Haemophilus influenzae type b conjugate vaccines

A modular synthetic route to size-defined immunogenic Haemophilus influenzae b antigens is key to the identification of an octasaccharide lead vaccine candidate

A Haemophilus influenzae b vaccine lead antigen was identified by the immunological evaluation of chemically precisely defined capsular polysaccharide repeating unit oligosaccharides.

The first glycoconjugate vaccine using isolated glycans was licensed to protect children from Haemophilus influenzae serotype b (Hib) infections. Subsequently, the first semisynthetic glycoconjugate vaccine using a mixture of antigens derived by polymerization targeted the same pathogen. Still, a detailed understanding concerning the correlation between oligosaccharide chain length and the immune response towards the polyribosyl-ribitol-phosphate (PRP) capsular polysaccharide that surrounds Hib remains elusive. The design of semisynthetic and synthetic Hib vaccines critically depends on the identification of the minimally protective epitope. Here, we demonstrate that an octasaccharide antigen containing four repeating disaccharide units resembles PRP polysaccharide in terms of immunogenicity and recognition by anti-Hib antibodies. Key to this discovery was the development of a modular synthesis that enabled access to oligosaccharides up to decamers. Glycan arrays containing the synthetic oligosaccharides were used to analyze anti-PRP sera for antibodies. Conjugates of the synthetic antigens and the carrier protein CRM197, which is used in licensed vaccines, were employed in immunization studies in rabbits.

Vaccine instability in the cold chain: mechanisms, analysis and formulation strategies

Instability of vaccines often emerges as a key challenge during clinical development (lab to clinic) as well as commercial distribution (factory to patient). To yield stable, efficacious vaccine dosage forms for human use, successful formulation strategies must address a combination of interrelated topics including stabilization of antigens, selection of appropriate adjuvants, and development of stability-indicating analytical methods. This review covers key concepts in understanding the causes and mechanisms of vaccine instability including (1) the complex and delicate nature of antigen structures (e.g., viruses, proteins, carbohydrates, protein-carbohydrate conjugates, etc.), (2) use of adjuvants to further enhance immune responses, (3) development of physicochemical and biological assays to assess vaccine integrity and potency, and (4) stabilization strategies to protect vaccine antigens and adjuvants (and their interactions) during storage. Despite these challenges, vaccines can usually be sufficiently stabilized for use as medicines through a combination of formulation approaches combined with maintenance of an efficient cold chain (manufacturing, distribution, storage and administration). Several illustrative case studies are described regarding mechanisms of vaccine instability along with formulation approaches for stabilization within the vaccine cold chain. These include live, attenuated (measles, polio) and inactivated (influenza, polio) viral vaccines as well as recombinant protein (hepatitis B) vaccines.

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.

Universal influenza B vaccine based on the maturational cleavage site of the hemagglutinin precursor

Conventional influenza vaccines can prevent infection, but their efficacy depends on the degree of antigenic "match" between the strains used for vaccine preparation and those circulating in the population. A universal influenza vaccine based on invariant regions of the virus, able to provide broadly cross-reactive protection, without requiring continuous manufacturing update, would solve a major medical need. Since the temporal and geographical dominance of the influenza virus type and/or subtype (A/H3, A/H1, or B) cannot yet be predicted, a universal vaccine, like the vaccines currently in use, should include both type A and type B influenza virus components. However, while encouraging preclinical data are available for influenza A virus, no candidate universal vaccine is available for influenza B virus. We show here that a peptide conjugate vaccine, based on the highly conserved maturational cleavage site of the HA(0) precursor of the influenza B virus hemagglutinin, can elicit a protective immune response against lethal challenge with viruses belonging to either one of the representative, non-antigenically cross-reactive influenza B virus lineages. We demonstrate that protection by the HA(0) vaccine is mediated by antibodies, probably through effector mechanisms, and that a major part of the protective response targets the most conserved region of HA(0), the P1 residue of the scissile bond and the fusion peptide domain. In addition, we present preliminary evidence that the approach can be extended to influenza A virus, although the equivalent HA(0) conjugate is not as efficacious as for influenza B virus.

Anthrax vaccine design: strategies to achieve comprehensive protection against spore, bacillus, and toxin

The successful use of Bacillus anthracis as a lethal biological weapon has prompted renewed research interest in the development of more effective vaccines against anthrax. The disease consists of three critical components: spore, bacillus, and toxin, elimination of any of which confers at least partial protection against anthrax. Current remedies rely on postexposure antibiotics to eliminate bacilli and pre- and postexposure vaccination to target primarily toxins. Vaccines effective against toxin have been licensed for human use, but need improvement. Vaccines against bacilli have recently been developed by us and others. Whether effective vaccines will be developed against spores is still an open question. An ideal vaccine would confer simultaneous protection against spores, bacilli, and toxins. One step towards this goal is our dually active vaccine, designed to destroy both bacilli and toxin. Existing and potential strategies towards potent and effective anthrax vaccines are discussed in this review.

Preclinical study of influenza virus A M2 peptide conjugate vaccines in mice, ferrets, and rhesus monkeys

A universal influenza virus vaccine that does not require frequent updates and/or annual immunizations will offer significant advantages over current seasonal flu vaccines. The highly conserved influenza virus A M2 membrane protein has been previously suggested as a potential antigen target for such a vaccine. Here, we report systematic evaluation of M2 peptide conjugate vaccines (synthetic peptides of M2 extracellular domain conjugated to keyhole limpet hemocyanin (KLH) or Neisseria meningitidis outer membrane protein complex (OMPC)) in mice, ferrets, and rhesus monkeys. The conjugate vaccines were highly immunogenic in all species tested and were able to confer both protection against lethal challenge of either H1N1 or H3N1 virus in mice and reduce viral shedding in the lower respiratory tracts of mice and ferrets. The protection against lethal challenge in mice could also be achieved by passive transfer of monkey sera containing high M2 antibody titers. In addition, we showed that M2 antisera were cross reactive with M2 peptides derived from a wide range of human influenza A strains, but they failed to react with M2 peptides of the pathogenic H5N1 virus (A/Hong Kong/97). The data presented here will permit better understanding of the potential of an M2-based vaccine approach.

Cocaine pharmacology and current pharmacotherapies for its abuse

Cocaine abuse continues to be prevalent and effective therapies for cocaine craving and addiction remain elusive. In the last decade immunopharmacotherapy has been proposed as a promising means to alleviate this illness. By using the organism's natural immune response, an anti-cocaine vaccine promotes the production of cocaine-specific antibodies that sequester the drug before their passage into the brain, where it exerts its reinforcing and thus addictive effects. A series of studies demonstrating the cocaine-blocking properties of various immunogenic conjugates will be reviewed in the context of the neuropsychopharmacological profile of the drug.

Emergence of drug resistance. Impact on bacterial meningitis

Antimicrobial resistance has emerged among the three major bacterial pathogens causing meningitis. Chloramphenicol resistance in the meningococcus recently has been described, and although intermediate penicillin resistance is common in some countries, the clinical importance of penicillin resistance in the meningococcus has yet to be established. Beta-lactamase-producing Haemophilus influenzae are relatively common, and chloramphenicol resistance is emerging. Third-generation cephalosporins are required to treat meningitis caused by these resistant strains. Pneumococcus resistance to penicillin and to chloramphenicol is widespread, and resistance to third-generation cephalosporins is found in many parts of the world. Correct management of these strains includes the addition of vancomycin or rifampin to therapy with third-generation cephalosporins.

New technologies for making vaccines

Technologies for making active vaccines fall into 3 general groups: live, subunit (killed or inactivated) and genetic. Each of these groups is further divisible into multiple categories, which include recombinant-derived antigens as well as native microorganisms and their components. In addition, there are new enabling technologies such as delivery systems and vectors which can be applied to these approaches. Most disease targets, whether infectious or noninfectious in origin, can be approached by the application of several different vaccine technologies, as can be tested during the discovery phase of research. The criteria for choosing early in a development program which of the vaccine technologies are likely to ultimately be most fruitful for a given application include: knowledge of the pathogenesis of the given infection/disease; technical feasibility; immunobiology and associated mechanisms; preclinical efficacy profile; anticipated clinical safety; regulatory; manufacturing; and marketing. All of these criteria should be considered together in making selections for an R&D program. This paper is reviewing the major vaccine technologies and relevant examples of how these criteria are used to make decisions in vaccine development.

Haemophilus influenzae type b conjugate vaccine stability: catalytic depolymerization of PRP in the presence of aluminum hydroxide

The structural stability of the Haemophilus influenzae type b (Hib) capsular polysaccharide, polyribosylribitolphosphate (PRP) in an aluminum hydroxide adsorbed, polysaccharide-protein conjugate vaccine was monitored using modifications of an HPLC assay developed by Tsai et al. [Tsai C-M, Gu X-X, Byrd RA. Quantification of polysaccharide in Haemophilus influenzae type b conjugate and polysaccharide vaccines by high-performance anion-exchange chromatography with pulsed amperometric detection. Vaccine 1993;12:700-706.]. As applied to products containing PRP conjugated to the outer membrane protein complex (OMPC) from Neisseria meningitidis, this assay allows direct measurement of the total PRP content in very complex samples including commercial vaccine products. In addition, with the use of a high-speed centrifugation step, the assay can be used to directly quantify any PRP that is not conjugated to the OMPC carrier protein. These results provide evidence of what appears to be a catalytic reaction taking place between the phosphodiester bond of PRP and the aluminum hydroxide adjuvant that results in hydrolysis of the PRP polymer into smaller chain lengths and liberation of PRP oligomers from the conjugate particle. The reaction approaches an asymptotic limit after approximately two years at 2-8 degrees C. Clinical studies which span this time period confirm that the modest decrease in conjugated PRP content over time does not impact the overall clinical effectiveness of PRP-OMPC-containing vaccines.

Development of a therapeutic vaccine for the treatment of cocaine addiction

No pharmacotherapies have yet been approved for the treatment of cocaine addiction. One new approach is to block the effects of cocaine with anti-cocaine antibodies induced by a therapeutic cocaine vaccine. A cocaine vaccine has been developed which induces a cocaine-specific antibody response in rodents. The antibody binds to cocaine in the circulation and can be shown to inhibit the ability of cocaine to enter the brain. Furthermore, anti-cocaine antibody can inhibit cocaine self-administration in rats. These data suggest that a cocaine vaccine may be a powerful therapeutic tool. The intent is to immunized motivated patients with the vaccine as part of a comprehensive treatment program. If the patient uses cocaine after being vaccinated, the antibody will inhibit the reinforcing activity of cocaine and decrease the likelihood of relapse.

Clinical immunology

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