübingen Choroideremia Gene Therapy (THOR) was a single-center, phase 2, open-label randomized clinical trial. Data were collected from January 11, 2016, to February 26, 2018. Twenty-four-month data are reported for 6 men with a molecularly confirmed diagnosis of CHM. Intention-to-treat analysis was used.

Interventions

Patients received AAV2-REP1 by a single, 0.1-mL subretinal injection of 1011 genome particles during vitrectomy into 1 eye randomly assigned to receive treatment.

Main Outcomes and Measures

Primary end point was change in best-corrected visual acuity (BCVA) on the Early Treatment Diabetic Retinopathy Study chart from baseline to month 24 in the treated eye vs the control eye. Secondary end points included microperimetry variables, change in fundus autofluorescence, and spectral-domain optical coherence tomographic evaluations from baseline to month 24 in the treated eye vs the control eye.

Results

On enrollment, the mean (SD) age of the 6 men included in the study was 54.9 (4.1) years. The mean (SD) BCVA score was 60.3 (13.4) (approximately 20/63 Snellen equivalent) in the study eyes and 69.3 (20.6) (approximately 20/40 Snellen equivalent) in the control eyes. At 24 months, the BCVA change was 3.7 (7.5) in the treated eyes and 0.0 (5.1) in the control eyes (difference, 3.7; 95% CI, -7.2 to 14.5; P = .43). Mean change in retinal sensitivity was 10.3 (5.5) dB in the treated eyes and 9.7 (4.9) dB in the control eyes (difference, 0.6; 95% CI, -10.2 to 11.4; P = .74). A total of 28 adverse events were reported; all were consistent with the surgical procedure (eg, conjunctival hyperemia, foreign body sensation), and none were regarded as severe.

Conclusions and Relevance

Among 6 participants, gene therapy with AAV2-REP1 was associated with maintenance or improvement of visual acuity, although no significant difference was found from control eyes. All safety issues were associated with the surgical procedure and none were judged severe. Continued investigations could more precisely define the efficacy and safety of gene therapy with AAV2-REP1 in CHM.

Trial Registration

ClinicalTrials.gov identifier: NCT02671539.

Helper-Dependent Adenovirus Transduces the Human and Rat Retina but Elicits an Inflammatory Reaction When Delivered Subretinally in Rats

The identification of >100 genes causing inherited retinal degeneration and the promising results of recent gene augmentation trials have led to an increase in the number of studies investigating the preclinical efficacy of viral-mediated gene transfer. Despite success using adeno-associated viruses, many disease-causing genes, such as ABCA4 or USH2A, are too large to fit into these vectors. One option for large gene delivery is the family of integration-deficient helper-dependent adenoviruses (HDAds), which efficiently transduce postmitotic neurons. However, HDAds have been shown in other organ systems to elicit an immune response, and the immunogenicity of HDAds in the retina has not been characterized. In this study, HDAd serotype 5 (HDAd5) was found to successfully transduce rod and cone photoreceptors in ex vivo human retinal organ cultures. The ocular inflammatory response to subretinal injection of the HDAd5 was evaluated using a rat model. Subretinal injection of HDAd5 carrying cytomegalovirus promoter-driven enhanced green fluorescent protein (HDAd5-CMVp-eGFP) elicited a robust inflammatory response by 3 days postinjection. This reaction included vitreous infiltration of ionized calcium-binding adapter molecule 1 (Iba1)-positive monocytes and increased expression of the proinflammatory protein, intercellular adhesion molecule 1 (ICAM-1). By 7 days postinjection, most Iba1-positive infiltrates migrated into the neural retina and ICAM-1 expression was significantly increased compared with buffer-injected control eyes. At 14 days postinjection, Iba1-positive cells persisted in the retinas of HDAd5-injected eyes, and there was thinning of the outer nuclear layer. Subretinal injection of an empty HDAd5 virus was used to confirm that the inflammatory response was in response to the HDAd5 vector and not due to eGFP-induced overexpression cytotoxicity. Subretinal injection of lower doses of HDAd5 dampened the inflammatory response, but also eGFP expression. Despite their larger carrying capacity, further work is needed to elucidate the inflammatory pathways involved and to identify an immunomodulation paradigm sufficient for safe and effective transfer of large genes to the retina using HDAd5.

Molecular Therapies for Choroideremia

Advances in molecular research have culminated in the development of novel gene-based therapies for inherited retinal diseases. We have recently witnessed several groundbreaking clinical studies that ultimately led to approval of Luxturna, the first gene therapy for an inherited retinal disease. In parallel, international research community has been engaged in conducting gene therapy trials for another more common inherited retinal disease known as choroideremia and with phase III clinical trials now underway, approval of this therapy is poised to follow suit. This chapter discusses new insights into clinical phenotyping and molecular genetic testing in choroideremia with review of molecular mechanisms implicated in its pathogenesis. We provide an update on current gene therapy trials and discuss potential inclusion of female carries in future clinical studies. Alternative molecular therapies are discussed including suitability of CRISPR gene editing, small molecule nonsense suppression therapy and vision restoration strategies in late stage choroideremia.

Outcome Measures Used in Ocular Gene Therapy Trials: A Scoping Review of Current Practice

Multiple gene therapy trials are occurring for a variety of ophthalmic diseases around the world. The safety of gene therapy in the eye has been established, and the next step is to reliably assess efficacy. This is primarily done through the use of imaging techniques and visual function measures. Standardized visual function assessments, however, were originally developed for a clinical setting and may not be suitable for detecting and quantifying therapeutic changes. This scoping review takes a comprehensive look at current practice in terms of the outcome measures defined at trial registration. These were compared to the outcome measures reported in the literature. All published trials reported the pre-registered primary outcome measure. A range of additional secondary outcomes were reported that were not originally planned. Gaps in gene therapy assessment exist and further discussion are required to find a way forward, particularly as more conditions progress to phase 2 and 3 trials. Several factors impacting on trial design and outcome measure choice are discussed.

Potential lifetime quality of life benefits of choroideremia gene therapy: projections from a clinically informed decision model

BACKGROUND

The first gene therapy for an inherited retinal dystrophy recently received market approval in the United States; multiple other gene therapies are in the clinical pipeline. Thus far, gene therapy has commanded prices in the range of $500,000 to over $1,000,000 for the one-time doses and have been indicated for highly orphan diseases where there is no other viable treatment option. To be adopted by healthcare systems, gene therapy will need to show clinical benefit in line with its increased costs. Before longitudinal patient studies are available, model-based estimations will be necessary to project the full clinical benefit of gene therapy.

METHODS

To investigate the lifetime benefit of gene therapy for the retinal dystrophy choroideremia, we have built a Markov model of disease progression informed by clinical data of AAV.REP1 and voretigene neparvovec (Luxturna, Spark Therapeutics). Gene therapy patient benefit was estimated by quality-adjusted life years (QALYs) in three hypothetical disease severity patient groups. The severity of disease was defined by the combined effect of remaining retinal area and visual acuity and assigned corresponding health utility values.

RESULTS

Early-stage patients treated with gene therapy were estimated to gain, in average, 14.30 QALYs over standard-of-care, mid-stage patients 6.22 QALYs, and late-stage patients 1.48 QALYs over untreated patients during their lifetime owing to treatment. Cost-effectiveness was not assessed as AAV.REP1 is still in clinical trials.

CONCLUSIONS

In young adults in the earlier stages of choroideremia, successful gene therapy is expected to provide a significant increase in health-related quality of life.

Performance of a Defect-Mapping Microperimetry Approach for Characterizing Progressive Changes in Deep Scotomas

Purpose

To examine whether a microperimetry testing strategy based on quantifying the spatial extent of functional abnormalities (termed “defect-mapping” strategy) could improve the detection of progressive changes in deep scotomas compared to the conventional thresholding strategy.

Methods

A total of 30 healthy participants underwent two microperimetry examinations, each using the defect-mapping and thresholding strategies at the first visit to examine the test–retest variability of each method. Testing was performed using an isotropic stimulus pattern centered on the optic nerve head (ONH), which acted as a model of a deep scotoma. These tests were repeated at a second visit, except using a smaller stimulus pattern and thereby increasing the proportion of test locations falling within the ONH (to simulate the progressive enlargement of a deep scotoma). The extent of change detected between visits relative to measurement variability was compared between the two strategies.

Results

Relative to their effective dynamic ranges, the test–retest variability of the defect-mapping strategy (1.8%) was significantly lower compared to the thresholding strategy (3.3%; P < 0.001). The defect-mapping strategy also captured a significantly greater extent of change between visits relative to variability (−4.70 t⁻¹) compared to the thresholding strategy (2.74 t⁻¹; P < 0.001).

Conclusions

A defect-mapping microperimetry testing strategy shows promise for capturing the progressive enlargement of deep scotomas more effectively than the conventional thresholding strategy.

Translational Relevance

Microperimetry testing with the defect-mapping strategy could provide a more accurate clinical trial outcome measure for capturing progressive changes in deep scotomas in eyes with atrophic retinal diseases, warranting further investigations.

Participant perspectives on a phase I/II ocular gene therapy trial (NCT02077361)

Background: To learn from the experiences of potential clinical trial participants, participants in a Phase 1 ocular gene therapy trial, and their partners to improve communications and trial conduct. Materials and methods: Primary and secondary qualitative analysis of semi-structured interviews of potential participants (n = 20), clinical trial participants (n = 2) and their partners (n = 2) in a gene therapy clinical trial for choroideremia (NCT02077361). Analysis included: 1) thematic analysis of transcribed entrance and exit semi-structured interviews with trial participants and their partners; and 2) secondary qualitative analysis of interviews with potential trial participants, conducted prior to the initiation of the clinical trial. Results: Participants and partners who had received information during the consent process had a better understanding of the risks and benefits of participation in a Phase 1 gene therapy clinical trial than potential trial participants. However, participants and partners reported deficiencies in communication throughout the trial. Results highlight additional opportunities for trial staff to reinforce initial information about the trial, communicate logistical information and individual outcome data, and express appreciation for participation. Conclusions: Our study enabled clinical trial participants to describe their experiences in a clinical trial for a novel gene therapy. We provide practical recommendations to future clinical trial staff on communications and conduct participant perspectives. Communications strategies should address changing information needs over the course of the trial, express appreciation for participation and enable feedback from participants and their supporting family members, friends, or caregivers.

Attenuation of Inherited and Acquired Retinal Degeneration Progression with Gene-based Techniques

Inherited retinal dystrophies cause progressive vision loss and are major contributors to blindness worldwide. Advances in gene therapy have brought molecular approaches into the realm of clinical trials for these incurable illnesses. Select phase I, II and III trials are complete and provide some promise in terms of functional outcomes and safety, although questions do remain over the durability of their effects and the prevalence of inflammatory reactions. This article reviews gene therapy as it can be applied to inherited retinal dystrophies, provides an update of results from recent clinical trials, and discusses the future prospects of gene therapy and genome surgery.

AAV cis-regulatory sequences are correlated with ocular toxicity

Adeno-associated viral (AAV) gene therapy is becoming an important therapeutic modality, especially for ocular diseases, due to its efficiency of gene delivery and relative lack of pathogenicity. However, AAV sometimes can cause inflammation and toxicity. We explored such effects using injections into the mouse eye. We found a strong correlation of toxicity and inflammation with the use of promoters that were broadly active, or specifically active in the retinal pigment epithelium. AAVs with photoreceptor-specific promoters were found to be nontoxic at all doses tested. These studies reveal that safer vectors can be designed if assays for relevant and specific cell types are developed and tested with a range of vectors with different genomic elements.

Adeno-associated viral vectors (AAVs) have become popular for gene therapy, given their many advantages, including their reduced inflammatory profile compared with that of other viruses. However, even in areas of immune privilege such as the eye, AAV vectors are capable of eliciting host-cell responses. To investigate the effects of such responses on several ocular cell types, we tested multiple AAV genome structures and capsid types using subretinal injections in mice. Assays of morphology, inflammation, and physiology were performed. Pathological effects on photoreceptors and the retinal pigment epithelium (RPE) were observed. Müller glia and microglia were activated, and the proinflammatory cytokines TNF-α and IL-1β were up-regulated. There was a strong correlation between cis-regulatory sequences and toxicity. AAVs with any one of three broadly active promoters, or an RPE-specific promoter, were toxic, while AAVs with four different photoreceptor-specific promoters were not toxic at the highest doses tested. There was little correlation between toxicity and transgene, capsid type, preparation method, or cellular contaminants within a preparation. The toxic effect was dose-dependent, with the RPE being more sensitive than photoreceptors. Our results suggest that ocular AAV toxicity is associated with certain AAV cis-regulatory sequences and/or their activity and that retinal damage occurs due to responses by the RPE and/or microglia. By applying multiple, sensitive assays of toxicity, AAV vectors can be designed so that they can be used safely at high dose, potentially providing greater therapeutic efficacy.

Adeno-Associated Viral Gene Therapy for Inherited Retinal Disease

Inherited retinal diseases (IRDs) are a group of rare, heterogenous eye disorders caused by gene mutations that result in degeneration of the retina. There are currently limited treatment options for IRDs; however, retinal gene therapy holds great promise for the treatment of different forms of inherited blindness. One such IRD for which gene therapy has shown positive initial results is choroideremia, a rare, X-linked degenerative disorder of the retina and choroid. Mutation of the CHM gene leads to an absence of functional Rab escort protein 1 (REP1), which causes retinal pigment epithelium cell death and photoreceptor degeneration. The condition presents in childhood as night blindness, followed by progressive constriction of visual fields, generally leading to vision loss in early adulthood and total blindness thereafter. A recently developed adeno-associated virus-2 (AAV2) vector construct encoding REP1 (AAV2-REP1) has been shown to deliver a functional version of the CHM gene into the retinal pigment epithelium and photoreceptor cells. Phase 1 and 2 studies of AAV2-REP1 in patients with choroideremia have produced encouraging results, suggesting that it is possible not only to slow or stop the decline in vision following treatment with AAV2-REP1, but also to improve visual acuity in some patients.

Choroideremia Gene Therapy Phase 2 Clinical Trial: 24-Month Results

PURPOSE

To report the final results of a phase 2 high-dose gene therapy clinical trial in choroideremia.

METHODS

Design: Phase 2 clinical trial.

PARTICIPANTS

Six men (aged 32-72 years) with genetically-confirmed advanced choroideremia. Patients received subfoveal injection of AAV2-REP1 (10¹¹ genome particles in 0.1 mL) in the worse-sighted eye.

OUTCOME MEASURES

Primary measure was best-corrected visual acuity (BCVA) change from baseline in the treated eye compared to the untreated eye. Secondary endpoints included change from baseline in microperimetry, fundus autofluorescence, and spectral-domain optical coherence tomography (OCT). Safety evaluations included adverse events, viral shedding in body fluids, and vector antibody responses.

RESULTS

Baseline mean ETDRS BCVA was 65.3 ± 8.8 (SD, range 56-77, 20/32-20/80) letters in the treated eyes and 77.0 ± 4.2 (69-81, 20/25-20/40) letters in the untreated eyes. At 2 years, 1 treated eye improved by 10 letters and another by 5 letters, while 1 untreated eye improved by 4 letters. All other eyes were within 2 letters of baseline. Baseline microperimetry sensitivities in the treated eyes were poor (1.2 ± 2.1 (0, 5.1) dB) and showed no significant change. No serious adverse event occurred. Two patients developed an atrophic retinal hole in a nonfunctioning macular area where baseline OCT showed preexisting thinning. Intraoperative microscope-integrated OCT allowed proper subretinal injection with avoidance of excessive foveal stretching and macular hole formation.

CONCLUSIONS

Sustained improvement or maintenance of BCVA is achievable in choroideremia with high-dose AAV2-REP1, indicating BCVA is a viable primary outcome in advanced choroideremia. Choroideremia gene therapy delivered with intraoperative OCT has a good safety profile.

Progress in the development of novel therapies for choroideremia

INTRODUCTION

There are no currently approved treatments for choroideremia, an X-linked progressive inherited retinal degeneration that leads to blindness by middle age. Several treatment options are being explored, but with major advances in adeno-associated vector (AAV) gene replacement therapy that has reached phase III clinical trials.

AREAS COVERED

In this review we discuss new insights into the clinical phenotyping and genetic testing of choroideremia patients, that aid disease characterisation, progression and patient inclusion into clinical trials. Recent advances in in-vitro studies have resulted in the development of functional assays that can be used to confirm the diagnosis in challenging cases and to quantify vector potency for use in clinical trials. We review the progress in current gene therapy trials and some considerations towards gene therapy approval for the treatment of choroideremia. Lastly, we discuss developments in alternative therapies including optogenetics.

EXPERT COMMENTARY

AAV gene replacement therapy is the most promising treatment strategy for choroideremia, that has developed exponentially over the last few years with a phase III clinical trial now underway. Optogenetics is a promising alternative strategy that might be applicable in late stages of degeneration.

Choroideremia: from genetic and clinical phenotyping to gene therapy and future treatments

Choroideremia is an X-linked inherited chorioretinal dystrophy leading to blindness by late adulthood. Choroideremia is caused by mutations in the CHM gene which encodes Rab escort protein 1 (REP1), an ubiquitously expressed protein involved in intracellular trafficking and prenylation activity. The exact site of pathogenesis remains unclear but results in degeneration of the photoreceptors, retinal pigment epithelium and choroid. Animal and stem cell models have been used to study the molecular defects in choroideremia and test effectiveness of treatment interventions. Natural history studies of choroideremia have provided additional insight into the clinical phenotype of the condition and prepared the way for clinical trials aiming to investigate the safety and efficacy of suitable therapies. In this review, we provide a summary of the current knowledge on the genetics, pathophysiology, clinical features and therapeutic strategies that might become available for choroideremia in the future, including gene therapy, stem cell treatment and small-molecule drugs with nonsense suppression action.

Novel CHM mutations in Polish patients with choroideremia - an orphan disease with close perspective of treatment

Background

Choroideremia (CHM) is a rare X-linked recessive retinal dystrophy characterized by progressive chorioretinal degeneration in the males affected. The symptoms include night blindness in childhood, progressive peripheral vision loss and total blindness in the late stages. The disease is caused by mutations in the CHM gene encoding Rab Escort Protein 1 (REP-1). The aim of the study was to identify the molecular basis of choroideremia in five families of Polish origin.

Methods

Six male patients from five unrelated families of Polish ethnicity, who were clinically diagnosed with choroideremia, were examined in this study. An ophthalmologic examination performed in all the probands included: best-corrected visual acuity, slit-lamp examination, funduscopy, fluorescein angiography and perimetry. The entire coding region encompassing 15 exons and the flanking intronic sequences of the CHM gene were amplified with PCR and directly sequenced in all the patients.

Results

Five variants in the CHM gene were identified in the five families examined. Two of the variants were new: c.1175dupT and c.83C > G, while three had been previously reported.

Conclusions

This study provides the first molecular genetic characteristics of patients with choroideremia from the previously unexplored Polish population.

The Blunt End: Surgical Challenges of Gene Therapy for Inherited Retinal Diseases

PURPOSE

To review barriers to effective transduction of cells in the subretinal plane during gene therapy surgery for inherited retinal dystrophies (IRD).

DESIGN

Perspective.

METHODS

Case-based learning in clinical trials and commercial applications of gene therapy in a tertiary care, university-affiliated hospital. MEDLINE search for publications relevant to retinal surgical technique for gene therapy, clinical trials results for gene therapy of IRD, adenoviral-associated viral vector design, and immune response to viral vectors.

RESULTS

The most important surgical issues are safe access to the subretinal space, intraoperative visualization with optical coherence tomography to protect the macula, and quantitation of viral dose. Other issues for retinal surgeons are patient selection, target zone planning, and control of inflammation. Vector-related issues that may affect the precision of treatment involve capsid interaction with the innate and adaptive immune systems and selective targeting of cell types.

CONCLUSIONS

Most current gene therapy vectors for monogenic IRD require physical proximity to target tissues under the retina in order to work. New surgical skills and new instrumentation are under development. So far, the host immune response does not seem to cause rejection of genes delivered by viral vectors but the efficiency of transduction can only be indirectly assessed by long-term visual outcomes.

Beneficial effects on vision in patients undergoing retinal gene therapy for choroideremia

Retinal gene therapy is increasingly recognized as a novel molecular intervention that has huge potential in treating common causes of blindness, the majority of which have a genetic aetiology1-5. Choroideremia is a chronic X-linked retinal degeneration that was first described in 18726. It leads to progressive blindness due to deficiency of Rab-escort protein 1 (REP1). We designed an adeno-associated viral vector to express REP1 and assessed it in a gene therapy clinical trial by subretinal injection in 14 patients with choroideremia. The primary endpoint was vision change in treated eyes 2 years after surgery compared to unoperated fellow eyes. Despite complications in two patients, visual acuity improved in the 14 treated eyes over controls (median 4.5 letter gain, versus 1.5 letter loss, P = 0.04), with 6 treated eyes gaining more than one line of vision (>5 letters). The results suggest that retinal gene therapy can sustain and improve visual acuity in a cohort of predominantly late-stage choroideremia patients in whom rapid visual acuity loss would ordinarily be predicted.