CRX gene therapy in mouse and human models of retinal dystrophies targeting dominant CRX-associated retinopathies – CuRAT

Inherited retinal dystrophies (IRDs) are genetically and clinically heterogeneous. Despite tremendous progress in IRD research over the past 10 years, these diseases still lead to legal blindness due to limited therapeutic options. The recent success of gene supplementation therapy in patients with Leber Congenital Amaurosis (LCA) caused by RPE65 mutations has highlighted the real interest in expanding this approach to other IRDs. Our previous work suggests that diseases due to dominant mutations in CRX, a transcription factor essential to photoreceptor development and maturation, are relevant candidates for gene supplementation. To date, over 50 mutations in the CRX gene are responsible for cone-rod dystrophies (CORD), LCA, and retinitis pigmentosa (RP).
Due to the clinical heterogeneity of patients carrying CRX mutations, our proposal aims to restore and/or maintain vision in two mouse models of retinopathies associated with CRX: an LCA model that we have already well characterized, and a novel CORD model. In this context, we will evaluate whether a gene replacement approach is able to compensate for the deleterious effects of CRX mutants for both clinical forms. Towards this aim, a CRX-expressing AAV vector will be administered, and its long-term efficacy evaluated, in both models. The recovery and preservation of retinal function will be tested by electroretinogram and optokinetic reflex recordings, and retinal morphology by optical coherence tomography. This efficacy study will be completed by histological and molecular analyses. Furthermore, in order to better understand disease pathophysiology and to validate a therapeutic approach in humans, we will complement these in vivo studies on iPSC-derived retinal organoids generated from three patients with CRX-associated LCA, CORD, or RP. By analyzing differential gene and protein expression, as well as the morphology of the organoids throughout retinal differentiation and maturation, we will establish a genotype-phenotype correlation and, hence, elucidate the basis for the differential clinical profiles associated with each mutation. Furthermore, we will obtain pertinent read-outs to assay the efficiency of an AAV-mediated gene replacement following the transduction of the patient organoids. In this way, we will determine whether all forms can benefit from our therapeutic approach, without negative effects linked with CRX overexpression.
At the end of this preclinical study, our expectation is to have demonstrated the efficacy of our gene therapy in mouse and human models with dominant CRX mutations. The potential clinical value of this project lies in the development of gene therapy to treat a broad spectrum of CRX-associated retinopathies and might serve as proof of concept for other dominant IRDs. This study may serve as a basis for further development of clinical trials.