Gene Editing therapy for Usher Syndrome Type IIA

JI Program: Exploratory

Usher Syndrome (USH) Type II is the most common type of USH, the leading genetic cause of deafness associated with blindness in the world, and there is currently no cure. Mutations on USH2A gene account for approximately 70% of USH2 cases. Gene editing can directly repair a defective gene, providing a promising therapeutic strategy for treatment of USH2A. We have developed a rabbit model carrying frameshift mutations on USH2A gene and showed early onset, progressive photoreceptor degeneration, similar to the retinitis pigmentosa (RP) symptoms observed in human patients. In parallel, we have developed an improved spCas9 variants, named meticulous integration Cas9 (miCas9), which greatly reduced both on-target and off-target insertion and deletion (indel) events and improved knock-in events by multiple folds. In this project, taking advantages of these two lines of promising work, we propose to develop an miCas9 mediated USH2A gene editing therapy in a novel USH2A rabbit model. We will use cultured rabbit fibroblasts and rabbit retina explants to optimize the CRISPR reagents, and test similar designed editing reagents in USH2A patient derived iPS cells and retinal organoids. Finally, the optimized editing reagents will be tested in vivo in the USH2A rabbit to evaluate the editing efficiency and safety of the USH2A gene editing therapy, including on- and off-target effects, biodistribution and toxicity. The long-term goal of this project is to generate data towards securing funding to further demonstrate whether miCas9 mediated gene editing can be used as a novel therapeutic strategy for treating USH2A.