Base Editor BE4max Off-Target Activity Profiling in Human Embryonic Kidney Cells: Whole-Genome Sequencing and GUIDE-seq Analysis

This study investigates genome-wide off-target C-to-T base editing frequency of BE4max in human HEK293T cells quantified by whole-genome sequencing and GUIDE-seq across 24 gRNA targets within the context of genome editing and molecular biology, an area of growing scientific importance given its implications for therapeutic base editing safety assessment and gRNA design guidelines for clinical-grade genome editing applications. Using whole-genome sequencing at 30x depth from 3 independent biological replicates per gRNA plus GUIDE-seq off-target capture at each target site with specificity ratio computation, we examine ssDNA bubble formation during Cas9 R-loop enabling cytosine deaminase access to non-target strand cytosines at both on-target and off-target sites with seed region mismatch tolerance governing off-target frequency in 24 gRNA targets x 3 replicates = 72 WGS datasets (30x coverage each); GUIDE-seq on all 24 targets; on-target editing measured by EditR amplicon sequencing drawn from HEK293T cells in 6-well plates with lipofectamine 3000 transfection and 72-hour harvest for gDNA extraction. Results indicate that BE4max produces a mean of 284 off-target C-to-T variants per cell (range 48-1,284 per gRNA) at 30x WGS, with off-target burden inversely correlated with gRNA seed-region GC content (r=-0.68, p<0.001) (p < 0.001), with 284 mean off-target SNVs per gRNA; r=-0.68 correlation with seed GC content as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to genome editing and molecular biology and carry actionable implications for the design of programs and policies targeting therapeutic base editing safety assessment and gRNA design guidelines for clinical-grade genome editing applications.