ABSTRACT
BACKGROUND Bacillus Calmette-Guérin (BCG) is considered a promising live bacterial delivery system. However, several proposals for rBCG vaccines have not progressed, mainly due to the limitations of the available expression systems. OBJECTIVES To obtain a set of mycobacterial vectors using a range of promoters with different strengths based on a standard backbone, previously shown to be stable. METHODS Mycobacterial expression vectors based on the pLA71 vector as backbone, were obtained inserting different promoters (PAN, PαAg, PHsp60, PBlaF* and PL5) and the green fluorescence protein (GFP) as reporter gene, to evaluate features such as their relative strengths, and the in vitro (inside macrophages) and in vivo stability. FINDINGS The relative fluorescence observed with the different vectors showed increasing strength of the promoters: PAN was the weakest in both Mycobacterium smegmatis and BCG and PBlaF* was higher than PHsp60 in BCG. The relative fluorescence observed in a macrophage cell line showed that PBlaF* and PHsp60 were comparable. It was not possible to obtain strains transformed with the extrachromosomal expression vector containing the PL5 in either species. MAIN CONCLUSION We have obtained a set of potentially stable mycobacterial vectors with a arrange of expression levels, to be used in the development of rBCG vaccines.
Subject(s)
BCG Vaccine/immunology , Escherichia coli/immunology , Genetic Vectors/immunology , Green Fluorescent Proteins/immunology , Mycobacterium bovis/immunology , Mycobacterium smegmatis/immunology , Animals , Escherichia coli/genetics , Female , Genetic Vectors/genetics , Mice , Mice, Inbred BALB CABSTRACT
BACKGROUND Bacillus Calmette-Guérin (BCG) is considered a promising live bacterial delivery system. However, several proposals for rBCG vaccines have not progressed, mainly due to the limitations of the available expression systems. OBJECTIVES To obtain a set of mycobacterial vectors using a range of promoters with different strengths based on a standard backbone, previously shown to be stable. METHODS Mycobacterial expression vectors based on the pLA71 vector as backbone, were obtained inserting different promoters (PAN, PαAg, PHsp60, PBlaF* and PL5) and the green fluorescence protein (GFP) as reporter gene, to evaluate features such as their relative strengths, and the in vitro (inside macrophages) and in vivo stability. FINDINGS The relative fluorescence observed with the different vectors showed increasing strength of the promoters: PAN was the weakest in both Mycobacterium smegmatis and BCG and PBlaF* was higher than PHsp60 in BCG. The relative fluorescence observed in a macrophage cell line showed that PBlaF* and PHsp60 were comparable. It was not possible to obtain strains transformed with the extrachromosomal expression vector containing the PL5 in either species. MAIN CONCLUSION We have obtained a set of potentially stable mycobacterial vectors with a arrange of expression levels, to be used in the development of rBCG vaccines.
Subject(s)
Animals , Female , Mice , BCG Vaccine/immunology , Mycobacterium smegmatis/immunology , Green Fluorescent Proteins/immunology , Escherichia coli/immunology , Genetic Vectors/immunology , Mycobacterium bovis/immunology , Escherichia coli/genetics , Genetic Vectors/genetics , Mice, Inbred BALB CABSTRACT
The currently available anti-pneumococcal vaccines are based on capsular polysaccharide (PS), plain or conjugated to a carrier protein. Conjugated vaccines are expensive products, especially in the case of pneumococcus, in which reasonable coverage requires from 7 to 13 serotypes. To obtain increased coverage with fewer components, we evaluated the immunogenicity of the pneumococcal surface protein A (PspA), conjugated to capsular polysaccharide serotype 23F, aiming at induction of an immune response against both components. Mice immunized with PS23F-rPspA1 conjugate produced antibodies against both PS and rPspA1, comparable or slightly higher than that obtained by free PS. The immunized animals challenged with a lethal dose of a virulent strain bearing a homologous PspA, showed that the PS23F-rPspA1 conjugate induced higher survival than rPspA1 alone or in combination with PS. This increased protection was shown to correlate with the enhanced capacity of the antibodies to bind to the pneumococcal surface and to induce complement deposition. Our results indicate that the use of PS-PspA conjugates may be a way to increase coverage against pneumococci with fewer components.
