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). Using these specific ADIs, we develop an RNA transformer adenosine base editor (RtABE) with high specificity. Fusing ADI to ADAR2, RtABE remains inactive until it binds to its target site. After binding to the target site, ADI is cleaved from ADAR2, 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.