In vitro isolation of variants of herpes simplex virus attenuated with altered thymidine kinase and DNA polymerase genes using carrageenans as selection agents

Natural polysaccharides known as carrageenans are potent and selective inhibitors of herpes simplex virus through blocking the interaction of the virus with the cellular receptor. Passaging the virus in vitro in the presence of carrageenans types k and iota enabled us to generate variants of herpes simplex type 2. At passage 22, four clones were selected for further characterization: iota 22-9, iota 22-12, k22-12 and k22-13. Variants showed a syncytial phenotype, grew at similar titers when compared to parental virus and exhibited moderate resistance to carrageenans. These were found to have a mutation in the thymidine kinase gene in the case of k22-13 (aa 149 Val to Ala) and in the DNA pol gene in the case of iota 22-12 (aa 789 Met to Thr). In variant k22-12, three substitutions in the DNA pol gene were identified. Variants were less virulent than parental strain when tested intravaginally or intranasally in mice. Attenuation correlated with higher levels of IL-6 and TNF-alpha in animals inoculated with the variants. Selective pressure on the external glycoproteins of the virus may generate viruses with alterations in genes unrelated to the target of action of the selection agent. Study of this type of variation might help us to understand the basis of persistent viral strategies, which in turn may play a role in the development of virus-host symbioses.