[Immunoprotection role of a hepatitis B virus DNA vaccine responsible to BAlb/c mice]

To investigate the specific immune response and the immunoprotection effects of cytotoxic T-lymphocyte (CTL), which is induced by hepatitis B virus (HBV) DNA vaccine pCMV-S2S, on BALB/c mouse with the attack of SP2/0-S2S cells, a BALB/c mouse myeloma cell line stably expressing the HBV preS2S antigen.

BALB/c mice were divided into 3 groups: experimental group (intramuscularly injected with pCMV-S2S), control group 1 (HBsAg vaccine immunizing) or control group 2 (plasmid pCMV immunizing), which were immunized thrice at week 0.4 and 8 respectively. Specific CTL activities of 3 mice of each group were measured by lactate dehydrogenase (LDH) release assays, 4w after the last boost. The other mice of each group were subcutaneously inoculated with SP2/0-S2S cells into one lateral of flanks. SP2/0-CMV cell without expressing preS2S was subcutaneously inoculated into another lateral of mouse flanks. The time of visible tumor formation and the size of tumor were recorded and observed. The life span and survival rate of mice after loaded with the tumor cells were analyzed by Log-Rank statistics and Kaplan-Meier Survival curve respectively.

The specific CTL lysis value of pCMV-S2S group mice was (34.21 +/- 1.38)%, higher than that of HBsAg group [(19.64 +/- 1.50)%] or pCMV group [(3.45 +/- 1.89)%] (P < 0.05). The visible SP2/0-S2S tumor formation rate in pCMV-S2S group mice was 58.3% lower than that in the pCMV group (91.7%), 10 d after inoculated with the tumor cells (P < 0.05). The tumor formation rates of the two control groups were no obvious difference. The date of the first mouse dying in pCMV-S2S group was 24d, delayed for 13d, compared with that in the two control groups. The average life span of pCMV-S2S group mice after loaded with the tumor cells was (31 +/- 1) d, longer than that of the two control groups (P < 0.05). The 4w survival rate of the pCMV-S2S group mice was obviously increased (75%), compared with the two control groups (P < 0.05). The average life span and the 4w survival rate of the two control group mice were no obvious difference.

The hepatitis B virus DNA pCMV-S2S vaccination may elicit substantial HBV preS2S-specific CTL response in vivo, which gives the mouse the immunoprotection against the attack of SP2/0-S2S cells. The results indicate that pCMV-S2S may be used to the immunoprotection from HBV infection.