Specific and efficient RNA A-to-I editing through cleavage of an ADAR inhibitor

RNA editing can be a promising therapeutic approach. However, ectopic expression of RNA editing enzymes has been shown to trigger off-target editing. Here we identified adenosine deaminase acting on RNA (ADAR) inhibitors (ADIs) that suppress the activity of the fused ADAR2 deamination domain (ADAR2_DD). Using these specific ADIs, we develop an RNA transformer adenosine base editor (RtABE) with high specificity. Fusing ADI to ADAR2_DD, RtABE remains inactive until it binds to its target site. After binding to the target site, ADI is cleaved from ADAR2_DD, and RtABE becomes active. RtABE can induce efficient editing in broad sequence contexts, including UAN, AAN, CAN and GAN. Using an adeno-associated virus for delivery of RtABE enables therapeutic RNA correction and restoration of α-L-iduronidase activity in Hurler syndrome mice with no substantial off-target editing. RtABE is a specific and efficient RNA editing system with a broad scope that may be a better alternative to existing RNA editing tools.