Naked plasmid DNA (pDNA) vaccine expressing herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) was tested for protective activity against acute HSV-1 infection in mice. The pDNA was intravenously injected into Balb/c mice via their tail vein under high pressure, and the vaccination was performed two times at an interval of 7 days. The gB gene vaccination significantly protected the mice from subsequent intraperitoneal challenge with a lethal dose of HSV-1, which killed all the animals given control plasmid or saline. The protective activity was correlated with the dose of the plasmid inoculated, the survival rate reaching 83% in mice vaccinated with 5 mg of pDNA. The vaccinated mice were also protected from latent HSV infection. The immunized mice showed significant elevation in neutralizing antibody against HSV-1 as well as serum levels of interleukin-12 (IL-12) and interferon-g (IFN-g). When mice were immunized with 5 mg of an Epstein-Barr virus (EBV)-based plasmid vector harboring the gB, the cytotoxic T lymphocytes (CTLs) activity and proliferative response for HSV-1 were also induced. The results strongly suggest that intravenous immunization of naked pDNA may induce humoral and cellular immune responses against the virus, leading to a significant prophylactic outcome against HSV-1 infection in mice.

Intravascular plasmid DNA (pDNA) vaccine encoding herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) effectively induces prophylactic immunity against lethal HSV-1 infection in mice. We investigated whether the vaccine potency is further improved by coadministration of cytokine genes together with a low dose of genetic vaccine. pDNA encoding IL-12, IL-15, IL-18 or IL-21 was capable of elevating survival rates of HSV-1-infected mice when coinjected with 1 mg of gB pDNA, while IL-10 gene delivery failed to affect the effectiveness of the genetic immunization. Although only 17% of mice survived acute HSV infection after the gB pDNA vaccination at a dose of 1 mg, all mice coadministered with 1 mg each of gB and IL-12 pDNAs not only survived the acute infection but also escaped latent infection. In these animals, the neutralizing antibody against HSV-1 was abundantly produced, and CTL activity against the gB antigen was augmented. Coadministration of the gB and IL-12 genes also elevated the serum level of interferon-g. Adaptive transfer experiments indicated that soluble factors contributed to preventive immunity, while cell components alone were not capable of protecting mice from fatal viral infection. These results strongly suggest potential usefulness of Th1 cytokine genes as effective molecular adjuvants that facilitate specific humoral as well as cellular immune responses elicited by intravascular molecular vaccination.