GLV-1h68 and its derivatives. (A) Schematic representation of the genomic structures of the recombinant vaccinia virus GLV-1h68 and its marker gene expression cassette removal derivatives. PE/L, P11, and P7.5 are VACV synthetic early/late, 11K, and 7.5K promoters, respectively. TfR is human transferin receptor inserted in the reverse orientation with respect to the promoter PE/L. (B) Marker gene expression and genotype verification. CV-1 cells were infected with each individual virus strain. Two days post-infection, the GFP expression was visualized by fluorescence microscopy and expression of β-galactosidase and β-glucuronidase was detected by X-gal and X-GLcA staining, respectively.