Threshold protective levels of serum IgG to Shigella lipopolysaccharide: re-analysis of Shigella vaccine trials data.

OBJECTIVES: Establishing a correlate of protection is essential for the development and licensure of Shigella vaccines. We examined potential threshold levels of serum IgG to Shigella lipopolysaccharide (LPS) that could predict protection against shigellosis. METHODS: We performed new analyses of serologic and vaccine efficacy (VE) data from two randomized vaccine-controlled trials of the Shigella sonnei-Pseudomonas aeruginosa recombinant exoprotein A (rEPA) conjugate conducted in young adults and children aged 1-4 years in Israel. Adults received either S. sonnei-rEPA (n = 183) or control vaccines (n = 277). Children received the S. sonnei-rEPA conjugate (n = 1384) or S. flexneri 2a-rEPA conjugate (n = 1315). VE against culture-proven shigellosis was determined. Sera were tested for IgG anti-S. sonnei LPS antibodies. We assessed the association of various levels of IgG anti-S. sonnei LPS antibodies with S. sonnei shigellosis risk using logistic regression models and the reverse cumulative distribution of IgG levels. RESULTS: Among adults, four vaccinees and 23 controls developed S. sonnei shigellosis; the VE was 74% (95% CI, 28-100%). A threshold of ≥1:1600 IgG anti-S. sonnei LPS titre was associated with a reduced risk of S. sonnei shigellosis and a predicted VE of 73.6% (95% CI, 65-80%). The IgG anti-S. sonnei LPS correlated with serum bactericidal titres. In children, a population-based level of 4.5 ELISA Units (EU) corresponding to 1:1072 titre, predicted VE of 63%, versus 71% observed VE in children aged 3-4 years. The predicted VE in children aged 2-4 years was 49%, consistent with the 52% observed VE. CONCLUSION: Serum IgG anti-S. sonnei LPS threshold levels can predict the degree of VE and can be used for the evaluation of new vaccine candidates.

Vaccination with Shigella flexneri 2a conjugate induces type 2a and cross-reactive type 6 antibodies in humans but not in mice.

Shigella flexneri (S. flexneri) 6 has emerged as an important cause of shigellosis. Our efficacy study of Shigella sonnei and S. flexneri 2a O-specific polysaccharide (O-SP) conjugates in 1-4year-olds had too few S. flexneri 2a cases for efficacy evaluation but surprisingly showed protection of 3-4year-olds, S. flexneri 2a-recipients, from S. flexneri 6 infection. To investigate this cross-protection antibodies to both Shigella types were investigated in all sera remaining from previous studies. Twenty to 30% of 3-44year-old humans injected with S. flexneri 2a conjugate responded with ≥4-fold increases of IgG anti type 6, p<0.00001. The specificity of these antibodies was shown by inhibition studies. S. flexneri 6 infection of 2 children induced besides S. flexneri 6, also S. flexneri 2a antibodies, at levels of S. flexneri 2a vaccinees. S. flexneri 2a antibodies induced by S. flexneri 6 conjugates could not be studied since no such conjugate was assessed in humans and mice responded almost exclusively to the O-SP of the injected conjugate, with no cross-reactive antibodies. Our results indicate induction of cross-reactive protective antibodies. The O-acetylated disaccharide shared by S. flexneri 6 and 2a O-SPs, is the likely basis for their cross-reactivity. S. flexneri 6 O-SP conjugates, alone and in combination with S. flexneri 2a, merit further investigation for broad S. flexneri protection.

Bacillus anthracis Capsular Conjugates Elicit Chimpanzee Polyclonal Antibodies That Protect Mice from Pulmonary Anthrax.

The immunogenicity of Bacillus anthracis capsule (poly-γ-D-glutamic acid [PGA]) conjugated to recombinant B. anthracis protective antigen (rPA) or to tetanus toxoid (TT) was evaluated in two anthrax-naive juvenile chimpanzees. In a previous study of these conjugates, highly protective monoclonal antibodies (MAbs) against PGA were generated. This study examines the polyclonal antibody response of the same animals. Preimmune antibodies to PGA with titers of >10(3) were detected in the chimpanzees. The maximal titer of anti-PGA was induced within 1 to 2 weeks following the 1st immunization, with no booster effects following the 2nd and 3rd immunizations. Thus, the anti-PGA response in the chimpanzees resembled a secondary immune response. Screening of sera from nine unimmunized chimpanzees and six humans revealed antibodies to PGA in all samples, with an average titer of 10(3). An anti-PA response was also observed following immunization with PGA-rPA conjugate, similar to that seen following immunization with rPA alone. However, in contrast to anti-PGA, preimmune anti-PA antibody titers and those following the 1st immunization were ≤300, with the antibodies peaking above 10(4) following the 2nd immunization. The polyclonal anti-PGA shared the MAb 11D epitope and, similar to the MAbs, exerted opsonophagocytic killing of B. anthracis. Most important, the PGA-TT-induced antibodies protected mice from a lethal challenge with virulent B. anthracis spores. Our data support the use of PGA conjugates, especially PGA-rPA targeting both toxin and capsule, as expanded-spectrum anthrax vaccines.

Toward a new vaccine for pertussis.

To overcome the limitations of the current pertussis vaccines, those of limited duration of action and failure to induce direct killing of Bordetella pertussis, a synthetic scheme was devised for preparing a conjugate vaccine composed of the Bordetella bronchiseptica core oligosaccharide with one terminal trisaccharide to aminooxylated BSA via their terminal ketodeoxyoctanate residues. Conjugate-induced antibodies, by a fraction of an estimated human dose injected into young outbred mice as a saline solution, were bactericidal against B. pertussis, and their titers correlated with their ELISA values. The carrier protein is planned to be genetically altered pertussis toxoid. Such conjugates are easy to prepare, stable, and should add both to the level and duration of immunity induced by current vaccine-induced pertussis antibodies and reduce the circulation of B. pertussis.

Experience with monocomponent acellular pertussis combination vaccines for infants, children, adolescents and adults--a review of safety, immunogenicity, efficacy and effectiveness studies and 15 years of field experience.

Combination vaccines containing a monocomponent acellular pertussis (aP) vaccine, manufactured at Statens Serum Institut (SSI), Denmark, have successfully controlled Bordetella pertussis infections in Denmark since 1997. The efficacy of this aP vaccine was 71% in a double-blind, randomised and controlled clinical trial. Its safety and immunogenicity have been demonstrated in infants, children, adolescents and adults. In approximately 500,000 children it was effective against pertussis requiring hospitalisation (VE: 93% after 3 doses) and against pertussis not requiring hospitalisation (VE: 78% after 3 doses). IgG antibodies against pertussis toxin (IgG anti-PT) response rates after booster vaccination of adults with tetanus, diphtheria and aP combination vaccine (TdaP) were considerably higher for this monocomponent aP vaccine containing 20µg pertussis toxoid, inactivated by hydrogen peroxide (92.0%), than for two multicomponent aP vaccines inactivated by formaldehyde and/or glutaraldehyde: 3-component aP with 8µg pertussis toxoid (77.2%) and 5-component aP with 2.5µg pertussis toxoid (47.1%), without compromising the safety profile. In Denmark where this monocomponent aP vaccine has been the only pertussis vaccine in use for 15 years, there has been no pertussis epidemic since 2002 (population incidence 36 per 100,000), in contrast to neighbouring countries, where epidemics have occurred. This monocomponent aP vaccine can be used in combination vaccines for primary and booster vaccination against pertussis in all age groups and is an important tool for successful pertussis control.

Effects of infection and disease with Mycobacterium tuberculosis on serum antibody to glucan and arabinomannan: two surface polysaccharides of this pathogen.

BACKGROUND: The role of the surface capsular polysaccharides (CPs) of Mycobacterium tuberculosis (Mtb) in the pathogenesis of infection and disease, as well their potential for use as diagnostic reagents and vaccine antigens, are unknown. METHODS: Serum antibody to two CPs of Mtb, arabinomannan (AM) and glucan (Glu), were studied in samples from 52 18-74 year-old HIV-seronegative, immunocompetent individuals in Houston Texas. The effects of Mtb exposure, infection and disease upon the levels of antibodies to these CPs were assessed. Subjects were grouped according to the standard international classification. RESULTS: IgA anti-Glu levels were significantly higher in the active and treated TB compared to a group that was PPD-negative without TB exposure history (p<0.05). Antibodies against AM demonstrated a similar pattern, with the exception that IgG anti-AM was higher in groups who had active TB or previously documented active TB, and IgA anti-AM was higher in subjects with previously documented active TB compared to the level in an unexposed, PPD-negative group (p<0.05). Serum IgG anti-Glu levels were higher in subjects with active TB or previously documented active TB than in the unexposed PPD-negative group, but the differences were not significant. CONCLUSIONS: These data suggest that the evaluation of antibody responses to the CP of Mtb may have utility for TB serodiagnosis, and that vaccines designed to induce humoral responses to TB CPs should be tested for their capacity to evoke anti-tuberculosis protective immunity.

A human IgG anti-Vi reference for Salmonella typhi with weight-based antibody units assigned.

Recent data showing the high incidence of typhoid fever in young children, the demonstration of safety and efficacy of a Vi conjugate for this age group, the safety and similar immunogenicity in infants when administrated concurrently with EPI vaccines, together with the interests of manufacturers and investigators in studying such conjugate vaccines prompted us to prepare a human IgG anti-Vi standard to facilitate this work. Volunteers were injected with an investigational Vi-recombinant Pseudomonas aeruginosa exoprotein A (Vi-rEPA) conjugate vaccine. Plasmas with the highest levels of IgG anti-Vi were pooled. The IgG anti-Vi content of this preparation, assayed by precipitin analysis with purified Vi, was 33 µg/ml. Accordingly, the estimated IgG anti-Vi protective level of 3.5 ELISA unit/ml, derived from our efficacy trial of Vi-rEPA in 2-5 years old children, is equivalent to 4.3 µg/ml. This reagent is suitable for comparison of immune response of Vi conjugate vaccines or for other purposes requiring anti-Vi measurement.

The capsular polysaccharide and lipopolysaccharide structures of two carbapenem resistant Klebsiella pneumoniae outbreak isolates.

Carbapenem resistant Klebsiella pneumoniae (CRKP) are isolated with increasing frequency, especially from immunocompromized patients. The capsular polysaccharide (CPS) types of CPKP were not determined. Investigation of two CRKP isolates from a 2011 outbreak at the Clinical Center, the National Institutes of Health, identified a new capsular type shared by the two isolates, similar to K. pneumonia K19 and K34 but structurally different than any published K. pneumoniae CPS repeating unit: The LPS of the two isolates was found to have no O-specific polysaccharide and the chemical structure of the core oligosaccharides agreed with the published data. If this structure type will be prevalent among CPKP isolates, our findings could facilitate rapid diagnosis and help to develop new therapeutic solutions to this antibiotic resistant pathogen.

Synthetic oligosaccharides as tools to demonstrate cross-reactivity between polysaccharide antigens.

Escherichia coli O148 is a nonencapsulated enterotoxigenic (ETEC) Gram negative bacterium that can cause diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome in humans. The surface-exposed O-specific polysaccharide (O-SP) of the lipopolysaccharide of this bacterium is considered both a virulence factor and a protective antigen. It is built up of the linear tetrasaccharide repeating unit [3)-α-L-Rhap-(1→2)-α-D-Glcp-(1→3)-α-D-GlcNAcp-(1→3)-α-L-Rhap-(1→] differing from that of the O-SP of Shigella dysenteriae type 1 (SD) only in that the latter contains a D-Galp residue in place of the glucose moiety of the former. The close similarity of the O-SPs of these bacteria indicated a possible cross-reactivity. To answer this question we synthesized several oligosaccharide fragments of E. coli O148 O-SP, up to a dodecasaccharide, as well as their bovine serum albumin or recombinant diphtheria toxin conjugates. Immunization of mice with these conjugates induced anti-O-SP-specific serum IgG antibody responses. The antisera reacted equally well with the LPSs of both bacteria, indicating cross-reactivity between the SD and E. coli O148 O-SPs that was further supported by Western-blot and dot-blot analyses, as well as by inhibition of binding between the antisera and the O-SPs of both bacteria.

Measurement of Haemophilus influenzae type a capsular polysaccharide antibodies in cord blood sera.

We measured anti-Haemophilus influenzae type a capsular polysaccharide serum immunoglobulin G antibodies in cord blood sera from Mexican (n = 68) and Chilean mothers (n = 72) by enzyme-linked immunosorbent assay. Measurable antibodies were found in 79.3% of samples. Immunoglobulin G antibodies correlated with serum bactericidal activity (r = 0.66). This enzyme-linked immunosorbent assay can be used for the evaluation of adaptive immune responses to Haemophilus influenzae type a and serosurveillance studies in populations at risk.

Phase 1 study of a recombinant mutant protective antigen of Bacillus anthracis.

A phase 1 study of a recombinant mutant protective antigen (rPA) vaccine was conducted in 186 healthy adults aged 18 to 45 years. Volunteers were randomized to receive one of three formulations of rPA (formalin treated, alum adsorbed, or both), in 10- or 20-µg dosages each, or the licensed vaccine, AVA. Three injections were given at 2-month intervals and a 4th 1 year after the 3rd. Vaccinees were examined at the clinic once following each injection, at 48 to 72 h postinjection. Adverse reactions were recorded in diaries for 7 days. Sera were collected before each injection and 1 week after the 1st, 2 weeks after the 3rd and 4th, and 1 year after the 4th. Serum anti-PA IgG was assayed by enzyme-linked immunosorbent assay (ELISA) and toxin neutralization assay (TNA). All formulations at both dosages were safe and immunogenic, inducing booster responses, with the highest antibody levels following the 4th injection (354 to 732 µg/ml). The lowest levels were induced by the formalin-only-treated rPA; there was no statistical difference between levels induced by alum-adsorbed and formalin-treated/alum-adsorbed rPA or by the two dosages. The antibody levels declined in all groups during the 1-year intervals after the 3rd and 4th injections but less so during the 2nd year, after the 4th injection (fold decreases were 10 to 25 versus 3.4 to 7.0, P < 0.001). There were too few AVA recipients for statistical comparisons, but their antibody levels followed those of rPA. Anti-rPA measured by ELISA correlated with TNA titers (r = 0.97). These data support studying alum-adsorbed rPA in children.

Capsular polysaccharide vaccine for Group B Neisseria meningitidis, Escherichia coli K1, and Pasteurella haemolytica A2.

We reviewed the literature that is the basis for our proposal that (2→8)-α-Neu5Ac conjugates will be safe and effective vaccines for Group B meningococci (GBMs), Escherichia coli K1, and Pasteurella haemolytica A2. Although (2→8)-α-Neu5Ac is a virulence factor and a protective antigen of these three pathogens, it is also a component of normal tissues (neural cell adhesion molecule). Natural, anti-(2→8)-α-Neu5Ac present in most adults, vaccine-induced antibodies, and even high levels of spontaneously appearing monoclonal anti-(2→8)-α-Neu5Ac did not cause autoimmunity. Although it is not possible to prove a null hypothesis, there are no epidemiologic, serologic, immunologic, or clinical data to indicate that (2→8)-α-Neu5Ac antibodies will induce pathology or an autoimmune disease. No increased pathology caused by these antibodies was found, even in neonates and infants of mothers recovered from GBM meningitis. The lack of pathology mediated by anti-(2→8)-α-Neu5Ac may be explained by different presentations of (2→8)-α-Neu5Ac on bacterial and mammalian cells and by the unusual physicochemical properties of anti-(2→8)-α-Neu5Ac. Based on clinical and experimental data collected over 30 y and because (2→8)-α-Neu5Ac is an essential virulence factor and a protective antigen for GBM, E. coli K1, and P. haemolytica A2, protein conjugates of it are easy to prepare using inexpensive and plentiful ingredients, and they would be compatible with routinely administered infant vaccines, clinical studies of these conjugates should proceed.

Comparative long-term adverse effects elicited by invasive group B and C meningococcal infections.

BACKGROUND: Given the identity between Neisseria meningitidis serogroup B (MenB) capsular polysaccharide (polysialic acid; PSA) and PSA found on neural cell adhesion molecules, it has been proposed that infection with MenB or vaccination with PSA may be associated with subsequent autoimmune or neurological disease. METHODS: We conducted 2 studies. The first was a retrospective nationwide study of invasive meningococcal disease (IMD) in Iceland (with 541 subjects) during the period 1975-2004, and we cross referenced this cohort with databases with respect to subsequent diagnosis of autoimmune disorders. A follow-up study involving 120 survivors of IMD was performed. The study included 70 patients with a history of MenB and 50 patients with N. meningitidis serogroup C (MenC) infection, who served as control subjects. Participants answered standardized questionnaires (Beck's Depression Inventory [BDI] II, Depression Anxiety Stress Scales [DASS], and Patient Health Questionnaire [PHQ]), and serum levels of immunoglobulin (Ig) G against MenB and MenC capsular polysaccharides were measured. RESULTS: The nationwide cohort had 9166 patient-years of follow up. No evidence of increased autoimmunity was found to be associated with MenB, compared with MenC. In the follow-up study, patients were evaluated 16.6 years after the infection, representing 2022 patient-years of observation. Comparable rates of most complications were recorded, but MenC infections were associated with arthritis (P = .008) and migraine headaches (P = .01) more frequently than were MenB infections. No difference was observed with respect to scores on BDI-II, DASS, or PHQ. IgG anti-MenB and anti-MenC capsular polysaccharide levels were not related to patient complaints. CONCLUSIONS: This study does not support the hypothesis that MenB infection may predispose to autoimmunity. MenC infections are associated with a higher prevalence of arthritis and migraine headaches. No evidence of antibody-associated pathology was detected at long-term follow-up.

Synthesis and antigenicity of BBGL-2 glycolipids of Borrelia burgdorferi, the causative agent of Lyme disease.

Borrelia burgdorferi is the etiological agent for Lyme disease (LD), the most common vector borne disease in the United States. There is no human vaccine against LD currently available. Our approach to a vaccine is based on its surface-exposed glycolipids. One group of these glycolipids termed BBGL-2 consists of 1,2-di-O-acyl-3-O-(α-d-galactopyranosyl)-sn-glycerol congeners having palmitic, oleic, stearic, linoleic, and myristic acids. In order to delineate the immunodominant region(s) of the BBGL-2 components, we embarked on a synthetic project to provide available structurally defined, homogeneous analogs of BBGL-2 that might help identify the best vaccine candidate. The antigenicity of the synthetic glycolipids was examined by dot-blot analysis using mice sera obtained by immunization with killed B. burgdorferi cells, with native BBGL-2 in complete Freund's adjuvant, as well as sera obtained from patients with Lyme disease. We found that the presence of two acyl groups in the glycerol moiety was essential for antigenicity. At least one of these groups must be an oleoyl moiety. Neither the anomeric configuration of the galactose nor the configuration of the glycerol at C-2 was a decisive factor. Based on these findings we designed an 'unnatural' BBGL-2 analog having the structure 3-O-(ß-d-galactopyranosyl)-1,2-di-O-oleoyl-dl-glycerol which is easier and less expensive to synthesize than the other BBGL-2 congeners prepared in this study. This substance proved to be antigenic and is considered a candidate vaccine for Lyme disease.

Assessment of intrapartum antibiotic prophylaxis for the prevention of early-onset group B Streptococcal disease.

BACKGROUND: Most early-onset group B streptococcal (GBS) disease in recent years has occurred in newborns of prenatally GBS-negative mothers who missed intrapartum antibiotic prophylaxis (IAP). We aimed to assess the accuracy of prenatal culture in predicting GBS carriage during labor, the IAP use, and occurrence of early-onset GBS disease. METHODS: We obtained vaginal-rectal swabs at labor for GBS culture from 5497 women of ≥ 32 weeks' gestation and surface cultures at birth from newborns between February 5, 2008 and February 4, 2009 at 3 hospitals in Houston, TX and Oakland, CA. Prenatal cultures were performed by a healthcare provider during routine care, and culture results were obtained from medical records. The accuracy of prenatal culture in predicting intrapartum GBS carriage was assessed by positive and negative predictive values. Mother-to-newborn transmission of GBS was assessed. Newborns were monitored for early-onset GBS disease. RESULTS: GBS carriage was 24.5% by prenatal and 18.8% by labor cultures. Comparing prenatal with labor GBS cultures of 4696 women, the positive predictive value was 50.5% and negative predictive value was 91.7%. IAP, administered to 93.3% of prenatally GBS-positive women, was 83.7% effective in preventing newborn's GBS colonization. Mother-to-newborn transmission of GBS occurred in 2.6% of elective cesarean deliveries. Two newborns developed early-onset GBS disease (0.36/1000 births); the prenatal GBS culture of one was negative, the other's was unknown. CONCLUSIONS: IAP was effective in interrupting mother-to-newborn transmission of GBS. However, approximately 10% of prenatally GBS-negative women were positive during labor and missed IAP, whereas approximately 50% of prenatally GBS-positive women were negative during labor and received IAP. These findings emphasize the need for rapid diagnostics during labor.

Oligosaccharide conjugates of Bordetella pertussis and bronchiseptica induce bactericidal antibodies, an addition to pertussis vaccine.

Pertussis is a highly contagious respiratory disease that is especially dangerous for infants and children. Despite mass vaccination, reported pertussis cases have increased in the United States and other parts of the world, probably because of increased awareness, improved diagnostic means, and waning vaccine-induced immunity among adolescents and adults. Licensed vaccines do not kill the organism directly; the addition of a component inducing bactericidal antibodies would improve vaccine efficacy. We investigated Bordetella pertussis and Bordetella bronchiseptica LPS-derived core oligosaccharide (OS) protein conjugates for their immunogenicity in mice. B. pertussis and B. bronchiseptica core OS were bound to aminooxylated BSA via their terminal Kdo residues. The two conjugates induced similar anti-B. pertussis LPS IgG levels in mice. B. bronchiseptica was investigated because it is easier to grow than B. pertussis. Using B. bronchiseptica genetically modified strains deficient in the O-specific polysaccharide, we isolated fractions of core OS with one to five repeats of the terminal trisaccharide, having at the nonreducing end a GlcNAc or GalNAc, and bound them to BSA at different densities. The highest antibody levels in mice were elicited by conjugates containing an average of 8-17 OS chains per protein and with one repeat of the terminal trisaccharide. Conjugate-induced antisera were bactericidal against B. pertussis, and the titers correlated with ELISA-measured antibody levels (r = 0.74). Such conjugates are easy to prepare and standardize; added to a recombinant pertussis toxoid, they may induce antibacterial and antitoxin immunity.

The Vi conjugate typhoid vaccine is safe, elicits protective levels of IgG anti-Vi, and is compatible with routine infant vaccines.

Typhoid fever remains a serious problem in developing countries. Current vaccines are licensed for individuals who are 5 years old or older. A conjugate of the capsular polysaccharide (CP) of Salmonella enterica serovar Typhi (Vi) bound to recombinant exoprotein A of Pseudomonas aeruginosa (Vi-rEPA) enhanced Vi immunogenicity and protected 2- to 5-year-olds in Vietnam. In this study, Vi-rEPA was evaluated for use in infants. A total of 301 full-term Vietnamese infants received Expanded Program on Immunization (EPI) vaccines alone or with Vi-rEPA or Haemophilus influenzae type b-tetanus toxoid conjugate (Hib-TT) at 2, 4, and 6 months and Vi-rEPA or Hib-TT alone at 12 months. Infants were visited 6, 24, and 48 h after each injection to monitor adverse reactions. Maternal, cord, and infant sera were assayed for IgG anti-Vi and for IgG antibodies to Hib CP and the diphtheria, tetanus, and pertussis toxins at 7, 12, and 13 months. No vaccine-related serious adverse reactions occurred. In the Vi-rEPA group, the IgG anti-Vi geometric mean (GM) increased from the cord level of 0.66 to 17.4 enzyme-linked immunosorbent assay units (EU) at 7 months, declined to 4.76 EU at 12 months, and increased to 50.1 EU 1 month after the 4th dose (95% of infants had levels of ≥ 3.5 EU, the estimated protective level). Controls had no increase of the IgG anti-Vi GM. Infants with cord anti-Vi levels of <3.5 EU responded with significantly higher IgG anti-Vi levels than those with levels of ≥ 3.5 EU. Anti-diphtheria, -tetanus, and -pertussis toxin levels were similar in all groups. Vi-rEPA was safe, induced protective anti-Vi levels, and was compatible with EPI vaccines, and it can be used in infants. High cord IgG anti-Vi levels partially suppressed infant responses to Vi-rEPA.

Evaluation of serum bactericidal antibody assays for Haemophilus influenzae serotype a.

Haemophilus influenzae type a (Hia) is an important pathogen for some American Indian, Alaskan native, and Northern Canada aboriginal populations. Assays to measure serum bactericidal activity (SBA) to Hia have not been developed or validated. Here, we describe two methods for the measurement of SBA: SBA with a viability endpoint (CFU counts) and SBA with a fluorometric endpoint using alamarBlue as the metabolic indicator. Both SBA assays measure Hia-specific functional antibody and correlate with anti-Hia IgG enzyme-linked immunosorbent assay (ELISA) concentration of naturally acquired antibodies.

Pre- and postexposure protection against virulent anthrax infection in mice by humanized monoclonal antibodies to Bacillus anthracis capsule.

One of the two essential virulence factors of Bacillus anthracis is the poly-γ-D-glutamic acid (γDPGA) capsule. Five γDPGA-specific antibody antigen-binding fragments (Fabs) were generated from immunized chimpanzees. The two selected for further study, Fabs 11D and 4C, were both converted into full-length IgG1 and IgG3 mAbs having human IgG1 or IgG3 constant regions. These two mAbs had similar binding affinities, in vitro opsonophagocytic activities, and in vivo efficacies, with the IgG1 and IgG3 subclasses reacting similarly. The mAbs bound to γDPGA specifically with estimated binding affinities (K(d)) of 35-70 nM and effective affinities (effective K(d)) of 0.1-0.3 nM. The LD(50) in an opsonophagocytic bactericidal assay was ≈10 ng/mL of 11D or 4C. A single 30-µg dose of either mAb given to BALB/c mice 18 h before challenge conferred about 50% protection against a lethal intratracheal spore challenge by the virulent B. anthracis Ames strain. More importantly, either mAb given 8 h or 20 h after challenge provided significant protection against lethal infection. Thus, these anti-γDPGA mAbs should be useful, alone or in combination with antitoxin mAbs, for achieving a safe and efficacious postexposure therapy for anthrax.