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

Monica E. Neugebauer, Alvin Hsu, Mandana Arbab, Nicholas A. Krasnow, Amber N. McElroy, Smriti Pandey, Jordan L. Doman, Tony P. Huang, Aditya Raguram, Samagya Banskota, Gregory A. Newby, Jakub Tolar, Mark J. Osborn, David R. Liu

Research output: Contribution to journalArticlepeer-review

72 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)673-685
Number of pages13
JournalNature biotechnology
Issue number5
StatePublished - May 2023

Bibliographical note

Funding Information:
This work was supported by US National Institutes of Health (NIH) grants R01EB027793, R01EB031172, U01AI142756, R35GM118062, RM1HG009490 and R01AR063070-08; the Bill and Melinda Gates Foundation; and the Howard Hughes Medical Institute. We thank P. Chen, K. Everette, D. Nelson, A. Sousa and J. Queenan for materials, discussion and technical advice. M.E.N. was supported by a Ruth L. Kirschstein National Research Service Awards Postdoctoral Fellowship (GM143776-02). A.H. is a National Science Foundation (NSF) Graduate Research Fellow. M.A. is a recipient of the NIH Pathway to Independence Award (K99/R00NS119743). J.L.D. is supported by the Hertz Foundation and the NSF Graduate Research Fellowship Program. A.R. is an NSF Graduate Research Fellow and was supported by an NIH training grant (T32 GM095490). G.A.N. is a Howard Hughes Medical Institute Fellow of the Helen Hay Whitney Foundation. M.J.O. receives funding from the Bill and Melinda Gates Foundation, the Saint Baldrick’s Foundation and the Kidz1stFund. J.T. receives funding from NIH R01 AR063070. For sourcing HSPCs, we acknowledge support from the National Institute of Diabetes and Digestive and Kidney Diseases under award U54DK106829: Fred Hutchinson Cancer Center Cooperative Center of Excellence in Hematology.

Publisher Copyright:
© 2022, The Author(s).

PubMed: MeSH publication types

  • Journal Article
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, N.I.H., Extramural


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