<p>Base editing (BE) can permanently correct over half of known human pathogenic genetic variants without requiring a repair template, thus serving as a promising therapeutic tool to treat a broad spectrum of genetic diseases. However, the broad activity windows of current base editors pose a major challenge to their therapeutic application. Here, we show that integrating a naturally occurring oligonucleotide binding module into the deaminase active center of TadA-8e, a highly active deoxyadenosine deaminase, enhances its editing specificity. When conjugated with a Cas9 nickase or alternative PAM Cas9 variants, the engineered TadA variant—TadA-NW1—consistently achieves robust A-to-G editing efficiencies within an editing window consisting of four nucleotides, substantially narrower than the 10-bp editing window of the TadA-8e-derived ABEs. Moreover, compared to ABE8e, ABE-NW1 shows significantly decreased Cas9-dependent and -independent off-target activity while maintaining similar on-target editing efficiency. Further, TadA-NW1 can be reprogrammed to perform desired cytidine deamination and adenine transversion within a restricted editing window. Finally, in a cystic fibrosis (CF) cell model, ABE-NW1 outperforms existing ABEs in accurately and efficiently correcting the CFTR W1282X variant, one of the most common CF-causing mutations. In all, we engineered a suite of base editors with refined activity windows, enabling more precise base editing. Importantly, this study presents a streamlined genome editor re-engineering strategy to accelerate the development of therapeutic base editing.</p>

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A streamlined base editor engineering strategy to reduce bystander editing

  • Izabella Valdez,
  • Ian O’Connor,
  • Divesh Patel,
  • Katherine Gierer,
  • Jan Harrington,
  • Ethan Ellis,
  • Stephen A. Caponetti,
  • Robert P. Sebra,
  • Hillary C. Valley,
  • Kevin Coote,
  • Martin Mense,
  • Samuele G. Marro,
  • Tingting Jiang

摘要

Base editing (BE) can permanently correct over half of known human pathogenic genetic variants without requiring a repair template, thus serving as a promising therapeutic tool to treat a broad spectrum of genetic diseases. However, the broad activity windows of current base editors pose a major challenge to their therapeutic application. Here, we show that integrating a naturally occurring oligonucleotide binding module into the deaminase active center of TadA-8e, a highly active deoxyadenosine deaminase, enhances its editing specificity. When conjugated with a Cas9 nickase or alternative PAM Cas9 variants, the engineered TadA variant—TadA-NW1—consistently achieves robust A-to-G editing efficiencies within an editing window consisting of four nucleotides, substantially narrower than the 10-bp editing window of the TadA-8e-derived ABEs. Moreover, compared to ABE8e, ABE-NW1 shows significantly decreased Cas9-dependent and -independent off-target activity while maintaining similar on-target editing efficiency. Further, TadA-NW1 can be reprogrammed to perform desired cytidine deamination and adenine transversion within a restricted editing window. Finally, in a cystic fibrosis (CF) cell model, ABE-NW1 outperforms existing ABEs in accurately and efficiently correcting the CFTR W1282X variant, one of the most common CF-causing mutations. In all, we engineered a suite of base editors with refined activity windows, enabling more precise base editing. Importantly, this study presents a streamlined genome editor re-engineering strategy to accelerate the development of therapeutic base editing.