Expression of hepatitis B virus S gene by herpes simplex virus type 1 vectors carrying alpha- and beta-regulated gene chimeras.

The domain of the hepatitis B virus (HBV) S gene specifying the HBV surface antigen (HBsAg) and comprising 25 base pairs of the 5'-transcribed noncoding region, the structural gene sequences, and the 3'-noncoding gene sequences including the polyadenylylation site was fused to the promoter-regulatory regions of the beta-thymidine kinase and of the alpha 4 gene of herpes simplex virus type 1 (HSV-1). The chimeric constructs were then inserted into the HSV-1 genome and specifically into the thymidine kinase gene by homologous recombination through flanking sequences. Cells infected with recombinants carrying the chimeric genes produced and excreted the HBsAg into the extracellular medium for at least 12 hr concurrently with the multiplication of the HSV-1 vector. The temporal patterns of expression and the observation that HBV S gene linked to the HSV-1 alpha promoter-regulatory region was regulated as an HSV-1 alpha gene indicate that the HBsAg gene chimeras inserted into the virus were regulated as viral genes. The HBsAg banded in isopycnic CsCl density gradients at a density of 1.17 g/cm3. Electron microscopic studies revealed that HBsAg harvested from the extracellular medium and banded in CsCl density gradients contained spherical particles 15-22 nm in diameter, characteristic of empty HBV envelopes. The results indicate that HSV-1 is a suitable vector for the expression of foreign genes placed under the control of HSV promoter-regulatory regions.