Treatment of a metabolic liver disease by in vivo prime editing in mice

Prime editing is a highly versatile CRISPR-based genome editing technology with the potential to correct the vast majority of pathogenic mutations ([1][1]) . However, correction of a disease phenotype in vivo in somatic tissues has not been demonstrated thus far. Here, we establish proof-of-concept for in vivo prime editing and repair the metabolic liver disease phenylketonuria (PKU) in mice. We first developed a size-reduced Sp Cas9 prime editor (PE) lacking the RNaseH domain of the reverse transcriptase (PE2Δ RnH ), and a linker- and NLS-optimized intein-split PE construct (PE2 p.1153) for delivery by adeno-associated virus (AAV) vectors. Systemic dual AAV-mediated delivery of this variant into the liver of neonatal mice enabled installation of a transversion mutation at the Dnmt1 locus with an average efficiency of 15%, and delivery of unsplit PE2Δ RnH using human adenoviral vector 5 (AdV5) further increased editing rates to 58%. PE2Δ RnH -encoding AdV5 was also used to correct the disease-causing mutation of the phenylalanine hydroxylase (Pah) enu2 allele in phenylketonuria (PKU) mice with an average efficiency of 8% (up to 17.3%), leading to therapeutic reduction of blood phenylalanine (L-Phe) levels. Our study demonstrates in vivo prime editing in the liver with high precision and editing rates sufficient to treat a number of metabolic liver diseases, emphasizing the potential of prime editing for future therapeutic applications. One Sentence Summary In vivo prime editing corrects phenylketonuria in mice. ### Competing Interest Statement D.B, L.V., and G.S are named on patent applications related to CRISPR-Cas technologies. [1]: #ref-1