Gene-Based Therapeutics for Inherited Retinal Diseases.

Inherited retinal diseases (IRDs) are a heterogenous group of orphan eye diseases that typically result from monogenic mutations and are considered attractive targets for gene-based therapeutics. Following the approval of an IRD gene replacement therapy for Leber's congenital amaurosis due to RPE65 mutations, there has been an intensive international research effort to identify the optimal gene therapy approaches for a range of IRDs and many are now undergoing clinical trials. In this review we explore therapeutic challenges posed by IRDs and review current and future approaches that may be applicable to different subsets of IRD mutations. Emphasis is placed on five distinct approaches to gene-based therapy that have potential to treat the full spectrum of IRDs: 1) gene replacement using adeno-associated virus (AAV) and nonviral delivery vectors, 2) genome editing via the CRISPR/Cas9 system, 3) RNA editing by endogenous and exogenous ADAR, 4) mRNA targeting with antisense oligonucleotides for gene knockdown and splicing modification, and 5) optogenetic approaches that aim to replace the function of native retinal photoreceptors by engineering other retinal cell types to become capable of phototransduction.

Surgical Removal of Internal Limiting Membrane and Layering of AAV Vector on the Retina Under Air Enhances Gene Transfection in a Nonhuman Primate.

Purpose: To determine if the surgical removal of the internal limiting membrane (ILM) in nonhuman primates (NHPs) will result in safe and effective transfection of adeno-associated viral (AAV2) vectors using green fluorescent protein (GFP) as a reporter. Methods: Six Macaca fascicularis NHP eyes underwent vitrectomy, ILM peel with layering of 1.7 × 1013 genome copies per milliliter of AAV2-GFP under air. Four control eyes underwent only vitrectomy and pooling under air. The intensity and area transfected was quantified in vivo with fundus autofluorescence (FAF) imaging. NHPs were euthanized 16 weeks postsurgery and immunohistochemical analysis assessed GFP expression at the cellular level. Results: There was a larger area of fluorescence in ILM peeled eyes then in non-ILM peeled eyes (50.7 [33.1-58.4] pixel2 versus 5.1 [0.6-7.6] pixel2, P < 0.01). The intensity of fluorescence was also higher in ILM peeled eyes (10.3 [2.2-18.5] vs. 1.9 [0.6-4.4], P = 0.05). Non-ILM peeled eyes displayed fluorescence confined to the foveal center. Histological sections showed colocalization in the Müller cell layer, ganglion cell layer, and photoreceptor cell layer in the ILM peeled eyes. In non-ILM peeled eyes GFP expression was only in the ganglion cell layer in three eyes and was confined to the immediate vicinity of the fovea. Conclusions: ILM appears to be the predominate barrier to AAV transfection. An efficacious and safe method of AAV2 gene delivery, taking into account the potential need for repeat treatments, appears to be the surgical removal of ILM and layering of AAV under air.v.

Evaluation of subconjunctival liposomal steroids for the treatment of experimental uveitis.

Non-infectious anterior uveitis (AU) is a potentially sight threatening inflammatory condition. The current gold standard for treatment is topical steroids, but low ocular bioavailability and compliance issues with the intensive dosing regimen limit the efficacy of this treatment. Liposomes as a drug delivery system may help to overcome these problems. We studied the efficacy of a PEG-liposomal formulation of liposomal steroids, administered as a single subconjunctival dose, in the treatment of experimental uveitis in rabbit eyes. Rabbits that received subconjunctival liposomal triamcinolone acetonide phosphate (LTAP) or liposomal prednisolone phosphate (LPP) had significantly lower mean inflammatory scores than untreated controls on Day 4 after induction of uveitis (LPP vs controls, p = 0.049) and 8 (LPP vs controls, p = 0.007; LTAP vs controls, p = 0.019), and lower scores than rabbits given topical PredForte1% 4 times a day on Day 8 (p = 0.03). After antigen rechallenge, the subconjunctival liposomal steroid groups continued to have greater suppression of inflammation than untreated controls on Day 11 (p = 0.02). Localization of liposomes in inflamed ocular tissue was confirmed by histology and immunostaining, and persisted in the eye for at least one month. Our study demonstrates that a single subconjunctival injection of liposomal steroids induces effective and sustained anti-inflammatory action.