Vaccination with a fusion DNA vaccine encoding hepatitis B surface antigen fused to the extracellular domain of CTLA4 enhances HBV-specific immune responses in mice: implication of its potential use as a therapeutic vaccine.

Fusion of specific antigens to extracellular domain of cytotoxic-T-lymphocyte-associated antigen 4 (CTLA4) represents a promising approach to increase the immunogenicity of DNA vaccines. We evaluated this interesting approach for its enhancement on HBV-specific immune responses and its antiviral effects in HBV transgenic mice. A fusion plasmid encoding the extracellular domain of CTLA4 linked with HBsAg was constructed. Mice were immunized by this fusion plasmid. Vaccination with the CTLA4-fused DNA not only induced much higher level of anti-HBs antibody, but also increased HBsAg-specific CD8+ response as well as CTL response in BALB/c mice. Furthermore, both Th1 and Th2 responses were augmented. In HBV transgenic mice, the levels of circulating HBsAg and HBV DNA replication were down-regulated by induction of higher anti-HBs antibody and HBsAg-specific CD8+ response after vaccination with the fusion plasmid. Thus, the CTLA4-fused DNA vaccine led to breakdown of immune tolerance to viral infection in HBV transgenic mice, which might be used as a therapeutic vaccine in HBV infection.