Efficient and precise programmable DNA knock-in without double-strand breaks.

Programmable gene knock-in holds substantial promise for treating genetic diseases and advancing cell therapies. However, achieving precise and efficient kilobase-scale DNA fragment integration remains challenging 1,2 . Here we report CRISPR kilobase-scale nickase-targeting (KNIT) editing for efficient, precise and programmable kilobase-scale DNA insertion without double-strand DNA cleavage, which is enabled through the coupling of a Cas9 nickase with a DNA donor recruiting system. KNIT editing facilitates programmable integration of DNA fragments from 0.7 kb to more than 10 kb and is effective across genomic loci and cell types. It achieves up to 89% efficiency and markedly reduces unintended insertion-deletion mutation (indels) rates, translocations and off-target editing. The system supports repeated insertion editing and multiloci gene knock-in with minimal translocations. Its enhanced version, KNIT editor 2, further improves efficiency via a single transfection. Moreover, in mutant cells with a pathological mutation, KNIT editing restores normal gene expression by inserting a therapeutic gene into a safe harbour locus or its native locus. Notably, KNIT editing enables non-viral and programmable chimeric antigen receptor T cell (CAR-T cell) engineering without double-strand breaks and with clinically relevant efficiencies. Moreover, the engineered CAR-T cells exhibit effective antitumour activity in vitro and in mouse models. Therefore, by achieving programmable and site-specific kilobase-scale DNA insertions without double-strand breaks while reducing unintended outcomes, KNIT editing provides a versatile platform for advancing personalized medicine.