Efficient Generation of Multi-gene Knockout Cell Lines and Patient-derived Xenografts Using Multi-colored Lenti-CRISPR-Cas9.

CRISPR-Cas9 based knockout strategies are increasingly used to analyze gene function. However, redundancies and overlapping functions in biological signaling pathways can call for generating multi-gene knockout cells, which remains a relatively laborious process. Here we detail the application of multi-color LentiCRISPR vectors to simultaneously generate single and multiple knockouts in human cells. We provide a complete protocol, including guide RNA design, LentiCRISPR cloning, viral production and transduction, as well as strategies for sorting and screening knockout cells. The validity of the process is demonstrated by the simultaneous deletion of up to four programmed cell death mediators in leukemic cell lines and patient-derived acute lymphoblastic leukemia xenografts, in which single cell cloning is not feasible. This protocol enables any lab with access to basic cellular biology equipment, a biosafety level 2 facility and fluorescence-activated cell sorting capabilities to generate single and multi-gene knockout cell lines or primary cells efficiently within one month.