Transcriptome- and genome-wide analysis of TadA-induced off-target deamination upon in vivo adenine base editing in the adult mouse liver

Adenine base editors (ABEs), consisting of laboratory-evolved TadA deaminases fused to nuclease impaired Cas9, enable the directed conversion of A•T to G•C base pairs on genomic DNA. While high editing efficiencies in non-dividing primary human cells support their potential for in vivo gene editing therapies, reports on transcriptome-wide off-target deamination warrant caution for application in patients. Here, we use adeno-associated viral (AAV) vectors and lipid nanoparticles (LNPs) to deliver ABEs into the mouse liver and to install splice mutations in PCSK9. We observe editing rates up to 85% with both delivery vehicles, and efficient reduction in PCSK9- and blood LDL levels. Detailed analysis of off-target effects further reveals that in vivo adenine base editing generates only few off-target edits on mRNA, and no detectable off-target mutations on genomic DNA. These findings support the safety and efficacy of AAV- and LNP- mediated in vivo adenine base editing and demonstrate its potential for therapeutic application.