Protection against plague following immunisation with microencapsulated V antigen is reduced by co-encapsulation with IFN-gamma or IL-4, but not IL-6

Technological Approaches for Improving Vaccination Compliance and Coverage

Vaccination has been well recognised as a critically important tool in preventing infectious disease, yet incomplete immunisation coverage remains a major obstacle to achieving disease control and eradication. As medical products for global access, vaccines need to be safe, effective and inexpensive. In line with these goals, continuous improvements of vaccine delivery strategies are necessary to achieve the full potential of immunisation. Novel technologies related to vaccine delivery and route of administration, use of advanced adjuvants and controlled antigen release (single-dose immunisation) approaches are expected to contribute to improved coverage and patient compliance. This review discusses the application of micro- and nano-technologies in the alternative routes of vaccine administration (mucosal and cutaneous vaccination), oral vaccine delivery as well as vaccine encapsulation with the aim of controlled antigen release for single-dose vaccination.

Innate endogenous adjuvants prime to desirable immune responses via mucosal routes

Vaccination is an effective strategy to prevent infectious or immune related diseases, which has made remarkable contribution in human history. Recently increasing attentions have been paid to mucosal vaccination due to its multiple advantages over conventional ways. Subunit or peptide antigens are more reasonable immunogens for mucosal vaccination than live or attenuated pathogens, however adjuvants are required to augment the immune responses. Many mucosal adjuvants have been developed to prime desirable immune responses to different etiologies. Compared with pathogen derived adjuvants, innate endogenous molecules incorporated into mucosal vaccines demonstrate prominent adjuvanticity and safety. Nowadays, cytokines are broadly used as mucosal adjuvants for participation of signal transduction of immune responses, activation of innate immunity and polarization of adaptive immunity. Desired immune responses are promptly and efficaciously primed on basis of specific interactions between cytokines and corresponding receptors. In addition, some other innate molecules are also identified as potent mucosal adjuvants. This review focuses on innate endogenous mucosal adjuvants, hoping to shed light on the development of mucosal vaccines.

Particle-mediated delivery of cytokines for immunotherapy

The ability of cytokines to direct the immune response to vaccination, infection and tumors has motivated their use in therapy to augment or shape immunity. To avoid toxic side effects associated with systemic cytokine administration, several approaches have been developed using particle-encapsulated cytokines to deliver this cargo to specific cell types and tissues. Initial work used cytokine-loaded particles to deliver proinflammatory cytokines to phagocytes to enhance antimicrobial and antitumor responses. These particles have also been used to create a cytokine depot at a local site to supplement prophylactic or antitumor vaccines or injected directly into solid tumors to activate immune cells to eliminate established tumors. Finally, recent advances have revealed that paracrine delivery of cytokines directly to T cells has the potential to enhance T-cell mediated therapies. The studies reviewed here highlight the progress in the last 30 years that has established the potential of particle-mediated cytokine immunotherapy.

Cytokines: the future of intranasal vaccine adjuvants

Due to its potential as an effective, needle-free route of immunization for use with subunit vaccines, nasal immunization continues to be evaluated as a route of immunization in both research and clinical studies. However, as with other vaccination routes, subunit vaccines often require the addition of adjuvants to induce potent immune responses. Unfortunately, many commonly used experimental vaccine adjuvants, such as cholera toxin and E. coli heat-labile toxin, are too toxic for use in humans. Because new adjuvants are needed, cytokines have been evaluated for their ability to provide effective adjuvant activity when delivered by the nasal route in both animal models and in limited human studies. It is the purpose of this paper to discuss the potential of cytokines as nasal vaccine adjuvants.

Prospects for new plague vaccines

The potential application of Yersinia pestis for bioterrorism emphasizes the urgent need to develop more effective vaccines against airborne infection. The current status of plague vaccines has been reviewed. The present emphasis is on subunit vaccines based on the F1 and LcrV antigens. These provide good protection in animal models but may not protect against F1 strains with modifications to the type III secretion system. The duration of protection against pneumonic infection is also uncertain. Other strategies under investigation include defined live-attenuated vaccines, DNA vaccines, mucosal delivery systems and heterologous immunization. The live-attenuated strain Y. pestis EV NIIEG protects against aerosol challenge in animal models and, with further modification to reduce residual virulence and to optimize respiratory protection, it could provide a shortcut to improved vaccines. The regulatory problems inherent in licensing vaccines for which efficacy data are unavailable and their possible solutions are discussed herein.

Vaccine adjuvants: current challenges and future approaches

For humans, companion animals, and food producing animals, vaccination has been touted as the most successful medical intervention for the prevention of disease in the twentieth century. However, vaccination is not without problems. With the development of new and less reactogenic vaccine antigens, which take advantage of molecular recombinant technologies, also comes the need for more effective adjuvants that will facilitate the induction of adaptive immune responses. Furthermore, current vaccine adjuvants are successful at generating humoral or antibody mediated protection but many diseases currently plaguing humans and animals, such as tuberculosis and malaria, require cell mediated immunity for adequate protection. A comprehensive discussion is presented of current vaccine adjuvants, their effects on the induction of immune responses, and vaccine adjuvants that have shown promise in recent literature.

Particulate delivery systems for vaccines: what can we expect?

In our attempts to thwart the unwanted attentions of microbes by prophylactic and therapeutic vaccination, the knowledge of interactions at the molecular level may prove to be an invaluable asset. This article examines how particulate delivery systems such as liposomes and polymer microspheres can be applied in the light of recent advances in immunological understanding. Some of the biological interactions of these delivery systems are discussed with relevance for antigen trafficking and molecular pathways of immunogenicity and emphasis on the possible interaction of liposomal components. In particular, traditional concepts such as antigen protection, delivery to antigen presenting cells and depot formation remain important aspects, whilst the inclusion of selected co-adjuvants and enhanced delivery of these moieties in conjunction with antigen now has a firm rationale.

Protection against bubonic and pneumonic plague with a single dose microencapsulated sub-unit vaccine

Protection against virulent plague challenge by the parenteral and aerosol routes was afforded by a single administration of microencapsulated Caf1 and LcrV antigens from Yersinia pestis in BALB/c mice. Recombinant Caf1 and LcrV were individually encapsulated in polymeric microspheres, to the surface of which additional antigen was adsorbed. The microspheres containing either Caf1 or LcrV were blended and used to immunise mice on a single occasion, by either the intra-nasal or intra-muscular route. Both routes of immunisation induced systemic and local immune responses, with high levels of serum IgG being developed in response to both vaccine antigens. In Elispot assays, secretion of cytokines by spleen and draining lymph node cells was demonstrated, revealing activation of both Th1 and Th2 associated cytokines; and spleen cells from animals immunised by either route were found to proliferate in vitro in response to both vaccine antigens. Virulent challenge experiments demonstrated that non-invasive immunisation by intra-nasal instillation can provide strong systemic and local immune responses and protect against high level challenge. Microencapsulation of these vaccine antigens has the added advantage that controlled release of the antigens occurs in vivo, so that protective immunity can be induced after only a single immunising dose.

Particulate delivery systems for biodefense subunit vaccines

Expanding identification of potentially protective subunit antigens and correlates of protection has provided a basis for the introduction of safer vaccines. Despite encouraging results in animal models, the significant potential of particulate delivery systems in vaccine design has not yet translated into effective vaccines available for use in humans. This review article will focus on the current status of the development of particulate vaccines, mainly liposomes and bio-degradable polymers, against potential agents for biowarfare: plague, anthrax, botulinum, and smallpox; and filoviruses: Marburg and Ebola.

Protective efficacy of a recombinant plague vaccine when co-administered with another sub-unit or live attenuated vaccine

Vaccines against bioterrorism agents offer the prospect of providing high levels of protection against airborne pathogens. However, the diversity of the bioterrorism threat means that it may be necessary to use several vaccines simultaneously. In this study we have investigated whether there are changes to the protective immune response to a recombinant sub-unit plague vaccine when it is co-administered with other sub-unit or live attenuated vaccines. Our results indicate that the co-administration of these vaccines did not influence the protection afforded by the plague vaccine. However, the co-administration of the plague sub-unit vaccine with a live vaccine resulted in markedly increased levels of IgG2a subclass antibodies, and markedly reduced levels of IgG1 subclass antibodies, to the plague sub-unit vaccine. This finding might have implications when considering the co-administration of other vaccine combinations.

Bioinformatics, genomics and evolution of non-flagellar type-III secretion systems: a Darwinian perpective

We review the biology of non-flagellar type-III secretion systems from a Darwinian perspective, highlighting the themes of evolution, conservation, variation and decay. The presence of these systems in environmental organisms such as Myxococcus, Desulfovibrio and Verrucomicrobium hints at roles beyond virulence. We review newly discovered sequence homologies (e.g., YopN/TyeA and SepL). We discuss synapomorphies that might be useful in formulating a taxonomy of type-III secretion. The problem of information overload is likely to be ameliorated by launch of a web site devoted to the comparative biology of type-III secretion ().

Comparative immunomodulatory properties of a chitosan-MDP adjuvant combination following intranasal or intramuscular immunisation

As the precise functions of adjuvants become clearer, opportunities are presented in their complementary use for the induction of tailored immune responses to subunit vaccines. Here we comparatively investigate the immunological outcome following intranasal or intramuscular immunisation with Helicobacter pylori urease admixed to a chitosan and muramyl di-peptide (MDP) combination. MDP appeared to limit the antigenicity of rUre by either administration route. Nasal administration of the combined adjuvant formulation resulted in an up-regulation of type I recall responses in splenocytes as opposed to adjuvantisation with chitosan alone. In contrast, intramuscular immunisation appeared to limit the responsiveness to the antigen when adjuvanted with chitosan and even more so when chitosan was combined with MDP, suggesting that the mechanism of adjuvantisation and adjuvant synergy differed depending on the immunisation route. Recognising the benefit of improved delivery of MDP intranasally due to the specific physiological effects of chitosan, we discuss the impact of the newly identified pathogen associated molecular pattern (PAMP) role of MDP with respect to the adjuvanticity of proposed chemical variants of this peptide adjuvant.