rAAV-compatible human mini promoters enhance transgene expression in rat retinal ganglion cells

Recombinant adeno-associated viral vectors (rAAV) are the safest and most effective gene delivery platform to drive the treatment of many inherited eye disorders in well-characterized animal models. The use in rAAV of ubiquitous promoters derived from viral sequences such as CMV/CBA (chicken β-actin promoter with cytomegalovirus enhancer) can lead to unwanted side effects such as pro-inflammatory immune responses and retinal cytotoxicity, thus reducing therapy efficacy. Thus, an advance in gene therapy is the availability of small promoters, that potentiate and direct gene expression to the cell type of interest, with higher safety and efficacy. In this study, we used six human mini-promoters packaged in rAAV2 quadruple mutant (Y-F) to test for transduction of the rat retina after intravitreal injection. After four weeks, immunohistochemical analysis detected GFP-labeled cells in the ganglion cell layer (GCL) for all constructs tested. Among them, Ple25sh1, Ple25sh2 and Ple53 promoted a widespread reporter-transgene expression in the GCL, with an increased number of GFP-expressing retinal ganglion cells when compared with the CMV/CBA vector. Moreover, Ple53 provided the strongest levels of GFP fluorescence in both cell soma and axons of retinal ganglion cells (RGCs) without any detectable adverse effects in retina function. Remarkably, a nearly 50-fold reduction in the number of intravitreally injected vector particles containing Ple53 promoter, still attained levels of transgene expression similar to CMV/CBA. Thus, the tested MiniPs show great potential for protocols of retinal gene therapy in therapeutic applications for retinal degenerations, especially those involving RGC-related disorders such as glaucoma.

Development of a translatable gene augmentation therapy for CNGB1-retinitis pigmentosa

In this study, we investigate a gene augmentation therapy candidate for the treatment of retinitis pigmentosa (RP) due to cyclic nucleotide-gated channel beta 1 (CNGB1) mutations. We use an adeno-associated virus serotype 5 with transgene under control of a novel short human rhodopsin promoter. The promoter/capsid combination drives efficient expression of a reporter gene (AAV5-RHO-eGFP) exclusively in rod photoreceptors in primate, dog, and mouse following subretinal delivery. The therapeutic vector (AAV5-RHO-CNGB1) delivered to the subretinal space of CNGB1 mutant dogs restores rod-mediated retinal function (electroretinographic responses and vision) for at least 12 months post treatment. Immunohistochemistry shows human CNGB1 is expressed in rod photoreceptors in the treated regions as well as restoration of expression and trafficking of the endogenous alpha subunit of the rod CNG channel required for normal channel formation. The treatment reverses abnormal accumulation of the second messenger, cyclic guanosine monophosphate, which occurs in rod photoreceptors of CNGB1 mutant dogs, confirming formation of a functional CNG channel. In vivo imaging shows long-term preservation of retinal structure. In conclusion, this study establishes the long-term efficacy of subretinal delivery of AAV5-RHO-CNGB1 to rescue the disease phenotype in a canine model of CNGB1-RP, confirming its suitability for future clinical development.

A clinically viable approach to restoring visual function using optogenetic gene therapy

Optogenetic gene therapies offer a promising strategy for restoring vision to patients with retinal degenerative diseases, such as retinitis pigmentosa (RP). Several clinical trials have begun in this area using different vectors and optogenetic proteins (Clinical Identifiers: NCT02556736, NCT03326336, NCT04945772, and NCT04278131). Here we present preclinical efficacy and safety data for the NCT04278131 trial, which uses an AAV2 vector and Chronos as the optogenetic protein. Efficacy was assessed in mice in a dose-dependent manner using electroretinograms (ERGs). Safety was assessed in rats, nonhuman primates, and mice, using several tests, including immunohistochemical analyses and cell counts (rats), electroretinograms (nonhuman primates), and ocular toxicology assays (mice). The results showed that Chronos-expressing vectors were efficacious over a broad range of vector doses and stimulating light intensities, and were well tolerated: no test article-related findings were observed in the anatomical and electrophysiological assays performed.

Comparison of different gene-therapy methods to treat Leber hereditary optic neuropathy in a mouse model

Introduction

Therapies for Leber hereditary optic neuropathy (LHON), in common with all disorders caused by mutated mitochondrial DNA, are inadequate. We have developed two gene therapy strategies for the disease: mitochondrial-targeted and allotopic expressed and compared them in a mouse model of LHON.

Methods

A LHON mouse model was generated by intravitreal injection of a mitochondrialtargeted Adeno-associated virus (AAV) carrying mutant human NADH dehydrogenase 4 gene (hND4/m.11778G>A) to induce retinal ganglion cell (RGC) degeneration and axon loss, the hallmark of the human disease. We then attempted to rescue those mice using a second intravitreal injection of either mitochondrial-targeted or allotopic expressed wildtype human ND4. The rescue of RGCs and their axons were assessed using serial pattern electroretinogram (PERG) and transmission electron microscopy.

Results

Compared to non-rescued LHON controls where PERG amplitude was much reduced, both strategies significantly preserved PERG amplitude over 15 months. However, the rescue effect was more marked with mitochondrial-targeted therapy than with allotopic therapy (p = 0.0128). Post-mortem analysis showed that mitochondrial-targeted human ND4 better preserved small axons that are preferentially lost in human LHON.

Conclusions

These results in a pre-clinical mouse model of LHON suggest that mitochondrially-targeted AAV gene therapy, compared to allotopic AAV gene therapy, is more efficient in rescuing the LHON phenotype.

Disease mechanisms of X-linked cone dystrophy caused by missense mutations in the red and green cone opsins

Cone photoreceptors are responsible for the visual acuity and color vision of the human eye. Red/green cone opsin missense mutations N94K, W177R, P307L, R330Q, and G338E have been identified in subjects with congenital blue cone monochromacy or color‐vision deficiency. Studies on disease mechanisms due to these cone opsin mutations have been previously carried out exclusively in vitro, and the reported impairments were not always consistent. Here we expressed these mutants via AAV specifically in vivo in M‐opsin knockout mouse cones to investigate their subcellular localization, the pathogenic effects on cone structure, function, and cone viability. We show that these mutations alter the M‐opsin structure, function, and localization. N94K and W177R mutants appeared to be misfolded since they localized exclusively in cone inner segments and endoplasmic reticulum. In contrast, P307L, R330Q, and G338E mutants were detected predominately in cone outer segments. Expression of R330Q and G338E, but not P307L opsins, also partially restored expression and correct localization of cone PDE6α’ and cone transducin γ and resulted in partial rescue of M‐cone‐mediated light responses. Expression of W177R and P307L mutants significantly reduced cone viability, whereas N94K, R330Q, and G338E were only modestly toxic. We propose that although the underlying biochemical and cellular defects caused by these mutants are distinct, they all seem to exhibit a dominant phenotype, resembling autosomal dominant retinitis pigmentosa associated with the majority of rhodopsin missense mutations. The understanding of the molecular mechanisms associated with these cone opsin mutants is fundamental to developing targeted therapies for cone dystrophy/dysfunction.

XIAP gene therapy effects on retinal ganglion cell structure and function in a mouse model of glaucoma

Glaucoma is a prevalent neurodegenerative disease that is characterized by progressive visual field loss. It is the leading cause of irreversible blindness in the world. The main risk factor for glaucoma is elevated intraocular pressure that results in the damage and death of retinal ganglion cells (RGCs) and their axons. The death of RGCs has been shown to be apoptotic. We tested the hypothesis that blocking the activation of apoptosis may be an effective strategy to prevent RGC death and preserve functional vision in glaucoma. In the magnetic microbead mouse model of induced ocular hypertension, inhibition of RGC apoptosis was targeted through viral-mediated ocular delivery of the X-linked inhibitor of apoptosis (XIAP) gene, a potent caspase inhibitor. Pattern electroretinograms revealed that XIAP therapy resulted in significant protection of both somal and axonal RGC function in glaucomatous eyes. Histology confirmed that the treated optic nerves showed preservation of axon counts and reduced glial cell infiltration. These results show that XIAP is able to provide both functional and structural protection of RGCs in the microbead model of glaucoma and provide important proof-of-principle for XIAP's efficacy as a neuroprotective treatment for glaucoma.

Examining Whether AOSLO-Based Foveal Cone Metrics in Achromatopsia and Albinism Are Representative of Foveal Cone Structure

Purpose

Adaptive optics scanning light ophthalmoscopy (AOSLO) imaging in patients with achromatopsia (ACHM) and albinism is not always successful. Here, we tested whether optical coherence tomography (OCT) measures of foveal structure differed between patients for whom AOSLO images were either quantifiable or unquantifiable.

Methods

The study included 166 subjects (84 with ACHM; 82 with albinism) with previously acquired OCT scans, AOSLO images, and best-corrected visual acuity (BCVA, if available). Foveal OCT scans were assessed for outer retinal structure, outer nuclear layer thickness, and hypoplasia. AOSLO images were graded as quantifiable if a peak cone density could be measured and/or usable if the location of peak density could be identified and the parafoveal mosaic was quantifiable.

Results

Forty-nine percent of subjects with ACHM and 57% of subjects with albinism had quantifiable AOSLO images. Older age and better BCVA were found in subjects with quantifiable AOSLO images for both ACHM (P = 0.0214 and P = 0.0276, respectively) and albinism (P = 0.0073 and P < 0.0004, respectively). There was a significant trend between ellipsoid zone appearance and ability to quantify AOSLO (P = 0.0028). In albinism, OCT metrics of cone structure did not differ between groups.

Conclusions

Previously reported AOSLO-based cone density measures in ACHM may not necessarily reflect the degree of remnant cone structure in these patients.

Translational Relevance

Until AOSLO is successful in all patients with ACHM and albinism, the possibility of the reported data from a particular cohort not being representative of the entire population remains an important issue to consider when interpreting results from AOSLO studies.

CNGB1-related rod-cone dystrophy: A mutation review and update

Cyclic nucleotide‐gated channel β1 (CNGB1) encodes the 240‐kDa β subunit of the rod photoreceptor cyclic nucleotide‐gated ion channel. Disease‐causing sequence variants in CNGB1 lead to autosomal recessive rod‐cone dystrophy/retinitis pigmentosa (RP). We herein present a comprehensive review and analysis of all previously reported CNGB1 sequence variants, and add 22 novel variants, thereby enlarging the spectrum to 84 variants in total, including 24 missense variants (two of which may also affect splicing), 21 nonsense, 19 splicing defects (7 at noncanonical positions), 10 small deletions, 1 small insertion, 1 small insertion–deletion, 7 small duplications, and 1 gross deletion. According to the American College of Medical Genetics and Genomics classification criteria, 59 variants were considered pathogenic or likely pathogenic and 25 were variants of uncertain significance. In addition, we provide further phenotypic data from 34 CNGB1‐related RP cases, which, overall, are in line with previous findings suggesting that this form of RP has long‐term retention of useful central vision despite the early onset of night blindness, which is valuable for patient counseling, but also has implications for it being considered a priority target for gene therapy trials.

Optical Coherence Tomography Artifacts Are Associated With Adaptive Optics Scanning Light Ophthalmoscopy Success in Achromatopsia

Purpose

To determine whether artifacts in optical coherence tomography (OCT) images are associated with the success or failure of adaptive optics scanning light ophthalmoscopy (AOSLO) imaging in subjects with achromatopsia (ACHM).

Methods

Previously acquired OCT and non-confocal, split-detector AOSLO images from one eye of 66 subjects with genetically confirmed achromatopsia (15 CNGA3 and 51 CNGB3) were reviewed along with best-corrected visual acuity (BCVA) and axial length. OCT artifacts in interpolated vertical volumes from CIRRUS macular cubes were divided into four categories: (1) none or minimal, (2) clear and low frequency, (3) low amplitude and high frequency, and (4) high amplitude and high frequency. Each vertical volume was assessed once by two observers. AOSLO success was defined as sufficient image quality in split-detector images at the fovea to assess cone quantity.

Results

There was excellent agreement between the two observers for assessing OCT artifact severity category (weighted kappa = 0.88). Overall, AOSLO success was 47%. For subjects with OCT artifact severity category 1, AOSLO success was 65%; for category 2, 47%; for category 3, 11%; and for category 4, 0%. There was a significant association between OCT artifact severity category and AOSLO success (P = 0.0002). Neither BCVA nor axial length was associated with AOSLO success (P = 0.07 and P = 0.75, respectively).

Conclusions

Artifacts in OCT volumes are associated with AOSLO success in ACHM. Subjects with less severe OCT artifacts are more likely to be good candidates for AOSLO imaging, whereas AOSLO was successful in only 7% of subjects with category 3 or 4 OCT artifacts. These results may be useful in guiding patient selection for AOSLO imaging.

Translational Relevance

Using OCT to prescreen patients could be a valuable tool for clinical trials that utilize AOSLO to reduce costs and decrease patient testing burden.

Interocular Symmetry of Foveal Cone Topography in Congenital Achromatopsia

Purpose: To determine the interocular symmetry of foveal cone topography in achromatopsia (ACHM) using non-confocal split-detection adaptive optics scanning light ophthalmoscopy (AOSLO). Methods: Split-detector AOSLO images of the foveal cone mosaic were acquired from both eyes of 26 subjects (mean age 24.3 years; range 8-44 years, 14 females) with genetically confirmed CNGA3- or CNGB3-associated ACHM. Cones were identified within a manually delineated rod-free zone. Peak cone density (PCD) was determined using an 80 × 80 μm sampling window within the rod-free zone. The mean and standard deviation (SD) of inter-cell distance (ICD) were calculated to derive the coefficient of variation (CV). Cone density difference maps were generated to compare cone topography between eyes. Results: PCD (mean ± SD) was 17,530 ± 9,614 cones/mm2 and 17,638 ± 9,753 cones/mm2 for right and left eyes, respectively (p = .677, Wilcoxon test). The mean (± SD) for ICD was 9.05 ± 2.55 µm and 9.24 ± 2.55 µm for right and left eyes, respectively (p = .410, paired t-test). The mean (± SD) for CV of ICD was 0.16 ± 0.03 µm and 0.16 ± 0.04 µm for right and left eyes, respectively (p = .562, paired t-test). Cone density maps demonstrated that cone topography of the ACHM fovea is non-uniform with local variations in cone density between eyes. Conclusions: These results demonstrate the interocular symmetry of the foveal cone mosaic (both density and packing) in ACHM. As cone topography can differ between eyes of a subject, PCD does not completely describe the foveal cone mosaic in ACHM. Nonetheless, these findings are of value in longitudinal monitoring of patients during treatment trials and further suggest that both eyes of a given subject may have similar therapeutic potential and non-study eye can be used as a control.

Evaluation of Photoreceptor Transduction Efficacy of Capsid-Modified Adeno-Associated Viral Vectors Following Intravitreal and Subretinal Delivery in Sheep

Gene augmentation therapy based on subretinal delivery of adeno-associated viral (AAV) vectors is proving to be highly efficient in treating several inherited retinal degenerations. However, due to potential complications and drawbacks posed by subretinal injections, there is a great impetus to find alternative methods of delivering the desired genetic inserts to the retina. One such method is an intravitreal delivery of the vector. Our aim was to evaluate the efficacy of two capsid-modified vectors that are less susceptible to cellular degradation, AAV8 (doubleY-F) and AAV2 (quadY-F+T-V), as well as a third, chimeric vector AAV[max], to transduce photoreceptor cells following intravitreal injection in sheep. We further tested whether saturation of inner limiting membrane (ILM) viral binding sites using a nonmodified vector, before the intravitreal injection, would enhance the efficacy of photoreceptor transduction. Only AAV[max] resulted in moderate photoreceptor transduction following intravitreal injection. Intravitreal injection of the two other vectors did not result in photoreceptor transduction nor did the saturation of the ILM before the intravitreal injection. However, two of the vectors efficiently transduced photoreceptor cells following subretinal injection in positive control eyes. Previous trials with the same vectors in both murine and canine models resulted in robust and moderate transduction efficacy, respectively, of photoreceptors following intravitreal delivery, demonstrating the importance of utilizing as many animal models as possible when evaluating new strategies for retinal gene therapy. The successful photoreceptor transduction of AAV[max] injected intravitreally makes it a potential candidate for intravitreal delivery, but further trials are warranted to determine whether the transduction efficacy is sufficient for a clinical outcome.

XIAP Protects Retinal Ganglion Cells in the Mutant ND4 Mouse Model of Leber Hereditary Optic Neuropathy

Purpose

Leber hereditary optic neuropathy (LHON) is a genetic form of vision loss that occurs primarily owing to mutations in the nicotinamide adenine dinucleotide dehydrogenase (ND) subunits that make up complex I of the electron transport chain. LHON mutations result in the apoptotic death of retinal ganglion cells. We tested the hypothesis that gene therapy with the X-linked inhibitor of apoptosis (XIAP) would prevent retinal ganglion cell apoptosis and reduce disease progression in a vector-induced mouse model of LHON that carries the ND4 mutation.

Methods

Adeno-associated virus (AAV) encoding full length hemagglutinin-tagged XIAP (AAV2.HA-XIAP) or green fluorescent protein (AAV2.GFP) was injected into the vitreous of DBA/1J mice. Two weeks later, the LHON phenotype was induced by AAV delivery of mutant ND4 (AAV2.mND4FLAG) to the vitreous. Retinal function was assessed by pattern electroretinography. Optic nerves were harvested at 4 months, and the effects of XIAP therapy on nerve fiber layer and optic nerve integrity were evaluated using immunohistochemistry, transmission electron microscopy and magnetic resonance imaging.

Results

During LHON disease progression, retinal ganglion cell axons are lost. Apoptotic cell bodies are seen in the nuclei of astrocytes or oligodendrocytes in the optic nerve, and there is thinning of the optic nerve and the nerve fiber layer of the retina. At 4 months after disease onset, XIAP gene therapy protects the nerve fiber layer and optic nerve architecture by preserving axon health. XIAP also decreases nuclear fragmentation in resident astrocytes or oligodendrocytes and decreases glial cell infiltration.

Conclusions

XIAP therapy improves optic nerve health and delays disease progression in LHON.

Clarin-1 expression in adult mouse and human retina highlights a role of Müller glia in Usher syndrome

Usher syndrome type 3 (USH3) is an autosomal recessively inherited disorder caused by mutations in the gene clarin‐1 (CLRN1), leading to combined progressive hearing loss and retinal degeneration. The cellular distribution of CLRN1 in the retina remains uncertain, either because its expression levels are low or because its epitopes are masked. Indeed, in the adult mouse retina, Clrn1 mRNA is developmentally downregulated, detectable only by RT‐PCR. In this study we used the highly sensitive RNAscope in situ hybridization assay and single‐cell RNA‐sequencing techniques to investigate the distribution of Clrn1 and CLRN1 in mouse and human retina, respectively. We found that Clrn1 transcripts in mouse tissue are localized to the inner retina during postnatal development and in adult stages. The pattern of Clrn1 mRNA cellular expression is similar in both mouse and human adult retina, with CLRN1 transcripts being localized in Müller glia, and not photoreceptors. We generated a novel knock‐in mouse with a hemagglutinin (HA) epitope‐tagged CLRN1 and showed that CLRN1 is expressed continuously at the protein level in the retina. Following enzymatic deglycosylation and immunoblotting analysis, we detected a single CLRN1‐specific protein band in homogenates of mouse and human retina, consistent in size with the main CLRN1 isoform. Taken together, our results implicate Müller glia in USH3 pathology, placing this cell type to the center of future mechanistic and therapeutic studies to prevent vision loss in this disease. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Optimal Inhibition of Choroidal Neovascularization by scAAV2 with VMD2 Promoter-driven Active Rap1a in the RPE

Age-related macular degeneration (AMD) is a multifactorial chronic disease that requires long term treatment. Gene therapy is being considered as a promising tool to treat AMD. We found that increased activation of Rap1a in the retinal pigment epithelium (RPE) reduces oxidative signaling to maintain barrier integrity of the RPE and resist neural sensory retinal angiogenesis from choroidal endothelial cell invasion. To optimally deliver constitutively active Rap1a (CARap1a) into the RPE of wild type mice, self-complementary AAV2 (scAAV2) vectors driven by two different promoters, RPE65 or VMD2, were generated and tested for optimal active Rap1a expression and inhibition of choroidal neovascularization (CNV) induced by laser injury. scAAV2-VMD2, but not scAAV2-RPE65, specifically and efficiently transduced the RPE to increase active Rap1a protein in the RPE. Mice with increased Rap1a from the scAAV2-VMD2-CARap1a had a significant reduction in CNV compared to controls. Increased active Rap1a in the RPE in vivo or in vitro inhibited inflammatory and angiogenic signaling determined by decreased activation of NF-κB and expression of VEGF without causing increased cell death or autophagy measured by increased LCA3/B. Our study provides a potential future strategy to deliver active Rap1a to the RPE in order to protect against both atrophic and neovascular AMD.

Dual ABCA4-AAV Vector Treatment Reduces Pathogenic Retinal A2E Accumulation in a Mouse Model of Autosomal Recessive Stargardt Disease

Autosomal recessive Stargardt disease is the most common inherited macular degeneration in humans. It is caused by mutations in the retina-specific ATP binding cassette transporter A4 (ABCA4) that is essential for the clearance of all-trans-retinal from photoreceptor cells. Loss of this function results in the accumulation of toxic bisretinoids in the outer segment disk membranes and their subsequent transfer into adjacent retinal pigment epithelium (RPE) cells. This ultimately leads to the Stargardt disease phenotype of increased retinal autofluorescence and progressive RPE and photoreceptor cell loss. Adeno-associated virus (AAV) vectors have been widely used in gene therapeutic applications, but their limited cDNA packaging capacity of ∼4.5 kb has impeded their use for transgenes exceeding this limit. AAV dual vectors were developed to overcome this size restriction. In this study, we have evaluated the in vitro expression of ABCA4 using three options: overlap, transplicing, and hybrid ABCA4 dual vector systems. The hybrid system was the most efficient of these dual vector alternatives and used to express the full-length ABCA4 in Abca4^-/- mice. The full-length ABCA4 protein correctly localized to photoreceptor outer segments. Moreover, treatment of Abca4^-/- mice with this ABCA4 hybrid dual vector system resulted in a reduced accumulation of the lipofuscin/N-retinylidene-N-retinylethanolamine (A2E) autofluorescence in vivo, and retinal A2E quantification supported these findings. These results show that the hybrid AAV dual vector option is both safe and therapeutic in mice, and the delivered ABCA4 transgene is functional and has a significant effect on reducing A2E accumulation in the Abca4^-/- mouse model of Stargardt disease.

Long-Term Structural Outcomes of Late-Stage RPE65 Gene Therapy

The form of hereditary childhood blindness Leber congenital amaurosis (LCA) caused by biallelic RPE65 mutations is considered treatable with a gene therapy product approved in the US and Europe. The resulting vision improvement is well accepted, but long-term outcomes on the natural history of retinal degeneration are controversial. We treated four RPE65-mutant dogs in mid-life (age = 5-6 years) and followed them long-term (4-5 years). At the time of the intervention at mid-life, there were intra-ocular and inter-animal differences in local photoreceptor layer health ranging from near normal to complete degeneration. Treated locations having more than 63% of normal photoreceptors showed robust treatment-related retention of photoreceptors in the long term. Treated regions with less retained photoreceptors at the time of the intervention showed progressive degeneration similar to untreated regions with matched initial stage of disease. Unexpectedly, both treated and untreated regions in study eyes tended to show less degeneration compared to matched locations in untreated control eyes. These results support the hypothesis that successful long-term arrest of progression with RPE65 gene therapy may only occur in retinal regions with relatively retained photoreceptors at the time of the intervention, and there may be heretofore unknown mechanisms causing long-distance partial treatment effects beyond the region of subretinal injection.

Rescue of M-cone Function in Aged Opn1mw-/- Mice, a Model for Late-Stage Blue Cone Monochromacy

Purpose

Previously we showed that AAV5-mediated expression of either human M- or L-opsin promoted regrowth of cone outer segments and rescued M-cone function in the treated M-opsin knockout (Opn1mw-/-) dorsal retina. In this study, we determined cone viability and window of treatability in aged Opn1mw-/- mice.

Methods

Cone viability was assessed with antibody against cone arrestin and peanut agglutinin (PNA) staining. The rate of cone degeneration in Opn1mw-/- mice was quantified by PNA staining. AAV5 vector expressing human L-opsin was injected subretinally into one eye of Opn1mw-/- mice at 1, 7, and 15 months old, while the contralateral eyes served as controls. M-cone-mediated retinal function was analyzed 2 and 13 months postinjection by full-field ERG. L-opsin transgene expression and cone outer segment structure were examined by immunohistochemistry.

Results

We showed that dorsal M-opsin dominant cones exhibit outer segment degeneration at an early age in Opn1mw-/- mice, whereas ventral S-opsin dominant cones were normal. The remaining M-opsin dominant cones remained viable for at least 15 months, albeit having shortened or no outer segments. We also showed that AAV5-mediated expression of human L-opsin was still able to rescue function and outer segment structure in the remaining M-opsin dominant cones when treatment was initiated at 15 months of age.

Conclusions

Our results showing that the remaining M-opsin dominant cones in aged Opn1mw-/- mice can still be rescued by gene therapy is helpful for establishing the window of treatability in future blue cone monochromacy clinical trials.

Toxicology and Pharmacology of an AAV Vector Expressing Codon-Optimized RPGR in RPGR-Deficient Rd9 Mice

Applied Genetic Technologies Corporation (AGTC) is developing a recombinant adeno-associated virus (rAAV) vector AGTC-501, also designated AAV2tYF-GRK1-RPGRco, to treat retinitis pigmentosa (RP) in patients with mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene. The vector contains a codon-optimized human RPGR cDNA (RPGRco) driven by a photoreceptor-specific promoter (G protein-coupled receptor kinase 1, GRK1) and is packaged in an AAV2 capsid with three surface tyrosine residues changed to phenylalanine (AAV2tYF). We conducted a safety and potency study of this vector administered by subretinal a injection in the naturally occurring RPGR-deficient Rd9 mouse model. Sixty Rd9 mice (20 per group) received a subretinal injection in the right eye of vehicle (control) or AAV2tYF-GRK1-RPGRco at one of two dose levels (4 × 10⁸ or 4 × 10⁹ vg/eye) and were followed for 12 weeks after injection. Vector injections were well tolerated, with no systemic toxicity. There was a trend towards reduced electroretinography b-wave amplitudes in the high vector dose group that was not statistically significant. There were no clinically important changes in hematology or clinical chemistry parameters and no vector-related ocular changes in life or by histological examination. Dose-dependent RPGR protein expression, mainly in the inner segment of photoreceptors and the adjacent connecting cilium region, was observed in all vector-treated eyes examined. Sequence integrity of the codon-optimized RPGR was confirmed by sequencing of PCR-amplified DNA, or cDNA reverse transcribed from total RNA extracted from vector-treated retinal tissues, and by sequencing of RPGR protein obtained from transfected HEK 293 cells. These results support the use of rAAV2tYF-GRK1-RPGRco in clinical studies in patients with XLRP caused by RPGR mutations.

Rescue of cone function in cone-only Nphp5 knockout mouse model with Leber congenital amaurosis phenotype

Purpose

Recessive mutations in the human IQCB1/NPHP5 gene are associated with Senior-Løken syndrome (SLS), a ciliopathy presenting with nephronophthisis and Leber congenital amaurosis (LCA). Nphp5-knockout mice develop LCA without nephronophthisis. Mutant rods rapidly degenerate while mutant cones survive for months. The purpose of this study was to reinitiate cone ciliogenesis in a Nphp5 ^-/-; Nrl ^-/- mouse with viral expression of full-length NPHP5 and rescue function.

Methods

Nphp5 ^-/- mice were mated with Nrl ^-/- mice to generate Nphp5^-/-; Nrl^-/- double-knockouts. Nphp5^-/-; Nrl^-/- mice and Nphp5^+/-; Nrl^-/- controls were phenotyped with confocal microscopy from postnatal day 10 (P10) until 6 months of age. Nphp5^-/-; Nrl^-/- mice and Nphp5^+/-; Nrl^-/- controls were injected at P15 with self-complementary adenoassociated virus 8 (Y733F) (AAV8(Y733F)) expressing GRK1-FL-cNPHP5. Expression of mutant NPHP5 was verified with confocal microscopy and electroretinography (ERG).

Results

In the Nphp5 ^-/- and cone-only Nphp5 ^-/-; Nrl ^-/- mice, cone outer segments did not form, but mutant cones continued to express cone pigments in the inner segments without obvious signs of cone cell death. The mutant cone outer nuclear layer (ONL) and the inner segments were stable for more than 6 months in the cone-only Nphp5 ^-/-; Nrl ^-/- retinas. Viral expression of NPHP5 initiated after eye opening showed that connecting cilia and RP1-positive axonemes were formed. Furthermore, cone pigments and other cone outer segment proteins (cone transducin and cone PDE6) were present in the nascent mutant cone outer segments, and rescued mutant cones exhibited a significant photopic b-wave (30% of Nphp5 ^+/-; Nrl ^-/- controls).

Conclusions

Nphp5^-/-; Nrl^-/- cones persistently express cone pigments in the inner segments without obvious degeneration, providing an extended duration interval for viral gene expression. Viral expression of full-length NPHP5 initiates ciliogenesis between P15 and P60, and mutant cones are, in part, functional, encouraging future retina gene replacement therapy.

Six Years and Counting: Restoration of Photopic Retinal Function and Visual Behavior Following Gene Augmentation Therapy in a Sheep Model of CNGA3 Achromatopsia

Achromatopsia causes severely reduced visual acuity, photoaversion, and inability to discern colors due to cone photoreceptor dysfunction. In 2010, we reported on day-blindness in sheep caused by a stop-codon mutation of the ovine CNGA3 gene and began gene augmentation therapy trials in this naturally occurring large animal model of CNGA3 achromatopsia. The purpose of this study was to evaluate long-term efficacy and safety results of treatment, findings that hold great relevance for clinical trials that started recently in CNGA3 achromatopsia patients. Nine day-blind sheep were available for long-term follow up. The right eye of each sheep was treated with a single subretinal injection of an Adeno-Associated Virus Type 5 (AAV5) vector carrying either a mouse (n = 4) or a human (n = 5) CNGA3 transgene under control of the 2.1-Kb red/green opsin promoter. The efficacy of treatment was assessed periodically with photopic maze tests and electroretinographic (ERG) recordings for as long as 74 months postoperatively. Safety was assessed by repeated ophthalmic examinations and scotopic ERG recordings. The retinas of three animals that died of unrelated causes >5 years post-treatment were studied histologically and immunohistochemically using anti-hCNGA3 and anti-red/green cone opsin antibodies. Passage time and number of collisions of treated sheep in the photopic maze test were significantly lower at all follow-up examinations as compared with pretreatment values (p = 0.0025 and p < 0.001, respectively). ERG Critical Flicker Fusion Frequency and flicker amplitudes at 30 and 40 Hz showed significant improvement following treatment (p < 0.0001) throughout the study. Ophthalmic examinations and rod ERG recordings showed no abnormalities in the treated eyes. Immunohistochemistry revealed the presence of CNGA3 protein in red/green opsin-positive cells (cones) of the treated eyes. Our results show significant, long-term improvement in cone function, demonstrating a robust rescue effect up to six years following a single treatment with a viral vector that provides episomal delivery of the transgene. This unique follow-up duration confirms the safe and stable nature of AAV5 gene therapy in the ovine achromatopsia model.

Complement C3-Targeted Gene Therapy Restricts Onset and Progression of Neurodegeneration in Chronic Mouse Glaucoma

Dysregulation of the complement system is implicated in neurodegeneration, including human and animal glaucoma. Optic nerve and retinal damage in glaucoma is preceded by local complement upregulation and activation, but whether targeting this early innate immune response could have therapeutic benefit remains undefined. Because complement signals through three pathways that intersect at complement C3 activation, here we targeted this step to restore complement balance in the glaucomatous retina and to determine its contribution to degeneration onset and/or progression. To achieve this, we combined adeno-associated virus retinal gene therapy with the targeted C3 inhibitor CR2-Crry. We show that intravitreal injection of AAV2.CR2-Crry produced sustained Crry overexpression in the retina and reduced deposition of the activation product complement C3d on retinal ganglion cells and the inner retina of DBA/2J mice. This resulted in neuroprotection of retinal ganglion cell axons and somata despite continued intraocular pressure elevation, suggesting a direct restriction of neurodegeneration onset and progression and significant delay to terminal disease stages. Our study uncovers a damaging effect of complement C3 or downstream complement activation in glaucoma, and it establishes AAV2.CR2-Crry as a viable therapeutic strategy to target pathogenic C3-mediated complement activation in the glaucomatous retina.

Cone Phosphodiesterase-6γ' Subunit Augments Cone PDE6 Holoenzyme Assembly and Stability in a Mouse Model Lacking Both Rod and Cone PDE6 Catalytic Subunits

Rod and cone phosphodiesterase 6 (PDE6) are key effector enzymes of the vertebrate phototransduction pathway. Rod PDE6 consists of two catalytic subunits PDE6α and PDE6β and two identical inhibitory PDE6γ subunits, while cone PDE6 is composed of two identical PDE6α’ catalytic subunits and two identical cone-specific PDE6γ’ inhibitory subunits. Despite their prominent function in regulating cGMP levels and therefore rod and cone light response properties, it is not known how each subunit contributes to the functional differences between rods and cones. In this study, we generated an rd10/cpfl1 mouse model lacking rod PDE6β and cone PDE6α’ subunits. Both rod and cone photoreceptor cells are degenerated with age and all PDE6 subunits degrade in rd10/cpfl1 mice. We expressed cone PDE6α’ in both rods and cones of rd10/cpfl1 mice by adeno-associated virus (AAV)-mediated delivery driven by the ubiquitous, constitutive small chicken β-actin promoter. We show that expression of PDE6α’ rescues rod function in rd10/cpfl1 mice, and the restoration of rod light sensitivity is attained through restoration of endogenous rod PDE6γ and formation of a functional PDE6α’γ complex. However, improved photopic cone responses were achieved only after supplementation of both cone PDE6α’ and PDE6γ’ subunits but not by PDE6α’ treatment alone. We observed a two fold increase of PDE6α’ levels in the eyes injected with both PDE6α’ plus PDE6γ’ relative to eyes receiving PDE6α’ alone. Despite the presence of both PDE6γ’ and PDE6γ, the majority of PDE6α’ formed functional complexes with PDE6γ’, suggesting that PDE6α’ has a higher association affinity for PDE6γ’ than for PDE6γ. These results suggest that the presence of PDE6γ’ augments cone PDE6 assembly and enhances its stability. Our finding has important implication for gene therapy of PDE6α’-associated achromatopsia.

ELOVL4-Mediated Production of Very Long-Chain Ceramides Stabilizes Tight Junctions and Prevents Diabetes-Induced Retinal Vascular Permeability

Tight junctions (TJs) involve close apposition of transmembrane proteins between cells. Although TJ proteins have been studied in detail, the role of lipids is largely unknown. We addressed the role of very long-chain (VLC ≥26) ceramides in TJs using diabetes-induced loss of the blood-retinal barrier as a model. VLC fatty acids that incorporate into VLC ceramides are produced by elongase elongation of very long-chain fatty acids protein 4 (ELOVL4). ELOVL4 is significantly reduced in the diabetic retina. Overexpression of ELOVL4 significantly decreased basal permeability, inhibited vascular endothelial growth factor (VEGF)- and interleukin-1β-induced permeability, and prevented VEGF-induced decrease in occludin expression and border staining of TJ proteins ZO-1 and claudin-5. Intravitreal delivery of AAV2-hELOVL4 reduced diabetes-induced increase in vascular permeability. Ultrastructure and lipidomic analysis revealed that ω-linked acyl-VLC ceramides colocalize with TJ complexes. Overall, normalization of retinal ELOVL4 expression could prevent blood-retinal barrier dysregulation in diabetic retinopathy through an increase in VLC ceramides and stabilization of TJs.

Human L- and M-opsins restore M-cone function in a mouse model for human blue cone monochromacy

Purpose

Blue cone monochromacy (BCM) is an X-linked congenital vision disorder characterized by complete loss or severely reduced L- and M-cone function. Patients with BCM display poor visual acuity, severely impaired color discrimination, myopia, nystagmus, and minimally detectable cone-mediated electroretinogram. Recent studies of patients with BCM with adaptive optics scanning laser ophthalmoscopy (AOSLO) showed that they have a disrupted cone mosaic with reduced numbers of cones in the fovea that is normally dominated by L- and M-cones. The remaining cones in the fovea have significantly shortened outer segments but retain sufficient structural integrity to serve as potential gene therapy targets. In this study, we tested whether exogenously expressed human L- and M-opsins can rescue M-cone function in an M-opsin knockout (Opn1mw-/- ) mouse model for BCM.

Methods

Adeno-associated virus type 5 (AAV5) vectors expressing OPN1LW, OPN1MW, or C-terminal tagged OPN1LW-Myc, or OPN1MW-HA driven by a cone-specific promoter were injected subretinally into one eye of Opn1mw-/- mice, while the contralateral eye served as the uninjected control. Expression of cone pigments was determined with western blotting and their cellular localization identified with immunohistochemistry. M-cone function was analyzed with electroretinogram (ERG). Antibodies against cone phototransduction proteins were used to study cone outer segment (OS) morphology in untreated and treated Opn1mw-/- eyes.

Results

We showed that cones in the dorsal retina of the Opn1mw-/- mouse do not form outer segments, resembling cones that lack outer segments in the human BCM fovea. We further showed that AAV5-mediated expression of either human M- or L-opsin individually or combined promotes regrowth of cone outer segments and rescues M-cone function in the treated Opn1mw-/- dorsal retina.

Conclusions

Exogenously expressed human opsins can regenerate cone outer segments and rescue M-cone function in Opn1mw-/- mice, thus providing a proof-of-concept gene therapy in an animal model of BCM.

Long-term photoreceptor rescue in two rodent models of retinitis pigmentosa by adeno-associated virus delivery of Stanniocalcin-1

Retinal degenerations, including age-related macular degeneration and the retinitis pigmentosa family of diseases, are among the leading causes of legal blindness in the United States. We previously found that Stanniocalcin-1 (STC-1) reduced photoreceptor loss in the S334ter-3 and Royal College of Surgeons rat models of retinal degeneration. The results were attributed in part to a reduction in oxidative stress. Herein, we tested the hypothesis that long-term delivery of STC-1 would provide therapeutic rescue in more chronic models of retinal degeneration. To achieve sustained delivery, we produced an adeno-associated virus (AAV) construct to express STC-1 (AAV-STC-1) under the control of a retinal ganglion cell targeting promoter human synapsin 1 (hSYN1). AAV-STC-1 was injected intravitreally into the P23H-1 and S334ter-4 rhodopsin transgenic rats at postnatal day 10. Tissues were collected at postnatal day 120 for confirmation of STC-1 overexpression and histologic and molecular analysis. Electroretinography (ERG) was performed in a cohort of animals at that time. Overexpression of STC-1 resulted in a significant preservation of photoreceptors as assessed by outer nuclear thickness in the P23H-1 (P < 0.05) and the S334ter-4 (P < 0.005) models compared to controls. Additionally, retinal function was significantly improved in the P23H-1 model with overexpressed STC-1 as assessed by ERG analysis (scotopic b-wave P < 0.005 and photopic b-wave P < 0.05). Microarray analysis identified common downstream gene expression changes that occurred in both models. Genes of interest based on their function were selected for validation by quantitative real-time PCR and were significantly increased in the S334ter-4 model.

Patients and animal models of CNGβ1-deficient retinitis pigmentosa support gene augmentation approach

Retinitis pigmentosa (RP) is a major cause of blindness that affects 1.5 million people worldwide. Mutations in cyclic nucleotide-gated channel β 1 (CNGB1) cause approximately 4% of autosomal recessive RP. Gene augmentation therapy shows promise for treating inherited retinal degenerations; however, relevant animal models and biomarkers of progression in patients with RP are needed to assess therapeutic outcomes. Here, we evaluated RP patients with CNGB1 mutations for potential biomarkers of progression and compared human phenotypes with those of mouse and dog models of the disease. Additionally, we used gene augmentation therapy in a CNGβ1-deficient dog model to evaluate potential translation to patients. CNGB1-deficient RP patients and mouse and dog models had a similar phenotype characterized by early loss of rod function and slow rod photoreceptor loss with a secondary decline in cone function. Advanced imaging showed promise for evaluating RP progression in human patients, and gene augmentation using adeno-associated virus vectors robustly sustained the rescue of rod function and preserved retinal structure in the dog model. Together, our results reveal an early loss of rod function in CNGB1-deficient patients and a wide window for therapeutic intervention. Moreover, the identification of potential biomarkers of outcome measures, availability of relevant animal models, and robust functional rescue from gene augmentation therapy support future work to move CNGB1-RP therapies toward clinical trials.

Safety and Efficacy of AAV5 Vectors Expressing Human or Canine CNGB3 in CNGB3-Mutant Dogs

Achromatopsia is an inherited retinal disorder of cone photoreceptors characterized by markedly reduced visual acuity, extreme light sensitivity, and absence of color discrimination. Approximately 50% of cases are caused by mutations in the cone photoreceptor-specific cyclic nucleotide gated channel beta subunit (CNGB3) gene. Studies in CNGB3-mutant dogs showed that subretinal injection of an AAV vector expressing human CNGB3, which has 76% amino acid identity with canine CNGB3, driven by a 2.1 kb human red cone opsin promoter (PR2.1) and packaged in AAV5 capsids (AAV5-PR2.1-hCNGB3) rescued cone photoreceptor function, but at high doses was associated with an inflammatory response (focal chorioretinitis) consistent with immune-mediated toxicity. AAV vectors containing the PR2.1 promoter packaged in AAV5 capsids and expressing either the native canine CNGB3 (AAV5-PR2.1-cCNGB3) or the human CNGB3 (AAV5-PR2.1-hCNGB3) were evaluated at different dose levels in CNGB3-mutant dogs. The vector expressing canine CNGB3 achieved somewhat better rescue of cone function but unexpectedly was associated with a greater degree of retinal toxicity than the vector expressing human CNGB3. Very low-level T-cell immune responses to some AAV or CNGB3 peptides were observed in animals that received the higher vector dose. There was a more than twofold increase in serum neutralizing antibodies to AAV in one of three animals in the low-dose group and in two of three animals in the high-dose group. No serum anti-hCNGB3 antibodies were detected in any animal. The results of this study do not support the hypothesis that the focal chorioretinitis seen with high doses of AAV5-PR2.1-hCNGB3 in the initial studies was due to an immune response to human CNGB3.

REPEATABILITY AND LONGITUDINAL ASSESSMENT OF FOVEAL CONE STRUCTURE IN CNGB3-ASSOCIATED ACHROMATOPSIA

PURPOSE

Congenital achromatopsia is an autosomal recessive disease causing substantial reduction or complete absence of cone function. Although believed to be a relatively stationary disorder, questions remain regarding the stability of cone structure over time. In this study, the authors sought to assess the repeatability of and examine longitudinal changes in measurements of central cone structure in patients with achromatopsia.

METHODS

Forty-one subjects with CNGB3-associated achromatopsia were imaged over a period of between 6 and 26 months using optical coherence tomography and adaptive optics scanning light ophthalmoscopy. Outer nuclear layer (ONL) thickness, ellipsoid zone (EZ) disruption, and peak foveal cone density were assessed.

RESULTS

ONL thickness increased slightly compared with baseline (0.184 μm/month, P = 0.02). The EZ grade remained unchanged for 34/41 subjects. Peak foveal cone density did not significantly change over time (mean change 1% per 6 months, P = 0.126).

CONCLUSION

Foveal cone structure showed little or no change in this group of subjects with CNGB3-associated achromatopsia. Over the time scales investigated (6-26 months), achromatopsia seems to be a structurally stable condition, although longer-term follow-up is needed. These data will be useful in assessing foveal cone structure after therapeutic intervention.

Highly Efficient Delivery of Adeno-Associated Viral Vectors to the Primate Retina

Adeno-associated virus (AAV) has emerged as the preferred vector for targeting gene expression to the retina. Subretinally injected AAV can efficiently transduce retinal pigment epithelium and photoreceptors in primate retina. Inner and middle primate retina can be transduced by intravitreally delivered AAV, but with low efficiency. This is due to dilution of vector, potential neutralization of capsid because it is not confined to the immune-privileged retinal compartment, and the presence of the inner limiting membrane (ILM), a barrier separating the vitreous from the neural retina. We here describe a novel "subILM" injection method that addresses all three issues. Specifically, vector is placed in a surgically induced, hydrodissected space between the ILM and neural retina. In an initial experiment, we injected viscoelastic (Healon(®)), a substance we confirmed was biocompatible with AAV, to create a subILM bleb and subsequently injected AAV2-GFP into the bleb after irrigation with basic salt solution. For later experiments, we used a Healon-AAV mixture to place single, subILM injections. In all cases, subILM delivery of AAV was well tolerated-no inflammation or gross structural changes were observed by ophthalmological examination or optical coherence tomography. In-life fluorescence imaging revealed profound transgene expression within the area of the subILM injection bleb that persisted for the study duration. Uniform and extensive transduction of retinal ganglion cells (RGCs) was achieved in the areas beneath the subILM bleb. Transduction of Müller glia, ON bipolar cells, and photoreceptors was also observed. Robust central labeling from green fluorescent protein-expressing RGCs confirmed their continued survival, and was observed in the lateral geniculate nucleus, the superior colliculus, and the pretectum. Our results confirm that the ILM is a major barrier to transduction by AAV in primate retina and that, when it is circumvented, the efficiency and depth to which AAV2 promotes transduction of multiple retinal cell classes are greatly enhanced.

Gene-based Therapy in a Mouse Model of Blue Cone Monochromacy

Cones are responsible for daylight, central, high acuity and color vision. Three proteins found in human cones, i.e. long-wavelength (L)-, middle-wavelength (M)-, and short-wavelength sensitive (S)-opsins, are responsible for red, green and blue color recognition, respectively. Human blue cone monochromacy (BCM) is characterized by functional loss of both L- and M-cone opsins due to mutations in the OPN1LW/OPN1MW gene cluster on the X chromosome. BCM patients, who rely on their vision from only S-cones and rods, suffer severely reduced visual acuity and impaired color vision. Recent studies show that there is sufficient cone structure remaining in the central fovea of BCM patients to consider AAV-mediated gene augmentation therapy. In contrast, mouse retina has only two opsins, S-opsin and M-opsin, but no L-opsin. We generated an M-opsin knockout mouse (Opn1mw -/-) expressing only S-opsin as a model for human BCM. We show that recombinant M-opsin delivered by AAV5 vectors rescues M-cone function in Opn1mw -/- mice. We also show that AAV delivered M-opsin localizes in the dorsal cone outer segments, and co-localizes with S-opsin in the ventral retina. Our study demonstrates that cones without M-opsin remain viable and respond to gene augmentation therapy, thereby providing proof-of-concept for cone function restoration in BCM patients.

Efficient Gene Delivery and Expression in Pancreas and Pancreatic Tumors by Capsid-Optimized AAV8 Vectors

Despite efforts to use adeno-associated viral (AAV) vector-mediated gene therapy for treatment of pancreatic ductal adenocarcinoma (PDAC), transduction efficiency remains a limiting factor and thus improvement of AAV delivery would significantly facilitate the treatment of this malignancy. Site-directed mutagenesis of specific tyrosine (Y) residues to phenylalanine (F) on the surface of various AAV serotype capsids has been reported as a method for enhancing gene transfer efficiencies. In the present studies, we determine whether Y-to-F mutations could also enhance AAV8 gene transfer in the pancreas to facilitate gene therapy for PDAC. Three different Y-to-F mutant vectors (a single-mutant, Y733F; a double-mutant, Y447F+Y733F; and a triple-mutant, Y275F+Y447F+Y733F) and wild-type AAV8 (WT-AAV8) were administered by intraperitoneal or tail-vein routes to Kras^G12D+/-, Kras^G12D+/-/Pten^+/-, and wild-type mice. The transduction efficiency of these vectors expressing the mCherry reporter gene was evaluated 2 weeks post administration in pancreas or PDAC and correlated with viral genome copy numbers. Our comparative and quantitative analyses of the transduction profiles demonstrated that the Y-to-F double-mutant exhibited the highest mCherry expression in pancreatic tissues (range 45-70%) compared with WT-AAV8 (7%; p < 0.01). We also detected a 7-fold higher level of vector genome copy numbers in normal pancreas following transduction with the double-mutant AAV8 compared with WT-AAV8 (10,285 vs. 1,500 vector copies/μg DNA respectively, p < 0.05). In addition, we observed that intraperitoneal injection of the double-mutant AAV8 led to a 15-fold enhanced transduction efficiency as compared to WT-AAV8 in mouse PDAC, with a corresponding ∼14-fold increase in vector genome copy numbers (26,575 vs. 2,165 copies/μg DNA respectively, p < 0.05). These findings indicate that the Y447+Y733F-AAV8 leads to a significant enhancement of transduction efficiency in both normal and malignant pancreatic tissues, suggesting the potential use of this vector in targeting pancreatic diseases in general, and PDAC in particular.

Gene Augmentation Therapy for a Missense Substitution in the cGMP-Binding Domain of Ovine CNGA3 Gene Restores Vision in Day-Blind Sheep

Purpose

Applying CNGA3 gene augmentation therapy to cure a novel causative mutation underlying achromatopsia (ACHM) in sheep.

Methods

Impaired vision that spontaneously appeared in newborn lambs was characterized by behavioral, electroretinographic (ERG), and histologic techniques. Deep-sequencing reads of an affected lamb and an unaffected lamb were compared within conserved genomic regions orthologous to human genes involved in similar visual impairment. Observed nonsynonymous amino acid substitutions were classified by their deleteriousness score. The putative causative mutation was assessed by producing compound CNGA3 heterozygotes and applying gene augmentation therapy using the orthologous human cDNA.

Results

Behavioral assessment revealed day blindness, and subsequent ERG examination showed attenuated photopic responses. Histologic and immunohistochemical examination of affected sheep eyes did not reveal degeneration, and cone photoreceptors expressing CNGA3 were present. Bioinformatics and sequencing analyses suggested a c.1618G>A, p.Gly540Ser substitution in the GMP-binding domain of CNGA3 as the causative mutation. This was confirmed by genetic concordance test and by genetic complementation experiment: All five compound CNGA3 heterozygotes, carrying both p.Arg236* and p.Gly540Ser mutations in CNGA3, were day-blind. Furthermore, subretinal delivery of the intact human CNGA3 gene using an adeno-associated viral vector (AAV) restored photopic vision in two affected p.Gly540Ser homozygous rams.

Conclusions

The c.1618G>A, p.Gly540Ser substitution in CNGA3 was identified as the causative mutation for a novel form of ACHM in Awassi sheep. Gene augmentation therapy restored vision in the affected sheep. This novel mutation provides a large-animal model that is valid for most human CNGA3 ACHM patients; the majority of them carry missense rather than premature-termination mutations.

Rationally Engineered AAV Capsids Improve Transduction and Volumetric Spread in the CNS

Adeno-associated virus (AAV) is the most common vector for clinical gene therapy of the CNS. This popularity originates from a high safety record and the longevity of transgene expression in neurons. Nevertheless, clinical efficacy for CNS indications is lacking, and one reason for this is the relatively limited spread and transduction efficacy in large regions of the human brain. Using rationally designed modifications of the capsid, novel AAV capsids have been generated that improve intracellular processing and result in increased transgene expression. Here, we sought to improve AAV-mediated neuronal transduction to minimize the existing limitations of CNS gene therapy. We investigated the efficacy of CNS transduction using a variety of tyrosine and threonine capsid mutants based on AAV2, AAV5, and AAV8 capsids, as well as AAV2 mutants incapable of binding heparan sulfate (HS). We found that mutating several tyrosine residues on the AAV2 capsid significantly enhanced neuronal transduction in the striatum and hippocampus, and the ablation of HS binding also increased the volumetric spread of the vector. Interestingly, the analogous tyrosine substitutions on AAV5 and AAV8 capsids did not improve the efficacy of these serotypes. Our results demonstrate that the efficacy of CNS gene transfer can be significantly improved with minor changes to the AAV capsid and that the effect is serotype specific.

Gene Therapy for Leber Hereditary Optic Neuropathy: Low- and Medium-Dose Visual Results

PURPOSE

To determine the effects of AAV2(Y444,500,730F)-P1ND4v2 in patients with Leber hereditary optic neuropathy (LHON).

DESIGN

Prospective open-label, unilateral single-dose, intravitreal injection of AAV2(Y444,500,730F)-P1ND4v2 per participant.

PARTICIPANTS

Fourteen patients with visual loss and mutated G11778A mitochondrial DNA.

METHODS

Intravitreal injection with the gene therapy vector AAV2(Y444,500,730F)-P1ND4v2 into 1 eye. Six participants with chronic bilateral visual loss lasting more than 12 months (group 1), 6 participants with bilateral visual loss lasting less than 12 months (group 2), and 2 participants with unilateral visual loss (group 3) were treated. Nine patients had at least 12 months of follow-up. Clinical testing included visual acuity, visual fields, optical coherence tomography, pattern electroretinography, and neuro-ophthalmic examinations. Generalized estimating equation methods were used for longitudinal analyses.

MAIN OUTCOME MEASURE

Loss of visual acuity.

RESULTS

For groups 1 and 2, month 12 average acuity improvements with treatment relative to baseline were 0.24 logarithm of the minimum angle of resolution (logMAR). Fellow eyes had a 0.09-logMAR improvement. A post hoc comparison found that at month 12, the difference between study eye minus fellow eye improvement in group 2 patients of 0.53 logMAR was greater than that observed in our prior acute natural history patients of 0.21 logMAR (P = 0.053). At month 18, the difference between study eye minus fellow eye improvement in our acute group 2 gene therapy patients of 0.96 was more than that observed in our prior acute natural history patients (0.17 logMAR; P < 0.001). Two patients demonstrated asymptomatic uveitis that resolved without treatment. Optical coherence tomography of treated eyes showed an average temporal retinal nerve fiber layer thickness of 54 μm before injection and 55 μm at month 12. For fellow eyes before injection, it was 56 μm, decreasing to 50 μm at month 12 (P = 0.013). Generalized estimating equations suggested that PERG amplitudes worsened more in treated eyes than in fellow eyes by approximately 0.05 μV (P = 0.009 exchangeable). No difference between eyes in outcomes of other visual function measures was evident.

CONCLUSIONS

Allotopic gene therapy for LHON at low and medium doses seems to be safe and does not damage the temporal retinal nerve fiber layer, opening the door next for testing of the high dose.

Gene Therapy in a Large Animal Model of PDE6A-Retinitis Pigmentosa

Despite mutations in the rod phosphodiesterase 6-alpha (PDE6A) gene being well-recognized as a cause of human retinitis pigmentosa, no definitive treatments have been developed to treat this blinding disease. We performed a trial of retinal gene augmentation in the Pde6a mutant dog using Pde6a delivery by capsid-mutant adeno-associated virus serotype 8, previously shown to have a rapid onset of transgene expression in the canine retina. Subretinal injections were performed in 10 dogs at 29–44 days of age, and electroretinography and vision testing were performed to assess functional outcome. Retinal structure was assessed using color fundus photography, spectral domain optical coherence tomography, and histology. Immunohistochemistry was performed to examine transgene expression and expression of other retinal genes. Treatment resulted in improvement in dim light vision and evidence of rod function on electroretinographic examination. Photoreceptor layer thickness in the treated area was preserved compared with the contralateral control vector treated or uninjected eye. Improved rod and cone photoreceptor survival, rhodopsin localization, cyclic GMP levels and bipolar cell dendrite distribution was observed in treated areas. Some adverse effects including foci of retinal separation, foci of retinal degeneration and rosette formation were identified in both AAV-Pde6a and control vector injected regions. This is the first description of successful gene augmentation for Pde6a retinitis pigmentosa in a large animal model. Further studies will be necessary to optimize visual outcomes and minimize complications before translation to human studies.

Optimization of Retinal Gene Therapy for X-Linked Retinitis Pigmentosa Due to RPGR Mutations

X-linked retinitis pigmentosa (XLRP) caused by mutations in the RPGR gene is an early onset and severe cause of blindness. Successful proof-of-concept studies in a canine model have recently shown that development of a corrective gene therapy for RPGR-XLRP may now be an attainable goal. In preparation for a future clinical trial, we have here optimized the therapeutic AAV vector construct by showing that GRK1 (rather than IRBP) is a more efficient promoter for targeting gene expression to both rods and cones in non-human primates. Two transgenes were used in RPGR mutant (XLPRA2) dogs under the control of the GRK1 promoter. First was the previously developed stabilized human RPGR (hRPGRstb). Second was a new full-length stabilized and codon-optimized human RPGR (hRPGRco). Long-term (>2 years) studies with an AAV2/5 vector carrying hRPGRstb under control of the GRK1 promoter showed rescue of rods and cones from degeneration and retention of vision. Shorter term (3 months) studies demonstrated comparable preservation of photoreceptors in canine eyes treated with an AAV2/5 vector carrying either transgene under the control of the GRK1 promoter. These results provide the critical molecular components (GRK1 promoter, hRPGRco transgene) to now construct a therapeutic viral vector optimized for RPGR-XLRP patients.

Overexpression of the X-Linked Inhibitor of Apoptosis Protects Against Retinal Degeneration in a Feline Model of Retinal Detachment

Retinal detachment is an acute disorder in humans that is caused by trauma or disease, and it can often lead to permanent visual deficits that result from the death of photoreceptors in the retina. The final pathway for photoreceptor cell death is apoptosis and necroptosis. The X-linked inhibitor of apoptosis (XIAP) has been shown to block both of these cell death pathways. This study tested the effects of XIAP on photoreceptor survival in a feline model of retinal detachment. The study was performed in 12 cats, divided into two experimental groups. Six animals received a subretinal injection of adeno-associated virus (AAV) carrying XIAP, and six animals received AAV carrying green fluorescent protein (GFP) as a control. Three weeks after viral delivery, retinas were detached by injecting C₃F₈ gas into the subretinal space. Optical coherence tomography revealed that the retinal detachments resolved within 3-6 weeks as the gas was slowly resorbed. Analysis of histological sections through the plane of the detachment showed significant preservation of the photoreceptor layer in AAV-XIAP-treated animals compared to AAV-GFP-treated animals at 9 weeks after the detachment. XIAP-treated detached retinas were similar to intact controls. These studies support the potential for XIAP therapy in the treatment of human retinal detachment.

rAAV8-733-Mediated Gene Transfer of CHIP/Stub-1 Prevents Hippocampal Neuronal Death in Experimental Brain Ischemia

Brain ischemia is a major cause of adult disability and death, and it represents a worldwide health problem with significant economic burden for modern society. The identification of the molecular pathways activated after brain ischemia, together with efficient technologies of gene delivery to the CNS, may lead to novel treatments based on gene therapy. Recombinant adeno-associated virus (rAAV) is an effective platform for gene transfer to the CNS. Here, we used a serotype 8 rAAV bearing the Y733F mutation (rAAV8-733) to overexpress co-chaperone E3 ligase CHIP (also known as Stub-1) in rat hippocampal neurons, both in an oxygen and glucose deprivation model in vitro and in a four-vessel occlusion model of ischemia in vivo. We show that CHIP overexpression prevented neuronal degeneration in both cases and led to a decrease of both eIF2α (serine 51) and AKT (serine 473) phosphorylation, as well as reduced amounts of ubiquitinated proteins following hypoxia or ischemia. These data add to current knowledge of ischemia-related signaling in the brain and suggest that gene therapy based on the role of CHIP in proteostasis may provide a new venue for brain ischemia treatment.

Safety and Biodistribution Evaluation in Cynomolgus Macaques of rAAV2tYF-PR1.7-hCNGB3, a Recombinant AAV Vector for Treatment of Achromatopsia

Applied Genetic Technologies Corporation (AGTC) is developing rAAV2tYF-PR1.7-hCNGB3, a recombinant adeno-associated viral (rAAV) vector expressing the human CNGB3 gene, for treatment of achromatopsia, an inherited retinal disorder characterized by markedly reduced visual acuity, extreme light sensitivity, and absence of color discrimination. We report here results of a study evaluating the safety and biodistribution of rAAV2tYF-PR1.7-hCNGB3 in cynomolgus macaques. Three groups of animals (n = 2 males and 2 females per group) received a subretinal injection in one eye of 300 μl containing either vehicle or rAAV2tYF-PR1.7-hCNGB3 at one of two concentrations (4 × 10(11) or 4 × 10(12) vector genomes/ml) and were evaluated over a 3-month period before being euthanized. Administration of rAAV2tYF-PR1.7-hCNGB3 was associated with a dose-related anterior and posterior segment inflammatory response that was greater than that observed in eyes injected with the vehicle control. Most manifestations of inflammation improved over time except that vitreous cells persisted in vector-treated eyes until the end of the study. One animal in the lower vector dose group was euthanized on study day 5, based on a clinical diagnosis of endophthalmitis. There were no test article-related effects on intraocular pressure, visual evoked potential responses, hematology or clinical chemistry parameters, or gross necropsy observations. Histopathological examination demonstrated minimal mononuclear infiltrates in all vector-injected eyes. Serum anti-AAV antibodies developed in all vector-injected animals. No animals developed antibodies to CNGB3. Biodistribution studies demonstrated high levels of vector DNA in the injected eye but minimal or no vector DNA in any other tissue. These results support the use of rAAV2tYF-PR1.7-hCNGB3 in clinical studies in patients with achromatopsia caused by CNGB3 mutations.

Safety and Biodistribution Evaluation in CNGB3-Deficient Mice of rAAV2tYF-PR1.7-hCNGB3, a Recombinant AAV Vector for Treatment of Achromatopsia

Applied Genetic Technologies Corporation (AGTC) is developing rAAV2tYF-PR1.7-hCNGB3, a recombinant adeno-associated virus (rAAV) vector expressing the human CNGB3 gene, for treatment of achromatopsia, an inherited retinal disorder characterized by markedly reduced visual acuity, extreme light sensitivity, and absence of color discrimination. We report here results of a study evaluating safety and biodistribution of rAAV2tYF-PR1.7-hCNGB3 in CNGB3-deficient mice. Three groups of animals (n = 35 males and 35 females per group) received a subretinal injection in one eye of 1 μl containing either vehicle or rAAV2tYF-PR1.7-hCNGB3 at one of two dose concentrations (1 × 10(12) or 4.2 × 10(12) vg/ml) and were euthanized 4 or 13 weeks later. There were no test-article-related changes in clinical observations, body weights, food consumption, ocular examinations, clinical pathology parameters, organ weights, or macroscopic observations at necropsy. Cone-mediated electroretinography (ERG) responses were detected after vector administration in the treated eyes in 90% of animals in the higher dose group and 31% of animals in the lower dose group. Rod-mediated ERG responses were reduced in the treated eye for all groups, with the greatest reduction in males given the higher dose of vector, but returned to normal by the end of the study. Microscopic pathology results demonstrated minimal mononuclear cell infiltrates in the retina and vitreous of some animals at the interim euthanasia and in the vitreous of some animals at the terminal euthanasia. Serum anti-AAV antibodies developed in most vector-injected animals. No animals developed antibodies to hCNGB3. Biodistribution studies demonstrated high levels of vector DNA in vector-injected eyes but little or no vector DNA in nonocular tissue. These results support the use of rAAV2tYF-PR1.7-hCNGB3 in clinical studies in patients with achromatopsia caused by CNGB3 mutations.

Cone-Specific Promoters for Gene Therapy of Achromatopsia and Other Retinal Diseases

Adeno-associated viral (AAV) vectors containing cone-specific promoters have rescued cone photoreceptor function in mouse and dog models of achromatopsia, but cone-specific promoters have not been optimized for use in primates. Using AAV vectors administered by subretinal injection, we evaluated a series of promoters based on the human L-opsin promoter, or a chimeric human cone transducin promoter, for their ability to drive gene expression of green fluorescent protein (GFP) in mice and nonhuman primates. Each of these promoters directed high-level GFP expression in mouse photoreceptors. In primates, subretinal injection of an AAV-GFP vector containing a 1.7-kb L-opsin promoter (PR1.7) achieved strong and specific GFP expression in all cone photoreceptors and was more efficient than a vector containing the 2.1-kb L-opsin promoter that was used in AAV vectors that rescued cone function in mouse and dog models of achromatopsia. A chimeric cone transducin promoter that directed strong GFP expression in mouse and dog cone photoreceptors was unable to drive GFP expression in primate cones. An AAV vector expressing a human CNGB3 gene driven by the PR1.7 promoter rescued cone function in the mouse model of achromatopsia. These results have informed the design of an AAV vector for treatment of patients with achromatopsia.

Targeting iodothyronine deiodinases locally in the retina is a therapeutic strategy for retinal degeneration

Recent studies have implicated thyroid hormone (TH) signaling in cone photoreceptor viability. Using mouse models of retinal degeneration, we found that antithyroid treatment preserves cones. This work investigates the significance of targeting intracellular TH components locally in the retina. The cellular TH level is mainly regulated by deiodinase iodothyronine (DIO)-2 and -3. DIO2 converts thyroxine (T4) to triiodothyronine (T3), which binds to the TH receptor, whereas DIO3 degrades T3 and T4. We examined cone survival after overexpression of DIO3 and inhibition of DIO2 and demonstrated the benefits of these manipulations. Subretinal delivery of AAV5-IRBP/GNAT2-DIO3, which directs expression of human DIO3 specifically in cones, increased cone density by 30-40% in a Rpe65^-/- mouse model of Lebers congenital amaurosis (LCA) and in a Cpfl1 mouse with Pde6c defect model of achromatopsia, compared with their respective untreated controls. Intravitreal and topical delivery of the DIO2 inhibitor iopanoic acid also significantly improved cone survival in the LCA model mice. Moreover, the expression levels of DIO2 and Slc16a2 were significantly higher in the diseased retinas, suggesting locally elevated TH signaling. We show that targeting DIOs protects cones, and intracellular inhibition of TH components locally in the retina may represent a novel strategy for retinal degeneration management.-Yang, F., Ma, H., Belcher, J., Butler, M. R., Redmond, T. M., Boye, S. L., Hauswirth, W. W., Ding, X.-Q. Targeting iodothyronine deiodinases locally in the retina is a therapeutic strategy for retinal degeneration.

PAX6 MiniPromoters drive restricted expression from rAAV in the adult mouse retina

Current gene therapies predominantly use small, strong, and readily available ubiquitous promoters. However, as the field matures, the availability of small, cell-specific promoters would be greatly beneficial. Here we design seven small promoters from the human paired box 6 (PAX6) gene and test them in the adult mouse retina using recombinant adeno-associated virus. We chose the retina due to previous successes in gene therapy for blindness, and the PAX6 gene since it is: well studied; known to be driven by discrete regulatory regions; expressed in therapeutically interesting retinal cell types; and mutated in the vision-loss disorder aniridia, which is in need of improved therapy. At the PAX6 locus, 31 regulatory regions were bioinformatically predicted, and nine regulatory regions were constructed into seven MiniPromoters. Driving Emerald GFP, these MiniPromoters were packaged into recombinant adeno-associated virus, and injected intravitreally into postnatal day 14 mice. Four MiniPromoters drove consistent retinal expression in the adult mouse, driving expression in combinations of cell-types that endogenously express Pax6: ganglion, amacrine, horizontal, and Müller glia. Two PAX6-MiniPromoters drive expression in three of the four cell types that express PAX6 in the adult mouse retina. Combined, they capture all four cell types, making them potential tools for research, and PAX6-gene therapy for aniridia.

Characterization of intravitreally delivered capsid mutant AAV2-Cre vector to induce tissue-specific mutations in murine retinal ganglion cells

Targeted expression of Cre recombinase in murine retinal ganglion cells (RGCs) by viral vector is an effective strategy for creating tissue-specific gene knockouts for investigation of genetic contribution to RGC degeneration associated with optic neuropathies. Here we characterize dosage, efficacy and toxicity for sufficient intravitreal delivery of a capsid mutant Adeno-associated virus 2 (AAV2) vector encoding Cre recombinase. Wild type and Rosa26 (R26) LacZ mice were intravitreally injected with capsid mutant AAV2 viral vectors. Murine eyes were harvested at intervals ranging from 2 weeks to 15 weeks post-injection and were assayed for viral transduction, transgene expression and RGC survival. 10(9) vector genomes (vg) were sufficient for effective in vivo targeting of murine ganglion cell layer (GCL) retinal neurons. Transgene expression was observed as early as 2 weeks post-injection of viral vectors and persisted to 11 weeks. Early expression of Cre had no significant effect on RGC survival, while significant RGC loss was detected beginning 5 weeks post-injection. Early expression of viral Cre recombinase was robust, well-tolerated and predominantly found in GCL neurons suggesting this strategy can be effective in short-term RGC-specific mutation studies in experimental glaucoma models such as optic nerve crush and transection experiments. RGC degeneration with Cre expression for more than 4 weeks suggests that Cre toxicity is a limiting factor for targeted mutation strategies in RGCs.

Residual Foveal Cone Structure in CNGB3-Associated Achromatopsia

PURPOSE

Congenital achromatopsia (ACHM) is an autosomal recessive disorder in which cone function is absent or severely reduced. Gene therapy in animal models of ACHM have shown restoration of cone function, though translation of these results to humans relies, in part, on the presence of viable cone photoreceptors at the time of treatment. Here, we characterized residual cone structure in subjects with CNGB3-associated ACHM.

METHODS

High-resolution imaging (optical coherence tomography [OCT] and adaptive optics scanning light ophthalmoscopy [AOSLO]) was performed in 51 subjects with CNGB3-associated ACHM. Peak cone density and inter-cone spacing at the fovea was measured using split-detection AOSLO. Foveal outer nuclear layer thickness was measured in OCT images, and the integrity of the photoreceptor layer was assessed using a previously published OCT grading scheme.

RESULTS

Analyzable images of the foveal cones were obtained in 26 of 51 subjects, with nystagmus representing the major obstacle to obtaining high-quality images. Peak foveal cone density ranged from 7,273 to 53,554 cones/mm2, significantly lower than normal (range, 84,733-234,391 cones/mm2), with the remnant cones being either contiguously or sparsely arranged. Peak cone density was correlated with OCT integrity grade; however, there was overlap of the density ranges between OCT grades.

CONCLUSIONS

The degree of residual foveal cone structure varies greatly among subjects with CNGB3-associated ACHM. Such measurements may be useful in estimating the therapeutic potential of a given retina, providing affected individuals and physicians with valuable information to more accurately assess the risk-benefit ratio as they consider enrolling in experimental gene therapy trials. (www.clinicaltrials.gov, NCT01846052.).

Occludin S490 Phosphorylation Regulates Vascular Endothelial Growth Factor-Induced Retinal Neovascularization

Occludin is a transmembrane tight junction protein that contributes to diverse cellular functions, including control of barrier properties, cell migration, and proliferation. Vascular endothelial growth factor (VEGF) induces phosphorylation of occludin at S490, which is required for VEGF-induced endothelial permeability. Herein, we demonstrate that occludin S490 phosphorylation also regulates VEGF-induced retinal endothelial cell proliferation and neovascularization. Using a specific antibody, phospho-occludin was located in centrosomes in endothelial cell cultures, animal models, and human surgical samples of retinal neovessels. Occludin S490 phosphorylation was found to increase with endothelial tube formation in vitro and in vivo during retinal neovascularization after induction of VEGF expression. More important, expression of occludin mutated at S490 to Ala, completely inhibited angiogenesis in cell culture models and in vivo. Collectively, these data suggest a novel role for occludin in regulation of endothelial proliferation and angiogenesis in a phosphorylation-dependent manner. These findings may lead to methods of regulating pathological neovascularization by specifically targeting endothelial cell proliferation.