Acellular pertussis vaccine composed of genetically inactivated pertussis toxin: safety and immunogenicity in 12- to 24- and 2- to 4-month-old children

MA, Tovar-Rosero YY, Oñate AA, O'Ryan M. Two centuries of vaccination: historical and conceptual approach and future perspectives

Over the past two centuries, vaccines have been critical for the prevention of infectious diseases and are considered milestones in the medical and public health history. The World Health Organization estimates that vaccination currently prevents approximately 3.5-5 million deaths annually, attributed to diseases such as diphtheria, tetanus, pertussis, influenza, and measles. Vaccination has been instrumental in eradicating important pathogens, including the smallpox virus and wild poliovirus types 2 and 3. This narrative review offers a detailed journey through the history and advancements in vaccinology, tailored for healthcare workers. It traces pivotal milestones, beginning with the variolation practices in the early 17th century, the development of the first smallpox vaccine, and the continuous evolution and innovation in vaccine development up to the present day. We also briefly review immunological principles underlying vaccination, as well as the main vaccine types, with a special mention of the recently introduced mRNA vaccine technology. Additionally, we discuss the broad benefits of vaccines, including their role in reducing morbidity and mortality, and in fostering socioeconomic development in communities. Finally, we address the issue of vaccine hesitancy and discuss effective strategies to promote vaccine acceptance. Research, collaboration, and the widespread acceptance and use of vaccines are imperative for the continued success of vaccination programs in controlling and ultimately eradicating infectious diseases.

The History of Pertussis Toxin

Besides the typical whooping cough syndrome, infection with Bordetella pertussis or immunization with whole-cell vaccines can result in a wide variety of physiological manifestations, including leukocytosis, hyper-insulinemia, and histamine sensitization, as well as protection against disease. Initially believed to be associated with different molecular entities, decades of research have provided the demonstration that these activities are all due to a single molecule today referred to as pertussis toxin. The three-dimensional structure and molecular mechanisms of pertussis toxin action, as well as its role in protective immunity have been uncovered in the last 50 years. In this article, we review the history of pertussis toxin, including the paradigm shift that occurred in the 1980s which established the pertussis toxin as a single molecule. We describe the role molecular biology played in the understanding of pertussis toxin action, its role as a molecular tool in cell biology and as a protective antigen in acellular pertussis vaccines and possibly new-generation vaccines, as well as potential therapeutical applications.

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.

Acellular pertussis vaccines for use among infants and young children

Pertussis is still one of the most common vaccine-preventable childhood diseases in developed countries. Infants, particularly those < 6 months, are the most susceptible and those who suffer the greatest disease burden and mortality. In the 1970s, concerns about the reactogenicity of whole-cell vaccines led to a decrease in vaccine coverage and later the re-emergence of the disease in many countries. The advent of acellular vaccines in recent years has constituted an important advance in the acceptance of this immunisation and consequently the control of the disease. The efficacy of acellular pertussis vaccines is approximately 59 - 93%, similar to whole-cell vaccines, but all available data confirm the substantial improvement in safety of the new vaccines. With the licensure of acellular pertussis vaccines and combined vaccines containing them, pertussis immunisation has become significantly developed. Furthermore, the possibility of continuing to vaccinate adolescents and adults with new diphtheria, tetanus, and pertussis (dTap) vaccines is an important step in achieving control and elimination of the disease.

Diphtheria-tetanus-acellular pertussis vaccine adsorbed (Triacelluvax; DTaP3-CB): a review of its use in the prevention of Bordetella pertussis infection

DTaP3-CB (Triacelluvax) is an acellular pertussis (aP) vaccine containing 3 antigens from purified Bordetella pertussis bacteria combined with diphtheria and tetanus toxoids (DT). In addition to purified filamentous haemagglutinin and pertactin, DTaP3-CB contains pertussis toxin which has been genetically rather than chemically detoxified. As shown in randomised, double-blind clinical trials in infants, DTaP3-CB elicits an immune response similar to or greater than that of whole cell (DTwP) vaccines. Results of a large multicentre study comparing DTaP3-CB with 12 acellular and 1 DTwP vaccine indicate that DTaP3-CB, like all acellular vaccines, induces variable immune responses to different pertussis antigens; however, antibody titres to pertussis toxin are normally higher after immunisation with the genetically detoxified vaccine than with other 3- or 4-component vaccines. When given as a fourth or fifth booster dose, DTaP3-CB produced a significant immune response in infants primed with 3 doses of either a DTaP or DTwP vaccine. Virtually all infants immunised with DTaP3-CB had a serological response to diphtheria and tetanus toxoids. Data from 2 very large efficacy studies indicate that DTaP3-CB has high and long lasting protective efficacy against culture-confirmed pertussis which is greater than that of a 2-component vaccine (DTaP2-SB) and the whole cell DTwP-CON vaccine after a 3-, 5- and 12-month immunisation schedule and after a 2-, 4- and 6-month schedule with the DTwP-CON vaccine. However, the DTwP-CON whole cell vaccine has been noted for its low immunogenicity in 1 study and low efficacy and immunogenicity in another study. On the other hand, DTaP3-CB vaccine has similar efficacy to DTaP3-SB (after immunisation at 2, 4 and 6 months), DTaP5-CON and DTwP-EVANS against culture-confirmed pertussis with > or =21 days cough in infants immunised according to a 3-, 5- and 12-month schedule. Infants immunised with DTaP3-CB experienced significantly fewer adverse events such as pain, redness, swelling and irritability than infants given DTwP. DTaP3-CB has a similar tolerability profile to other acellular vaccines and is associated with similar rates of local tenderness, irritability, fever (> or =40 degrees C) and persistent crying. Comparative trials have shown that infants immunised with DTaP3-CB had a lower incidence of pain at the site of injection and fever (> or =38 degrees C) compared with other acellular vaccines, although this may have little clinical significance. Concomitant administration of DTaP3-CB with hepatitis B, oral polio or Haemophilus influenzae type B vaccines did not affect the immunogenicity of these other paediatric vaccines.

CONCLUSION

Data from clinical trials with DTaP3-CB vaccine indicate that this vaccine induces high and long lasting efficacy. It is at least as efficacious as most whole cell vaccines and generally similar in efficacy to the most efficacious acellular pertussis vaccines containing 3 or more pertussis antigens. DTaP3-CB is better tolerated than whole cell vaccines and has a similar tolerability profile to other acellular vaccines; the possible lower risk of severe adverse events remains to be confirmed. The low reactogenicity of DTaP3-CB is likely to make it well tolerated and therefore well accepted for the immunisation of infants, thereby enabling wider implementation of vaccination programmes.

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.

An acellular pertussis vaccine in healthy adults: safety and immunogenicity. Pennridge Pediatric Associates

Recent data indicate that Bordetella pertussis can be an important cause of illness in adolescents and adults. In a randomized observer- and subject-blinded study, adults (> or = 18 years of age) received an acellular pertussis (aP) vaccine containing genetically inactivated pertussis toxin (PT), filamentous hemagglutinin (FHA) and pertactin (PRN), or a saline placebo, and were monitored for safety and immunogenicity. IgG antibodies to PT, FHA, and PRN were measured by enzyme-linked immunosorbent assay (ELISA) and PT neutralization by a Chinese hamster ovary (CHO) cell assay. Local reactions, more common in the aP group, were mild and transient. One month after immunization, geometric mean ELISA antibody concentrations for the aP and placebo groups, respectively, were: anti-PT, 463 and 7.6; anti-FHA, 417 and 18; and anti-PRN, 855 and 14. The anti-PT neutralization titers for the aP and placebo groups were 1:3439 and 1:58 respectively. This aP vaccine is a safe and immunogenic candidate booster vaccine against pertussis for adults.

An economic evaluation of universal pertussis vaccination in Italy

An economic evaluation was performed of universal acellular pertussis vaccination in Italy, where until recently the overall coverage of pertussis vaccination was estimated at 50%. Over the last two years coverage seems to have increased rapidly. By means of a mathematical simulation model, the consequences of pertussis vaccination in terms of both health effects and economic costs were calculated for a single birth cohort followed for 6 years. Incremental analyses were performed for each additional 10% increase in coverage from 50-90%. The results indicate that a 50% coverage rate of pertussis vaccination in Italy was not optimal on the basis of cost-effectiveness and cost-benefit considerations. Additional increases in coverage were found to yield extra health gains at modest net costs or even potential net savings to the health care sector. For example, an increase in coverage to 90% would yield direct net savings of US$42 per extra vaccinee in comparison to a situation of 50% coverage. The total net savings for this strategy would be well over US$100 per additional vaccinee. In the sensitivity analysis, the positive relationship between incremental coverage and incremental efficiency remained unchanged.

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.

Economic evaluation of pertussis prevention by whole-cell and acellular vaccine in Germany

Acellular pertussis vaccines are less reactogenic than whole cell pertussis vaccines, but they are also more expensive. Based on simulation models, we compared the costs and effects of three alternative pertussis vaccination strategies in German children to "no prevention": (1) vaccination with whole-cell vaccine at 45% coverage (vaccine efficacy 90%), (2) vaccination with acellular vaccine at 45% coverage (vaccine efficacy 85%), and (3) vaccination with acellular vaccine at 90% coverage. In the two low coverage scenarios expected annual savings in direct medical costs through prevention of disease were larger for whole-cell than for acellular vaccination (252 vs 216 million DM, respectively). Direct costs for treating the more important adverse events induced by whole-cell vaccination (16.9 million DM annually) did not outweigh the higher direct costs of pertussis infections not prevented with the acellular vaccine and the higher price of the acellular vaccine. However, vaccination with acellular pertussis vaccine rapidly becomes as cost saving as vaccination with whole-cell vaccine as soon as vaccination coverage can be raised from 45% to 52.5% with acellular vaccine. Acellular vaccination is also the superior alternative when considering indirect cost savings resulting from reduction in work-loss due to adverse events.

CONCLUSION

In our simulations, the most cost-effective pertussis prevention strategy was the use of an effective whole-cell vaccine with a high coverage rate. Introduction of the more expensive acellular pertussis vaccines becomes cost saving if at least a 7.5% increase in coverage is achieved. If also non-medical indirect costs to parents resulting from vaccine associated side-effects are accounted for, acellular vaccines may be more cost-effective also in countries with already high whole-cell vaccine coverage.

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.

A cellular pertussis vaccine (Infanrix-DTPa; SB-3). A review of its immunogenicity, protective efficacy and tolerability in the prevention of Bordetella pertussis infection

SB-3 (Infanrix-DTPa) is one of a new generation of vaccines for immunisation against pertussis (whooping cough), diphtheria and tetanus. It is a 3-component (pertussis toxin, filamentous haemagglutinin and pertactin) chemically inactivated acellular pertussis pertussis-diphtheria-tetanus toxoid (DTaP) vaccine, and it differs from conventional whole-cell pertussis-diphtheria-tetanus toxoid (DTwP) vaccines in that it comprises inactivated purified Bordetella pertussis antigens rather than whole cells of the bacillus. SB-3, like a number of other DTaP vaccines, elicits a similar or more often, a significantly greater immune response than various DTwP vaccines in healthy infants and young children. initial data from comparative studies indicate that SB-3 also remains immunogenic when given in combination with hepatitis B vaccine or concurrently administered with Haemophilus influenzae type b (HbOC) conjugate vaccine. A combination of SB-3 and H. influenzae type b tetanus (PRP-T) conjugate vaccine results in lower anti-PRP antibody response than when both vaccines are administered concurrently. Data from two large, multicentre, German and Italian studies in infants indicate that the protective efficacy of SB-3 against pertussis was significantly better than one DTwP (DTwP-CON) but similar to another one (DTwP-BW) under investigation. Compared with another DTaP vaccine (BIO-3), SB-3 was just as protective. Overall, the data from these 2 studies indicate that primary vaccination with SB-3 provides effective protection against pertussis, even under the stringent conditions of a household contact with typical pertussis. As the other DTaP vaccines, SB-3 is better tolerated than DTwP vaccines, with a significantly lower incidence of common adverse events such as local reactions (swelling, pain and a erythema), irritability, fever, persistent crying and local tenderness. Clinical experience with SB-3 thus far indicates that, like other DTaP vaccines, it is associated with significantly fewer common (non-serious) adverse events than DTwP vaccines. Less clear is whether it has any advantage over DTwP vaccines with respect to protective efficacy or over other DTaP vaccines with respect to tolerability and protective efficacy. Nevertheless, the available data support the use of SB-3 for infant immunisation, as well as providing a suitable basis for the development of new combination vaccines.

Effect of priming with diphtheria and tetanus toxoids combined with whole-cell pertussis vaccine or with acellular pertussis vaccine on the safety and immunogenicity of a booster dose of an acellular pertussis vaccine containing a genetically inactivated pertussis toxin in fifteen- to twenty-one-month-old children. Italian Multicenter Group for the Study of Recombinant Acellular Pertussis Vaccine

OBJECTIVE

To evaluate the safety and the immunogenicity of a booster dose of recombinant acellular pertussis vaccine combined with diphtheria and tetanus toxoids (DTaP, Biocine SpA) in 15- to 21-month-old children primed in infancy with either whole-cell diphtheria-tetanus-pertussis (DTwP) vaccine or DTaP vaccine.

DESIGN

Open-label second phase of a double-masked, controlled trail, with masked analysis of serum samples.

PARTICIPANTS AND SETTING

Three hundred fifty children, 15 to 21 months of age, who had been primed at 2, 4, and 6 months of age with either three doses of DTaP vaccine (n = 173) or DTwP vaccine (n = 177). The children were enrolled in eight vaccination centers in Italy.

INTERVENTIONS

All children received a booster dose of the DTaP vaccine and were examined for safety at 48 hours and at 7 days after vaccination. Serum samples for evaluation of immunogenicity were obtained from 196 (55%) of the 350 children.

MAIN OUTCOME MEASURES

IgG antibodies to pertussis toxin (Ptox), filamentous hemagglutinin, 69-kilodalton protein, and tetanus toxoid were measured by enzyme-linked immunosorbent assay. Pertussis toxin-neutralizing antibodies were measured by the Chinese hamster ovary cell toxin neutralization assay.

MAIN RESULTS

Adverse reactions to DTaP were infrequent, and there was no difference in the incidence of local or systemic reactions in children given DTaP as a fourth dose in comparison with a first dose. One month after the DTaP booster vaccination, both groups had 6- to 40-fold increases in serum antibody concentrations to all antigens tested; the concentrations against the three pertussis antigens were higher in the DTaP-primed children (p < 0.05). The antibody titers to diphtheria and tetanus toxoids were higher in the DTwP-primed group (p < 0.05), but both groups had protective titers. The geometric mean ratio of anti-Ptox neutralizing antibody per unit of IgG anti-Ptox antibody was higher in the DTaP-primed group (p < 0.001).

CONCLUSIONS

There are quantitative and qualitative differences in booster responses to DTaP vaccine in young children, depending on whether they were given DTaP or DTwP as primary immunization. This DTaP vaccine is safe and highly immunogenic as a booster.

Hsp70: a carrier molecule with built-in adjuvanticity

One problem associated with the development of subunit vaccines is their limited immunogenicity, due to their physico-chemical structure, their inability to encounter the correct MHC restriction element, or the need for strong adjuvants to be delivered along with them. These problems are usually solved by conjugating target epitopes (peptides or oligosaccharides) with carrier proteins which provide a source of T-cell epitopes recognised by a large proportion of the vaccinated individuals. We have shown that mycobacterial hsp65 and hsp70 exert a strong helper effect in vivo when conjugated to synthetic peptides or oligosaccharides. Interestingly, this helper effect did not require the need for any adjuvant, either in mice or in monkeys. The helper effect mediated by the hsp65 required that animals were previously primed with either live BCG or the hsp65 alone; on the other hand, such a priming was not required when the hsp70 was used in the conjugates. Similar results were obtained with HSP molecules from Escherichia coli. This may suggest that the adjuvant-free helper effect observed applies not only to mycobacterial HSP, but also to HSP from other prokaryotes. These findings suggest that microbial hsp70 could be considered for the design of conjugated vaccine constructs for eventual human use.

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.

Engineered human vaccines

The limitations of human vaccines in use at present and the design requirements for a new generation of human vaccines are discussed. The progress in engineering of human vaccines for bacteria, viruses, parasites, and cancer is reviewed, and the data from human studies with the engineered vaccines are discussed, especially for cancer and AIDS vaccines. The final section of the review deals with the possible future developments in the field of engineered human vaccines and the requirement for effective new human adjuvants.

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

We studied the immunogenicity of an acellular pertussis vaccine composed of genetically detoxified pertussis toxin (PT-9K/129G), filamentous haemagglutinin, and a 69-kilodalton protein, pertactin, in 30 children aged 12 to 24 months and in 80 infants aged 2 to 4 months. A significant increase of the neutralizing titer and of the titers against pertussis toxin, filamentous hemagglutinin, and pertactin, as determined by enzyme-linked immunosorbent assay, was achieved after three doses of vaccine in all the children; a significant increase of these antibody titers was obtained in 100%, 96.1%, 93.5%, and 98.7% of the infants, respectively.

Recombinant acellular pertussis vaccine--from the laboratory to the clinic: improving the quality of the immune response

Vaccination is the most effective way to prevent infectious diseases. Recombinant DNA technologies have provided powerful new tools to develop vaccines that were previously impossible or difficult to make, and to improve the vaccines that were already available but had been developed using old technology. In the case of whooping cough, an effective vaccine (composed of killed bacterial cells) is available, but its use is controversial because of the many side effects that have been associated with it. An improved vaccine against this disease should contain pertussis toxin, a molecule that needs to be detoxified in order to be included in the vaccine. Classical methods of detoxification, such as formaldehyde treatment have been used to inactivate this toxin. We have used recombinant DNA technologies to clone the pertussis toxin gene, express it in bacteria, map the B and T cell epitopes of the molecule, and to identify the amino acids that are important for enzymatic activity and toxicity. Finally, we have used this information to mutate the gene in the chromosome of Bordetella pertussis in order to obtain a strain that produces a molecule that is already non-toxic. This genetically inactivated pertussis toxin was tested extensively in animal models and clinical trials and was found to induce an immune response that is superior in quality and quantity to that induced by the vaccines produced by conventional technologies.

Progress towards the development of new vaccines against whooping cough

Acellular vaccines against whooping cough are in the final stage of clinical testing and are likely to become available for mass immunization in the near future. Over a dozen vaccines of similar composition have been developed by vaccine companies and research laboratories; all of them contain a detoxified form of pertussis toxin (PT) that may be present alone or combined with one or more other non-toxic proteins, such as filamentous haemagglutinin (FHA), pertactin (69 kDa), and the agglutinogens (AGG). Most of the vaccines contain a PT that has been inactivated by chemical treatment, a process that reduces the immunogenicity of the molecule and may not completely eliminate the risk of reversion to toxicity. To avoid these problems, we have constructed by genetic manipulation a mutant of Bordetella pertussis that produces a non-toxic form of PT. This molecule (PT-9K/129G) contains two amino acid substitutions in the S1 subunit (Arg9-->Lys and Glu129-->Gly) which abolish the enzymatic activity of the S1 subunit and all the toxic properties of PT, without changing the immunological properties of the wild-type toxin. Following extensive preclinical studies, which have shown that PT-9K/129G is safe and more antigenic than the toxin treated with chemical agents, this molecule was tested for safety and immunogenicity in adult volunteers, 18-month-old children and 2-month-old infants. The molecule has been tested alone, combined with FHA and pertactin and also combined with diphtheria and tetanus toxoids.(ABSTRACT TRUNCATED AT 250 WORDS)