Ubiquitin Conjugation of Hepatitis B Virus Core Antigen DNA Vaccine Leads to Enhanced Cell-Mediated Immune Response in BALB/c Mice

Background: nearly 350 million persons worldwide are chronically infected with hepatitis b virus (hbv). ubiquitin (ub) is a highly conserved small regulatory protein, ubiquitous in eukaryotes, that usually serves as a signal for the target protein that is recognised and degraded in proteasomes . the ub-mediated processing of antigens is rapid and efficient and stimulates cell-mediated immune responses. accordingly, ub-mediated processing of antigens has been widely used in chronic-infection and cancer studies to improve immune response.objectives: many clinical trials have shown that dna vaccine potency needs to be greatly enhanced. here, we report a new strategy for designing an hbv dna vaccine using the ubiquitin (ub) sequence. the aim of this study was to investigate a novel dna vaccination, based on the expression of hbv core antigen (hbcag), fused to ub to enhance dna vaccine potency.materials and methods: mouse ubiquitin fused to the hbcag gene and cloned into the eukaryotic vector pcdna3.1 (-). balb/c mice were immunized with recombinant pub-hbcag or phbcag dna vaccine. lymphocyte proliferation assay, intracellular ifn-? assay, ctl cytotoxicity assay, and antibody assay were performed to analyze the cellular and humoral immune responses to our dna constructs.results: hbcag was expressed effectively in the cos-7 cells that were transiently transfected with pub-hbcag. strong anti-hbc igg responses were elicited in mice that were immunized with pub-hbcag. the endpoint titers of anti-hbc peaked at 1:656100 on the 42nd day after the third immunization. pub-hbcag stimulated greater lymphocyte proliferation and induced higher levels of il-2 and ifn-? and a greater percentage of hbcag-specific cd8+ t cells in mice than phbcag. in the ctl assay, the specific lysis rate reached 56.5% at an effector:target ratio of 50:1 in mice that were immunized with pub-hbcag.conclusions: pub-hbcag elicits specific anti-hbc responses and induces hbc-specific ctl responses in immunized balb/c mice. our results imply that ub can be used as a molecular adjuvant that enhances the potency of dna vaccines.