Guide-dependent off-target genomic DNA loci (CRISPR OTEs)

Guide-dependent off-target genomic DNA loci are unintended sites within the genome where CRISPR-Cas nucleases or other programmable DNA-binding proteins induce modifications due to sequence similarity with the intended target. These sites are characterized by partial complementarity to the single-guide RNA (sgRNA) and the presence of a permissive Protospacer Adjacent Motif (PAM), which allows the nuclease to bind and cleave despite mismatches (Fu et al., 2013). The resulting double-strand breaks are typically repaired by cellular mechanisms like non-homologous end joining (NHEJ), which can introduce permanent insertions or deletions (indels). In clinical applications, these off-target effects pose a major safety concern, as they can lead to the disruption of tumor suppressor genes or the activation of oncogenes, potentially causing genotoxicity or cancer (Zhang et al., 2015). To ensure the safety of CRISPR-based therapeutics like exagamglogene autotemcel, researchers use specialized assays such as GUIDE-seq or CIRCLE-seq to map these loci and optimize guide RNA design for maximum specificity (Tsai et al., 2015). Minimizing activity at these loci is a primary goal in the engineering of high-fidelity Cas variants and the development of precision gene-editing technologies (Kleinstiver et al., 2016).

Other names

Off-target effectsOTEsNon-specific cleavage sitesGuide-dependent off-targetsMismatched genomic lociOff-target genomic sites

The Cas9 nuclease, guided by an sgRNA, recognizes a Protospacer Adjacent Motif (PAM) and binds to a DNA sequence with partial complementarity, leading to unintended double-strand breaks (DSBs) that are repaired by error-prone pathways like Non-Homologous End Joining (NHEJ) (Fu et al., 2013).