Evaluation of Biodegradable Microparticles for Mucosal Vaccination Against Diphtheria Toxoid: Nasal Efficacy Studies in Guinea Pigs

Objectives

In this study, poly-(ɛ-caprolactone) (PCL) and poly-(lactic-co-glycolic acid) (PLGA) microparticles encapsulating diphtheria toxoid (DT) were investigated for their potential as a mucosal vaccine delivery system.

Materials and Methods

Antigen-containing microparticles were prepared using the double emulsion (w/o/w) solvent evaporation method.

Results

The average geometric diameter of the particles was found to be between 7 and 24 µm, which is suitable for uptake by the antigen-presenting cells in the nasal mucosa. Although the differences were insignificant, the PLGA polymer-containing formulations exhibited the highest encapsulation efficiency. Microparticle formulations, prepared with both PLGA and PCL polymers, were successfully produced at high production yields. The in vitro release profile was presented as a biexponential process with an initial burst effect due to the release of the protein adsorbed on the microsphere surface, and the subsequent sustained release profile is the result of protein diffusion through the channels or pores formed in the polymer matrix. DT-loaded microparticles, DT solution in phosphate-buffered saline (PBS), and empty microparticles (control) were administered via nasal route and subcutaneously to guinea pigs. The antibody content of each serum sample was determined using an enzyme-linked immunosorbent assay (ELISA).

Conclusion

Absorbance values of the ELISA test showed that PLGA- and PCL-bearing microparticles could stimulate an adequate systemic immune response with intranasal vaccination. In addition, PLGA and PCL microparticles resulted in significantly increased IgG titers with intranasal administration as a booster dose following subcutaneous administration. PCL polymer elicited a high immune response compared with PLGA polymer (p <0.05).

Peptide-Protein Conjugation and Characterization to Develop Vaccines for Group A Streptococcus

Peptide conjugates have been widely used for developing vaccines that prevent common bacterial infections for which peptides alone are either ineffective or provide only short-term protection. Among several carrier proteins, diphtheria toxoid and CRM₁₉₇ (a genetically detoxified diphtheria toxin) are considered safe and have been used in several licensed vaccines. For developing a vaccine against group A streptococcus (GAS), antigens from conserved region of M protein and the IL-8 protease, SpyCEP, have been identified. In this chapter, we describe a method for producing peptide-conjugate subunit GAS vaccines, which involves maleimide conjugation of peptides to a carrier protein and their subsequent characterization.

Levels of antibodies specific to diphtheria toxoid, tetanus toxoid, and Haemophilus influenzae type b in healthy children born to Tdap-vaccinated mothers

INTRODUCTION

Vaccination of pregnant women protects both women and their newborns against some infectious diseases. Thailand implemented tetanus toxoid (TT) vaccination of pregnant women in 1977, which was replaced by tetanus-diphtheria toxoid (dT) vaccination in 2005. The tetanus-diphtheria-acellular pertussis (Tdap) vaccine has been recommended for pregnant women at 27-36 weeks of gestation since 2012 in several countries. Data on antibody responses to diphtheria toxoid (DT), TT, and Hemophilus influenzae type b (Hib) induced by combined vaccines in children born to TT-vaccinated and/or Tdap-vaccinated mothers are limited.

MATERIAL AND METHODS

We investigated anti-DT, anti-TT, and anti-Hib IgG responses in a cohort of Thai children (ClinicalTrial.gov NCT02408926) born to mothers who received a TT-containing and/or the Tdap vaccine during pregnancy. Children born to Tdap-vaccinated mothers were randomized to receive either a hexavalent (Infanrix-hexa) or pentavalent (Quinvaxem) vaccine, whereas children born to TT-vaccinated mothers received only Quinvaxem vaccine at 2, 4, 6, and 18 months of age. IgG levels were evaluated at birth (cord blood), 2 (pre-primary), 7 (post-primary), 18 (pre-booster), and 19 months of age (post-booster) using a commercially available enzyme-linked immunoassay.

RESULTS

Seroprotective concentrations of anti-DT, anti-TT, and anti-Hib IgG were achieved in >90% and >99% of children following primary and booster vaccination, respectively. Among children born to Tdap-vaccinated mothers, the pentavalent vaccine induced higher levels of anti-Hib IgG than the hexavalent vaccine after primary and booster vaccination. Significantly higher anti-Hib IgG levels were observed among children receiving the pentavalent vaccine and who were born to TT-vaccinated mothers than among children receiving the pentavalent vaccine and born to Tdap-vaccinated mothers after primary and booster vaccination.

CONCLUSIONS

Vaccination with a TT-containing and/or the Tdap vaccine during pregnancy did not compromise the seroprotection rate achieved following primary and booster immunization in individuals receiving either the pentavalent or hexavalent vaccine.

Spectroscopic characterisation of a series of Salmonella Typhi Vi-diphtheria toxoid glycoconjugate antigens differing in polysaccharide-protein ratio

Glycoconjugate vaccines consisting of the Salmonella enterica subsp. enterica serovar Typhi (S. Typhi) Vi capsular polysaccharide (PS) covalently attached to a suitable carrier protein have become available to support mass paediatric vaccination campaigns against typhoid. One developmental vaccine from the International Vaccine Institute (IVI) uses diphtheria toxoid (DTx) as the carrier protein. Several investigational conjugates with different PS:protein ratios were prepared, as previously reported by the IVI group, for physicochemical and immunochemical characterisation. We describe here the further spectroscopic characterisation of this series of glycoconjugate immunogen bulks using NMR spectroscopy, circular dichroism and absorption spectroscopy. We have used several mathematical approaches to extract information from the spectroscopic data not previously applied to glycoconjugates. These complementary approaches provide information on (i) the integrity of the carrier protein, (ii) consistency between batches of vaccine components, (iii) the polysaccharide: protein ratio (iv) the O-acetylation of the Vi in the conjugate (v) the stability of the O-acetylation of the Vi, and (vi) the presence of residual process reagents in the bulk. The utility of the data analysis approaches is discussed. Together, these analytical methods provide important characterisation of Vi-DTx conjugates to support development and quality control of commercial products.

Diphtheria toxoid nanoparticles improve learning and memory impairment in animal model of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder involving memory. The present study aimed at evaluating the effects of encapsulated diphtheria toxoid (DT) on behavioral learning impairment, and XBP1 mRNA splicing in AD.

METHODS

A DT-loaded nanoparticle (NP) carrier was prepared using the ionic gelation method. Sixty-three rats were divided into nine groups: (1) healthy, (2-4) sham, and (5-9) AD models: (5) AD was induced by intracerebroventricular injection of amyloid beta (Aβ) 1-42. (6) The rats received a subcutaneous diphtheria vaccine only 28 days before Aβ injection. (7) The rats received an intranasal diphtheria vaccine, in group 8, induced by administering empty chitosan NPs. 9) it was induced by administering chitosan NPs carrying DT. Morris water maze (MWM) test was used to examine the animals' learning and memory. Also, X-box binding protein 1 (XBP-1) mRNA gene splicing was studied in the hippocampus by reverse-transcription polymerase chain reaction (RT-PCR).

RESULTS

For the first time, chitosan NPs were prepared with an average diameter size of 40 nm and the effectiveness of approximately 70% during DT encapsulation. In comparison with the healthy group, the AD models exhibited significant impairment of learning and memory (P < 0.05), while DT-administrated animals showed significant improvements in learning and memory impairment (P < 0.05). XBP-1 mRNA gene splicing was only detected in an untreated AD group, while encapsulated DT completely inhibited splicing.

CONCLUSION

The therapeutic effects of DT chitosan NPs against learning and memory impairment were observed in this study, and XBP1 mRNA splicing was reported in the animal models.

Immunogenicity of diphtheria toxoid and poly(I:C) loaded cationic liposomes after hollow microneedle-mediated intradermal injection in mice

In this study, we aimed to investigate the immunogenicity of cationic liposomes loaded with diphtheria toxoid (DT) and poly(I:C) after hollow microneedle-mediated intradermal vaccination in mice. The following liposomal formulations were studied: DT loaded liposomes, a mixture of free DT and poly(I:C)-loaded liposomes, a mixture of DT-loaded liposomes and free poly(I:C), and liposomal formulations with DT and poly(I:C) either individually or co-encapsulated in the liposomes. Reference groups were DT solution adjuvanted with or without poly(I:C) (DT/poly(I:C)). The liposomal formulations were characterized in terms of particle size, zeta potential, loading and release of DT and poly(I:C). After intradermal injection of BALB/c mice with the formulations through a hollow microneedle, the immunogenicity was assessed by DT-specific ELISAs. All formulations induced similar total IgG and IgG1 titers. However, all the liposomal groups containing both DT and poly(I:C) showed enhanced IgG2a titers compared to DT/poly(I:C) solution, indicating that the immune response was skewed towards a Th1 direction. This enhancement was similar for all liposomal groups that contain both DT and poly(I:C) in the formulations. Our results reveal that a mixture of DT encapsulated liposomes and poly(I:C) encapsulated liposomes have a similar effect on the antibody responses as DT and poly(I:C) co-encapsulated liposomes. These findings may have implications for future design of liposomal vaccine delivery systems.

Polysaccharide conjugate vaccine protein carriers as a "neglected valency" - Potential and limitations

The development of vaccines against polysaccharide-encapsulated pathogens (e.g. Haemophilus influenzae type b, pneumococci, meningococci) is challenging because polysaccharides do not elicit a strong and long-lasting immune response (i.e. T-cell independent). This can be overcome by conjugating the polysaccharide to a protein carrier (e.g. tetanus toxoid, cross-reacting material 197 [CRM]), which vastly improves the immune response and induces memory to the polysaccharide (T-cell dependent). Although it is well documented that protein carriers additionally induce an immune response against themselves, this potential "additional valency" has so far not been recognized. The only exception is for the protein D carrier (derived from non-typeable Haemophilus influenzae [NTHi]) used in a pneumococcal conjugate vaccine, which may have a beneficial impact on NTHi acute otitis media. In this review, we describe the immunogenicity of various protein carriers and discuss their potential dual function: as providers of T-cell helper epitopes and as protective antigens. If this "additional valency" could be proven to be protective, it may be possible to consider its potential effect on the number of required immunizations. We also describe the potential for positive or negative interference between conjugate vaccines using the same protein carriers, the resulting desire for novel carriers, and information on potential new carriers. The range of conjugate vaccines is ever expanding, with different carriers and methods of conjugation. We propose that new conjugate vaccine trials should assess immunogenicity to both the polysaccharide and carrier. Ultimately, this so-far "neglected valency" could be an exploitable characteristic of polysaccharide conjugate vaccines.

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.

Collaborative study for the calibration of a replacement International Standard for diphtheria toxoid for use in flocculation test

We present the results of a collaborative study for the establishment of a replacement International Standard (IS) for diphtheria toxoid for use in flocculation test and its calibration in Lf units. Calibration was performed using Ramon flocculation method, standardized using the 2nd IS. The candidate standard was assigned a unitage of 1870 Lf/ampoule based on results from 25 laboratories in 15 different countries and was established as the 3rd IS for diphtheria toxoid for use in flocculation test by the WHO Expert Committee on Biological Standardization (ECBS) in October 2015. The study also assessed the use of alternative methods for measuring Lf. Participants were asked to determine the Lf value of the candidate standard using an Enzyme Linked Immunosorbent Assay (ELISA) established at NIBSC, or other suitable in-house method. 10 laboratories performed ELISA according to the NIBSC protocol, 1 laboratory performed flocculation using laser-light scattering according to an in-house protocol, and 1 laboratory performed another in-house ELISA. Results suggest these methods may provide suitable alternatives to the Ramon flocculation test, subject to validation, and that the new standard could act as a suitable reference preparation in these methods.

Structural and antigenic features of the synthetic SF23 peptide corresponding to the receptor binding fragment of diphtheria toxin

The SF23 peptide corresponding to the receptor binding fragment of diphtheria toxin (residues 508-530) has been synthesized. This fragment forming a protruding beta hairpin has been chosen because it is the less mutable B-cell epitope. Affine chromatography and ELISA show that antibodies from the sera of persons infected by toxigenic Corynebacterium diphtheriae and those immunized by diphtheria toxoid are able to bind the synthetic SF23 peptide. There are antibodies recognizing the SF23 peptide in the serum of horses hyperimmunized with diphtheria toxoid. Analysis of circular dichroism spectra show formation of beta hairpin by the peptide. Taken together, the results showed that the structure of the less mutable epitope of C. diphtheriae toxin was reproduced by the short SF23 peptide. Since antibodies against that epitope should block its interactions with cellular receptor (heparin-binding epidermal growth factor), the SF23 peptide can be considered as a promising candidate for synthetic vaccine development. Fluorescence quenching studies showed the existence of chloride and phosphate binding sites on the SF23 molecule. Phosphate containing adjuvants (aluminum hydroxyphosphate or aluminum hydroxyphosphate sulfate) are recommended to increase the SF23 immunogenic properties.

Safety and immunogenicity of a fully liquid vaccine containing five-component pertussis-diphtheria-tetanus-inactivated poliomyelitis-Haemophilus influenzae type b conjugate vaccines administered at two, four, six and 18 months of age

OBJECTIVE

The safety, immunogenicity and lot consistency of a fully liquid, five-component acellular pertussis combination vaccine, comprised of diphteria, tetanus and acellular pertussis, inactivated polio vaccine, Haemophilus influenzae type b (DTaP-IPV-Hib [Pediacel, sanofi pasteur, Canada]) were assessed and compared with that of Hib vaccine reconstituted with the five-component acellular pertussis combination vaccine (DTaP-IPV//Hib, Pentacel [sanofi pasteur, Canada]).

METHODS

Infants were recruited at vaccine study centres in Montreal, Quebec; Simon Fraser Health Region, British Columbia, and southern Alberta after the protocol had been approved by the relevant institutional ethics committees. Written informed consent was obtained from the parents or guardians of all subjects. At two months of age, the infants were randomly assigned to receive one of three consecutive production lots of DTaP-IPV-Hib by intramuscular injection. Reactions to vaccinations were assessed by parental observation and through telephone interviews conducted by study nurses. Blood samples were obtained at two, six, seven, 18 and 19 months of age for measurement of antibodies to vaccine antigens.

RESULTS

Most injection site and systemic reactions were mild or moderate, and of brief duration. All infants were protected against tetanus, diphtheria and all three polio serotypes after both primary and booster vaccinations. Antibody responses to pertussis antigens were similar to those observed in Swedish infants, in whom the five-component vaccine was shown to be 85% effective. Proportions of infants with antipolyribosylribitol phosphate antibody of 0.15 mug/mL or greater and 1.0 mug/mL or greater, were 97.9% and 88.9%, respectively, following primary immunization, and 100% and 99% following booster vaccination. Safety and immunogenicity results with both reconstituted and fully liquid combination vaccines were comparable.

CONCLUSIONS

The fully liquid combination vaccine was comparable in terms of safety and immunogenicity with the reconstituted combination vaccine.