Prime-Boost Immunization of Codon Optimized HIV-1 CRF01_AE Gag in BCG with Recombinant Vaccinia Virus Elicits MHC Class I and II Immune Responses in Mice

Advances and challenges in recombinant Mycobacterium bovis BCG-based HIV vaccine development: lessons learned

INTRODUCTION

Human Immunodeficiency Virus/Acquired Immune Deficiency Syndrome, tuberculosis, and malaria are responsible for most human deaths produced by infectious diseases worldwide. Vaccination against HIV requires generation of memory T cells and neutralizing antibodies, mucosal immunity, and stimulation of an innate immune responses. In this context, the use of Mycobacterium bovis bacillus Calmette-Guérin (BCG) as a live vaccine vehicle is a promising approach for T-cell induction.

AREAS COVERED

In this review, we provide a comprehensive summary of the literature regarding immunogenicity studies in animal models performed since 2005. Furthermore, we provide expert commentary and 5-year view on how the development of potential recombinant BCG-based HIV vaccines involves careful selection of the HIV antigen, expression vectors, promoters, BCG strain, preclinical animal models, influence of preexisting immunity, and safety issues, for the rational design of recombinant BCG:HIV vaccines to prevent HIV transmission in the general population.

EXPERT COMMENTARY

The three critical issues to be considered when developing a rBCG:HIV vaccine are codon optimization, antigen localization, and plasmid stability in vivo. The use of integrative expression vectors are likely to improve the mycobacterial vaccine stability and immunogenicity to develop not only recombinant BCG-based vaccines expressing second generation of HIV-1 immunogens but also other major pediatric pathogens to prime protective responses shortly following birth.

Role for Gr-1+ cells in the control of high-dose Mycobacterium bovis recombinant BCG

Mycobacterium bovis bacillus Calmette-Guérin (BCG) is an attractive target for development as a live vaccine vector delivering transgenic antigens from HIV and other pathogens. Most studies aimed at defining the clearance of BCG have been performed at doses between 10(2) and 10(4) CFU. Interestingly, however, recombinant BCG (rBCG) administered at doses of >10(6) CFU effectively generates antigen-specific T-cell responses and primes for heterologous boost responses. Thus, defining clearance at high doses might aid in the optimization of rBCG as a vector. In this study, we used bioluminescence imaging to examine the kinetics of rBCG transgene expression and clearance in mice immunized with 5 × 10(7) CFU rBCG expressing luciferase. Similar to studies using low-dose rBCG, our results demonstrate that the adaptive immune response is necessary for long-term control of rBCG beginning 9 days after immunizing mice. However, in contrast to these reports, we observed that the majority of mycobacterial antigen was eliminated prior to day 9. By examining knockout and antibody-mediated depletion mouse models, we demonstrate that the rapid clearance of rBCG occurs in the first 24 h and is mediated by Gr-1(+) cells. As Gr-1(+) granulocytes have been described as having no impact on BCG clearance at low doses, our results reveal an unappreciated role for Gr-1(+) neutrophils and inflammatory monocytes in the clearance of high-dose rBCG. This work demonstrates the potential of applying bioluminescence imaging to rBCG in order to gain an understanding of the immune response and increase the efficacy of rBCG as a vaccine vector.