Unbiased detection of off-target cleavage by CRISPR-Cas9 and TALENs using integrase-defective lentiviral vectors

The utility of CRISPR-Cas9 and TALENs for genome editing may be compromised by their off-target activity. We show that integrase-defective lentiviral vectors (IDLVs) can detect such off-target cleavage with a frequency as low as 1%. In the case of Cas9, we find frequent off-target sites with a one-base bulge or up to 13 mismatches between the single guide RNA (sgRNA) and its genomic target; which refines sgRNA design.