Regulation of retinal function but nonrescue of vision in RPE65-deficient dogs treated with doxycycline-regulatable AAV vectors

Optimized Subretinal Injection Technique for Gene Therapy Approaches

Gene therapy for inherited eye diseases requires local viral vector delivery by intraocular injection. Since large animal models are lacking for most of these diseases, genetically modified mouse models are commonly used in preclinical proof-of-concept studies. However, because of the relatively small mouse eye, adverse effects of the subretinal delivery procedure itself may interfere with the therapeutic outcome. The method described here aims to provide the details relevant to perform a transscleral pars plana virus-mediated gene transfer to achieve an optimized therapeutic effect in the small mouse eye.

Development of Inducible CD19-CAR T Cells with a Tet-On System for Controlled Activity and Enhanced Clinical Safety

The tetracycline regulatory system has been widely used to control the transgene expression. With this powerful tool, it might be possible to effectively control the functional activity of chimeric antigen receptor (CAR) T cells and manage the severe side effects after infusion. In this study, we developed novel inducible CD19CAR (iCAR19) T cells by incorporating a one-vector Tet-on system into the CD19CAR construct. The iCAR19 T cells showed dox-dependent cell proliferation, cytokine production, CAR expression, and strong CD19-specific cytotoxicity. After 48 h of dox induction, the relative CAR expression of induced cells was five times greater than that of uninduced cells. Twenty-four hours after dox removal, CAR expression significantly decreased by more than 60%. In cytotoxicity assays, dox-treated cells induced significantly higher specific lysis against target cells. These results suggested that the activity of iCAR19 T cells was successfully controlled by our Tet-on system, offering an enhanced safety profile while maintaining a robust anti-tumor effect. Besides, all manufacture processes of the lentiviral vectors and the T cells were conducted according to the Good Manufacturing Practice (GMP) standards for subsequent clinical translation.

Advanced Ocular Injection Techniques for Therapy Approaches

Treatment approaches for inherited eye diseases require local therapeutic molecule delivery by intraocular injection. One important factor that can influence the study outcome is the quality of intraocular administration. The intracompartmental structure (e.g., vitreous) of the eye allows a sustainable release of therapeutic biologicals using an intravitreal delivery. The protocol described here aims at providing the details relevant to perform a transscleral pars plana intravitreal transfer in small eyes using a genetically modified stem cell system. The fact that cells and therewith visually distinct particles are implanted, allows for the assessment of the implantation site and the distribution, and possibilities for temporal follow up studies-hence, valuable information becomes available which can be used to fine-tune the intravitreal delivery technique.

AAV-mediated Gene Therapy Halts Retinal Degeneration in PDE6β-deficient Dogs

We previously reported that subretinal injection of AAV2/5 RK.cpde6β allowed long-term preservation of photoreceptor function and vision in the rod-cone dysplasia type 1 (rcd1) dog, a large animal model of naturally occurring PDE6β deficiency. The present study builds on these earlier findings to provide a detailed assessment of the long-term effects of gene therapy on the spatiotemporal pattern of retinal degeneration in rcd1 dogs treated at 20 days of age. We analyzed the density distribution of the retinal layers and of particular photoreceptor cells in 3.5-year-old treated and untreated rcd1 dogs. Whereas no rods were observed outside the bleb or in untreated eyes, gene transfer halted rod degeneration in all vector-exposed regions. Moreover, while gene therapy resulted in the preservation of cones, glial cells and both the inner nuclear and ganglion cell layers, no cells remained in vector-unexposed retinas, except in the visual streak. Finally, the retinal structure of treated 3.5-year-old rcd1 dogs was identical to that of unaffected 4-month-old rcd1 dogs, indicating near complete preservation. Our findings indicate that gene therapy arrests the degenerative process even if intervention is initiated after the onset of photoreceptor degeneration, and point to significant potential of this therapeutic approach in future clinical trials.

RANGE: Gene Transfer of Reversibly Controlled Polycistronic Genes

We developed a single vector recombinant adeno-associated viral (rAAV) expression system for spatial and reversible control of polycistronic gene expression. Our approach (i) integrates the advantages of the tetracycline (Tet)-controlled transcriptional silencer tTS(Kid) and the self-cleaving 2A peptide bridge, (ii) combines essential regulatory components as an autoregulatory loop, (iii) simplifies the gene delivery scheme, and (iv) regulates multiple genes in a synchronized manner. Controlled by an upstream Tet-responsive element (TRE), both the ubiquitous chicken β-actin promoter (CAG) and the neuron-specific synapsin-1 promoter (Syn) could regulate expression of tTS(Kid) together with two 2A-linked reporter genes. Transduction in vitro exhibited maximally 50-fold regulation by doxycycline (Dox). Determined by gene delivery method as well as promoter, highly specific tissues were transduced in vivo. Bioluminescence imaging (BLI) visualized reversible "ON/OFF" gene switches over repeated "Doxy-Cycling" in living mice. Thus, the reversible rAAV-mediated N-cistronic gene expression system, termed RANGE, may serve as a versatile tool to achieve reversible polycistronic gene regulation for the study of gene function as well as gene therapy.Molecular Therapy - Nucleic Acids (2013) 2, e85; doi:10.1038/mtna.2013.15; published online 9 April 2013.

Restoration of vision in the pde6β-deficient dog, a large animal model of rod-cone dystrophy

Defects in the β subunit of rod cGMP phosphodiesterase 6 (PDE6β) are associated with autosomal recessive retinitis pigmentosa (RP), a childhood blinding disease with early retinal degeneration and vision loss. To date, there is no treatment for this pathology. The aim of this preclinical study was to test recombinant adeno-associated virus (AAV)-mediated gene addition therapy in the rod-cone dysplasia type 1 (rcd1) dog, a large animal model of naturally occurring PDE6β deficiency that strongly resembles the human pathology. A total of eight rcd1 dogs were injected subretinally with AAV2/5RK.cpde6β (n = 4) or AAV2/8RK.cpde6β (n = 4). In vivo and post-mortem morphological analysis showed a significant preservation of the retinal structure in transduced areas of both AAV2/5RK.cpde6β- and AAV2/8RK.cpde6β-treated retinas. Moreover, substantial rod-derived electroretinography (ERG) signals were recorded as soon as 1 month postinjection (35% of normal eyes) and remained stable for at least 18 months (the duration of the study) in treated eyes. Rod-responses were undetectable in untreated contralateral eyes. Most importantly, dim-light vision was restored in all treated rcd1 dogs. These results demonstrate for the first time that gene therapy effectively restores long-term retinal function and vision in a large animal model of autosomal recessive rod-cone dystrophy, and provide great promise for human treatment.

Gene therapy for Leber congenital amaurosis: advances and future directions

BACKGROUND

Leber congenital amaurosis (LCA) is a congenital retinal dystrophy that results in significant and often severe vision loss at an early age. Comprehensive analysis of the genetic mutations and phenotypic correlations in LCA patients has allowed for significant improvements in understanding molecular pathways of photoreceptor degeneration and dysfunction. The purpose of this article is to review the literature on the subject of retinal gene therapy for LCA, including historical descriptions, preclinical animal studies, and human clinical trials.

METHODS

A literature search of peer-reviewed and indexed publications from 1996-2011 using the PubMed search engine was performed. Key terms included "Leber congenital amaurosis", LCA, RPE65, "cone-rod dystrophy", "gene therapy", and "human trials" in various combinations. Seminal articles prior to 1996 were selected from primary sources and reviews from the initial search. Articles were chosen based on pertinence to clinical, genetic, and therapeutic topics reviewed in this manuscript. Fundus photographs from LCA patients were obtained retrospectively from the clinical practice of one of the authors (R.A.S).

RESULTS

Herein, we reviewed the literature on LCA as a genetic disease, the results of human gene therapy trials to date, and possible future directions towards treating inherited retinal diseases at the genetic level. Original descriptions of LCA by Theodor Leber and subsequent research demonstrate the severity of this disease with early-onset blindness. Discoveries of the causative heritable mutations revealed genes and protein products involved in photoreceptor development and visual transduction. Animal models have provided a means to test novel therapeutic strategies, namely gene therapy. Stemming from these experiments, three independent clinical trials tested the safety of subretinal delivery of viral gene therapy to patients with mutations in the RPE65 gene. More recently, efficacy studies have been conducted with encouraging results.

CONCLUSIONS

Initial safety studies indicated promising results of subretinal delivery of viral vector with subclinical immunologic or surgical sequelae. Overall, these initial studies demonstrate that viral vector gene therapy results are very promising, safe, and effective. Future studies measuring potential improvement in photoreceptor function may rely on recent advances in retinal imaging and electrophysiologic testing.

Optimized technique for subretinal injections in mice

Subretinal injections in mice become increasingly important. Currently, the most prominent application is in gene therapy of inherited eye diseases by means of viral vector delivery to photoreceptors or the retinal pigment epithelium (RPE). Since there are no large animal models for most of these diseases, genetically modified mouse models are commonly used in preclinical proof-of-concept studies. However, because of the relatively small mouse eye, adverse effects of the subretinal delivery procedure itself may interfere with the therapeutic outcome. The protocol described here concerns a transscleral pars plana subretinal injection in small eyes, and may be used for but not limited to virus-mediated gene transfer.

Interactions between AAV-2 and HSV-1: implications for hybrid vector design

Herpes simplex virus type 1 (HSV-1)-based amplicon vectors have a transgene capacity of up to 150 kbp and can efficiently transduce many different cell types in culture and in vivo without causing cytopathic effects. However, these vectors do not support long-term transgene expression. Adeno-associated virus type 2 (AAV-2) has the capacity to integrate its genome into a specific site on human chromosome 19, but AAV-2-derived gene therapy vectors have a transgene capacity of only 4.5 kb. To combine the large transgene capacity of HSV-1 with the potential for site-specific genomic integration and long-term transgene expression of AAV-2, HSV/AAV hybrid vectors have been developed. This review describes the design, applications and limitations of these hybrid vectors. However, as HSV-1 is a full helper virus for AAV-2 replication, the main focus is the analysis of the molecular mechanisms of interaction between the two viruses. The knowledge of these interactions will have direct implications on the design of novel HSV/AAV hybrid vectors.