Unsupervised correction of gene-independent cell responses to CRISPR-Cas9 targeting

Francesco Iorio, Fiona M. Behan, Emanuel Gonçalves, Shriram G. Bhosle, Elisabeth Chen, Rebecca Shepherd, Charlotte Beaver, Rizwan Ansari, Rachel Pooley, Piers Wilkinson, Sarah Harper, Adam P. Butler, Euan A. Stronach, Julio Saez-Rodriguez, Kosuke Yusa, Mathew J. Garnett

Genome editing by CRISPR-Cas9 technology allows large-scale screening of gene essentiality in cancer. A confounding factor when interpreting CRISPR-Cas9 screens is the high false-positive rate in detecting essential genes within copy number amplified regions of the genome. We have developed the computational tool CRISPRcleanR which is capable of identifying and correcting gene-independent responses to CRISPR-Cas9 targeting. CRISPRcleanR uses an unsupervised approach based on the segmentation of single-guide RNA fold change values across the genome, without making any assumption about the copy number status of the targeted genes. Applying our method to existing and newly generated genome-wide essentiality profiles from 15 cancer cell lines, we demonstrate that CRISPRcleanR reduces false positives when calling essential genes, correcting biases within and outside of amplified regions, while maintaining true positive rates. Established cancer dependencies and essentiality signals of amplified cancer driver genes are detectable post-correction. CRISPRcleanR reports sgRNA fold changes and normalised read counts, is therefore compatible with downstream analysis tools, and works with multiple sgRNA libraries. CRISPRcleanR is a versatile open-source tool for the analysis of CRISPR-Cas9 knockout screens to identify essential genes.