Published online Aug 7, 2006. doi: 10.3748/wjg.v12.i29.4727
Revised: August 28, 2005
Accepted: October 10, 2005
Published online: August 7, 2006
AIM: To test the feasibility of delivering a plasmid encoding IL-15 as a DNA vaccine adjuvant for improving the immune responses induced by hepatitis B virus core gene DNA vaccine.
METHODS: We used RT-PCR based strategies to develop IL-15 expression constructs. We first confirmed that the gene could be expressed in Escherichia coli due to the poor expression of IL-15. Then the bioactivity of IL-15 plasmid expression product was identified by CTLL-2 proliferation assay. One hundred micrograms of DNA from each of the IL-15 eukaryotic expressed plasmid and the recombinant plasmid harboring DNA encoding the 144 amino acids of the N-terminus of HBV core gene (abbreviated pHBc144) was used to co-immunize C57 BL/6 mice. The titer of anti-HBcIgG was detected by ELISA and the antigen-specific CD8+ T cells (CD8+IFN-γ+ T cells) were detected by intracellular cytokine staining at different time points.
RESULTS: After co-immunization by pIL-15 and pHBc144 DNA vaccine the antigen-specific CD8+ cells of mice increased gradually, the first peak of immune response appeared 14 d later, then the number of antigen-specific CD8+ Ts cells decreased gradually and maintained at a steady level in 3 mo. After boosting, the number of antigen-specific CD8+ T cells reached the second peak 10 d later with a double of the 1st peak, then the number of antigen-specific CD8+ T cells decreased slowly. IL-15 as a gene adjuvant had no significant effect on humoral immune responses induced by hepatitis B virus core gene DNA vaccine, but increased the memory antigen-specific CD8+ T cells induced by hepatitis B virus core gene DNA vaccine.
CONCLUSION: DNA vaccine constructed by HBc Ag 1-144 amino acid induces effective cell immunity, and cytokine plasmid-delivered IL-15 enhances the longevity of CD8+ T cells.