AAV-mediated genome editing is influenced by the formation of R-loops.
Recombinant adeno-associated viral vectors (rAAV) hold a natural ability to stimulate homologous recombination (AAV-HR). Moreover, they are also reported to randomly integrate into numerous locations throughout the genome. Here, we describe DNA/RNA immune precipitation sequencing (DRIP-seq) studies in HEPA1-6 cells and whole murine liver to detect genomic r-loops. Through genetic and pharmacological manipulation of r-loops formation, we showed a significant enhancement of AAV-HR. Notably, we were able to detect different levels of r-loops along the Albumin locus. Both in vitro and in vivo experiments showed that the 3' end of Albumin (high r-loops) is efficiently edited by AAV-HR, whereas the upstream region (low r-loops) did not result in any detectable vector integration. In addition, we were also able to find an interesting correlation between previously reported off-target rAAV integration and r-loop enriched genomic regions. Thus, we conclude that highly transcribed genes accumulate high levels of r-loops, and this could lead to rAAV vector genome integration. These findings may shed light on mechanisms for improving the safety and efficacy of genome editing and may enhance our ability to predict regions most susceptible to insertional mutagenesis with canonical rAAV vectors. Overall design: R-loops detection by S9.6 immunoprecipitation extracts  HEPA1-6 cells and mouse liver