Comparison of Immune Responses to Two Quadrivalent Meningococcal Conjugate Vaccines (CRM197 and Diphtheria Toxoid) in Healthy Adults

BACKGROUND

After the introduction of the meningococcal ACWY-CRM197 conjugate vaccine (MenACWY-CRM) in 2012 and the meningococcal ACWY-diphtheria toxoid conjugate vaccine (MenACWY-DT) in 2014, immunization was recommended for certain high-risk groups including new military recruits in Korea. However, comparative immunogenicity studies for these vaccines have not been performed in Korea. Here, we compared the immunogenicity of these two vaccines in healthy adults.

METHODS

A total of 64 adults, 20-49 years of age, were randomly divided into two groups (1:1) to receive either of the two vaccines. The sera were obtained before and 1 month after vaccination and tested for serogroup-specific serum bactericidal activity using baby rabbit complement.

RESULTS

There were no significant differences post-vaccination in the geometric mean indices and the seropositive rate to all serogroups between the vaccines. The proportion of seropositive subjects after vaccination ranged from 88% to 100%.

CONCLUSION

Both meningococcal conjugate vaccines showed good immunogenicity in healthy Korean adults without statistically significant differences. Further investigations for serotype distribution of circulating meningococci and the immune interference between other diphtheria toxin-containing vaccines concomitantly used for military recruits are needed to optimize immunization policies.

TRIAL REGISTRATION

Clinical Research Information Service Identifier: KCT0002460.

Coated and Hollow Microneedle-Mediated Intradermal Immunization in Mice with Diphtheria Toxoid Loaded Mesoporous Silica Nanoparticles

PURPOSE

To examine the immunogenicity of diphtheria toxoid (DT) loaded mesoporous silica nanoparticles (MSNs) after coated and hollow microneedle-mediated intradermal immunization in mice.

METHODS

DT was loaded into MSNs and the nanoparticle surface was coated with a lipid bilayer (LB-MSN-DT). To prepare coated microneedles, alternating layers of negatively charged LB-MSN-DT and positively charged N-trimethyl chitosan (TMC) were coated onto pH-sensitive microneedle arrays via a layer-by-layer approach. Microneedle arrays coated with 5 or 3 layers of LB-MSN-DT were used to immunize mice and the elicited antibody responses were compared with those induced by hollow microneedle-injected liquid formulation of LB-MSN-DT. Liquid DT formulation with and without TMC (DT/TMC) injected by a hollow microneedle were used as controls.

RESULTS

LB-MSN-DT had an average size of about 670 nm and a zeta potential of -35 mV. The encapsulation efficiency of DT in the nanoparticles was 77%. The amount of nano-encapsulated DT coated onto the microneedle array increased linearly with increasing number of the coating layers. Nano-encapsulated DT induced stronger immune responses than DT solution when delivered intradermally via hollow microneedles, but not when delivered via coated microneedles.

CONCLUSION

Both the nano-encapsulation of DT and the type of microneedles affect the immunogenicity of the antigen.

Vaccines to combat the opioid crisis: Vaccines that prevent opioids and other substances of abuse from entering the brain could effectively treat addiction and abuse

Novel vaccines against substances of abuse generate a strong antibody response that prevents the drug from entering the brain. These could become a safe and efficient tool to combat a growing crisis of opioid abuse.

Antigenic fingerprinting of diphtheria toxoid adsorbed to aluminium phosphate

The antigenicity of alum-adsorbed diphtheria toxoid (DTd) was determined in combination vaccines, containing DTd, tetanus toxoid and inactivated poliovirus. A panel of monoclonal antibodies was used, covering five epitopes, distributed over the antigen. The resulting antigenic fingerprint of DTd demonstrates consistency of adsorption at antigen level in final product combination vaccines. The antigenic quality of DTd alone, adsorbed to aluminium phosphate, was also determined and compared with pre-adsorbed toxoid (starting material as well as toxoid desorbed from aluminium phosphate). Some epitopes became less accessible after adsorption, while others became relatively better exposed. Some epitopes disappeared almost completely upon adsorption, but were re-established after desorption of the antigen. The results indicate that DTd is adsorbed to aluminium phosphate in a preferred orientation and not randomly.

Immunogenicity and efficacy of a rationally designed vaccine against vascular endothelial growth factor in mouse solid tumor models

Vascular endothelial growth factor (VEGF) plays an important role in the progression of various cancers. The VEGF-specific antibody bevacizumab combined with chemotherapy was shown to significantly improve progression-free survival in certain cancers. However, repeated administration is necessary for effective suppression of VEGF, thereby making the therapy expensive and cumbersome. Thus, it is urgent to develop alternative reagents such as VEGF vaccines. Here we report that DTT-VEGF, a VEGF-based antigen consisting of the receptor-binding domain of VEGF and diphtheria toxin T domain (DTT), not only stimulated neutralizing antibody response, but also induced type 1 immune response as well as anti-tumor cytotoxic T lymphocytes in mice when administered with aluminum hydroxide adjuvant. The antibodies triggered by DTT-VEGF immunization inhibited the binding of VEGF to VEGF receptor and downregulated the serum VEGF levels in tumor-bearing mice. VEGF-specific IgG2a and IgG2b antibodies as well as type 1 cytokines were stimulated by DTT-VEGF vaccination. The splenocytes from DTT-VEGF-immunized mice showed cytotoxic activity against B16-F10 cells expressing VEGF. Extensive necrosis with severe hemorrhage and enhanced CD8+ T cell infiltration were observed in tumors from DTT-VEGF-immunized mice. The percentages of CD31+ vascular areas in the tumor sections from DTT-VEGF-immunized mice were significantly lower than those of control mice. DTT-VEGF significantly inhibited tumor growth in preventive and therapeutic vaccination settings in mouse models. Our data suggest that DTT is an effective antigen carrier to break immune self-tolerance and our vaccine design has potential to be used for human cancer therapy.

Immunogenicity of MenACWY-CRM in Korean Military Recruits: Influence of Tetanus-Diphtheria Toxoid Vaccination on the Vaccine Response to MenACWY-CRM

The quadrivalent meningococcal conjugate vaccine (MenACWY-CRM) has been introduced for military recruits in Korea since 2012. This study was performed to evaluate the immunogenicity of MenACWY-CRM in Korean military recruits. In addition, the influence of tetanus-diphtheria toxoids (Td) vaccination on the vaccine response to MenACWY-CRM was analyzed. A total of 75 military recruits were enrolled. Among them, 18 received a dose of MenACWY-CRM only (group 1), and 57 received Td three days before MenACWY-CRM immunization (group 2). The immunogenicity of MenACWY-CRM was compared between the two groups. The serum bactericidal activity with baby rabbit complement was measured before and three weeks after immunization against serogroups A, C, W-135, and Y. The geometric mean titers (GMTs) against four serogroups were significantly increased in both groups after immunization. Compared to group 2, group 1 exhibited significantly higher vaccine responses in several aspects: post-immune GMTs against serogroup A and C, seroresponse rates against serogroup A, and a fold increases of titers against serogroup A, C, and Y. MenACWY-CRM was immunogenic against all vaccine-serogroups in Korean military recruits. Vaccine response to MenACWY-CRM was influenced by Td administered three days earlier.

Modulation of benzo[a]pyrene induced neurotoxicity in female mice actively immunized with a B[a]P-diphtheria toxoid conjugate

Benzo[a]pyrene (B[a]P) is a small molecular weight carcinogen and the prototype of polycyclic aromatic hydrocarbons (PAHs). While these compounds are primarily known for their carcinogenicity, B[a]P and its metabolites are also neurotoxic for mammalian species. To develop a prophylactic immune strategy against detrimental effects of B[a]P, female Balb/c mice immunized with a B[a]P-diphtheria toxoid (B[a]P-DT) conjugate vaccine were sub-acutely exposed to 2mg/kg B[a]P and behavioral performances were monitored in tests related to learning and memory, anxiety and motor coordination. mRNA expression of the NMDA receptor (NR1, 2A and 2B subunits) involved in the above behavioral functions was measured in 5 brain regions. B[a]P induced NMDA1 expression in three (hippocampus, amygdala and cerebellum) of five brain regions investigated, and modulated NMDA2 in two of the five brain regions (frontal cortex and cerebellum). Each one of these B[a]P-effects was reversed in mice that were immunized against this PAH, with measurable consequences on behavior such as anxiety, short term learning and memory. Thus active immunization against B[a]P with a B[a]P-DT conjugate vaccine had a protective effect and attenuated the pharmacological and neurotoxic effects even of high concentrations of B[a]P.

Quality control of routine, experimental and real-time aged diphtheria toxoids by in vitro analytical techniques

Physicochemical and immunochemical techniques can be used to assess the quality of diphtheria toxoid vaccines. In a previous paper [Metz B, Jiskoot W, Hennink WE, Crommelin DJA, Kersten GFA. Physicochemical and immunochemical techniques predict the quality of diphtheria toxoid vaccines. Vaccine 2003;22(2):156-67], techniques were introduced which indicated toxoid quality with respect to safety and potency: SDS-PAGE, primary amino group determination, fluorescence/denaturation, circular dichroism and biosensor analyses. These analyses were performed with experimental toxoids from one toxin batch. In the present study, the quality of regular vaccine batches of different manufacturers, the properties of real-time aged products and a number of experimental toxoids were investigated, using the above-mentioned analytical techniques. We had the unique opportunity to analyse toxoids that were up to 40 years old. The real-time aged diphtheria toxoids showed hardly any structural differences as compared to the recently prepared products in both the analytical chemical techniques and the conventional potency and safety tests. The analytical assays discriminated between regular diphtheria toxoids and experimental toxoids prepared by methylation, acetylation or glutaraldehyde treatment. The analytical data showed a clear correlation with potency and safety of these toxoids. Based on the results, we refined the described physicochemical and immunochemical criteria that a standard diphtheria toxoid has to meet. We recommend further validation of these techniques for quality control of diphtheria toxoid vaccine because of their high precision and easy performance as compared to conventional in vivo procedures.

Collaborative study for the validation of serological methods for potency testing of diphtheria toxoid vaccine (part 2)

The study is a contribution to the EDQM's efforts to meet some of the expectations of the 3 Rs: Replacement, Reduction and Refinement of animal assays as proposed by Russell and Burch in 1959 and adopted by the European Union in 1986, and specifically to validate alternative assays to replace, for batch-release purposes, the European Pharmacopoeia (Ph. Eur.) in vivo direct challenge procedures for the potency determination of diphtheria toxoid vaccines. The study results may be used in support of the replacement of the multi-dilution direct challenge procedures in different animal models by a single dilution serology test, where appropriate, and to use sera from the same animals for potency testing of several components in combined vaccines. With regard to the latter, the present study explores the possibility of testing both diphtheria and tetanus toxoid potencies using serum from the same animals.

Diphtheria toxoid loaded poly-(epsilon-caprolactone) nanoparticles as mucosal vaccine delivery systems

Poly-(epsilon-caprolactone) (PCL), a poly(lactide-co-glycolide) (PLGA)-PCL blend and co-polymer nanoparticles encapsulating diphtheria toxoid (DT) were investigated for their potential as a mucosal vaccine delivery system. The nanoparticles, prepared using a water-in-oil-in-water (w/o/w) double emulsion solvent evaporation method, demonstrated release profiles which were dependent on the properties of the polymers. An in vitro experiment using Caco-2 cells showed significantly higher uptake of PCL nanoparticles in comparison to polymeric PLGA, the PLGA-PCL blend and co-polymer nanoparticles. The highest uptake mediated by the most hydrophobic nanoparticles using Caco-2 cells was mirrored in the in vivo studies following nasal administration. PCL nanoparticles induced DT serum specific IgG antibody responses significantly higher than PLGA. A significant positive correlation between hydrophobicity of the nanoparticles and the immune response was observed following intramuscular administration. The positive correlation between hydrophobicity of the nanoparticles and serum DT specific IgG antibody response was also observed after intranasal administration of the nanoparticles. The cytokine assays showed that the serum IgG antibody response induced is different according to the route of administration, indicated by the differential levels of IL-6 and IFN-gamma. The nanoparticles eliciting the highest IgG antibody response did not necessarily elicit the highest levels of the cytokines IL-6 and IFN-gamma.

In vitro pyrogenicity of the diphtheria, tetanus and acellular pertussis components of a trivalent vaccine

We have earlier found that a trivalent vaccine, containing antigenic components from both Gram-positive and Gram-negative bacteria, induced secretion of the endogenous pyrogen interleukin 6 (IL-6) when added to fresh human blood in vitro. The results of the present study showed that the IL-6 secretion was induced by toxoids derived from the Gram-positive bacterium Corynebacterium diphtheriae. However, fresh whole blood from different donors reacted differently to the stimulation. The blood from some donors induced secretion of large concentrations of IL-6, while the blood from other donors induced essentially no IL-6 secretion as a response to stimulation with diphtheria toxoid or a mixture of diphtheria and tetanus toxoids. Repeated testing over several years using blood from the same donor confirmed a donor-dependency of the reaction. This donor-dependency was only found for the toxoid, since blood from all donors reacted with approximately similar IL-6 production to stimulation by endotoxin from the Gram-negative bacterium Escherichia coli, known to be mediated via the toll-like receptor (TLR) 4. Also, no donor-dependecy was found to highly purified lipoteichoic acid from the Gram-positive bacteria Bacillus subtilis and Staphylococcus aureus, known to be mediated via TLR-2 and TLR-6. The receptors involved in stimulation by diphtheria toxoid are not known, but may differ from those used by endotoxin and lipoteichoic acid.

Oral vaccination against diphtheria using polyacryl starch microparticles as adjuvant

Oral vaccination offers the advantage of eliciting both a mucosal and a systemic immune response. This study investigated the use of polyacryl starch microparticles as adjuvant for oral vaccination against diphtheria. Diphtheria toxin or cross-reacting material (CRM197) were covalently conjugated to the microparticles and fed to mice by oral gavage. Investigation of formaldehyde treatment as a means of either detoxifying (diphtheria toxin) or stabilising (CRM197) these formulations were also made. We show that all our formulations given orally or parenterally to mice induced a strong systemic immune response. Only formulations given orally induced a mucosal IgA-response. Furthermore, our formulations given parenterally or orally induced a strong diphtheria toxin-neutralising antibody response.

Lactic acid triggers, in vitro, thiomersal to degrade protein in the presence of PLGA microspheres

Microspheres of polymers like poly(lactic-co-glycolic acid) (PLGA) have been studied as a vehicle for controlled release vaccines. They require materials and processes that might change the protein antigenicity. Lactic acid is produced during microsphere degradation that occurs in tandem with protein liberation. In addition, most of the proteins that have been used in microencapsulation studies contain Thimerosal((R))(TM) and this can introduce another undesirable effect for their stability. We demonstrated in vitro that the thiosalycilic acid (TSA), produced after the reduction of TM by lactic acid, reduces the S-S bridge of the previously incubated diphtheric toxoid (Dtxd). This reduction is immediately followed by blocking the two -SH formed by the same TSA molecules. In the light of these conclusions it is necessary now, to reinterpret the in vitro protein degradation-stabilization data in the presence of PLGA microspheres, mainly for those proteins which contain S-S. We propose that all the PLGA microspheres microencapsulation studies and protein structural considerations should be done in the absence of TM as preservative.

Immunogenicity and efficacy of Cryptococcus neoformans capsular polysaccharide glucuronoxylomannan peptide mimotope-protein conjugates in human immunoglobulin transgenic mice

Peptide mimotopes of capsular polysaccharides have been proposed as antigens for vaccines against encapsulated pathogens. In this study, we determined the antibody response to and efficacy of P13, a peptide mimetic of the Cryptococcus neoformans capsular polysaccharide glucuronoxylomannan (GXM), in mice that produce human antibodies. P13 was conjugated to tetanus toxoid (TT) or diphtheria toxoid (DT) and administered subcutaneously in Alhydrogel with or without CpG to mice transgenic for human immunoglobulin loci (XenoMouse mice) and expressing either immunoglobulin G2 (IgG2) (G2 mice) or IgG4 (G4 mice). Mice were vaccinated and revaccinated two or three times. The serum antibody responses of the mice to GXM and P13 and antibody idiotype expression were analyzed by an enzyme-linked immunosorbent assay. The results showed that both P13-TT and P13-DT were antigenic, inducing a mimetic response to P13 in both G2 and G4 mice, and immunogenic, inducing a mimotope response including VH3 (idiotype)-positive antibodies to GXM in G2 but not G4 mice. CpG led to higher titers of IgG to P13 and GXM in P13-TT-vaccinated G2 mice. C. neoformans challenge of P13-protein conjugate-vaccinated and control G2 mice induced anamnestic IgG- and VH3-positive responses to GXM and was associated with a significantly decreased risk of death and a prolongation of survival in P13-DT-vaccinated mice compared to phosphate-buffered saline-treated or protein carrier-vaccinated mice. These findings reveal that P13 elicited a human antibody response with VH3 expression in human immunoglobulin transgenic mice that has been observed for human antibodies to GXM and support the concept that peptide mimotope-based vaccines may hold promise for the treatment of C. neoformans infections.

Ionic interfaces and diphtheria toxoid interactions

We present here a systematic study on the purification of the diphtheria toxoid (Dtxd) produced at the Instituto Butantan, by adding only one step on the entire process of its production. Aliquots of 1.0 ml of Dtxd were added to an equal amount of Q-Sepharose previously equilibrated with 500 mM Tris, pH 5.0-9.0 (increments of 0.5 pH units). The best condition for the Dtxd monomer adsorption was achieved at pH 9.0. The best condition for desorption was obtained with 300 mM NaCl. After studying the gel binding capacity for Dtxd, a column (C20/20) equilibrated with 500 mM Tris, pH 9.0, was prepared. The purification factor for Dtxd was 1.5. The final recovery of Dtxd was 68.75%, with 90.31% purity. The process methodology presented here is a very realistic sequence of separation steps, which is perfectly compatible with the production requirements. Vaccination with "toxoid highly purified toxin" is known to confer a strong immunity on people in the absence of undesirable reactions, which led experts of European Pharmacopoeia to recommend its use both for children and adult vaccination.

A Vaccination Strategy for the Long-Term Suppression of Androgens in Advanced Prostate Cancer

OBJECTIVES

We have previously reported the ability of D17DT (formerly GnRH-DT) vaccination to produce castrate levels of androgens in men with advanced prostate cancer. This study examines the efficacy and tolerability of 3 and 15 micrograms of D17DT in 12 patients with advanced prostate cancer to establish a dose-response relationship.

METHODS

12 patients received either 3 or 15 micrograms of D17DT as 3 deep intramuscular injections over 6 weeks. Outcome was assessed in terms of physical and biochemical evaluations of clinical progression and antibody titres.

RESULTS

Significant titres of anti-GnRH antibodies were detected in 2 out of 6 subjects who received 15 micrograms of D17DT; suppression of testosterone to castrate levels accompanied by a significant and prolonged reduction in PSA was also demonstrated. No responses were seen following treatment with 3 micrograms of D17DT.

CONCLUSION

The induction of anti-GnRH antibodies through vaccination with 15 micrograms D17DT can produce and sustain castrate levels of testosterone in men with advanced prostate cancer.

Physicochemical and immunochemical techniques predict the quality of diphtheria toxoid vaccines

The most critical step in the production of diphtheria vaccines is the inactivation of the toxin by formaldehyde. Diphtheria toxoid (DTx) is produced during this inactivation process through partly unknown, chemical modifications of the toxin. Consequently, diphtheria vaccines are difficult to characterise completely and the quality of the toxoids is routinely determined with potency and safety tests. This article describes the possibility of monitoring the quality in diphtheria vaccine production with a selection of physicochemical and immunochemical tests as an alternative to established in vivo tests. To this end, diphtheria toxin was treated with increasing formaldehyde concentrations resulting in toxoid products varying in potency and residual toxicity. Differences in the quality of the experimental toxoids were also assessed with physicochemical and immunochemical techniques. The results obtained with several of these analyses, including SDS-PAGE, primary amino group determination, fluorescence spectroscopy, circular dichroism (CD) and biosensor analysis, showed a clear correlation with the potency and safety tests. A set of criteria is proposed that a diphtheria toxoid must comply with, i.e. an apparent shift of the B-fragment on SDS-PAGE, a reduction of primary amino groups in a diphtheria molecule, an increased resistance to denaturation, an increased circular dichroism signal in the near-UV region and a reduced binding to selected monoclonal antibodies. In principle, a selected set of in vitro analyses can replace the classical in vivo tests to evaluate the quality of diphtheria toxoid vaccines, provided that the validity of these tests is demonstrated in extensive validation studies and regulatory acceptance is obtained.

Comparative quantitation for the protein content of diphtheria and tetanus toxoids by DC protein assay and Kjeldahl method

DPT, a combination vaccine against diphtheria, tetanus and pertussis is available since many years and still continued in the national immunisation schedule of many countries. Although highly potent, reactions to DPT vaccine are well known, mainly attributed to the factors like Pertussis component, aluminum adjuvant and lower purity of tetanus and diphtheria toxoids. The latter most important aspect has become a matter of concern, specially for the preparation of next generation combination vaccines with more number of antigens in combination with DPT. Purity of toxoid is expressed as Lf (Limes flocculation) per mg of protein nitrogen. The Kjeldahl method (KM) of protein nitrogen estimation suggested by WHO and British Pharmacopoeia is time consuming and less specific. Need has been felt to explore an alternative method which is quick and more specific for toxoid protein determination. DC (detergent compatible) protein assay, an improved Lowry's method, has been found to be much more advantageous than Kjeldahl method.

Stabilization of alum-adjuvanted vaccine dry powder formulations: mechanism and application

Studies were performed to elucidate the mechanism of alum gel coagulation upon freezing and drying and its relationship to vaccine potency loss and to develop a novel freeze-drying process for the production of stable alum-adjuvanted vaccine formulations suitable for conventional needle injection and epidermal powder immunization (EPI). The alum hydroxide-adjuvanted hepatitis-B surface antigen (Alum-HBsAg) and the alum phosphate-adjuvanted diphtheria and tetanus toxoids (Alum-DT) were dehydrated by freeze drying (FD), spray drying (SD), air drying (AD), or spray freeze drying (SFD). After drying by FD, SD, or AD, alum gels coagulated when examined by optical microscopy and particle size analysis. In addition, desorption of antigen molecules from the coagulated when examined by optical microscopy and particle size analysis. In addition, desorption of antigen molecules from the coagulated alum gel upon reconstitution appeared to be difficult, as indicated by attenuated band intensity on SDS-PAGE. In contrast, SFD alum gels turned a homogenous suspension upon reconstitution, suggesting minimal alum coagulation. In the mouse model, the in vivo immunogenicity of SFD Alum-HBsAg was preserved, whereas the FD Alum-HBsAg suffered significant immunogenicity loss. Grinding of coagulated FD Alum-HBsAg into smaller particles could partially recover the immunogenicity. In a guinea pig study using EPI, the SD Alum-DT formulation was not immunogenic, but the SFD Alum-DT formulations had a vaccine potency comparable to that of the untreated DT administered by I.M. injection. Overall, the relationship of coagulation of alum gel upon reconstitution and the loss of vaccine potency was established in this study. Alum gels became highly coagulated after dehydration by spray drying and traditional freeze-drying processes. However, freezing rate played a critical role in preserving the adjuvant effect of alum and fast freezing decreased the tendency of alum coagulation. Spraying the alum gel into liquid nitrogen represents the fastest freezing rate achievable and resulted in no discernible alum coagulation. Therefore, SFD presents a novel and effective drying process for alum-adjuvanted vaccine formulations and is particularly valuable for dry powder applications such as EPI.

The role of the adsorption process for production and control combined adsorbed vaccines

For the production and control of adsorbed vaccines it is necessary to know and respect some basic features of adsorption. Among others these are the surface charges of adsorbents and antigens, the pH of the medium, the buffer components and the maturation process. They are important for the adsorption behaviour and have influence on the stability of the adsorbate and potency of the vaccine. Individually different conditions for optimal adsorption of antigens can be respected with a production strategy, where every antigen is adsorbed separately in a controlled manner, before it is mixed with other antigens to the final bulk vaccine. This strategy is favoured over strategies with sequential or competitive adsorption of the antigens.

Physicochemical analysis of purified diphtheria toxoids: is toxoided then purified the same as purified then toxoided?

Diphtheria toxin can be converted into a highly immunogenic and irreversibly detoxified vaccine either using the conventional process in which the crude toxin is formalinised and subsequently purified (DTxd(conv)) or by detoxification of the highly purified toxin (DTxd(new)). In this study, both DTxd(new) and DTxd(conv) were evaluated by use of physico-chemical methods. For some methods, results were also compared to those obtained for cross-reacting material (CRM197), which is a non-toxic mutant of diphtheria toxin. DTxd(new) was assayed to have a specific purity of at least 2300 LF/mg protein N, thereby exceeding Pharm. Eur. requirements by up to 35%. Superior purity of DTxd(new) could also be demonstrated by size exclusion HPLC experiments and by amino acid composition studies. Far-UV circular dichroism spectroscopy revealed that the secondary structure of DTxd(new) almost resembled that of CRM197, suggesting only minor molecular changes during detoxification. This study worked out differences between purified diphtheria toxoids. Physico-chemical means revealed the advantages of DTxd(new) being the purer and more defined product, thus making it highly efficient for its use as a vaccine carrier as well as a component of vaccine combinations.

Capillary electrophoretic analysis of meningococcal polysaccharide-diphtheria toxoid conjugate vaccines

Protein-polysaccharide conjugate vaccines are large, complex molecules that present challenges in terms of characterization. Free solution capillary electrophoresis using alkaline (pH 9-10) borate or glycine/NaOH buffers permitted electrophoresis of diphtheria toxoid (Dt) or meningococcal polysaccharide-Dt conjugates as well-formed, relatively broad peaks. Resolution was observed between the conjugate and the Dt peaks for some serotypes; however, overlap between Dt and one or more conjugate peaks was observed with both buffers. Inclusion of SDS in the separation buffer at a level above the critical micelle concentration allowed separation of Dt and Dt-conjugates of meningococcal serotypes A, C, Y and W135. Using borate/SDS, a linear relationship between peak area and Dt concentration was observed between approximately 2 mg/ml and 20 microg/ml. A linear relationship between Dt peak area and injection times from 10 to 50 seconds was also observed. Capillary electrophoresis may therefore be a useful method for quantifying free protein level in meningococcal-Dt conjugate vaccines.

Induction of systemic and mucosal antibody responses in mice immunized intranasally with aluminium-non-adsorbed diphtheria toxoid together with recombinant cholera toxin B subunit as an adjuvant

Nasal mucosal immunization is very attractive for vaccination to prevent various bacterial and viral infectious diseases because of induction of systemic and mucosal immune responses. The aim of the present study was to investigate the possibility of changing the immunization procedure of diphtheria toxoid (DT) from intramuscular or subcutaneous injection to intranasal administration. Intranasal immunization with aluminium-non-adsorbed diphtheria toxoid (nDT) together with recombinant cholera toxin B subunit (rCTB, 10 microg) induced, at a concentration of 5 Lf, high levels of serum DT-specific IgG antibody responses and high or moderate levels of the specific IgA antibody responses in all mice and only a slight level of the specific IgE antibody responses in some mice. Furthermore, sufficiently high diphtheria antitoxin titres more than 0.1 international units (IU) ml(-1) were obtained from mice which showed high levels of serum DT-specific IgG antibody responses. Under the same experimental conditions, induction of significant levels of mucosal DT-specific IgA antibody responses occurred in the nasal cavity, the lung, the saliva and vaginal secretions and the small and large intestines of all mice, although there were different titres between individual mice. Similar results were also obtained with rCTB-specific serum IgG and IgA and mucosal IgA antibody responses; serum rCTB-specific IgE antibody titres were not detected. These results show that intranasal administration of nDT with rCTB must be a very useful means for vaccination against diphtheria.

Inhibition of the myotoxic activity of Bothrops asper myotoxin II in mice by immunization with its synthetic 13-mer peptide 115-129

The region comprising amino acid residues 115-129 of myotoxin II, a Lys49 phospholipase A2 from the venom of Bothrops asper, was previously shown to constitute a heparin binding site, and to be associated with its toxic activities. The corresponding synthetic peptide, KKYRYYLKPLCKK, was coupled to diphtheria toxoid as a carrier, and utilized as an immunogen in mice, to explore the possible protection from the myotoxic activity induced by myotoxin II in vivo. Mice receiving peptide-carrier injections produced antibodies to peptide 115-129, which cross-reacted to myotoxin II, as determined by enzyme-immunoassay. In contrast, no antibodies against peptide 115-129 were detected in mice immunized with myotoxin II, despite the strong antibody response to the whole antigen. Thus, region 115-129 of myotoxin II is not an immunodominant B-cell epitope in the mouse. After immunization with conjugated peptide or myotoxin II, mice were challenged with myotoxin II, and the extent of myonecrosis was estimated by determining their plasma creatine kinase activity, in comparison to non-immunized mice. After the challenge, both the group immunized with myotoxin II, and the group immunized with peptide 115-129, had a significant reduction of myonecrosis. These results demonstrate that region 115-129 of myotoxin II constitutes a neutralizing epitope, and provide further evidence for the relevance of this region in its myotoxic effect in vivo.

Physico-chemical and antigenic properties of tetanus and diphtheria toxoids and steps towards improved stability

Physico-chemical, antigenic and immunogenic properties may be altered during microencapsulation of antigens and their release from poly(lactic acid) and poly(lactic-co-glycolic acid) microspheres. Here, the physico-chemical, conformational and antigenic stability of tetanus and diphtheria toxoids was studied in aqueous solutions stressed by elevated temperature and the presence of lactic and glycolic acids. Further, the stabilising effect of albumin was investigated. The analytical tools used were fluorimetry, circular dichroism spectroscopy, turbidimetry, electrophoresis and ELISA. Elevated temperatures altered the physico-chemical and antigenic properties of the toxoids to a greater extent than the acids (50 mM) did. Substantial unfolding and chemical changes of tryptophan were observed upon 1-4 weeks of incubation at 60 degreesC. At 4 degreesC, only minor conformational changes were observed, even in the presence of the acids. Furthermore, 40% of the tetanus toxoid antigenicity was lost after 7 days at 37 degreesC. This loss increased in the presence of the acids. At 60 degreesC, the antigenicity had completely vanished. Very importantly, 0.5% albumin preserved the tetanus antigenicity over 6 weeks' incubation at 37 degreesC, regardless of the presence of glycolic acid. This qualifies albumin as potential stabilising additive for toxoid loaded poly(lactic acid) and poly(lactic-co-glycolic acid) microspheres.

Bactericidal activity of Lys49 and Asp49 myotoxic phospholipases A2 from Bothrops asper snake venom--synthetic Lys49 myotoxin II-(115-129)-peptide identifies its bactericidal region

Mammalian group-II phospholipases A2 (PLA2) of inflammatory fluids display bactericidal properties, which are dependent on their enzymatic activity. This study shows that myotoxins II (Lys49) and III (Asp49), two group-II PLA2 isoforms from the venom of Bothrops asper, are lethal to a broad spectrum of bacteria. Since the catalytically inactive Lys49 myotoxin II isoform has similar bactericidal effects to its catalytically active Asp49 counterpart, a bactericidal mechanism that is independent of an intrinsic PLA2 activity is demonstrated. Moreover, a synthetic 13-residue peptide of myotoxin II, comprising residues 115-129 (common numbering system) near the C-terminal loop, reproduced the bactericidal effect of the intact protein. Following exposure to the peptide or the protein, accelerated uptake of the hydrophobic probe N-phenyl-N-naphthylamine was observed in susceptible but not in resistant bacteria, indicating that the lethal effect was initiated on the bacterial membrane. The outer membrane, isolated lipopolysaccharide (LPS), and lipid A of susceptible bacteria showed higher binding to the myotoxin II-(115-129)-peptide than the corresponding moieties of resistant strains. Bacterial LPS chimeras indicated that LPS is a relevant target for myotoxin II-(115-129)-peptide. When heterologous LPS of the resistant strain was present in the context of susceptible bacteria, the chimera became resistant, and vice versa. Myotoxin II represents a group-II PLA2 with a direct bactericidal effect that is independent of an intrinsic enzymatic activity, but adscribed to the presence of a short cluster of basic/hydrophobic amino acids near its C-terminal loop.

In vitro determination of antigen quality: biosensor analysis and fluorescence spectroscopy

We are probing the potential of two techniques to monitor the quality of antigens in vitro. Structural and conformational differences between diphtheria toxin and toxoid are detected via biosensor analysis (BIA-core) and fluorescence spectrometry. With BIA-core the interaction kinetics between toxin and toxoid and a monoclonal antibody were established. The fluorescence properties of both antigens were determined with respect to fluorescence intensity and emission maximum as a function of guanidinium hydrochloride concentration. In all cases clear differences were found between toxin and toxoid. Antibody affinity of the toxoid was lower compared with toxin, caused by lower binding and higher release rates. Fluorescence intensity of toxoid was reduced by about 50%. Toxoid was less sensitive to guanidinium hydrochloride-induced denaturation, reflected in a diminished shift of the emission maximum.

Chitosan and chitosan/ethylene oxide-propylene oxide block copolymer nanoparticles as novel carriers for proteins and vaccines

PURPOSE

The aim of this study was to investigate the interaction between the components of novel chitosan (CS) and CS/ethylene oxide-propylene oxide block copolymer (PEO-PPO) nanoparticles and to evaluate their potential for the association and controlled release of proteins and vaccines.

METHODS

The presence of PEO-PPO on the surface of the nanoparticles and its interaction with the CS was identified by X-ray photoelectron spectroscopy (XPS). The mechanism of protein association was elucidated using several proteins, bovine serum albumin (BSA), and tetanus and diphtheria toxoids, and varying the formulation conditions (different pH values and concentrations of PEO-PPO), and the stage of protein incorporation into the nanoparticles formation medium.

RESULTS

BSA and tetanus and diphtheria toxoids were highly associated with CS nanoparticles partly due to electrostatic interactions between the carboxyl groups of the protein and the amine groups of CS. PEO-PPO also interacted electrostatically with CS, thus competing with the proteins for association with CS nanoparticles. A visible amount of PEO-PPO was projected towards the outer phase of the nanoparticles. Proteins were released from the nanoparticles at an almost constant rate, the intensity of which was closely related to the protein loading. Furthermore, the tetanus vaccine was released in the active form for at least 15 days.

CONCLUSIONS

CS and CS/PEO-PPO nanoparticles prepared by a very mild ionic crosslinking technique are novel and suitable systems for the entrapment and controlled release of proteins and vaccines.

Comparison of the conformation, hydrophobicity, and model membrane interactions of diphtheria toxin to those of formaldehyde-treated toxin (diphtheria toxoid): formaldehyde stabilization of the native conformation inhibits changes that allow membrane insertion

Toxoids are inactivated protein toxins that are used in vaccines. The behavior of diphtheria toxin reacted with formaldehyde (diphtheria toxoid) was compared to that of diphtheria toxin in order to understand the nature of the changes that occur in toxoids upon protein reaction with formaldehyde. Despite the intramolecular cross-links in the toxoid, the conformations of the toxoid and the toxin were very similar in both the native and low pH-induced membrane-penetrating states as judged by fluorescence and hydrophobicity properties. However, the toxoid underwent thermal-, low-pH-, and guanidinium chloride-induced conformational changes only at more extreme conditions than needed to induce such changes in the toxin. This implies that formaldehyde modification stabilizes the native conformation relative to several conformations that involve different degrees of unfolding. The stabilization to conformational changes induced by low pH is particularly interesting because low pH induces partial unfolding of the toxin to a molten globule-like state. It was found that the toxoid only gained the ability to interact with model membrane vesicles at a lower pH than the toxin. Because low-pH-induced unfolding and membrane interaction are critical steps in the entry of diphtheria toxin into cells, the resistance of the toxoid to these changes may be linked to its lack of toxicity. The implications of these results for the construction of toxoids are discussed.

Stabilization of tetanus and diphtheria toxoids against moisture-induced aggregation

The progress toward single-dose vaccines has been limited by the poor solid-state stability of vaccine antigens within controlled-release polymers, such as poly(lactide-co-glycolide). For example, herein we report that lyophilized tetanus toxoid aggregates during incubation at 37 degrees C and elevated humidity--i.e., conditions relevant to its release from such systems. The mechanism and extent of this aggregation are dependent on the moisture level in the solid protein, with maximum aggregation observed at intermediate moisture contents. The main aggregation pathway is consistent with formaldehyde-mediated cross-linking, where reactive electrophiles created and stored in the vaccine upon formalinization (exposure to formaldehyde during vaccine preparation) react with nucleophiles of a second vaccine molecule to form intermolecular cross-links. This process is inhibited by the following: (i) succinylating the vaccine to block reactive amino groups; (ii) treating the vaccine with sodium cyanoborohydride, which presumably reduces Schiff bases and some other electrophiles created upon formalinization; and (iii) addition of low-molecular-weight excipients, particularly sorbitol. The moisture-induced aggregation of another formalinized vaccine, diphtheria toxoid, is also retarded by succinylation, suggesting the generality of this mechanism for formalinized vaccines. Hence, mechanistic stability studies of the type described herein may be important for the development of effective single-dose vaccines.

Quantitation of the protein content of diphtheria and tetanus toxoids by the Biuret method during production of combined vaccines

The protein content of 15 batches of diphtheria toxoid and 12 batches of tetanus toxoid was measured by Biuret method and was compared to the values obtained by the Kjeldahl method. Statistical analysis did not show any difference between the two methods. The Biuret method, is specific, easy to carry out and takes less time for protein estimation of purified toxoids during production of combined vaccines.

Role of aluminium in skin reactions after diphtheria-tetanus-pertussis-poliomyelitis vaccination: an experimental study in rabbits

The occurrence of subcutaneous nodules at the injection site is one of the complications of diphtheria-tetanus-pertussis-poliomyelitis vaccination, but the causes and mechanisms involved are still poorly understood. An experimental study in the New Zealand rabbit enabled us to determine the frequency of occurrence of these nodules, how long they persist and the histopathologic features of the cells involved. Aluminium (Al) assays by electrothermal atomic absorption spectrometry allowed us to study concentrations both in nodules and the organism (serum, normal skin). The results show an absence of Al diffusion outside nodules, a correlation between infiltrate intensity and Al concentration in nodules and modifications in the histological constituents of nodule cells. The histological picture indicates a foreign body reaction to Al. All these data underscore the role of Al in the formation of early postvaccinal nodules at the injection site.

A nondestructive method for peptide bond conjugation of antigenic haptens to a diphtheria toxoid carrier, exemplified by two antisera specific to acetolactate synthase

A method for the preparation of an activated protein carrier is described: Protein carboxyl groups are transformed into N-hydroxysulfosuccinimide esters, a structure that will react with primary amino groups under amide bond formation. Although the activated ester is unstable under aqueous conditions, a significant amount of hapten molecules can be bound covalently to the carrier under very mild conditions. Ligands can be peptides or other molecules possessing a primary amino group. The method avoids the risk of ligand polymerization and no derivatization of the ligand prior to conjugation is needed. Residual unreacted ligand molecules can therefore be recovered in their native form by size exclusion chromatography. The method was used to conjugate two synthetic sugar beet acetolactate synthetase (E.C. 4.1.3.18) peptides to diphtheria toxoid. Antibodies were raised against both of the conjugates. The specificity of these antibodies against sugar beet acetolactate synthetase was verified using immunoblotting, ELISA, and immunoprecipitation.

Aluminum compounds used as adjuvants in vaccines

The structure of nine commercially manufactured aluminum-containing adjuvants was investigated by X-ray diffraction, infrared spectroscopy, transmission electron micrography, and energy dispersive spectrometry. Seven samples which were labeled as aluminum hydroxide were identified as boehmite, a crystalline aluminum oxyhydroxide [AlO(OH)]. However, the degree of crystallinity varied between the samples. Two samples which were labeled as aluminum phosphate were found to be amorphous aluminum hydroxyphosphate. Buffer anions and sulfate anions substitute for hydroxyls in the amorphous aluminum hydroxide formed by the in situ alum precipitation method. Finally, the aluminum-containing adjuvant in diphtheria and tetanus toxoid, U.S.P., produced by three manufacturers was characterized.