DNA immunization encoding the secreted nonstructural protein 3 (NS3) of hepatitis C virus and enhancing the Th1 type immune response.

To induce a sustained and specific cellular immune response to hepatitis C virus (HCV), DNA immunization of mice was performed using plasmids containing the HCV nonstructural gene 3 (HCV/NS3). Plasmids were constructed such that the NS3 gene was expressed in a secreted form, a nonsecreted form or as a membrane-bound antigen. The plasmid encoding the secreted antigen induced the strongest humoral and cellular immunity and favoured the T-helper type 1 (Th1) pathway as shown by cytokine profiles and switching of antibody subclasses. Our study indicates that DNA immunization with a secreted form of HCV/NS3 is an effective means of inducing primary Th1 immune responses in the murine model.