DNA-based immunization with chimeric vectors for the induction of immune responses against the hepatitis C virus nucleocapsid.

Vectors expressing the first 58 amino acids of the hepatitis C virus (HCV) nucleocapsid alone or as a fusion protein with the middle (pre-S2 and S) or major (S) surface antigens of hepatitis B virus (HBV) were constructed. Intramuscular immunization of BALB/c mice with the chimeric constructs in the form of naked DNA elicited humoral responses to antigens from both viruses within 2 to 6 weeks postinjection. No anti-HCV responses were obtained in mice immunized with the vector expressing the HCV sequence in the nonfusion context. Sera from chimera-injected mice specifically recognized both HCV capsid and HBV surface antigens in enzyme-linked immunosorbent assay and immunoblot testing. Anti-HCV serum titers formed plateaus of approximately 1:3,000; these remained stable until the end of the study (18 weeks postinfection). Anti-HBV immune responses were found to be lower in the chimera-injected animals (< 200 mIU/ml) than in those immunized with the native HBV vector (> 2,000 mIU/ml). This is the first report of the use of DNA-based immunization for the generation of immune responses to an HCV protein. In addition, these findings show that it is possible to elicit responses to viral epitopes from two distinct viruses via DNA immunization with chimeric vectors.