Diane Williamson

Vaccine delivery using nanoparticles

Vaccination has had a major impact on the control of infectious diseases. However, there are still many infectious diseases for which the development of an effective vaccine has been elusive. In many cases the failure to devise vaccines is a consequence of the inability of vaccine candidates to evoke appropriate immune responses. This is especially true where cellular immunity is required for protective immunity and this problem is compounded by the move toward devising sub-unit vaccines. Over the past decade nanoscale size (<1000 nm) materials such as virus-like particles, liposomes, ISCOMs, polymeric, and non-degradable nanospheres have received attention as potential delivery vehicles for vaccine antigens which can both stabilize vaccine antigens and act as adjuvants. Importantly, some of these nanoparticles (NPs) are able to enter antigen-presenting cells by different pathways, thereby modulating the immune response to the antigen. This may be critical for the induction of protective Th1-type immune responses to intracellular pathogens. Their properties also make them suitable for the delivery of antigens at mucosal surfaces and for intradermal administration. In this review we compare the utilities of different NP systems for the delivery of sub-unit vaccines and evaluate the potential of these delivery systems for the development of new vaccines against a range of pathogens.

Potential of the β-glucans to enhance innate resistance to biological agents

The use of numerous mushroom species in traditional medicine has been widely documented, with their observed immunomodulatory effects now attributed, in part, to bioactive components called β-glucans. The β-glucans are of particular interest since they are naturally occurring polymers of glucose, are orally active when taken as food supplements and have a long track record of safe use. Due to their immunomodulatory properties, purified β-glucans have been used clinically as part of a combination therapy for a variety of cancers and their potential anti-infective properties have received attention. This review relates the structure of β-glucans to their function, with a particular focus on their documented immunomodulatory effects and the mechanisms by which they affect inter- and intracellular function, resulting in potential antimicrobial benefits. Overall, the benefits of dietary supplementation with β-glucans in order to enhance innate resistance to biological agents are evaluated.

Exploitation of bacterial N-linked glycosylation to develop a novel recombinant glycoconjugate vaccine against Francisella tularensis.

Glycoconjugate-based vaccines have proved to be effective at producing long-lasting protection against numerous pathogens. Here, we describe the application of bacterial protein glycan coupling technology (PGCT) to generate a novel recombinant glycoconjugate vaccine. We demonstrate the conjugation of the Francisella tularensis O-antigen to the Pseudomonas aeruginosa carrier protein exotoxin A using the Campylobacter jejuni PglB oligosaccharyltransferase. The resultant recombinant F. tularensis glycoconjugate vaccine is expressed in Escherichia coli where yields of 3 mg l−1 of culture were routinely produced in a single-step purification process. Vaccination of BALB/c mice with the purified glycoconjugate boosted IgG levels and significantly increased the time to death upon subsequent challenge with F. tularensis subsp. holarctica. PGCT allows different polysaccharide and protein combinations to be produced recombinantly and could be easily applicable for the production of diverse glycoconjugate vaccines.

Characterisation of the immune response to the UK human anthrax vaccine

The UK human anthrax vaccine consists of the alum-precipitated culture supernatant of Bacillus anthracis Sterne. In addition to protective antigen (PA), the key immunogen, the vaccine also contains a number of other bacteria- and media-derived proteins. These proteins may contribute to the transient side effects experienced by some individuals and could influence the development of the PA-specific immune response. Bacterial cell-wall components have been shown to be potent immunomodulators. B. anthracis expresses two S-layer proteins, EA1 and Sap, which have been demonstrated to be immunogenic in animal studies. These are also immunogenic in man so that convalescent and post-immunisation sera contain specific antibodies to Ea1, and to a lesser extent, to Sap. To determine if these proteins are capable of modifying the protective immune response to PA, A/J mice were immunised with equivalent amounts of recombinant PA and S-layer proteins in the presence of alhydrogel. IgG isotype profiles were determined and the animals were subsequently challenged with spores of B. anthracis STI. The results suggest that there was no significant shift in IgG isotype profile and that the presence of the S-layer proteins did not adversely affect the protective immune response induced by PA.

Specific Activation of Dendritic Cells Enhances Clearance of Bacillus anthracis following Infection

Dendritic cells are potent activators of the immune system and have a key role in linking innate and adaptive immune responses. In the current study we have used ex vivo pulsed bone marrow dendritic cells (BMDC) in a novel adoptive transfer strategy to protect against challenge with Bacillus anthracis, in a murine model. Pre-pulsing murine BMDC with either recombinant Protective Antigen (PA) or CpG significantly upregulated expression of the activation markers CD40, CD80, CD86 and MHC-II. Passive transfusion of mice with pulsed BMDC, concurrently with active immunisation with rPA in alum, significantly enhanced (p<0.001) PA-specific splenocyte responses seven days post-immunisation. Parallel studies using ex vivo DCs expanded from human peripheral blood and activated under the same conditions as the murine DC, demonstrated that human DCs had a PA dose-related significant increase in the markers CD40, CD80 and CCR7 and that the increases in CD40 and CD80 were maintained when the other activating components, CpG and HK B. anthracis were added to the rPA in culture. Mice vaccinated on a single occasion intra-muscularly with rPA and alum and concurrently transfused intra-dermally with pulsed BMDC, demonstrated 100% survival following lethal B. anthracis challenge and had significantly enhanced (p<0.05) bacterial clearance within 2 days, compared with mice vaccinated with rPA and alum alone.

Natural cutaneous anthrax infection, but not vaccination, induces a CD4+ T cell response involving diverse cytokines

BackgroundWhilst there have been a number of insights into the subsets of CD4+ T cells induced by pathogenic Bacillus anthracis infections in animal models, how these findings relate to responses generated in naturally infected and vaccinated humans has yet to be fully established. We describe the cytokine profile produced in response to T cell stimulation with a previously defined immunodominant antigen of anthrax, lethal factor (LF), domain IV, in cohorts of individuals with a history of cutaneous anthrax, compared with vaccinees receiving the U.K. licenced Anthrax Vaccine Precipitated (AVP) vaccine.FindingsWe found that immunity following natural cutaneous infection was significantly different from that seen after vaccination. AVP vaccination was found to result in a polarized IFNγ CD4+ T cell response, while the individuals exposed to B. anthracis by natural infection mounted a broader cytokine response encompassing IFNγ, IL-5, −9, −10, −13, −17, and −22.ConclusionsVaccines seeking to incorporate the robust, long-lasting, CD4 T cell immune responses observed in naturally acquired cutaneous anthrax cases may need to elicit a similarly broad spectrum cellular immune response.

Plague: Infections of Companion Animals and Opportunities for Intervention.

Plague is a zoonotic disease, normally circulating in rodent populations, transmitted to humans most commonly through the bite of an infected flea vector. Secondary infection of the lungs results in generation of infectious aerosols, which pose a significant hazard to close contacts. In enzootic areas, plague infections have been reported in owners and veterinarians who come into contact with infected pets. Dogs are relatively resistant, but can import infected fleas into the home. Cats are acutely susceptible, and can present a direct hazard to health. Reducing roaming and hunting behaviours, combined with flea control measures go some way to reducing the risk to humans. Various vaccine formulations have been developed which may be suitable to protect companion animals from contracting plague, and thus preventing onward transmission to man. Since transmission has resulted in a number of fatal cases of plague, the vaccination of domestic animals such as cats would seem a low cost strategy for reducing the risk of infection by this serious disease in enzootic regions.