Intranasal murine model of Bordetella pertussis infection. I. Prediction of protection in human infants by acellular vaccines

Liposome and QS-21 Combined Adjuvant Induces theHumoral and Cellular Responses of Acellular Pertussis Vaccine in a Mice Model

The resurgence of pertussis in vaccinated communities may be related to the reduced long-term immunity induced by acellular pertussis vaccines. Therefore, developing improved pertussis vaccine candidates that could induce strong Th1 or Th17 cellular immunity is an urgent need. The use of new adjuvants may well meet this requirement. In this research, we developed a novel adjuvant candidate by combining liposome and QS-21 adjuvant. Adjuvant activity, protective efficacy, the level of neutralizing antibody against PT, and the resident memory T (T_RM) cells in lung tissue after vaccination were studied. We then performed B. pertussis respiratory challenge in mice after they received vaccination with traditional aluminum hydroxide and the novel adjuvant combination. Results showed that the liposome + QS-21 adjuvant group had a rapid antibody and higher antibody (PT, FHA, Fim) level, induced anti-PT neutralizing antibody and recruited more IL-17A-secreting CD4⁺ T_RM cells along with IL-17A-secreting CD8⁺ T_RM cells in mice, which provided robust protection against B. pertussis infection. These results provide a key basis for liposome + QS-21 adjuvant as a promising adjuvant candidate for developing an acellular pertussis vaccine that elicits protective immunity against pertussis.

Evaluation of acellular pertussis vaccine: comparisons among different strains of mice

The current study was designed to comparatively analyze the reactions of different mouse strains in response to acellular pertussis(aP) vaccine, with attempt to further provide a reference for aP vaccine evaluation. NIH mice, ICR mice, and BALB/c mice adopted from different pharmacopoeias and studies were utilized to measure the immune protection and immunogenicity of the same batch of aP vaccine according to the MICA from some Asian pharmacopoeias and the pertussis serological potency test (PTST) method from European Pharmacopoeia. Based on our results, the aP vaccine detected by NIH mice had the best potency. So the NIH mice were more suitable for detecting the immune protection of aP vaccine by the Modified intracerebral challenge assay (MICA)method. Given that the levels of PT-IgG and FHA-IgG antibodies in ICR mice were the highest, and the levels of Th1 and Th2 cells were significantly increased (P < 0.01), it was more suitable for the detection of immunogenicity of aP vaccine by PSPT method. Spleen lymphocytes were stimulated by PT and FHA. And the levels of IL-4 in ICR mice and NIH mice were significantly increased, so were the levels of IL-17, IL-23, IL-27, and TNF-α in BALB/c mice. NIH mice have stronger adaptive immunity and the weakest inflammatory response, and ICR mice have enhanced adaptive immunity and inflammatory responses, both of which can be thereby used for evaluation by different pharmacopoeia methods. NIH was more suitable for the MICA method of Chinese Pharmacopoeia, and ICR for the PSPT method of European Pharmacopoeia.

The role of bactericidal and opsonic activity in immunity against Bordetella pertussis

INTRODUCTION

Pertussis vaccines have drastically reduced the disease burden in humans since their implementation. Despite their success, pertussis remains an important global public health challenge. Bordetella pertussis resurgence could be a result of greater surveillance combined with improved diagnosis methods, changes in Bordetella pertussis biology, vaccine schedules, and/or coverage. Additionally, mechanisms of protection conferred by acellular pertussis (aP) and whole-cell pertussis (wP) vaccines differ qualitatively. There are no clear immune correlates of protection for pertussis vaccines. Pertussis antigens can induce toxin neutralizing antibodies, block adherence or engage complement mediated phagocytic/bactericidal killing.

AREAS COVERED

We reviewed the existing evidence on antibody-mediated serum bactericidal and opsonophagocytic activity and discussed the relevance of these functional antibodies in the development of next-generation pertussis vaccines.

EXPERT OPINION

Current paradigm proposes that wP vaccines may confer greater herd protection than aP vaccines due to their enhanced clearance of bacteria from the nasopharynx in animal models. Functional antibodies may contribute to the reduction of nasal colonization, which differentiates aP and wP vaccines. Understanding the intrinsic differences in protective immune responses elicited by each class of vaccines will help to identify biomarkers that can be used as immunological end points in clinical trials.

Long-Term Analysis of Pertussis Vaccine Immunity to Identify Potential Markers of Vaccine-Induced Memory Associated With Whole Cell But Not Acellular Pertussis Immunization in Mice

Over two decades ago acellular pertussis vaccines (aP) replaced whole cell pertussis vaccines (wP) in several countries. Since then, a resurgence in pertussis has been observed, which is hypothesized to be linked, in part, to waning immunity. To better understand why waning immunity occurs, we developed a long-term outbred CD1 mouse model to conduct the longest murine pertussis vaccine studies to date, spanning out to 532 days post primary immunization. Vaccine-induced memory results from follicular responses and germinal center formation; therefore, cell populations and cytokines involved with memory were measured alongside protection from challenge. Both aP and wP immunization elicit protection from intranasal challenge by decreasing bacterial burden in both the upper and lower airways, and by generation of pertussis specific antibody responses in mice. Responses to wP vaccination were characterized by a significant increase in T follicular helper cells in the draining lymph nodes and CXCL13 levels in sera compared to aP mice. In addition, a population of B. pertussis+ memory B cells was found to be unique to wP vaccinated mice. This population peaked post-boost, and was measurable out to day 365 post-vaccination. Anti-B. pertussis and anti-pertussis toxoid antibody secreting cells increased one day after boost and remained high at day 532. The data suggest that follicular responses, and in particular CXCL13 levels in sera, could be monitored in pre-clinical and clinical studies for the development of the next-generation pertussis vaccines.

Non-primate animal models for pertussis: back to the drawing board?

Despite considerable progress in the understanding of clinical pertussis, the contemporary emergence of antimicrobial resistance for Bordetella pertussis and an evolution of concerns with acellular component vaccination have both sparked a renewed interest. Although simian models of infection best correlate with the observed attributes of human infection, several animal models have been used for decades and have positively contributed in many ways to the related science. Nevertheless, there is yet the lack of a reliable small animal model system that mimics the combination of infection genesis, variable upper and lower respiratory infection, systemic effects, infection resolution, and vaccine responses. This narrative review examines the history and attributes of non-primate animal models for pertussis and places context with the current use and needs. Emerging from the latter is the necessity for further such study to better create the optimal model of infection and vaccination with use of current molecular tools and a broader range of animal systems. KEY POINTS: • Currently used and past non-primate animal models of B. pertussis infection often have unique and focused applications. • A non-primate animal model that consistently mimics human pertussis for the majority of key infection characteristics is lacking. • There remains ample opportunity for an improved non-primate animal model of pertussis with the use of current molecular biology tools and with further exploration of species not previously considered.

Effectiveness of experimental and commercial pertussis vaccines in the elimination of Bordetella pertussis isolates with different genetic profiles in murine model

The aim of this study was to compare the elimination of Bordetella pertussis clinical isolates, representing different genotypes in relation to alleles encoding virulence factors (MLST-multi-locus antigen sequence typing), MLVA type (multi-locus variable-number tandem repeat analysis) and PFGE group (pulsed-field gel electrophoresis) from the lungs of naive mice or mice were immunised with the commercial whole-cell pertussis vaccine, the acellular pertussis vaccine and the experimental whole-cell pertussis vaccine. Molecular data indicate that the resurgence of pertussis in populations with high vaccine coverage is associated with genomic adaptation of B. pertussis, to vaccine selection pressure. Pertactin-negative B. pertussis isolates were suspected to contribute to the reduced vaccine effectiveness. It was shown that one of the isolates used is PRN deficient. The mice were intranasally challenged with bacterial suspension containing approximately 5 × 10 7 CFU/ml B. pertussis. The immunogenicity of the tested vaccines against PT (pertussis toxin), PRN (pertactin), FHA (filamentous haemagglutinin) and FIM (fimbriae types 2 and 3) was examined. The commercial whole-cell and acellular pertussis vaccines induced an immunity effective at eliminating the genetically different B. pertussis isolates from the lungs. However, the elimination of the PRN-deficient isolate from the lungs of mice vaccinated with commercial vaccines was delayed as compared to the PRN ( +) isolate, suggesting phenotypic differences with the circulating isolates and vaccine strains. The most effective vaccine was the experimental vaccine with the composition identical to that of the strains used for infection.

Vaccine-Induced Cellular Immunity against Bordetella pertussis: Harnessing Lessons from Animal and Human Studies to Improve Design and Testing of Novel Pertussis Vaccines

Pertussis ('whooping cough') is a severe respiratory tract infection that primarily affects young children and unimmunised infants. Despite widespread vaccine coverage, it remains one of the least well-controlled vaccine-preventable diseases, with a recent resurgence even in highly vaccinated populations. Although the exact underlying reasons are still not clear, emerging evidence suggests that a key factor is the replacement of the whole-cell (wP) by the acellular pertussis (aP) vaccine, which is less reactogenic but may induce suboptimal and waning immunity. Differences between vaccines are hypothesised to be cell-mediated, with polarisation of Th1/Th2/Th17 responses determined by the composition of the pertussis vaccine given in infancy. Moreover, aP vaccines elicit strong antibody responses but fail to protect against nasal colonisation and/or transmission, in animal models, thereby potentially leading to inadequate herd immunity. Our review summarises current knowledge on vaccine-induced cellular immune responses, based on mucosal and systemic data collected within experimental animal and human vaccine studies. In addition, we describe key factors that may influence cell-mediated immunity and how antigen-specific responses are measured quantitatively and qualitatively, at both cellular and molecular levels. Finally, we discuss how we can harness this emerging knowledge and novel tools to inform the design and testing of the next generation of improved infant pertussis vaccines.

Acellular Pertussis Vaccine Inhibits Bordetella pertussis Clearance from the Nasal Mucosa of Mice

Bordetella pertussis whole-cell vaccines (wP) caused a spectacular drop of global pertussis incidence, but since the replacement of wP with acellular pertussis vaccines (aP), pertussis has resurged in developed countries within 7 to 12 years of the change from wP to aP. In the mouse infection model, we examined whether addition of further protective antigens into the aP vaccine, such as type 2 and type 3 fimbriae (FIM2/3) with outer membrane lipooligosaccharide (LOS) and/or of the adenylate cyclase toxoid (dACT), which elicits antibodies neutralizing the CyaA toxin, could enhance the capacity of the aP vaccine to prevent colonization of the nasal mucosa by B. pertussis. The addition of the toxoid and of the opsonizing antibody-inducing agglutinogens modestly enhanced the already high capacity of intraperitoneally-administered aP vaccine to elicit sterilizing immunity, protecting mouse lungs from B. pertussis infection. At the same time, irrespective of FIM2/3 with LOS and dACT addition, the aP vaccination ablated the natural capacity of BALB/c mice to clear B. pertussis infection from the nasal cavity. While wP or sham-vaccinated animals cleared the nasal infection with similar kinetics within 7 weeks, administration of the aP vaccine promoted persistent colonization of mouse nasal mucosa by B. pertussis.

Increasing FIM2/3 antigen-content improves efficacy of Bordetella pertussis vaccines in mice in vivo without altering vaccine-induced human reactogenicity biomarkers in vitro

Current acellular-pertussis (aP) vaccines appear inadequate for long-term pertussis control because of short-lived efficacy and the increasing prevalence of pertactin-negative isolates which may negatively impact vaccine efficacy. In this study, we added fimbriae (FIM)2 and FIM3 protein to licensed 2-, 3- or 5-component aP vaccines (Pentavac®, Boostrix®, Adacel®, respectively) to assess whether an aP vaccine with enhanced FIM content demonstrates enhanced efficacy. Vaccine-induced protection was assessed in an intranasal mouse challenge model. In addition, potential reactogenicity was measured by biomarkers in a human whole blood assay (WBA) in vitro and benchmarked the responses against licensed whole cell pertussis (wP) and aP vaccines including Easyfive®, Pentavac® and Pentacel®. The results show that commercial vaccines demonstrated reduced efficacy against pertactin-negative versus pertactin-positive strains. However, addition of higher amounts of FIM2/3 to aP vaccines reduced lung colonization and increased vaccine efficacy against a pertactin-negative strain in a dose-dependent manner. Improvements in efficacy were similar for FIM2 and FIM3-expressing strains. Increasing the amount of FIM2/3 proteins in aP formulations did not alter vaccine-induced biomarkers of potential reactogenicity including prostaglandin E₂, cytokines and chemokines in human newborn cord and adult peripheral blood tested in vitro. These results suggest that increasing the quantity of FIM proteins in current pertussis vaccine formulations may further enhance vaccine efficacy against B. pertussis infection without increasing the reactogenicity of the vaccine.

IL-17-dependent SIgA-mediated protection against nasal Bordetella pertussis infection by live attenuated BPZE1 vaccine

BPZE1 is a live attenuated Bordetella pertussis vaccine for nasal administration to mimic the natural route of infection. Here, we studied the mechanism of BPZE1-induced immunity in the murine nasal cavity in contrast to acellular vaccine (aPV), although both vaccines protected against lung colonization. Transfer of splenocytes or serum from BPZE1-vaccinated or aPV-vaccinated mice protected naïve mice against lung colonization but not against nasal colonization. However, transfer of nasal washes from BPZE1-vaccinated mice resulted in protection against nasal colonization, which was lost in IgA-deficient or poly-Ig receptor-deficient mice, indicating that it depends on secretory IgA (SIgA) induction induced in the nose. BPZE1-induced protection against nasal colonization was long-lived despite the relatively rapid decay of SIgA, indicating a potent BPZE1-induced local memory response, likely due to CD4⁺ tissue-resident memory T cells induced in the nose by BPZE1. These cells produced interleukin-17 (IL-17), known to be important for SIgA secretion. Furthermore, BPZE1 failed to protect Il17^-/- mice against nasal colonization by B. pertussis and induced only background levels of nasal SIgA. Thus, our results show important differences in the protective mechanism between the upper and the lower murine respiratory tract and demonstrate an IL-17-dependent SIgA-mediated mechanism of BPZE1-induced protection against B. pertussis nasopharyngeal colonization.

Evaluation of Adenylate Cyclase Toxoid Antigen in Acellular Pertussis Vaccines by Using a Bordetella pertussis Challenge Model in Mice

Bordetella pertussis is the primary causative agent of pertussis (whooping cough), which is a respiratory infection that leads to a violent cough and can be fatal in infants. There is a need to develop more effective vaccines because of the resurgence of cases of pertussis in the United States since the switch from the whole-cell pertussis vaccines (wP) to the acellular pertussis vaccines (aP; diphtheria-tetanus-acellular-pertussis vaccine/tetanus-diphtheria-pertussis vaccine). Adenylate cyclase toxin (ACT) is a major virulence factor of B. pertussis that is (i) required for establishment of infection, (ii) an effective immunogen, and (iii) a protective antigen. The C-terminal repeats-in-toxin domain (RTX) of ACT is sufficient to induce production of toxin-neutralizing antibodies. In this study, we characterized the effectiveness of vaccines containing the RTX antigen against experimental murine infection with B. pertussis RTX was not protective as a single-antigen vaccine against B. pertussis challenge, and adding RTX to 1/5 human dose of aP did not enhance protection. Since the doses of aP used in murine studies are not proportionate to mouse/human body masses, we titrated the aP from 1/20 to 1/160 of the human dose. Mice receiving 1/80 human aP dose had bacterial burden comparable to those of naive controls. Adding RTX antigen to the 1/80 aP base resulted in enhanced bacterial clearance. Inclusion of RTX induced production of antibodies recognizing RTX, enhanced production of anti-pertussis toxin, decreased secretion of proinflammatory cytokines, such as interleukin-6, and decreased recruitment of total macrophages in the lung. This study shows that adding RTX antigen to an appropriate dose of aP can enhance protection against B. pertussis challenge in mice.

Protective effects of in vivo-expressed autotransporters against Bordetella pertussis infection

Bordetella pertussis causes whooping cough, a severe and prolonged respiratory disease that results inhas high morbidity and mortality rates, particularly in developing countries. The number incidence of whooping cough cases is increasing in many countries despite high vaccine coverage. Causes for the re-emergence of the disease include the limited duration of protection conferred by the acellular pertussis vaccines (aP)s and pathogenic adaptations that involve antigenic divergence from vaccine strains. Therefore, current vaccines therefore need to be improved. In the present study, we focused on five autotransporters: namely SphB1, BatB, SphB2, Phg, and Vag8, which were previously found to be expressed by B. bronchiseptica during the course of infection in rats and examined their protective efficiencies as vaccine antigens. The passenger domains of these proteins were produced in recombinant forms and used as antigens. An intranasal murine challenge assay showed that immunization with a mixture of SphB1 and Vag8 (SV) significantly reduced bacterial load in the lower respiratory tract and a combination of aP and SV acts synergistically in effects of conferring protection against B. pertussis infection, implying that these antigens have potential as components to for improvinge th the currently available acellular pertussis vaccine.

Novel intranasal pertussis vaccine based on bacterium-like particles as a mucosal adjuvant

Pertussis, or whooping cough, has recently reemerged as a major public health threat despite high levels of vaccination. The development of a novel pertussis vaccine, especially an intranasal (i.n.) vaccine is undoubtedly necessary, and mucosal adjuvants have been explored to enhance the immune response. In the present study, bacterium-like particles (BLPs) were adopted as a mucosal adjuvant for an i.n. pertussis vaccine and evaluated on the ability to induce serum and mucosal antibodies as well as potency against i.n. challenge in mice. Groups with or without aluminum adjuvant were also evaluated through both i.n. and intraperitoneal inoculations. Vaccination with BLPs via the i.n. route led to rapid IgG and IgA production and provided strong protection against inflammation induced by infection. The results support an i.n. pertussis vaccine with BLPs adjuvant as a promising candidate to elicit protective immunity against whooping cough.

Principles of vaccine potency assays

Compared with biologics, vaccine potency assays represent a special challenge due to their unique compositions, multivalency, long life cycles and global distribution. Historically, vaccines were released using in vivo potency assays requiring immunization of dozens of animals. Modern vaccines use a variety of newer analytical tools including biochemical, cell-based and immunochemical methods to measure potency. The choice of analytics largely depends on the mechanism of action and ability to ensure lot-to-lot consistency. Live vaccines often require cell-based assays to ensure infectivity, whereas recombinant vaccine potency can be reliably monitored with immunoassays. Several case studies are presented to demonstrate the relationship between mechanism of action and potency assay. A high-level decision tree is presented to assist with assay selection.

Immunogenicity and protective efficacy of a newly developed tri-component diphtheria, tetanus, and acellular pertussis vaccine in a murine model

BACKGROUND/PURPOSE

Although assessing the immunogenicity and protective efficacy of acellular pertussis (aP) vaccines via murine model studies faces limitations, preliminary assessments have been achieved by evaluating respiratory challenge and humoral and cellular immunity.

METHODS

We performed a long-term intranasal respiratory challenge with reference and clinically isolated strains of Bordetella pertussis. Simultaneously, we assessed humoral and cellular immunity for evaluating the immunogenicity of a newly developed tri-component diphtheria-tetanus-aP (DTaP) vaccine. Moreover, comparative assessment was made by performing the same evaluations with a commercially available tri-component DTaP vaccine as the positive control.

RESULTS

Both groups showed significantly increased levels of antibodies against pertussis toxin, filamentous hemagglutinin and pertactin, and the levels of interferon-γ and interleukin-10 were significantly increased after two doses of vaccination. Furthermore, since cross cell-mediated immune reactivity between the two vaccines was detected, the possibility of interchangeability was indirectly suggested. Although the positive control group showed significantly higher titers in antibody responses for filamentous hemagglutinin and pertactin compared to the experimental group, anti-pertussis toxin antibody titers of the two groups were not significantly different and the protective efficacy against the clinical and reference strains was maintained in both groups for 18 weeks.

CONCLUSION

The results showed inferior immunogenicity of the new DTaP vaccine compared to a commercial vaccine despite comparable cellular immunity and protective efficacy. Some efforts are necessary for improving immunogenicity against filamentous hemagglutinin and pertactin before conducting human clinical trials.

Development of vaccines against pertussis caused by Bordetella holmesii using a mouse intranasal challenge model

Bordetella holmesii is recognized as the third causative agent of pertussis (whooping cough) in addition to Bordetella pertussis and Bordetella parapertussis. Pertussis caused by B. holmesii is not rare around the world. However, to date, there is no effective vaccine against B. holmesii. We examined the protective potency of pertussis vaccines available in Japan and vaccines prepared from B. holmesii. A murine model of respiratory infection was exploited to evaluate protective potency. No Japanese commercial pertussis vaccines were effective against B. holmesii. In contrast, a wBH vaccine and an aBH vaccine prepared from B. holmesii were both protective. Passive immunization with sera from mice immunized with aBH vaccine established protection against B. holmesii, indicating that B. holmesii-specific serum antibodies might play an important role in protection. Immuno-proteomic analysis with sera from mice immunized with aBH vaccine revealed that the sera recognized a BipA-like protein of B. holmesii. An aBH vaccine prepared from a BipA-like protein-deficient mutant strain did not have a protective effect against B. holmesii. Taken together, our results suggest that the BipA-like protein plays an important role in the protective efficacy of aBH vaccine.

Assessment of safety and efficacy against Bordetella pertussis of a new tetanus-reduced dose diphtheria-acellular pertussis vaccine in a murine model

BACKGROUND

Tetanus-reduced dose diphtheria-acellular pertussis (Tdap) vaccination during adolescence was introduced in response to the resurgence of pertussis in various countries. A new Tdap vaccine was manufactured in Korea as a countermeasure against a predicted Tdap vaccine shortage. This study was performed to evaluate the immunogenicity, safety, and protection efficacy against Bordetella pertussis of the new Tdap vaccine in a murine model.

METHODS

Four-week-old BABL/c mice were used for assessment of immunogenicity and protection efficacy. A single dose of primary diphtheria-tetanus-acellular pertussis (DTaP) vaccine was administered, followed by a single dose of Tdap booster vaccine after a 12-week interval. Anti-pertussis toxin (PT), anti-filamentous hemagglutinin (FHA), and anti-pertactin (PRN) IgG titers were measured before primary vaccination, and before and after booster vaccination. An intranasal challenge test was performed after booster vaccination to determine protection efficacy. To assess safety, mouse weight gain test and leukocytosis promotion test were performed using 4-week-old ddY female mice.

RESULTS

Anti-PT and anti-FHA IgG titers after booster vaccination were significantly higher than those before booster vaccination with either the new vaccine or a commercially available Tdap vaccine (P = 0.01 for all occasions). After booster vaccination, no significant difference was observed between the two vaccines in antibody titers against pertussis antigens (P = 0.53 for anti-PT IgG, P = 0.91 for anti-FHA IgG, P = 0.39 for anti-PRN IgG). In the intranasal challenge test, inoculated B. pertussis was eradicated 7 days after infection. On days 4 and 7 after infection, colony counts of B. pertussis were not significantly different between the new and positive control vaccine groups (P = 1.00). Mean body weight changes and leukocyte counts of the new vaccine, positive control, and negative control groups were not significantly different 7 days after vaccination (P = 0.87 and P = 0.37, respectively). All leukocyte counts in the new vaccine group were within a mean ± 3 standard deviations range.

CONCLUSIONS

A murine model involving a single dose primary DTaP vaccination followed by a single dose Tdap booster vaccination can be used for non-clinical studies of Tdap vaccines. The new Tdap vaccine manufactured in Korea exhibited comparable immunogenicity, protection efficacy, and safety with a commercially available Tdap vaccine.

A Bordetella pertussis proteoliposome induces protection in mice without affecting the immunogenicity of diphtheria and tetanus toxoids in a trivalent formulation

In this study, a formulation of Bordetella pertussis proteoliposome (PLBp), diphtheria, and tetanus toxoids and alum (DT-PLBp) was evaluated as a trivalent vaccine candidate in BALB/c mice. Vaccine-induced protection was estimated using the intranasal challenge for pertussis and enzyme-linked immunosorbent assay fvto assess serological responses for diphtheria or tetanus. Both, diphtheria-tetanus-whole cell pertussis (DTP) and diphtheria-tetanus vaccines (DT) were used as controls. Animals immunized with DT-PLBp, PLBp alone, and DTP showed total reduction of CFU in lungs 7 days after intranasal challenge. Likewise, formulations DT-PLBp, DTP, and DT elicited antibody levels ≥2 IU/mL against tetanus and diphtheria, considered protective when neutralization tests are used. Overall, results showed that combination of PLBp with tetanus and diphtheria toxoids did not affect the immunogenicity of each antigen alone.

Reciprocal interference of maternal and infant immunization in protection against pertussis

BACKGROUND

Because of the current re-emergence of pertussis, vaccination during the 3rd trimester of pregnancy is recommended in several countries in order to protect neonates by placental transfer of maternal antibodies. Here, we examined the potential reciprocal interference of mother and infant vaccination in protection against pertussis in mice.

METHODS

Female mice were vaccinated with acellular pertussis vaccines and protection against Bordetella pertussis challenge, as well as functional antibodies were measured in their offspring with or without re-vaccination.

RESULTS

Maternal immunization protected the offspring against B. pertussis challenge, but protection waned quickly and was lost after vaccination of the infant mice with the same vaccine. Without affecting antibody titers, infant vaccination reduced the protective functions of maternally-derived antibodies, evidenced both in vitro and in vivo. Protection induced by infant vaccination was also affected by maternal antibodies. However, when mothers and infants were immunized with two different vaccines, no interference of infant vaccination on the protective effects of maternal antibodies was noted.

CONCLUSION

It may be important to determine the functionality of antibodies to evaluate potential interference of maternal and infant vaccination in protection against pertussis.

Pertactin negative Bordetella pertussis demonstrates higher fitness under vaccine selection pressure in a mixed infection model

Whooping cough or pertussis is a highly infectious respiratory disease in humans caused by Bordetella pertussis. The use of acellular vaccines (ACV) has been associated with the recent resurgence of pertussis in developed countries including Australia despite high vaccination coverage where B. pertussis strains that do not express pertactin (Prn), a key antigenic component of the ACV, have emerged and become prevalent. In this study, we used an in vivo competition assay in mice immunised with ACV and in naïve (control) mice to compare the proportion of colonisation with recent clinical Prn positive and Prn negative B. pertussis strains from Australia. The Prn negative strain colonised the respiratory tract more effectively than the Prn positive strain in immunised mice, out-competing the Prn positive strain by day 3 of infection. However, in control mice, the Prn positive strain out-competed the Prn negative strain. Our findings of greater ability of Prn negative strains to colonise ACV-immunised mice are consistent with reports of selective advantage for these strains in ACV-immunised humans.

T-cell immune responses to Bordetella pertussis infection and vaccination

The recent immunological investigations, stemming from the studies performed in the nineties within the clinical trials of the acellular pertussis vaccines, have highlighted the important role played by T-cell immunity to pertussis in humans. These studies largely confirmed earlier investigations in the murine respiratory infection models that humoral immunity alone is not sufficient to confer protection against Bordetella pertussis infection and that T-cell immunity is required. Over the last years, knowledge of T-cell immune response to B. pertussis has expanded broadly, taking advantage of the general progress in the understanding of anti-bacterial immunity and of refinements in methods to approach immunological investigations. In particular, experimental models of B. pertussis infection highlighted the cooperative role played by T-helper (Th)1 and Th17 cells for protection. Furthermore, the new baboon experimental model suggested a plausible explanation for the differences observed in the strength and persistence of protective immunity induced by the acellular or whole-cell pertussis vaccines and natural infection in humans, contributing to explain the upsurge of recent pertussis outbreaks. Despite the progress, open questions remain, the answer to them will possibly provide better tools to fight one of the hardest-to-control vaccine preventable disease.

Needle-free and adjuvant-free epicutaneous boosting of pertussis immunity: Preclinical proof of concept

The limited durability of pertussis vaccine-induced protection requires novel approaches to reactivate immunity and limit pertussis resurgence in older children and adults. We propose that periodic boosters could be delivered using a novel epicutaneous delivery system (Viaskin) to deliver optimized pertussis antigens such as genetically-detoxified pertussis toxin (rPT). To best mimic the human situation in which vaccine-induced memory cells persist, whereas antibodies wane, we developed a novel adoptive transfer murine model of pertussis immunity. This allowed demonstrating that a single application of Viaskin delivering rPT and/or pertactin and filamentous hemagglutinin effectively reactivates vaccine-induced pertussis immunity and protects against Bordetella pertussis challenge. Recalling pertussis immunity without needles nor adjuvant may considerably facilitate the acceptance and application of periodic boosters.

Preliminary study on the immunogenicity of a newly developed GCC Tdap vaccine and its protection efficacy against Bordetella pertussis in a murine intranasal challenge model

Purpose

Active reduced dose tetanus-diphtheria-acellular pertussis (Tdap) vaccination for adolescents and adults is necessary because waning immunity after primary diphtheria-tetanus-pertussis vaccination is related to the recent emergence of pertussis. This study was conducted to compare the immunogenicity and protection efficacy against Bordetella pertussis between a new GCC Tdap vaccine and a commercially available Tdap vaccine in a murine model.

Materials and Methods

BALB/c mice were immunized with two doses of diphtheria-tetanus-acellular pertussis (DTaP) vaccine for priming and a subsequent Tdap booster vaccination. According to the type of booster vaccine, mice were divided into four groups: commercially available Tdap vaccine in group 1 and GCC Tdap vaccines of different combinations of pertussis antigens in groups 2 to 4. Humoral and cell-mediated immune responses and protection efficacy using a murine intranasal challenge model after booster vaccination were compared among the four groups.

Results

Every group showed significant increases in antibody titers against pertussis antigens such as pertussis toxin, filamentous hemagglutinin, and pertactin after booster vaccination. Spleen cells showed both Th1 and Th2 cell-mediated immune responses stimulated by pertussis antigens in all groups without any significant difference. In the intranasal B. pertussis infection model, bacteria were eradicated in all groups five days after challenge infection.

Conclusion

This preliminary study did not show significantly different immunogenicity or protection efficacy of the new GCC Tdap vaccines compared to the commercially available Tdap vaccine, although a more extensive study is necessary to assess the differing efficacies of the new GCC Tdap vaccines.

Whole-cell pertussis vaccine potency assays: the Kendrick test and alternative assays

Whole-cell pertussis vaccines are still widely used across the globe and have been shown to produce longer lasting immunity against pertussis infection than acellular pertussis vaccines. Therefore, whole-cell vaccines are likely to continue to be used for the foreseeable future. The intracerebral mouse protection test (Kendrick test) is effective for determining the potency of whole-cell pertussis vaccines and is the only test that has shown a correlation with protection in children. Here we review the Kendrick test in terms of international requirements for vaccine potency and critical technical points to be considered for a successful test including test validity, in-house references and statistical analysis. There are objections to the Kendrick test on animal welfare and technical grounds. Respiratory challenge assays, nitric oxide induction assay and serological assays have been developed and have been proposed as possible methods which might provide alternatives to the Kendrick test. These methods and their limitations are also briefly discussed. Establishment of validated in vitro correlates of protection has yet to be achieved. New technical developments, such as genome sequence and the use of gene microarrays to screen responses triggered by vaccine components may also provide leads to alternative assays to the Kendrick test by identifying biomarkers of protection.

Shortcomings of pertussis vaccines: why we need a third generation vaccine

First generation whole-cell (wP) and second generation acellular (aP) pertussis vaccines have been highly effective in preventing childhood deaths due to pertussis, yet both vaccines have drawbacks that have limited their long-term usefulness. These include issues of reactogenicity and potency in the case of wP, and limited durability of protection and the potential for selection of escape mutants in the case of aP. Neither vaccine prevents disease in neonatal infants who continue to die from pertussis. A third generation of pertussis vaccines that provides broad, durable protection is needed. In the meantime, countries using wP should continue to do so, while countries using aP need to consider policies and schedules that reduce pertussis transmission to unvaccinated infants. In this respect, maternal vaccination appears to be a promising solution.

The mouse intranasal challenge model for potency testing of whole-cell pertussis vaccines

INTRODUCTION

A mouse intracerebral challenge model is used for potency testing of whole-cell pertussis (wP) vaccines. We investigated the use of a mouse nasopharyngeal challenge model, which better reflects the clinical features of pertussis disease, to differentiate between efficacy of wP vaccines.

METHODS

Efficacy of three wP vaccines (Quinvaxem(®), Easyfive(®) and Pentavac(®)) was tested in the nasopharyngeal challenge model. Mice were vaccinated at 4 and 7 weeks and challenged with Bordetella pertussis at 9 weeks. Vaccine efficacy was determined based on CFU in the lungs 5 days after challenge.

RESULTS

The mouse nasopharyngeal challenge model has the capacity to differentiate between the efficacy of whole cell pertussis vaccines.

CONCLUSION

The mouse nasopharyngeal challenge model could be considered as a potency and release assay for wP vaccines. Whether this model directly correlates with clinical vaccine efficacy requires further investigations. Whether this model directly correlates with clinical vaccine efficacy requires further investigations. The mouse nasopharyngeal challenge model could be considered as a potency and release assay for wP vaccines.

Acellular pertussis vaccines and the role of pertactin and fimbriae

The introduction of acellular pertussis (Pa) vaccines in countries with a low uptake of whole-cell pertussis (Pw) vaccines has led to a dramatic reduction in pertussis disease. Diphtheria-tetanus-acellular pertussis (DTPa) vaccines have also ensured continued high level disease protection in these countries following the shift from Pw- to Pa-containing vaccines, and allowed pertussis booster programs to be implemented. Vaccines containing between one and five components have been licensed and implemented. Those with three or more components consisting of filamentous hemagglutinin (FHA), pertussis toxin (PT) and pertactin (PRN) are considered to be more effective than one/two-component Pa vaccines that contain only PT or both PT and FHA. Changes in circulating Bordetella pertussis strains may impact vaccine efficacy and, thus, incidence and transmission of pertussis and deserve to be followed carefully. To date, vaccine-induced shifts among fimbriae (FIM) are reported and this could impact the efficacy of FIM-containing vaccines. Currently, FIM3 appears to be dominant in most European countries, Canada and Australia. Data obtained from a DTPa5 vaccine containing FIM2 and FIM3 have indicated a shift towards an increase in FIM3-expressing B. pertussis clinical breakthrough cases when compared with control vaccine. By contrast, relatively minor PT and PRN sequence polymorphisms have been identified without demonstrable association with vaccination programs. Adsorption of PRN to aluminum salt appears critical for optimal protective capacity in murine pertussis lung challenge. In addition, clinical studies have shown anti-PRN antibody levels to be higher when PRN is adsorbed at a 8-microg dosage versus non-adsorbed PRN at a 3-microg dosage. The available data, therefore, demonstrate that appropriately formulated acellular vaccines containing PT and PRN are the preferred option for pertussis immunization.

A proteoliposome formulation derived from Bordetella pertussis induces protection in two murine challenge models

Whooping cough remains a health problem despite high vaccination coverage. It has been recommended that development of new strategies provide long-lasting immunity. The aim of this work was to evaluate the potential of proteoliposomes (PL) extracted from Bordetella pertussis as a vaccine candidate against whooping cough. The size of the B. pertussis PL was estimated to be 96.7 ± 50.9 nm by Scanning Correlation Spectroscopy and the polydispersity index was 0.268. Western blots using monoclonal antibodies revealed the presence of pertussis toxin, pertactin, and fimbriae 3. The Limulus Amebocyte Lisate (LAL) assay showed endotoxin levels lower than those reported for whole cell pertussis licensed vaccines, while the Pyrogen Test indicated 75 ng/mL/Kg. The PL showed high protection capacity in mouse challenge models. There was 89.7% survival in the intracerebral challenge and total reduction of the number of CFU in the intranasal challenge. No significant differences (p > 0.05) were observed between mice immunized with B. pertussis PL and the Cuban DTwP vaccine, whichever challenge model used. These results encouraged us to continue the development of the B. pertussis PL as a component of a new combined vaccine formulated with tetanus and diphtheria toxoids or as a booster dose for adolescents and adults.

Identification of a new protective antigen of Bordetella pertussis

Antigenic proteins whose expression is induced under iron starvation, an environmental condition that bacterial pathogens have to face during colonization, might be potential candidates for improved vaccine. By mean of immune proteomics we identified novel antigens of Bordetella pertussis maximally expressed under iron limitation. Among them, Bp1152 (named as IRP1-3) showed a particularly strong reaction with human IgG purified from pooled sera of pertussis-infected individuals. Computer analysis showed IRP1-3 as a dimeric membrane protein potentially involved in iron uptake. Experimental data revealed the surface-exposure of this protein and showed its increase under iron starvation to be independent of bacterial virulence phase. Immunization of mice with the recombinant IRP1-3 resulted in a strong antibody response. These antibodies not only recognized the native protein on bacterial surface but also promote effective bacterial phagocytosis by human PMN, a key protecting activity against this pathogen. Accordingly, IRP1-3 proved protective against B. pertussis infection in mouse model. Expression of IRP1-3 was found conserved among clinical isolates of B. pertussis and positively regulated by iron starvation in these strains. Taken together these results suggest that this protein might be an interesting novel vaccine candidate.

Induction of Bordetella pertussis-specific immune memory by DTPa vaccines

Several vaccines are available against pertussis, differing by the number of Bordetella pertussis antigens that they contain as well as their formulation. The GlaxoSmithKline Biologicals (GSK Bio) tricomponent DTPa vaccine (DTPa3, Infanrix™), and the Sanofi-Pasteur (SP) five-component formulation (DTPa5, Pediacel™) were shown to have comparable short-term efficacy in clinical trials. However, potential differences in long-term protection were recently suggested, which might reflect the elicitation of different specific immune memory by the two vaccines. Therefore, the purpose of the present study was to investigate in mice the immune responses against B. pertussis, and particularly the establishment of specific B cell memory after immunization with DTPa3 and DTPa5 vaccines. Whereas intranasal challenge experiments showed similar protection with both vaccines, DTPa3 induced higher antibody levels to FHA and PRN than DTPa5. Further, the frequency of memory B cells was investigated by B cell ELISPOT. Higher frequencies of PT- and PRN-specific memory B cells were evidenced after vaccination with DTPa3, compared with DTPa5. Although the origin of such difference is unclear, the use of two different adjuvants (aluminum phosphate versus hydroxide) is proposed as a possible explanation. In conclusion, this study proposes that the induction of higher levels of B. pertussis antigen-specific memory B cells with DTPa3 participate to the suggested longer persistence of protection observed with this vaccine, as compared with DTPa5.

Acellular pertussis vaccination facilitates Bordetella parapertussis infection in a rodent model of bordetellosis

Despite over 50 years of population-wide vaccination, whooping cough incidence is on the rise. Although Bordetella pertussis is considered the main causative agent of whooping cough in humans, Bordetella parapertussis infections are not uncommon. The widely used acellular whooping cough vaccines (aP) are comprised solely of B. pertussis antigens that hold little or no efficacy against B. parapertussis. Here, we ask how aP vaccination affects competitive interactions between Bordetella species within co-infected rodent hosts and thus the aP-driven strength and direction of in-host selection. We show that aP vaccination helped clear B. pertussis but resulted in an approximately 40-fold increase in B. parapertussis lung colony-forming units (CFUs). Such vaccine-mediated facilitation of B. parapertussis did not arise as a result of competitive release; B. parapertussis CFUs were higher in aP-relative to sham-vaccinated hosts regardless of whether infections were single or mixed. Further, we show that aP vaccination impedes host immunity against B. parapertussis-measured as reduced lung inflammatory and neutrophil responses. Thus, we conclude that aP vaccination interferes with the optimal clearance of B. parapertussis and enhances the performance of this pathogen. Our data raise the possibility that widespread aP vaccination can create hosts more susceptible to B. parapertussis infection.

Synergic effect of genotype changes in pertussis toxin and pertactin on adaptation to an acellular pertussis vaccine in the murine intranasal challenge model

The Bordetella pertussis pertussis toxin and pertactin (Prn) are protective antigens and are contained in acellular pertussis vaccines. Polymorphisms in the A subunit of pertussis toxin (PtxA) and pertactin have been proposed to mediate vaccine resistance and contribute to pertussis reemergence. To test this hypothesis, previous studies compared clinical isolates expressing different alleles for the proteins. However, other virulence factors or virulence factor expression levels also may vary, confounding the analysis. To overcome these limitations, we constructed isogenic mutants of B. pertussis Tohama expressing the alleles ptxA1 or ptxA2 and prn1 or prn2 and compared the efficacies of an acellular pertussis vaccine against the mutants in a mouse model. While the vaccine was effective against all of the B. pertussis strains regardless of the allele expression pattern, the strain expressing ptxA1 and prn2 displayed a survival advantage over the other strains. These results suggest that an allele shift to the ptxA1 prn2 genotype may play a role in the emergence of pertussis in vaccinated populations.

Dose response of attenuated Bordetella pertussis BPZE1-induced protection in mice

Despite the availability of efficacious vaccines, the incidence of whooping cough is still high in many countries and is even increasing in countries with high vaccine coverage. Most severe and life-threatening pertussis cases occur in infants who are too young to be sufficiently protected by current vaccine regimens. As a potential solution to this problem, we have developed an attenuated live Bordetella pertussis vaccine strain, named BPZE1. Here, we show that after a single administration, BPZE1 induces dose-dependent protection against challenge with virulent B. pertussis in low-dose and in high-dose intranasal mouse lung colonization models. In addition, we observed BPZE1 dose-dependent antibody titers to B. pertussis antigens, as well as cell-mediated immunity, evidenced by the amounts of gamma interferon (IFN-gamma) released from spleen cells upon stimulation with B. pertussis antigens. These two parameters may perhaps be used as readouts in clinical trials in humans that are currently being planned.

Production and characterization of recombinant pertactin, fimbriae 2 and fimbriae 3 from Bordetella pertussis

BACKGROUND

Bordetella pertussis is a causative agent of pertussis or whooping cough in humans. Pertactin (Prn), fimbriae 2 (Fim2) and fimbriae 3 (Fim3) of B. pertussis are important virulence factors and immunogens which have been included in some acellular pertussis vaccines. In this present study, we cloned, expressed and purified Prn, Fim2 and Fim3, respectively. The immunogenicity and protective efficacy of the three recombinant proteins (rPrn, rFim2 and rFim3) were investigated in mouse model.

RESULTS

Three recombinant proteins with amount of 12 to 25 mg/L were produced. Compared to the control mice only immunized with adjuvant, serum IgG antibody responses were significantly induced in the mice immunized with rPrn, rFim2 or rFim3 (P < 0.001 for all three proteins). Furthermore, T cell responses characteristic of increased production of IL-2 and TNF-alpha (only for rPrn) were elicited in the mice immunized with the three proteins (P < 0.05 for all three proteins). Immunization with rPrn, but not with rFim2 or rFim3, significantly enhanced clearance of bacteria in the lungs of mice after intranasal challenge with B. pertussis (P < 0.05). When tested in a lethal intracerebral infection model, certain protection was observed in mice immunized with rPrn.

CONCLUSIONS

We have developed an efficient method to produce large amounts of rPrn, rFim2, and rFim3 from B. pertussis. The three recombinant proteins induced both humoral and cellular immune responses in mice. Immunization with rPrn also conferred protection against pertussis in mouse infection models. Our results indicated that the recombinant proteins still retain their immunological properties and highlighted the potential of the recombinant proteins for the future development of the B. pertussis vaccines.

First report and detailed characterization of B. pertussis isolates not expressing Pertussis Toxin or Pertactin

Bordetella pertussis isolates not expressing Pertussis Toxin (PT) or Pertactin (PRN) have been collected, for the first time in 2007, in France, a highly vaccinated country with acellular vaccines. Non-expression was due to deletion of the entire ptx locus, to IS481 insertion in the prn gene or deletion of a part of this gene. Genome sequencing does not indicate any regions of differences when compared to other circulating isolates. It nevertheless shows some sequence differences and an increased number of repeated sequences. The infant infected by the isolate not expressing pertussis toxin, did not present hyperlymphocytosis. All isolates were found less pathogen in animal or cellular models; their circulation raises the problem of clinical and biological diagnoses.

Pertussis toxin inhibits early chemokine production to delay neutrophil recruitment in response to Bordetella pertussis respiratory tract infection in mice

Pertussis is an acute respiratory disease of humans caused by the bacterium Bordetella pertussis. Pertussis toxin (PT) plays a major role in the virulence of this pathogen, including important effects that it has soon after inoculation. Studies in our laboratory and other laboratories have indicated that PT inhibits early neutrophil influx to the lungs and airways in response to B. pertussis respiratory tract infection in mice. Previous in vitro and in vivo studies have shown that PT can affect neutrophils directly by ADP ribosylating G(i) proteins associated with surface chemokine receptors, thereby inhibiting neutrophil migration in response to chemokines. However, in this study, by comparing responses to wild-type (WT) and PT-deficient strains, we found that PT has an indirect inhibitory effect on neutrophil recruitment to the airways in response to infection. Analysis of lung chemokine expression indicated that PT suppresses early neutrophil recruitment by inhibiting chemokine upregulation in alveolar macrophages and other lung cells in response to B. pertussis infection. Enhancement of early neutrophil recruitment to the airways in response to WT infection by addition of exogenous keratinocyte-derived chemokine, one of the dominant neutrophil-attracting chemokines in mice, further revealed an indirect effect of PT on neutrophil chemotaxis. Additionally, we showed that intranasal administration of PT inhibits lipopolysaccharide-induced chemokine gene expression and neutrophil recruitment to the airways, presumably by modulation of signaling through Toll-like receptor 4. Collectively, these results demonstrate how PT inhibits early inflammatory responses in the respiratory tract, which reduces neutrophil influx in response to B. pertussis infection, potentially providing an advantage to the pathogen in this interaction.