2015 American Society of Gene and Cell Therapy Annual meeting in New Orleans, LA - Highlights - GUIDE-Seq reveals a plethora of previously undetected off-target effects with CRISPR

Shengdar Tsai (K. Joung lab, Massachusetts General Hospital, Boston, USA) presented an already published method (http://goo.gl/3pkSxI) to determine off-target effects of CRISPR in an unbiased way. The method is based on the incorporation of a double-stranded oligo by non-homologous end-joining into double-stranded breaks, amplification of the ODN template from genomic DNA and sequencing of the genomic context. This 'genome-wide unbiased identification of double-stranded breaks enabled by sequencing' (GUIDE-Seq) revealed plenty of off-target cleavage with S. pyogenes Cas9. Most of the off-target sites were not predictable by existing biased methods (http://crispr.mit.edu/ and CHiP-Seq), making this method an important addition to the CRISPR toolbox. CRISPR was able to tolerate up to 6 mismatches in the gRNA hybridization, this is much more than previously predicted. Check out the paper for more information.