# Evolution of an adenine base editor into a small, efficient cytosine base editor with low off-target activity

Article · Neugebauer ME, Hsu A, Arbab M, Krasnow NA, McElroy AN, Pandey S, Doman JL, Huang TP, Raguram A, Banskota S, Newby GA, Tolar J, Osborn MJ, Liu DR

- Archive id: doi:10.1038/s41587-022-01533-6
- Published: 2022-11-10
- Venue: Nature biotechnology
- DOI: https://doi.org/10.1038/s41587-022-01533-6
- PMID: 36357719
- PMCID: PMC10188366
- Citations: 238
- Source URL: https://doi.org/10.1038/s41587-022-01533-6
- PDF: https://europepmc.org/articles/PMC10188366/pdf
- Provenance: europepmc

## Abstract

Cytosine base editors (CBEs) are larger and can suffer from higher off-target activity or lower on-target editing efficiency than current adenine base editors (ABEs). To develop a CBE that retains the small size, low off-target activity and high on-target activity of current ABEs, we evolved the highly active deoxyadenosine deaminase TadA-8e to perform cytidine deamination using phage-assisted continuous evolution. Evolved TadA cytidine deaminases contain mutations at DNA-binding residues that alter enzyme selectivity to strongly favor deoxycytidine over deoxyadenosine deamination. Compared to commonly used CBEs, TadA-derived cytosine base editors (TadCBEs) offer similar or higher on-target activity, smaller size and substantially lower Cas-independent DNA and RNA off-target editing activity. We also identified a TadA dual base editor (TadDE) that performs equally efficient cytosine and adenine base editing. TadCBEs support single or multiplexed base editing at therapeutically relevant genomic loci in primary human T cells and primary human hematopoietic stem and progenitor cells. TadCBEs expand the utility of CBEs for precision gene editing.

_Abstract reproduced under CC-BY (article license as recorded by Europe PMC; abstract reproduced unmodified apart from markup removal)._

Topics: [CRISPR & Gene-Editing Therapies](https://space-kitty.com/topics/gene-editing-therapies)

Cited in dossiers:
- [CRISPR & Gene-Editing Therapies: State of the Field (October 2026)](https://space-kitty.com/dossiers/gene-editing-therapies)

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