Structure-Immunogenicity Relationship of α- and β-Tetrasaccharide Glycoforms from Bacillus anthracis Exosporium and Fragments Thereof

Synthesis and preliminary immunologic properties of di-/trisaccharide-conjugates related to Bacillus anthracis

Herein, the di- and trisaccharide mimics of the hexasaccharide antigen related to Bacillus anthracis were synthesized and covalently coupled with carrier proteins, such as keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA), to form the corresponding glycoconjugates 1-6. 2,3,4,6-Tetra-O-benzyl thioglycoside and 2-deoxyl-2-phthalylamino-3,4,6-tri-O-benzyl thioglycoside were applied as glycosyl donors to guarantee α or β-configuration of the newly formed glycosidic bonds. Glutaraldehyde was used as a homobifunctional cross-linker for high-efficiency coupling. The synthetic KLH-glycoconjugates 2, 4 and 6 were also used to vaccinate female Balb/c mice and the preliminary results of ELISA uncovered that all three KLH-conjugates could induce immune responses and generate oligosaccharide-specific total IgG antibodies. The trisaccharide 8, the glycosyl part of glycoconjugate 4, is of great immunogenicity.

Convergent evolution of diverse Bacillus anthracis outbreak strains toward altered surface oligosaccharides that modulate anthrax pathogenesis

Bacillus anthracis, a spore-forming gram-positive bacterium, causes anthrax. The external surface of the exosporium is coated with glycosylated proteins. The sugar additions are capped with the unique monosaccharide anthrose. The West African Group (WAG) B. anthracis have mutations rendering them anthrose deficient. Through genome sequencing, we identified 2 different large chromosomal deletions within the anthrose biosynthetic operon of B. anthracis strains from Chile and Poland. In silico analysis identified an anthrose-deficient strain in the anthrax outbreak among European heroin users. Anthrose-deficient strains are no longer restricted to West Africa so the role of anthrose in physiology and pathogenesis was investigated in B. anthracis Sterne. Loss of anthrose delayed spore germination and enhanced sporulation. Spores without anthrose were phagocytized at higher rates than spores with anthrose, indicating that anthrose may serve an antiphagocytic function on the spore surface. The anthrose mutant had half the LD50 and decreased time to death (TTD) of wild type and complement B. anthracis Sterne in the A/J mouse model. Following infection, anthrose mutant bacteria were more abundant in the spleen, indicating enhanced dissemination of Sterne anthrose mutant. At low sample sizes in the A/J mouse model, the mortality of ΔantC-infected mice challenged by intranasal or subcutaneous routes was 20% greater than wild type. Competitive index (CI) studies indicated that spores without anthrose disseminated to organs more extensively than a complemented mutant. Death process modeling using mouse mortality dynamics suggested that larger sample sizes would lead to significantly higher deaths in anthrose-negative infected animals. The model was tested by infecting Galleria mellonella with spores and confirmed the anthrose mutant was significantly more lethal. Vaccination studies in the A/J mouse model showed that the human vaccine protected against high-dose challenges of the nonencapsulated Sterne-based anthrose mutant. This work begins to identify the physiologic and pathogenic consequences of convergent anthrose mutations in B. anthracis.

Oligomerization of IC43 resulted in improved immunogenicity and protective efficacy against Pseudomonas aeruginosa lung infection

IC43, a truncate form of outer membrane proteins OprF_190-342 and OprI_21-83 from Pseudomonas aeruginosa, is a promising candidate antigen and exists as monomer in solution. In this study, we generated the heptamer of IC43 by carrier protein aided oligomerization, which was confirmed by gel-filtration and chemical cross-linking analysis. The carrier protein naturally exists as a homo-heptamer, and IC43 was displayed on the surface of the carrier protein in the fusion protein. Immunization with this fusion protein resulted in increased level of antigen specific IgG antibodies and higher survival rate after infection. The improved efficacy was correlated with lower bacteria burden, inflammation and tissue damage in the lungs of immunized mice. Further studies revealed that immunization with this fusion protein resulted in increased levels of IL-4 and antigen specific IgG1, suggesting a stronger Th2 immune response was induced. The improved immunogenicity may be attributed to the exposure of more epitopes on the antigen, which was confirmed by results from immune-dominant peptide mapping and passive immunization. These results demonstrated a possible strategy to improve the immunogenicity of an antigen by carrier protein aided oligomerization.

Gold nanoparticles morphology does not affect the multivalent presentation and antibody recognition of Group A Streptococcus synthetic oligorhamnans

The development of novel delivery systems capable of enhancing the antibody binding affinity and immunoactivity of short length saccharide antigens is at the forefront of modern medicine. In this regard, gold nanoparticles (AuNPs) raised great interest as promising nano-vaccine platform, as they do not interfere with the desired immune response and their surface can be easily functionalized, enabling the antigen multivalent presentation. In addition, the nanoparticles morphology can have a great impact on their biological properties. Gram-positive Group A Streptococcus (GAS) is a bacterium responsible for many infections and represents a priority healthcare concern, but a universal vaccine is still unavailable. Since all the GAS strains have a cell wall characterized by a common polyrhamnose backbone, this can be employed as alternative antigen to develop an anti-GAS vaccine. Herein, we present the synthesis of two oligorhamnoside fragments and their corresponding oligorhamnoside-AuNPs, designed with two different morphologies. By competitive ELISA we assessed that both symmetric and anisotropic oligorhamnan nanoparticles inhibit the binding of specific polyclonal serum much better than the unconjugated oligosaccharides.

Nucleotide polymorphism assay for the identification of west African group Bacillus anthracis: a lineage lacking anthrose

Background

The exosporium of the anthrax-causing Bacillus anthracis endospores display a tetrasaccharide composed of three rhamnose residues and an unusual sugar termed anthrose. Anthrose is a proposed potential target for immunotherapy and for specific detection of B. anthracis. Although originally thought to be ubiquitous in B. anthracis, previous work identified an anthrose negative strain from a West African lineage isolated from cattle that could represent a vaccine escape mutant. These strains carry genes required for expression of the anthrose operon but premature stop codons resulting from an 8-bp insertion in BAS3320 (an amino-transferase) and a C/T substitution at position 892 of the BAS3321 (a glycosyltransferase) gene prevent anthrose expression. Various other single nucleotide polymorphisms (SNPs) have been identified throughout the operon and could be the basis for detection of anthrose-deficient strains.

Results

In this study, we evaluated rhAmp genotypic assays based on SNPs at positions 892 and 1352 of BAS3321 for detection and differentiation of anthrose negative (Ant⁻) West African strains. Discrimination of anthrose negative West African isolates was achieved with as low as 100 fg of DNA, whereas consistent genotyping of Sterne necessitated at least 1 pg of DNA.

Conclusions

Screening of a global panel of B. anthracis isolates showed anthrose-expressing alleles are prevalent worldwide whereas the anthrose-deficient phenotype is to date limited to West Africa. Our work also revealed a third, previously unreported anthrose genotype in which the operon is altogether missing from a Polish B. anthracis isolate.