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Noninvasive gene delivery to foveal cones for vision restoration
Hanen Khabou, … , José-Alain Sahel, Deniz Dalkara
Hanen Khabou, … , José-Alain Sahel, Deniz Dalkara
Published January 25, 2018
Citation Information: JCI Insight. 2018;3(2):e96029. https://doi.org/10.1172/jci.insight.96029.
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Resource and Technical Advance Ophthalmology Therapeutics

Noninvasive gene delivery to foveal cones for vision restoration

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Abstract

Intraocular injection of adeno-associated viral (AAV) vectors has been an evident route for delivering gene drugs into the retina. However, gaps in our understanding of AAV transduction patterns within the anatomically unique environments of the subretinal and intravitreal space of the primate eye impeded the establishment of noninvasive and efficient gene delivery to foveal cones in the clinic. Here, we establish new vector-promoter combinations to overcome the limitations associated with AAV-mediated cone transduction in the fovea with supporting studies in mouse models, human induced pluripotent stem cell–derived organoids, postmortem human retinal explants, and living macaques. We show that an AAV9 variant provides efficient foveal cone transduction when injected into the subretinal space several millimeters away from the fovea, without detaching this delicate region. An engineered AAV2 variant provides gene delivery to foveal cones with a well-tolerated dose administered intravitreally. Both delivery modalities rely on a cone-specific promoter and result in high-level transgene expression compatible with optogenetic vision restoration. The model systems described here provide insight into the behavior of AAV vectors across species to obtain safety and efficacy needed for gene therapy in neurodegenerative disorders.

Authors

Hanen Khabou, Marcela Garita-Hernandez, Antoine Chaffiol, Sacha Reichman, Céline Jaillard, Elena Brazhnikova, Stéphane Bertin, Valérie Forster, Mélissa Desrosiers, Céline Winckler, Olivier Goureau, Serge Picaud, Jens Duebel, José-Alain Sahel, Deniz Dalkara

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Figure 2

Model for the regulation of transgene expression under the control of PR2.1 and PR1.7 synthetic promoters and mouse cone arrestin (mCAR) promoter.

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Model for the regulation of transgene expression under the control of PR...
(A) Red opsin gene is located on the X chromosome. It has its own proximal promoter and shares its enhancer sequence with green opsin gene. Chromosomal loops between the enhancer and the red opsin proximal promoter provide cell-type specificity of gene expression. PPred, proximal promoter of red opsin gene; LCR, locus control region. (B) Schematic representation of PR2.1 and PR1.7 promoter constructs. Interaction with inhibitory transcription factors such as COUP-TFI (chicken ovalbumin upstream promoter-transcription factor), that binds the 337bp region specific to PR2.1 might explain low expression levels obtained with PR2.1 compared with PR1.7 in macaque cones subretinally (18). On the other hand, activator TFs such as CEBPB (CCAAT/enhancer binding protein β) and GTF2I (general transcription factor II-I) that are not specific to cones likely lead to off-target expression in other retinal cells when injected into the vitreous. ITRs, inverted terminal repeats. (C) Structure of cone arrestin 3 genomic locus region. Transcription starting sites (TSS) of mouse arrestin 3 (mArr3) gene and mouse pyrimidinergic receptor P2Y4 (mP2ry4) gene are separated by 10.5 kilobases. The short 521-bp mCAR promoter used in this study is shown in blue and the supposed regulatory region referred to as “Reg” in magenta. (D) Structure of the 521-bp mCAR promoter portion used in this study. This sequence contains CRX-binding sites (CBS) and SP (Specificity Protein) binding sites. It also contains 1 TATA and 1 TATA-like box. (E) Interactome network of several transcription factors that bind cone arrestin genomic promoter analyzed using the STRING tool. CRX (cone-rod homeobox protein), SP, RARA (retinoic acid receptor α), RXRA (retinoid X receptor α), and THRB (thyroid hormone receptor β 2). (F) NR-MED1 transcription regulator complex confers gene expression specificity. MED1 (mediator complex subunit 1) is a transcription activator when associated to nuclear receptors (NRs). RARA, RXRA, and THRB are NRs. Several NR binding sites for RARA, RXRA, and THRB were found in the Reg region. AAV, adeno-associated virus; mCAR, mouse cone arrestin promoter; PR1.7 and PR2.1, promoters of 1.7 and 2.1 kilobases in length, respectively, based on the human red opsin gene enhancer and promoter sequences.

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