Biochemical transformation of mouse cells by varicella-zoster virus

Mouse L cells lacking the enzyme thymidine kinase (Ltk-) were infected with varicella-zoster virus (VZV). Even though virus did not replicate in Ltk- cells, the presence of virus antigen could be observed by use of an anti-complement immunofluorescent technique at 4 h post-infection and the VZV-specific thymidine kinase could be detected in VZV-infected Ltk- cells. Ltk-cells were converted to a tk+ phenotype (Ltk+) by infection with cell-associated VZV. Clones possessing the ability to grow in selective medium were isolated and cultured successfully for more than 20 passages. One of the clones grew very slowly, but other clones showed almost the same growth rate as that of the parental Ltk- cells. The chromosome analyses of Ltk- cells and transformed cells revealed that the isolated clones were of mouse origin. VZV-specific antigen could be detected in the nuclei of Ltk+ cell clones by an immunofluorescent test, while tk activity was greatly enhanced in extracts prepared from transformed cells and its activity was neutralized by hyperimmune serum against VZV.