Efficiency of genome editing using modified single-stranded oligodeoxyribonucleotides in human cells

Single-stranded oligodeoxyribonucleotide (ssODN) gene editing has emerged as a promising therapeutic strategy. However, further improvements in efficiency are desired for practical application. The effects of strand length and locked nucleic acid (LNA) modification on ssODN genome editing were investigated by introducing an assay cassette into the genome of HEK293T cells and measuring precise base deletions of eight bases. The introduction of LNAs into ssODNs, five pairs of LNAs at 25-35 nt from the centre and one pair at 20-25 nt, showed approximately 18-fold higher efficiency than unmodified ssODNs of the same length in the study using 70 nt ssODNs. In addition, genome editing efficiency was further improved when LNAs were introduced at the same positions as the 70 nt ssODN, which showed the highest efficiency for the 90 nt ssODN. However, in some cases, the same number of LNA modifications could conversely reduce the efficiency, and the modification positions in the ssODN method were successfully optimised in the present study. Furthermore, the oligo DNA was shown to be effective not only for deletions but also for base substitutions, with an editing efficiency of 0.63% per cell.