Hantaan virus (HTNV) is a causative agent of hemorrhagic fever with renal syndrome (HFRS). More than 100,000 cases of HFRS are reported yearly, with a mortality rate of between 2% and 10%. But, there is no effective and safe vaccine against HFRS. Even though neutralizing antibodies against the HTNV have been proven to be critical against viral infections, the cellular immune responses to HTNV are also assumed to be important for viral clearance. This study has examined the cellular and humoral immune responses against the HTNV nucleocapsid protein (NP) elicited by virus infection or DNA vaccination to investigate the immunogenicity of NP.
To examine the cellular immune response against HTNV NP, C57BL/6 mice were injected with HTNV intraperitoneal. The NP-specific CD8+ T cell response was analyzed using a 51Cr-release assay, intracellular cytokine assay, enzyme-linked immunospot assay and tetramer binding assay against H-2Kb restricted CTL epitopes of NP (M6 and N1 peptide). Using these methods, it was found that HTNV infection elicited a strong NP-specific CD8+ T cell response at 8 days after infection, and several different methods to check the NP-specific CD8+ T cell response showed a perfect correlation among analyses. To examine the humoral immune response against HTNV NP, the NP-specific antibody response was analyzed using an enzyme linked immunosorbent assay (ELISA). HTNV infection elicited the NP-specific humoral immune response which was began at 4~5 days after infection.
DNA vaccine has been shown to elicit both humoral and cellular immune responses, and confer protection against some viral, bacterial and parasitic pathogens. Therefore, DNA vaccine strategy was applied to HTNV in this study. Sindbis virus-based expression vector was carefully designed and constructed, in order to induce the transient high level expression of target gene. In the case of DNA vaccination by plasmid encoding nucleocapsid gene, a single dose injection of 100㎍ of plasmid DNA into quardriceps muscle of C57BL/6 mice induced a high level of humoral and cellular immune response. The NP-specific antibody response was elicited 2~4 weeks after immunization and maximized at 6~10 weeks and sustained for over 14 weeks. NP-specific CD8+ T cell response reached its peak 2~3 weeks after immunization. Even though NP-specific CD8+ T cell response after DNA vaccination was not strong as the HTNV infection, but the pattern of response was similar to that of HTNV infection.
In a challenge test with the recombinant vaccinia virus expressing NP (rVV-HTNV-N), the rVV-HTNV-N titers in DNA vaccinated mice were decreased about 100 fold compared control mice. Even though challenge with rVV-HTNV-N in HTNV infected mice were perfectly protected, but DNA vaccination showed the partial protection.
In conclusion, this study showed that (i) HTNV infection in C57BL/6 mice elicited the strong NP-specific CD8+ T cell response at 8 days after infection, (ii) DNA vaccination with plasmid encoding HTNV nucleocapsid gene also elicited the strong NP-specific humoral and cellular immune responses, and (iii) DNA vaccination elicited the partial protective immunity against challenge with the recombinant vaccinia virus expressing NP. (iv) DNA vaccine expressing HTNV NP was shown to be a possible vaccine candidate against HTNV infection.