Development of gene therapies for retinal degenerations

Abstract

The studies described in this thesis explore potential gene therapies for retinal degenerative diseases using adeno-associated virus (AAV) vectors for gene delivery. Inherited retinal degenerations (IRDs) are a leading cause of vision loss for people of working age and exhibit extreme genetic heterogeneity, with over 270 known genes implicated. Retinitis pigmentosa (RP), a progressive rod-cone dystrophy, represents the most common IRD and can be caused by mutations in any of over 80 different genes. The research presented in Chapter 2 of this thesis relates to X-linked RP (XLRP) caused by mutation of the RP2 gene. Through a collaborative effort, retinal organoids (ROs) were used to model this form of XLRP. A novel early-onset rod degeneration phenotype emerged in RP2 null ROs, which could be prevented by highly efficient transduction with an AAV RP2 gene replacement vector. In Chapter 3, the feasibility of a gene editing-based treatment for rhodopsin-linked autosomal dominant RP (RHO-ADRP) was explored. A dual AAV CRISPR-Cas9 based platform was developed to test the efficiency of this strategy in photoreceptors of a humanised mouse model of RHO-ADRP. Alongside the development of gene-specific treatment strategies for monogenic IRDs, there is also considerable interest in exploring gene-independent therapeutics that can modulate common degenerative mechanisms. Such strategies may circumvent the substantial genetic heterogeneity of IRDs and, moreover, be applicable to multifactorial ocular disorders. Of note, bioenergetic perturbation is emerging as a major underlying factor in diseases of the retina and optic nerve, including glaucoma the most common cause of irreversible blindness. The study presented in the final research chapter of this thesis examined whether modulating such features of disease, using an AAV gene therapy approach, could be beneficial in a glaucomatous context. When tested in a murine model of chronic ocular hypertension, retinal ganglion cell body density was significantly preserved in eyes treated with this gene therapy. Overall, the data presented in this thesis support the immense potential of gene therapies for the treatment of monogenic and multifactorial retinal degenerations.