Susceptibility of human herpesvirus 6 to antiviral compounds by flow cytometry analysis

Background: The emergence of human herpesvirus 6 (HHV-6) as a human pathoge n led to the possibility of specific therapy against HHV-6 and the developm ent of standardized susceptibility assays of HHV-6 to antivirals. Methods: We have developed a flow cytometry method to analyze the multiplic ation of the HST strain of human herpesvirus 6 (HHV-6) variant B in vitro u sing monoclonal antibodies specific to virus proteins. This method was subs equently used to determine the sensitivity of HST multiplication in MT4 cel ls to four antiviral compounds of three different classes: acyclovir (ACV) and ganciclovir (GCV), two acyclic guanosine analogs; cidofovir (CDV), an a cyclic nucleoside phosphonate; and phosphonoformic acid (PFA), a pyrophosph ate analog. Results: The 50% inhibitory concentrations (IC50) of ACV, GCV, CDV, and PFA determined by flow cytometry assay were 25.3, 6.4, 0.95, and 6.0 mu M, res pectively (5.7, 1.6 0.3, and 1.8 mu g/ml, respectively). These data togethe r with the results of cytotoxicity assays confirmed the high efficiency and selectivity of CDV and PFA against HHV-6 B in vitro, suggested by previous results. Conclusions: Our flow cytometric assay appeared as a reproducible specific method to characterize HHV-6 susceptibility to antiviral compounds. It can be considered as a convenient alternative to the other immunologic and DNA hybridization assays used for that purpose. Cytometry 40:135-140, 2000. (C) 2000 Wiley-Liss, Inc.