Off-target genomic DNA sites with sequence similarity to PD-L1 gRNA protospacer (PD-L1 gRNA off-targets)

Off-target genomic DNA sites with sequence similarity to PD-L1 gRNA protospacer represent unintended genomic loci where CRISPR-Cas9 systems may induce double-strand breaks due to sequence homology with the guide RNA (gRNA) designed for PD-L1 (CD274) (Su et al., 2016, PMID: 27558804). These sites typically contain several mismatches compared to the intended 20-nucleotide protospacer but are still recognized by the Cas9-gRNA complex, leading to non-specific cleavage (Zhang et al., 2015, PMID: 25673487). In the context of cancer immunotherapy, where PD-L1 is knocked out to prevent immune evasion, off-target effects can lead to permanent mutations in unrelated genes, potentially causing genotoxicity or oncogenic transformation (Fu et al., 2013, PMID: 23354101). The identification of these sites is a critical safety requirement for clinical translation, often involving bioinformatic tools and experimental assays like GUIDE-seq or CIRCLE-seq to map the off-targetome (Tsai et al., 2015, PMID: 25513782). Managing these risks involves optimizing gRNA design, using high-fidelity Cas9 variants, or employing base editing technologies to minimize unintended genomic alterations (Rees & Liu, 2018, PMID: 30356159). Ultimately, these sites are not therapeutic targets but rather safety liabilities that must be monitored to ensure the integrity of the patient's genome during gene therapy.

Other names

CRISPR off-target sitesNon-specific genomic cleavage sitesPD-L1 gRNA-related off-targetsGenomic off-target loci

Unintended DNA cleavage at sites with sequence homology to the gRNA, followed by error-prone repair mechanisms such as non-homologous end joining (NHEJ).