HBcAg18–27 epitope fused to HIV-Tat49–57 adjuvanted with CpG ODN induces immunotherapeutic effects in transgenic mice

Successful immunotherapy of chronic hepatitis B virus (HBV) infection is expected to be characterized by enhanced activation of immune responses. Combining the specificity of hepatitis B core antigen (HBcAg) cytotoxic T lymphocyte (CTL) epitope, the cell-penetrating property of human immunodeficiency virus-1 (HIV)-Tat peptide, and the adjuvanticity of CpG oligodeoxynucleotides (CpG ODNs) may elicit strong immune responses and therapeutic effects in HBV infection. We synthesized a fusion peptide containing HBcAg18–27 CTL epitope and HIV-Tat49–57 peptide. The fusion peptide was intramuscularly injected to HBV transgenic mice with CpG ODN as adjuvant at 2-week intervals three times. The percentages of CD3+, CD4+ and CD8+ cells in spleen lymphocytes and the levels of circulating interferon (IFN)-γ and interleukin (IL)-2 were determined for the evaluation of immune responses and the levels of serum HBV DNA and the expression of hepatitis B surface antigen (HBsAg) and HBcAg in liver tissue were determined for the assessment of therapeutic effects. Our results showed that the synthesized fusion peptide adjuvanted with CpG ODN could induce significant increase of the percentages of CD3+, CD4+ and CD8+ cells and the levels of IFN-γ and IL-2, indicating the strong immune responses, and reduced HBV DNA levels and decreased expression of HBsAg and HBcAg in liver tissue, suggesting the therapeutic effects. Collectively, our study supports that HBcAg18–27 CTL epitope fused to HIV-Tat49–57 peptide adjuvanted with CpG ODN may be a promising strategy for immunotherapy of chronic HBV infection.