Anthrax vaccination induced anti-lethal factor IgG: fine specificity and neutralizing capacity

The efficacy biomarker of the currently licensed anthrax vaccine (AVA) is based on quantity and neutralizing capacity of anti-protective antigen (anti-PA) antibodies. However, animal studies have demonstrated that antibodies to lethal factor (LF) can provide protection against in vivo bacterial spore challenges. Improved understanding of the fine specificities of humoral immune responses that provide optimum neutralization capacity may enhance the efficacy of future passive immune globulin preparations to treat and prevent inhalation anthrax morbidity and mortality. This study (n = 1000) was designed to identify AVA vaccinated individuals who generate neutralizing antibodies and to determine what specificities correlate with protection. The number of vaccine doses, years post vaccination, and PA titer were associated with in vitro neutralization, reinforcing previous reports. In addition, African American individuals had lower serologic neutralizing activity than European Americans, suggesting a genetic role in the generation of these neutralizing antibodies. Of the vaccinated individuals, only 69 (6.9%) had moderate levels of anti-LF IgG compared to 244 (24.4%) with low and 687 (68.7%) with extremely low levels of IgG antibodies to LF. Using overlapping decapeptide analysis, we identified six common LF antigenic regions targeted by those individuals with moderate levels of antibodies to LF and high in vitro toxin neutralizing activity. Affinity purified antibodies directed against antigenic epitopes within the PA binding and ADP-ribotransferase-like domains of LF were able to protect mice against lethal toxin challenge. Findings from these studies have important implications for vaccine design and immunotherapeutic development.     

Serological responses to Anthrax Vaccine Precipitated (AVP) increase with time interval between booster doses

We undertook a Phase 4 clinical trial to assess the effect of time interval between booster doses on serological responses to AVP. The primary objective was to evaluate responses to a single booster dose in two groups of healthy adults who had previously received a complete 4-dose primary course. Group A had received doses on schedule while Group B had not had one for ≥2 years. Secondary objectives were to evaluate the safety and tolerability of AVP booster doses, and to gain information on correlates of protection to aid future anthrax vaccine development. Blood samples were taken on Day 1 before dosing, and on Days 8, 15, 29 and 120, to measure Toxin Neutralisation Assay (TNA) NF₅₀ values and concentrations of IgG antibodies against Protective Antigen (PA), Lethal Factor (LF) and Edema Factor (EF) by ELISA.For each serological parameter, fold changes from baseline following the trial AVP dose were greater in Group B than Group A at every time-point studied. Peak responses correlated positively with time since last AVP dose (highest values being observed after intervals of ≥10 years), and negatively with number of previous doses (highest values occurring in individuals who had received a primary course only). In 2017, having reviewed these results, the Joint Committee on Vaccination and Immunisation (JCVI) updated UK anthrax vaccination guidelines, extending the interval between routine AVP boosters from one to 10 years.Booster doses of AVP induce significant IgG responses against the three anthrax toxin components, particularly PA and LF. Similarly high responses were observed in TNA, a recognised surrogate for anthrax vaccine efficacy. Analysis of the 596 TNA results showed that anti-PA and anti-LF IgG make substantial independent contributions to neutralisation of anthrax lethal toxin. AVP may therefore have advantages over anthrax vaccines that depend on generating immunity to PA alone.     

Correlation between anthrax lethal toxin neutralizing antibody levels and survival in guinea pigs and nonhuman primates vaccinated with the AV7909 anthrax vaccine candidate

The anthrax vaccine candidate AV7909 is being developed as a next generation vaccine for a post-exposure prophylaxis (PEP) indication against anthrax. AV7909 consists of the Anthrax Vaccine Adsorbed (AVA, BioThrax®) bulk drug substance adjuvanted with the immunostimulatory oligodeoxynucleotide (ODN) compound, CPG 7909. The addition of CPG 7909 to AVA enhances both the magnitude and the kinetics of antibody responses in animals and human subjects, making AV7909 a suitable next-generation vaccine for use in a PEP setting. The studies described here provide initial information on AV7909-induced toxin-neutralizing antibody (TNA) levels associated with the protection of animals from lethal Bacillus anthracis challenge. Guinea pigs or nonhuman primates (NHPs) were immunized on Days 0 and 28 with various dilutions of AV7909, AVA or a saline or Alhydrogel + CPG 7909 control. Animals were challenged via the inhalational route with a lethal dose of aerosolized B. anthracis (Ames strain) spores and observed for clinical signs of disease and mortality. The relationship between pre-challenge serum TNA levels and survival following challenge was determined in order to calculate a threshold TNA level associated with protection. Immunisation with AV7909 induced a rapid, highly protective TNA response in guinea pigs and NHPs. Surprisingly, the TNA threshold associated with a 70% probability of survival for AV7909 immunized animals was substantially lower than the threshold which has been established for the licensed AVA vaccine. The results of this study suggest that the TNA threshold of protection against anthrax could be modified by the addition of an immune stimulant such as CPG 7909 and that the TNA levels associated with protection may be vaccine-specific.     

Cross-species prediction of human survival probabilities for accelerated anthrax vaccine absorbed (AVA) regimens and the potential for vaccine and antibiotic dose sparing

Anthrax vaccine adsorbed (AVA, BioThrax) was recently approved by the Food and Drug Administration (FDA) for a post-exposure prophylaxis (PEP) indication in adults 18–65 years of age. The schedule is three doses administered subcutaneous (SC) at 2-week intervals (0, 2, and 4 weeks), in conjunction with a 60-day course of antimicrobials. The Public Health Emergency Medical Countermeasures Enterprise (PHEMCE) developed an animal model to support assessment of a shortened antimicrobial PEP duration following Bacillus anthracis exposure. A nonhuman primate (NHP) study was completed to evaluate the efficacy of a two dose anthrax vaccine absorbed (AVA) schedule (0, 2 weeks) aerosol challenged with high levels of B. anthracis spores at week 4– the time point at which humans would receive the third vaccination of the approved PEP schedule. Here we use logistic regression models to combine the survival data from the NHP study along with serum anthrax lethal toxin neutralizing activity (TNA) and anti-PA IgG measured by enzyme linked immunosorbent assay (ELISA) data to perform a cross-species analysis to estimate survival probabilities in vaccinated human populations at this time interval (week 4 of the PEP schedule). The bridging analysis demonstrated that high levels of NHP protection also yield high predicted probability of human survival just 2 weeks after the second dose of vaccine with the full or half antigen dose regimen. The absolute difference in probability of human survival between the full and half antigen dose was estimated to be at most approximately 20%, indicating that more investigation of the half-antigen dose for vaccine dose sparing strategies may be warranted.     

Neutralizing antibody and functional mapping of Bacillus anthracis protective antigen—The first step toward a rationally designed anthrax vaccine

Anthrax is defined by the Centers for Disease Control and Prevention as a Category A pathogen for its potential use as a bioweapon. Current prevention treatments include Anthrax Vaccine Adsorbed (AVA). AVA is an undefined formulation of Bacillus anthracis culture supernatant adsorbed to aluminum hydroxide. It has an onerous vaccination schedule, is slow and cumbersome to produce and is slightly reactogenic. Next-generation vaccines are focused on producing recombinant forms of anthrax toxin in a well-defined formulation but these vaccines have been shown to lose potency as they are stored. In addition, studies have shown that a proportion of the antibody response against these vaccines is focused on non-functional, non-neutralizing regions of the anthrax toxin while some essential functional regions are shielded from eliciting an antibody response. Rational vaccinology is a developing field that focuses on designing vaccine antigens based on structural information provided by neutralizing antibody epitope mapping, crystal structure analysis, and functional mapping through amino acid mutations. This information provides an opportunity to design antigens that target only functionally important and conserved regions of a pathogen in order to make a more optimal vaccine product. This review provides an overview of the literature related to functional and neutralizing antibody epitope mapping of the Protective Antigen (PA) component of anthrax toxin.     

Temperature-mediated recombinant anthrax protective antigen aggregate development: Implications for toxin formation and immunogenicity

Anthrax vaccines containing recombinant PA (rPA) as the only antigen face a stability issue: rPA forms aggregates in solution after exposure to temperatures ⩾40 °C, thus losing its ability to form lethal toxin (LeTx) with Lethal Factor. To study rPA aggregation’s impact on immune response, we subjected rPA to several time and temperature combinations. rPA treated at 50 °C for 30 min formed high mass aggregates when analyzed by gel electrophoresis and failed to form LeTx as measured by a macrophage lysis assay (MLA). Aggregated rPA-formed LeTx was about 30 times less active than LeTx containing native rPA. Mice immunized with heat-treated rPA combined with Al(OH)₃ developed antibody titers about 49 times lower than mice immunized with native rPA, as measured by a Toxicity Neutralization Assay (TNA). Enzyme Linked Immunosorbent Assay (ELISA) of the same immune sera showed anti-rPA titers only 2–7 times lower than titers elicited by native rPA. Thus, rPA’s ability to form LeTx correlates with its production of neutralizing antibodies, and aggregation significantly impairs the protein’s antibody response. However, while these findings suggest MLA has some value as an in-process quality test for rPA in new anthrax vaccines, they also confirm the superiority of TNA for use in vaccine potency.     

A novel live attenuated anthrax spore vaccine based on an acapsular Bacillus anthracis Sterne strain with mutations in the htrA,lef and cya genes

We recently reported the development of a novel, next-generation, live attenuated anthrax spore vaccine based on disruption of the htrA (High Temperature Requirement A) gene in the Bacillus anthracis Sterne veterinary vaccine strain. This vaccine exhibited a highly significant decrease in virulence in murine, guinea pig and rabbit animal models yet preserved the protective value of the parental Sterne strain. Here, we report the evaluation of additional mutations in the lef and cya genes, encoding for the toxin components lethal factor (LF) and edema factor (EF), to further attenuate the SterneΔhtrA strain and improve its compatibility for human use. Accordingly, we constructed seven B. anthracis Sterne-derived strains exhibiting different combinations of mutations in the htrA, cya and lef genes. The various strains were indistinguishable in growth in vitro and in their ability to synthesise the protective antigen (PA, necessary for the elicitation of protection). In the sensitive murine model, we observed a gradual increase (ΔhtrA < ΔhtrAΔcya < ΔhtrAΔlef < ΔhtrAΔlefΔcya) in attenuation – up to 10⁸-fold relative to the parental Sterne vaccine strain. Most importantly, all various SterneΔhtrA derivative strains did not differ in their ability to elicit protective immunity in guinea pigs. Immunisation of guinea pigs with a single dose (10⁹ spores) or double doses (>10⁷ spores) of the most attenuated triple mutant strain SterneΔhtrAlef^MUTΔcya induced a robust immune response, providing complete protection against a subsequent respiratory lethal challenge. Partial protection was observed in animals vaccinated with a double dose of as few as 10⁵ spores. Furthermore, protective immune status was maintained in all vaccinated guinea pigs and rabbits for at least 40 and 30 weeks, respectively.     

Enhanced early innate and T cell-mediated responses in subjects immunized with Anthrax Vaccine Adsorbed Plus CPG 7909 (AV7909)

NuThrax™ (Anthrax Vaccine Adsorbed with CPG 7909 Adjuvant) (AV7909) is in development. Samples obtained in a phase Ib clinical trial were tested to confirm biomarkers of innate immunity and evaluate effects of CPG 7909 (PF-03512676) on adaptive immunity. Subjects received two intramuscular doses of commercial BioThrax^® (Anthrax Vaccine Adsorbed, AVA), or two intramuscular doses of one of four formulations of AV7909. IP-10, IL-6, and C-reactive protein (CRP) levels were elevated 24–48 h after administration of AV7909 formulations, returning to baseline by Day 7. AVA (no CPG 7909) resulted in elevated IL-6 and CRP, but not IP-10. Another marker of CpG, transiently decreased absolute lymphocyte counts (ALCs), correlated with transiently increased IP-10. Cellular recall responses to anthrax protective antigen (PA) or PA peptides were assessed by IFN-γ ELISpot assay performed on cryopreserved PBMCs obtained from subjects prior to immunization and 7 days following the second immunization (study day 21). One-half of subjects that received AV7909 with low-dose (0.25 mg/dose) CPG 7909 possessed positive Day 21 T cell responses to PA. In contrast, positive T cell responses occurred at an 11% average rate (1/9) for AVA-treated subjects. Differences in cellular responses due to dose level of CPG 7909 were not associated with differences in humoral anti-PA IgG responses, which were elevated for recipients of AV7909 compared to recipients of AVA. Serum markers at 24 or 48 h (i.e. % ALC decrease, or increase in IL-6, IP-10, or CRP) correlated with the humoral (antibody) responses 1 month later, but did not correlate with cellular ELISpot responses. In summary, biomarkers of early responses to CPG 7909 were confirmed, and adding a CpG adjuvant to a vaccine administered twice resulted in increased T cell effects relative to vaccine alone. Changes in early biomarkers correlated with subsequent adaptive humoral immunity but not cellular immunity.     

An anthrax subunit vaccine candidate based on protective regions of Bacillus anthracis protective antigen and lethal factor

Studies have confirmed the key role of Bacillus anthracis protective antigen (PA) in the US and UK human anthrax vaccines. However, given the tripartite nature of the toxin, other components, including lethal factor (LF), are also likely to contribute to protection. We examined the antibody and T cell responses to PA and LF in human volunteers immunized with the UK anthrax vaccine (AVP). Individual LF domains were assessed for immunogenicity in mice when given alone or with PA. Based on the results obtained, a novel fusion protein comprising D1 of LF and the host cell-binding domain of PA (D4) was assessed for protective efficacy. Murine protection studies demonstrated that both full-length LF and D1 of LF conferred complete protection against a lethal intraperitoneal challenge with B. anthracis STI spores. Subsequent studies with the LFD1-PAD4 fusion protein showed a similar level of protection. LF is immunogenic in humans and is likely to contribute to the protection stimulated by AVP. A single vaccine comprising protective regions from LF and PA would simplify production and confer a broader spectrum of protection than that seen with PA alone.     

Evaluation of anthrax vaccine safety in 18 to 20 year olds: A first step towards age de-escalation studies in adolescents

Background/objectivesAnthrax vaccine adsorbed (AVA, BioThrax^®) is recommended for post-exposure prophylaxis administration for the US population in response to large-scale Bacillus anthracis spore exposure. However, no information exists on AVA use in children and ethical barriers exist to performing pre-event pediatric AVA studies. A Presidential Ethics Commission proposed a potential pathway for such studies utilizing an age de-escalation process comparing safety and immunogenicity data from 18 to 20 year-olds to older adults and if acceptable proceeding to evaluations in younger adolescents. We conducted exploratory summary re-analyses of existing databases from 18 to 20 year-olds (n = 74) compared to adults aged 21 to 29 years (n = 243) who participated in four previous US government funded AVA studies.MethodsData extracted from studies included elicited local injection-site and systemic adverse events (AEs) following AVA doses given subcutaneously at 0, 2, and 4 weeks. Additionally, proportions of subjects with ≥4-fold antibody rises from baseline to post-second and post-third AVA doses (seroresponse) were obtained.ResultsRates of any elicited local AEs were not significantly different between younger and older age groups for local events (79.2% vs. 83.8%, P = 0.120) or systemic events (45.4% vs. 50.5%, P = 0.188). Robust and similar proportions of seroresponses to vaccination were observed in both age groups.ConclusionsAVA was safe and immunogenic in 18 to 20 year-olds compared to 21 to 29 year-olds. These results provide initial information to anthrax and pediatric specialists if AVA studies in adolescents are required.     

Analysis of anti-protective antigen IgG subclass distribution in recipients of anthrax vaccine adsorbed (AVA) and patients with cutaneous and inhalation anthrax

The anti-PA IgG1, IgG2, IgG3, and IgG4 subclass responses to clinical anthrax and to different numbers of anthrax vaccine adsorbed (AVA, BioThrax) injections were determined in a cross-sectional study of sera from 63 vaccinees and 13 clinical anthrax patients. The data show that both vaccination with three AVA injections and clinical anthrax elicit anti-PA IgG1, IgG2, and IgG3 subclass responses. An anti-PA IgG4 response was detected in AVA recipients after the fourth injection. The anthrax lethal toxin (LTx) neutralization efficacy of sera from recipients who received 4 to > or =10 AVA injections did not vary significantly in relation to changes in distribution of anti-PA IgG1 and IgG4 subclasses.     

Antibody response to a delayed booster dose of anthrax vaccine and botulinum toxoid

We evaluated the prevalence and concentration of serum antibodies 18-24 months after primary inoculation with anthrax and botulinum vaccines, and assessed the reactogenicity and immunogenicity of a significantly delayed booster dose of these vaccines. Five hundred and eight male active-duty military personnel received one, two or three inoculations with anthrax vaccine and/or botulinum toxoid in 1990/1991 in preparation for Operations Desert Shield/Desert Storm. Subjects were vaccinated with the licensed anthrax vaccine, adsorbed (AVA) and pentavalent (ABCDE) botulinum toxoid (PBT) BB-IND 3723. Anthrax protective antigen (PA) IgG antibody was measured in serum using an immunocapture enzyme-linked immunosorbent assay (ELISA). A mouse neutralization test was used to determine the titer of Clostridium botulinum type A antitoxin in serum samples. The prevalence of anti-PA IgG was 30% in individuals 18-24 months after priming with one, two or three doses of AVA. After boosting, 99% of volunteers had detectable anti-PA IgG; only two individuals failed to respond. The prevalence of antibodies against botulinum toxin type A was 28% 18-24 months after initial priming. Following boosting, 99% of volunteers had serum titers >0.02IU/ml, and 97% responded with titers > or =0.25IU/ml.Systemic reactions to booster vaccinations could not be specifically ascribed to one or the other vaccine, but were generally mild and of brief duration. Forty-five percent of volunteers reported one or more systemic reactions over the course of 7 days. Injection site reactions of any kind occurred in 25% of AVA recipients and in 16% of PBT recipients; persistence of local reactions beyond 7 days was infrequent.While the kinetics and durability of immune responses must be studied, these findings suggest that booster doses of anthrax vaccine and botulinum toxoid sufficient to stimulate a robust anamnestic response may be given at times distant from receipt of the primary inoculations.     

In vitro correlate of immunity in a rabbit model of inhalational anthrax

A serological correlate of vaccine-induced immunity was identified in the rabbit model of inhalational anthrax. Animals were inoculated intramuscularly at 0 and 4 weeks with varying doses of Anthrax Vaccine Adsorbed (AVA) ranging from a human dose to a 1:256 dilution in phosphate-buffered saline (PBS). At 6 and 10 weeks, both the quantitative anti-protective antigen (PA) IgG ELISA and the toxin-neutralizing antibody (TNA) assays were used to measure antibody levels to PA. Rabbits were aerosol-challenged at 10 weeks with a lethal dose (84–133 LD₅₀) of Bacillus anthracis spores. All the rabbits that received the undiluted and 1:4 dilution of vaccine survived, whereas those receiving the higher dilutions of vaccine (1:16, 1:64 and 1:256) had deaths in their groups. Results showed that antibody levels to PA at both 6 and 10 weeks were significant (P<0.0001) predictors of survival.     

Efficacy of the AV7909 anthrax vaccine candidate in guinea pigs and nonhuman primates following two immunizations two weeks apart

The anthrax vaccine candidate AV7909 is being developed as a next-generation vaccine for post-exposure prophylaxis (PEP) against inhalational anthrax. In clinical studies, two vaccinations with AV7909 administered either two or four weeks apart induced an enhanced immune response compared to BioThrax® (Anthrax Vaccine Adsorbed) (AVA). Anthrax toxin-neutralizing antibody (TNA) levels on Day 70 following initial vaccination that were associated with protection of animals exposed to inhalational anthrax were previously reported for the 0, 4-week AV7909 vaccination regimen. The current study shows that a 0, 2-week AV7909 vaccination regimen protected guinea pigs (GPs) and nonhuman primates (NHPs) against a lethal inhalational anthrax challenge on Days 28 and 70 after the first immunization. An earlier induction of protective TNA levels using a 0, 2-week AV7909 vaccination regimen may provide benefit over the currently approved AVA PEP 0, 2, and 4-week vaccination regimen.     

The association between physical activity and liver fat after five years of follow-up in a primary prevention multi-ethnic cohort

Objective: Excess liver fat (LF) is associated with dyslipidemia, insulin resistance and cardiovascular disease. Evidence suggests that there is an independent relationship between physical activity (PA) and LF although little is known of the role of PA intensity in reducing LF. The purpose was to evaluate whether meeting PA guidelines, the amount of PA and the intensity of PA at baseline were associated with LF after five-years.Methods: Men and women (n = 478) living in Vancouver, Canada of Aboriginal, Chinese, European or South Asian background completed baseline measurements in 2004–2005. Liver fat was assessed using CT scans at 5-year follow-up, and PA using a PA questionnaire at baseline as well as demographics and anthropometry.Results: In separate unadjusted models, meeting moderate–vigorous PA (MVPA) guidelines (p = 0.009), vigorous PA (p = 0.002) and MVPA (p = 0.017) but not moderate PA (p = 0.068) was predictive of LF at five years (p = 0.009). In multiple linear regression models, when adjusted for covariates, meeting MVPA guidelines and MVPA with LF at five years was no longer significant (p > 0.05) while vigorous PA remained significant (p = 0.021).Conclusion: Meeting PA guidelines through MVPA may not be adequate to prevent the accumulation of LF and PA guidelines may require revision. Vigorous PA should be encouraged to prevent LF accumulation.     

Evaluation of early immune response-survival relationship in cynomolgus macaques after Anthrax Vaccine Adsorbed vaccination and Bacillus anthracis spore challenge

Anthrax Vaccine Adsorbed (AVA, BioThrax) is approved by the US Food and Drug Administration for post-exposure prophylaxis (PEP) of anthrax in adults. The PEP schedule is 3 subcutaneous (SC) doses (0, 14 and 28 days), in conjunction with a 60 day course of antimicrobials.The objectives of this study were to understand the onset of protection from AVA PEP vaccination and to assess the potential for shortening the duration of antimicrobial treatment (http://www.phe.gov/Preparedness/mcm/phemce/Documents/2014-phemce-sip.pdf). We determined the efficacy against inhalation anthrax in nonhuman primates (NHP) of the first two doses of the PEP schedule by infectious challenge at the time scheduled for receipt of the third PEP dose (Day 28). Forty-eight cynomolgus macaques were randomized to five groups and vaccinated with serial dilutions of AVA on Days 0 and 14. NHP were exposed to Bacillus anthracis Ames spores on Day 28 (target dose 200 LD₅₀ equivalents). Anti-protective antigen (PA) IgG and toxin neutralizing antibody (TNA) responses to vaccination and in post-challenge survivors were determined. Post-challenge blood and selected tissue samples were assessed for B. anthracis at necropsy or end of study (Day 56). Pre-challenge humoral immune responses correlated with survival, which ranged from 24 to 100% survival depending on vaccination group. Surviving, vaccinated animals had elevated anti-PA IgG and TNA levels for the duration of the study, were abacteremic, exhibited no apparent signs of infection, and had no gross or microscopic lesions. However, survivors had residual spores in lung tissues.We conclude that the first two doses of the PEP schedule provide high levels of protection by the scheduled timing of the third dose. These data may also support consideration of a shorter duration PEP antimicrobial regimen.     

Specific memory B cell response and participation of CD4+ central and effector memory T cells in mice immunized with liposome encapsulated recombinant NE protein based Hepatitis E vaccine candidate

BackgroundLiposome encapsulated neutralizing epitope protein of Hepatitis E virus (HEV), rNEp, our Hepatitis E vaccine candidate, was shown to be immunogenic and safe in pregnant and non-pregnant mice and yielded sterilizing immunity in rhesus monkeys.MethodsThe current study in Balb/c mice assessed the levels and persistence of anti-HEV IgG antibodies by ELISA, frequencies of B, memory B, T and memory T cells by flow cytometry and HEV-specific IgG secreting memory B cells by ELISPOT till 420 days post immunization (PI) with 5 μg rNEp encapsulated in liposome based adjuvant (2 doses, 4 weeks apart). Mice immunized with a lower dose (1 μg) were assessed only for anamnestic response post booster dose.ResultsVaccine candidate immunized mice (5 μg dose) elicited strong anti-HEV IgG response that was estimated to persist for lifetime. At day 120 PI, frequency of memory B cells was higher in immunized mice than those receiving adjuvant alone. Anti-HEV IgG titers were lower in mice immunized with 1 μg dose. A booster dose yielded a heightened antibody response in mice with both high (>800 GMT, 5 μg) and low (⩽100 GMT, 1 μg) anti-HEV IgG titers. At day 6th post booster dose, HEV-specific antibody secreting plasma cells (ASCs) were detected in 100% and 50% of mice with high and low anti-HEV IgG titers, respectively, whereas the frequencies of CD4⁺ central and effector memory T cells were high in mice with high anti-HEV IgG titers only.ConclusionsTaken together, the vaccine candidate effectively generates persistent and anamnestic antibody response, elicits participation of CD4⁺ memory T cells and triggers memory B cells to differentiate into ASCs upon boosting. This approach of assessing the immunogenicity of vaccine candidate could be useful to explore the longevity of HEV-specific memory response in future HEV vaccine trials in human.     

Effect of Tdap when administered before,with or after the 13-valent pneumococcal conjugate vaccine (coadministered with the quadrivalent meningococcal conjugate vaccine) in adults: A randomised controlled trial

Sequential or co-administration of vaccines has potential to alter the immune response to any of the antigens. Existing literature suggests that prior immunisation of tetanus/diphtheria-containing vaccines can either enhance or suppress immune response to conjugate pneumococcal or meningococcal vaccines. We examined this interaction among adult Australian travellers before attending the Hajj pilgrimage 2014. We also investigated tolerability of these vaccines separately and concomitantly. We randomly assigned each participant to one of three vaccination schedules. Group A received adult tetanus, diphtheria and acellular pertussis vaccine (Tdap) 3–4 weeks before receiving CRM197-conjugated 13-valent pneumococcal vaccine (PCV13) and CRM197-conjugated quadrivalent meningococcal vaccine (MCV4). Group B received all three vaccines on one day. Group C received PCV13 and MCV4 3–4 weeks before Tdap. Blood samples collected at baseline, each vaccination visit and 3–4 weeks after vaccination were tested using the pneumococcal opsonophagocytic assay (OPA) and by ELISA for diphtheria and tetanus antibodies. Funding for meningococcal serology was not available. Participants completed symptom diaries after each vaccination. A total of 111 participants aged 18–64 (median 40) years were recruited. No statistically significant difference was detected across the three groups in achieving OPA titre ⩾1:8 post vaccination. However, compared to other groups, Group A had a statistically significant lower number of subjects achieving ⩾4-fold rise in serotype 3, and also significantly lower geometric mean titres (GMTs) to six (of 13) pneumococcal serotypes (3, 5, 18C, 4, 19A and 9V). Group C (given prior PCV13 and MVC4) had statistically significant higher pre-Tdap geometric mean concentration (GMC) of anti-diphtheria IgG; however, there was no difference across the three groups following Tdap. Anti-tetanus IgG GMCs were similar across the groups before and after Tdap. No serious adverse events were reported. In conclusion, Tdap vaccination 3–4 weeks before concomitant administration of PCV13 and MCV4 significantly reduced the antibody response to six of the 13 pneumococcal serotypes in adults.The trial is registered at the Australian New Zealand Clinical Trials Registry (ANZCTR): ACTRN12613000536763.     

CHRONOVAC VOYAGEUR: A study of the immune response to yellow fever vaccine among infants previously immunized against measles

For administration of multiple live attenuated vaccines, the Advisory Committee on Immunization Practices recommends either simultaneous immunization or period of at least 28 days between vaccines, due to a possible reduction in the immune response to either vaccine.The main objective of this study was to compare the immune response to measles (alone or combined with mumps and rubella) and yellow fever vaccines among infants aged 6–24 months living in a yellow fever non-endemic country who had received measles and yellow fever vaccines before travelling to a yellow fever endemic area.Subjects and methods: A retrospective, multicenter case-control study was carried out in 7 travel clinics in the Paris area from February 1st 2011 to march 31, 2015. Cases were defined as infants immunized with the yellow fever vaccine and with the measles vaccine, either alone or in combination with mumps and rubella vaccine, with a period of 1–27 days between each immunization. For each case, two controls were matched based on sex and age: a first control group (control 1) was defined as infants having received the measles vaccine and the yellow fever vaccine simultaneously; a second control group (control 2) was defined as infants who had a period of more than 27 days between receiving the measles vaccine and yellow fever vaccine.The primary endpoint of the study was the percentage of infants with protective immunity against yellow fever, measured by the titer of neutralizing antibodies in a venous blood sample.Results: One hundred and thirty-one infants were included in the study (62 cases, 50 infants in control 1 and 19 infants in control 2). Of these, 127 (96%) were shown to have a protective titer of yellow fever antibodies. All 4 infants without a protective titer of yellow fever antibodies were part of control group 1.Discussion: The measles vaccine, alone or combined with mumps and rubella vaccines, appears to have no influence on humoral immune response to the yellow fever vaccine when administered between 1 and 27 days. The absence of protective antibodies against yellow fever was observed only among infants who received both vaccines simultaneously.Conclusion: These results may support a revision of current vaccination recommendations concerning the administration of these two live attenuated vaccines either on the same day or at least 28 days apart. Our findings show no statistically significant difference if the interval between both vaccines is more than 24 h, but the immune response seems to be reduced when the two vaccines are given at the same time.