Co-delivery of GM-CSF gene enhances the immune responses of hepatitis C viral core protein-expressing DNA vaccine: Role of dendritic cells

Hepatitis C virus (HCV) infection has become a critical public health problem worldwide. In Taiwan, it has been estimated that more than 300,000 people, 2% of the general population, have HCV infection. It has been well documented that direct delivery of gene intramuscularly can generate both humoral and cellular immunity, which more closely simulates the conditions of infection. In this study, female Balb/c mice immunized with HCV core plasmid DNA with or without adjuvant GM-CSF cytokine gene could induce both cellular immune response and HCV core-specific antibody titers after injection. Furthermore, the mice immunized with HCV core plus GM-CSF genes showed higher antibodytiter and cytotoxic T cell activity compared to those of mice immunized with HCV core gene only (P < 0.05). To explore the effect of GM-CSF gene, the mice were immunized with reporter gene and cytokine gene plasmid. Increased levels of reporter protein and infiltrating cells around muscle tissue were noted. Moreover, the protein could be detected in inguinal node 24 hr after injection, especially in mice immunized with HCV/core plasmid plus GM-CSF gene. It was also observed that reporter protein expressing CD11c⁺ dendritic cells could be seen in the inguinal node. These data suggest that the GM-CSF gene did enhance HCV core specific immune response when co-immunized with HCV core DNA plasmid. Although more studies are needed, dendritic cells that appeared around the naked DNA injection area and that local lymph nodes might play a critical role in the immune response induced by naked DNA immunization.