Use of SV40 to immunize against hepatitis B surface antigen: implications for the use of SV40 for gene transduction and its use as an immunizing agent.

We have described a novel gene transfer system, in which replication-incompetent, T antigen-deleted simian virus-40 (SV40) is used as the transduction vehicle. We report here successful immunization using such an SV40-derived viral vector. Hepatitis B surface antigen (HBsAg) cDNA was cloned downstream of two tandem SV40 early promoters to yield a T antigen-deficient SV40 derivative, SV(HBS). Cultured TC7 cells were exposed to SV(HBS), and expression of HBsAg was detected 24 h later by Northern blot and RT-PCR analysis. Immunochemistry and Western blot analysis were also performed 24 h after infection to detect expression of HBsAg. Once it was ascertained that we could express HBsAg in this way, we used SV(HBS) to elicit anti-HBs. SV(HBS) was injected intraperitoneally or subcutaneously into mice every 4 weeks. These mice were bled every 2 weeks and their sera assayed for antibody activity against HBsAg and SV40. Production of anti-HBs was measured by ELISA and confirmed by Western blot analysis, both of which demonstrated significant levels of anti-HBs after the second injection. We also tested production of anti-SV40 antibodies by the ability of sera to neutralize SV(HBS) infectivity. We found no evidence of neutralization of SV(HBS) infectivity even after eight inoculations. Thus, replication-incompetent SV40 is itself not a strong antigen. Our data suggest that SV40-based transduction systems may be a useful vehicle for immunization and for other gene transfer applications when a need for multiple inoculations is anticipated.