To develop an alternative treatment method based on immune checkpoint blockade, Deng et al. designed a novel and efficient CRISPR/Cas9 genome editing system delivered by cationic copolymer aPBAE to downregulate PD-L1 expression on tumor cells via specifically knocking out Cyclin-dependent kinase 5 (Cdk5) gene in vivo. This evidence concerns the gene CD274 and neoplasm.