Vaccination with ubiquitin-hepatitis B core antigen-cytoplasmic transduction peptide enhances the hepatitis B virus-specific cytotoxic T-lymphocyte immune response and inhibits hepatitis B virus replication in transgenic mice

Chronic hepatitis B virus (HBV) infection is characterized by functionally impaired type 1 T-helper cell (Th1) immunity and poor HBV-specific T-cell responses. Ubiquitin (Ub), a highly conserved small regulatory protein, commonly serves as a signal for target proteins that are recognized and degraded in proteasomes. The rapid degradation of Ub-mediated antigens results in efficient stimulation of cell-mediated immune responses. Thus, the Ub-HBV core antigen (HBcAg)-cytoplasmic transduction peptide (CTP) fusion protein was designed for specific delivery of a foreign modified antigen to the cytoplasm of antigen-presenting cells. HBV transgenic mice were used to determine whether Ub-HBcAg-CTP would restore HBV-specific immune responses and anti-viral immunity in these animals. The results demonstrated that synthesized Ub-HBcAg-CTP not only significantly increased the levels of interleukin-2 and interferon (IFN)-gamma compared with those in the HBcAg-CTP, IFN-alpha, Ub-HBcAg, HBcAg and phosphate-buffered saline groups, but additionally induced the highest IFN-gamma(+) CD8(+) T-cell numbers and HBV-specific cytotoxic T lymphocyte (CTL) responses, indicating a strong immune response. In addition, enhancement of specific CTL activity provoked by the fusion protein reduced hepatitis B surface antigen (HBsAg) and HBV DNA serum levels and diminished the expression of HBsAg and HBcAg in liver tissue of HBV transgenic mice, suggesting that there was a therapeutic effect. In conclusion, the present study provided evidence that Ub-HBcAg-CTP activated the Th1-dependent immunity, triggered functional T cell responses and subsequently inhibited viral replication in HBV transgenic mice. These observations suggested that the fusion protein may represent an innovative and promising candidate for active immunotherapy during chronic and persistent HBV.