Abstract
BackgroundAcyclovir (ACV)-resistant (ACVr) herpes simplex virus type 1 (HSV-1) infections are concern in immunocompromised patients. Most clinical ACVr HSV-1 isolates have mutations in the viral thymidine kinase (vTK) genes. The vTK-associated ACVr HSV-1 shows reduced virulence, but the association between the level of resistance and the virulence of the vTK-associated ACVr HSV-1 is still unclear.MethodsThe virulence in mice of 5 vTK-associated ACVr HSV-1 clones with a variety of ACV sensitivities, when inoculated through intracerebral and corneal routes, was evaluated in comparison with ACV-sensitive (ACVs) parent HSV-1 TAS.ResultsAlthough all the 5 ACVr HSV-1 clones and ACVs HSV-1 TAS showed a similar single-step growth capacity in vitro, the virulence of ACVr HSV-1 clones significantly decreased. A 50% lethal dose (LD50) of each clone was closely correlated with 50% inhibitory concentrations (IC50), demonstrating that the higher the ACV-sensitvity, the the higher the virulence among the ACVr clones. One of the ACVr HSV-1 clones with a relatively low IC50 value maintained similar virulence to that of the parent TAS. The infection in mice with ACVr HSV-1 due to a single amino acid substitution in vTK induced local diseases, keratitis and dermatitis, while vTK-deficient clone did not.ConclusionsA statistically significant correlation between the virulence and susceptibility to ACV among ACVr HSV-1 clones was demonstrated.
Highlights
Acyclovir (ACV)-resistant (ACVr) herpes simplex virus type 1 (HSV-1) infections are concern in immunocompromised patients
Re-characterization of HSV-1 clones used in the present study: sensitivity to ACV and nucleotide sequence of the viral thymidine kinase (TK) gene The sensitivity of all the HSV-1 clones (ACVs HSV-1 TAS and ACVr HSV-1 clones) used was re-assessed and confirmed that the order in sensitivity to ACV among the HSV-1 clones used was the same as that in the previous study [21]
In vitro viral replication of ACVr HSV-1 All ACVr HSV-1 clones showed comparable viral replication to that of HSV-1 TAS at each time point in Vero cells (Fig. 1), being consistent with previous studies indicating that viral thymidine kinase (vTK) activity is not essential for viral replication in tissue culture [13, 17, 26]
Summary
Acyclovir (ACV)-resistant (ACVr) herpes simplex virus type 1 (HSV-1) infections are concern in immunocompromised patients. Most clinical ACVr HSV-1 isolates have mutations in the viral thymidine kinase (vTK) genes. Acyclovir (ACV, 2-amino-1,9-dihydro-9-((2-hydroxyethoxy)methyl)-6H-purin-6- one) is an effective first-line antiviral drug to treat herpes simplex virus type 1 (HSV-1) infections. ACV-resistant (ACVr) HSV-1 emerges with high frequency in immunocompromised patients [2,3,4]. Most of clinical ACVr HSV-1 isolates have mutations in the thymidine kinase (TK) genes, and the remaining having mutations in the viral DNA polymerase genes [5,6,7,8,9]. Viral thymidine kinase-deficient HSV-1 impaired viral replication, virulence, establishment of latency, and reactivation in mice [9, 11, 13,14,15,16,17].
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