Should fimbriae be included in pertussis vaccines? Studies on ELISA IgG anti-Fim2/3 antibodies after vaccination and infection

Bordetella bronchiseptica and Bordetella pertussis: Similarities and Differences in Infection, Immuno-Modulation, and Vaccine Considerations

Bordetella pertussis and Bordetella bronchiseptica belong to the genus Bordetella, which comprises 14 other species. B. pertussis is responsible for whooping cough in humans, a severe infection in children and less severe or chronic in adults. These infections are restricted to humans and currently increasing worldwide. B. bronchiseptica is involved in diverse respiratory infections in a wide range of mammals. For instance, the canine infectious respiratory disease complex (CIRDC), characterized by a chronic cough in dogs. At the same time, it is increasingly implicated in human infections, while remaining an important pathogen in the veterinary field. Both Bordetella can evade and modulate host immune responses to support their persistence, although it is more pronounced in B. bronchiseptica infection. The protective immune responses elicited by both pathogens are comparable, while there are important characteristics in the mechanisms that differ. However, B. pertussis pathogenesis is more difficult to decipher in animal models than those of B. bronchiseptica because of its restriction to humans. Nevertheless, the licensed vaccines for each Bordetella are different in terms of formulation, route of administration and immune responses induced, with no known cross-reaction between them. Moreover, the target of the mucosal tissues and the induction of long-lasting cellular and humoral responses are required to control and eliminate Bordetella. In addition, the interaction between both veterinary and human fields are essential for the control of this genus, by preventing the infections in animals and the subsequent zoonotic transmission to humans.

DTaP5-HBV-IPV-Hib pediatric hexavalent combination vaccine for use in children from 6 weeks through to 4 years of age

Introduction: Combination vaccines reduce the number of injections received by children, hence improving timeliness and coverage, and general acceptability among caregivers and health-care providers. The most recent hexavalent vaccine, DTaP5-HBV-IPV-Hib, has been also approved by the FDA.Areas covered: DTaP5-HBV-IPV-Hib has demonstrated good immunogenic and safety profiles, not inferior to other hexavalent vaccines already in use in the European market. Either (2p+1/3p+1) immunization schedules can be used with no significant differences. A low incidence of severe adverse events has been shown, similar to other combination vaccines. No issues have arisen when concomitantly administered with other vaccines.Expert opinion: The inclusion of two additional acellular pertussis components (FIM2 and FIM3) might yield better protection against the disease, but this remains to be clinically proven. The new vaccine uses Hib with unique protein carrier (PRP-OMPC) which elicits higher earlier immune response without compromising safety. Compliance with the immunization schedules is expected to increase by decreasing the number of injections needed in combined vaccines for a single visit. In addition, the improvements on the ease-of-use by its liquid-formulation, makes the vaccine preparation more acceptable for use in clinics and may reduce the odds of administration errors.

Vaccine acquired pertussis immunity was weakened at 4 years of age and asymptomatic pertussis infection was suspected based on serological surveillance

Serological surveillance of pertussis antibodies was performed in 118 children aged 1-12 years. The positivity of pertussis toxin (PT) antibodies was low at 4-6 years and significantly higher at 8-9 years, compared with those at 6 years. Fimbriae 2 (Fim2) antibody showed similar response to the PT antibody. Higher antibody titers against Fim3 were observed among subjects ≥5 years and highest at 8 years. Data demonstrated that the vaccine-induced antibodies decayed by 4-5 years and subclinical pertussis infection was suspected thereafter, suggesting the need for additional dose at around 4-5 years.

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.

Bordetella Pertussis virulence factors in the continuing evolution of whooping cough vaccines for improved performance

Despite high vaccine coverage, whooping cough caused by Bordetella pertussis remains one of the most common vaccine-preventable diseases worldwide. Introduction of whole-cell pertussis (wP) vaccines in the 1940s and acellular pertussis (aP) vaccines in 1990s reduced the mortality due to pertussis. Despite induction of both antibody and cell-mediated immune (CMI) responses by aP and wP vaccines, there has been resurgence of pertussis in many countries in recent years. Possible reasons hypothesised for resurgence have ranged from incompliance with the recommended vaccination programmes with the currently used aP vaccine to infection with a resurged clinical isolates characterised by mutations in the virulence factors, resulting in antigenic divergence with vaccine strain, and increased production of pertussis toxin, resulting in dampening of immune responses. While use of these vaccines provide varying degrees of protection against whooping cough, protection against infection and transmission appears to be less effective, warranting continuation of efforts in the development of an improved pertussis vaccine formulations capable of achieving this objective. Major approaches currently under evaluation for the development of an improved pertussis vaccine include identification of novel biofilm-associated antigens for incorporation in current aP vaccine formulations, development of live attenuated vaccines and discovery of novel non-toxic adjuvants capable of inducing both antibody and CMI. In this review, the potential roles of different accredited virulence factors, including novel biofilm-associated antigens, of B. pertussis in the evolution, formulation and delivery of improved pertussis vaccines, with potential to block the transmission of whooping cough in the community, are discussed.

Impact of age and vaccination history on long-term serological responses after symptomatic B. pertussis infection, a high dimensional data analysis

Capturing the complexity and waning patterns of co-occurring immunoglobulin (Ig) responses after clinical B. pertussis infection may help understand how the human host gradually loses protection against whooping cough. We applied bi-exponential modelling to characterise and compare B. pertussis specific serological dynamics in a comprehensive database of IgG, IgG subclass and IgA responses to Ptx, FHA, Prn, Fim2/3 and OMV antigens of (ex-) symptomatic pertussis cases across all age groups. The decay model revealed that antigen type and age group were major factors determining differences in levels and kinetics of Ig (sub) classes. IgG-Ptx waned fastest in all age groups, while IgA to Ptx, FHA, Prn and Fim2/3 decreased fast in the younger but remained high in older (ex-) cases, indicating an age-effect. While IgG1 was the main IgG subclass in response to most antigens, IgG2 and IgG3 dominated the anti-OMV response. Moreover, vaccination history plays an important role in post-infection Ig responses, demonstrated by low responsiveness to Fim2/3 in unvaccinated elderly and by elevated IgG4 responses to multiple antigens only in children primed with acellular pertussis vaccine (aP). This work highlights the complexity of the immune response to this re-emerging pathogen and factors determining its Ig quantity and quality.

Laboratory Diagnosis of Pertussis

The introduction of vaccination in the 1950s significantly reduced the morbidity and mortality of pertussis. However, since the 1990s, a resurgence of pertussis has been observed in vaccinated populations, and a number of causes have been proposed for this phenomenon, including improved diagnostics, increased awareness, waning immunity, and pathogen adaptation. The resurgence of pertussis highlights the importance of standardized, sensitive, and specific laboratory diagnoses, the lack of which is responsible for the large differences in pertussis notifications between countries. Accurate laboratory diagnosis is also important for distinguishing between the several etiologic agents of pertussis-like diseases, which involve both viruses and bacteria. If pertussis is diagnosed in a timely manner, antibiotic treatment of the patient can mitigate the symptoms and prevent transmission. During an outbreak, timely diagnosis of pertussis allows prophylactic treatment of infants too young to be (fully) vaccinated, for whom pertussis is a severe, sometimes fatal disease. Finally, reliable diagnosis of pertussis is required to reveal trends in the (age-specific) disease incidence, which may point to changes in vaccine efficacy, waning immunity, and the emergence of vaccine-adapted strains. Here we review current approaches to the diagnosis of pertussis and discuss their limitations and strengths. In particular, we emphasize that the optimal diagnostic procedure depends on the stage of the disease, the age of the patient, and the vaccination status of the patient.

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.

Immunization with the recombinant Cholera toxin B fused to Fimbria 2 protein protects against Bordetella pertussis infection

This study examined the immunogenic properties of the fusion protein fimbria 2 of Bordetella pertussis (Fim2)—cholera toxin B subunit (CTB) in the intranasal murine model of infection. To this end B. pertussis Fim2 coding sequence was cloned downstream of the cholera toxin B subunit coding sequence. The expression and assembly of the fusion protein into pentameric structures (CTB-Fim2) were evaluated by SDS-PAGE and monosialotetrahexosylgaglioside (GM1-ganglioside) enzyme-linked immunosorbent assay (ELISA). To evaluate the protective capacity of CTB-Fim2, an intraperitoneal or intranasal mouse immunization schedule was performed with 50 μg of CTB-Fim2. Recombinant (rFim2) or purified (BpFim2) Fim2, CTB, and phosphate-buffered saline (PBS) were used as controls. The results showed that mice immunized with BpFim2 or CTB-Fim2 intraperitoneally or intranasally presented a significant reduction in bacterial lung counts compared to control groups (P < 0.01 or P < 0.001 , resp.). Moreover, intranasal immunization with CTB-Fim2 induced significant levels of Fim2-specific IgG in serum and bronchoalveolar lavage (BAL) and Fim2-specific IgA in BAL. Analysis of IgG isotypes and cytokines mRNA levels showed that CTB-Fim2 results in a mixed Th1/Th2 (T-helper) response. The data presented here provide support for CTB-Fim2 as a promising recombinant antigen against Bordetella pertussis infection.

Modeling rates of infection with transient maternal antibodies and waning active immunity: application to Bordetella pertussis in Sweden

Serological surveys provide reliable information from which to calculate forces (instantaneous rates) of infection, but waning immunity and clinical consequences that depend on residual immunity complicate interpretation of results. We devised a means of calculating these rates that accounts for passively acquired maternal antibodies that decay or active immunity that wanes, permitting re-infection. We applied our method to pertussis (whooping cough) in Sweden, where vaccination was discontinued from 1979 to 1995. A national cross-sectional serosurvey of antibodies to pertussis toxin, which peak soon after infection and then decay, was conducted shortly after vaccination resumed. Together with age-specific contact rates in Finland, contemporary forces of infection enable us to evaluate the recent assertion that the probability of infection upon contact is age-independent. We find elevated probabilities among children, adolescents and young adults, whose contacts may be more intimate than others. Products of contact rates and probabilities of infection permit transmission modeling and estimation of the intrinsic reproduction number. In contrast to another recent estimate, ours approximates the ratio of life expectancy and age at first infection. Our framework is sufficiently general to accommodate more realistic sojourn distributions and additional lifetime infections.

Antibody responses to Bordetella pertussis Fim2 or Fim3 following immunization with a whole-cell, two-component, or five-component acellular pertussis vaccine and following pertussis disease in children in Sweden in 1997 and 2007

Bordetella pertussis fimbriae (Fim2 and Fim3) are components of a five-component acellular pertussis vaccine (diphtheria-tetanus-acellular pertussis vaccine [DTaP5]), and antibody responses to fimbriae have been associated with protection. We analyzed the IgG responses to individual Fim2 and Fim3 in sera remaining from a Swedish placebo-controlled efficacy trial that compared a whole-cell vaccine (diphtheria-tetanus-whole-cell pertussis vaccine [DTwP]), a two-component acellular pertussis vaccine (DTaP2), and DTaP5. One month following three doses of the Fim-containing vaccines (DTwP or DTaP5), anti-Fim2 geometric mean IgG concentrations were higher than those for anti-Fim3, with a greater anti-Fim2/anti-Fim3 IgG ratio elicited by DTaP5. We also determined the responses in vaccinated children following an episode of pertussis. Those who received DTaP5 showed a large rise in anti-Fim2 IgG, reflecting the predominant Fim2 serotype at the time. In contrast, those who received DTwP showed an equal rise in anti-Fim2 and anti-Fim3 IgG concentrations, indicating that DTwP may provide a more efficient priming effect for a Fim3 response following contact with B. pertussis. Anti-Fim2 and anti-Fim3 IgG concentrations were also determined in samples from two seroprevalence studies conducted in Sweden in 1997, when no pertussis vaccine was used and Fim2 isolates predominated, and in 2007, when either DTaP2 or DTaP3 without fimbriae was used and Fim3 isolates predominated. Very similar distributions of anti-Fim2 and anti-Fim3 IgG concentrations were obtained in 1997 and 2007, except that anti-Fim3 concentrations in 1997 were lower. This observation, together with the numbers of individuals with both anti-Fim2 and anti-Fim3 IgG concentrations, strongly suggests that B. pertussis expresses both Fim2 and Fim3 during infection.

A phase I clinical study of a live attenuated Bordetella pertussis vaccine--BPZE1; a single centre, double-blind, placebo-controlled, dose-escalating study of BPZE1 given intranasally to healthy adult male volunteers

Background

Acellular pertussis vaccines do not control pertussis. A new approach to offer protection to infants is necessary. BPZE1, a genetically modified Bordetella pertussis strain, was developed as a live attenuated nasal pertussis vaccine by genetically eliminating or detoxifying 3 toxins.

Methods

We performed a double-blind, placebo-controlled, dose-escalating study of BPZE1 given intranasally for the first time to human volunteers, the first trial of a live attenuated bacterial vaccine specifically designed for the respiratory tract. 12 subjects per dose group received 10³, 10⁵ or 10⁷ colony-forming units as droplets with half of the dose in each nostril. 12 controls received the diluent. Local and systemic safety and immune responses were assessed during 6 months, and nasopharyngeal colonization with BPZE1 was determined with repeated cultures during the first 4 weeks after vaccination.

Results

Colonization was seen in one subject in the low dose, one in the medium dose and five in the high dose group. Significant increases in immune responses against pertussis antigens were seen in all colonized subjects. There was one serious adverse event not related to the vaccine. Other adverse events were trivial and occurred with similar frequency in the placebo and vaccine groups.

Conclusions

BPZE1 is safe in healthy adults and able to transiently colonize the nasopharynx. It induces immune responses in all colonized individuals. BPZE1 can thus undergo further clinical development, including dose optimization and trials in younger age groups.

Trial Registration

ClinicalTrials.gov NCT01188512

Antibody responses to individual Bordetella pertussis fimbrial antigen Fim2 or Fim3 following immunization with the five-component acellular pertussis vaccine or to pertussis disease

Bordetella pertussis expresses two serologically distinct fimbriae (Fim2 and Fim3) which are included in the Sanofi Pasteur 5-component acellular pertussis vaccine, and antibody responses to these antigens have been shown to be associated with protection. Studies to date have assessed the IgG response to this vaccine using a copurified mixture of Fim2 and Fim3, and the response to the individual antigens has not been characterized. We have purified separate Fim2 and Fim3 from strains that express either Fim2 or Fim3 and have used these antigens in an enzyme-linked immunosorbent assay (ELISA) to quantify IgG responses following immunization with 5-component acellular pertussis vaccine in 15-month-old, 4- to 6-year-old, and 11- to 18-year-old subjects. All individuals showed increases in Fim2 and Fim3 IgG concentrations following immunization, with 3-fold-greater Fim2 than Fim3 IgG concentrations seen in the younger two age groups. Fim2 IgG concentrations were 1.5-fold greater than Fim3 IgG concentrations in the 11- to 18-year-olds. We have also compared Fim2 and Fim3 IgG concentrations in individuals with prolonged cough who were diagnosed as having recent pertussis using a pertussis toxin (Ptx) IgG ELISA with individuals with prolonged cough but without elevated Ptx IgG concentrations. Individuals with evidence of recent pertussis had greater Fim3 IgG concentrations, consistent with the predominant serotype of isolates obtained in the United Kingdom. However, a surprising number of individuals had moderate Fim2 IgG concentrations despite very few isolates of that serotype obtained in the sampling period.

Impaired long-term maintenance and function of Bordetella pertussis specific B cell memory

Frequent occurrence of whooping cough in vaccinated populations suggests limited duration of vaccine-induced immunological memory. To investigate peculiarities in B cell memory specific for pertussis antigens P.69 pertactin (P.69 Prn), pertussis toxin (Ptx) and filamentous hemagglutinin (FHA), we monitored the induction and maintenance of specific serum IgG, long-lived bone marrow (BM)-derived plasma cell (PC) and splenic memory B cell (B(mem)) populations in a long-term preclinical vaccination model. Groups of BALB/c mice were primed and boosted (day 28) with a combined diphtheria (D), tetanus (T), acellular pertussis (aP) vaccine (DTaP) or whole cell pertussis (P) vaccine (DTP) and the immune status was followed over time. Levels of pertussis specific IgG, induced after primary and booster immunization, peaked at day 98 to decline thereafter. This was not paralleled by a decay, but rather an increase in BM resident specific PC, over time (>1 year). In contrast, splenic B(mem) peaked after booster immunization to decline till background levels. Late recall of immunological memory more than 1 year after primary and booster vaccination, however, did reveal a rapid proliferative response of pre-existing B(mem) but failed to evoke an anamnestic IgG response. A combination of waning P-antigen specific IgG production by PC and poor functions of the B(mem) compartment such as self-maintenance and anamnestic IgG responses could be a hallmark of waning pertussis immunity. A better understanding of the mechanisms of limited immunological memory to pertussis may help to improve current vaccines.

Antibody response patterns to Bordetella pertussis antigens in vaccinated (primed) and unvaccinated (unprimed) young children with pertussis

In a previous study, it was found that the antibody response to a nonvaccine pertussis antigen in children who were vaccine failures was reduced compared with the response in nonvaccinated children who had pertussis. In two acellular pertussis vaccine efficacy trials in Sweden, we studied the convalescent-phase enzyme-linked immunosorbent assay (ELISA) geometric mean values (GMVs) in response to pertussis toxin (PT), filamentous hemagglutinin (FHA), pertactin (PRN), and fimbriae (FIM 2/3) in vaccine failures and controls with pertussis. In Germany, the antibody responses to Bordetella pertussis antigens PT, FHA, PRN, and FIM-2 were analyzed by ELISA according to time of serum collection after onset of illness in children with pertussis who were vaccine failures or who were previously unvaccinated. Antibody values were also compared by severity of clinical illness. In Sweden, infants who had received a PT toxoid vaccine and who were vaccine failures had a blunted response to the nonvaccine antigen FHA compared with the response in children who had received a PT/FHA vaccine. Similarly, infants who had pertussis and who had received a PT/FHA vaccine had a blunted response to the nonvaccine antigens PRN and FIM 2/3 compared with the response in children who were vaccine failures and who had received a PT, FHA, PRN, and FIM 2/3 vaccine. In Germany, in sera collected from 0 to 15 days after pertussis illness onset, the GMVs for all 4 antigens (PT, FHA, PRN, and FIM-2) were significantly lower in an unvaccinated group than in children who were diphtheria-tetanus-acellular pertussis (DTaP) vaccine failures. In the unvaccinated group, the GMV of the PT antibody rose rapidly over time so that it was similar to that of the DTaP vaccine recipients at the 16- to 30-day period. In contrast, the antibody responses to FHA, PRN, and FIM-2 at all time periods were lower in the diphtheria-tetanus vaccine (DT) recipients than in the DTaP vaccine failures. In both Sweden and Germany, children with less severe illness had lower antibody responses than children with typical pertussis. Our findings indicate that upon exposure and infection, previous vaccinees have more-robust antibody responses to the antigens contained in the vaccine they had received than to Bordetella antigens that were not in the vaccine they had received. In addition, over time the antibody responses to FHA, PRN, and FIM-2 were greater in children with vaccine failure (primed subjects) than in unvaccinated children (unprimed subjects) whereas the responses to PT were similar in the primed and unprimed children, as determined from sera collected after 15 days of illness. Our findings lend support to the idea that DTaP vaccines should contain multiple antigens.