Off-target activity inhibitors for guided endonucleases

Incidence of off-target DNA cleavage when using CRISPR Cas systems for gene modification are lessened or avoided by using oligonucleotides of rational design and which are antisense to target sequence of the guide RNA or other targeting nucleic acid sequence. Whether in vitro or in vivo, a target nucleic acid comprising a targeted sequence is exposed to the CRISPR enzyme and relevant guiding RNA (or ribonucleoprotein complex) with the antisense oligonucleotide. The antisense oligonucleotide is exposed to the target nucleic acid substantially simultaneously, separately or sequentially together with the CRISPR enzyme or ribonucleoprotein complex.