Metabolic, humoral, and cellular responses in adult volunteers immunized with the genetically inactivated pertussis toxin mutant PT-9K/129G

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.

Genetically detoxified pertussis toxin displays near identical structure to its wild-type and exhibits robust immunogenicity

The mutant gdPT R9K/E129G is a genetically detoxified variant of the pertussis toxin (PTx) and represents an attractive candidate for the development of improved pertussis vaccines. The impact of the mutations on the overall protein structure and its immunogenicity has remained elusive. Here we present the crystal structure of gdPT and show that it is nearly identical to that of PTx. Hydrogen-deuterium exchange mass spectrometry revealed dynamic changes in the catalytic domain that directly impacted NAD⁺ binding which was confirmed by biolayer interferometry. Distal changes in dynamics were also detected in S2-S5 subunit interactions resulting in tighter packing of B-oligomer corresponding to increased thermal stability. Finally, antigen stimulation of human whole blood, analyzed by a previously unreported mass cytometry assay, indicated broader immunogenicity of gdPT compared to pertussis toxoid. These findings establish a direct link between the conserved structure of gdPT and its ability to generate a robust immune response.

Characterization of Individual Human Antibodies That Bind Pertussis Toxin Stimulated by Acellular Immunization

Despite high vaccination rates, the incidence of whooping cough has steadily been increasing in developing countries for several decades. The current acellular pertussis (aP) vaccines all include the major protective antigen pertussis toxin (PTx) and are safer, but they appear to be less protective than infection or older, whole-cell vaccines. To better understand the attributes of individual antibodies stimulated by aP, we isolated plasmablast clones recognizing PTx after booster immunization of two donors. Five unique antibody sequences recognizing native PTx were recovered and expressed as recombinant human IgG1 antibodies. The antibodies all bind different epitopes on the PTx S1 subunit, B oligomer, or S1-B subunit interface, and just one clone neutralized PTx in an in vitro assay. To better understand the epitopes bound by the nonneutralizing S1-subunit antibodies, comprehensive mutagenesis with yeast display provided a detailed map of the epitope recognized by antibodies A8 and E12. Residue R76 is required for antibody A8 binding and is present on the S1 surface but is only partially exposed in the holotoxin, providing a structural explanation for A8's inability to neutralize holotoxin. The B-subunit-specific antibody D8 inhibited PTx binding to a model receptor and neutralized PTx in vitro as well as in an in vivo leukocytosis assay. This is the first study, to our knowledge, to identify individual human antibodies stimulated by the acellular pertussis vaccine and demonstrates the feasibility of using these approaches to address outstanding issues in pertussis vaccinology, including mechanisms of accelerated waning of protective immunity despite repeated aP immunization.

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 adolescents

BACKGROUND

The epidemiology of pertussis is changing, with a clear increase in the number of cases diagnosed in adolescents and adults. This development has spurred studies and anticipated licensure of safer diphtheria, tetanus, acellular pertussis combined (Tdap) vaccines for this older population.

METHODS

Literature review.

RESULTS

Tdap vaccines are safe and immunogenic when administered to adolescents and adults. Correlates of immunity to pertussis after Tdap vaccination have not been established, but various combinations of antibody to pertussis antigens (pertussis toxin, filamentous hemagglutinin, pertactin, and fimbriae) provide protection. The importance of the number of antigens in Tdap vaccines for protection against mild pertussis disease is unclear. Pertussis vaccination establishes herd immunity after sufficient uptake within communities and countries. As experience with TdaP vaccines has accumulated, a 1-2% occurrence of large, local injection-site reactions with all TdaP vaccine products have been observed for booster doses in children 4-6 years of age. The frequency of large local reactions appears lower in adolescents and adults. The pathophysiologic mechanisms for the local reactions are not established, but a majority appears to be immunoglobulin E-mediated-reactive edema, and a minority appears to be immunoglobulin G-mediated Arthus-type reactions.

CONCLUSIONS

Tdap vaccines appear safe and immunogenic. The economic impact of pertussis provides a cost-benefit justification for widespread use of Tdap vaccine boosting in adolescents.

Pertussis Toxin (PTX) B Subunit and the Nontoxic PTX Mutant PT9K/129G Inhibit Tat-Induced TGF-β Production by NK Cells and TGF-β-Mediated NK Cell Apoptosis

We show that the pertussis toxin B oligomer (PTX-B), and the PTX mutant PT9K/129G, which is safely administered in vivo, inhibit both transcription and secretion of TGF-beta elicited by HIV-1 Tat in NK cells. Tat-induced TGF-beta mRNA synthesis is also blocked by the ERK1 inhibitor PD98059, suggesting that ERK1 is needed for TGF-beta production. Moreover, Tat strongly activates the c-Jun component of the multimolecular complex AP-1, whereas TGF-beta triggers c-Fos and c-Jun. Of note, treatment of NK cells with PTX-B or PT9K/129G inhibits Tat- and TGF-beta-induced activation of AP-1. TGF-beta enhances starvation-induced NK cell apoptosis, significantly reduces transcription of the antiapoptotic protein Bcl-2, and inhibits Akt phosphorylation induced by oligomerization of the triggering NK cell receptor NKG2D. All these TGF-beta-mediated effects are prevented by PTX-B or PT9K/129G through a PI3K-dependent mechanism, as demonstrated by use of the specific PI3K inhibitor, LY294002. Finally, PTX-B and PT9K/129G up-regulate Bcl-x(L), the isoform of Bcl-x that protects cells from starvation-induced apoptosis. It is of note that in NK cells from patients with early HIV-1 infection, mRNA expression of Bcl-2 and Bcl-x(L) was consistently lower than that in healthy donors; interestingly, TGF-beta and Tat were detected in the sera of these patients. Together, these data suggest that Tat-induced TGF-beta production and the consequent NK cell failure, possibly occurring during early HIV-1 infection, may be regulated by PTX-B and PT9K/129G.

Acellular Pertussis Vaccine Safety and Efficacy in Children, Adolescents and Adults

This review offers a perspective on the acellular pertussis vaccine efficiency trials concluded in the 1990s and presents the main conclusions of a meta-analysis of 52 studies that assessed the safety and efficacy of the diphtheria-tetanus (DT)-whole cell pertussis (DTwP) and DT-acellular pertussis (DTaP) vaccines administered to children. A clear serological correlate of immunity to pertussis following DTaP vaccination was not identified despite an intensive analysis. It can be speculated that this may be because various combinations of antibody to agglutinogens (pertussis toxin, filamentous haemagglutinin, pertactin and fimbriae) provide protection, or because serum antibody levels and responses do not uniformly reflect mucosal IgA antibody levels.Long-term efficacy following DTaP vaccination is becoming characterised and cell-mediated immunity (T-cell memory) may have importance. DTaP vaccination appears to establish herd immunity after sufficient uptake within communities and countries. As experience with DTaP vaccine safety has accumulated, a 1-2% occurrence of large, local injection reactions with all products has been defined for booster doses. The pathophysiological mechanisms for the reactions are not established but a majority appear likely to be IgE-mediated reactive oedema and a minority to be IgG-mediated reactive Arthus-type reactions. DTwP and DTaP combinations with other vaccines have been studied and licensed; the most controversial combination products are the DTaP/Haemophilus influenzae type B polysaccharide conjugate vaccines. Pertussis epidemiology is changing with a clear increase in occurrence in adolescents and adults. This development has spurred studies and licensure of safer DTaP vaccines for this older population. The economic impact of pertussis and transmission from adults to vulnerable infants provides a cost-benefit justification for widespread use of DTaP vaccines in all age groups with routine boosting every 10 years.

New generation of mucosal adjuvants for the induction of protective immunity

Invasion of infectious agents through mucosal surfaces can be prevented by use of the common mucosal immune system (CMIS), which interconnects inductive tissues, including Peyer's patches (PPs) and nasopharyngeal-associated lymphoreticular tissue (NALT), and effector tissues of the intestinal and respiratory tracts. In order for the CMIS to induce maximal protective mucosal immunity, co-administration of mucosal adjuvant has been shown to be essential. When vaccine antigen is administered together with mucosal adjuvant, antigen-specific T-helper (Th) 1 and Th2 cells, cytotoxic T lymphocytes (CTLs) and IgA B cell responses are effectively induced by oral or nasal routes via the CMIS. In the early stages of induction of mucosal immune response, the uptake of orally or nasally administered antigens is achieved through a unique set of antigen-sampling cells, M cells located in follicle-associated epithelium (FAE) of inductive sites. After successful uptake, the antigens are immediately processed and presented by the underlying dendritic cells (DCs). Elucidation of the molecular/cellular characteristics of M cells and mucosal DCs will greatly facilitate the design of a new generation of effective mucosal adjuvants and of a vaccine delivery vehicle that maximises the use of the CMIS. Our recent efforts at mucosal vaccine development have focused on nasal administration of vaccine antigen together with nontoxic mutant-based or cytokine-/chemokine-based adjuvant for the induction of the protective immunity. To this end, a chimeric form of a nontoxic adjuvant combining the merits of mutant cholera toxin A subunit (mCT-A) and heat labile toxin B subunit (LT-B) was created as the second generation of detoxified toxin-based mucosal adjuvant. When a vaccine antigen was coexpressed together with an immune stimulatory/delivery molecule in crop seed, this edible vaccine is not only effective but also extremely practical in that it can be produced in huge quantities and preserved and shipped over long distances at room temperature without altering the quality of the vaccine. Because such qualities would greatly facilitate global vaccination, this new generation edible vaccines with a built-in adjuvant and/or M cell-targeted edible vaccine promises to be a powerful weapon for combating infectious diseases and bioterrorism.

Immunity to Bordetella pertussis

Bordetella pertussis exploits extracellular and intracellular niches in the respiratory tract and a variety of immune evasion strategies to prolong its survival in the host. This article reviews evidence of complementary roles for cellular and humoral immunity in protection. It discusses the effector mechanisms of bacterial elimination, the strategies employed by the bacteria to subvert protective immune responses and the immunological basis for systemic and neurological responses to infection and vaccination.

Stimulation of HIV gp120-specific cytolytic T lymphocyte responses in vitro and in vivo using a detoxified pertussis toxin vector

CD8+ cytolytic T lymphocytes (CTL) are almost certainly an important component of a potentially protective immune response to HIV. To test the ability of pertussis toxin (PT) to deliver an HIV-derived major histocompatibility complex (MHC) class I peptide for CTL stimulation, we constructed a fusion of the gp120 P18-I10 CTL epitope with a genetically detoxified derivative of PT (PT9K/129G) and assayed this fusion for its ability to stimulate a gp120-specific CTL response in vitro and in vivo. Antigen-presenting cells incubated with this fusion protein were lysed by P18-I10-specific CTL in vitro and this activity was shown to be MHC class I restricted. The activity was inhibited by brefeldin A but was not inhibited by proteasome inhibitors, possibly because PT undergoes retrograde intracellular transport through the Golgi apparatus to the endoplasmic reticulum and delivers epitopes directly to nascent class I molecules. Mice immunized intraperitoneally with a single dose of the fusion protein without adjuvant raised a strong gp120-specific CTL response in the spleen. This CTL response was dependent on (1) the dose of fusion administered, (2) the fusion of the epitope with the toxin (since coadministration of peptide and toxin gave no response), and (3) the activity of CD8+ cells. These data demonstrate that this detoxified derivative to PT, which is already a component of a licensed vaccine for humans, could represent a useful vaccine vector molecule for stimulation of HIV-specific CTL responses.

The binding subunit of pertussis toxin inhibits HIV replication in human macrophages and virus expression in chronically infected promonocytic U1 cells

We have recently shown that the binding subunit of pertussis toxin (PTX-B) inhibits the entry and replication of macrophage-tropic (R5) HIV-1 strains in activated primary T lymphocytes. Furthermore, PTX-B suppressed the replication of T cell-tropic (X4) viruses at a postentry level in the same cells. In this study we demonstrate that PTX-B profoundly impairs entry and replication of the HIV-1(ADA) (R5), as well as of HIV pseudotyped with either murine leukemia virus or vesicular stomatitis virus envelopes, in primary monocyte-derived macrophages. In addition, PTX-B strongly inhibited X4 HIV-1 replication in U937 promonocytic cells and virus expression in the U937-derived chronically infected U1 cell line stimulated with cytokines such as TNF-alpha and IL-6. Of interest, TNF-alpha-mediated activation of the cellular transcription factor NF-kappaB was unaffected by PTX-B. Therefore, PTX-B may represent a novel and potent inhibitor of HIV-1 replication to be tested for efficacy in infected individuals. In support of this proposition, a genetically modified mutant of PTX (PT-9K/129G), which is safely administered for prevention of Bordetella pertussis infection, showed an in vitro anti-HIV profile superimposable to that of PTX-B.

Adult formulation of a five component acellular pertussis vaccine combined with diphtheria and tetanus toxoids and inactivated poliovirus vaccine is safe and immunogenic in adolescents and adults

BACKGROUND

Pertussis is increasingly recognized as an important cause of cough illness in adolescents and adults.

PURPOSE

To evaluate the safety and antibody response to a single dose of an adult formulation of a five component (pertussis toxoid, filamentous hemagglutinin, pertactin, fimbriae 2 and 3) acellular pertussis vaccine (aP) combined with diphtheria and tetanus toxoids (TdaP) and inactivated poliovirus vaccine (TdaP-IPV) in adolescents and adults and to assess the response to a second dose of the acellular pertussis vaccine in a subset of the adults.

POPULATION AND SETTING

The study addressed 1207 healthy participants (736 adults and 466 adolescents) recruited in five Canadian communities.

STUDY DESIGN

In a randomized, observer-blind, controlled clinical trial, adult participants received Td followed at a separate visit by aP, TdaP followed by IPV or TdaP-IPV; adolescents received Td-IPV followed at a separate visit by aP or TdaP-IPV. A subgroup of adults was given a booster of aP 1 month after TdaP.

OUTCOME MEASURES

Antibody titers measured before and 1 month after each immunization; adverse events enumerated at 24 h, 72 h and 8 to 10 days.

RESULTS

The aP vaccine given by itself was associated with adverse events less frequently than were Td, Td-IPV, TdaP or TdaP-IPV vaccines, but reaction rates did not differ significantly among the latter products. The antibody response against Bordetella pertussis antigens was vigorous in all groups, although adults given the TdaP-IPV vaccine had lower antibody titers against filamentous hemagglutinin, pertactin, diphtheria and tetanus antibodies than those given TdaP vaccine. Similarly adolescents given TdaP-IPV had lower antibody titers against pertussis toxin, filamentous hemagglutinin, fimbriae and agglutinins than those given Td-IPV and aP alone. A second dose of acellular pertussis vaccine was not associated with increased adverse events in adults but elicited increased antibody titers over that achieved by a single dose only against pertussis toxin.

CONCLUSIONS

This adult formulation five component aP vaccine given as TdaP-IPV is safe and immunogenic in adolescents and adults and is a candidate vaccine for adolescent and adult immunization programs.

An adult formulation of a five-component acellular pertussis vaccine combined with diphtheria and tetanus toxoids is safe and immunogenic in adolescents and adults

Pertussis is increasingly being recognized as an important cause of cough illness in adolescents and adults. To evaluate the safety and immunogenicity of an adult formulation of a five-component (pertussis toxoid, filamentous hemagglutinin, pertactin, fimbriae 2 and 3) acellular pertussis vaccine combined with diphtheria and tetanus toxoids, we randomly allocated 749 healthy adolescents and adults from 12-54 years of age recruited from five Canadian communities to receive either tetanus-diphtheria vaccine (Td), acellular pertussis vaccine (aP) or combined diphtheria-tetanus-acellular pertussis vaccine (TdaP). Subjects and personnel were unaware of the vaccine allocation. Antibody levels were measured before and one month postimmunization; adverse events were collected at 24 and 72 h and 8 to 10 days. Adverse events were reported in similar frequency amongst the three vaccine groups. Moderate pain at the injection site was reported less frequently in the aP group than the TdaP group (10.7% compared to 19.4%; relative risk 0.6, 95% confidence interval 0.3-0.9). Chills were reported less frequently after Td (5.3%) than after TdaP (12.5%; relative risk 0.4, 95% confidence interval 0.2-0.9). There were no statistically significant differences between recipients of Td and TdaP in tetanus and diphtheria antitoxin levels achieved. Antibody response against Bordetella pertussis antigens was vigorous in all groups although recipients of aP alone had higher levels of antibody levels against pertussis toxoid, fimbriae, and agglutinins and lower antibody levels against pertactin than did TdaP recipients. We conclude that this adult formulation 5-component acellular pertussis vaccine is safe and immunogenic in adolescents and adults and is a candidate vaccine for adolescent and adult immunization programs.

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.

Induction of CD4(+) and CD8(+) Bordetella pertussis toxin subunit S1 specific T cells by immunization with synthetic peptides

In this study two synthetic peptides from the Bordetella pertussis toxin subunit S1 were conjugated to human anti-idiotypic antibodies and used as an immunogen in cancer patients to induce immunity. The aims of the present report are to explain why no carrier or adjuvant effect of the conjugated pertussis peptides could be established regarding induction of responses against the anti-idiotype and to explore the type and quality of induced anti-pertussis immune responses. The lack of carrier and adjuvant effect of the peptides might be related to the fact that the anti-idiotypic antibodies by themselves include helper epitopes and that none of the patients had a detectable T cell response against any of the selected peptides before immunization, which might be a requirement for an adjuvant effect. However, three of four immunized patients mounted a humoral as well as cellular response against the pertussis peptides used. The induced T cell immunity was restricted to one of the two peptides in responding patients. Established T cell lines and MHC blocking studies indicated that the T cell epitopes of the two peptides had a different MHC restriction. The type of T cell response induced seemed to govern the humoral response. The only durable antibody response was accompanied by the presence of a CD4(+) T cell response against the same peptide. Immunization with an anti-idiotype conjugated to synthetic peptides might thus induce both a B and a T cell response against the peptides and the type of induced T cells (CD4 or CD8) governs the quality of the humoral response. Moreover, the possibility of boosting or inducing a response against the antigen from which the peptide sequences were deduced also seemed 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.

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.

Cytokine mRNA expression and proliferative responses induced by pertussis toxin, filamentous hemagglutinin, and pertactin of Bordetella pertussis in the peripheral blood mononuclear cells of infected and immunized schoolchildren and adults

Pertussis infection is increasingly recognized in older children and adults, indicating the need of booster immunizations in these age groups. We investigated the induction of pertussis-specific immunity in schoolchildren and adults after booster immunization and natural infection. The expression of mRNA of gamma interferon (IFN-gamma), interleukin-2 (IL-2), IL-4, and IL-5 in the peripheral blood mononuclear cells (PBMCs) was assayed by reverse transcription-PCR. The PBMCs of 17 children immunized with one dose of an acellular vaccine containing pertussis toxin (PT), filamentous hemagglutinin (FHA), and pertactin (PRN) significantly proliferated in vitro after stimulation with the vaccine antigens. The PBMCs of seven infected individuals markedly proliferated in the presence of PT and FHA, but the cells of only two of these subjects responded to PRN. At least one of the antigens induced mRNA for IL-4 and/or IL-5 in the cells of 93% of tested vaccinees and patients, and FHA induced IFN-gamma mRNA in the cells of two-thirds of them. Expression of mRNA for IFN-gamma correlated with the production of the cytokine protein. Anti-FHA immunoglobulin G antibodies significantly correlated with FHA-induced proliferative responses both before and after immunization. These results show that booster immunization with acellular pertussis vaccine induces both antibody- and cell-mediated immune responses in schoolchildren. Further, booster immunization and natural infection seem to induce the expression of mRNA of T-helper 1 (Th1) and Th2 type cytokines in similar manners. This observation supports the use of acellular pertussis vaccines for booster immunizations of older children, adolescents, and adults.

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.

Distinct T-cell subtypes induced with whole cell and acellular pertussis vaccines in children

Recent clinical trials have demonstrated that new generation acellular pertussis vaccines can confer protection against whooping cough. However, the mechanism of protective immunity against Bordetella pertussis infection induced by vaccination remains to be defined. We have examined cellular immune responses in children immunized with a range of acellular and whole cell pertussis vaccines. Immunization of children with a potent whole-cell vaccine induced B. pertussis-specific T cells that secreted interferon-gamma (IFN-gamma), but not interleukin-5 (IL-5). In contrast, T cells from children immunized with acellular pertussis vaccines secreted IFN-gamma and/or IL-5 following stimulation with B. pertussis antigens in vitro. These observations suggest that protective immunity conferred by whole-cell vaccines, like natural immunity, is mediated by type 1 T cells, whereas the mechanism of immune protection generated with acellular vaccines may be more heterogeneous, involving T cells that secreted type 1 and type 2 cytokines.

MF59 adjuvant enhances antibody responses of infant baboons immunized with Haemophilus influenzae type b and Neisseria meningitidis group C oligosaccharide-CRM197 conjugate vaccine

The ability of the adjuvant MF59 to enhance the immunogenicity of polysaccharide-protein conjugate vaccines was investigated in infant baboons. MF59 consists of stable droplets (<250 nm) of the metabolizable oil squalene and two surfactants, polyoxyethylene sorbitan monooleate and sorbitan trioleate, in an oil-in-water emulsion. In humans, MF59 is well tolerated and enhances the immunogenicity of recombinant protein subunit or particle vaccines. Its effect on the immunogenicity of polysaccharide-protein conjugate vaccines is unknown. Baboons 1 to 4 months of age were immunized intramuscularly with Neisseria meningitidis group C and Haemophilus influenzae type b (Hib) oligosaccharide-CRM197 conjugate vaccines. The lyophilized vaccines were reconstituted with phosphate-buffered saline (PBS), Al(OH)3 (alum), or MF59. Groups of five animals each were given three injections of the respective formulations, with one injection every 4 weeks. Four weeks after each immunization, the MF59 group had up to 7-fold-higher geometric mean anticapsular-antibody titers than the alum group and 5- to 10-fold-higher N. meningitidis group C bactericidal-antibody titers. Twenty-one weeks after the third immunization, the MF59 group still showed 5- to 10-fold-higher anticapsular-antibody titers. The antibody responses of the animals given the vaccines reconstituted with PBS were low at all times measured. Both the MF59 and alum groups, but not the PBS group, showed booster antibody responses to unconjugated Hib and N. meningitidis group C polysaccharides, results consistent with induction of memory B cells. Thus, MF59 may be useful for accelerating and augmenting immunity to polysaccharide-protein conjugate vaccines in infants.

Pertussis-specific cell-mediated immunity in infants after vaccination with a tricomponent acellular pertussis vaccine

The aim of this study was to investigate pertussis-specific cell-mediated immunity in infants vaccinated with a tricomponent acellular vaccine. Infants were investigated during a primary vaccination schedule from the third month of life to the sixth month as well as before and after a booster at 15 to 24 months. This is the first report of specific cell-mediated immune responses to pertussis-related antigens in infants below the age of 12 months. Our data show that the vaccine induces T-cell responses specific for the vaccine components, detoxified pertussis toxin, filamentous hemagglutinin, and pertactin, that increase progressively over the course of the vaccination schedule. In contrast to declining antibody titers, cell-mediated immune responses are stable over the postprimary to prebooster period. Vaccination results in a progressive increase in the number of T cells that express activation marker CD45RO preferentially on CD4-positive T cells after stimulation with pertussis antigens. Measurements of cytokine secretion profiles demonstrated a preferential induction of interleukin 2- and gamma interferon-producing T-helper 1 cells and only low production of interleukin 10. The observed persistence of the specific cell-mediated immunity may have a bearing on the protective mechanisms induced by pertussis vaccination. Cell-mediated immunity requires further study, particularly to improve our understanding of the persistence of protection afforded by vaccination up to the administration of booster doses.

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.

A mutant pertussis toxin molecule that lacks ADP-ribosyltransferase activity, PT-9K/129G, is an effective mucosal adjuvant for intranasally delivered proteins

We examined the capacity of a genetically detoxified derivative of pertussis toxin (PTX), PT-9K/129G, to act as a mucosal adjuvant for an intranasally (i.n.) administered tetanus vaccine. Groups of mice were immunized i.n. with the nontoxic C-terminal 50-kDa portion of tetanus toxin (fragment C [Frg C]) either alone or mixed with PT-9K/129G, PTX, or cholera toxin (CT) or were immunized subcutaneously (s.c.) with an equivalent amount of Frg C adsorbed to alhydrogel. In response to a single immunization, mice receiving Frg C plus PT-9K/129G or CT i.n. and parenterally immunized mice developed high-titer (> 20,000) anti-Frg C antibodies, whereas mice immunized i.n. with Frg C plus PTX or with Frg C alone seroconverted only after being boosted. The serum anti-Frg C response was dominated by immunoglobulin G1 (IgG1) in mice immunized with Frg C plus PT-9K/129G, with Frg C plus PTX, or s.c. In contrast, IgG1, IgG2a, and IgG2b contributed almost equally to the Frg C response when CT was the adjuvant. Anti-Frg C IgE was detected only in the sera of mice immunized i.n. with Frg C plus PTX and immunized s.c. with Frg C plus alhydrogel. High levels of IgA antibodies were present in nasal lavage fluid from mice immunized i.n. with Frg C plus PT-9K/129G, PTX, or CT but not in that from mice given Frg C alone i.n. or parenterally. The mucosal adjuvanticity of PT-9K/129G was manifested in inbred as well as outbred mice. A single i.n. dose of Frg C plus either PT-9K/129G or PTX (with high specific activity) was sufficient to protect all immunized mice from tetanus toxin challenge, in contrast to the case for mice that received Frg C alone i.n. We conclude that the pertussis toxin analog PT-9K/129G, which is devoid of ADP-ribosyltransferase activity, is a potent mucosal adjuvant for vaccines delivered via the respiratory tract.

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.

Formaldehyde treatment of proteins can constrain presentation to T cells by limiting antigen processing

Proteins to be used as vaccines are frequently treated with formaldehyde, although little is known about the effects of this treatment on protein antigenicity. To investigate the effect of formaldehyde treatment on antigen recognition by T cells, we compared the in vitro T-cell response to proteins that have been formaldehyde treated with the response to untreated proteins. We found that peripheral blood mononuclear cells from individuals vaccinated with three formaldehyde-treated proteins (pertussis toxin, filamentous hemagglutinin, pertactin) of Bordetella pertussis showed little or no response to the formaldehyde-treated proteins but proliferated very well in response to the corresponding untreated protein. These findings were further confirmed with CD4+ T-cell clones specific for defined epitopes of the bacterial proteins. We found that some epitopes are presented poorly or not at all when formaldehyde-treated proteins are used, whereas other epitopes are equally presented to T-cell clones when either formaldehyde-treated or untreated antigens are used. However, T-cell recognition could be restored by either antigen degradation before formaldehyde treatment or heat denaturation after such treatment. Parallel digestion with trypsin of both formaldehyde-treated and untreated proteins showed that fragments generated from the two forms of the same antigen were different in size. These results demonstrate that formaldehyde treatment can constrain antigen presentation to T cells and that this may be due to an altered proteolytic processing of formaldehyde-treated proteins.

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.

Acellular pertussis diphtheria-tetanus-pertussis vaccine containing separately purified pertussis toxoid, filamentous haemagglutinin and 69 kDa outer membrane protein as a booster in children

In two double-blind, randomized, comparative studies involving a total of 218 children, an acellular pertussis (DTPa) vaccine containing diphtheria and tetanus toxoids and pertussis components filamentous haemagglutinin (FHA), pertussis toxoid (PT), and 69 kDa outer membrane protein (69 kDa OMP) was administered as a booster to 17-month-old and 5-year-old children with a history of routine whole-cell diphtheria-tetanus-pertussis (DTPw) vaccination. The control groups in these studies received DTPw vaccine. Among 17-month-old toddlers, significantly lower proportions of DTPa vaccine recipients had local pain (7.3%), redness (14.5%) and swelling (9.1%) than DTPw vaccine recipients (23.6%, 30.9% and 23.6%, respectively). A trend toward fewer local reactions was also seen in 5-year-old children vaccinated with DTPa in private practice and public clinics although differences were not statistically significant. Fever (rectal temperature > or = 38 degrees C) was reported more frequently for DTPw vaccine recipients in both age groups. While no differences existed between groups in terms of geometric mean antibody titres (GMTs) prior to booster vaccination, anti-PT antibody GMTs were higher among DTPa vaccine recipients than among DTPw vaccine recipients after booster vaccination. The difference was statistically significant in 5-year-old subjects. Furthermore, significantly higher anti-FHA and anti-69 kDa OMP GMTs were seen in DTPa vaccine recipients in both age groups. In pre-vaccination seropositive subjects and in pre-vaccination seronegative subjects the rate of immune response to pertussis antigens was higher for DTPa than for DTPw vaccine recipients with the exception of the rate of response induced to 69 kDa OMP in 5-year-old children.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibody responses in the serum and respiratory tract of mice following oral vaccination with liposomes coated with filamentous hemagglutinin and pertussis toxoid

Mice were orally vaccinated with liposomes coated with filamentous hemagglutinin (FHA) and detoxified pertussis toxin (PT) of Bordetella pertussis. FHA- and PT-specific immunoglobulin G (IgG) was detected in serum, and both IgG and IgA were detected in lung washes following the immunization. Antibody responses in mice immunized with liposomes coated with FHA and PT were significantly higher than those in mice immunized with free FHA and PT, which demonstrated the adjuvanticity of the liposome carrier. The results indicate the potential usefulness of this approach for eliciting immune responses against FHA and PT (and perhaps other pertussis antigens) in humans and its possible utility in large-scale vaccination to protect against both B. pertussis infection and disease.

Adjuvants--a balance between toxicity and adjuvanticity

Adjuvants have been used to augment the immune response in experimental immunology as well as in practical vaccination for more than 60 years. The chemical nature of adjuvants, their mode of action and the profile of their side effects are highly variable. Some of the side effects can be ascribed to an unintentional stimulation of different mechanisms of the immune system whereas others may reflect general adverse pharmacological reactions. The most common adjuvants for human use today are still aluminium hydroxide, aluminium phosphate and calcium phosphate although oil emulsions, products from bacteria and their synthetic derivatives as well as liposomes have also been tested or used in humans. In recent years monophosphoryl lipid A, ISCOMs with Quil-A and Syntex adjuvant formulation (SAF) containing the threonyl derivative of muramyl dipeptide have been under consideration for use as adjuvants in humans. At present the choice of adjuvants for human vaccination reflects a compromise between a requirement for adjuvanticity and an acceptable low level of side effects.

Proliferative responses to purified and fractionated Bordetella pertussis antigens in mice immunized with whole-cell pertussis vaccine

The specificity of the cell-mediated immune response to Bordetella pertussis following immunization of C57B1 mice with a whole-cell pertussis vaccine was assessed in a proliferation assay. A proliferative response of lymph node lymphocytes to the filamentous haemagglutinin, the 69 kDa outer membrane protein and the agglutinogens 2 and 3 was demonstrated. The proliferative cells were T cells of the CD4+ phenotype. In addition, several as yet uncharacterized antigens expressed by B. pertussis were shown to induce a proliferative response, also mediated by T cells of the CD4+ phenotype. Although a range of different immunization schedules and preparations of pertussis toxin were used, no specific proliferative responses to pertussis toxin, which is regarded as a protective antigen of major importance from B. pertussis, were found.

Identification of murine T-cell epitopes on the S4 subunit of pertussis toxin

The aim of the present study was to identify murine T-cell epitopes on pertussis toxin subunit S4. Six mouse strains with five different haplotypes at the H-2 locus were immunized with the pertussis toxin B oligomer. Lymph node lymphocytes were isolated and stimulated in an in vitro proliferation assay with pertussis toxin components and 11 overlapping synthetic peptides synthesized on the basis of the primary sequence of S4. In vitro proliferative responses to the synthetic peptides revealed the presence of four distinct murine T-cell epitopes on subunit S4. The recognition of the peptides was major histocompatibility complex restricted. Immunizing four of the six mouse strains with the synthetic peptides showed that the peptides which were demonstrated to contain T-cell epitopes following immunization with the B oligomer were able to induce proliferative responses to detoxified pertussis toxin and pertussis toxin components containing subunit S4. One of the identified murine T-cell epitopes corresponded to one of the major human T-cell epitopes previously identified on subunit S4. It is hoped that this murine model system will facilitate the development of a synthetic immunogen mimicking the protective properties of pertussis toxin.

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.

Identification of human T-cell epitopes on the S4 subunit of pertussis toxin

Ten adult humans were vaccinated with the Japanese acellular pertussis vaccine JNIH-3, containing detoxified pertussis toxin (PT), formaldehyde, and filamentous hemagglutinin. The vaccination induced a specific antibody response to PT and filamentous hemagglutinin, and a Western blot (immunoblot) analysis of the antibody response to PT revealed antibodies to PT subunits S1, S2, S3, S4 and S5. The response of peripheral lymphocytes to PT was assessed in an in vitro proliferation assay. A proliferative response to detoxified PT and PT dimers S2-S4 and S3-S4 was found, and it was further demonstrated that the proliferative response to detoxified PT and dimer S2-S4 was mediated by T cells of the CD4+ phenotype. The specificity of the proliferative response to subunit S4 was analyzed with a range of synthetic peptides synthesized on the basis of the primary sequence of subunit S4. The proliferative response to the peptides revealed two major and one minor T-cell epitope located in the NH2-terminal end of subunit S4.

Risks connected with the use of conventional and genetically engineered vaccines

A review is given of real and potential risks connected with the use of conventional and genetically engineered live and dead vaccines. Special attention is given to live carrier vaccines expressing one or more heterologous genes of other microorganisms. Because most carrier vaccines are still in an experimental phase, there is only limited experience with the risks of carrier vaccines. There are three potential risks of live carrier vaccines which will be discussed: 1. Changes in cell, tissue, of host tropism, and virulence of the carrier through the incorporation of foreign genes. 2. Exchange of genetic information with other vaccine or wild-type strains of the carrier organism. 3. Spread in the environment. Only limited experimental data are available on changes in biological behaviour of microorganisms through the incorporation of foreign genes. For example, there are indications that vaccinia virus carrying the attachment protein G of respiratory syncytial virus (RSV) replicates better in lungs of mice than vaccinia virus carrying other genes of RSV. Poxviruses carry genes that probably determine their replication in different hosts. Exchange of such host tropism genes might alter their host spectrum. Recombination between herpesvirus vaccine or wild-type strains may lead to the appearance of virulent strains with of without heterologous genes. Before carrier vaccines are applied, these risks must be thoroughly evaluated case-by-case. Potential methods for the design of safe carrier vaccines are discussed.

Properties of pertussis toxin B oligomer assembled in vitro from recombinant polypeptides produced by Escherichia coli

The subunits that make up the pentameric B oligomer of pertussis toxin (S2, S3, S4, and S5) were individually synthesized as recombinant polypeptides in Escherichia coli, isolated as insoluble inclusion bodies, and assembled into a multimeric form in vitro by spontaneous association following treatment with a chaotropic agent, reduction, and reoxidation. The recombinant B multimer, purified by fetuin-Sepharose affinity chromatography, contained all four of the individual subunits and possessed the mitogenic and hemagglutinating activities characteristic of the native B oligomer. Immunization of mice with the recombinant B oligomer elicited antibodies that neutralized pertussis toxin in vitro and, moreover, provided protection in vivo against the leukocytosis-promoting activity of the toxin. These results demonstrate the potential for assembly of complex multimeric proteins from recombinant DNA-derived polypeptides and provide a novel means for production of an acellular pertussis vaccine component.

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

To determine whether a nontoxic derivative of pertussis toxin obtained by recombinant DNA technology, PT-9K/129G, is a good candidate for a new pertussis vaccine, we examined the safety and the immunogenicity in children of a vaccine containing 15 micrograms of PT-9K/129G protein and 0.5 mg of aluminum hydroxide per dose. Fifty-three children 12 to 24 months of age and 21 infants aged 2 to 4 months were injected with two and three doses, respectively. The vaccine did not induce significant local or systemic reactions and elicited an increase of antibody titer in more than 98% of the children. The geometric mean of the toxin-neutralizing titers increased after each dose and was 85 units in children given two doses and 196 units in those given three doses. Two children who had detectable antibody levels before the first immunization had a high response (greater than 320 units) to the first vaccine dose. The findings suggest that PT-9K/129G is a promising antigen to be included in the development of acellular pertussis vaccines.

Interaction of the pertussis toxin peptide containing residues 30-42 with DR1 and the T-cell receptors of 12 human T-cell clones

The interaction of the immunodominant pertussis toxin peptide containing residues 30-42 (p30-42) with soluble DR1 molecules and the T-cell receptor (TCR) of 12 DR1-restricted human T-cell clones has been analyzed. Peptide analogues of p30-42 containing single alanine substitutions were used in DR1-binding and T-cell proliferation assays to identify the major histocompatibility complex and TCR contact residues. Each T-cell clone was found to recognize p30-42 with a different fine specificity. However, a common core comprising amino acids 33-39 was found to be important for stimulation of all T-cell clones. Within this core two residues, Leu33 and Leu36, interact with the DR1 molecule, whereas Asp34, His35, Thr37, and Arg39 are important for TCR recognition in most of the clones. Computer modeling of the structure of p30-42 showed that an alpha-helical conformation is compatible with the experimental data. The analysis of TCR rearrangement revealed that the peptide was recognized by T-cell clones expressing different variable region alpha (V alpha) and variable region beta (V beta) chains, although a preferential use of V alpha 8-V beta 13 and V alpha 11-V beta 18 combinations was found in clones from the same donor. Understanding the details of the interaction of antigenic peptides with the major histocompatibility complex and TCR molecules should provide the theoretical basis to design T-cell epitopes and obtain more immunogenic vaccines.