Fatme Mawas

Immunogenicity in a Mouse Model of a Conjugate Vaccine Made with a Synthetic Single Repeating Unit of Type 14 Pneumococcal Polysaccharide Coupled to CRM197

ABSTRACT Oligosaccharides (OSs) related to the pneumococcal type 14 capsular polysaccharide (Pn14PS) were studied for their ability to inhibit the binding between anti-PS14 antisera and native PS14. A synthetic tetrasaccharide corresponding to the repeating unit of the Pn14PS, a hexasaccharide mimic, and an octasaccharide fragment obtained by Pn14PS depolymerization were good inhibitors. CRM197 conjugates of the tetrasaccharide and an octasaccharide mimic were prepared by using either adipic acid diester or diethyl squarate linkers. The conjugate with the tetrasaccharide chains induced anti-Pn14PS antibodies when injected subcutaneously into mice, as determined by an enzyme-linked immunosorbent assay, and antibody titers increased with oligosaccharide loading. The adipic acid-linked tetrasaccharide conjugates elicited higher antibody titers than those prepared with a squarate spacer. The lower anti-Pn14PS antibody response of the octasaccharide mimic conjugate indicates the importance of the backbone galactose residue for an appropriate antibody response. The OS-CRM197 conjugate prepared from a single repeat unit of the Pn14PS is a potential vaccine candidate.

Immunity under the skin: potential application for topical delivery of vaccines

With the technological advances in biomedical sciences and the better understanding of how the immune system works, new immunisation strategies and vaccine delivery options, such sprays, patches, and edible formulations have been developed. This has opened up the possibility of administering vaccines without the use of needles and syringes. Already topical immunisation is a reality and it has the potential to make vaccine delivery more equitable, safer, and efficient. Furthermore, it would increase the rate of vaccine compliance and greatly facilitate the successful implementation of worldwide mass vaccination campaigns against infectious diseases. This review gives a brief account of the latest developments of application of candidate vaccine antigens onto bare skin and describes some of our recent observations using peptide and glycoconjugate vaccines as immunogens.

Serotype of Streptococcus pneumoniae capsular polysaccharide can modify the Th1/Th2 cytokine profile and IgG subclass response to pneumococal-CRM197 conjugate vaccines in a murine model

The cellular and antibody responses to type 14 and type 19F Streptococcus pneumoniae capsular polysaccharides (PS) conjugated to CRM(197) were investigated in a mouse model developed for pre-clinical evaluation and quality control of pneumococcal conjugate vaccines. Total IgG antibody and IgG subclasses against PS and the carrier protein for both conjugates were measured in addition to the T cell proliferation and cytokine profiles induced by these conjugates. While unconjugated PS 14 and 19F were at best only weakly immunogenic, both types of conjugate induced strong primary and secondary IgG responses to PS. The responses induced by the two conjugates to the carrier protein were very different; a high level of anti-CRM(197) IgG was induced only by the PS19F conjugate whereas a very weak response was induced by the PS14 conjugate. Interestingly, the IgG subclass distribution was different for the two conjugates; for PS19F conjugate, the IgG response was almost completely of IgG1 subclass with low levels of IgG3 and IgG2a while the response to PS14 conjugate was mainly of the IgG1 and IgG2a subclasses with a low level of IgG3. The anti-CRM(197) IgG subclass distribution was identical with that to the corresponding conjugated PS. Both types of conjugate induced strong T cell proliferation to recall antigens but induced different patterns of cytokine response in immune spleen cells which were indicative of a Th0 response or a mixture of Th1 and Th2 responses with a bias towards Th2 response in PS19F-CRM(197) immunised mice. In conclusion, PS14- and PS19F-CRM(197) conjugates induced different IgG subclass patterns as a result of inducing different patterns of cytokine response to the carrier protein. This indicates that the serotype of PS can modify the Th1/Th2 response to the carrier protein, which has a direct effect and can predict the IgG subclass of the PS response. Finally, we conclude that this model appears suitable for studying the immunogenicity and immune interaction of different components of multivalent pneumococcal conjugate vaccines and may be applicable to their pre-clinical evaluation and quality control.

Current progress with Moraxella catarrhalis antigens as vaccine candidates

The success of the immunization programs against Haemophilus influenzae type b and, more recently, Streptococcus pneumoniae in developed and some developing countries has demonstrated that invasive disease caused by these bacteria can be very effectively controlled by vaccination. There is also evidence that pneumococcal vaccines can reduce the incidence of acute otitis media in children. More complete control of this disease would be achieved if infections caused by Moraxella catarrhalis and nontypeable H. influenzae, the other common agents of otitis media in children and of a number of respiratory-associated infections in both children and adults, could also be controlled. Since these bacteria do not possess capsules and are not known to secrete exotoxins, the search for vaccine candidates has focused on the conserved epitopes exposed on the bacterial outer membrane. In this article, we review the contribution of M. catarrhalis to disease and recent advances in the development and testing of various vaccine candidates against this bacterium, including those still in the development stage and those approaching clinical trials. Recommendations are proposed for approaches needed for the standardization of assays and use of appropriate animal models for quality-control testing of these vaccine candidates. Regulatory issues surrounding vaccines of this type are also discussed.

Physico-chemical and immunological examination of the thermal stability of tetanus toxoid conjugate vaccines

The thermal stability of meningococcal C (MenC)- and Haemophilus influenzae b (Hib)-tetanus toxoid (TT) conjugate vaccines was investigated using spectroscopic and chromatographic techniques and immunogenicity assays in animal models. In this stability study, both the bulk concentrate and final fills were incubated at -20, 4, 23, 37 or 55 degrees C for 5 weeks or subjected to cycles of freeze-thawing. The structural stability, hydrodynamic size and molecular integrity of the treated vaccines were monitored by circular dichroism (CD), fluorescence and nuclear magnetic resonance (NMR) spectroscopic techniques, size exclusion chromatography (FPLC-SEC), and high performance anion exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD). Only storage at 55 degrees C for 5 weeks caused some slight unfolding and modification in the tertiary structure of the carrier protein in the MenC-TT conjugate. Substantial loss of saccharide content from the MenC conjugates was observed at 37 and 55 degrees C. Unexpectedly, the experimental immunogenicity of MenC-TT vaccine adsorbed to Alhydrogel was significantly reduced only by repeated freeze-thawing, but not significantly decreased by thermal denaturation. Neither the molecular integrity nor the immunogenicity of the lyophilised Hib-TT vaccines was significantly affected by freeze-thawing or by storage at high temperature. In conclusion, the MenC- and Hib-TT conjugate vaccines were relatively stable when stored at higher temperatures, though when MenC-TT vaccine was adsorbed to Alhydrogel, it was more vulnerable to repeated freeze-thawing. When compared with CRM(197) conjugate vaccines studied previously using similar techniques, the tetanus toxoid conjugates were found to have higher relative thermal stability in that they retained immunogenicity following storage at elevated temperatures.

Antigenicity and Immunogenicity of a Synthetic Oligosaccharide-Protein Conjugate Vaccine against Haemophilus influenzae Type b

ABSTRACT Polysaccharide-protein conjugates as vaccines have proven to be very effective in preventing Haemophilus influenzae type b infections in industrialized countries. However, cost-effective technologies need to be developed for increasing the availability of anti-H. influenzae type b vaccines in countries from the developing world. Consequently, vaccine production with partially synthetic antigens is a desirable goal for many reasons. They may be rigidly controlled for purity and effectiveness while at the same time being cheap enough that they may be made universally available. We describe here the antigenicity and immunogenicity of several H. influenzae type b synthetic oligosaccharide-protein conjugates in laboratory animals. The serum of H. influenzae type b-immunized animals recognized our synthetic H. influenzae type b antigens to the same extent as the native bacterial capsular polysaccharide. Compared to the anti-H. influenzae type b vaccine employed, these synthetic versions induced similar antibody response patterns in terms of titer, specificity, and functional capacity. The further development of synthetic vaccines will meet urgent needs in the less prosperous parts of the world and remains our major goal.

Successful Induction of Protective Antibody Responses against Haemophilus influenzae Type b and Diphtheria after Transcutaneous Immunization with the Glycoconjugate Polyribosyl Ribitol Phosphate—Cross-Reacting Material197 Vaccine

We examined the antibody responses elicited in rats after transcutaneous immunization (TCI) with the Haemophilus influenzae type b (Hib)-cross-reacting material (CRM(197)) glycoconjugate vaccine coadministered with cholera toxin or mutants of heat-labile enterotoxin of Escherichia coli (LTK63 and LTR72) as adjuvants. The glycoconjugate vaccine was immunogenic, eliciting high antibody responses to the capsular polysaccharide of Hib and to diphtheria toxin. Passively transferred immune serum protected infant rats against challenge with the Hib Eagan strain and exhibited strong neutralizing activity against diphtheria toxin both in vitro and in vivo. The finding that TCI of rats can elicit antibody responses surpassing the minimum levels required for protective immunity against Hib and diphtheria suggests that this immunization strategy holds a lot of promise for future pediatric use. However, further studies are required to confirm the potential of TCI with glycoconjugate vaccines in humans.

Suppression and Modulation of Cellular and Humoral Immune Responses to Haemophilus influenzae Type B (Hib) Conjugate Vaccine in Hib-Diphtheria-Tetanus Toxoids-Acellular Pertussis Combination Vaccines: A Study in a Rat Model

We assessed a rat model to evaluate the immunogenicity of Haemophilus influenzae type b (Hib) conjugate vaccines and the effect on Hib immunogenicity of combining 2 Hib vaccines (Hib-tetanus toxoid [TT]-A and Hib-TT-B) with diphtheria-TT-acellular pertussis (DTaP)(3) or DTaP(5)/inactivated poliovirus (IPV) vaccines. Rats were immunized subcutaneously with Hib alone or with Hib and DTaP-based vaccines; anti-Hib capsular polysaccharide IgG, poly-ribosyl-ribitol-phosphate (PRP), IgG subclass, and cellular immune responses were evaluated. Results showed a significant reduction in the antibody response to PRP when Hib-TT-A was administered in combination with DTaP(3) and showed changes in the anti-PRP IgG subclass distribution between the separate and combination groups. However, combining Hib-TT-B with DTaP(5)/IPV did not reduce the anti-PRP antibody response. These results suggest that the model can predict the effect of combined administration of Hib and DTaP vaccines on Hib immunogenicity and would be suitable for preclinical studies of mechanisms of interference in Hib/DTaP vaccines.

Mucosal Antibodies to the C Terminus of Toxin A Prevent Colonization of Clostridium difficile

ABSTRACT Mucosal immunity is considered important for protection against Clostridium difficile infection (CDI). We show that in hamsters immunized with Bacillus subtilis spores expressing a carboxy-terminal segment (TcdA26–39) of C. difficile toxin A, no colonization occurs in protected animals when challenged with C. difficile strain 630. In contrast, animals immunized with toxoids showed no protection and remained fully colonized. Along with neutralizing toxins, antibodies to TcdA26–39 (but not to toxoids), whether raised to the recombinant protein or to TcdA26–39 expressed on the B. subtilis spore surface, cross-react with a number of seemingly unrelated proteins expressed on the vegetative cell surface or spore coat of C. difficile. These include two dehydrogenases, AdhE1 and LdhA, as well as the CdeC protein that is present on the spore. Anti-TcdA26–39 mucosal antibodies obtained following immunization with recombinant B. subtilis spores were able to reduce the adhesion of C. difficile to mucus-producing intestinal cells. This cross-reaction is intriguing yet important since it illustrates the importance of mucosal immunity for complete protection against CDI.

A retrospective study on the quality of Haemophilus influenzae type b vaccines used in the UK between 1996 and 2004.

Following the reduction in efficacy of Hib-TT vaccines in the primary immunization schedule observed in the U.K. between 1999 and 2003, batches of vaccine manufactured by two different companies were retrospectively examined by the National Institute for Biological Standards and Control. The study evaluated 41 batches of the Hib-TT vaccines manufactured between 1994 and 2003, assaying potency (total PRP saccharide content), integrity (% free saccharide), consistency (molecular sizing), and immunogenicity, as well as reviewing data previously obtained at the time of release. The study indicated the stability of the lyophilized final fill vaccines to extend well past their assigned shelf-lives, and found no trends in the endotoxin content, total saccharide or % free saccharide content. A trend towards slightly larger conjugates was observed over time in Hib-TT A, evidenced in both the manufacturer’s data obtained at the time that samples were submitted for testing and in data obtained from the retrospective analysis. The study confirmed that that there had been no significant change in the quality of the Hib vaccines that could possibly account for the change reported in their protective efficacy in the U.K. The study also demonstrated the value of independent testing of vaccines from the time of licensure and in the ongoing monitoring and re-examination of selected batches, as necessary, to assure their continuing quality, safety and consistency.