Direct genome editing of patient-derived xenografts using CRISPR-Cas9 enables rapid in vivo functional genomics

Patient-derived xenografts (PDXs) constitute a powerful set of preclinical models for in vivo cancer research, reflecting the spectrum of genomic alterations and therapeutic liabilities of human cancers 1-4 . In contrast to either cancer cell lines or genetically engineered mouse models, the utility of PDXs has been limited by the inability to perform targeted genome editing of these tumors. To address this limitation, we have generated a lentiviral platform for CRISPR-Cas9 editing of PDXs using a tightly regulated, inducible Cas9 vector that does not require in vitro culture for selection of transduced cells. We demonstrate the utility of this platform in PDXs (1) to analyze genetic dependencies by targeted gene disruption and (2) to analyze mechanisms of acquired drug resistance by site-specific gene editing using templated homology-directed repair. This flexible system has broad application to other explant models and substantially augments the utility of PDXs as genetically programmable models of human cancer.