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

A novel whole blood assay to quantify the release of T cell associated cytokines in response to Bordetella pertussis antigens

BACKGROUND

Bordetella pertussis continues to cause whooping cough globally even in countries with high immunisation coverage. Booster vaccinations with acellular pertussis vaccines are thus used in children, adolescents, and adults. T cell immunity is crucial for orchestrating the immune response after vaccination. However, T cell assays can be expensive and difficult to implement in large clinical trials. In this study, a whole blood (WB) stimulation assay was developed to identify secreted T cell associated cytokines in different age groups after acellular pertussis booster vaccination.

MATERIAL AND METHODS

Longitudinal WB samples were collected from a small set of subjects (n = 38) aged 7-70 years participating in a larger ongoing clinical trial. For assay development, samples were diluted and incubated with purified inactivated pertussis toxin (PT), filamentous haemagglutinin (FHA), inactivated B. pertussis lysate, and complete medium (M) as stimulating conditions, with anti-CD28 and anti-CD49d as co-stimulants. Different timepoints around the vaccination (D0, D7, D14, D28), WB dilution factor (1:2, 1:4) and incubation time (24 h, 48 h, 72 h) were compared. Responses to 15 cytokines were tested with Luminex/multiplex immunoassay.

RESULTS

The optimized assay consisted of WB incubation with M, PT, and FHA (including the two co-stimulants). After 48 h incubation, supernatants were collected for measurement of seven selected T cell associated cytokines (IL-2, IL-5, IL-10, IL-13, IL-17 A, IL-17F, and IFN-y) from samples before and 28 days after vaccination. PT stimulation showed a trend for upregulation of IL-2, IL-13, and IL-17 A/F for adult subjects, whereas the responses of all cytokines were downregulated for the paediatric subjects. Furthermore, PT and FHA-stimulated WB showed diverse cytokine producing profiles.

CONCLUSIONS

The developed WB-based cytokine assay was shown to be less costly, easy to perform, and functional in differently aged individuals. Further, it requires only a small amount of fresh blood, which is beneficial especially for studies including infants. Our results support the use of this assay for other immunological studies in the future.

A literature review and evidence-based evaluation of the Dutch national immunisation schedule yield possibilities for improvements

National Immunisation Programmes (NIPs) develop historically. Its performance (disease incidences, vaccination coverage) is monitored. Reviewing the schedule as a whole could inform on further optimisation of the programme, i.e., providing maximal protection with the lowest number of doses. We systematically evaluated the performance and strategies of the Dutch pathogen-specific NIP schedules through literature review, assessment of surveillance data and expert opinions. Pathogen-specific vaccinations were categorised according to their strategy of protection: I) elimination or eradication, II) herd immunity or III) 'only' individual protection. The schedule of each vaccine-component was evaluated based on fixed criteria: 1. Is the achieved protection adequate? 2. Is the intended protection achieved? 3. Does the programme include too many or too few doses? 4. Is the timing optimal or acceptable? and 5. Are there drawbacks of the NIP for (part of) the population? Identified issues were explored using surveillance data and literature. Using fixed criteria facilitated comparison between pathogens and revealed opportunities to optimise the Dutch NIP by: i. Reducing the number of polio and tetanus vaccinations; ii. prolonging the interval between diphtheria, pertussis, tetanus, polio, hepatitis B, and Hib vaccine doses for improved effectiveness; iii. Expedite the second measles vaccination from 9 to 2-4 years of age to offer unvaccinated children and primary vaccine failures an earlier chance to be protected; and iv. Delaying the second mumps vaccination to enhance protection in adolescents/young adults. No schedule adaptations were deemed necessary for the vaccines against HPV, rubella, pneumococcal disease, and meningococcal disease. Based on this evaluation the NITAG advised to move the DTaP-IPV-HBV-Hib-booster from age 11 to 12 months, the second MMR-dose from 9 to 2-4 years, replace the Tdap-IPV at 4 years with a Tdap at 5-6 years and move the dt-IPV from 9 to 14 years. Implementation of these changes is planned for 2025.

Antibody and B-cell Immune Responses Against Bordetella Pertussis Following Infection and Immunization

Neither immunization nor recovery from natural infection provides life-long protection against Bordetella pertussis. Replacement of a whole-cell pertussis (wP) vaccine with an acellular pertussis (aP) vaccine, mutations in B. pertussis strains, and better diagnostic techniques, contribute to resurgence of number of cases especially in young infants. Development of new immunization strategies relies on a comprehensive understanding of immune system responses to infection and immunization and how triggering these immune components would ensure protective immunity. In this review, we assess how B cells, and their secretory products, antibodies, respond to B. pertussis infection, current and novel vaccines and highlight similarities and differences in these responses. We first focus on antibody-mediated immunity. We discuss antibody (sub)classes, elaborate on antibody avidity, ability to neutralize pertussis toxin, and summarize different effector functions, i.e. ability to activate complement, promote phagocytosis and activate NK cells. We then discuss challenges and opportunities in studying B-cell immunity. We highlight shared and unique aspects of B-cell and plasma cell responses to infection and immunization, and discuss how responses to novel immunization strategies better resemble those triggered by a natural infection (i.e., by triggering responses in mucosa and production of IgA). With this comprehensive review, we aim to shed some new light on the role of B cells and antibodies in the pertussis immunity to guide new vaccine development.

Evolution of Bordetella pertussis in the acellular vaccine era in Norway, 1996 to 2019

We described the population structure of Bordetella pertussis (B. pertussis) in Norway from 1996 to 2019 and determined if there were evolutionary shifts and whether these correlated with changes in the childhood immunization program. We selected 180 B. pertussis isolates, 22 from the whole cell vaccine (WCV) era (1996-1997) and 158 from the acellular vaccine (ACV) era (1998-2019). We conducted whole genome sequencing and determined the distribution and frequency of allelic variants and temporal changes of ACV genes. Norwegian B. pertussis isolates were evenly distributed across a phylogenetic tree that included global strains. We identified seven different allelic profiles of ACV genes (A-F), in which profiles A1, A2, and B dominated (89%), all having pertussis toxin (ptxA) allele 1, pertussis toxin promoter (ptxP) allele 3, and pertactin (prn) allele 2 present. Isolates with ptxP1 and prn1 were not detected after 2007, whereas the prn2 allele likely emerged prior to 1972, and ptxP3 before the early 1980s. Allele conversions of ACV genes all occurred prior to the introduction of ACV. Sixteen percent of our isolates showed mutations within the prn gene. ACV and its booster doses (implemented for children in 2007 and adolescents in 2013) might have contributed to evolvement of a more uniform B. pertussis population, with recent circulating strains having ptxA1, ptxP3, and prn2 present, and an increasing number of prn mutations. These strains clearly deviate from ACV strains (ptxA1, ptxP1, prn1), and this could have implications for vaccine efficiency and, therefore, prevention and control of pertussis.

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.

Seroprevalence of antibodies against diphtheria, tetanus, and pertussis among healthy Thai adolescents

OBJECTIVE

To determine the seroprevalence of antibodies against of diphtheria, tetanus, and pertussis among Thai adolescents.

METHODS

A cross-sectional study was conducted among Thai adolescents aged 11-20 years who had completed five doses of diphtheria, tetanus, and pertussis (DTP)-containing vaccine during childhood, either diphtheria toxoid, tetanus toxoid, whole-cell pertussis (DTwP) or diphtheria toxoid, tetanus toxoid, acellular pertussis (DTaP) vaccine. Protective antibodies against diphtheria, tetanus, and pertussis were defined as anti-diphtheria toxoid IgG ≥0.1 IU/ml, anti-tetanus toxoid IgG ≥0.1 IU/ml, and anti-Bordetella pertussis toxin IgG ≥5 IU/ml, respectively.

RESULTS

Of 220 adolescents (median age 16 years), 45% had received a tetanus toxoid, reduced diphtheria toxoid (Td) booster vaccine during adolescence, and none (0%) had received a tetanus toxoid, reduced diphtheria toxoid, acellular pertussis (Tdap) booster vaccine. Overall, 50%, 99%, and 57% of adolescents demonstrated protective antibodies against diphtheria, tetanus, and pertussis, respectively. The geometric mean concentrations (GMCs) of antibodies against diphtheria (p = 0.06) and tetanus (p < 0.001) were higher among adolescents who had received Td vaccine. Nevertheless, the antibody levels against both diseases waned over time, regardless of Td booster vaccination. Likewise, pertussis antibody levels gradually declined after the fifth childhood dose of DTwP/DTaP vaccine.

CONCLUSIONS

Approximately half of these healthy Thai adolescents had not maintained protective antibodies against diphtheria and pertussis. A booster vaccination with diphtheria toxoid and/or acellular pertussis-containing vaccines is a crucial strategy to prevent such diseases in this population.

A cross-sectional study of Bordetella pertussis seroprevalence and estimated duration of vaccine protection against pertussis in St. Petersburg, Russia

BACKGROUND

In Russia as in other countries introduction of infant vaccination against pertussis in 1950s led to dramatic decrease of whooping cough. The current vaccination schedule includes a 3-dose infant series and toddler booster; the pre-school booster was cancelled in 1980s and never reintroduced. Whole-cell vaccines, and in a smaller proportion acellular vaccines are used for all doses. However, pertussis incidence in urban settings is high with highest burden in school children. We conducted a study of seroprevalence of recent pertussis infection to estimate the duration of protection from the 4-dose series.

MATERIALS AND METHODS

Sera sample from 395 St Petersburg children aged ≥3 years and <14 years were tested for pertussis toxin antibodies using a commercial PT ELISA test. Only children with completed 4-dose vaccination course were included in the study. Age-specific seroprevalence of recent pertussis infection was analyzed for trends.

RESULTS

Children fully vaccinated against pertussis at 3 years old had significant delays in infant vaccination schedule: only 83.5% received at least one dose of pertussis vaccine at 6 months of age and 25.6% received their toddler booster before 24 months-old. Overall, 10.6% of children demonstrated the serological signs of the infection in the last 12 months. A clear trend (r² = 0.692) of increasing proportion of infection in the last 12 months was observed in children who had received their last dose of vaccine 6 years and more prior to the study.

CONCLUSION

Our study demonstrates that Russian children become susceptible to infection at or soon after entering school. The results confirm the waning of vaccine-elicited immunity around school-age and support the need for a booster dose at that age.

Immune responses to vaccine-preventable diseases among toddlers and preschool children after primary immunization and first booster in Northwestern Algiers, Algeria

OBJECTIVES

To determine immune responses to selected vaccine-preventable communicable diseases: pertussis, diphtheria and Haemophilus influenzae type b (Hib) in Algerian toddlers and preschool children after primary vaccination and first booster, recruited from three local healthcare facilities in Northwestern Algiers.

METHODS

The information of demographic characteristics and vaccination status were collected for each subject by questionnaire. Specific antibody levels and Hib antibody avidity were determined using commercial ELISA kits.

RESULTS

A total of eighty-one subjects aged between 19 and 55 months were studied. Almost all subjects were fully protected against diphtheria (76/81; 93.83%; 95% CI: 86.35-97.33) and invasive Hib disease (29/30; 96.67%; 95% CI: 83.33-99.41), while only 20/78 (25.64%; 95% CI: 17.26-36.31) had anti-PT (pertussis toxin) antibody levels above 25 IU/ml. A significant decrease of anti-PT antibody levels was observed until the age of 36 months (p = 0.02). GMTs (geometric mean titers) of anti-PT antibodies were low, but remain significantly higher in children ≤36 months of age (p = 0.02). Both GMT and rates of ≥0.15 μg/ml, ≥1 μg/ml, and ≥5 μg/ml titers were significantly higher in Hib-vaccinated subjects (p < 0.01). Relative Hib-avidity index (≥50%) and GMAI (geometric mean avidity index) were high in both Hib-vaccinated and -unvaccinated groups.

CONCLUSIONS

As shown in the present study, young children were fully protected against diphtheria and Hib, but showed low immunity to pertussis. Further sero-epidemiological studies including a large number of subjects with a wider range of age are needed to explore the immunity level in older children, adolescents and adults.

Incidence of pertussis in subjects aged 50years and older in France in 2013-2014

OBJECTIVE

To assess the incidence of pertussis (whooping cough) in subjects aged 50years and older in France.

METHODS

Participating family physicians (FPs) using the patient record management software AxiSanté^® included patients aged 50years and older, who had signed an informed consent form, presenting with persistent cough for 7 to 21days. Bordetella genetic material was detected by polymerase chain reaction (PCR) on nasopharyngeal samples collected at the FP's discretion.

RESULTS

A total of 42 FPs included 129 patients from June 2013 to August 2014 (large cities: 38; medium-sized cities: 57; rural areas: 34); 106 samples were analyzed. Overall, 30 pertussis cases were diagnosed: 10 cases confirmed by PCR, 18 purely clinical cases, and two direct epidemiological cases. The crude incidence rate per 100,000 patients aged≥50years was 103.6 (95% CI: 69.9-47.9): 77.1 in large cities, 103.1 in medium-sized cities, and 143.9 in rural areas. The extrapolated incidence rate per 100,000 persons aged≥50years was 187.1 (95% CI: 126.2-67.1): 131.1 in large cities, 256.1 in medium-sized cities, and 242.2 in rural areas.

CONCLUSION

The population aged 50years and older can serve as a reservoir. Its role in Bordetella pertussis circulation should be taken into account for pertussis booster vaccination programs.

Whooping cough surveillance in France in pediatric private practice in 2006-2015

BACKGROUND

Increasing incidence of whooping cough (pertussis) has been reported in many countries, attributed to a switch from whole-cell pertussis-containing vaccine (wPV) to acellular PV (aPV) and circulation of the pertactin non-producing Bordetella pertussis. The present study aimed to estimate the duration of immunity conferred by PVs in children in France with data from an ongoing pediatric ambulatory surveillance of pertussis.

METHODS

A total of 64 pediatricians throughout France enrolled children with suspected pertussis. A standardized data form was used to collect data on age sex, vaccination status, brand of wPV or aPV and source of infection. Confirmed cases were positive on culture and/or real-time Polymerase Chain Reaction (for B.-non-classified or B. pertussis or B. parapertussis) and/or pertussis serology.

RESULTS

Between October 2006 and December 2015, 149 cases of confirmed Bordetella infections were reported, 86 infected with B. pertussis and 55 B. non-classified. Fifteen children (10.1%) were not vaccinated, and 26 (17.4%) were partially vaccinated. The mean age was greater for children who received 4 doses of wPV (11.3±2.2, p<0.001) or a combination of wPV and aPV (10.5±3.3, p<0.001) than only aPV (7.2±2.4years). The mean duration of cough before a visit to a pediatrician was longer for children with wPV or a combination of wPV and aPV than only aPV (23.8±10.1 and 25.0±25.6vs 13.6±10.0days).

CONCLUSION

Despite the use of a more sensitive diagnostic method and emergence of pertactin non producing B. pertussis, in France context, aPV-induced immunity still protects against pertussis; however, the mean duration of immunity is about 6 to 7years, compared to 9years for wPV vaccine, after the primary vaccination and one booster (3+1 doses).

The Effect of Maternal Pertussis Immunization on Infant Vaccine Responses to a Booster Pertussis-Containing Vaccine in Vietnam

BACKGROUND

 Maternal vaccination with an acellular pertussis (aP)-containing vaccine is a recommended strategy in a growing number of industrialized countries, to protect young infants from disease. Little is known on the effect of this strategy in low- and middle-income countries. Following a previous report on the effect of adding a pertussis and diphtheria component to the tetanus vaccination program in pregnant women in Vietnam, we report on infant immune responses to a booster aP vaccine dose in this randomized controlled clinical trial.

METHODS

 Thirty infants of Tdap (tetanus, diphtheria, and acellular pertussis)-vaccinated pregnant women and 37 infants of women vaccinated with a tetanus-only vaccine received a fourth aP-containing vaccine dose in the second year of life. Blood was taken 1 month after the fourth infant dose. Immunoglobulin G (IgG) antibodies against pertussis toxin (PT), filamentous hemagglutinin (FHA), pertactin (Prn), tetanus toxoid (TT), and diphtheria toxoid (DT) were measured using commercially available enzyme-linked immunosorbent assays (ELISA).

RESULTS

 One month after the booster dose, significantly lower antibody titers were measured in the Tdap group for anti-TT IgG (P < .001) only. Anti-DT IgG, anti-PT IgG, anti-Prn IgG, and anti-FHA IgG antibody titers were comparable for both groups. A rise in antibody concentrations was elicited for all (except DT) antigens after boosting.

CONCLUSIONS

 The present results indicate that the blunting of infant pertussis responses induced by maternal immunization, measured after a primary series of aP vaccines, was resolved with the booster aP vaccine dose. These results add to the evidence for national and international decision makers on maternal immunization as a vaccination strategy for protection of young infants against infectious diseases.

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.

Surveillance of pertussis: methods and implementation

INTRODUCTION

Pertussis or whooping cough is a respiratory disease caused by Bordetella pertussis or, to a lesser extent, by B. parapertussis. Vaccines against pertussis have been widely used for more than 50 years and have led to a significant reduction of morbidity and mortality. However, even in countries with a high vaccine coverage, the disease is still not well controlled. Surveillance is urgently needed.

AREAS COVERED

This review summarizes surveillance methods and gives examples that may be used when setting up a surveillance program or analyzing an outbreak. Expert commentary: Pertussis surveillance is urgently required in order to define the burden of disease, to adapt vaccine strategies according to the type of pertussis vaccine used and to follow the evolution of the bacteria.

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.

Humoral and cell mediated immune responses to a pertussis containing vaccine in pregnant and nonpregnant women

Vaccination of pregnant women is recommended for some infectious diseases in order to protect both women and offspring through high titres of maternal IgG antibodies. Less is known on the triggering of cellular immune responses by vaccines administered during pregnancy. In an ongoing study on maternal pertussis vaccination (2012-2014) 18 pregnant women were vaccinated with a tetanus-diphtheria-acellular pertussis (Tdap) containing vaccine (Boostrix®) during the third pregnancy trimester. Sixteen age-matched nonpregnant women received the same vaccine in the same time period. A blood sample was taken at the moment of, but before vaccination and one month and one year after vaccination. Anti-Pertussis Toxin (PT), filamentous hemagglutinin (FHA), pertactin (Prn), tetanus toxin (TT) and diphtheria toxin (DT) antibodies were measured by ELISA. Cellular immune responses were analyzed using a diluted whole blood assay, measuring proliferation, and cytokine release in response to vaccine antigens PT, FHA, TT, and to pokeweed mitogen (PWM) as polyclonal stimulus. Antibody levels to all five vaccine components increased significantly and to the same extent after vaccination in pregnant and nonpregnant women. One year after vaccination, antibody titres had decreased particularly to PT, but they were still significantly higher to all antigens than before vaccination. In contrast, proliferative and IFN-γ responses were increased to TT, PT, and FHA in nonpregnant women one month after vaccination, whereas in pregnant women only TT specific T cell responses were increased and to a lesser extent than in the control group. One year after vaccination, cellular responses equaled the baseline levels detected prior to vaccination in both groups. In conclusion, a Tdap vaccination can increase vaccine specific IgG antibodies to the same extent in pregnant and in nonpregnant women, whereas the stimulation of vaccine specific Th1 type cellular immune responses with this acellular vaccine is transient and impaired during pregnancy.

Identification of pertussis-specific effector memory T cells in preschool children

Whooping cough remains a problem despite vaccination, and worldwide resurgence of pertussis is evident. Since cellular immunity plays a role in long-term protection against pertussis, we studied pertussis-specific T-cell responses. Around the time of the preschool acellular pertussis (aP) booster dose at 4 years of age, T-cell memory responses were compared in children who were primed during infancy with either a whole-cell pertussis (wP) or an aP vaccine. Peripheral blood mononuclear cells (PBMCs) were isolated and stimulated with pertussis vaccine antigens for 5 days. T cells were characterized by flow-based analysis of carboxyfluorescein succinimidyl ester (CFSE) dilution and CD4, CD3, CD45RA, CCR7, gamma interferon (IFN-γ), and tumor necrosis factor alpha (TNF-α) expression. Before the aP preschool booster vaccination, both the proliferated pertussis toxin (PT)-specific CD4(+) and CD8(+) T-cell fractions (CFSE(dim)) were higher in aP- than in wP-primed children. Post-booster vaccination, more pertussis-specific CD4(+) effector memory cells (CD45RA(-) CCR7(-)) were induced in aP-primed children than in those primed with wP. The booster vaccination did not appear to significantly affect the T-cell memory subsets and functionality in aP-primed or wP-primed children. Although the percentages of Th1 cytokine-producing cells were alike in aP- and wP-primed children pre-booster vaccination, aP-primed children produced more Th1 cytokines due to higher numbers of proliferated pertussis-specific effector memory cells. At present, infant vaccinations with four aP vaccines in the first year of life result in pertussis-specific CD4(+) and CD8(+) effector memory T-cell responses that persist in children until 4 years of age and are higher than those in wP-primed children. The booster at 4 years of age is therefore questionable; this may be postponed to 6 years of age.

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.

Improved pertussis vaccines based on adjuvants that induce cell-mediated immunity

Bordetella pertussis is a Gram-negative bacterium that causes the severe and sometimes lethal respiratory disease whooping cough in infants and children. There has been a recent resurgence in the number of cases of pertussis in several countries with high vaccine coverage. This has been linked with waning or ineffective immunity induced by current acellular pertussis vaccines. These acellular pertussis vaccines are formulated with alum as the adjuvant, which promotes strong antibody responses but is less effective at inducing Th1-type responses crucial for effective bacterial clearance. Studies in animal models have demonstrated that replacing alum with alternative adjuvants, such as toll-like receptor agonists, can promote more robust cell-mediated immunity and confer a high level of protection against infection following respiratory challenge.

Pertussis-specific memory B-cell and humoral IgG responses in adolescents after a fifth consecutive dose of acellular pertussis vaccine

In order to impede the increase in pertussis incidence in the adolescent group, a school-leaving booster dose administered at the age of 14 to 16 years will be introduced in Sweden in 2016. Preceding this introduction, an open-label, randomized, multicenter, clinical trial without a control group and with blinded analysis was performed, investigating both safety and immunogenicity. Reported here are the memory B-cell and serological responses detected in a smaller cohort (n = 34) of the 230 subjects recruited to the study. All subjects had received primary vaccination consisting of three doses of diphtheria-tetanus-5-component pertussis (DTaP5) vaccine, at 3, 5, and 12 months of age, and a tetanus-low-dose diphtheria-5-component pertussis (Tdap5) vaccine booster at 5.5 years. In this study, the subjects were randomly assigned and received either a Tdap1 or Tdap5 booster. Of the 230 participants, 34 subjects had samples available for evaluation of IgG-producing memory B-cell responses. Both vaccine groups had significant increases in pertussis toxin-specific serum IgG levels, but only the 1-component group showed significant increases in pertussis toxin-specific memory B cells. The 5-component group had significant increases in filamentous hemagglutinin- and pertactin-specific memory B-cell and serum IgG levels; these were not seen in the 1-component group, as expected. In conclusion, this study shows that a 5th consecutive dose of an acellular pertussis vaccine induces B-cell responses in vaccinated adolescents. (This study has been registered at EudraCT under registration no. 2008-008195-13 and at ClinicalTrials.gov under registration no. NCT00870350.).

Bordetella pertussis pathogenesis: current and future challenges

Pertussis, also known as whooping cough, has recently re-emerged as a major public health threat despite high levels of vaccination against the aetiological agent Bordetella pertussis. In this Review, we describe the pathogenesis of this disease, with a focus on recent mechanistic insights into B. pertussis virulence-factor function. We also discuss the changing epidemiology of pertussis and the challenges facing vaccine development. Despite decades of research, many aspects of B. pertussis physiology and pathogenesis remain poorly understood. We highlight knowledge gaps that must be addressed to develop improved vaccines and therapeutic strategies.

Bordetella pertussis proteins dominating the major histocompatibility complex class II-presented epitope repertoire in human monocyte-derived dendritic cells

Knowledge of naturally processed Bordetella pertussis-specific T cell epitopes may help to increase our understanding of the basis of cell-mediated immune mechanisms to control this reemerging pathogen. Here, we elucidate for the first time the dominant major histocompatibility complex (MHC) class II-presented B. pertussis CD4(+) T cell epitopes, expressed on human monocyte-derived dendritic cells (MDDC) after the processing of whole bacterial cells by use of a platform of immunoproteomics technology. Pertussis epitopes identified in the context of HLA-DR molecules were derived from two envelope proteins, i.e., putative periplasmic protein (PPP) and putative peptidoglycan-associated lipoprotein (PAL), and from two cytosolic proteins, i.e., 10-kDa chaperonin groES protein (groES) and adenylosuccinate synthetase (ASS). No epitopes were detectable from known virulence factors. CD4(+) T cell responsiveness in healthy adults against peptide pools representing epitope regions or full proteins confirmed the immunogenicity of PAL, PPP, groES, and ASS. Elevated lymphoproliferative activity to PPP, groES, and ASS in subjects within a year after the diagnosis of symptomatic pertussis suggested immunogenic exposure to these proteins during clinical infection. The PAL-, PPP-, groES-, and ASS-specific responses were associated with secretion of functional Th1 (tumor necrosis factor alpha [TNF-α] and gamma interferon [IFN-γ]) and Th2 (interleukin 5 [IL-5] and IL-13) cytokines. Relative paucity in the natural B. pertussis epitope display of MDDC, not dominated by epitopes from known protective antigens, can interfere with the effectiveness of immune recognition of B. pertussis. A more complete understanding of hallmarks in B. pertussis-specific immunity may advance the design of novel immunological assays and prevention strategies.

The UK pertussis epidemic: implications for immunisation

The UK is currently experiencing an epidemic of pertussis (whooping cough), in spite of the fact that uptake of immunisation against this disease has remained consistently high for some time. The number of cases is far higher in adults and adolescents, but there has also been a huge increase in the burden of disease among infants under 3 months, in whom the outcome is potentially far more serious. Last year, 14 infants died from the disease, prompting the Joint Committee on Vaccination and Immunisation (JCVI) to recommend vaccination for all women in the third trimester of pregnancy. This article looks at the background to the current epidemic, outlining the history of the disease; the underpinning immunological principles that have influenced attempts to control its spread to date; the current immunisation schedule; and other possible measures being considered.

Epidemiology of whooping cough & typing of Bordetella pertussis

Bordetella pertussis is a Gram-negative human-restricted bacterium that evolved from the broad-range mammalian pathogen, Bordetella bronchiseptica. It causes whooping cough or pertussis in humans, which is the most prevalent vaccine-preventable disease worldwide. The introduction of the pertussis whole-cell vaccination for young children, followed by the introduction of the pertussis acellular vaccination (along with booster vaccination) for older age groups, has affected the bacterial population and epidemiology of the disease. B. pertussis is relatively monomorphic worldwide, but nevertheless, different countries are facing different epidemiological evolutions of the disease. Although it is tempting to link vaccine-driven phenotypic and genotypic evolution of the bacterium to epidemiology, many other factors should be considered and surveillance needs to continue, in addition to studies investigating the impact of current clinical isolates on vaccine efficacy.

Differential T- and B-cell responses to pertussis in acellular vaccine-primed versus whole-cell vaccine-primed children 2 years after preschool acellular booster vaccination

This study investigated long-term cellular and humoral immunity against pertussis after booster vaccination of 4-year-old children who had been vaccinated at 2, 3, 4, and 11 months of age with either whole-cell pertussis (wP) or acellular pertussis (aP) vaccine. Immune responses were evaluated until 2 years after the preschool booster aP vaccination. In a cross-sectional study (registered trial no. ISRCTN65428640), blood samples were taken from wP- and aP-primed children prebooster and 1 month and 2 years postbooster. Pertussis vaccine antigen-specific IgG levels, antibody avidities, and IgG subclasses, as well as T-cell cytokine levels, were measured by fluorescent bead-based multiplex immunoassays. The numbers of pertussis-specific memory B cells and gamma interferon (IFN-γ)-producing T cells were quantified by enzyme-linked immunosorbent spot assays. Even 2 years after booster vaccination, memory B cells were still present and higher levels of pertussis-specific antibodies than prebooster were found in aP-primed children and, to a lesser degree, also in wP-primed children. The antibodies consisted mainly of the IgG1 subclass but also showed an increased IgG4 portion, primarily in the aP-primed children. The antibody avidity indices for pertussis toxin and pertactin in aP-primed children were already high prebooster and remained stable at 2 years, whereas those in wP-primed children increased. All measured prebooster T-cell responses in aP-primed children were already high and remained at similar levels or even decreased during the 2 years after booster vaccination, whereas those in wP-primed children increased. Since the Dutch wP vaccine has been replaced by aP vaccines, the induction of B-cell and T-cell memory immune responses has been enhanced, but antibody levels still wane after five aP vaccinations. Based on these long-term immune responses, the Dutch pertussis vaccination schedule can be optimized, and we discuss here several options.

T-cell responses before and after the fifth consecutive acellular pertussis vaccination in 4-year-old Dutch children

Immunization with acellular pertussis vaccine (aP) induces higher specific antibody levels and fewer adverse reactions than does immunization with the whole-cell vaccine (wP). However, antibody levels in infants induced by both types of pertussis vaccines wane already after 1 year. Therefore, long-term T-cell responses upon vaccination might play a role in protection against pertussis. In a cross-sectional study (ISRCTN65428640), we investigated T-helper (Th) cell immune responses in wP- or aP-vaccinated children before and after an aP low-dose or high-dose preschool booster at 4 years of age in The Netherlands. T cells were stimulated with pertussis vaccine antigens. The numbers of gamma interferon-producing cells and Th1, Th2, Th17, and interleukin-10 (IL-10) cytokine concentrations were determined. In addition, pertussis-specific IgE levels were measured in plasma. Children being vaccinated with aP vaccinations at 2, 3, 4, and 11 months of age still showed higher pertussis-specific T-cell responses at 4 years of age than did wP-vaccinated children. These T-cell responses failed to show a typical increase in cytokine production after a fifth aP vaccination but remained high after a low-dose booster and seemed to decline even after a high-dose booster. Importantly, elevated IgE levels were induced after this booster vaccination. In contrast, wP-vaccinated children had only low prebooster T-cell responses, and these children showed a clear postbooster T-cell memory response even after a low-dose booster vaccine. Four high-dose aP vaccinations in infancy induce high T-cell responses still present even 3 years after vaccination and enhanced IgE responses after preschool booster vaccination. Therefore, studies of changes in vaccine dosage, timing of pertussis (booster) vaccinations, and the possible association with local side effects are necessary.

Two-component cluster analysis of a large serodiagnostic database for specificity of increases of IgG antibodies against pertussis toxin in paired serum samples and of absolute values in single serum samples

Measuring IgG antibodies against pertussis toxin (IgG-Ptx) with an enzyme-linked immunosorbent assay (ELISA) can be used to diagnose pertussis infection; however, the cutoff points are not unanimously defined. To determine the diagnostic specificity of increases of IgG-Ptx in paired sera and of absolute values in single serum samples, we applied a two-component cluster analysis to serum samples of patients suspected for pertussis, whose sera had been submitted to a routine diagnostic laboratory between 2003 and 2009, and had been assayed with an in-house IgG-Ptx ELISA calibrated with the international FDA lot 3 IgG-Ptx reference serum. Children eligible for the acellular pertussis vaccination were excluded to avoid interference from a vaccine-induced IgG-Ptx rise. Binary distribution mixtures were fitted to the data. Receiver operating characteristic (ROC) curves were calculated for absolute values in single samples (n = 14,452) and increases in paired samples (n = 2,455). For both parameters, two subpopulations could be identified: a population with high reactivity (persons with pertussis infection) and a population with low reactivity (persons without pertussis infection). For absolute values in single samples, the area under the curve (AUC) of the ROC curve was 0.993 and the optimum cutoff (with the highest cumulative value of specificity plus sensitivity) was 67.7 IU/ml (95% confidence interval, 63.9 to 74.1; sensitivity, 96.4%; specificity, 95.7%). A previously determined diagnostic cutoff of 125 IU/ml was associated with a sensitivity of 88.1% and a specificity of 98.8%. For increases in paired sera, the AUC was 0.999 and the optimum cutoff was 3.1-fold (95% CI, 2.8 to 3.4; sensitivity, 99.6%; specificity, 99.2%). Given the methodology of this study, estimates of sensitivity probably are overrated (because pertussis patients without IgG-Ptx response are not detected), but estimates of specificities can be considered very accurate.

Impact of postpartum information about pertussis booster to parents in a university maternity hospital

Parent-to-infant transmission of pertussis remains an issue in France. Although adult booster vaccination was introduced in 2004 as part of a cocooning strategy targeted primarily to parents of young infants, vaccination coverage in this population has remained low. The aim of this study was to evaluate the impact on vaccination coverage, over two consecutive years, of a protocol in which information about the pertussis booster and a prescription for pertussis vaccine were given to parents upon discharge from a French university maternity hospital. A questionnaire was administered to mothers two months after delivery, during two 3-month periods in 2008 and 2009. Participation rates were 67% (first period) and 76.3% (second period). Information about pertussis was delivered mainly by paediatricians and midwives and was considered clear and pertinent in more than 95% of cases. In 2009, 69% of mothers and 63% of fathers who received a prescription for pertussis vaccine before discharge from the maternity declared being vaccinated, with no difference as compared to 2008. Vaccination was done by a general practitioner (95.9%) and mostly in the first month after birth (81%). Postpartum information about pertussis was successfully implemented and well understood by parents in the maternity hospital and should contribute towards increasing pertussis vaccination coverage in parents of young children.

Accelerating control of pertussis in England and Wales

Pertussis incidence among infants can be reduced by early completion of the primary vaccination schedule.

A genomics-based approach to assessment of vaccine safety and immunogenicity in children

Immune responses to vaccines in infants and young children are typically Th2-biased, giving rise to concerns regarding potential atopy-like side effects, and antagonism of Th1-associated sterilising immunity. Conventional immunological methodology has limited capacity to effectively address these problems because of the inherent complexity of the immune responses involved. In the present study, we sought to develop an unbiased systems biology approach to elucidate superficially similar Th2-associated responses to paediatric vaccines and allergens, and to differentiate between them via gene coexpression network analysis. We demonstrate below that in immune responses to the diptheria/acellular pertussis/tetanus and pneumococcal polysaccharide conjugate vaccines, potentially antagonistic Th1-/IFN-associated and Th2-associated gene networks coexist in an apparent state of dynamic equilibrium, whereas in Th2-dominant allergen-specific responses of atopics the Th1 and IFN networks are respectively disrupted and downregulated. Capacity to detect and interpret these covert differences between responses to vaccines and allergens relies on the use of sophisticated algorithms that underpin coexpression network analysis, which identify genes that function co-ordinately in complex pathways. This methodology has significant potential to identify covert interactions between inflammatory pathways triggered by vaccination, and as such may be a useful tool in prediction of vaccine safety/efficacy.

Impact of infant and preschool pertussis vaccinations on memory B-cell responses in children at 4 years of age

Whooping cough, caused by Bordetella pertussis, is reemerging in the vaccinated population. Antibody levels to pertussis antigens wane rapidly after both whole-cell (wP) and acellular pertussis (aP) vaccination and protection may largely depend on long-term B- and T-cell immunity. We studied the effect of wP and aP infant priming at 2, 3, 4 and 11 months according to the Dutch immunization program on pertussis-specific memory B-cell responses before and after a booster vaccination with either a high- or low-pertussis dose vaccine at 4 years of age. Purified B-cells were characterized by FACS-analysis and after polyclonal stimulation, memory B-cells were detected by ELISPOT-assays specific for pertussis toxin, filamentous haemagglutinin and pertactin. Before and after the booster, higher memory B-cell responses were measured in aP primed children compared with wP primed children. In contrast with antibody levels, no dose-effect was observed on the numbers of memory B-cell responses. In aP primed children a fifth high-dose aP vaccination tended to induce even lower memory B-cell responses than a low-dose aP booster. In both wP and aP primed children, the number of memory B-cells increased after the booster and correlated with the pertussis-specific antibody concentrations and observed affinity maturation. This study indicates that aP vaccinations in the first year of life induce higher pertussis-specific memory B-cell responses in children 4 years of age compared with Dutch wP primary vaccinations. Since infant aP vaccinations have improved protection against whooping cough in children despite waning antibody levels, this suggests that an enhanced memory B-cell pool induction may have an important role in protection. However, the pertussis-dose of the preschool booster needs to be considered depending on the vaccine used for priming to optimize long-term protection against whooping cough.

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.

Long-term immunity against pertussis induced by a single nasal administration of live attenuated B. pertussis BPZE1

Duration of vaccine-induced immunity plays a key role in the epidemiology and in the pattern of transmission of a vaccine-preventable disease. In the case of whooping cough, its re-emergence has been attributed, at least partly, to the waning of immunity conferred by current pertussis vaccines. We have recently developed a highly attenuated live vaccine, named BPZE1, which has been shown to be safe and to induce strong protective immunity against Bordetella pertussis infection in mice. In this study, we evaluated the long-term immunogenicity and protective efficacy induced by a single intranasal dose of BPZE1. Up to 1 year after immunization, BPZE1 showed significantly higher efficacy to protect adult and infant mice against B. pertussis infection than two administrations of an acellular pertussis vaccine (aPV). B. pertussis-specific antibodies were induced by live BPZE1 and by aPV, with increasing amounts during the first 6 months post-immunization before a progressive decline. Cell-mediated immunity was also measured 1 year after immunization and showed the presence of memory T cells in the spleen of BPZE1-immunized mice. Both cell-mediated and humoral immune responses were involved in the long-lasting protection induced by BPZE1, as demonstrated by adoptive transfer experiments to SCID mice. These data highlight the potential of the live attenuated BPZE1 candidate vaccine as part of a strategy to solve the problem of waning protective immunity against B. pertussis observed with the current aPV vaccines.

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.

Immunological fingerprinting method for differentiation of serum samples in research-oriented biobanks

An immunoenzymatic serum fingerprinting method was developed to establish a serum sample fingerprint based on IgG titers obtained with three different antigens. Three widely expressed antigens were selected for their capacity to induce long-lasting humoral immune responses. This fingerprinting method may be used to differentiate between two serum samples and to determine whether they come from the same primary blood specimen. The method showed a specificity of 99.5%. This method is suitable as a quality control method for biobanked serum samples.

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.

Reverse genetics technology for Rift Valley fever virus: current and future applications for the development of therapeutics and vaccines

The advent of reverse genetics technology has revolutionized the study of RNA viruses, making it possible to manipulate their genomes and evaluate the effects of these changes on their biology and pathogenesis. The fundamental insights gleaned from reverse genetics-based studies over the last several years provide a new momentum for the development of designed therapies for the control and prevention of these viral pathogens. This review summarizes the successes and stumbling blocks in the development of reverse genetics technologies for Rift Valley fever virus and their application to the further dissection of its pathogenesis and the design of new therapeutics and safe and effective vaccines.