Immunomodulators and delivery systems for vaccination by mucosal routes

Zonula occludens toxin acts as an adjuvant through different mucosal routes and induces protective immune responses

Zonula occludens toxin (Zot) is produced by Vibrio cholerae and has the ability to increase mucosal permeability by reversibly affecting the structure of tight junctions. Because of this property, Zot is a promising tool for mucosal drug and antigen (Ag) delivery. Here we show that Zot acts as a mucosal adjuvant to induce long-lasting and protective immune responses upon mucosal immunization of mice. Indeed, the intranasal delivery of ovalbumin with two different recombinant forms of Zot in BALB/c mice resulted in high Ag-specific serum immunoglobulin G titers that were maintained over the course of a year. Moreover, His-Zot induced humoral and cell-mediated responses to tetanus toxoid in C57BL/6 mice and protected the mice against a systemic challenge with tetanus toxin. In addition, we found that Zot also acts as an adjuvant through the intrarectal route and that it has very low immunogenicity compared to the adjuvant Escherichia coli heat-labile enterotoxin. Finally, by using an octapeptide representing the putative binding site of Zot and of its endogenous analogue zonulin, we provide evidence that Zot may bind a mucosal receptor on nasal mucosa and may mimic an endogenous regulator of tight junctions to deliver Ags in the submucosa. In conclusion, Zot is a novel and effective mucosal adjuvant that may be useful for the development of mucosal vaccines.

Animal models paving the way for clinical trials of attenuated Salmonella enterica serovar Typhi live oral vaccines and live vectors

Attenuated Salmonella enterica serovar Typhi (S. Typhi) strains can serve as safe and effective oral vaccines to prevent typhoid fever and as live vectors to deliver foreign antigens to the immune system, either by the bacteria expressing antigens through prokaryotic expression plasmids or by delivering foreign genes carried on eukaryotic expression systems (DNA vaccines). The practical utility of such live vector vaccines relies on achieving a proper balance between minimizing the vaccine's reactogenicity and maximizing its immunogenicity. To advance to clinical trials, vaccine candidates need to be pre-clinically evaluated in relevant animal models that attempt to predict what their safety and immunogenicity profile will be when administered to humans. Since S. Typhi is a human-restricted pathogen, a major obstacle that has impeded the progress of vaccine development has been the shortcomings of the animal models available to assess vaccine candidates. In this review, we summarize the usefulness of animal models in the assessment of the degree of attenuation and immunogenicity of novel attenuated S. Typhi strains as vaccine candidates for the prevention of typhoid fever and as live vectors in humans.

Current advances in antifertility vaccines for fertility control and noncontraceptive applications

The search for effective antifertility vaccines has been actively pursued for decades in clinical applications as contraceptives or in the treatment of hormone-dependent conditions. More recently, innovations have seen immunocontraception being employed successfully in veterinary and farming applications, as well as in population control of a number of different wildlife species. Although the basic principle behind these vaccines is the same, design considerations and criteria for commercialization are very different. This review will examine current advances in this field and evaluate the future scope of antifertility vaccines.

Lactobacilli as live vaccine delivery vectors: progress and prospects

Evidence is accumulating that lactobacilli influence the immune response in a strain-dependent manner. This immunomodulatory capacity is important for the development of the immune response, and also identifies Lactobacillus as a potent oral vaccine carrier. Most of our current knowledge of the use of lactobacilli for vaccination purposes has been obtained with tetanus toxin fragment C (TTFC) as the model antigen. This knowledge, together with our ever-increasing understanding of the immune system and recent developments in cloning and expression techniques, should enable the utilisation of antigens other than TTFC and has made the development of lactobacilli as live vaccines a realistic prospect.

Specific immune responses and enhancement of murine pulmonary clearance of Moraxella catarrhalis by intranasal immunization with a detoxified lipooligosaccharide conjugate vaccine

Moraxella catarrhalis is an important human mucosal pathogen. This study investigated the effect of intranasal immunization with a detoxified-lipooligosaccharide-cross-reactive mutant of diphtheria toxin (dLOS-CRM) vaccine candidate on pulmonary clearance following an aerosol challenge of mice with M. catarrhalis. Intranasal immunization with dLOS-CRM plus cholera toxin induced a significantly dose-dependent increase of immunoglobulin A (IgA) and IgG in the nasal wash, lung lavage fluid, saliva, and fecal extract. In addition, serum IgG, IgM, and IgA against LOS of M. catarrhalis were detected. LOS-specific antibody-forming cells were found in the nasal passages, spleens, nasally associated lymphoid tissues, cervical lymph nodes, lungs, and Peyer's patches using an enzyme-linked immunospot assay. The dLOS-CRM vaccine induced a significant bacterial clearance (70 to 90%) of both homologous and heterologous strains in the lungs compared to that observed in the controls (P < 0.01). Intriguingly, intranasal immunization with dLOS-CRM showed a higher level of bacterial clearance compared with subcutaneous injections with dLOS-CRM. These data indicate that dLOS-CRM induces specific mucosal and systemic immunity through intranasal immunization and also provides effective bacterial clearance. On the basis of these results, we believe that dLOS-CRM should undergo continued testing to determine whether it would induce protective immune response in humans.

Pathogen-specific regulatory T cells provoke a shift in the Th1/Th2 paradigm in immunity to infectious diseases

Current dogma suggests that immunity to infection is controlled by distinct type 1 (Th1) and type 2 (Th2) subpopulations of T cells discriminated on the basis of cytokine secretion and function. However, a further subtype of T cells, with immunosuppressive function and cytokine profiles distinct from either Th1 or Th2 T cells, termed regulatory T (Tr) cells has been described. Although considered to have a role in the maintenance of self-tolerance, recent studies suggest that Tr cells can be induced against bacterial, viral and parasite antigens in vivo and might prevent infection-induced immunopathology or prolong pathogen persistence by suppressing protective Th1 responses. These observations have significant implications for our understanding of the role of T cells in immunity to infectious diseases and for the development of new therapies for immune-mediated disorders.

Edible genetically modified microorganisms and plants for improved health

The development of new strategies for the delivery of vaccine antigens or immune modulators to the mucosal tissue includes innovative approaches such as the use of genetically modified food microorganisms and plants. Even though the 'proof-of-concept' has recently been established for these two systems, key questions mainly related to efficacy and risk of breaking oral tolerance remain to be critically addressed in the immediate future.