Selection of the same mutation in the U69 protein kinase gene of human herpesvirus-6 after prolonged exposure to ganciclovir in vitro and in vivo

After serial passage in the presence of increasing concentrations of gancic lovir (GCV) in vitro, a human herpesvirus-6 (HHV-6) mutant exhibiting a dec reased sensitivity to the drug was isolated. Analysis of drug susceptibilit y showed that the IC50 of this mutant was 24-, 52- and 3-fold higher than t hat of the wild-type (wt) IC50 in the case of GCV, cidofovir and foscarnet, respectively. Genotypic analysis showed two single nucleotide changes as c ompared to the wild-type: an A --> G substitution of the U69 protein kinase (PK) gene resulted in an (MV)-V-318 amino acid substitution and the other change, located in the C-terminal part of the U38 gene, resulted in an A(96 1)V amino acid substitution within the DNA polymerase. The (MV)-V-313 chang e was located within the consensus sequence DISPMN of the putative catalyti c domain VI of the PK. This change was homologous to the (MV)-V-460 and (MI )-I-460 changes that had been reported previously within the consensus sequ ence DITPMN of the human cytomegalovirus (HCMV) UL97 PK and associated with the resistance of HCMV to GCV. The (MV)-V-318 change was also detected by PCR in HHV-6-infected PBMCs from an AIDS patient who had been treated with GCV for a long period of time and exhibited a clinically GCV-resistant HCMV infection. These findings provide strong circumstantial evidence that the (MV)-V-318 change of the PK gene is associated with resistance to GCV and r aise the question of cross resistance to this drug among different betaherp esviruses.