TEG-seq: an ion torrent-adapted NGS workflow for in cellulo mapping of CRISPR specificity.

GUIDE-seq was developed to detect CRISPR/Cas9 off-target. However, as originally reported, it was associated with a high level of nonspecific amplification. In an attempt to improve it, we developed target-enriched GUIDE-seq (TEG-seq). The sensitivity level reached 0.1-10 reads-per-million  depending on the NGS platform used, which was equivalent to 0.0002-1% measured by Targeted Amplicon-seq. Application of TEG-seq was demonstrated for the evaluation of various Cas9/gRNA configurations, which suggests delivery of Cas9/gRNA ribonucleoprotein results in significantly fewer off-targets than Cas9/gRNA plasmid. TEG-seq was also applied to 22 gRNAs with relatively high in silico ranking score that targeted the biological relevant SNPs. The result indicated the initial selection of gRNAs with high score is important, although it cannot exclude the possibility of off-target.