Determination of serum neutralizing antibodies reveals important difference in quality of antibodies against pertussis toxin in children after infection

The effect of pertussis vaccination in pregnancy on the immunogenicity of acellular or whole-cell pertussis vaccination in Gambian infants (GaPS): a single-centre, randomised, controlled, double-blind, phase 4 trial

BACKGROUND

Vaccinating women against pertussis in pregnancy protects young infants from severe disease and death. Vaccination-induced maternally derived antibodies, however, might subsequently modulate (and specifically blunt) the infant's serological response to their primary series of pertussis vaccinations. We examined the effect of pertussis immunisation in pregnancy on the immunogenicity of primary acellular or whole-cell pertussis vaccines in a west African cohort.

METHODS

GaPs was a randomised, controlled, double-blind, phase 4 trial conducted in The Gambia. We used a predefined block randomisation scheme to randomly assign healthy, HIV-negative, pregnant participants (1:1) to receive a pertussis-containing (tetanus-diphtheria-acellular pertussis-inactivated polio virus [Tdap-IPV]) or tetanus-toxoid only vaccine at 28-34 weeks' gestation. At the same time, their infants were randomly assigned (1:1) to receive diphtheria-tetanus-acellular pertussis (DTaP) or diphtheria-tetanus-whole-cell pertussis (DTwP) primary vaccine at 8, 12, and 16 weeks postnatally. Participants and trial staff were masked to the allocation of the maternal vaccine. The field team and participants became unmasked to the allocation of the infant vaccine at 16 weeks; laboratory staff and all other investigators remained masked to infant vaccine allocation until the end of the trial. The primary outcome was geometric mean concentration (GMC) of infant pertussis toxin-specific antibodies at 20 weeks and 9 months postnatally and was assessed in infants who received all three doses of the primary vaccine. Secondary outcomes included memory B-cell responses, and exploratory outcomes were total pertussis-specific antibody binding concentrations and functional antibody titres (pertussis toxin-specific neutralising activity [PTNA] and serum bactericidal activity [SBA]). Vaccine reactogenicity was assessed in mothers and infants for 3 days after each vaccine dose. Pregnant women had an extra safety visit 7 days after vaccination. The study is registered with ClinicalTrials.gov, NCT03606096.

FINDINGS

Between Feb 13, 2019, and May 17, 2021, we enrolled 343 maternal-infant pairs. 239 (77%) infants were included in the per-protocol immunogenicity analysis. Among infants of mothers receiving Tdap-IPV in pregnancy, at 20 weeks postnatally, the GMCs of anti-pertussis toxin IgG were more than three-fold lower in infants vaccinated with three doses of DTwP (n=64) than in infants vaccinated with three doses of DTaP (n=53; adjusted geometric mean ratio 0·28, 98·75% CI 0·16-0·50). This difference persisted up to 9 months (0·31, 0·17-0·55). Conversely, among infants born to tetanus toxoid-immunised mothers, post-vaccination GMCs of anti-pertussis toxin IgG at 9 months were higher in those vaccinated with DTwP (n=58) than in those vaccinated with DTaP (n=64; 2·02, 1·15-3·55). Tdap-IPV immunisation in pregnancy blunted anti-pertussis toxin IgG following primary vaccination in all infants but particularly in those receiving DTwP, with GMCs of anti-pertussis toxin IgG more than eight-fold lower in DTwP-vaccinated infants born to Tdap-IPV-vaccinated mothers than in DTwP-vaccinated infants born to tetanus toxoid-immunised mothers (0·12, 98·75% CI 0·07-0·22 at 20 weeks; 0·07, 0·03-0·17 at 9 months). Similarly, DTwP-vaccinated infants born to Tdap-IPV-vaccinated mothers also showed significant blunting of PTNA, SBA, total pertussis-specific antibody binding, and memory B-cell responses after primary immunisation, whereas minimal blunting was observed among DTaP-vaccinated infants. However, the absolute levels of these responses generated by DTwP-vaccinated infants remained similar to or, in many cases, were higher than those generated by DTaP-vaccinated infants. There was no difference in reactogenicity between the two maternal vaccines, with most reactions graded 0 or 1. There were no serious adverse events related to vaccination or trial participation.

INTERPRETATION

Vaccinating women with Tdap-IPV in pregnancy was safe and well tolerated in a sub-Saharan African setting and boosted the quantity and quality of pertussis-specific antibodies in infants in early life. Although Tdap-IPV was associated with relative blunting of the immune response to the DTwP primary vaccination series, pertussis-specific antibody quality and memory B-cell responses were nevertheless preserved, regardless of the vaccine given during pregnancy.

FUNDING

GaPs was conducted as part of the Pertussis Correlates Of Protection Europe (PERISCOPE) consortium, which received funding from the Innovative Medicines Initiative 2 Joint Undertaking under grant agreement 115910. This Joint Undertaking receives support from the EU's Horizon 2020 research and innovation programme, the European Federation of Pharmaceutical Industries and Associations, and the Bill & Melinda Gates Foundation.

A novel outer membrane vesicle adjuvant improves vaccine protection against Bordetella pertussis

Pertussis is a vaccine-preventable respiratory disease caused by the Gram negative coccobacillus Bordetella pertussis. The licensed acellular pertussis (aP) vaccines protect against disease but do not prevent bacterial colonization and transmission. Here, we developed and tested an intranasal vaccine composed of aP antigens combined with T-vant, a novel adjuvant derived from bacterial outer membrane vesicles, that elicits both mucosal and systemic immune responses. We hypothesized that immunization of mice with aP-T-vant would enhance mucosal immunity and eliminate B. pertussis in the respiratory tract. In contrast to mice immunized intramuscularly with the licensed aP vaccine, intranasal immunization with aP-T-vant eliminated bacteria in both the lung and nasopharynx. Protection was associated with IFN-gamma and IL-17-producing, non-circulating CD4 + T cells in the lung and nasopharynx, and sterilizing immunity in the nasopharynx was dependent on IL-17. Novel mucosal adjuvants, such as T-vant, warrant further investigation to enhance the efficacy of next generation pertussis vaccines.

Comparative Evaluation of Recombinant and Acellular Pertussis Vaccines in a Murine Model

Since the 2000s, sporadic outbreaks of whooping cough have been reported in advanced countries, where the acellular pertussis vaccination rate is relatively high, and in developing countries. Small-scale whooping cough has also continued in many countries, due in part to the waning of immune protection after childhood vaccination, necessitating the development of an improved pertussis vaccine and vaccination program. Currently, two different production platforms are being actively pursued in Korea; one is based on the aP (acellular pertussis) vaccine purified from B. pertussis containing pertussis toxoid (PT), filamentous hemagglutin (FHA) and pertactin (PRN), and the other is based on the recombinant aP (raP), containing genetically detoxified pertussis toxin ADP-ribosyltransferase subunit 1 (PtxS1), FHA, and PRN domain, expressed and purified from recombinant E. coli. aP components were further combined with diphtheria and tetanus vaccine components as a prototype DTaP vaccine by GC Pharma (GC DTaP vaccine). We evaluated and compared the immunogenicity and the protective efficacy of aP and raP vaccines in an experimental murine challenge model: humoral immunity in serum, IgA secretion in nasal lavage, bacterial clearance after challenge, PTx (pertussis toxin) CHO cell neutralization titer, cytokine secretion in spleen single cell, and tissue resident memory CD4+ T cell (CD4+ TRM cell) in lung tissues. In humoral immunogenicity, GC DTaP vaccines showed high titers for PT and PRN and showed similar patterns in nasal lavage and IL-5 cytokine secretions. The GC DTaP vaccine and the control vaccine showed equivalent results in bacterial clearance after challenge, PTx CHO cell neutralization assay, and CD4+ TRM cell. In contrast, the recombinant raP vaccine exhibited strong antibody responses for FHA and PRN, albeit with low antibody level of PT and low titer in PTx CHO neutralization assay, as compared to control and GC DTaP vaccines. The raP vaccine provided a sterile lung bacterial clearance comparable to a commercial control vaccine after the experimental challenge in murine model. Moreover, raP exhibited a strong cytokine response and CD4+ TRM cell in lung tissue, comparable or superior to the experimental and commercial DTaP vaccinated groups. Contingent on improving the biophysical stability and humoral response to PT, the raP vaccine warrants further development as an effective alternative to aP vaccines for the control of a pertussis outbreak.

The Neonatal Immune System and Respiratory Pathogens

Neonates are more susceptible to some pathogens, particularly those that cause infection in the respiratory tract. This is often attributed to an incompletely developed immune system, but recent work demonstrates effective neonatal immune responses to some infection. The emerging view is that neonates have a distinctly different immune response that is well-adapted to deal with unique immunological challenges of the transition from a relatively sterile uterus to a microbe-rich world, tending to suppress potentially dangerous inflammatory responses. Problematically, few animal models allow a mechanistic examination of the roles and effects of various immune functions in this critical transition period. This limits our understanding of neonatal immunity, and therefore our ability to rationally design and develop vaccines and therapeutics to best protect newborns. This review summarizes what is known of the neonatal immune system, focusing on protection against respiratory pathogens and describes challenges of various animal models. Highlighting recent advances in the mouse model, we identify knowledge gaps to be addressed.

Evaluation of serum anti-pertussis toxin IgA antibodies for the diagnosis of Bordetella pertussis infection in young children

BACKGROUND

The determination of serum anti-pertussis toxin (PT) IgG antibodies is recommended for the diagnosis and surveillance of pertussis. However, the diagnostic power of anti-PT IgG can be hampered by possible interference from previous vaccinations. We aim to assess if anti-PT IgA antibodies can be well induced by Bordetella pertussis (B. pertussis) infections in children, and their capacity to improve pertussis serodiagnosis.

METHODS

Serum samples from 172 hospitalized children younger than 10 years old with confirmed pertussis were tested. Pertussis was confirmed by culture, PCR and/or serology. Anti-PT IgA antibodies were determined with commercial ELISA kits.

RESULTS

Sixty-four (37.2 %) subjects had anti-PT IgA antibodies greater than or equal to 15 IU/ml, and 52 (30.2 %) of them had anti-PT IgA antibodies greater than or equal to 20 IU/ml. No children with negative anti-PT IgG (less than 40 IU/ml) were observed to have anti-PT IgA antibodies greater than or equal to 15 IU/ml. Of patients younger than one year of age, about 50 % had an IgA antibody response. Moreover, the proportion of subjects with anti-PT IgA antibodies greater than or equal to 15 IU/ml among PCR negative subjects was significantly higher than that among PCR positive subjects (76.9 % vs 35.5 %).

CONCLUSIONS

The determination of anti-PT IgA antibodies does not seem to have added value for the serodiagnosis of pertussis in children older than one year of age. However, for infants, determination of serum anti-PT IgA antibodies appears to be useful for the diagnosis of pertussis especially when PCR and culture are negative. The results should be interpreted with caution as the number of subjects included in this study was limited.

Effect of Immunization During Pregnancy and Pre-existing Immunity on Diphtheria-Tetanus-Acellular Pertussis Vaccine Responses in Infants

Immunization during pregnancy (IP) against pertussis is recommended in many countries to protect infants. Although maternal antibodies can influence the infants' antibody responses to primary vaccinations, their effect on the development of functional antibodies and B cells remain poorly studied. We investigated the maternal immune response to IP and the effect of IP and pre-existing antibodieson infants' primary vaccine responses in an open-label, non-randomized trial. Forty-seven mothers received tetanus-diphtheria-acellular pertussis (Tdap) vaccine during pregnancy, and 22 mothers were included as controls. Sixty-nine infants received primary doses of DTaP at three and five months of age. Geometric mean concentrations of antibodies to pertussis toxin, filamentous haemagglutinin, pertactin, diphtheria, and tetanus toxins, pertussis toxin neutralizing antibodies (PTNAs), and plasma and memory B-cell frequencies were studied at delivery, and at three, five and six months. Levels of antibodies, PTNAs, and frequencies of memory B-cells were significantly increased at delivery and up to six months after in mothers with IP compared to those without IP (all p < 0.05, except for PT-specific memory B-cells). In vaccinated pregnant women, high pre-existing antibody levels were positively correlated with higher antibody responses after IP. IP blunted the infants' antibody and plasma B-cell responses to all vaccine antigens, except for tetanus toxin. This blunting effect was the strongest in infants with high concentrations of maternal antibodies. In conclusion, IP resulted in significantly higher concentrations of antibodies in infants up to three months of age (all p < 0.05); but was associated with blunting of various infants' vaccine responses.

Pertussis toxin neutralizing antibody response after an acellular booster vaccination in Dutch and Finnish participants of different age groups

Pertussis incidence has increased in many countries and the disease occurs among all age groups, suggesting the need for booster immunizations through life. In addition to determining the concentration of anti-pertussis toxin (PT) antibodies, the ability of PT neutralizing antibodies (PTNAs) could be used to assess vaccine responses.

Altogether 258 participants [7–10-year-old (N = 73), 11–15-year-old (N = 85), 20–35-year-old (N = 50) and 60–70-year-old (N = 50)] were included. Sera were collected before, one month, and one year after a single dose of a three pertussis component containing acellular pertussis vaccine. The adolescents were primed in childhood either by acellular or whole-cell vaccination. PTNA titres were determined by a Chinese hamster ovary cell assay and anti-PT IgG/IgA antibody concentrations by multiplex immunoassay.

In all age groups, a significant increase in levels of PTNAs and anti-PT IgG was observed one month after vaccination and remained at least two-fold higher one year post-booster, in comparison to pre-booster. Young adults had the lowest response. The strongest increase in PTNAs was observed in participants who had ≥10 IU/mL concentration of anti-PT IgG antibodies pre-booster. At pre-booster, whole-cell-primed adolescents had higher PTNAs than acellular-primed peers (p = 0.047). One year post-booster, the Finnish whole-cell-primed adolescents had a higher level of PTNAs than acellular-primed adolescents (p = 0.049), however, this was not observed in Dutch adolescents. In conclusion, PTNAs increased after vaccination in all age groups, and the strongest increase was related to the presence of high pre-booster antibodies.

Evaluation of Anti-PT Antibody Response after Pertussis Vaccination and Infection: The Importance of Both Quantity and Quality

Pertussis toxin (PT) is considered the main virulence factor causing whooping cough or pertussis. The protein is widely studied and its composition was revealed and sequenced already during the 1980s. The human immune system creates a good response against PT when measured in quantity. However, the serum anti-PT antibodies wane rapidly, and only a small amount of these antibodies are found a few years after vaccination/infection. Therefore, multiple approaches to study the functionality (quality) of these antibodies, e.g., avidity, neutralizing capacity, and epitope specificity, have been investigated. In addition, the long-term B cell memory (Bmem) to PT is crucial for good protection throughout life. In this review, we summarize the findings from functional PT antibody and Bmem studies. These results are discussed in line with the quantity of serum anti-PT antibodies. PT neutralizing antibodies and anti-PT antibodies with proper avidity are crucial for good protection against the disease, and certain epitopes have been identified to have multiple functions in the protection. Although PT-specific Bmem responses are detectable at least five years after vaccination, long-term surveillance is lacking. Variation of the natural boosting of circulating Bordetella pertussis in communities is an important confounding factor in these memory studies.