AAV8-delivered twin prime editor with Pah transgene

AAV8-delivered twin prime editor with Pah transgene is an experimental three-vector, liver-directed **in vivo gene-editing and gene-insertion approach** for murine phenylketonuria caused by phenylalanine hydroxylase deficiency. Two AAV8 vectors encode split-intein-reconstituted halves of a PE2 twin prime editor designed to install a Bxb1 attB sequence at the endogenous *Pah* locus, while a third AAV8 vector carries a liver-specific *Pah* expression cassette. The intended dual-flap integration strategy uses recombinatorial AAV inverted terminal repeats to facilitate site-specific insertion of the therapeutic *Pah* transgene without an exogenous recombinase. In the reported PAH-deficient mouse study, plasma phenylalanine initially declined, but no detectable twin-prime-editing events or transgene integration were found by PCR sequencing; the investigators attributed the result in part to insufficient nuclear trafficking of the split PE2 editor and proposed newer prime-editor generations for follow-up studies.