Targeting the locus for liver-directed gene therapy.

Clinical application of somatic genome editing requires therapeutics that are generalizable to a broad range of patients. Targeted insertion of promoterless transgenes can ensure that edits are permanent and broadly applicable while minimizing risks of off-target integration. In the liver, the Albumin () locus is currently the only well-characterized site for promoterless transgene insertion. Here, we target the locus with adeno-associated viral (AAV) delivery of CRISPR-Cas9 and achieve rates of 6% to 16% of targeted hepatocytes, with no evidence of toxicity. We further show that the endogenous promoter can drive robust and sustained expression of therapeutic proteins, such as apolipoprotein E (), dramatically reducing plasma lipids in a model of hypercholesterolemia. Finally, we demonstrate that -targeted fumarylacetoacetate hydrolase () can correct and rescue the severe metabolic liver disease hereditary tyrosinemia type I. In summary, we identify and validate as a novel integration site that supports durable transgene expression in the liver for gene therapy applications.