Translation of CRISPR Genome Surgery to the Bedside for Retinal Diseases.

In recent years, there has been accelerated growth of clustered regularly interspaced short palindromic repeats (CRISPR) genome surgery techniques. Genome surgery holds promise for diseases for which a cure currently does not exist. In the field of ophthalmology, CRISPR offers possibilities for treating inherited retinal dystrophies. The retina has little regenerative potential, which makes treatment particularly difficult. For such conditions, CRISPR genome surgery methods have shown great potential for therapeutic applications in animal models of retinal dystrophies. Much anticipation surrounds the potential for CRISPR as a therapeutic, as clinical trials of ophthalmic genome surgery are expected to begin as early as 2018. This mini-review summarizes preclinical CRISPR applications in the retina and current CRISPR clinical trials.

Clustered Regularly Interspaced Short Palindromic Repeats-Based Genome Surgery for the Treatment of Autosomal Dominant Retinitis Pigmentosa.

PURPOSE: To develop a universal gene therapy to overcome the genetic heterogeneity in retinitis pigmentosa (RP) resulting from mutations in rhodopsin (RHO). DESIGN: Experimental study for a combination gene therapy that uses both gene ablation and gene replacement. PARTICIPANTS: This study included 2 kinds of human RHO mutation knock-in mouse models: RhoP23H and RhoD190N. In total, 23 RhoP23H/P23H, 43 RhoP23H/+, and 31 RhoD190N/+ mice were used for analysis. METHODS: This study involved gene therapy using dual adeno-associated viruses (AAVs) that (1) destroy expression of the endogenous Rho gene in a mutation-independent manner via an improved clustered regularly interspaced short palindromic repeats-based gene deletion and (2) enable expression of wild-type protein via exogenous cDNA. MAIN OUTCOME MEASURES: Electroretinographic and histologic analysis. RESULTS: The thickness of the outer nuclear layer (ONL) after the subretinal injection of combination ablate-and-replace gene therapy was approximately 17% to 36% more than the ONL thickness resulting from gene replacement-only therapy at 3 months after AAV injection. Furthermore, electroretinography results demonstrated that the a and b waves of both RhoP23H and RhoD190N disease models were preserved more significantly using ablate-and-replace gene therapy (P < 0.001), but not by gene replacement monotherapy. CONCLUSIONS: As a proof of concept, our results suggest that the ablate-and-replace strategy can ameliorate disease progression as measured by photoreceptor structure and function for both of the human mutation knock-in models. These results demonstrate the potency of the ablate-and-replace strategy to treat RP caused by different Rho mutations. Furthermore, because ablate-and-replace treatment is mutation independent, this strategy may be used to treat a wide array of dominant diseases in ophthalmology and other fields. Clinical trials using ablate-and-replace gene therapy would allow researchers to determine if this strategy provides any benefits for patients with diseases of interest.