INSERT-seq enables high resolution mapping of genomically integrated DNA using nanopore sequencing

Comprehensive characterization of genome engineering with viral vectors, transposons, CRISPR/Cas mediated DNA integration and other DNA editors remains relevant for their development and safe use in human gene therapy. Currently, described methods for measuring DNA integration in edited cells rely on short read based technologies. Due to the repetitive nature of the human genome, short read based methods can potentially overlook insertion events in repetitive regions. We modelled the impact of read length in resolving insertion sites, which suggested a significant drop in insertion site detection with shorter read length. Based on that, we developed a method that combines targeted amplification of integrated DNA, UMI-based correction of PCR bias and Oxford Nanopore long-read sequencing for robust analysis of DNA integration in a genome. This method, called INSERT-seq, is capable of detecting events occurring at a frequency of up to 0.1%. INSERT-seq presents a complete handling of all insertions independently of repeat size. The experimental pipeline improves the number mappable insertions at repetitive regions by 7.3% and repeats larger than the long read sequencing size are processed computationally to perform a peak calling in a repeat database. INSERT-seq is a simple, cheap and robust method to quantitatively characterise DNA integration in diverse ex-vivo and in-vivo samples.