Off-target genomic loci (Programmed cell death 1 ligand 1 guide RNA)

Off-target genomic loci with partial complementarity to PD-L1 guide RNA (gRNA) refer to unintended DNA sequences within the genome that possess sufficient sequence homology to the gRNA used in CRISPR-Cas9 systems targeting the CD274 (PD-L1) gene (Zhang et al., 2015, Science). These sites are susceptible to unintended binding and cleavage by the Cas9 nuclease, which can lead to permanent mutations through error-prone repair mechanisms like non-homologous end joining (Su et al., 2016, Scientific Reports). While the intended therapeutic target is the PD-L1 protein to disrupt the PD-1/PD-L1 immune checkpoint and enhance anti-tumor T-cell responses, these off-target sites represent a significant safety concern in gene therapy (Pardoll, 2012, Nature Reviews Cancer). Unintended modifications at these loci can result in genotoxicity, chromosomal translocations, or the disruption of tumor suppressor genes, potentially leading to oncogenesis (Tsai et al., 2015, Nature Biotechnology). Consequently, rigorous identification and characterization of these loci using methods such as GUIDE-seq or CIRCLE-seq are essential for the clinical translation of PD-L1-directed genome editing (Fu et al., 2013, Nature Biotechnology). Monitoring these sites serves as a critical safety biomarker during the preclinical and clinical evaluation of ex vivo or in vivo gene-editing therapies.

Other names

CRISPR off-target sitesUnintended genomic modificationsNon-specific cleavage sitesPD-L1 gRNA off-targetsCD274 off-target loci

Unintended double-strand DNA cleavage followed by error-prone repair mechanisms such as non-homologous end joining (NHEJ).