Programmable C•G-to-G•C base editors (CGBEs) have broad scientific and therapeutic potential, but their editing outcomes have proved difficult to predict and their editing efficiency and product purity are often low. We describe a suite of engineered CGBEs paired with machine learning models to enable efficient, high-purity C•G-to-G•C base editing. We performed a CRISPR interference (CRISPRi) screen targeting DNA repair genes to identify factors that affect C•G-to-G•C editing outcomes and used these insights to develop CGBEs with diverse editing profiles. We characterized ten promising CGBEs on a library of 10,638 genomically integrated target sites in mammalian cells and trained machine learning models that accurately predict the purity and yield of editing outcomes (R = 0.90) using these data. These CGBEs enable correction to the wild-type coding sequence of 546 disease-related transversion single-nucleotide variants (SNVs) with >90% precision (mean 96%) and up to 70% efficiency (mean 14%). Computational prediction of optimal CGBE–single-guide RNA pairs enables high-purity transversion base editing at over fourfold more target sites than achieved using any single CGBE variant.
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The target library sequencing data generated during this study are available at the NCBI Sequence Read Archive database under PRJNA631290. Data from the Repair-seq screens are available under PRJNA721212. Processed target library data used for training machine learning models have been deposited under the following DOIs: https://doi.org/10.6084/m9.figshare.12275645 and https://doi.org/10.6084/m9.figshare.12275654.
Code used for analysis of CRISPRi screens is available at https://github.com/jeffhussmann/repair-seq. Codes used for target library data processing and analysis iare available at https://github.com/maxwshen/lib-dataprocessing and https://github.com/maxwshen/lib-analysis, respectively. The machine learning models for CGBEs trained on target library data are available as a part of the BE-Hive interactive web application at https://crisprbehive.design and the BE-Hive Python package at https://github.com/maxwshen/be_predict_efficiency and https://github.com/maxwshen/be_predict_bystander.
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This work was supported by US NIH (nos. U01AI142756, UG3AI150551, RM1HG009490, R35GM118062, R35GM138167 and P30CA072720), HHMI and Princeton University. B.A. acknowledges a Searle Scholars award. The authors acknowledge NSF Graduate Research Fellowships to L.W.K., M.W.S. and T.A.S.; a NWO Rubicon Fellowship to M.A.; a Jane Coffin Childs postdoctoral fellowship to A.V.A.; fellowship support from the NSF and Hertz Foundation to J.L.D.; a Helen Hay Whitney postdoctoral fellowship to G.A.N.; a Damon Runyon Postdoctoral Fellowship to D.Y.; a Singapore A*STAR NSS fellowship to B.M.; and NIH Ruth L. Kirschstein National Research Service Award no. F31NS115380 to J.M.R. J.A.H. was the Rebecca Ridley Kry Fellow of the Damon Runyon Cancer Research Foundation.
J.A.H. is a consultant for Tessera Therapeutics. J.M.R. is a consultant for Maze Therapeutics. J.S.W. is a consultant for, and holds equity in, Maze Therapeutics, Chroma Medicine and KSQ Therapeutics. B.A. was a member of a ThinkLab Advisory Board for, and holds equity in, Celsius Therapeutics. D.R.L. is a consultant for, and holds equity in, Beam Therapeutics, Prime Medicine, Pairwise Plants and Chroma Medicine. The remaining authors declare no competing interests.
Peer review information Nature Biotechnology thanks Jia Chen, Leopold Parts and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Supplementary Figs. 1–15, Discussion 1–6, Sequences and References.
Supplementary Table 1. CRISPRi sgRNA library. Supplementary Table 2. Changes in base editing outcomes for all genes in CRISPRi screens. Supplementary Table 3. Base editing outcomes in a library of disease-related alleles correctable by editing C•G to G•C or to A•T. Supplementary Table 4. CGBE targets, amplicons and oligos used for this study.
All C•G-to-G•C editing yield, purity and indel outcomes for all experiments in this manuscript. T-tests can be generated for any pairwise comparison in this file.
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Koblan, L.W., Arbab, M., Shen, M.W. et al. Efficient C•G-to-G•C base editors developed using CRISPRi screens, target-library analysis, and machine learning.
Nat Biotechnol (2021). https://doi.org/10.1038/s41587-021-00938-z