DNA binding of the Bordetella pertussis H1 homolog alters in vitro DNA flexibility

BpH1, the Bordetella pertussis H1 homolog, interacts with chromosomal DNA. With DNase I protection assays, we demonstrate in this study that BpH1 binds DNA in a nonspecific manner and that it may cover DNA fragments from end to end. Although the binding was shown to be nonspecific, preferential binding sites and sites resistant to BpH1 binding were identified within and upstream of the pertussis toxin promoter sequence. In the presence of DNA ligase, BpH1 favored the formation of multimeric DNA fragments of various sizes and prevented ring closures, suggesting a diminished flexibility of the DNA fragments and thus indicating that BpH1 acts as a macromolecular crowding agent.

The pertussis toxin liberation genes of Bordetella pertussis are transcriptionally linked to the pertussis toxin operon

The DNA sequence of the pertussis toxin operon (ptx) of Bordetella pertussis predicts that transcription of the operon ends downstream from the ptxS3 gene at a possible stem-loop structure. Secretion of the assembled pertussis toxin into the culture medium required the expression of 8 genes arranged in an operon (ptl) and lying 55 bp downstream from the ptx and ptl operons are cotranscribed and coregulated by the P(TOX) promoter. Deletion of the 55-bp DNA region caused an increase in the amount of the ptl transcripts. It is likely that this DNA region is involved in regulation of the ptx-pti expression.

Induction of antigen-specific antibodies in vaginal secretions by using a nontoxic mutant of heat-labile enterotoxin as a mucosal adjuvant

Immunization of the female reproductive tract is important for protection against sexually transmitted diseases and other pathogens of the reproductive tract. However, intravaginal immunization with soluble antigens generally does not induce high levels of secretory immunoglobulin A (IgA). We recently developed safe mucosal adjuvants by genetically detoxifying Escherichia coli heat-labile enterotoxin, a molecule with a strong mucosal adjuvant activity, and here we describe the use of the nontoxic mutant LTK63 to induce a response in the mouse vagina against ovalbumin (Ova). We compared intravaginal and intranasal routes of immunization for induction of systemic and vaginal responses against LTK63 and Ova. We found that LTK63 is a potent mucosal immunogen when given by either the intravaginal or intranasal route. It induces a strong systemic antibody response and IgG and long-lasting IgA in the vagina. The appearance of vaginal IgA is delayed in the intranasally immunized mice, but the levels of vaginal anti-LTK63 IgA after repeated immunizations are higher in the intranasally immunized mice than in the intravaginally immunized mice. LTK63 also acts as a mucosal adjuvant, inducing a serum response against Ova, when given by both the intravaginal and intranasal routes. However, vaginal IgA against Ova is stimulated more efficiently when LTK63 and antigen are given intranasally. In conclusion, our results demonstrate that LTK63 can be used as a mucosal adjuvant to induce antigen-specific antibodies in vaginal secretions and show that the intranasal route of immunization is the most effective for this purpose.

Acellular pertussis vaccines: a turning point in infant and adolescent vaccination

Whooping cough, an infectious disease caused by the gram-negative bacterium Bordetella pertussis, is a life-threatening disease that cannot be controlled by antibiotic treatment or other procedures of modern medicine. Immunization, using a vaccine made of heat-killed bacteria, has been the only way to prevent the disease and keep the infection under control. However, the high reactogenicity of the whole-cell vaccine available so far has made vaccination very controversial, and vaccine use has been restricted to the minimum doses strictly necessary to protect infants during the first few years of life, when the disease is most dangerous. This policy left unsolved the problem of controlling the circulation of the pathogens that are still spreading undisturbed in the population, even after decades of vaccine use. Today, the introduction of acellular vaccines that are efficacious and virtually free of side effects suggests that the new vaccines can be used safely to immunize not only infants, toddlers, and preschool children, but also adolescents and adults, making possible the complete control of the disease and infection, so that policies addressing the eradication of the disease become feasible. The absence of constraints for the use of pertussis vaccine will allow the rational design of the optimal combinations of vaccines for each age.

Lipid interaction of the 37-kDa and 58-kDa fragments of the Helicobacter pylori cytotoxin

Helicobacter pylori cytotoxin vacA (95 kDa) causes a vacuolar degeneration of epithelial cells. There is evidence that this protein toxin acts inside cells, and hence has to cross a cell membrane. This cytotoxin is frequently obtained as two fragments of 58 kDa (p58) and 37 kDa (p37) and it is available only in minute amounts. Here, its membrane interaction was studied with the two fragments, produced in Escherichia coli. Light scattering and energy transfer experiments show that p37 and p58 cause aggregation and fusion of small unilamellar lipid vesicles; only a reversible aggregation is induced at neutral pH, whereas at acid pH fusion also takes place. p58, but not p37, causes potassium efflux from liposomes and this occurs only at acid pH. Hydrophobic photolabelling with photoactivatable phosphatidylcholines inserted into liposomes shows that both fragments are labelled at neutral pH. The amount of labelling of the two fragments is much higher at acid pH, consistent with a further penetration into the hydrophobic core of the lipid bilayer. Tryptophan fluorescence measurements indicate that the two fragments undergo a pH-driven conformational change. These data are consistent with cytotoxin entry in the cell cytosol via an intracellular acidic compartment.

Genetic detoxification of bacterial toxins: a new approach to vaccine development

Chemically detoxified bacterial toxins (toxoids) have been successfully used as vaccines for the prevention of many bacterial infectious diseases. Today, nontoxic derivatives of bacterial toxins can be obtained by mutagenesis of the toxin genes. These genetically inactivated toxins are superior to the classical toxoids both in safety and in immunogenicity and therefore they should replace the old toxoids in the existing vaccines. In addition, they represent a novel class of immunogens with unique properties, some of which may be used for innovative approaches to vaccination.

Mucosal and systemic immunogenicity of a recombinant, non-ADP-ribosylating pertussis toxin: effects of formaldehyde treatment

The effect of formaldehyde treatment on the mucosal and systemic immunogenicity of the genetically detoxified pertussis toxin (PT-9K/129G) was investigated. Groups of BALB/c were immunized intranasally (i.n.) or subcutaneously (s.c.) with untreated, lightly formaldehyde treated (LFT) or heavily formaldehyde treated (HFT) recombinant pertussis toxin (PT) mutant, PT-9K/129G. Intranasal immunization with native PT-9K/ 129G induced significant levels of anti-toxin antibodies in serum and IgA anti-toxin responses in nasal and lung lavages of these mice. Similar local and systemic responses were observed following intransal immunization with LFT toxin. However, i.n. immunization with HFT toxin failed to induce a local IgA response and elicited a much diminished anti-toxin response in the serum. In contrast, the total antibody response following s.c. immunization was not significantly affected. In addition, i.n. immunization with native PT-9K/129G induced low but detectable levels of toxin neutralizing antibodies in the serum. These results show that native PT-9K/129G protein acts as a mucosal immunogen in mice and that this activity is greatly diminished by HFT of the protein.

Expression of fragment C of tetanus toxin fused to a carboxyl-terminal fragment of diphtheria toxin in Salmonella typhi CVD 908 vaccine strain

We report the expression of fragment C of tetanus toxin (FC) fused to the eukaryotic cell binding domain (the carboxyl-terminus) of diphtheria toxin (FC-bDt fusion) in attenuated Salmonella typhi live vector vaccine strain CVD 908. The FC-bDt protein fusion was constructed using plasmid pTETnir15 which carries the gene encoding FC under control of the nirB promoter (nirBP). The open reading frame for FC was modified to incorporate an in-frame glycine-proline hinge region and a set of four restriction sites at the 3' end of the FC gene. A 482 bp DNA fragment encoding the eukaryotic cell binding domain of diphtheria toxin was then inserted at the 3' end of the modified FC gene to create an in-frame FC-bDt fusion gene. The resulting plasmid, pOG215, was able to express the FC-bDt fusion protein in both Escherichia coli DH5a and S. typhi CVD 908, as evidenced by Western immunoblots using anti-FC and anti-C-terminal diphtheria toxin monoclonal antibodies. Maximum expression of the FC-bDt fusion protein was achieved by growing CVD 908(pOG215) at the low oxidation-reduction potential of thioglycollate broth, i.e. in conditions that activate nirBP and drive transcription of the FC-bDt fusion gene. Whereas maximum expression of FC alone was also observed using thioglycollate broth, expression of bDt alone was unsuccessful using a variety of growth conditions. FC fusions constitute one strategy to "rescue" expression of proteins which are otherwise difficult to express.

Both immunization with protein and recombinant vaccinia virus can stimulate CTL specific for the E7 protein of human papilloma virus 16 in H-2d mice

The transforming protein E7 of human papilloma virus type 16 can stimulate cytotoxic T lymphocytes (CTL) which can protect experimental animals against growth of E7 expressing tumour cells. In this study we compared CTL responses in mice immunized with either E7 protein in MF59 adjuvant or with recombinant vaccinia virus expressing E7 (Vac-E7). We have chosen H-2d mice because no E7-specific CTL responses have been described in this MHC haplotype. Immunization of these mice with Vac-E7 generated CTL which lysed target cells infected with Vac-E7 or transfected with the E7 gene. CTL from mice immunized with E7 protein in MF59 adjuvant showed specificity for the same target cells. Antibody blocking experiments revealed that both immunization with Vac-E7 and E7 protein stimulated CD8+ effector CTL. The find specificity of CTL induced by the two immunization protocols was similar. A major CTL epitope was mapped to the carboxyl terminal amino acids 48-98 of the E7 protein. Peptide isolation from E7 expressing cells followed by HPLC separation indicated that CTL induced by immunization with protein and Vac-E7 recognized the same HPLC purified peptide fractions. Together, the study suggests that vaccines based on protein can activate CTL with similar fine specificity to CTL induced by vaccines based on recombinant vaccinia virus.

Helicobacter pylori cytotoxin: importance of native conformation for induction of neutralizing antibodies

We have attempted to express the Helicobacter pylori vacuolating cytotoxin in Escherichia coli. Although the 95-kDa VacA polypeptide was expressed abundantly, it completely lacked any biological activity. In addition, this material failed to induce neutralizing antibodies after immunization of rabbits. In contrast, highly purified high-molecular-mass cytotoxin from the supernatant of H. pylori cultures was active in a HeLa cell assay and effectively induced a neutralizing response in rabbits. Neutralizing sera were shown to contain a high proportion of antibodies which recognized conformational epitopes found only on the native toxin. The data indicate that toxin-neutralizing epitopes are conformational and that potential vaccines based on the cytotoxin may benefit from the use of the intact molecule.

Low pH activates the vacuolating toxin of Helicobacter pylori, which becomes acid and pepsin resistant

The protein toxin VacA, produced by cytotoxic strains of Helicobacter pylori, causes a vacuolar degeneration of cells, which eventually die. VacA is strongly activated by a short exposure to acidic solutions in the pH 1.5-5.5 range, followed by neutralization. Activated VacA has different CD and fluorescence spectra and a limited proteolysis fragmentation pattern from VacA kept at neutral pH. Moreover, activated VacA is resistant to pH 1.5 and to pepsin. The relevance of these findings to pathogenesis of H. pylori-induced gastrointestinal ulcers is discussed.

Response of the bvg regulon of Bordetella pertussis to different temperatures and short-term temperature shifts

Bordetella pertussis produces a number of virulence factors whose expression is coordinately regulated by the bvgAS locus. Transcription of virulence genes is repressed by environmental factors such as low temperature (25 degrees C) and chemical stimuli. Temperature shift of bacterial cultures from 25 degrees C to 37 degrees C activates two classes of bvg-regulated virulence genes: the early genes, which are activated within 10 min, and late genes, which require 2-4 h for activation. During the interval between the activation of the early and late genes, the intracellular concentration of BvgA increases 50-fold. It has been proposed that this increased concentration may be required for the activation of the late genes. Here we have analysed the response of the bvg locus to intermediate temperature and to repeated temperature shifts. Temperature shifts of B. pertussis cultures from 22 degrees C to 28 degrees C or 35 degrees C resulted in the synthesis of low, intermediate, and high amounts of BvgA. This implied that the intracellular concentration of BvgA is temperature-dependent. We have also observed that the amount of virulence factors produced correlates with the BvgA concentration. When bacteria grown at 37 degrees C were shifted to 22 degrees C, transcription from the adenylate cyclase toxin haemolysis promoter (PAC) was repressed after 30 min, while transcription from the bvg (P1) and filamentous haemagglutinin (PFHA) promoters was repressed after 2 h. During this time, the amount of BvgA did not decrease.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of interleukin-8 secretion from gastric epithelial cells by a cagA negative isogenic mutant of Helicobacter pylori

The ability of Helicobacter pylori strains to induce interleukin-8 (IL-8) gene expression and protein secretion from gastric epithelial cell lines in vitro is variable. This cellular response is associated with bacterial expression of the CagA protein present in type I H pylori strains. To determine the role of CagA in this host cell response, an isogenic cagA negative mutant, N6.XA3, was constructed. The cagA negative isogenic mutant and the wild-type parental cagA positive strain, N6, were cocultured with AGS, ST-42 and KATO-3 gastric epithelial cell lines and secreted interleukin-8 assayed by enzyme linked immunosorbent assay. In all three cell lines there was no significant difference in the IL-8 secretion induced by the cagA negative isogenic mutant, N6.XA3, and the wild-type parent strain, N6. These studies show that CagA is not the inducer of IL-8 secretion from gastric epithelial cells. As all wild-type CagA positive strains studied to date induce IL-8, the bacterial factor(s) inducing this inflammatory response is closely associated with the expression of CagA.

Role of the Helicobacter pylori virulence factors vacuolating cytotoxin, CagA, and urease in a mouse model of disease

The pathogenic role of Helicobacter pylori virulence factors has been studied with a mouse model of gastric disease. BALB/c mice were treated orally with different amounts of sonic extracts of cytotoxic H. pylori strains (NCTC 11637, 60190, 84-183, and 87A300 [CagA+/Tox+]). The pathological effects on histological sections of gastric mucosae were assessed and were compared with the effects of treatments with extracts from noncytotoxic strains (G21 and G50 [CagA-/Tox-]) and from strains that express either CagA alone (D931 [CagA+/Tox-]) or the cytotoxin alone (G104 [CagA-/Tox+]). The treatment with extracts from cytotoxic strains induced various epithelial lesions (vacuolation, erosions, and ulcerations), recruitment of inflammatory cells in the lamina propria, and a marked reduction of the mucin layer. Extracts of noncytotoxic strains induced mucin depletion but no other significant pathology. Crude extracts of strain D931, expressing CagA alone, caused only mild infiltration of inflammatory cells, whereas extracts of strain G104, expressing cytotoxin alone, induced extensive epithelial damage but little inflammatory reaction. Loss of the mucin layer was not associated with a cytotoxic phenotype, since this loss was observed in mice treated with crude extracts of all strains. The pathogenic roles of CagA, cytotoxin, and urease were further assessed by using extracts of mutant strains of H. pylori defective in the expression of each of these virulence factors. The results obtained suggest that (i) urease activity does not play a significant role in inducing the observed gastric damage, (ii) cytotoxin has an important role in the induction of gastric epithelial cell lesions but not in eliciting inflammation, and (iii) other components present in strains which carry the cagA gene, but distinct from CagA itself, are involved in eliciting the inflammatory response.

The Arg7Lys mutant of heat-labile enterotoxin exhibits great flexibility of active site loop 47-56 of the A subunit

The heat-labile enterotoxin from Escherichia coli (LT) is a member of the cholera toxin family. These and other members of the larger class of AB5 bacterial toxins act through catalyzing the ADP-ribosylation of various intracellular targets including Gs alpha. The A subunit is responsible for this covalent modification, while the B pentamer is involved in receptor recognition. We report here the crystal structure of an inactive single-site mutant of LT in which arginine 7 of the A subunit has been replaced by a lysine residue. The final model contains 103 residues for each of the five B subunits, 175 residues for the A1 subunit, and 41 residues for the A2 subunit. In this Arg7Lys structure the active site cleft within the A subunit is wider by approximately 1 A than is seen in the wild-type LT. Furthermore, a loop near the active site consisting of residues 47-56 is disordered in the Arg7Lys structure, even though the new lysine residue at position 7 assumes a position which virtually coincides with that of Arg7 in the wild-type structure. The displacement of residues 47-56 as seen in the mutant structure is proposed to be necessary for allowing NAD access to the active site of the wild-type LT. On the basis of the differences observed between the wild-type and Arg7Lys structures, we propose a model for a coordinated sequence of conformational changes required for full activation of LT upon reduction of disulfide bridge 187-199 and cleavage of the peptide loop between the two cysteines in the A subunit.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

IL-1 stimulates a diverging signaling pathway in EL4 6.1 thymoma cells. IL-2 release, but not IL-2 receptor expression, is sensitive to pertussis toxin

We reassessed the involvement of Bordetella pertussis toxin (PTX)-sensitive proteins in the IL-1 signaling pathway on the responses induced by IL-1 on the murine thymoma cell line EL4 6.1. We demonstrate that the ADP-ribosyltransferase activity of PTX, and not its cell-anchoring B oligomer part, is responsible for the inhibition of IL-1-induced IL-2 release, since 1) the concentration of PTX (&lt; or = 1 ng/ml) required to block the secretion is 100 to 1000 times lower than the concentration needed with the B oligomer; and 2) the mutated PT-9K/129G, devoid of ADP-ribosyltransferase activity, was inactive at 100 ng/ml. We found that partial ADP-ribosylation of the Gi2/Gi3 proteins before stimulation with IL-1 was sufficient to obtain full inhibition of IL-2 release. PTX did not however inhibit the appearance on the cell surface of the high affinity IL-2 receptors or the IL-2 release induced by PMA. In addition, we show that PTX prevented the expression of the IL-2 mRNA induced by IL-1, without affecting the binding of IL-2 specific nuclear factors to the T cell distal element of the IL-2 promoter. Furthermore, PTX also inhibited IL-1-induced proliferation of non-transformed thymocytes. In conclusion, our results demonstrate that IL-1-induced IL-2 release is sensitive to PTX-catalyzed ADP-ribosylation and that IL-1 activates a diverging pathway on EL4 6.1 cells.

IL-1 stimulates a diverging signaling pathway in EL4 6.1 thymoma cells. IL-2 release, but not IL-2 receptor expression, is sensitive to pertussis toxin

We reassessed the involvement of Bordetella pertussis toxin (PTX)-sensitive proteins in the IL-1 signaling pathway on the responses induced by IL-1 on the murine thymoma cell line EL4 6.1. We demonstrate that the ADP-ribosyltransferase activity of PTX, and not its cell-anchoring B oligomer part, is responsible for the inhibition of IL-1-induced IL-2 release, since 1) the concentration of PTX (< or = 1 ng/ml) required to block the secretion is 100 to 1000 times lower than the concentration needed with the B oligomer; and 2) the mutated PT-9K/129G, devoid of ADP-ribosyltransferase activity, was inactive at 100 ng/ml. We found that partial ADP-ribosylation of the Gi2/Gi3 proteins before stimulation with IL-1 was sufficient to obtain full inhibition of IL-2 release. PTX did not however inhibit the appearance on the cell surface of the high affinity IL-2 receptors or the IL-2 release induced by PMA. In addition, we show that PTX prevented the expression of the IL-2 mRNA induced by IL-1, without affecting the binding of IL-2 specific nuclear factors to the T cell distal element of the IL-2 promoter. Furthermore, PTX also inhibited IL-1-induced proliferation of non-transformed thymocytes. In conclusion, our results demonstrate that IL-1-induced IL-2 release is sensitive to PTX-catalyzed ADP-ribosylation and that IL-1 activates a diverging pathway on EL4 6.1 cells.

Construction of nontoxic derivatives of cholera toxin and characterization of the immunological response against the A subunit

Using computer modelling, we have identified some of the residues of the A subunit of cholera toxin (CT) and heat-labile toxin that are involved in NAD binding, catalysis, and toxicity. Here we describe the site-directed mutagenesis of the CT gene and the construction of CT mutants. Nine mutations of the A subunit gene were generated. Six of them encoded proteins that were fully assembled in the AB5 structure and were nontoxic; these proteins were CT-D53 (Val-53-->Asp), CT-K63 (Ser-63-->Lys), CT-K97 (Val-97-->Lys), CT-K104 (Tyr-104-->Lys), CT-S106 (Pro-106-->Ser), and the double mutant CT-D53/K63 (Val-53-->Asp, Ser-63-->Lys). Two of the mutations encoded proteins that were assembled into the AB5 structure but were still toxic; these proteins were CT-H54 (Arg-54-->His) and CT-N107 (His-107-->Asn). Finally, one of the mutant proteins, CT-E114 (Ser-114-->Glu), was unable to assemble the A and the B subunits and produced only the B oligomer. The six nontoxic mutants were purified from the culture supernatants of recombinant Vibrio cholerae strains and further characterized. The CT-K63 mutant, which was the most efficient in assembly of the AB5 structure, was used to immunize rabbits and was shown to be able to induce neutralizing antibodies against both the A and B subunits. This molecule may be useful for the construction of improved vaccines against cholera.

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.

Immunogenicity of meningococcal B polysaccharide conjugated to tetanus toxoid or CRM197 via adipic acid dihydrazide

Vaccine development against Group B Neisseria meningitidis is complicated by the nature of the capsular polysaccharide, which is alpha 2-8-linked poly-sialic acid, identical in structure to the poly-sialic acid found in many mammalian tissues during development. To test the feasibility of a vaccine based on this polysaccharide, we synthesized several conjugates of meningococcal B polysaccharide linked to a carrier protein (tetanus toxoid or diphtheria CRM197), via an adipic acid dihydrazide (ADH) spacer. All conjugates induced a strong immune response. However, most of the antibodies were not directed against the Meningococcus B polysaccharide and could not be inhibited by the purified polysaccharide alone. Further investigations showed that the antibodies recognized an epitope composed by the junction between the spacer and the polysaccharide and protein, that is not present in the native polysaccharide and is generated during the coupling reaction. This epitope becomes immunodominant with respect to the poorly immunogenic polysaccharide. While the majority of the immune response is directed against the above epitope, the conjugates induced also an immune response against the Meningococcus B polysaccharide. The anti-Meningococcus B antibodies elicited are of the IgM and IgG class and are inhibitable by the polysaccharide. Moreover, they are bactericidal, thus suggesting that they would induce protection against disease.