To simplify the titration of infectious varicella-zoster virus (VZV), we generated a reporter cell line that produced luciferase in a dose-dependent manner upon infection with cell-free VZV. A few VZV-infected cells were detectable by coculturing with the cell line. We demonstrated the usefulness of the cell line for antiviral studies.Varicella-zoster virus (VZV) causes varicella on primary infection and zoster upon reactivation. Both conditions may be associated with severe complications (1). For the treatment of VZVassociated diseases, acyclovir (ACV), valaciclovir, and famciclovir have been used widely (1,25). The number of approved drugs for treating VZV diseases is limited, and all of them have the same mode of action. The development of resistant strains and the ineffectiveness of available antivirals at preventing complications have necessitated a search for alternative compounds (7,8,25,33). Several new compounds have been under investigation (13,20,21,31,32). Plaque reduction assays have been routinely used to screen and evaluate candidate compounds, but this method is made laborious and time consuming due to the slow growth of VZV in tissue culture. Some methods aimed at reducing the inconvenience have been developed (26,27,34), as has a biochemical assay for characterization of ACV-resistant strains (29). However, the unavailability of a rapid, high-throughput assay for titrating VZV has hampered efforts both to screen new compounds and to detect drug-resistant strains in a timely fashion.Previously, we established a reporter cell line for human herpesvirus 8 and demonstrated its practical uses (10,11,14). We report here the generation of a similar cell line for VZV by use of the following approach: (i) selection of the most suitable promoter from various promoters, (ii) identification of the minimum sequence length for efficient activation of the selected promoter to avoid nonspecific activation, (iii) establishment of a cell line that contains the reporter gene under the control of the minimum promoter, and (iv) characterization of the clone that performed best.Characterization of individual VZV promoters and global VZV gene expression have been reported previously (4, 5, 12).On the basis of those studies, various DNA fragments containing known or putative VZV promoters (Table 1) were amplified from the nucleocapsid DNA of VZV pOka strain by PCR, cloned into a luciferase vector pGL3-Basic, and then analyzed for their responses to VZV infection in transient transfection experiments using BSC40 cells (3) and MeWo cells (9). Among the promoters examined, the ORF9 promoter was most strongly activated in both cell lines (Fig. 1). Activation of each promoter was also analyzed by cotransfection with a plasmid expressing VZV IE62. The correlation between infection-and IE62-mediated activation (Fig. 1C) was good, indicating that infection-mediated activation was VZV specific.The minimal essential region for the ORF9 promoter was
