Pertussis-specific cell-mediated immunity in infants after vaccination with a tricomponent acellular pertussis vaccine

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.

Pertussis in Lao PDR: Seroprevalence and disease

OBJECTIVES

Pertussis is a debilitating vaccine-preventable infection. The aim of this study was to determine susceptibility and exposure to pertussis in Lao PDR in different age groups and subpopulations.

METHODS

A total 3072 serum samples were obtained from different cohorts: children with documented vaccination, pre-schoolers, schoolchildren, blood donors, healthcare workers (HCWs), and pregnant women and paired cord blood. Samples were tested for anti-pertussis toxin IgG antibodies. A history of Bordetella pertussis exposure was defined according to antibody titres. Four hundred and seventy-five throat swabs and nasopharyngeal aspirates were analysed by PCR for the presence of B. pertussis in symptomatic children at the Children's Hospital in Vientiane.

RESULTS

Overall pertussis seroprevalence was 57.5%. The prevalence of titres indicating acute infection or recent vaccination or infection/vaccination within the last 12 months ranged from 7.4% (100/1356) in adults to 21.4% (25/117) in pre-schoolers (age 1-5 years). B. pertussis was detected in 1.05% (5/475) of children with respiratory symptoms in Vientiane Capital.

CONCLUSIONS

It is suggested that routine childhood vaccination, in particular outreach, as well as vaccination of HCWs should be strengthened. A childhood booster and vaccination of pregnant mothers should be considered. There is also a need to improve reporting and to introduce pertussis testing in at least one central facility.

Pertussis Vaccines and Vaccination Strategies. An Ever-Challenging Health Problem

Vaccines and vaccination against pertussis (whooping cough) have had one of the longest and most complex history, with alternating splendour and public disbelief, enthusiasm and concerns, overall resulting in changes in composition and replacement of vaccines, and associated vaccination strategies, including use of different vaccines in different countries, with no apparent equals for other bacterial vaccines. Of this both frustrating and exciting venue no end has been reached. In this note, I am shortly recapitulating the history of pertussis vaccines, from the inactivated, whole-cell vaccine to the acellular ones, with their merits and limitations, particularly concerning the debated issue of waning immunity, and a glimpse on a new vaccine proposal. Some reflections on the complexity and apparent peculiarity of this field are also made to the final scope of discussing aspects of the evolving strategies of disease control in a high-income country.

Human Immune Responses to Pertussis Vaccines

Pertussis still represents a major cause of morbidity and mortality worldwide. Although vaccination is the most powerful tool in preventing pertussis and despite nearly 70 years of universal childhood vaccination, incidence of the disease has been rising in the last two decades in countries with high vaccination coverage. Two types of vaccines are commercially available against pertussis: whole-cell pertussis vaccines (wPVs) introduced in the 1940s and still in use especially in low and middle-income countries; less reactogenic acellular pertussis vaccines (aPVs), licensed since the mid-1990s.In the last years, studies on pertussis vaccination have highlighted significant gaps and major differences between the two types of vaccines in the induction of protective anti-pertussis immunity in humans. This chapter will discuss the responses of the immune system to wPVs and aPVs, with the aim to enlighten critical points needing further efforts to reach a good level of protection in vaccinated individuals.

Soluble CD30 and Lymphocyte Activation Gene-3 (CD223), as Potential Serological Markers of T Helper-Type Cytokine Response Induced by Acellular Pertussis Vaccine

T cell responses are involved in vaccine-induced immunity to pertussis but no easy-to-monitor, serological markers are available to assess these responses. The lymphocyte activation gene-3 (CD223) molecule is present on, and released by, activated T helper (Th) 1 cells, whereas CD30 molecules have been associated with Th2 immune responses. Starting from the recent knowledge of the cytokine profile induced by pertussis vaccination, we examined the levels of soluble (s)CD223 and sCD30 proteins in child recipients of acellular pertussis (aP) and diphtheria-tetanus (DT) vaccines and in children receiving DT vaccine only, as control. The correlation of the two proteins with specific antibody and T cell responses was assessed. The main findings are: i) sCD223 and sCD30 levels are inversely related, suggesting that the two markers are the expression of different and counter-regulated T-cell responses; ii) sCD30 level correlated with induction of T cell proliferation to pertussis vaccine antigens and antibody response to pertussis toxin. Overall, sCD30 and sCD223 levels seem to be promising candidate markers to assess the induction of Th-type responses in vaccine recipients.

What Is Wrong with Pertussis Vaccine Immunity? Inducing and Recalling Vaccine-Specific Immunity

The high incidence of pertussis in vaccinated adolescents suggests the failing of immune memory. We argue that acellular pertussis vaccines generate memory cells that are effectively reactivated by boosters better than by Bordetella pertussis exposure. We propose that there are two main causes. One is the induction of vaccine-specific immunity rather than pathogen-specific immunity. The second is that strictly mucosal infections such as B. pertussis poorly reactivate memory B and T cells residing deep in lymph nodes or tissues. Developing new vaccines for infants or adolescents will be immunologically and economically challenging. Let us hope that maternal and infant immunization, to date the most effective strategies against pertussis death, will remain so.

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.

Bordetella PlrSR regulatory system controls BvgAS activity and virulence in the lower respiratory tract

Bacterial pathogens coordinate virulence using two-component regulatory systems (TCS). The Bordetella virulence gene (BvgAS) phosphorelay-type TCS controls expression of all known protein virulence factor-encoding genes and is considered the "master virulence regulator" in Bordetella pertussis, the causal agent of pertussis, and related organisms, including the broad host range pathogen Bordetella bronchiseptica We recently discovered an additional sensor kinase, PlrS [for persistence in the lower respiratory tract (LRT) sensor], which is required for B. bronchiseptica persistence in the LRT. Here, we show that PlrS is required for BvgAS to become and remain fully active in mouse lungs but not the nasal cavity, demonstrating that PlrS coordinates virulence specifically in the LRT. PlrS is required for LRT persistence even when BvgAS is rendered constitutively active, suggesting the presence of BvgAS-independent, PlrS-dependent virulence factors that are critical for bacterial survival in the LRT. We show that PlrS is also required for persistence of the human pathogen B. pertussis in the murine LRT and we provide evidence that PlrS most likely functions via the putative cognate response regulator PlrR. These data support a model in which PlrS senses conditions present in the LRT and activates PlrR, which controls expression of genes required for the maintenance of BvgAS activity and for essential BvgAS-independent functions. In addition to providing a major advance in our understanding of virulence regulation in Bordetella, which has served as a paradigm for several decades, these results indicate the existence of previously unknown virulence factors that may serve as new vaccine components and therapeutic or diagnostic targets.

Lin28b Regulates Fetal Regulatory T Cell Differentiation through Modulation of TGF-β Signaling

Immune tolerance between the fetus and mother represents an active process by which the developing fetus must not mount immune responses to noninherited Ags on chimeric maternal cells that reside in fetal tissue. This is, in part, mediated by the suppressive influence of CD4⁺FOXP3⁺CD25⁺ regulatory T cells (Tregs). Fetal secondary lymphoid organs have an increased frequency of Tregs and, as compared with adult T cells, fetal naive CD4⁺ T cells exhibit a strong predisposition to differentiate into Tregs when stimulated. This effect is mediated by the TCR and TGF-β pathways, and fetal T cells show significantly increased Treg differentiation in response to anti-CD3 and TGF-β stimulation. Naive fetal T cells also exhibit increased signaling through the TGF-β pathway, with these cells demonstrating increased expression of the signaling mediators TGF-βRI, TGF-βRIII, and SMAD2, and higher levels of SMAD2/SMAD3 phosphorylation. Increased fetal Treg differentiation is mediated by the RNA-binding protein Lin28b, which is overexpressed in fetal T cells as compared with adult cells. When Lin28b expression is decreased in naive fetal T cells, they exhibit decreased Treg differentiation that is associated with decreased TGF-β signaling and lowered expression of TGF-βRI, TGF-βRIII, and SMAD2. Lin28b regulates the maturation of let-7 microRNAs, and these TGF-β signaling mediators are let-7 targets. We hypothesize that loss of Lin28b expression in fetal T cells leads to increased mature let-7, which causes decreased expression of TGF-βRI, TGF-βRIII, and SMAD2 proteins. A reduction in TGF-β signaling leads to reduced Treg numbers.

Pertussis: Microbiology, Disease, Treatment, and Prevention

Pertussis is a severe respiratory infection caused by Bordetella pertussis, and in 2008, pertussis was associated with an estimated 16 million cases and 195,000 deaths globally. Sizeable outbreaks of pertussis have been reported over the past 5 years, and disease reemergence has been the focus of international attention to develop a deeper understanding of pathogen virulence and genetic evolution of B. pertussis strains. During the past 20 years, the scientific community has recognized pertussis among adults as well as infants and children. Increased recognition that older children and adolescents are at risk for disease and may transmit B. pertussis to younger siblings has underscored the need to better understand the role of innate, humoral, and cell-mediated immunity, including the role of waning immunity. Although recognition of adult pertussis has increased in tandem with a better understanding of B. pertussis pathogenesis, pertussis in neonates and adults can manifest with atypical clinical presentations. Such disease patterns make pertussis recognition difficult and lead to delays in treatment. Ongoing research using newer tools for molecular analysis holds promise for improved understanding of pertussis epidemiology, bacterial pathogenesis, bioinformatics, and immunology. Together, these advances provide a foundation for the development of new-generation diagnostics, therapeutics, and vaccines.

Rediscovering Pertussis

Pertussis, caused by Bordetella (B.) pertussis, a Gram-negative bacterium, is a highly contagious airway infection. Especially in infants, pertussis remains a major health concern. Acute infection with B. pertussis can cause severe illness characterized by severe respiratory failure, pulmonary hypertension, leucocytosis, and death. Over the past years, rising incidence rates of intensive care treatment in young infants were described. Due to several virulence factors (pertussis toxin, tracheal cytotoxin, adenylate cyclase toxin, filamentous hemagglutinin, and lipooligosaccharide) that promote bacterial adhesion and invasion, B. pertussis creates a unique niche for colonization within the human respiratory tract. The resulting long-term infection is mainly caused by the ability of B. pertussis to interfere with the host's innate and adaptive immune system. Although pertussis is a vaccine-preventable disease, it has persisted in vaccinated populations. Epidemiological data reported a worldwide increase in pertussis incidence among children during the past years. Either acellular pertussis (aP) vaccines or whole-cell vaccines are worldwide used. Recent studies did not detect any differences according to pertussis incidence when comparing the different vaccines used. Most of the currently used aP vaccines protect against acute infections for a period of 6-8 years. The resurgence of pertussis may be due to the lack of herd immunity caused by missing booster immunizations among adolescents and adults, low vaccine coverages in some geographic areas, and genetic changes of different B. pertussis strains. Due to the rising incidence of pertussis, probable solution strategies are discussed. Cocooning strategies (vaccination of close contact persons) and immunizations during pregnancy appear to be an approach to reduce neonatal contagiousness. During the past years, studies focused on the pathway of the immune modulation done by B. pertussis to provide a basis for the identification of new therapeutic targets to enhance the host's immune response and to probably modulate certain virulence factors.

Th1 versus Th2 T cell polarization by whole-cell and acellular childhood pertussis vaccines persists upon re-immunization in adolescence and adulthood

The recent increase in cases of whooping cough among teenagers in the US suggests that the acellular Bordetella pertussis vaccine (aP) that became standard in the mid 1990s might be relatively less effective than the whole-bacteria formulation (wP) previously used since the 1950s. To understand this effect, we compared antibody and T cell responses to a booster immunization in subjects who received either the wP or aP vaccine as their initial priming dose in childhood. Antibody responses in wP- and aP-primed donors were similar. Magnitude of T cell responses was higher in aP-primed individuals. Epitope mapping revealed the T cell immunodominance patterns were similar for both vaccines. Further comparison of the ratios of IFNγ and IL-5 revealed that IFNγ strongly dominates the T cell response in wP-primed donors, while IL-5 is dominant in aP primed individuals. Surprisingly, this differential pattern is maintained after booster vaccination, at times from eighteen years to several decades after the original aP/wP priming. These findings suggest that childhood aP versus wP vaccination induces functionally different T cell responses to pertussis that become fixed and are unchanged even upon boosting.

Bordetella filamentous hemagglutinin and fimbriae: critical adhesins with unrealized vaccine potential

Pertussis, or whooping cough, is a highly contagious respiratory disease that is caused by the Gram-negative bacterium Bordetella pertussis, which is transmitted exclusively from human to human. While vaccination against B. pertussis has been successful, replacement of the whole cell vaccine with an acellular component vaccine has correlated with reemergence of the disease, especially in adolescents and infants. Based on their presumed importance in mediating adherence to host tissues, filamentous hemagglutinin (FHA) and fimbria (FIM) were selected as components of most acellular pertussis vaccines. In this review, we describe the biogenesis of FHA and FIM, recent data that show that these factors do, in fact, play critical roles in adherence to respiratory epithelium, and evidence that they also contribute to persistence in the lower respiratory tract by modulating the host immune response. We also discuss shortcomings of whole cell and acellular pertussis vaccines and the possibility that FHA and FIM could serve as effective protective antigens in next-generation vaccines.

Waning and aging of cellular immunity to Bordetella pertussis

While it is clear that the maintenance of Bordetella pertussis-specific immunity evoked both after vaccination and infection is insufficient, it is unknown at which pace waning occurs and which threshold levels of sustained functional memory B and T cells are required to provide long-term protection. Longevity of human cellular immunity to B. pertussis has been studied less extensively than serology, but is suggested to be key for the observed differences between the duration of protection induced by acellular vaccination and whole cell vaccination or infection. The induction and maintenance of levels of protective memory B and T cells may alter with age, associated with changes of the immune system throughout life and with accumulating exposures to circulating B. pertussis or vaccine doses. This is relevant since pertussis affects all age groups. This review summarizes current knowledge on the waning patterns of human cellular immune responses to B. pertussis as addressed in diverse vaccination and infection settings and in various age groups. Knowledge on the effectiveness and flaws in human B. pertussis-specific cellular immunity ultimately will advance the improvement of pertussis vaccination strategies.

Roads to the development of improved pertussis vaccines paved by immunology

Current acellular pertussis vaccines have various shortcomings, which may contribute to their suboptimal efficacy and waning immunity in vaccinated populations. This calls for the development of new pertussis vaccines capable of inducing long-lived protective immunity. Immunization with whole cell pertussis vaccines and natural infection with Bordetella pertussis induce distinct and more protective immune responses when compared with immunization with acellular pertussis vaccines. Therefore, the immune responses induced with whole cell vaccine or after infection can be used as a benchmark for the development of third-generation vaccines against pertussis. Here, we review the literature on the immunology of B. pertussis infection and vaccination and discuss the lessons learned that will help in the design of improved pertussis vaccines.

To develop improved pertussis vaccines capable of inducing long-lived protective immunity, lessons have to be learned from immunology of Bordetella pertussis infection and current vaccination.

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.

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.

Immune responses to pertussis antigens in infants and toddlers after immunization with multicomponent acellular pertussis vaccine

Given the resurgence of pertussis despite high rates of vaccination with the diphtheria-tetanus-acellular pertussis (DTaP) vaccine, a better understanding of vaccine-induced immune responses to Bordetella pertussis is needed. We investigated the antibody, cell-mediated, and cytokine responses to B. pertussis antigens in children who received the primary vaccination series (at 2, 4, and 6 months) and first booster vaccination (at 15 to 18 months) with 5-component acellular pertussis (aP) vaccine. The majority of subjects demonstrated a 4-fold increase in antibody titer to all four pertussis antigens (pertussis toxin [PT], pertactin [PRN], filamentous hemagglutinin [FHA], and fimbriae [FIM]) following the primary series and booster vaccination. Following the primary vaccine series, the majority of subjects (52 to 67%) mounted a positive T cell proliferative response (stimulation index of ≥ 3) to the PT and PRN antigens, while few subjects (7 to 12%) mounted positive proliferative responses to FHA and FIM. One month after booster vaccination (age 16 to 19 months), our study revealed significant increase in gamma interferon (IFN-γ) production in response to the PT and FIM antigens, a significant increase in IL-2 production with the PT, FHA, and PRN antigens, and a lack of significant interleukin-4 (IL-4) secretion with any of the antigens. While previous reports documented a mixed Th1/Th2 or Th2-skewed response to DTaP vaccine in children, our data suggest that following the first DTaP booster, children aged 16 to 19 months have a cytokine profile consistent with a Th1 response, which is known to be essential for clearance of pertussis infection. To better define aP-induced immune responses following the booster vaccine, further studies are needed to assess cytokine responses pre- and postbooster in DTaP recipients.

Challenges in vaccination of neonates, infants and young children

All neonates, infants and young children receive multiple priming doses and booster vaccinations in the 1st and 2nd year of life to prevent infections by viral and bacterial pathogens. Despite high vaccine compliance, outbreaks of vaccine-preventable infections are occurring worldwide. These data strongly argue for an improved understanding of the immune responses of neonates, infants and young children to vaccine antigens and further study of the exploitable mechanisms to achieve more robust and prolonged immunity with fewer primary and booster vaccinations in the pediatric population. This review will focus on our recent work involving infant and young child immunity following routine recommended vaccinations. The discussion will address vaccine responses with respect to four areas: (1) systemic antibody responses, (2) memory B-cell generation, (3) CD4 T-cell responses, and (4) APC function.

Toxicity and potency evaluation of pertussis vaccines

Current methods for determining the potency and toxicity of pertussis vaccines are outdated and require improvement. The intracerebral challenge test is effective for determining the potency of whole-cell vaccines but is objectionable on animal welfare and technical grounds. The same applies to its modification for assaying acellular pertussis vaccines. Respiratory challenge methods offer an interim solution pending establishment of validated in vitro correlates of protection, for example nitric oxide induction. Their evaluation is being promoted by the World Health Organization through the Pertussis Vaccines Working Group. Current toxicity assays based on weight gain and histamine sensitization of mice are imprecise and need replacement. Limits need to be established for specific toxin content of both acellular and whole-cell vaccines and should be supported by specific assays. More precise methods based on determination of ribosyltransferase activity in tandem with receptor-binding assays are under evaluation. Genome sequence data and the use of gene microarrays to screen responses triggered by vaccine components may also provide leads to improved methods for assessing both toxicity and immunogenicity.

Relative contribution of Th1 and Th17 cells in adaptive immunity to Bordetella pertussis: towards the rational design of an improved acellular pertussis vaccine

Whooping cough caused by Bordetella pertussis is a re-emerging infectious disease despite the introduction of safer acellular pertussis vaccines (Pa). One explanation for this is that Pa are less protective than the more reactogenic whole cell pertussis vaccines (Pw) that they replaced. Although Pa induce potent antibody responses, and protection has been found to be associated with high concentrations of circulating IgG against vaccine antigens, it has not been firmly established that host protection induced with this vaccine is mediated solely by humoral immunity. The aim of this study was to examine the relative contribution of Th1 and Th17 cells in host immunity to infection with B. pertussis and in immunity induced by immunization with Pw and Pa and to use this information to help rationally design a more effective Pa. Our findings demonstrate that Th1 and Th17 both function in protective immunity induced by infection with B. pertussis or immunization with Pw. In contrast, a current licensed Pa, administered with alum as the adjuvant, induced Th2 and Th17 cells, but weak Th1 responses. We found that IL-1 signalling played a central role in protective immunity induced with alum-adsorbed Pa and this was associated with the induction of Th17 cells. Pa generated strong antibody and Th2 responses, but was fully protective in IL-4-defective mice, suggesting that Th2 cells were dispensable. In contrast, Pa failed to confer protective immunity in IL-17A-defective mice. Bacterial clearance mediated by Pa-induced Th17 cells was associated with cell recruitment to the lungs after challenge. Finally, protective immunity induced by an experimental Pa could be enhanced by substituting alum with a TLR agonist that induces Th1 cells. Our findings demonstrate that alum promotes protective immunity through IL-1β-induced IL-17A production, but also reveal that optimum protection against B. pertussis requires induction of Th1, but not Th2 cells.

Immunity to the respiratory pathogen Bordetella pertussis

Bordetella pertussis causes whooping cough, a severe respiratory tract infection in infants and children, and also infects adults. Studies in murine models have shown that innate immune mechanisms involving dendritic cells, macrophages, neutrophils, natural killer cells, and antimicrobial peptides help to control the infection, while complete bacterial clearance requires cellular immunity mediated by T-helper type 1 (Th1) and Th17 cells. Whole cell pertussis vaccines (wP) are effective, but reactogenic, and have been replaced in most developed countries by acellular pertussis vaccines (aP). However, the incidence of pertussis is still high in many vaccinated populations; this may reflect sub-optimal, waning, or escape from immunity induced by current aP. Protective immunity generated by wP appears to be mediated largely by Th1 cells, whereas less efficacious alum-adjuvanted aP induce strong antibody Th2 and Th17 responses. New generation aP that induce Th1 rather than Th2 responses are required to improve vaccine efficacy and prevent further spread of B. pertussis.

Both CD4⁺ and CD8⁺ lymphocytes participate in the IFN-γ response to filamentous hemagglutinin from Bordetella pertussis in infants, children, and adults

Infant CD4⁺ T-cell responses to bacterial infections or vaccines have been extensively studied, whereas studies on CD8⁺ T-cell responses focused mainly on viral and intracellular parasite infections. Here we investigated CD8⁺ T-cell responses upon Bordetella pertussis infection in infants, children, and adults and pertussis vaccination in infants. Filamentous hemagglutinin-specific IFN-γ secretion by circulating lymphocytes was blocked by anti-MHC-I or -MHC-II antibodies, suggesting that CD4⁺ and CD8⁺ T lymphocytes are involved in IFN-γ production. Flow cytometry analyses confirmed that both cell types synthesized antigen-specific IFN-γ, although CD4⁺ lymphocytes were the major source of this cytokine. IFN-γ synthesis by CD8⁺ cells was CD4⁺ T cell dependent, as evidenced by selective depletion experiments. Furthermore, IFN-γ synthesis by CD4⁺ cells was sometimes inhibited by CD8⁺ lymphocytes, suggesting the presence of CD8⁺ regulatory T cells. The role of this dual IFN-γ secretion by CD4⁺ and CD8⁺ T lymphocytes in pertussis remains to be investigated.

Th2-polarisation of cellular immune memory to neonatal pertussis vaccination

Current infant vaccination against pertussis in North America and Australia requires three doses of vaccines including diphtheria, tetanus and acellular pertussis antigens (DTaP) at 2, 4 and 6 months of age. Interest is growing in the possibility that vaccination at birth might provide earlier protection of infants, but early vaccination also gives rise to concerns over the potential for excessive Th2-polarisation of pertussis-specific T-cell memory profiles. We evaluated this issue as part of a small pilot study comparing infants receiving a monovalent acellular pertussis vaccine (aP) at birth or birth and at 1 month, followed by DTaP at 2, 4 and 6 months with infants receiving DTaP only from 2 months. We compared in vitro Th-memory responses at 8 months and pertussis-specific IgG in serum at 2, 4, 6 and 8 months. Neonatal vaccination elicited earlier IgG responses, but accompanying Th-memory profiles displayed a strong Th2 bias with high IL-5 and IL-13 production. The correlation between T-cell memory profiles and other clinical outcomes should be evaluated in larger trials of neonatal aP vaccine.

Cellular immunity as a potential cause of local reactions to booster vaccination with diphtheria and tetanus toxoids and acellular pertussis antigens

BACKGROUND

Booster doses of diphtheria-tetanus-acellular pertussis (DTaP) vaccines restore waning serum antibody values but frequently cause local inflammation. Cell-mediated immunity (CMI) develops after primary DTaP vaccination and might contribute to local reactions to booster doses, a possibility explored in this study.

METHODS

Healthy 4 to 5-year-old children were bled before DTaP.IPV booster vaccination. Peripheral blood mononuclear cells were tested for proliferative responses to D toxoid (DT), T toxoid, pertussis toxoid, pertactin, filamentous hemagglutinin and fimbriae (FIM) types 2, 3, and cytokine release patterns assessed. Proliferative responses were examined in relation to prebooster serum antibody concentrations and local reaction rates, previously reported.

RESULTS

Among 167 subjects tested, proliferative response rates were: filamentous hemagglutinin 95%, pertussis toxoid 90%, T toxoid 84%, pertactin 67%, DT 41%, and FIM 31%. Responses were present to 3 to 6 antigens in 87% of subjects and absent altogether in 2%. Subjects without residual pertussis antibodies often had CMI to pertussis antigens. Subjects with CMI had higher corresponding serum antibody concentrations before the booster, compared with CMI-negative subjects. CMI responses were mixed TH1/TH2 type by cytokine profile for all antigens. Injection site erythema (>or=5 mm) was twice as frequent in those with than without CMI to DT (P=0.009) or FIM (P=0.042, Fisher exact test), the only antigens evaluable.

CONCLUSION

CMI to vaccine antigens was often detectable in children before preschool booster vaccination and preliminary evidence suggests a role for CMI in local reactions to this dose.

Monocyte-derived interleukin-10 depresses the Bordetella pertussis- specific gamma interferon response in vaccinated infants

Antigen-specific gamma interferon (IFN-gamma) has been demonstrated to participate in protection against Bordetella pertussis infection. Circulating mononuclear cells from B. pertussis-infected and from pertussis-vaccinated infants secrete high amounts of IFN-gamma after in vitro stimulation by B. pertussis antigens, but with a large variation in the secreted IFN-gamma levels between individuals. We show here that the inhibition of the specific IFN-gamma response can be at least partially attributed to IL-10 secretion by monocytes. This IL-10 secretion was not associated with polymorphisms at positions -1082, -819, and -592 of the IL-10 gene promoter, suggesting that other genetic or environmental factors affect IL-10 expression and secretion.

Immunity to pertussis 5 years after booster immunization during adolescence

BACKGROUND

We conducted a 5-year follow-up study on the persistence of pertussis-specific antibody and cell-mediated immunity after booster immunization of adolescents aged 11-13 years with a tricomponent acellular pertussis vaccine (Boostrix; trials diphtheria-tetanus-acellular pertussis [Tdap]-004/030).

METHODS

Cellular and humoral immunity to pertussis toxin (PT), filamentous hemagglutinin, and pertactin were measured in adolescents (age, 16 years) 5 years after booster immunization. Similar investigations were performed for control adolescents who had received only diphtheria and tetanus booster vaccination.

RESULTS

Five years after pertussis booster vaccination, the geometric mean concentrations of immunoglobulin G (IgG) elicited by each of the 3 pertussis vaccine antigens decreased from 1-month and 3-year postvaccination levels, but with the exception of PT IgG, were still higher than the prevaccination levels. PT IgG levels were undetectable in 28% of the subjects, but 44% of those subjects still tested positive for cell-mediated immunity to PT. Filamentous hemagglutinin IgG and pertactin IgG levels were significantly higher in Tdap-boosted adolescents than in the control subjects. Antibody concentrations at 1 month after vaccination strongly predicted antibody persistence. Cell-mediated immunity levels to PT, filamentous hemagglutinin, and pertactin persisted above the prebooster levels measured 5 years earlier.

CONCLUSIONS

The results of the present study of adolescents indicate that the interval between acellular pertussis booster immunizations might be extended beyond 5 years.

Long-term humoral and cell-mediated immunity after acellular pertussis vaccination compares favourably with whole-cell vaccines 6 years after booster vaccination in the second year of life

Humoral and cell-mediated immune responses (CMI) were evaluated in subjects 3 and 6 years after primary and booster vaccination with either three-component acellular (Pa) or whole-cell (Pw) vaccines. Low anti-pertussis toxin (PT) antibody levels confirmed the absence of pertussis disease, consistent with ongoing protection. Anti-pertactin (PRN) antibodies, remained at higher levels in Pa-vaccinated subjects. At year 6, CMI responses continued to be present and were higher in Pa-vaccinated than Pw-vaccinated subjects. Long-term protection with Pa vaccines can be expected to be at least as good as that provided by efficacious Pw vaccines.

Cellular immunity in adolescents and adults following acellular pertussis vaccine administration

Cell-mediated immune (CMI) responses to an acellular pertussis vaccine administered to 49 subjects, a subset of participants in the National Institutes of Health-funded adult acellular pertussis vaccine efficacy trial, were evaluated and compared with antibody responses to vaccine antigens. Levels of proliferation of and cytokine secretion from lymphocytes cultured in the presence of pertussis toxin, filamentous hemagglutinin, or pertactin were measured before vaccination and 1 month and 1 year after vaccination. Statistically significant increases in lymphocyte stimulation indices and cytokine secretion were noted at both 1 month and 1 year after vaccination. Brisk pertussis antigen-specific immunoglobulin G responses were also noted at 1 month after vaccination, but these responses had declined by nearly 50% at 1 year after vaccination. These studies clearly demonstrate that both cellular and humoral immune responses occur after the administration of acellular pertussis vaccines to adolescents and adults but that the CMI responses are of greater magnitude and longer duration. CMI responses may be a better correlate of long-term protection.

Cellular immunity in healthy volunteers treated with an octavalent conjugate Pseudomonas aeruginosa vaccine

Humoral immunity in response to an octavalent O-polysaccharide-toxin A conjugate Pseudomonas aeruginosa vaccine is well studied, and a phase III clinical study in cystic fibrosis (CF) patients is currently ongoing. In contrast, little is known about cellular immunity induced by this vaccine. Fifteen healthy volunteers were immunized on days 1 and 60. Parameters of cellular immunity were studied before vaccination on day 1, and on day 74. Analyses included flow cytometry of whole blood and antigen-induced proliferation of and cytokine production by lymphocyte cultures. The effects of immunization on the composition of peripheral blood lymphocytes as determined by flow cytometry were minor. In contrast, after immunization a highly significant increase of proliferation in response to stimulation with detoxified toxin A was noted: the stimulation index rose from 1.4 on day 1 to 42.2 on day 74 (restimulation with 0.4 microg/ml; P = 0.003). Immunization led to significant production of interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha by antigen-stimulated lymphocytes. In contrast, no significant induction of interleukin (IL)-4 or IL-10 was observed. In conclusion, immunization of healthy volunteers led to activation of cellular immunity including strong antigen-specific proliferation and cytokine production. In CF patients priming of the cellular immune system towards a Th1-like pattern would be of potential advantage. Therefore, confirmatory analyses in immunized CF patients with and without chronic infection with P. aeruginosa are foreseen.

Cellular immunity in healthy volunteers treated with an octavalent conjugate Pseudomonas aeruginosa vaccine

Humoral immunity in response to an octavalent O-polysaccharide-toxin A conjugate Pseudomonas aeruginosa vaccine is well studied, and a Phase III clinical study in cystic fibrosis (CF) patients is currently ongoing. In contrast, little is known about cellular immunity induced by this vaccine. Fifteen healthy volunteers were immunized on days 1 and 60. Parameters of cellular immunity were studied before vaccination on day 1, and on day 74. Analyses included flow cytometry of whole blood, and antigen-induced proliferation of and cytokine production by lymphocyte cultures. The effects of immunization on the composition of peripheral blood lymphocytes as determined by flow cytometry were minor. In contrast, after immunization a highly significant increase of proliferation in response to stimulation with detoxified toxin A was noted: the stimulation index rose from 1.4 on day 1 to 42.2 on day 74 (restimulation with 0.4 microg/ml; P = 0.003). Immunization led to significant production of interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha by antigen-stimulated lymphocytes. In contrast, no significant induction of interleukin (IL)-4 or IL-10 was observed. In conclusion, immunization of healthy volunteers led to activation of cellular immunity including strong antigen-specific proliferation and cytokine production. In CF patients priming of the cellular immune system towards a Th1-like pattern would be of potential advantage. Therefore, confirmatory analyses in immunized CF patients with and without chronic infection with P. aeruginosa are foreseen.

Overview of pertussis: focus on epidemiology, sources of infection, and long term protection after infant vaccination

BACKGROUND

Pertussis, or whooping cough, is a bacterial disease characterized by paroxysmal cough often accompanied by inspiratory whoop and posttussive emesis. Although the introduction of whole-cell pertussis vaccine in the 1940s led to a significant decline in the incidence of pertussis, there has been a gradual increase in reported pertussis cases since 1980. Some of these cases are in infants too young to have received routine pertussis vaccination, and many are in adolescents immunized previously as young children.

METHODS

Based on a literature review, an overview of pertussis is provided, focusing on epidemiology, sources of infection, and trends in incidence patterns, particularly among adolescents. Issues surrounding long-term protection after infant vaccination are also discussed.

RESULTS

The most dramatic increase in pertussis incidence has been among adolescents and young adults. Waning vaccine-induced immunity and refinements in the diagnosis of pertussis have contributed to the rise in the occurrence of pertussis in older age groups. Disease rates in infants have also increased. Determining the source of infection in infants can be challenging, but studies have demonstrated that many infant cases are attributable to infections in adolescent or adult family members.

CONCLUSIONS

Pertussis is on the rise, particularly in adolescents. Booster vaccination of adolescents with less-reactogenic acellular pertussis vaccines appears to be the most logical approach to disease prevention in adolescents and reduced transmission to young infants.

Molecular pathogenesis, epidemiology, and clinical manifestations of respiratory infections due to Bordetella pertussis and other Bordetella subspecies

Bordetella respiratory infections are common in people (B. pertussis) and in animals (B. bronchiseptica). During the last two decades, much has been learned about the virulence determinants, pathogenesis, and immunity of Bordetella. Clinically, the full spectrum of disease due to B. pertussis infection is now understood, and infections in adolescents and adults are recognized as the reservoir for cyclic outbreaks of disease. DTaP vaccines, which are less reactogenic than DTP vaccines, are now in general use in many developed countries, and it is expected that the expansion of their use to adolescents and adults will have a significant impact on reducing pertussis and perhaps decrease the circulation of B. pertussis. Future studies should seek to determine the cause of the unique cough which is associated with Bordetella respiratory infections. It is also hoped that data gathered from molecular Bordetella research will lead to a new generation of DTaP vaccines which provide greater efficacy than is provided by today's vaccines.

Acellular Pertussis Vaccine Safety and Efficacy in Children, Adolescents and Adults

This review offers a perspective on the acellular pertussis vaccine efficiency trials concluded in the 1990s and presents the main conclusions of a meta-analysis of 52 studies that assessed the safety and efficacy of the diphtheria-tetanus (DT)-whole cell pertussis (DTwP) and DT-acellular pertussis (DTaP) vaccines administered to children. A clear serological correlate of immunity to pertussis following DTaP vaccination was not identified despite an intensive analysis. It can be speculated that this may be because various combinations of antibody to agglutinogens (pertussis toxin, filamentous haemagglutinin, pertactin and fimbriae) provide protection, or because serum antibody levels and responses do not uniformly reflect mucosal IgA antibody levels.Long-term efficacy following DTaP vaccination is becoming characterised and cell-mediated immunity (T-cell memory) may have importance. DTaP vaccination appears to establish herd immunity after sufficient uptake within communities and countries. As experience with DTaP vaccine safety has accumulated, a 1-2% occurrence of large, local injection reactions with all products has been defined for booster doses. The pathophysiological mechanisms for the reactions are not established but a majority appear likely to be IgE-mediated reactive oedema and a minority to be IgG-mediated reactive Arthus-type reactions. DTwP and DTaP combinations with other vaccines have been studied and licensed; the most controversial combination products are the DTaP/Haemophilus influenzae type B polysaccharide conjugate vaccines. Pertussis epidemiology is changing with a clear increase in occurrence in adolescents and adults. This development has spurred studies and licensure of safer DTaP vaccines for this older population. The economic impact of pertussis and transmission from adults to vulnerable infants provides a cost-benefit justification for widespread use of DTaP vaccines in all age groups with routine boosting every 10 years.

Pertussis-specific cell-mediated and humoral immunity in adolescents 3 years after booster immunization with acellular pertussis vaccine

We evaluated pertussis-specific cell-mediated immunity (CMI) and humoral immunity in adolescents 3 years after they received an acellular pertussis booster immunization. Two hundred sixty-four adolescents were examined for immunoglobulin G antibodies, and 49 were examined for CMI against Bordetella pertussis antigens 40 months after receiving the booster. A control group of similarly aged adolescents who had received diphtheria and tetanus vaccination 3 years earlier was included for comparison. Pertussis-specific CMI persisted at greater than prebooster immunization levels. Although they had decreased by the 3-year follow-up, antibody levels remained significantly higher than prebooster immunization levels. Antibodies against pertussis antigens and CMI against filamentous hemagglutinin and pertactin were significantly higher in vaccinated adolescents than in control subjects. The acellular pertussis booster immunization provides long-term CMI and humoral immunity lasting for >or=3 years. The significantly higher immunity observed in the diphtheria, tetanus, and acellular pertussis vaccine recipients, compared with that in control subjects, indicates that these responses are more likely to have resulted from the booster immunization than from the boosting effects of natural B. pertussis infection.

T-cell immune response assessment as a complement to serology and intranasal protection assays in determining the protective immunity induced by acellular pertussis vaccines in mice

The relative value of antibodies and/or T-cell immune responses to Bordetella pertussis antigens in the immunity induced by acellular pertussis (aP) vaccines is still an open issue, probably due to the incomplete knowledge on the mechanisms of protective immunity to pertussis. The relevance of T-cell immune responses in protection from pertussis has been demonstrated in murine and human models of infection; thus, in this study, the ability of different vaccine preparations of three component (pertussis toxin, filamentous hemagglutinin, and pertactin) aP vaccines to induce T-cell responses was investigated in mice. All vaccine preparations examined passed the immunogenicity control test, based on antibody titer assessment, according to European Pharmacopoeia standards, and protected mice from B. pertussis intranasal challenge, but not all preparations were able to prime T cells to pertussis toxin, the specific B. pertussis antigen. In particular, one vaccine preparation was unable to induce proliferation and gamma interferon (IFN-gamma) production while the other two gave borderline results. The evaluation of T-cell responses to pertussis toxin antigen may provide information on the protective immunity induced by aP vaccines in animal models. Considering the critical role of the axis interleukin-12-IFN-gamma for protection from pertussis, our results suggest that testing the induction of a key protective cytokine such as IFN-gamma could be an additional tool for the evaluation of the immune response induced by aP vaccines.

Pertussis: persistent pathogen, imperfect vaccines

Routine use of pertussis vaccines has diminished the incidence of this disease but has not eliminated the pathogen. Pertussis remains a significant cause of disease in both very young infants and in the adolescent and adult populations. Acellular pertussis vaccines have fewer adverse reactions compared with whole-cell pertussis vaccines. Although efficacious against severe disease, current vaccines may not be as efficacious against milder forms of infection. New methodologies for understanding disease pathogenesis, immune responses and vaccine development are needed to effectively interrupt continued transmission of this pathogen.

Whole-cell Bordetella pertussis vaccine component modulates the mouse immune response to an unrelated soluble antigen

Several factors are involved in the selective activation of Th1 or Th2 cells, such as different physical characteristics of antigens and the type of antigen-presenting cells involved in the immune response, among others. To study the influence of a particulate antigen on Th1/Th2 cell differentiation during the immune response to another antigen, we analysed the immune response to tetanus toxoid (soluble antigen) in BALB/c mice immunized with one of the three following vaccines: tetanus and diphtheria toxoids (DT), or DT associated with whole-cell Bordetella pertussis or its soluble antigens (DTPw and DTPa, respectively). Similar total antibody levels were observed for all vaccines. DT vaccine showed a higher IgG1/IgG2a ratio than the similar values observed for DTPw and DTPa vaccines. DT- and DTPa-primed spleen cells showed a Th2 (IL-5) profile while a Th1/Th2 (IFN gamma, IL-5) profile was observed for DTPw. IL-6 was only produced by DTPw-primed cells. Besides, IL-12 levels induced by DTPw were three times higher than the ones induced by both DT and DTPa. Our findings indicate that whole-cell B. pertussis priming modifies the tetanus immune response from Th2 to Th1/Th2 type probably via inflammatory mechanisms. In addition, in the light of conflicting reports regarding the mechanisms of protection induced by DTP vaccines, we studied the pertussis immune response. Only DTPw immunization generated memory T cells capable of proliferating with B. pertussis as an in vitro stimulus. Results might indicate that these cells may not play a key role in protecting against B. pertussis when the host is vaccinated with DTPa.