Quantifying in vitro B. anthracis growth and PA production and decay: a mathematical modelling approach

Protective antigen (PA) is a protein produced by Bacillus anthracis. It forms part of the anthrax toxin and is a key immunogen in US and UK anthrax vaccines. In this study, we have conducted experiments to quantify PA in the supernatants of cultures of B. anthracis Sterne strain, which is the strain used in the manufacture of the UK anthrax vaccine. Then, for the first time, we quantify PA production and degradation via mathematical modelling and Bayesian statistical techniques, making use of this new experimental data as well as two other independent published data sets. We propose a single mathematical model, in terms of delay differential equations (DDEs), which can explain the in vitro dynamics of all three data sets. Since we did not heat activate the B. anthracis spores prior to inoculation, germination occurred much slower in our experiments, allowing us to calibrate two additional parameters with respect to the other data sets. Our model is able to distinguish between natural PA decay and that triggered by bacteria via proteases. There is promising consistency between the different independent data sets for most of the parameter estimates. The quantitative characterisation of B. anthracis PA production and degradation obtained here will contribute towards the ambition to include a realistic description of toxin dynamics, the host immune response, and anti-toxin treatments in future mechanistic models of anthrax infection.

Visualization of immune pathways that enhance the neutralizing antibody response to vaccines after primary immunization

We examined the relationship between the association of a vaccine antigen with immune cells in secondary lymphoid organs shortly after immunization and the resulting neutralizing antibody response induced by that antigen using three antigenic forms of anthrax protective antigen (PA) that induce qualitatively different antibody responses. The three PA forms used were wild-type PA, which binds to anthrax toxin receptors and elicits a robust antibody response that includes both neutralizing and non-neutralizing antibodies; a receptor-binding-deficient (RBD) mutant form of PA, which does not bind cellular receptors and elicits only barely detectable antibody responses; and an engineered chimeric form of PA, which binds cholera toxin receptors and elicits a robust total antibody response but a poor neutralizing antibody response. We found that both wild-type PA and the PA chimera associated with immune cells in secondary lymphoid organs after immunization, but the RBD mutant PA exhibited minimal association, revealing a relationship between antigen binding to toxin receptors on immune cells after immunization and subsequent antibody responses. A portion of wild-type PA that bound to immune cells was cell surface-associated and maintained its native conformation. Much lower amounts of conformationally intact PA chimera were associated with immune cells after immunization, correlating with the lower neutralizing antibody response elicited by the PA chimera. Thus, binding of an antigen to receptors on immune cells in secondary lymphoid organs after immunization and maintenance of conformational integrity of the cell-associated antigen help dictate the magnitude of the resulting neutralizing antibody response, but not necessarily the total antibody response.IMPORTANCEMany vaccines protect by the induction of antibodies that neutralize the action of the pathogen. Here, we followed the fate of three antigenic forms of a vaccine antigen in secondary lymphoid organs after immunization to investigate events leading to a robust neutralizing antibody response. We found that the magnitude of the neutralizing antibody response, but not the total antibody response, correlates with the levels of conformationally intact antigen associated with immune cells in secondary lymphoid organs after primary immunization. We believe that these results provide important insights into the genesis of neutralizing antibody responses induced by vaccine antigens and may have implications for vaccine design.

LETHAL TOXIN NEUTRALIZING ANTIBODY RESPONSE INDUCED FOLLOWING ORAL VACCINATION WITH A MICROENCAPSULATED BACILLUS ANTHRACIS STERNE STRAIN 34F2 VACCINE PROOF-OF-CONCEPT STUDY IN WHITE-TAILED DEER (ODOCOILEUS VIRGINIANUS)

Improved methods are needed to prevent wildlife deaths from anthrax. Caused by Bacillus anthracis, naturally occurring outbreaks of anthrax are frequent but unpredictable. The commercially available veterinary vaccine is labeled for subcutaneous injection and is impractical for large-scale wildlife vaccination programs; therefore, oral vaccination is the most realistic method to control and prevent these outbreaks. We reported the induction of an anthrax-specific lethal toxin (LeTx) neutralizing antibody response in mice following oral vaccination with alginate microcapsules containing B. anthracis Sterne strain 34F2 spores, coated with poly-L-lysine (PLL) and vitelline protein B (VpB). We continued evaluating our novel vaccine formulation through this proof-of-concept study in white-tailed deer (WTD; Odocoileus virginianus; n = 9). We orally vaccinated WTD via needle-free syringe with three formulations of the encapsulated vaccine: 1) PLL-VpB-coated microcapsules with 107-8 spores/ml (n = 5), 2) PLL-VpB-coated microcapsules with 109-10 spores/ml (n = 2), and 3) PLL-coated microcapsules with 109-10 spores/ml (n = 2). Although the limited sample sizes require continued experimentation, we observed an anthrax-specific antibody response in WTD serum following oral vaccination with PLL-coated microcapsules containing 109 spores/ ml. Furthermore, this antibody response neutralized anthrax LeTx in vitro, suggesting that continued development of this vaccine may allow for realistic wildlife anthrax vaccination programs.

In Vitro Protection and Titer Duration of Anthrax-Specific Antibodies Following Subcutaneous Vaccination of White-tailed Deer (Odocoileus virginianus) with Bacillus anthracis Sterne 34F2 Strain Spores

Outbreaks of anthrax, caused by the soilborne bacterium Bacillus anthracis, are a continuous threat to free-ranging livestock and wildlife in enzootic regions of the United States, sometimes causing mass mortalities. Injectable anthrax vaccines are commercially available for use in livestock, and although hand injection is not a cost- or time-effective long-term management plan for prevention in wildlife, it may provide a tool for managers to target selectively animals of high conservation or economic value. Vaccine-induced anthrax-specific antibody responses have been reported previously in white-tailed deer (Odocoileus virginianus), but the protective nature was not determined. In this study, five white-tailed deer were subcutaneously vaccinated with one dose (1 mL) of the Anthrax Spore Vaccine. Eight blood collections by jugular venipuncture were conducted over 146 d to measure the anthrax-specific antibody response in each deer's serum over time. Antibodies were first detected by ELISA and later with toxin neutralization assays to estimate in vitro protection. Average peak absorbance by ELISA occurred at 14 d postvaccination, whereas average peak in vitro protection occurred at 28 d postvaccination. Observed in vitro protection on average for white-tailed deer after this single-dose vaccination protocol lasted 42-56 d postvaccination, although three individuals still maintained lethal toxin-neutralizing serum antibody titers out to 112 d postvaccination. Vaccination responses were variable but effective to some degree in all white-tailed deer.

Spatial analysis of human and livestock anthrax in Lai Chau province, Vietnam (2004-2021)

Anthrax is reported globally with varying disease intensity and seasonality among countries. In Vietnam, anthrax epidemiology and ecology remain understudied. We used historical data of human and livestock anthrax from 2004 to 2021 in Lai Chau province, to identify spatial clusters of human and livestock anthrax, describe epidemiological characteristics, and compare livestock anthrax vaccine coverage to human and livestock disease incidence. Local Moran's I (LISA) using spatial Bayes smoothed commune-level cumulative incidence (per 10,000) for the study period, epidemiological descriptive statistics, livestock vaccine coverage data, and annual incidence rates (per 10,000) at provincial level were used. LISA identified a human anthrax hotspot (high-high) in the southeast which did not overlap spatially with livestock anthrax hotspots in southeastern and northeastern communes. Most human cases were male, aged 15-59 years, handled sick animals, and/or consumed contaminated meat. Almost all cases were reported by grassroot health facilities with a delay of 6.3 days between exposure and case notification to the national surveillance system. 80 % of human cases were reported from June-October. The increase in disease incidence occurred shortly after livestock anthrax vaccine coverage decreased. This study informs vaccination strategy and targeted surveillance and control measures in newly identified high-risk areas and seasons of anthrax.

Efficacy of different AV7909 dose regimens in a nonclinical model of pulmonary anthrax

Pulmonary anthrax caused by exposure to inhaled Bacillus anthracis, the most lethal form of anthrax disease, is a continued military and public health concern for the United States. The vaccine AV7909, consisting of the licensed anthrax drug substance AVA adjuvanted with CpG7909, induces high levels of toxin neutralizing antibodies in healthy adults using fewer doses than AVA. This study compares the ability of one- or two-dose regimens of AV7909 to induce a protective immune response in guinea pigs challenged with a lethal dose of aerosolized B. anthracis spores 6 weeks after the last vaccine dose. The results indicated that AV7909 was less effective when delivered as a single dose compared to the two-dose regimen that resulted in dose-dependent protection against death. The toxin neutralizing assay (TNA) titer and anti-PA IgG responses were proportional to the protective efficacy, with a 50% TNA neutralizing factor (NF50) greater than 0.1 associated with survival in animals receiving two doses of vaccine. The strong protection at relatively low TNA NF50 titers in this guinea pig model supports the exploration of lower doses in clinical trials to determine if these protective levels of neutralizing antibodies can be achieved in humans; however, protection with a single dose may not be feasible.

Single Low-Dose Nanovaccine for Long-Term Protection against Anthrax Toxins

Anthrax infections caused by Bacillus anthracis are an ongoing bioterrorism and livestock threat worldwide. Current approaches for management, including extended passive antibody transfusion, antibiotics, and prophylactic vaccination, are often cumbersome and associated with low patient compliance. Here, we report on the development of an adjuvanted nanotoxoid vaccine based on macrophage membrane-coated nanoparticles bound with anthrax toxins. This design leverages the natural binding interaction of protective antigen, a key anthrax toxin, with macrophages. In a murine model, a single low-dose vaccination with the nanotoxoids generates long-lasting immunity that protects against subsequent challenge with anthrax toxins. Overall, this work provides a new approach to address the ongoing threat of anthrax outbreaks and bioterrorism by taking advantage of an emerging biomimetic nanotechnology.

Antibodies against Anthrax Toxins: A Long Way from Benchlab to the Bedside

Anthrax is an acute disease caused by the bacterium Bacillus anthracis, and is a potential biowarfare/bioterrorist agent. Its pulmonary form, caused by inhalation of the spores, is highly lethal and is mainly related to injury caused by the toxins secretion. Antibodies neutralizing the toxins of B. anthracis are regarded as promising therapeutic drugs, and two are already approved by the Federal Drug Administration. We developed a recombinant human-like humanized antibody, 35PA83 6.20, that binds the protective antigen and that neutralized anthrax toxins in-vivo in White New Zealand rabbits infected with the lethal 9602 strain by intranasal route. Considering these promising results, the preclinical and clinical phase one development was funded and a program was started. Unfortunately, after 5 years, the preclinical development was cancelled due to industrial and scientific issues. This shutdown underlined the difficulty particularly, but not only, for an academic laboratory to proceed to clinical development, despite the drug candidate being promising. Here, we review our strategy and some preliminary results, and we discuss the issues that led to the no-go decision of the pre-clinical development of 35PA83 6.20 mAb. Our review provides general information to the laboratories planning a (pre-)clinical development.

A multipathogen DNA vaccine elicits protective immune responses against two class A bioterrorism agents, anthrax and botulism

Abstract

The potential use of biological agents has become a major public health concern worldwide. According to the CDC classification, Bacillus anthracis and Clostridium botulinum, the bacterial pathogens that cause anthrax and botulism, respectively, are considered to be the most dangerous potential biological agents. Currently, there is no licensed vaccine that is well suited for mass immunization in the event of an anthrax or botulism epidemic. In the present study, we developed a dual-expression system-based multipathogen DNA vaccine that encodes the PA-D4 gene of B. anthracis and the HCt gene of C. botulinum. When the multipathogen DNA vaccine was administered to mice and guinea pigs, high level antibody responses were elicited against both PA-D4 and HCt. Analysis of the serum IgG subtype implied a combined Th1/Th2 response to both antigens, but one that was Th2 skewed. In addition, immunization with the multipathogen DNA vaccine induced effective neutralizing antibody activity against both PA-D4 and HCt. Finally, the protection efficiency of the multipathogen DNA vaccine was determined by sequential challenge with 10 LD₅₀ of B. anthracis spores and 10 LD₅₀ of botulinum toxin, or vice versa, and the multipathogen DNA vaccine provided higher than 50% protection against lethal challenge with both high-risk biothreat agents. Our studies suggest the strategy used for this anthrax-botulinum multipathogen DNA vaccine as a prospective approach for developing emergency vaccines that can be immediately distributed on a massive scale in response to a biothreat emergency or infectious disease outbreak.

Key points • A novel multipathogen DNA vaccine was constructed against anthrax and botulism. • Robust immune responses were induced following vaccination. • Suggests a potential vaccine development strategy against biothreat agents.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-11812-6.

US disaster planners' attitudes regarding preevent vaccine for first responders and point-of-dispensing workers

Disaster planners' attitudes toward pre-event anthrax and smallpox vaccine for first responders and point-of-dispensing (POD) workers have not been examined. An online questionnaire was sent to US Cities Readiness Initiative (CRI) and non-CRI public health disaster planners in 2013. Multivariate logistic regressions were used to assess determinants of belief that first responders and POD workers should be offered the anthrax and/or smallpox vaccine before an event. A total of 301 disaster planners participated. Only half (50.6%, n=126) were aware of the ACIP recommendation that first responders could be offered pre-event anthrax vaccine. Many (66.0%, n=164) believed that pre-event anthrax vaccine should be offered to first responders. The oldest respondents were least likely to believe anthrax vaccine should be given (OR: 0.27, 0.12, 0.63, p<.001). Fewer disaster planners believed that pre-event anthrax vaccine should be offered to POD workers compared to first responders (55.0% vs 66.0%, X(2)=151, p<.001). Almost 20% (18.3%, n=47) reported having already received pre-event smallpox vaccine. Among the unvaccinated (n=210), half (52.0%, n=105) were willing to receive pre-event smallpox vaccine if it was offered free of charge. Half (53.4%, n=133) believed that POD workers should be offered smallpox vaccine before an event. Many disaster planners support pre-event anthrax vaccination for first responders and POD workers, and about half support pre-event smallpox vaccine for POD workers. Jurisdictions should consider partnering with first responder agencies to implement a pre-event anthrax vaccination program.

Changing patterns of human anthrax in Azerbaijan during the post-Soviet and preemptive livestock vaccination eras

We assessed spatial and temporal changes in the occurrence of human anthrax in Azerbaijan during 1984 through 2010. Data on livestock outbreaks, vaccination efforts, and human anthrax incidence during Soviet governance, post-Soviet governance, preemptive livestock vaccination were analyzed. To evaluate changes in the spatio-temporal distribution of anthrax, we used a combination of spatial analysis, cluster detection, and weighted least squares segmented regression. Results indicated an annual percent change in incidence of (+)11.95% from 1984 to 1995 followed by declining rate of -35.24% after the initiation of livestock vaccination in 1996. Our findings also revealed geographic variation in the spatial distribution of reporting; cases were primarily concentrated in the west early in the study period and shifted eastward as time progressed. Over twenty years after the dissolution of the Soviet Union, the distribution of human anthrax in Azerbaijan has undergone marked changes. Despite decreases in the incidence of human anthrax, continued control measures in livestock are needed to mitigate its occurrence. The shifting patterns of human anthrax highlight the need for an integrated "One Health" approach that takes into account the changing geographic distribution of the disease.

Aluminum adjuvant linked to Gulf War illness induces motor neuron death in mice

Gulf War illness (GWI) affects a significant percentage of veterans of the 1991 conflict, but its origin remains unknown. Associated with some cases of GWI are increased incidences of amyotrophic lateral sclerosis and other neurological disorders. Whereas many environmental factors have been linked to GWI, the role of the anthrax vaccine has come under increasing scrutiny. Among the vaccine's potentially toxic components are the adjuvants aluminum hydroxide and squalene. To examine whether these compounds might contribute to neuronal deficits associated with GWI, an animal model for examining the potential neurological impact of aluminum hydroxide, squalene, or aluminum hydroxide combined with squalene was developed. Young, male colony CD-1 mice were injected with the adjuvants at doses equivalent to those given to US military service personnel. All mice were subjected to a battery of motor and cognitive-behavioral tests over a 6-mo period postinjections. Following sacrifice, central nervous system tissues were examined using immunohistochemistry for evidence of inflammation and cell death. Behavioral testing showed motor deficits in the aluminum treatment group that expressed as a progressive decrease in strength measured by the wire-mesh hang test (final deficit at 24 wk; about 50%). Significant cognitive deficits in water-maze learning were observed in the combined aluminum and squalene group (4.3 errors per trial) compared with the controls (0.2 errors per trial) after 20 wk. Apoptotic neurons were identified in aluminum-injected animals that showed significantly increased activated caspase-3 labeling in lumbar spinal cord (255%) and primary motor cortex (192%) compared with the controls. Aluminum-treated groups also showed significant motor neuron loss (35%) and increased numbers of astrocytes (350%) in the lumbar spinal cord. The findings suggest a possible role for the aluminum adjuvant in some neurological features associated with GWI and possibly an additional role for the combination of adjuvants.

A viral nanoparticle with dual function as an anthrax antitoxin and vaccine

The recent use of Bacillus anthracis as a bioweapon has stimulated the search for novel antitoxins and vaccines that act rapidly and with minimal adverse effects. B. anthracis produces an AB-type toxin composed of the receptor-binding moiety protective antigen (PA) and the enzymatic moieties edema factor and lethal factor. PA is a key target for both antitoxin and vaccine development. We used the icosahedral insect virus Flock House virus as a platform to display 180 copies of the high affinity, PA-binding von Willebrand A domain of the ANTXR2 cellular receptor. The chimeric virus-like particles (VLPs) correctly displayed the receptor von Willebrand A domain on their surface and inhibited lethal toxin action in in vitro and in vivo models of anthrax intoxication. Moreover, VLPs complexed with PA elicited a potent toxin-neutralizing antibody response that protected rats from anthrax lethal toxin challenge after a single immunization without adjuvant. This recombinant VLP platform represents a novel and highly effective, dually-acting reagent for treatment and protection against anthrax.

Anthrax is caused by the spore-forming, Gram-positive bacterium Bacillus anthracis. The toxic effects of B. anthracis are predominantly due to an AB-type toxin made up of the receptor-binding subunit protective antigen (PA) and two enzymatic subunits called lethal factor and edema factor. Protective immunity to B. anthracis infection is conferred by antibodies against PA, which is the primary component of the current anthrax vaccine. Although the vaccine is safe and effective, it requires multiple injections followed by annual boosters. The development of a well-characterized vaccine that induces immunity after a single injection is an important goal. We developed a reagent that combines the functions of an anthrax antitoxin and vaccine in a single compound. It is based on multivalent display of the anthrax toxin receptor, ANTXR2, on the surface of an insect virus. We demonstrate that the recombinant virus-like particles protect rats from anthrax intoxication and that they induce a potent immune response against lethal toxin when coated with PA. This immune response protected animals against lethal toxin challenge after a single administration without adjuvant. The PA-coated particles have significant advantages as an immunogen compared to monomeric PA and form the basis for development of an improved anthrax vaccine.

CpG oligonucleotides accelerate and boost the immune response elicited by AVA, the licensed anthrax vaccine

Synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs act as immune adjuvants, improving the immune response elicited by coadministered vaccines. Combining CpG ODN with anthrax vaccine adsorbed (AVA), the licensed human vaccine, can increase the speed, magnitude and avidity of the resultant anti-anthrax response in mice, rhesus macaques and humans. Adsorbing the CpG ODN onto cationic poly(actide-coglycolides) microparticles further boosts immunity to coadministered AVA. The antibody response induced by CpG ODN plus AVA confers protection against systemic anthrax challenge in multiple animal models. These findings suggest that CpG ODN, alone or in combination with other adjuvants and delivery strategies, may support the development of prophylactic and therapeutic vaccines against biothreat pathogens.

Project BioShield: what it is, why it is needed, and its accomplishments so far

Project BioShield is a comprehensive effort involving the US Department of Health and Human Services (HHS), its component agencies, and other partner federal agencies to speed the research, development, acquisition, and availability of medical countermeasures to improve the government's preparedness for and ability to counter chemical, biological, radiological, and nuclear threat agents. The legislation authorizes use of the Special Reserve Fund, which makes available $5.6 billion over 10 years for the advanced development and purchase of medical countermeasures. This appropriation is intended to provide an economic incentive to the pharmaceutical industry to develop medical countermeasures for which the government is the only significant market. Acquisitions under Project BioShield are restricted to products in development that are potentially licensable within 8 years from the time of contract award. In exercising the procurement authorities under Project BioShield, HHS has launched acquisition programs to address each of the 4 threat agents, including Bacillus anthracis (anthrax), smallpox virus, botulinum toxins, and radiological/nuclear agents, originally deemed by the Department of Homeland Security to be threats to the US population sufficient to affect national security. At the time of writing, 7 contracts have been awarded: (1) recombinant protective antigen anthrax vaccine, the next-generation anthrax vaccine (contract terminated in December 2006 for default); (2) anthrax vaccine adsorbed, the currently licensed anthrax vaccine; (3) anthrax therapeutics (monoclonal); (4) anthrax therapeutics (human immune globulin); (5) the pediatric formulation of potassium iodide; (6) Ca- and Zn-diethylenetriaminepentaacetate (DTPA), chelating agents to treat ingestion of certain radiological particles; and (7) botulinum antitoxins. Additional acquisition contracts are expected to be awarded in 2007.

[Molecular study of Argentine strains of Bacillus anthracis]

Bacillus anthracis is one of the most monomorphic bacteria known and epidemiological studies of this microorganism have been hampered by the lack of molecular markers. For the genotyping of fourteen Argentine field strains and the vaccine strain Steme 34F2 the presence or absence of the virulence plasmids as well as vrrA locus containing a variable-number tandem repeat (VNTR) and presenting a polymorphism involving five variants, were analyzed. Strains were isolated from cows, sheep and pigs during outbreaks occurred in Buenos Aires, Entre Ríos, Santa Fe and La Pampa in the past fifty years. All of the field strains presented plasmids pXO1 and pXO2, except for a strain isolated from pig that only presented plasmid pXO2. All the strains and the vaccine strain belonged to the same VNTR variant that was defined by sequencing the vrrA locus from three of the isolates and the strain 34F2. These sequences were completely identical and corresponded to the variant VNTR4. Thus, the fourteen Argentine B. anthracis strains studied showed great uniformity at molecular level even though they had been isolated from different mammal species within a wide time period and covering an extensive geographical area.

CpG oligonucleotides improve the protective immune response induced by the licensed anthrax vaccine

Synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs act as immune adjuvants, improving the response elicited by a coadministered vaccine. Combining CpG ODN with anthrax vaccine adsorbed (AVA, the licensed human vaccine) increases the speed, magnitude, and avidity of the resultant antibody response. IgG Abs against anthrax protective antigen (PA) protect mice, guinuea pigs, and rhesus macaques from infection.

Low doses of antigen coupled to anti-CR2 mAbs induce rapid and enduring IgG immune responses in mice and in cynomolgus monkeys

The complement system and B cell complement receptor 2 (CR2), specific for C component C3dg, play important roles in both the innate and adaptive immune response. We used hapten and protein conjugates of anti-CR2 mAbs as models for C3dg-opsonized antigens and immune complexes to examine the handling of and immune response to these reagents in mice and in non-human primates (NHP). Mice immunized and boosted i.v. with only 100 ng of Alexa 488 rat anti-mouse CR1/2 mAb 7G6 had strong IgG immune responses to the Alexa 488 hapten and to rat IgG, compared to very weak immune responses in mice treated with a comparable isotype control; larger doses of Alexa 488 mAb 7G6 did not increase the immune response. A vaccine constructed by cross-linking anthrax protective antigen to mAb 7G6 proved to be effective at low doses in generating sufficiently high titer serum IgG antibodies to neutralize anthrax lethal toxin in vitro and to protect mice from i.v. challenge with anthrax lethal toxin. When biotinylated HB135, a mouse mAb specific for human CR2, was injected i.v. into NHP, the probe manifested the same initial marginal zone B cell binding and subsequent localization to follicular dendritic cells as we have previously reported for comparable experiments in mice. Moreover, i.v. immunization of NHP with 1 microg/kg of Alexa 488 mAb HB135 promoted an IgG immune response to the Alexa 488 hapten and to mouse IgG. Taken together, these results demonstrate the efficacy of using anti-CR2 mAbs as antigen carriers for i.v. immunization with small amounts of antigens without adjuvant.

Recombinant protective antigen 102 (rPA102): profile of a second-generation anthrax vaccine

Recent terrorist attacks involving the use of Bacillus anthracis spores have stimulated interest in the development of new vaccines for anthrax prevention. Studies of the pathogenesis of anthrax and of the immune responses following infection and immunization underscore the pivotal role that antibodies to the protective antigen play in protection. The most promising vaccine candidates contain purified recombinant protective antigen. Clinical trials of one of these, recombinant protective antigen (rPA)102, are underway. Initial results suggest that rPA102 is well tolerated and immunogenic. Additional trials are necessary to identify optimal formulations and immunization regimens for pre- and postexposure prophylaxis. Future licensure of these and other candidate vaccines will depend on their safety and immunogenicity profiles in humans, and their ability to confer protection in animal models of inhalational anthrax.

Diversity of Bacillus anthracis strains in Georgia and of vaccine strains from the former Soviet Union

Despite the increased number of anthrax outbreaks in Georgia and the other Caucasian republics of the former Soviet Union, no data are available on the diversity of the Bacillus anthracis strains involved. There is also little data available on strains from the former Soviet Union, including the strains previously used for vaccine preparation. In this study we used eight-locus variable-number tandem repeat analyses to genotype 18 strains isolated from infected animals and humans at different sites across Georgia, where anthrax outbreaks have occurred in the last 10 years, and 5 strains widely used for preparation of human and veterinary vaccines in the former Soviet Union. Three different genotypes affiliated with the A3.a cluster were detected for the Georgian isolates. Two genotypes were previously shown to include Turkish isolates, indicating that there is a regional strain pattern in the South Caucasian-Turkish region. Four of the vaccine strains were polymorphic, exhibiting three different patterns of the cluster A1.a genotype and the cluster A3.b genotype. The genotype of vaccine strain 71/12, which is considered an attenuated strain in spite of the presence of both of the virulence pXO plasmids, appeared to be a novel genotype in the A1.a cluster.

Molecular study of genes involved in virulence regulatory pathways in Bacillus anthracis vaccine strain "Carbosap"

This study investigated the genetic bases of attenuation in the Bacillus anthracis vaccine strain "Carbosap" used in Italy against anthrax in cattle and sheep. Twelve genes involved in virulence regulatory pathways underwent sequence analysis in comparison with a B. anthracis virulent strain.

Short-course postexposure antibiotic prophylaxis combined with vaccination protects against experimental inhalational anthrax

Prevention of inhalational anthrax after Bacillus anthracis spore exposure requires a prolonged course of antibiotic prophylaxis. In response to the 2001 anthrax attack in the United States, approximately 10,000 people were offered 60 days of antibiotic prophylaxis to prevent inhalational anthrax, but adherence to this regimen was poor. We sought to determine whether a short course of antibiotic prophylaxis after exposure could protect non-human primates from a high-dose spore challenge if vaccination was combined with antibiotics. Two groups of 10 rhesus macaques were exposed to approximately 1,600 LD50 of spores by aerosol. Both groups were given ciprofloxacin by orogastric tube twice daily for 14 days, beginning 1-2 h after exposure. One group also received three doses of the licensed human anthrax vaccine (anthrax vaccine adsorbed) after exposure. In the ciprofloxacin-only group, four of nine monkeys (44%) survived the challenge. In contrast, all 10 monkeys that received 14 days of antibiotic plus anthrax vaccine adsorbed survived (P = 0.011). Thus postexposure vaccination enhanced the protection afforded by 14 days of antibiotic prophylaxis alone and completely protected animals against inhalational anthrax. These data provide evidence that postexposure vaccination can shorten the duration of antibiotic prophylaxis required to protect against inhalational anthrax and may impact public health management of a bioterrorism event.

UK armed forces responses to an informed consent policy for anthrax vaccination: A paradoxical effect?

BACKGROUND

In recognition of concerns that anthrax vaccination might be a trigger for "Gulf war syndrome", anthrax vaccinations were offered to UK armed forces in the 2003 Iraq conflict using explicit as opposed to implicit consent, as is the policy for all other vaccinations. This paper examines responses of personnel to this policy.

METHODS

Qualitative analysis of free text responses to a question inviting comments on any concerns about the anthrax vaccination, asked in the context of a questionnaire assessing military health amongst 1000 members of the UK armed forces following the invasion of Iraq in 2003.

RESULTS

Two hundred and two (20.2%) respondents made comments reflecting concerns about the vaccine's effectiveness and its safety. These appeared to be magnified by suspicions about the motives behind the informed consent policy for anthrax but not other vaccinations.

CONCLUSION

While the informed consent policy for anthrax vaccinations was intended to decrease concern, it may inadvertently have had the opposite effect.

Immunogenicity and Protective Efficacy of Bacillus anthracis Poly-γ-d-glutamic Acid Capsule Covalently Coupled to a Protein Carrier Using a Novel Triazine-based Conjugation Strategy

The capsular polypeptide of Bacillus anthracis is composed of a unique polyglutamic acid polymer in which D-glutamate monomers are joined by gamma-peptidyl bonds. The capsule is poorly immunogenic, and efforts at exploiting the polymer for vaccine development have focused on increasing its inherent immunogenicity through chemical coupling to immune-stimulating protein carriers. The usual strategy has employed carbodiimide-based condensing reagents for activation of free alpha-carboxyl groups, despite reports that this chemistry may lead to chain scission. We have purified the high molecular mass capsule to >95% homogeneity and have demonstrated that the polymer contains >99% poly-gamma-D-glutamic acid. The predominant structure of the polymer as assessed by circular dichroism and multiangle laser light scattering was unordered at near-neutral pH. We investigated the effects of various activation chemistries, and we demonstrated that carbodiimide treatment under aqueous conditions results in significant cleavage of the gamma-peptidyl bond, whereas scission is significantly reduced in nonaqueous polar solvents, although undesired side chain modification was still observed. An activation chemistry was developed using the triazine-based reagent 4-(4,6-dimethoxy (1,3,5)triazin-2-yl)-4-methylmorpholinium chloride, which allowed for controlled and reproducible derivatization of alpha-carbonyls. In a two-pot reaction scheme, activated capsule was derivatized with a sulfhydryl-reactive heterobifunctional moiety and was subsequently coupled to thiolated carrier protein. This conjugate elicited very high capsule-specific immune titers in mice. More importantly, mice immunized with conjugated capsule exhibited good protection against lethal challenge from a virulent B. anthracis strain in two models of infection. We also showed, for the first time, that treatment of capsule with carbodiimide significantly reduced recognition by capsule-specific antisera concurrent with the reagent-induced reduction of polymer mass. The data suggested that for vaccine development, maintenance of the high mass of the polymer may be important.

Achievements of the Soviet biological weapons programme and implications for the future

The military-biological complex of the former Union of Soviet Socialist Republics was a true Frankenstein's Monster, with a powerful scientific potential--or good and for ill. This article examines both the direct scientific results of the twin biological weapons (BWs) programmes run by the 'civilian' Biopreparat and by the Ministry of Defence (MoD) and the public health benefits that sprang, despite the original intent, out of those programmes. The authors will also explore the potential for both crop and livestock destruction and for enhanced agricultural methods growing out of the parallel Soviet programme under the management of the Special Directorate of the Ministry of Agriculture. In the last section of the article the authors discuss the situation in the military-biological complex that arose after former President Boris Yeltsin's 1992 decree abolishing all research and development on offensive BWs. The possibility is considered that expertise, technologies and materials from the former Soviet BWs programme have leaked out of Russia, because the living standards in Russia remain low and the overwhelming majority of scientists have a miserable existence.

Induction of protective immunity to anthrax lethal toxin with a nonhuman primate adenovirus-based vaccine in the presence of preexisting anti-human adenovirus immunity

Prevention or therapy for bioterrorism-associated anthrax infections requires rapidly acting effective vaccines. We recently demonstrated (Y. Tan, N. R. Hackett, J. L. Boyer, and R. G. Crystal, Hum. Gene Ther. 14:1673-1682, 2003) that a single administration of a recombinant serotype 5 adenovirus (Ad) vector expressing anthrax protective antigen (PA) provides rapid protection against anthrax lethal toxin challenge. However, approximately 35 to 50% of humans have preexisting neutralizing antibodies against Ad5. This study assesses the hypothesis that a recombinant adenovirus vaccine based on the nonhuman primate-derived serotype AdC7, against which humans do not have immunity, expressing PA (AdC7PA) will protect against anthrax lethal toxin even in the presence of preexisting anti-Ad5 immunity. Naive and Ad5-immunized BALB/c mice received (intramuscularly) 10(8) to 10(11) particle units (PU) of AdC7PA, Ad5PA (a human serotype Ad5-based vector expressing a secreted form of PA), or AdNull (an Ad5 vector with no transgene). Robust anti-PA immunoglobulin G and neutralizing antibodies were detected by 2 to 4 weeks following administration of AdC7PA to naive or Ad5 preimmunized mice, whereas low anti-PA titers were detected in Ad5-preimmunized mice following administration of Ad5PA. To assess protection in vivo, naive or mice previously immunized against Ad5 were immunized with AdC7PA or Ad5PA and then challenged with a lethal intravenous dose of Bacillus anthracis lethal toxin. Whereas Ad5PA protected naive mice against challenge with B. anthracis lethal toxin, Ad5PA was ineffective in mice that were previously immunized against Ad5. In contrast, AdC7PA functioned effectively not only to protect naive mice but also to protect Ad5-preimmunized mice, with 100% survival after lethal toxin challenge. These data suggest the nonhuman-based vector AdC7PA is an effective vaccine for the development of protective immunity against B. anthracis and importantly functions as a "sero-switch" base for an adenovirus vaccine to function in the context of preexisting anti-Ad immunity.

[Characterization of Bacillus anthracis typical virulent test strain 81/1]

The results of the prolonged and many-sided study of B. anthracis strain 81/1 by different authors are presented. The cultural and morphological, biochemical, antigenic, molecular-genetic characteristics of this strain give grounds for regarding it as a typical test strain to be used for the determination of the vaccines immunogenicity, the effectiveness of antibiotics and immunomodulators.

The capsule of Bacillus anthracis behaves as a thymus-independent type 2 antigen

Bacillus anthracis elaborates a homopolymeric capsule composed of gamma-D-glutamic acid residues. Mice were immunized with formalin-fixed encapsulated B. anthracis bacilli, and the serum antibody response to a gamma-D-glutamyl capsular epitope was measured. Antiglutamyl antibodies were elicited in athymic BALB/c Nu/Nu, BALB/c Nu/+, and CBA/J mice but not in CBA/N xid mice. These response patterns define the capsule of B. anthracis as a thymus-independent type 2 antigen.

Vaccines against biologic agents: uses and developments

Although the Geneva protocol that prohibits the use of chemical and biologic weapons was ratified in 1925, many countries failed to accept this protocol: others stipulated retaliation, and some, like the United States, did not ratify the protocol for decades. This delay allowed the continued development of chemical and biologic agents. Members of the health care community are responsible for determining the best way to protect society from the potentially devastating effects of these biologic agents. Ideally,these diseases would be prevented from ever developing into systemic illnesses. In the past, vaccination has been a successful means of eradicating disease. Vaccines remain a hopeful therapy for the future, but time is short,and there are many obstacles.Information regarding bioterrorism agents and their treatments comes mainly from dated data or from in vitro or animal studies that may not apply to human treatment and disease. Additionally, the current threat of bioterrorism does not allow enough time for accurate, well-designed,controlled studies in humans before the release of investigational vaccines. Furthermore, some human studies would not be safe or ethical. Finally,many members of society suffer from illnesses that would put them at high risk to receive prophylactic vaccination. It is therefore naive to believe that vaccines would be the ultimate protection from these agents. In addition to vaccine development, there must be concurrent investigations into disease management and treatment. Even in instances in which vaccination is known to be an effective means of disease protection. biologic agents may be presented in a manner that renders vaccines ineffective. Virulent strains of organisms may be used, more than one organism may be used in tandem to increase virulence, and strains may be selected for antibiotic and vaccine resistance. Genetically engineered strains may use virulence factors other than those targeted in vaccines, and high concentrations of organisms may overcome vaccine protection. Finally,exposure may not be immediately noted until it is too late to vaccinate, as was the case with anthrax. Even in a case, such as smallpox, in which postexposure vaccination is possible, patients will still develop disease, and the health care system may be overwhelmed. The United States government has been defensively planning and researching the use of vaccines and chemoprophylaxis against any potential biologic agents since at least 1953, and resources are still lacking. There are inadequate stockpiles of vaccine to protect the entire population. The pharmaceutical industry also lacks a means of mass producing vaccines ina short timeframe. There is no policy in place for the use of vaccines that are yet unlicensed and experimental but may be the only therapy in the event ofa terrorist attack. Investigations into these solutions have been instituted only after the September 11, 2001, attacks heightened the awareness of terrorism. Although vaccination is an effective means of prophylaxis and a means of terminating epidemics or treating active disease, there is also resistance from the general public. In some instances there is a lack of acceptance of vaccines, or the risk of side effects is too great. In other cases, a questionable benefit does not justify the expense of mass vaccination. Because of this uncertainty, mass vaccination is deemed an impractical solution to the threat of bioterrorism. Extending vaccination with most vaccines to include all members of society who may be first responders in the event of an attack should be considered. In all instances, the benefit-to-risk must be weighed ratio when deciding how and when to offer preemptive prophylaxis to protect society from a real but unknown threat.

The osmoprotectants glycine and its methyl derivatives prevent the thermal inactivation of protective antigen of Bacillus anthracis

Protective antigen (PA) is the main immunogenic constituent of all vaccines against anthrax. It is known to lose its biological activity even at 37 degrees C. Its thermolabile nature has, thus, remained a cause of concern as even transient exposure of the vaccine to higher temperature could compromise its efficacy. Various types of cosolvent excipients have been used to stabilize a number of proteins with variable success. However, no comprehensive and systematic study to stabilize anthrax PA molecule using this approach has ever been undertaken. We have carried out a systematic study on the effect of osmoprotectants like glycine and its methyl derivatives, sarcosine, dimethylglycine, and betaine, on the thermostability of PA. The thermal stability of PA was found to be highly sensitive to pH with maxima at pH 7.9. All the cosolvent additives used were able to enhance the thermal stability of PA as inferred from an increase in T(1/2) values, the temperature at which 50% activity was retained during short-term incubation. Glycine was found to be the best stabilizer, while the ability of its methyl derivatives to stabilize PA decreased with an increase in the number of substituted methyl groups suggesting perturbation of hydrophobic interactions. On extended incubation at 40 degrees C the half-life of PA thermal inactivation increased more than four times in the presence of glycine. Thus, glycine could be used as an effective stabilizer to enhance the shelf life of recombinant vaccine against anthrax.

Protective Immunity Evoked Against Anthrax Lethal Toxin After a Single Intramuscular Administration of an Adenovirus-Based Vaccine Encoding Humanized Protective Antigen

Because of the need to develop a vaccine to rapidly protect the civilian population in response to a bioterrorism attack with Bacillus anthracis, we designed AdsechPA, a replication-deficient human serotype 5 adenovirus encoding B. anthracis protective antigen (PA) with codons optimized for expression in mammalian cells. With a single intramuscular administration to mice of 10(9) particle units of AdsechPA, a dose that can be scaled to human use, anti-PA antibodies were evoked more rapidly and at a higher level than with a single administration of the new U.S. military recombinant PA/Alhydrogel vaccine. Importantly, AdsechPA afforded approximately 2.7-fold more protection than the recombinant PA vaccine against B. anthracis lethal toxin challenge 4 weeks after a single vaccination. Even at 11 days postvaccination, AdsechPA provided some survival benefit, whereas the rPA/Alhydrogel vaccine provided none. In the context that equivalent human doses of Ad vectors have already been demonstrated to be safe in humans, a single administration of AdsechPA may provide the means to rapidly protect the civilian population against B. anthracis in response to a bioterrorism attack.

Novel in vitro functional assays for the determination of anthrax toxin components

The characterisation and evaluation of the UK licensed human anthrax vaccine depends on several in vivo tests that determine its safety and potency. Assays for the determination of functionally active and/or immunoreactive toxin components and S-layer proteins have been developed and applied to the characterisation of anthrax vaccine. These technologies may support production of consistent and effective vaccines, and may ultimately reduce the requirements for in vivo testing.

[Anthrax and carbuncle: two sides of the same coin]

The disease caused by Bacillus anthracis is one of the most critical concerns to the general public and public health authorities due both to the anthrax cases caused by the intentional release of the germ in the USA at the close of 2001 when letters and packages were contaminated with anthrax spores, and the current threat of biological warfare. After a brief excursus on the history of the terms Anthrax and Carbuncle, we survey the main evidence of anthrax found in the ancient literature, and deal with the identification of the pathogenic agent responsible for the disease and the subsequent discovery of the first anthrax vaccine and its use in order to control the spread of the disease in the cattle. Finally, we examine some of the most important episodes of occupational exposure to the Bacillus anthracis that occurred in the past two centuries and the preventive measures applied both to employees and the workplace.

Bacillus anthracis: current knowledge in relation to contamination of food

In this article, information related to anthrax and its etiologic agent, Bacillus anthracis, in food is reviewed. The major topics discussed include the taxonomic relationship of B. anthracis to other Bacillus species, methods used for the recovery of the organism from surfaces and foods, routes of infection, the pathogenesis of the organism, the microbial ecology of the vegetative cell and spore in foods and the environment, chemical and physical treatments for spore inactivation, and the control of the disease in animals.

Bacillus anthracis

The events of 11 September 2001 and the subsequent anthrax outbreaks have shown that the West needs to be prepared for an increasing number of terrorist attacks, which may include the use of biological warfare. Bacillus anthracis has long been considered a potential biological warfare agent, and this review will discuss the history of its use as such. It will also cover the biology of this organism and the clinical features of the three disease forms that it can produce: cutaneous, gastrointestinal, and inhalation anthrax. In addition, treatment and vaccination strategies will be reviewed.