Preparation of pneumococcal capsular polysaccharide-protein conjugate vaccines utilizing new fragmentation and conjugation technologies

Impact and Control of Sugar Size in Glycoconjugate Vaccines

Glycoconjugate vaccines have contributed enormously to reducing and controlling encapsulated bacterial infections for over thirty years. Glycoconjugate vaccines are based on a carbohydrate antigen that is covalently linked to a carrier protein; this is necessary to cause T cell responses for optimal immunogenicity, and to protect young children. Many interdependent parameters affect the immunogenicity of glycoconjugate vaccines, including the size of the saccharide antigen. Here, we examine and discuss the impact of glycan chain length on the efficacy of glycoconjugate vaccines and report the methods employed to size polysaccharide antigens, while highlighting the underlying reaction mechanisms. A better understanding of the impact of key parameters on the immunogenicity of glycoconjugates is critical to developing a new generation of highly effective vaccines.

A semisynthetic glycoconjugate provides expanded cross-serotype protection against Streptococcus pneumoniae

Streptococcus pneumoniae (S. pneumoniae)infections are the leading cause of child mortality globally. Currentvaccines fail to induceaprotective immune response towards a conserved part of the pathogen,resulting in newserotypescausing disease. Therefore, new vaccinestrategies are urgently needed.Described is atwo-pronged approach combiningS. pneumoniaeproteins, pneumolysin (Ply) and pneumococcal surface protein A (PspA),with aprecisely defined synthetic oligosaccharide,wherebythe carrier protein actsas a serotype-independent antigen to provideadditional protection. Proof of concept in mice and swine modelsrevealed thatthe conjugatesinhibited colonization of the nasopharynx, decreased the bacterial load and reduced disease severity in the bacteria challenge model. Immunization of piglets provided the first evidence for the immunogenicity and protective potential of synthetic glycoconjugate vaccine in a large animal model.Acombination of synthetic oligosaccharides with proteins from the target pathogen opens the path to create broadly cross-protective ("universal") pneumococcal vaccines.

Comparative Study of Immunogenic Properties of Purified Capsular Polysaccharides from Streptococcus suis Serotypes 3, 7, 8, and 9: the Serotype 3 Polysaccharide Induces an Opsonizing IgG Response

Streptococcus suis is an encapsulated bacterium and one of the most important swine pathogens and a zoonotic agent for which no effective vaccine exists. Bacterial capsular polysaccharides (CPSs) are poorly immunogenic, but anti-CPS antibodies are essential to the host defense against encapsulated bacteria. In addition to the previously known serotypes 2 and 14, which are nonimmunogenic, we have recently purified and described the CPS structures for serotypes 1, 1/2, 3, 7, 8, and 9.

Streptococcus suis is an encapsulated bacterium and one of the most important swine pathogens and a zoonotic agent for which no effective vaccine exists. Bacterial capsular polysaccharides (CPSs) are poorly immunogenic, but anti-CPS antibodies are essential to the host defense against encapsulated bacteria. In addition to the previously known serotypes 2 and 14, which are nonimmunogenic, we have recently purified and described the CPS structures for serotypes 1, 1/2, 3, 7, 8, and 9. Here, we aimed to elucidate how these new structurally diverse CPSs interact with the immune system to generate anti-CPS antibody responses. CPS-stimulated dendritic cells produced significant levels of C–C motif chemokine ligand 3 (CCL3), partially via Toll-like receptor 2 (TLR2)- and myeloid differentiation factor 88-dependent pathways, and CCL2, via TLR-independent mechanisms. Mice immunized with purified serotype 3 CPS adjuvanted with TiterMax Gold produced an opsonizing IgG response, whereas other CPSs or adjuvants were negative. Mice hyperimmunized with heat-killed S. suis serotypes 3 and 9 both produced anti-CPS type 1 IgGs, whereas serotypes 7 and 8 remained negative. Also, mice infected with sublethal doses of S. suis serotype 3 produced primary anti-CPS IgM and IgG responses, of which only IgM were boosted after a secondary infection. In contrast, mice sublethally infected with S. suis serotype 9 produced weak anti-CPS IgM and IgG responses following a secondary infection. This study provides important information on the divergent evolution of CPS serotypes with highly different structural and/or biochemical properties within S. suis and their interaction with the immune system.

Elicitation of integrated immunity in mice by a novel pneumococcal polysaccharide vaccine conjugated with HBV surface antigen

The conjugation of polysaccharides with an effective carrier protein is critical for the development of effective bacterial polysaccharide vaccines. Therefore, the identification and optimization of carrier proteins to induce an effective immune response is necessary for developing a combined vaccine. In the current study, we utilized hepatitis B virus surface antigen (HBsAg) as a novel carrier protein combined with a capsular polysaccharide molecule to develop a new pneumococcal conjugated vaccine. The specific antibodies and T cell immune response against the capsular polysaccharide and HBsAg in the mice immunized with this conjugated vaccine were evaluated. In addition, the unique gene profiles of immune cells induced by this conjugated vaccine in the immunized mice were analyzed. Our results demonstrated that the vaccine consisting of pneumonia type 33 F capsular polysaccharide (Pn33Fps) conjugated with HBsAg can induce strong specific immune responses against both antigens in vivo in immunized mice. Furthermore, the conjugated vaccine induced higher expression of genes related to the activation of immunity and higher antibody titers against Pn33Fps and HBsAg in mice than those obtained via vaccination with a single antigen. Analyses of the dynamic expression changes in immunity-related genes in mice immunized with Pn33Fps_HBs, Pn33Fps, or HBsAg indicated the potent immunogenicity of the conjugated vaccine. In addition, a pathological evaluation of the organs from immunized mice further suggested that the conjugated vaccine is safe. Together, these results indicate that a conjugated vaccine consisting of Pn33Fps with HBsAg is a novel and effective vaccine.

Why might regional vaccinology networks fail? The case of the Dutch-Nordic Consortium

We analyzed an attempt to develop and clinically test a pneumococcal conjugate vaccine for the developing world, undertaken by public health institutions from the Netherlands, Sweden, Denmark, Norway and Finland: the Dutch Nordic Consortium (DNC), between 1990 and 2000. Our review shows that the premature termination of the project was due less to technological and scientific challenges and more to managerial challenges and institutional policies. Various impeding events, financial and managerial challenges gradually soured the initially enthusiastic collaborative spirit until near the end the consortium struggled to complete the minimum objectives of the project. By the end of 1998, a tetravalent prototype vaccine had been made that proved safe and immunogenic in Phase 1 trials in adults and toddlers in Finland. The planned next step, to test the vaccine in Asia in infants, did not meet approval by the local authorities in Vietnam nor later in the Philippines and the project eventually stopped.

The Dutch DNC member, the National Institute of Public Health and the Environment (RIVM) learned important lessons, which subsequently were applied in a following vaccine technology transfer project, resulting in the availability at affordable prices for the developing world of a conjugate vaccine against Haemophilus influenzae type b. We conclude that vaccine development in the public domain with technology transfer as its ultimate aim requires major front-end funding, committed leadership at the highest institutional level sustained for many years and a competent recipient-manufacturer, which needs to be involved at a very early stage of the development.

At the national level, RIVM’s policy to consolidate its national manufacturing task through securing a key global health position in support of a network of public vaccine manufacturers proved insufficiently supported by the relevant ministries of the Dutch government. Difficulties to keep up with high costs, high-risk innovative vaccine development and production in a public sector setting led to the gradual loss of production tasks and to the 2009 Government decision to privatize the vaccine production tasks of the Institute.

Characterization and immunogenicity of meningococcal group C conjugate vaccine prepared using hydrazide-activated tetanus toxoid

The steps to produce, purify and control an immunogenic Brazilian conjugate vaccine against group C meningococcus (MenCPS-TT) using hydrazide-activated tetanus toxoid were developed. The conjugation methodology reduced the reaction time easily allowing scale-up. One freeze-dried pilot vaccine lot purified by tangential filtration, showed satisfactory quality control results including safety and stability. The pilot vaccine was immunogenic in mice in a dose-dependent fashion generating a 10-20-fold rise in IgG response in mice. The vaccine also induced high bactericidal titers. Vaccine concentrations of 1 and 0.1 microg showed higher avidity indices, suggesting induction of immunologic memory. These results support initiation of Phase I clinical studies with the MenCPS-TT conjugate vaccine.

Versatile and efficient synthesis of protein–polysaccharide conjugate vaccines using aminooxy reagents and oxime chemistry

Applications of oxime chemistry are described for the efficient bioconjugation of proteins and polysaccharides for the preparation of conjugate vaccines. A number of approaches are described in this manuscript to functionalize proteins and polysaccharides with aminooxy (AO) groups and aldehydes which could then be covalently linked to each other via oxime formation, without the need for reduction. By using limiting numbers of active groups on each component, the extent of inter- and intramolecular crosslinking could be controlled. The approaches described are compatible and complementary to a number of chemistries currently used in conjugate vaccine synthesis. Oxime chemistry can be used to both simplify the synthesis of and increase yields of conjugate vaccines. Mice immunized with pneumococcal type 14 conjugates that were made using oxime chemistry mounted significant anti-polysaccharide immune responses. The primary immune response could be boosted, indicating that the polysaccharide conjugate had characteristics of a T cell dependent antigen.

Immunogenicity and Protective Efficacy of Bacillus anthracis Poly-γ-d-glutamic Acid Capsule Covalently Coupled to a Protein Carrier Using a Novel Triazine-based Conjugation Strategy

The capsular polypeptide of Bacillus anthracis is composed of a unique polyglutamic acid polymer in which D-glutamate monomers are joined by gamma-peptidyl bonds. The capsule is poorly immunogenic, and efforts at exploiting the polymer for vaccine development have focused on increasing its inherent immunogenicity through chemical coupling to immune-stimulating protein carriers. The usual strategy has employed carbodiimide-based condensing reagents for activation of free alpha-carboxyl groups, despite reports that this chemistry may lead to chain scission. We have purified the high molecular mass capsule to >95% homogeneity and have demonstrated that the polymer contains >99% poly-gamma-D-glutamic acid. The predominant structure of the polymer as assessed by circular dichroism and multiangle laser light scattering was unordered at near-neutral pH. We investigated the effects of various activation chemistries, and we demonstrated that carbodiimide treatment under aqueous conditions results in significant cleavage of the gamma-peptidyl bond, whereas scission is significantly reduced in nonaqueous polar solvents, although undesired side chain modification was still observed. An activation chemistry was developed using the triazine-based reagent 4-(4,6-dimethoxy (1,3,5)triazin-2-yl)-4-methylmorpholinium chloride, which allowed for controlled and reproducible derivatization of alpha-carbonyls. In a two-pot reaction scheme, activated capsule was derivatized with a sulfhydryl-reactive heterobifunctional moiety and was subsequently coupled to thiolated carrier protein. This conjugate elicited very high capsule-specific immune titers in mice. More importantly, mice immunized with conjugated capsule exhibited good protection against lethal challenge from a virulent B. anthracis strain in two models of infection. We also showed, for the first time, that treatment of capsule with carbodiimide significantly reduced recognition by capsule-specific antisera concurrent with the reagent-induced reduction of polymer mass. The data suggested that for vaccine development, maintenance of the high mass of the polymer may be important.

Development of experimental carbohydrate-conjugate vaccines composed of Streptococcus pneumoniae capsular polysaccharides and the universal helper T-lymphocyte epitope (PADRE®)

Experimental carbohydrate-conjugate vaccines composed of the 13 amino acid universal Pan HLA-DR Epitope (PADRE) and Streptococcus pneumoniae capsular polysaccharides from serotypes 14, 6B and 9V were produced. Simple carbodiimide-mediated condensation chemistry was used to conjugate the PADRE synthetic peptide to the three chemically different capsular polysaccharides in a 1:1 molar ratio. The immunogenicity of the PADRE peptide component of the conjugate vaccines was confirmed by the induction of PADRE-specific CD4+ helper T cell (HTL) responses following immunization of C57BL/6 mice. High titer antibody responses specific for polysaccharides of S. pneumoniae serotypes 14, 6B and 9V were induced using Complete Freund's Adjuvant (CFA) and alhydrogel Al(OH)3 formulations. The HTL, or carrier, effect of the PADRE synthetic peptide was only evident using the PADRE-polysaccharide conjugates; simple mixtures of the PADRE peptide and polysaccharides were essentially nonimmunogenic. The functional or potential protective value of the polysaccharide-specific antibodies was measured as a function of opsonophagocytic activity for the 6B serotype. High titers of opsonophagocytic activity were measured in sera from mice immunized with formulations containing both adjuvants. These data demonstrate that the PADRE synthetic peptide can induce the HTL responses needed to support the development of antibodies specific for bacterial carbohydrates used in conjugate vaccines.

Recent advances in the development of peptide vaccines for hepatitis B

The control of hepatitis B by vaccination is arguably one of medicine's greatest achievements in terms of protecting infants and adults at high risk of infection. Paradoxically, however, the existence of a large reservoir of chronically infected individuals will not diminish the risk of infection by those coming into close contact with such persons until universal infant immunisation is practised globally and vaccines are in place to ensure maximum efficacy in those with impaired immune responses, immunity is achieved with fewer doses, and immunisation as an adjunct to the antiviral treatment of chronic carriers is adopted. These imperatives have continued to stimulate research into vaccines based on chemically synthesised short peptides, and those systems best suited for their delivery. This review discusses the potential of synthetic peptide formulations as efficient inducers of both humoral and cellular immune responses against hepatitis B, and reviews recent advances in peptide delivery. Synthetic peptide and delivery systems technologies will, amongst others, be of paramount importance in the global fight for the eradication of hepatitis B in the 21st century.

The adjuvant effect of synthetic oligodeoxynucleotide containing CpG motif converts the anti-Haemophilus influenzae type b glycoconjugates into efficient anti-polysaccharide and anti-carrier polyvalent vaccines

Synthetic oligodeoxynucleotides containing CpG immunostimulatory sequences (ISS) have been shown to act as potent adjuvants of type 1 immune responses when co-administered with protein or peptide vaccines. We have recently shown that ISS can increase the anti-polysaccharide (CHO) and anti-tetanus toxoid (TT) or anti-diphtheria (CRM) toxoid antibody levels if used as adjuvant of anti-Haemophilus influenzae type b (Hib) CHO vaccine conjugated with TT or CRM. The analysis of anti-TT and anti-CRM IgG subclasses showed a significant increase in IgG2a, IgG2b and/or IgG3 in the presence of ISS. Anti-TT and anti-CRM antibodies were shown to neutralize the activity of both the tetanus and diphtheria toxin in vivo or in vitro tests respectively. These data show that ISS have the potential to increase host antibody response against both the CHO and the protein component of a conjugated vaccine, and encourage the investigation to identify strategies of vaccination with schedules aimed at the valuation of protein carriers as protective immunogens.