Protective-antigen (PA) based anthrax vaccines confer protection against inhalation anthrax by precluding the establishment of a systemic infection

Pathogenicity and Genomic Characterization of a Novel Genospecies, Bacillus shihchuchen, of the Bacillus cereus Group Isolated from Chinese Softshell Turtle (Pelodiscus sinensis)

The Chinese softshell turtle (CST; Pelodiscus sinensis) is a freshwater aquaculture species of substantial economic importance that is commercially farmed across Asia, particularly in Taiwan. Although diseases caused by the Bacillus cereus group (Bcg) pose a major threat to commercial CST farming systems, information regarding its pathogenicity and genome remains limited. Here, we investigated the pathogenicity of Bcg strains isolated in a previous study and performed whole-genome sequencing. Pathogenicity analysis indicated that QF108-045 isolated from CSTs caused the highest mortality rate, and whole-genome sequencing revealed that it was an independent group distinct from other known Bcg genospecies. The average nucleotide identity compared to other known Bcg genospecies was below 95%, suggesting that QF108-045 belongs to a new genospecies, which we named Bacillus shihchuchen. Furthermore, genes annotation revealed the presence of anthrax toxins, such as edema factor and protective antigen, in QF108-045. Therefore, the biovar anthracis was assigned, and the full name of QF108-045 was Bacillus shihchuchen biovar anthracis. In addition to possessing multiple drug-resistant genes, QF108-045 demonstrated resistance to various types of antibiotics, including penicillins (amoxicillin and ampicillin), cephalosporins (ceftifour, cephalexin, and cephazolin), and polypeptides, such as vancomycin.

A novel bicistronic DNA vaccine with enhanced protective immune response against Bacillus anthracis through DNA prime-protein boost vaccination approach

Anthrax, by Bacillus anthracis, remains a dreadful fatal hazard worldwide. The currently used anthrax vaccines are plagued by numerous issues that limit their widespread use. As an immunization approach targeting both extracellular antigens and toxins of B. anthracis may achieve better sterile immunity, the present investigation designed a bicistronic secretory anti-anthrax DNA vaccine targeting immune response against toxin and cells. The efficacy of the vaccine was compared with monocistronic DNA vaccines and the currently used anthrax vaccine. For this, mice were immunized with the developed vaccine containing pag (encoding protective antigen to block toxin) and eag genes (encoding EA1 to target cells) of B. anthracis through DNA-prime/Protein-boost (D/P) and DNA prime/DNA-boost (D/D) approaches. There was a >2 and > 5 fold increase in specific antibody level by D/D and D/P approaches respectively, on 42nd days post-immunization (dpi). Serum cytokine profiling showed that both Th1 and Th2 immune responses were elicited, with more Th2 responses in D/P strategy. More importantly, challenge with 100 times LD₅₀ of B. anthracis at 42nd dpi exhibited maximum cumulative survival (83.33 %) by bicistronic D/P approach. Remarkably, immunization with EA1 delayed mortality onset in infection. The study forms the first report on complement-dependent bactericidal activity of antiEA1 antibodies. In short, co-immunization of PA and EA1 through the developed bicistronic DNA vaccine would be an effective immunization approach in anthrax vaccination. Further, D/P strategy could enhance vaccine-induced immunity against B. anthracis. Altogether, the study generates certain critical insights having direct applications in next-generation vaccine development against anthrax.

Progress towards the Development of a NEAT Vaccine for Anthrax II: Immunogen Specificity and Alum Effectiveness in an Inhalational Model

Bacillus anthracis is the causative agent of anthrax disease, presents with high mortality, and has been at the center of bioweapon efforts. The only currently U.S. FDA-approved vaccine to prevent anthrax in humans is anthrax vaccine adsorbed (AVA), which is protective in several animal models and induces neutralizing antibodies against protective antigen (PA), the cell-binding component of anthrax toxin. However, AVA requires a five-course regimen to induce immunity, along with an annual booster, and is composed of undefined culture supernatants from a PA-secreting strain. In addition, it appears to be ineffective against strains that lack anthrax toxin. Here, we investigated a vaccine formulation consisting of recombinant proteins from a surface-localized heme transport system containing near-iron transporter (NEAT) domains and its efficacy as a vaccine for anthrax disease. The cocktail of five NEAT domains was protective against a lethal challenge of inhaled bacillus spores at 3 and 28 weeks after vaccination. The reduction of the formulation to three NEATs (IsdX1, IsdX2, and Bslk) was as effective as a five-NEAT domain cocktail. The adjuvant alum, approved for use in humans, was as protective as Freund's Adjuvant, and protective vaccination correlated with increased anti-NEAT antibody reactivity and reduced bacterial levels in organs. Finally, the passive transfer of anti-NEAT antisera reduced mortality and disease severity, suggesting the protective component is comprised of antibodies. Collectively, these results provide evidence that a vaccine based upon recombinant NEAT proteins should be considered in the development of a next-generation anthrax vaccine.

Development of a novel multiepitope chimeric vaccine against anthrax

Bacillus anthracis (BA), the etiological agent of anthrax, secretes protective antigen (PA), lethal factor (LF), and edema factor (EF) as major virulence mediators. Amongst these, PA-based vaccines are most effective for providing immunity against BA, but their low shelf life limits their usage. Previous studies showed that B-cell epitopes, ID II and ID III present in PA domain IV possess higher toxin neutralization activity and elicit higher antibody titer than ID I. Moreover, N-terminal region of both LF and EF harbors PA-binding sites which share 100% identity with each other. Here, in this study, we have developed an epitope-based chimeric vaccine (ID-LFn) comprising ID II-ID III region of PA and N-terminal region of LF. We have also evaluated its protective efficacy as well as stability and found it to be more stable than PA-based vaccine. Binding reactivities of ID-LFn with anti-PA/LF/EF antibodies were determined by ELISA. The stability of chimeric vaccine was assessed using circular dichroism spectroscopy. ID-LFn response was characterized by toxin neutralization, lymphocyte proliferation isotyping and cytokine profiling. The protective efficacy was analyzed by challenging ID-LFn-immunized mice with B. anthracis (pXO1⁺ and pXO2⁺). ID-LFn was found to be significantly stable as compared to PA. Anti-ID-LFn antibodies recognized PA, LF as well as EF. The T-cell response and the protective efficacy of ID-LFn were found to be almost similar to PA. ID-LFn exhibits equal protective efficacy in mice and possesses more stability as compared to PA along with the capability of recognizing PA, LF and EF at the same time. Thus, it can be considered as an improved vaccine against anthrax with better shelf life. ID-LFn, a novel multiepitope chimeric anthrax vaccine: ID-LFn comprises of immunodominant epitopes of domain 4 of PA and N-terminal homologous stretch of LF and EF. The administration of this protein as a vaccine provides protection against anthrax.

Recombinant anthrax protective antigen: Observation of aggregation phenomena by TEM reveals specific effects of sterols

Negatively stained transmission electron microscope images are presented that depict the aggregation of recombinant anthrax protective antigen (rPA83 monomer and the PA63 prepore oligomer) under varying in vitro biochemical conditions. Heat treatment (50°C) of rPA83 produced clumped fibrils, but following heating the PA63 prepore formed disordered aggregates. Freeze-thaw treatment of the PA63 prepore generated linear flexuous aggregates of the heptameric oligomers. Aqueous suspensions of cholesterol microcrystals were shown to bind small rPA83 aggregates at the edges of the planar bilayers. With PA63 a more discrete binding of the prepores to the crystalline cholesterol bilayer edges occurs. Sodium deoxycholate (NaDOC) treatment of rPA83 produced quasi helical fibrillar aggregate, similar but not identical to that produced by heat treatment. Remarkably, NaDOC treatment of the PA63 prepores induced transformation into pores, with a characteristic extended ß-barrel. The PA63 pores aggregated as dimers, that aggregated further as angular chains and closed structures in higher NaDOC concentrations. The significance of the sterol interaction is discussed in relation to its likely importance for PA action in vivo.

Expression and refolding of the protective antigen of Bacillus anthracis: A model for high-throughput screening of antigenic recombinant protein refolding

Bacillus anthracis protective antigen (PA) is a well known and relevant immunogenic protein that is the basis for both anthrax vaccines and diagnostic methods. Properly folded antigenic PA is necessary for these applications. In this study a high level of PA was obtained in recombinant Escherichia coli. The protein was initially accumulated in inclusion bodies, which facilitated its efficient purification by simple washing steps; however, it could not be recognized by specific antibodies. Refolding conditions were subsequently analyzed in a high-throughput manner that enabled nearly a hundred different conditions to be tested simultaneously. The recovery of the ability of PA to be recognized by antibodies was screened by dot blot using a coefficient that provided a measure of properly refolded protein levels with a high degree of discrimination. The best refolding conditions resulted in a tenfold increase in the intensity of the dot blot compared to the control. The only refolding additive that consistently yielded good results was L-arginine. The statistical analysis identified both cooperative and negative interactions between the different refolding additives. The high-throughput approach described in this study that enabled overproduction, purification and refolding of PA in a simple and straightforward manner, can be potentially useful for the rapid screening of adequate refolding conditions for other overexpressed antigenic proteins.