anti-PA IgG Antibody Research Articles

Human Exposure to Naturally Occurring Bacillus anthracis in the Kars Region of Eastern Türkiye.

Environmental contamination with Bacillus anthracis spores poses uncertain threats to human health. We undertook a study to determine whether inhabitants of the anthrax-endemic region of Kars in eastern Türkiye could develop immune responses to anthrax toxins without recognised clinical infection. We measured anti-PA and anti-LF IgG antibody concentrations by ELISA in serum from 279 volunteers, 105 of whom had previously diagnosed anthrax infection (100 cutaneous, 5 gastrointestinal). Of the 174 without history of infection, 72 had prior contact with anthrax-contaminated material. Individuals were classified according to demographic parameters, daily working environment, and residence type. All villages in this study had recorded previous animal or human anthrax cases. Stepwise regression analyses showed that prior clinical infection correlated strongly with concentrations at the upper end of the ranges observed for both antibodies. For anti-PA, being a butcher and duration of continuous exposure risk correlated with high concentrations, while being a veterinarian or shepherd, time since infection, and town residence correlated with low concentrations. For anti-LF, village residence correlated with high concentrations, while infection limited to fingers or thumbs correlated with low concentrations. Linear discriminant analysis identified antibody concentration profiles associated with known prior infection. Profiles least typical of prior infection were observed in urban dwellers with known previous infection and in veterinarians without history of infection. Four individuals without history of infection (two butchers, two rural dwellers) had profiles suggesting unrecognised prior infection. Healthy humans therefore appear able to tolerate low-level exposure to environmental B. anthracis spores without ill effect, but it remains to be determined whether this exposure is protective. These findings have implications for authorities tasked with reducing the risk posed to human health by spore-contaminated materials and environments.

Detecting specific memory t and b cells in volunteers annually revaccinated with live anthrax vaccine

Currently, live anthrax vaccine has been used for vaccine prophylaxis in Russia and neighbor countries for seve ral decades, but precise mechanism of post-vaccination protection mechanism remains unclear. Here, we provide data on examining serum antibody level against protective antigen (PA) and lethal factor (LF) in repeatedly vaccinated volun teers at early stage (5–8 days) and 1 month after the performing pre-scheduled annual revaccination. Amount of peripheral blood antigen-specific memory T cells after previous vaccinations was analyzed. It was showed that frequency of CD3+CD45RO+CD62L– memory effector T cells was increased in the majority of volunteers on day 5-8 day after performing pre-scheduled annual revaccination that peaked at day 7 by elevating it by 2-fold compared with the control group. Percentage of anthrax-specific central memory T cells did not increase at early stage after vaccination, whereas amount of activated CD3+CD45RO+CD62L+HLA-DR+ subset within this memory T cell population was increased. Likewise, percentage of activated CD3+CD45RO+CD62L–HLA-DR+ effector memory T cell subset was also increased. Moreover, serum anti-PA IgG were detected on day 5–8 day after pre-scheduled annual revaccination in half of volunteers, whereas anti-LF IgG were found only in a single volunteer. Rapidly elevated amount of serum anthrax-specific IgG antibodies evidences about sustained memory B cell response in peripheral blood samples in volunteers after pre-scheduled annual revaccination. However, percentage of CD19+CD27+ memory B cells was not significantly elevated at early stage after revaccination that tended to increase. Both helper and cytotoxic T cell subsets were activated on day 5–8 after revaccination revealed by upregulated expression of CD69 and/or CD25 markers, with the latter predominantly found on helper T cells, thereby accounting for their high proliferative activity, whereas the former — on cytotoxic T cell subsets. Detection of anti-PA IgG antibodies correlates with protection against anthrax, which was confirmed in animal models. Unfortunately, the level of serum anti-PA IgG antibodies rapidly declines after vaccination. Ability of memory B cells to rapidly trigger production of anthrax-specific antibodies in response to revaccination suggests that anti-anthrax immunity may be evaluated by measuring frequency of peripheral blood anthrax-specific memory B and T cells.

Self-conjugated protective antigen elicits strong and durable protective antibody response against anthrax

Anthrax is an acute and highly lethal disease caused by Bacillus anthracis. Protective antigen (PA) is the primary candidate antigen for the anthrax vaccines. However, PA suffers from poor immunogenicity with short-term anti-PA antibody response. High effectiveness, durable immunity, and minimal risk are required for development of an effective anthrax vaccine. In the present study, PA was self-conjugated by 8-arm polyethylene glycol (PEG) and further by thioester chemistry. As a result, 3–5 PA molecules were covalently conjugated and functioned as an antigen delivery system. The conjugate (PA-PEG) could maintain the structural properties of PA and increase the thermal stability of PA. PA-PEG could elicit a robust anti-PA IgG and neutralization antibody response in the magnitude and quality. The antibodies could be largely maintained for 180 days after three immunizations of PA-PEG. PA-PEG effectively stimulated the maturation of dendritic cell and rapidly induced the germinal center (GC) reaction. The percentages of the GC B-cells and T follicular helper (Tfh) cells were thus significantly augmented. The inflammatory response elicited by PA-PEG was comparable to those by PBS and PA. Therefore, PA-PEG is expected as an effective anthrax vaccine candidate with durable immunoprotection against anthrax.

Role of the Antigen Capture Pathway in the Induction of a Neutralizing Antibody Response to Anthrax Protective Antigen.

ABSTRACTToxin neutralizing antibodies represent the major mode of protective immunity against a number of toxin-mediated bacterial diseases, including anthrax; however, the cellular mechanisms that lead to optimal neutralizing antibody responses remain ill defined. Here we show that the cellular binding pathway of anthrax protective antigen (PA), the binding component of anthrax toxin, determines the toxin neutralizing antibody response to this antigen. PA, which binds cellular receptors and efficiently enters antigen-presenting cells by receptor-mediated endocytosis, was found to elicit robust anti-PA IgG and toxin neutralizing antibody responses. In contrast, a receptor binding-deficient mutant of PA, which does not bind receptors and only inefficiently enters antigen-presenting cells by macropinocytosis, elicited very poor antibody responses. A chimeric protein consisting of the receptor binding-deficient PA mutant tethered to the binding subunit of cholera toxin, which efficiently enters cells using the cholera toxin receptor rather than the PA receptor, elicited an anti-PA IgG antibody response similar to that elicited by wild-type PA; however, the chimeric protein elicited a poor toxin neutralizing antibody response. Taken together, our results demonstrate that the antigen capture pathway can dictate the magnitudes of the total IgG and toxin neutralizing antibody responses to PA as well as the ratio of the two responses.

The Fluorocycline TP-271 Is Efficacious in Models of Aerosolized Bacillus anthracis Infection in BALB/c Mice and Cynomolgus Macaques.

The fluorocycline TP-271 was evaluated in mouse and nonhuman primate (NHP) models of inhalational anthrax. BALB/c mice were exposed by nose-only aerosol to Bacillus anthracis Ames spores at a level of 18 to 88 lethal doses sufficient to kill 50% of exposed individuals (LD50). When 21 days of once-daily dosing was initiated at 24 h postchallenge (the postexposure prophylaxis [PEP] study), the rates of survival for the groups treated with TP-271 at 3, 6, 12, and 18 mg/kg of body weight were 90%, 95%, 95%, and 84%, respectively. When 21 days of dosing was initiated at 48 h postchallenge (the treatment [Tx] study), the rates of survival for the groups treated with TP-271 at 6, 12, and 18 mg/kg TP-271 were 100%, 91%, and 81%, respectively. No deaths of TP-271-treated mice occurred during the 39-day posttreatment observation period. In the NHP model, cynomolgus macaques received an average dose of 197 LD50 of B. anthracis Ames spore equivalents using a head-only inhalation exposure chamber, and once-daily treatment of 1 mg/kg TP-271 lasting for 14 or 21 days was initiated within 3 h of detection of protective antigen (PA) in the blood. No (0/8) animals in the vehicle control-treated group survived, whereas all 8 infected macaques treated for 21 days and 4 of 6 macaques in the 14-day treatment group survived to the end of the study (56 days postchallenge). All survivors developed toxin-neutralizing and anti-PA IgG antibodies, indicating an immunologic response. On the basis of the results obtained with the mouse and NHP models, TP-271 shows promise as a countermeasure for the treatment of inhalational anthrax.

Anti-Pseudomonas aeruginosa IgG antibodies and chronic airway infection in bronchiectasis

BackgroundIdentification of chronic Pseudomonas aeruginosa (PA) infection is important in the management of bronchiectasis, but requires repeated sputum sampling. We hypothesized that serum anti-PA IgG antibodies could diagnose chronic PA infection at a single visit. MethodsClinically stable bronchiectasis patients were studied prospectively. Chronic PA infection was defined as 2 or more positive sputum samples at least 3 months apart and/or failure to clear PA following eradication treatment. Baseline serum anti-PA IgG was determined by a validated ELISA kit. ResultsA total of 408 patients were included. Sixty of them (14.7%) had chronic PA infection and had higher anti-PA IgG levels (median 6.2 vs. 1.3 units, p < 0.001). Antibody levels showed direct significant correlations with exacerbation frequency, the bronchiectasis severity index and sputum inflammatory markers. Fifty-seven patients with chronic PA infection had a positive test, giving 95% sensitivity, 74.4% specificity and AUROC of 0.87. During follow-up, 38 patients had a new PA isolation. Eradication at 12 months was achieved in 89.5% of subjects with a negative antibody test and 15.8% of patients with a positive test. ConclusionsAnti-PA IgG test is highly accurate to detect chronic PA infection in bronchiectasis patients. In addition, it may be a marker of disease severity and treatment response.

Dissociation between anti-porcine albumin and anti-Gal antibody responses in non-human primate recipients of intraportal porcine islet transplantation.

To understand humoral responses elicited after xenotransplantation, we compared the induction of anti-non-Gal antibodies vs. anti-Gal antibodies in non-human primates (NHPs) after intraportal porcine islet transplantation (PITX). Anti-Gal and anti-non-Gal IgGs were analyzed in serial plasma samples of NHP recipients after PITX by enzyme-linked immunosorbent assay (ELISA) using synthetic Gal and by flow cytometry using α-1,3-galactosyltransferase gene knockout (GTKO) porcine endothelial cells, respectively. Anti-non-Gal IgG was detected in some recipients after PITX. The specificity of anti-non-Gal IgG was investigated by two-dimensional electrophoresis of the protein extract from GTKO porcine endothelial cells, Western blot analysis of recipient pre- and post-PITX plasma, and MALDI-TOF/TOF mass spectrometry, revealing albumin, a non-glycosylated protein in the serum supplement of the islets solution, as a putative antigen for anti-non-Gal IgG. The binding of IgG antibodies to human albumin (HA), bovine albumin (BA), porcine albumin (PA), and Gal was compared by ELISA in pre- and post-PITX plasma samples of 30 NHP recipients subjected to intraportal PITX, which were grouped according to the use of CD40-CD154 blockade and sirolimus. One of the immunoblot-matched spots was identified as BA by mass spectrometry. By ELISA, the plasma used in the immunoblot analysis revealed strong IgG binding to BA and PA, but not to HA. Anti-PA, anti-BA, and anti-Gal antibodies in NHP recipients 1 month after PITX were detected in 5 (100%), 3 (60%), and 5 (100%), respectively, of the 5 recipients receiving various immunosuppression (IS) without CD40-CD154 blockade (group I) and in 0 (0%), 0 (0%), and 4 (16%), respectively, of the 25 recipients receiving IS with CD40-CD154 blockade and sirolimus (group II). This finding revealed significant differences between the groups (P < 0.0001, P = 0.0011 and P = 0.0013, respectively). Interestingly, among 15 recipients achieving graft survival longer than 1 month in group II, anti-PA IgG was detected in only 1 recipient (6.7%) 180 days after PITX. However, an increase in anti-Gal IgG was detected in 7 recipients (46.7%) despite maintenance IS with anti-CD154 and sirolimus. This result indicates that anti-Gal IgG is more frequently induced than anti-PA IgG (P = 0.0352). Moreover, induction IS with anti-CD154 and sirolimus suppressed anti-Gal IgG, but not anti-PA and anti-BA IgG, responses in sensitized recipients given a repeat transplantation. In NHP recipients of PITX, anti-PA and anti-BA IgG antibodies are elicited by porcine serum included as a supplement in porcine islet preparation. IS including CD40-CD154 blockade and sirolimus suppresses these antibody responses in naïve recipients, but not in sensitized recipients. The elicitation of anti-xenogenic albumin antibodies, a humoral response to a model protein antigen, is distinct from that of anti-Gal antibodies, a response to carbohydrate antigen.

Immunogenicity and safety of four different dosing regimens of anthrax vaccine adsorbed for post-exposure prophylaxis for anthrax in adults

BackgroundStrategies to implement post exposure prophylaxis (PEP) in case of an anthrax bioterror event are needed. To increase the number of doses of vaccine available we evaluated reducing the amount of vaccine administered at each of the vaccinations, and reducing the number of doses administered. MethodsHealthy male and non-pregnant female subjects between the ages of 18 and 65 were enrolled and randomized 1:1:1:1 to one of four study arms to receive 0.5mL (standard dose) of vaccine subcutaneously (SQ) at: (A) days 0, 14; (B) days 0 and 28; (C) days 0, 14, and 28; or (D) 0.25mL at days 0, 14, and 28. A booster was provided on day 180. Safety was assessed after each dose. Blood was obtained on days 0, 7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 84, 100, 180, and 201 and both Toxin Neutralizing antibody and anti-PA IgG antibody measured. ResultsAlmost all subjects developed some local reactions with 46–64% reported to be of moderate severity and 3.3% severe during the primary series. Vaccine groups that included a day 14 dose induced a ≥4 fold antibody rise in more subjects on days 21, 28, and 35 than the arm without a day 14 dose. However, schedules with a full day 28 dose induced higher peak levels of antibody that persisted longer. The half dose regimen did not induce antibody as well as the full dose study arms. ConclusionDepending on the extent of the outbreak, effectiveness of antibiotics and availability of vaccine, the full dose 0, 28 or 0, 14, 28 schedules may have advantages.

Anthrax vaccine adsorbed: Further evidence supporting continuing the vaccination series rather than restarting the series when doses are delayed

Whether to restart or continue the series when anthrax vaccine doses are missed is a frequent medical management problem. We applied the noninferiority analysis model to this prospective study comparing the Bacillus anthracis protective antigen (PA) IgG antibody response and lethal toxin neutralization activity at day 28 to the anthrax vaccine adsorbed (AVA) (Biothrax®) administered on schedule or delayed. A total of 600 volunteers were enrolled: 354 in the on-schedule cohort; 246 in the delayed cohort. Differences were noted in immune responses between cohorts (p<0.0001) and among the racial categories (p<0.0001). Controlling for covariates, the delayed cohort was non-inferior to the on-schedule cohort for the rate of 4-fold rise in both anti-PA IgG concentration (p<0.0001) and TNA ED50 titers (p<0.0001); as well as the mean log10-transformed anti-PA IgG concentration (p<0.0001) and the mean log10-transformed TNA ED50 titers (p<0.0001). Providing a missed AVA dose after a delay as long as 5–7 years, elicits anti-PA IgG antibody and TNA ED50 responses that are robust and non-inferior to the responses observed when the 6-month dose is given on-schedule. These important data suggest it is not necessary to restart the series when doses of the anthrax vaccine are delayed as long as 5 or more years.

Increased long-term immunity to Bacillus anthracis protective antigen in mice immunized with a CIA06B-adjuvanted anthrax vaccine

Anthrax is an acute infectious disease caused by Bacillus anthracis. We previously reported that the adjuvant CIA06B, which consists of TLR4 agonist CIA05 and aluminum hydroxide (alum), enhanced the immune response to anthrax protective antigen (PA) in mice. This study was carried out to determine whether CIA06B can enhance long-term immune responses to PA in mice. BALB/c mice were immunized intramuscularly three times at 2-week intervals with recombinant PA alone or PA combined with alum or CIA06B. At 8 and 24 weeks post-immunization, the immunological responses including serum anti-PA IgG antibody titer, toxin-neutralizing antibody titer, splenic cytokine secretion and the frequency of PA-specific memory B cells were assessed. Compared with mice injected with PA alone or PA plus alum, mice injected with PA plus CIA06B had higher titers of serum anti-PA IgG antibodies, and higher frequencies of PA-specific memory B cells and interferon-γ secreting cells. Furthermore, anti-PA antibodies induced by CIA06B were more effective in neutralizing anthrax toxin. These results demonstrated that CIA06B is capable of providing long-term immunity when used as an adjuvant in a PA-based anthrax vaccine.

A combination of the TLR4 agonist CIA05 and alum promotes the immune responses to Bacillus anthracis protective antigen in mice

Anthrax is an infectious disease caused by Bacillus anthracis. The currently licensed human anthrax vaccines contain protective antigen (PA) as a major protective component and alum as an adjuvant. In this study, we investigated whether CIA05, a TLR4 agonist, is able to promote the immune response to an anthrax vaccine adjuvanted with alum. BALB/c mice were immunized intraperitoneally three times at 2-week intervals with a recombinant B. anthracis PA alone or in combination with CIA05 in the absence or presence of alum, and immune responses were determined 2 or 3weeks after the third immunization. The results showed that the combination of CIA05 and alum significantly increased both serum anti-PA IgG antibody and toxin-neutralizing antibody titers, and the adjuvant effects were greater when lower antigen doses were used for immunization. Both CIA05 and alum stimulated PA-specific splenocyte secretion of interleukin (IL)-4, IL-5, and IL-6. A combination of the two yielded synergistic effects on IL-4 secretion, but CIA05 tended to repress IL-5 and IL-6 secretions induced by alum. Co-administration of CIA05 and alum also increased GL7 expression in B220+CD24+ splenic cells, indicating the ability to activate B cells. These data suggest that CIA05, combined with alum, could be used to achieve higher immune responses to PA, leading to the development of an effective anthrax vaccine.

Efficacy of recombinant anthrax vaccine against Bacillus anthracis aerosol spore challenge: Preclinical evaluation in rabbits and Rhesus monkeys

This report describes the immunogenicity and protective efficacy of Escherichia coli-expressed recombinant protective antigen (rPA) in New Zealand White rabbits and Rhesus Macaques against an aerosol challenge with Bacillus anthracis spores (IVRI strain, tox+cap+). A dose-ranging study was performed in which it became evident that the level of anti-PA IgG and toxin-neutralizing antibody titer was directly proportional to the dose of rPA administered. However, the onset time of primary and secondary immune response was not dependent on the dosage. Revaccination of primed animals with the same threshold dose yielded a robust and rapid secondary response. Quantitative differences in peak titers were obtained for both the animal models, in addition to qualitative differences in the immune kinetics. In spite of a weak priming response, the secondary response in rabbits peaked earlier than that in macaques once the booster dose was administered. However, evaluation of the post-challenge quantitative anti-rPA ELISA titer measurements indicated higher titers for non-human primates as compared to the lagomorphs. Importantly, 100% protection was seen for the dosage groups that received > or = 25 microg rPA, following a challenge against a target dose of 1000 LD(50) of aerosolized spores of Bacillus anthracis.

Enhancement of the immune responses of mice to Bacillus anthracis protective antigen by CIA07 combined with alum

Anthrax is an acute zoonotic disease caused by infection with Bacillus anthracis. B. anthracis spores are highly resistant to environmental degradation and are used as a biological weapon. In this study, we investigated the adjuvant activity of CIA07 to anthrax protective antigen (PA). A/J mice were immunized intraperitoneally once, or twice with a 4-week interval, with recombinant PA alone or combined with alum, CpG1826, or CIA07 as adjuvant, and serum anti-PA IgG antibody responses were measured 4 weeks after each immunization. All three adjuvants significantly enhanced anti-PA IgG antibody titer 4 weeks after the priming and boosting immunizations, and alum gave the highest titer. In order to evaluate the adjuvant activity of CIA07 in the presence of alum, Balb/c mice were immunized 3 times at 1-week intervals with PA in combination with alum, CIA07 or alum plus CIA07, and the immune responses were assessed 2 weeks after the third immunization. The serum anti-PA IgG antibody titer of the CIA07-treated group was 14-fold higher than the group given PA alone, and the coadministration of CIA07 with alum further increased the titer 3.5-fold (P < 0.05). The toxin neutralizing activity of the sera from the mice given the combination of CIA07 and alum was 109-times higher than the animals given PA alone. The mice given CIA07 plus alum also showed a marked increase in the number of IFN-gamma-, IL-2-, and IL-4-producing CD4(+) T cells among their splenocytes. These data suggest the potential of CIA07 in combination with alum as an adjuvant for the development of a potent anthrax vaccine.

Potentiation of an anthrax DNA vaccine with electroporation

DNA vaccines are a promising method of immunization against biothreats and emerging infections because they are relatively easy to design, manufacture, store and distribute. However, immunization with DNA vaccines using conventional delivery methods often fails to induce consistent, robust immune responses, especially in species larger than the mouse. Intramuscular (i.m.) delivery of a plasmid encoding anthrax toxin protective antigen (PA) using electroporation (EP), a potent DNA delivery method, rapidly induced anti-PA IgG and toxin neutralizing antibodies within 2 weeks following a single immunization in multiple experimental species. The delivery procedure is particularly dose efficient and thus favorable for achieving target levels of response following vaccine administration in humans. These results suggest that EP may be a valuable platform technology for the delivery of DNA vaccines against anthrax and other biothreat agents.

PLGA-dendron nanoparticles enhance immunogenicity but not lethal antibody production of a DNA vaccine against anthrax in mice

Dendriplexes, complexes of dendrons and condensed plasmids containing the gene for protective antigen (PA) of Bacillus anthracis, were encapsulated in poly-lactide- co-glycolide (PLGA) particles using the double emulsion method. The two dendrons employed are a dendron with three C 18 chains (C 18 dendron) and one with no attached hydrocarbon chains (the C 0 dendron). Three types of particles were examined, namely PLGA-C 18 dendriplexes, PLGA-C 0 dendriplexes and the control PLGA-naked DNA system. These were characterised by standard biophysical methods such as photon correlation spectroscopy (PCS) and scanning electron microscopy to select the complexes for in vivo testing. Three intramuscular immunizations were carried out using 14 μg of DNA per dose at weekly intervals in BALB/c mice. Antibodies against rPA were measured using ELISA. Results indicate that the PLGA-C 18 dendriplex particles produced superior levels of anti-PA IgG antibodies in comparison to animals immunized with the PLGA-C 0 dendriplex particles. The level of antibody production was dependent on the number of immunizations, higher antibody levels being measured after two booster vaccinations. However toxin neutralizing antibodies were absent in all treatment groups, and it is likely that the mice lack protection against lethal toxin and anthrax infection. Further studies are needed to optimize the formulation of DNA vaccines and increase the level of anti-lethal toxin antibodies and enhance their functionality.

Comparative vaccine efficacy of different isoforms of recombinant protective antigen against Bacillus anthracis spore challenge in rabbits

The next-generation human anthrax vaccine developed by the United States Army Medical Research Institute of Infectious Diseases (USAMRIID) is based upon purified Bacillus anthracis recombinant protective antigen (rPA) adsorbed to aluminum hydroxide adjuvant (Alhydrogel). In addition to being safe, and effective, it is important that such a vaccine be fully characterized. Four major protein isoforms detected in purified rPA by native PAGE during research and development were reduced to two primary isoforms in bulk material produced by an improved process performed under Good Manufacturing Practices (GMP). Analysis of both rPA preparations by a protein-isoaspartyl-methyl-transferase assay (PIMT) revealed the presence of increasing amounts of iso-aspartic acid correlating with isoform content and suggesting deamidation as the source of rPA charge heterogeneity. Additional purification of GMP rPA by anion exchange chromatography separated and enriched the two principal isoforms. The in vitro and in vivo biological activities of each isoform were measured in comparison to the whole GMP preparation. There was no significant difference in the biological activity of each isoform compared to GMP rPA when analyzed in the presence of lethal factor using a macrophage lysis assay. Vaccination with the two individual isoforms revealed no differences in cytotoxicity neutralization antibody titers when compared to the GMP preparation although one isoform induced more anti-PA IgG antibody than the GMP material. Most importantly, each of the two isoforms as well as the whole GMP preparation protected 90–100% of rabbits challenged parenterally with 129 LD 50 of B. anthracis Ames spores. The equivalent biological activity and vaccine efficacy of the two isoforms suggests that further processing to separate isoforms is unnecessary for continued testing of this next-generation anthrax vaccine.

Determination of serum IgG antibodies to Bacillus anthracis protective antigen in environmental sampling workers using a fluorescent covalent microsphere immunoassay

Aims: To evaluate potential exposure to Bacillis anthracis (Ba) spores in sampling/decontamination workers in the aftermath of an anthrax terror attack. Methods: Fifty six serum samples were obtained from workers...

Anthrax vaccine: immunogenicity and safety of a dose-reduction, route-change comparison study in humans

Anthrax vaccine adsorbed (AVA), an effective countermeasure against anthrax, is administered as six subcutaneous (SQ) doses over 18 months. To optimize the vaccination schedule and route of administration, we performed a prospective pilot study comparing the use of fewer AVA doses administered intramuscularly (IM) or SQ with the current schedule and route. We enrolled 173 volunteers, randomized to seven groups, who were given AVA once IM or SQ; two doses, 2 or 4 weeks apart, IM or SQ; or six doses at 0, 2, 4 weeks and 6, 12, and 18 months (control group, licensed schedule and route). IM administration of AVA was associated with fewer injection site reactions than SQ administration. Following the first SQ dose of AVA, compared to males, females had a significantly higher rate of injection site reactions such as erythema, induration and subcutaneous nodules ( P<0.001). Reaction rates decreased with a longer dose interval between the first two doses. The peak anti-PA IgG antibody response of subjects given two doses of AVA 4 weeks apart IM or SQ was comparable to that seen among subjects who received three doses of AVA at 2-week intervals. The IM route of administering this aluminum hydroxide adsorbed vaccine is safe and has comparable peak anti-PA IgG antibody levels when two doses are administered 4 weeks apart compared to the licensed initial dose schedule of three doses administered 2 weeks apart. A large pivotal study is being planned by the Centers for Disease Control and Prevention to confirm these results.