Molecular characterization of precise in vivo targeted gene integration in human cells using AAVHSC15

PLoS One. 2020 May 26;15(5):e0233373. doi: 10.1371/journal.pone.0233373. eCollection 2020.

Abstract

Targeted gene integration via precise homologous recombination (HR)-based gene editing has the potential to correct genetic diseases. AAV (adeno-associated virus) can mediate nuclease-free gene integration at a disease-causing locus. Therapeutic application of AAV gene integration requires quantitative molecular characterization of the edited sequence that overcome technical obstacles such as excess episomal vector genomes and lengthy homology arms. Here we describe a novel molecular methodology that utilizes quantitative next-generation sequencing to characterize AAV-mediated targeted insertion and detects the presence of unintended mutations. The methods described here quantify targeted insertion and query the entirety of the target locus for the presence of insertions, deletions, single nucleotide variants (SNVs) and integration of viral components such as inverted terminal repeats (ITR). Using a humanized liver murine model, we demonstrate that hematopoietic stem-cell derived AAVHSC15 mediates in vivo targeted gene integration into human chromosome 12 at the PAH (phenylalanine hydroxylase) locus at 6% frequency, with no sign of co-incident random mutations at or above a lower limit of detection of 0.5% and no ITR sequences at the integration sites. Furthermore, analysis of heterozygous variants across the targeted locus using the methods described shows a pattern of strand cross-over, supportive of an HR mechanism of gene integration with similar efficiencies across two different haplotypes. Rapid advances in the application of AAV-mediated nuclease-free target integration, or gene editing, as a new therapeutic modality requires precise understanding of the efficiency and the nature of the changes being introduced to the target genome at the molecular level. This work provides a framework to be applied to homologous recombination gene editing platforms for assessment of introduced and natural sequence variation across a target site.

MeSH terms

  • Animals
  • Dependovirus / physiology*
  • Gene Editing / methods*
  • Genetic Vectors / administration & dosage
  • HEK293 Cells
  • High-Throughput Nucleotide Sequencing
  • Humans
  • Liver / chemistry*
  • Mice
  • Models, Animal
  • Mutation
  • Phenylalanine Hydroxylase / genetics*
  • Sequence Analysis, DNA
  • Virus Integration

Substances

  • Phenylalanine Hydroxylase

Grants and funding

All authors are current or former employees of Homology Medicines, Inc. This work is funded by Homology Medicines, Inc. https://www.homologymedicines.com/ The funder provided support in the form of salaries for all authors, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.