Prime-boost vaccination using recombinant Mycobacterium bovis BCG and recombinant vaccinia virus DIs harboring HIV-1 CRF01_AE gag in mice: influence of immunization routes.

We have previously reported that live vector-based HIV-1 gag vaccine candidate using BCG as a vector was achievable in BALB/c mice. Although the gag-specific CTL induced by this live candidate vaccine is significantly high, persistence of CTL remains unclear. Thus, efforts were made to explore the potential of recombinant Vaccinia virus DIs strain harboring the same HIV-1 CRF01_AE gag gene (rVaccinia/ HIV-1gagE) present in the BCG construct, using different immunization routes. After one month following a single subcutaneous (s.c.) injection of rBCG/HIV-1gagE, higher CTL responses were recognized against various peptide epitopes along the whole gag protein compared to that by intradermal (i.d.) route. A prime-boost regimen having only rDIs/HIV-1gagE injected i.d. induced very low CTL levels. However, within two months, by priming with rBCG/HIV-1gagE s.c. and boosting with rVaccinia/HIV-1gagE intravenously (i.v.), CTL levels were greater (20-68% specific cell lysis) than those obtained by priming and boosting both i.d. (18-35%). After seven months, both prime-boost immunization with rBCG/HIV-lgagE s.c. and with rVaccinia/HIV-1gagE either i.v. or i.d. sustained similar CTL levels. Our studies exhibit that the prime-boost vaccination of rBCG/HIV-1gagE following by rVaccinia/HIV-1gagE i.d. could be used to elicit prolonged CTL responses as well as memory T-cells in mice, which might be more practical than using i.v. route.

Enhancement of cell-mediated immune response in mice by whole HIV-1 gag in Mycobacterium bovis BCG as a live vaccine candidate.

In this study, we employed a recombinant Mycobacterium bovis Bacille Calmette-Guerin (BCG) harboring whole HIV-1 CRF01_AE gag DNA as a candidate vaccine to investigate specific cell-mediated immunity in BALB/c mice. Construction of the stable expression recombinant BCG was achieved by demonstrating by Western blot detection of protein of approximately 55 kDa. By a single injection of 0.1 mg of the recombinant HIV-1 gag protein expressing BCG subcutaneously into mice, after 2 weeks various specific cytotoxic T-lymphocyte (CTL) responses were exhibited against a single gag epitope of amino acid positions 294-304, and also against various peptide regions along the entire gag protein with moderate CTL activities (10-35% specific cell lysis), which increased to relatively high levels (50-68%) after one month. However, after two months activities were 3-3.7 fold lower. On the other hand, gag-specific lymphocyte proliferation was detected 9.3 fold higher than that of non-immunized mouse spleen cells. Our results indicate that in mice, BCG can be used as a recombinant live vector to induce cellular immune responses to HIV-1 gag antigen.