To test whether cells resistant to viral infection or drug treatment could be selected by transient transfection of pooled sgRNA plasmids (Fig. 1A and supplemental Table S1), we mixed three sgRNA plasmids specific to the hypoxanthine-guanine phosphoribosyltransferase (HPRT1) gene with the library of 30,840 sgRNA plasmids and co-transfected this mixture into HeLa cells with the Cas9 plasmid. Here, HPRT1 is linked to viral infectious disease.