Immunogenicity of an acellular pertussis vaccine composed of genetically inactivated pertussis toxin combined with filamentous hemagglutinin and pertactin in infants and children

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.

Boosting Teenagers With Acellular Pertussis Vaccines Containing Recombinant or Chemically Inactivated Pertussis Toxin: A Randomized Clinical Trial

BACKGROUND

Protection induced by acellular pertussis (aP) vaccines is partial and short-lived, especially in teenagers, calling for novel immunization strategies.

METHODS

We conducted an investigator-driven proof-of-concept randomized controlled trial in aP-primed adolescents in Geneva to assess the immunogenicity and reactogenicity of a novel recombinant aP (r-aP) vaccine including recombinant pertussis toxin (PT) and filamentous hemagglutinin (FHA) coadministered with tetanus-diphtheria toxoids (Td), compared to a licensed tetanus-diphtheria-aP vaccine containing chemically detoxified PT (cd/Tdap). The primary immunological endpoints were day 28/365 geometric mean concentrations (GMCs) of total and neutralizing anti-PT antibodies. Memory B cells were assessed.

RESULTS

Sixty-two aP-primed adolescents were randomized and vaccinated with r-aP + Td or cd/Tdap. Reactogenicity, adverse events, and baseline GMCs were similar between the groups. Day 28 PT-neutralizing GMCs were low after cd/Tdap (73.91 [95% confidence interval {CI}, 49.88-109.52] IU/mL) and approximately 2-fold higher after r-aP + Td (127.68 [95% CI, 96.73-168.53] IU/mL; P = .0162). Anti-PT GMCs were also low after cd/Tdap (52.43 [95% CI, 36.41-75.50] IU/mL) and 2-fold higher after r-aP + Td (113.74 [95% CI, 88.31-146.50] IU/mL; P = .0006). Day 28 anti-FHA GMCs were similar in both groups. Day 365 anti-PT (but not PT-neutralizing) GMCs remained higher in r-aP + Td vaccinees. PT-specific memory B cells increased significantly after r-aP + Td but not cd/Tdap boosting.

CONCLUSIONS

Boosting aP-primed adolescents with r-aP induced higher anti-PT and PT-neutralizing responses than cd/Tdap and increased PT-specific memory B cells. Despite this superior immunogenicity, r-aP may have to be given repeatedly, earlier, and/or with novel adjuvants to exert an optimal influence in aP-primed subjects.

CLINICAL TRIALS REGISTRATION

NCT02946190.

New Pertussis Vaccines: A Need and a Challenge

Effective diphtheria, tetanus toxoids, whole-cell pertussis (wP) vaccines were used for massive immunization in the 1950s. The broad use of these vaccines significantly reduced the morbidity and mortality associated with pertussis. Because of reports on the induction of adverse reactions, less-reactogenic acellular vaccines (aP) were later developed and in many countries, especially the industrialized ones, the use of wP was changed to aP. For many years, the situation of pertussis seemed to be controlled with the use of these vaccines, however in the last decades the number of pertussis cases increased in several countries. The loss of the immunity conferred by the vaccines, which is faster in the individuals vaccinated with the acellular vaccines, and the evolution of the pathogen towards geno/phenotypes that escape more easily the immunity conferred by the vaccines were proposed as the main causes of the disease resurgence. According to their composition of few immunogens, the aP vaccines seem to be exerting a greater selection pressure on the circulating bacterial population causing the prevalence of bacterial isolates defective in the expression of vaccine antigens. Under this context, it is clear that new vaccines against pertussis should be developed. Several vaccine candidates are in preclinical development and few others have recently completed phaseI/phaseII trials. Vaccine candidate based on OMVs is a promising candidate since appeared overcoming the major weaknesses of current aP-vaccines. The most advanced development is the live attenuated-vaccine BPZE1 which has successfully completed a first-in-man clinical trial.

Genetically detoxified pertussis toxin (PT-9K/129G): implications for immunization and vaccines

Pertussis toxin (PT) is one of the major virulence factors of Bordetella pertussis and the primary component of all pertussis vaccines available to date. Because of its various noxious effects the toxin needs to be detoxified. In all currently available vaccines, detoxification is achieved by treatment with high quantity of chemical agents such as formaldehyde, glutaraldehyde or hydrogen peroxide. Although effective in detoxification, this chemical treatment alters dramatically the immunological properties of the toxin. In contrast, PT genetically detoxified through the substitution of two residues necessary for its enzymatic activity maintains all functional and immunological properties. This review describes in detail the characteristics of this PT-9K/129G mutant and shows that it is non-toxic and a superior immunogen compared with chemically detoxified PT. Importantly, data from an efficacy trial show that the PT-9K/129G-based vaccine induces earlier and longer-lasting protection, further supporting the hypothesis that PT-9K/129G represents an ideal candidate for future pertussis vaccine formulations.

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.

Immunogenicity of a three-component acellular pertussis vaccine administered at birth

OBJECTIVE

To evaluate within the first 6 months of birth the immunogenicity of a 3-component acellular pertussis (aP) vaccine containing filamentous hemagglutinin (FHA), pertactine (PRN), and genetically detoxified pertussis toxin (PT) in infants who received a dose of vaccine at birth, in addition to the recommended schedule administered at 3, 5, and 11 months. Furthermore, we investigated the influence of maternal antibodies on aP vaccine response.

METHODS

We used enzyme-linked immunosorbent assay to evaluate immunoglobulin G antibody levels in 45 infants immunized at birth and at 3, 5, and 11 months (group 1) and in 46 infants immunized at the ages of 3, 5, and 11 months (group 2). All mothers were also tested at delivery.

RESULTS

At the age of 5 months the geometric mean titer of anti-PT, anti-FHA, and anti-PRN was significantly greater in group 1 (who had received 2 doses) than in group 2 (1 dose). At 6 months geometric mean titers were significantly higher in group 1 than in group 2 for anti-PRN and anti-FHA, whereas no significant differences were observed for anti-PT.

CONCLUSIONS

Immunization at birth may be important for an earlier prevention of the pertussis disease in infants under 6 months, especially in Italy, where the recommended ages for aP vaccine administration are 3, 5, and 11 months.

Quality control of biotechnology-derived vaccines: technical and regulatory considerations

Vaccines for human use have been produced for decades using classical manufacturing methods including culture of viruses and bacteria followed by various concentration-, inactivation-, detoxification-, conjugation production processes. Availability of techniques for molecular biology and for the complete chemical synthesis of genes provides prospects of genetic engineering of microorganisms so as to generate novel biotechnological/biological-derived vaccines. The potential large-scale availability of biotechnology-derived vaccines makes feasible their evaluation in the prevention and/or treatment of various infectious, chronic, degenerative and cancer human diseases. There are potential safety concerns that arise from the novel manufacturing processes and from the complex structural and biological characteristics of the products. These products have distinguishing characteristics to which consideration should be given in a well-defined quality control testing programme. The evaluation of their quality, safety, efficacy and stability necessitate complex analytical methods and appropriate physicochemical, biochemical and immunochemical methods for the analysis of the molecular entity. A flexible approach to the control of these novel products is being developed by regulatory authorities so that recommendations can be modified in the light of experience of research and development in vaccinology, production and use of biotechnology products and with the further development of new technologies.

Cloning and immunologic characterization of a truncated Bordetella bronchiseptica filamentous hemagglutinin fusion protein

Filamentous hemagglutinin (FHA) is an outer-membrane associated adhesin conserved within the genus Bordetella. FHA provides protection against B. pertussis infections in humans and is a component of acellular whooping cough vaccines. Furthermore, FHA serves as a protective antigen in several animal models of infection with B. bronchiseptica and may serve as a protective antigen of canine bordetellosis. In this study, polyclonal anti-B. pertussis FHA antiserum was used to identify an immunoreactive clone from the genomic DNA library of a canine B. bronchiseptica field isolate. The nucleotide and predicted amino acid sequences of the immunoreactive clone were compared to fhaB and FhaB from B. pertussis revealing 94% identity at the nucleic acid level, and 86% identity at the protein level. A truncated fusion protein (FHAt) was prepared which included a conserved domain homologous to the immunodominant region in the FHA of B. pertussis [Leininger E, Bowen S, Renauld-Mongen G, Rouse JH, Menozzi FD, Locht C, Heron I, Brennan MJ. Immunodominant domain present on the Bordetella pertussis vaccine component filamentous hemagglutinin. J. Infect. Dis. 1997;175:1423-1431; Wilson DR, Siebers A, Finlay BB. Antigenic analysis of Bordetella pertussis filamentous hemagglutinin with phage display libraries and rabbit anti-filamentous hemagglutinin polyclonal antibodies. Infect. Immun. 1998;66:4884-4894]. FHAt was shown to be safe and antigenic in rabbits. FHAt induced the formation of antibodies that inhibit the hemagglutination associated with full length B. pertussis FHA, and inhibit adherence of B. bronchisepitca to canine fibroblasts by as much as 65%. This information may have implications for the development of safe and efficacious subunit vaccines for the prevention of canine bordetellosis and may contribute to future acellular whooping cough vaccines.

Genetically derived toxoids for use as vaccines and adjuvants

Until very recently, development of vaccines has been based on an empirical approach. For example, bacterial toxins have been detoxified using empirical chemical treatment. Progress in biotechnology and molecular biology has allowed the fine knowledge of the structure-function relationship of several bacterial toxins. Thanks to this, the genetic attenuation of bacterial toxins has been made possible. Following this approach, a genetically detoxified pertussis toxin has been produced. This molecule is now the component of an acellular pertussis vaccine, which has been shown to be highly immunogenic and efficacious in infants. The same strategy of molecular detoxification of bacterial toxins has been applied to cholera toxin and to the Escherichia coli heat-labile enterotoxin. Toxin mutants devoid of any toxic activity have been produced and shown in animals to be highly immunogenic and to exhibit strong adjuvanticity when administered at mucosal sites in conjunction with several antigens. These successful results show that rational design of stronger and safer vaccines is feasible.

Novel molecular biology approaches to acellular vaccines

Bacterial toxins are commonly detoxified by chemical treatment in order to use them in human vaccines. We have used site-directed mutagenesis of toxin genes to obtain bacteria that produce naturally nontoxic mutants of bacterial toxins, such as pertussis toxin (PT), cholera toxin (CT) and Escherichia coli heat-labile enterotoxin (LT). Genetically detoxified PT showed a superior safety and immunogenicity in animal models, phase I and phase II clinical trials, and a superior protective efficacy in the early and late stage of a phase III efficacy trial, proving in a definitive and extensive way that genetic detoxification of bacterial toxins can, and should, replace chemical treatment. The results obtained with genetically inactivated LT and CT indicate that genetic detoxification of bacterial toxins can be used not only to produce vaccines for systemic immunization that are superior to the ones produced by conventional technologies, but suggest that these type of molecules may be the prototype molecules for the design and construction of innovative vaccines with a totally new design, such as mucosally delivered preventive and therapeutic vaccines.

Molecular basis of vaccination

Vaccines represent the most cost-effective means to prevent infectious diseases. Most of the vaccines which are currently available were developed long before the era of molecular biology and biotechnology. They were obtained following empirical approaches leading to the inactivation or to the attenuation of microorganisms, without any knowledge neither of the mechanisms of pathogenesis of the disease they were expected to protect from, nor of the immune responses elicited by the infectious agents or by the vaccine itself. The past two decades have seen an impressive progress in the field of immunology and molecular biology, which have allowed a better understanding of the interactions occurring between microbes and their hosts. This basic knowledge has represented an impetus towards the generation of better vaccines and the development of new vaccines. In this monograph we briefly summarize some of the most important biotechnological approaches that are currently followed in the development of new vaccines, and provide details on an approach to vaccine development: the genetic detoxification of bacterial toxins. Such an approach has been particularly successful in the rational design of a new vaccine against pertussis, which has been shown to be extremely efficacious and safe. It has been applied to the construction of powerful mucosal adjuvants, for administration of vaccines at mucosal surfaces.

Whole-cell and acellular pertussis vaccines

OBJECTIVE

To provide a review of pertussis vaccines, including information on efficacy, adverse reactions, and antibody production following administration of both whole-cell and acellular pertussis vaccines.

DATA SOURCES

A MEDLINE search and extensive review of journals was conducted to identify the information for this review.

DATA EXTRACTION

Pertinent studies reporting experience with pertussis vaccinations were reviewed.

DATA SYNTHESIS

The differences in efficacy, adverse reactions, and antibody responses between whole-cell and acellular pertussis vaccines are emphasized. The status of acellular pertussis vaccination in the US is defined.

CONCLUSIONS

Acellular (chemically detoxified or recombinant) pertussis vaccine formulation appears to cause fewer adverse reactions than whole-cell vaccine in most studies. Clinical efficacy and safety in the very young has not been well established. Thus, acellular pertussis vaccine is reserved for the 4th and 5th doses in the US. Oral or intranasal formulations of the pertussis vaccine are being evaluated.

Comparative study of a whole-cell pertussis vaccine and a recombinant acellular pertussis vaccine. The Italian Multicenter Group for the Study of Recombinant Acellular Pertussis Vaccine

The safety and immunogenicity of an acellular pertussis vaccine containing the genetically detoxified pertussis toxin PT-9K/129G, filamentous hemagglutinin, and pertactin, together with diphtheria and tetanus toxoids, were compared with those of a whole-cell pertussis component-diphtheria-tetanus vaccine. Four hundred eighty infants were enrolled into this prospective, multicenter, double-blind study. Each infant was randomly given three doses of one of the two vaccines at 2, 4, and 6 months of age. Both local and systemic adverse reactions, reported within 48 hours and 7 days of each injection, were less frequent after the acellular vaccine than after the whole-cell vaccine. The enzyme-linked immunosorbent assay titers to pertussis toxin, filamentous hemagglutinin, and pertactin, as well as the pertussis toxin-neutralizing titer measured by the Chinese hamster ovary cell assay, were significantly higher after the acellular vaccine was given. Both vaccines induced adequate levels of anti-diphtheria and anti-tetanus antibodies. We conclude that the recombinant acellular pertussis vaccine produces fewer reactions than the whole-cell vaccine and provides a high antibody response against the antigens of Bordetella pertussis involved in bacterial adhesion and systemic toxic effects.

Toxin inactivation and antigen stabilization: two different uses of formaldehyde

Since the 1920s, when Ramon discovered the detoxifying properties of formaldehyde, this compound has been used to inactivate toxins, whole bacterial cells and viruses. With the development of vaccines that are detoxified by genetic manipulation, formaldehyde has a new role as a stabilizer of such genetically detoxified antigens.