Adenovirus vector expressing functional herpes simplex virus ICP0.

ICP0, one of the five immediate-early (IE) gene products of herpes simplex virus (HSV), is a potent activator of transcription. To assess the biological activities of ICP0 and to explore its mechanisms of action, two helper-independent recombinant adenoviruses were constructed. In each recombinant, the E1 region was substituted with the ICP0-encoding genomic segment under the control of either the adenovirus major late promoter (MLP-0) or the HSV IE-0 promoter (0PRO-0). Infection of HeLa cells or 293 cells (a human embryo kidney cell line expressing adenovirus 5 E1a and -b functions) with the MLP-0 recombinant results in the synthesis of more IE-0 mRNA and ICP0 protein than did infection with the 0PRO-0 recombinant. Although 293 cells infected with MLP-0 accumulate 5- to 10-fold more IE-0 mRNA late in the infection than cells infected with HSV, the level of the protein product, ICP0, increased only slightly. In 293 cells, both recombinants could replicate, albeit at a slower rate and with lower final yields than wild-type adenovirus. Neither virus replicates its DNA in HeLa cells, and thus ICP0 cannot substitute for adenovirus E1a; however, the level of ICP0 that accumulates in MLP-0-infected HeLa cells was comparable to that of HSV-infected HeLa cells. In a functional test, we demonstrated that the adeno-ICP0 recombinant viruses can transactivate a transfected TK-CAT cassette, indicating that the ICP0 is biologically active.