Priming with a Recombinant Pantothenate Auxotroph of Mycobacterium bovis BCG and Boosting with MVA Elicits HIV-1 Gag Specific CD8+ T Cells

Abstract

A safe and effective HIV vaccine is required to significantly reduce the number of people becoming infected with HIV each year. In this study wild type Mycobacterium bovis BCG Pasteur and an attenuated pantothenate auxotroph strain (BCGΔpanCD) that is safe in SCID mice, have been compared as vaccine vectors for HIV-1 subtype C Gag. Genetically stable vaccines BCG[pHS400] (BCG-Gag) and BCGΔpanCD[pHS400] (BCGpan-Gag) were generated using the Pasteur strain of BCG, and a panothenate auxotroph of Pasteur respectively. Stability was achieved by the use of a codon optimised gag gene and deletion of the hsp60-lysA promoter-gene cassette from the episomal vector pCB119. In this vector expression of gag is driven by the mtrA promoter and the Gag protein is fused to the Mycobacterium tuberculosis 19 kDa signal sequence. Both BCG-Gag and BCGpan-Gag primed the immune system of BALB/c mice for a boost with a recombinant modified vaccinia virus Ankara expressing Gag (MVA-Gag). After the boost high frequencies of predominantly Gag-specific CD8+ T cells were detected when BCGpan-Gag was the prime in contrast to induction of predominantly Gag-specific CD4+ T cells when priming with BCG-Gag. The differing Gag-specific T-cell phenotype elicited by the prime-boost regimens may be related to the reduced inflammation observed with the pantothenate auxotroph strain compared to the parent strain. These features make BCGpan-Gag a more desirable HIV vaccine candidate than BCG-Gag. Although no Gag-specific cells could be detected after vaccination of BALB/c mice with either recombinant BCG vaccine alone, BCGpan-Gag protected mice against a surrogate vaccinia virus challenge.

Robust Immunity to an Auxotrophic Mycobacterium bovis BCG-VLP Prime-Boost HIV Vaccine Candidate in a Nonhuman Primate Model

“…The safety of our ⌬panCD BCG vaccine was indicated by the development of fewer granulomas in the spleen and a reduced level of inflammation in the liver of vaccinated mice compared with the corresponding wild-type BCG recombinant results (49). The safety of BCG-vectored vaccines is a relevant issue, as vaccination of HIVinfected children with a clinical BCG (wild type) has been observed to be responsible for mycobacterial disease in 10% of these immunocompromised individuals (31,33).…”

“…We have previously shown that priming with this rBCG vaccine (rBCGpan-Gag), in a prime-boost combination with an antigen-matched recombinant MVA, elicits HIV-specific CD8 ϩ T cells in mice (49). This study sought to further evaluate the immunogenicity of this rBCG vaccine prime/ Gag VLP boost in nonhuman primates by characterizing the cellular immune response generated in immunized animals in terms of breadth, polyfunctionality, and phenotype of memory T cells.…”

“…DQ191755). The genetic stability of vaccine stocks was confirmed in vitro and shown to be maintained after in vitro passage for 30 generations and in vivo by restriction enzyme mapping of DNA plasmids isolated from rBCG recovered from mice splenocytes (49). The vaccine and rBCG control stocks were stored at Ϫ80°C until further use.…”

“…A recombinant BCG vaccine expressing the full-length HIV-1 subtype C gag gene (rBCGpanGag) was prepared as previously described by Chapman et al (49), using M. bovis BCG mc 2 6000 (BCG ⌬panCD), a pantothenic auxotroph strain derived from M. bovis BCG Pasteur 1172 P2 (Statens Serum Institute, Denmark). A control rBCG (rBCGpan-control) was prepared in an identical manner using BCG ⌬panCD that was transformed using an empty shuttle vector (not containing gag) designated pCONEPI (GenBank accession no.…”

“…By modifying the mycobacterial shuttle vector, we were able to generate a more stable rBCG vaccine expressing HIV-1 subtype C Gag (rBCGpan-Gag) using a pantothenate auxotroph of Pasteur BCG (BCG ⌬panCD). The rBCG with improved stability elicited robust HIV-specific CD8 ϩ T cell responses in BALB/c mice when used in a prime-boost combination with a recombinant modified vaccinia virus Ankara (rMVA) expressing a matching Gag antigen (49). In the current study, we investigated the immune response of baboons to a primary vaccination with rBCGpan-Gag and a boost with Gag VLPs.…”