Genome-wide CRISPR screening identifies genes in recombinant human embryonic kidney 293 cells for increased ammonia resistance

Ammonia, a byproduct of glutamine metabolism, inhibits cell growth and reduces product yield and quality in mammalian cell culture. To identify novel genes associated with ammonia resistance, a genome-wide CRISPR knockout screening was conducted in monoclonal antibody (mAb)-producing human embryonic kidney 293 (HEK-mAb) cells using a virus-free, recombinase-mediated cassette exchange-based gRNA interrogation method. The knockout cell library was subcultured for five consecutive passages under 20 mM NH₄Cl, enriching cells with a sgRNA that conferred a proliferation advantage under high-ammonia conditions. Next-generation sequencing analysis of the enriched population identified three target genes -WNT3, TSPAN1, and CYHR1-among 19,114 genes. Knockout of these genes in HEK-mAb cells resulted in a 1.33- to 1.56-fold increase in maximum viable cell concentration and a 1.28- to 1.58-fold increase in maximum mAb concentration under 20 mM NH₄Cl. Notably, WNT3 knockout maintained N-glycan galactosylation proportions of mAb despite ammonia stress. These findings highlight the effectiveness of genome-wide CRISPR knockout screening in identifying novel gene targets for ammonia-resistant HEK293 cell, offering a promising strategy for improving mAb production.