Effects of the adjuvant cholera toxin on dendritic cells: stimulatory and inhibitory signals that result in the amplification of immune responses

Cholera toxin induces food allergy through Th2 cell differentiation which is unaffected by Jagged2

AIMS

Cholera toxin is often used to induce food allergies. However, its exact mode of action and effect remain ambiguous. In this study, we established a BALB/c mouse cholera toxin/ovalbumin-induced food allergy model to determine the molecular basis and signaling mechanisms of the immune regulation of cholera toxin during food allergy.

MATERIALS AND METHODS

The adjuvant activity of cholera toxin was analyzed by establishing mouse allergy model, and the allergic reaction of each group of mice was evaluated. The effect of cholera toxin on Th1/Th2 cell differentiation was analyzed to further explore the role of cholera toxin in allergen immune response. We stimulated bone marrow-derived dendritic cells (BMDCs) with cholera toxin in vitro to investigate the effect of cholera toxin on Notch ligand expression. BMDCs and naive CD4⁺T cells were co-cultured in vitro, and their cytokine levels were examined to investigate whether cholera toxin regulates Th cell differentiation via the Jagged2 Notch signaling pathway.

KEY FINDINGS

The results showed that in the presence of allergens, cholera toxin promotes Th2 cell differentiation and enhances the body's immune response. Cholera toxin induces expression of the Notch ligand Jagged2, but Jagged2 Notch signaling pathway is not required to promote BMDCs-mediated differentiation of Th2 cells.

SIGNIFICANCE

This study initially revealed the mechanism by which cholera toxin plays an adjuvant role in food allergy, and provides reference for future related research.

Cocoa Diet and Antibody Immune Response in Preclinical Studies

The ability of cocoa to interact with the immune system in vitro and in vivo has been described. In the latter context, a cocoa-enriched diet in healthy rats was able to modify the immune system's functionality. This fact could be observed in the composition and functionality of lymphoid tissues, such as the thymus, spleen, and lymph nodes. Consequently, immune effector mechanisms, such as antibody synthesis, were modified. A cocoa-enriched diet in young rats was able to attenuate the serum levels of immunoglobulin (Ig) G, IgM, and IgA and also the intestinal IgM and IgA secretion. Moreover, in immunized rats, the intake of cocoa decreased specific IgG1, IgG2a, IgG2c, and IgM concentrations in serum. This immune-regulator potential was then tested in disease models in which antibodies play a pathogenic role. A cocoa-enriched diet was able to partially prevent the synthesis of autoantibodies in a model of autoimmune arthritis in rats and was also able to protect against IgE and T helper 2-related antibody synthesis in two rat models of allergy. Likewise, a cocoa-enriched diet prevented an oral sensitization process in young rats. In this review, we will focus on the influence of cocoa on the acquired branch of the immune function. Therefore, we will focus on how a cocoa diet influences lymphocyte function both in the systemic and intestinal immune system. Likewise, its potential role in preventing some antibody-induced immune diseases is also included. Although further studies must characterize the particular cocoa components responsible for such effects and nutritional studies in humans need to be carried out, cocoa has potential as a nutraceutical agent in some hypersensitivity status.

Effect of a cocoa diet on the small intestine and gut-associated lymphoid tissue composition in an oral sensitization model in rats

Previous studies have attributed to the cocoa powder the capacity to attenuate the immune response in a rat oral sensitization model. To gain a better understanding of cocoa-induced mechanisms at small intestinal level, 3-week-old female Lewis rats were fed either a standard diet or a diet containing 10% cocoa for 4 weeks with or without concomitant oral sensitization with ovalbumin (OVA). Thereafter, we evaluated the lymphocyte composition of the Peyer's patches (PPL), small intestine epithelium (IEL) and lamina propria (LPL). Likewise, gene expression of several immune molecules was quantified in the small intestine. Moreover, histological samples were used to evaluate the proportion of goblet cells, IgA+ cells and granzyme+cells as well. In cocoa-fed animals, we identified a five-time reduction in the percentage of IgA+ cells in intestinal tissue together with a decreased proportion of TLR4+ IEL. Analyzing the lymphocyte composition, almost a double proportion of TCRγδ+cells and an increase of NK cell percentage in PPL and IEL were found. In addition, a rise in CD25+, CD103+ and CD62L- cell proportions was observed in CD4+ PPL from cocoa-fed animals, along with a decrease in gene expression of CD11b, CD11c and IL-10. These results suggest that changes in PPL and IEL composition and in the gene expression induced by the cocoa diet could be involved, among other mechanisms, on its tolerogenic effect.

Modulation of Phenotype and Function of Human CD4+CD25+ T Regulatory Lymphocytes Mediated by cAMP-Elevating Agents

We have shown that cholera toxin (CT) and other cyclic AMP (cAMP)-elevating agents induce upregulation of the inhibitory molecule CTLA-4 in human resting CD4⁺ T lymphocytes, which following the treatment acquired suppressive functions. In this study, we evaluated the effect of cAMP-elevating agents on human CD4⁺CD25⁺ T cells, which include the T regulatory cells (Tregs) that play a pivotal role in the maintenance of immunological tolerance. We found that cAMP-elevating agents induce upregulation of CTLA-4 in CD4⁺CD25⁻ and further enhance its expression in CD4⁺CD25⁺ T cells. We observed an increase of two isoforms of mRNA coding for the membrane and the soluble CTLA-4 molecules, suggesting that the regulation of CTLA-4 expression by cAMP is at the transcriptional level. In addition, we found that the increase of cAMP in CD4⁺CD25⁺ T cells converts the CD4⁺CD25⁺Foxp3⁻ T cells in CD4⁺CD25⁺Foxp3⁺ T cells, whereas the increase of cAMP in CD4⁺CD25⁻ T cells did not upregulate Foxp3 in the absence of activation stimuli. To investigate the function of these cells, we performed an in vitro suppression assay by culturing CD4⁺CD25⁺ T cells untreated or pre-treated with CT with anti-CD3 mAbs-stimulated autologous peripheral blood mononuclear cell. We found that CT enhances the inhibitory function of CD4⁺CD25⁺ T cells, CD4⁺, and CD8⁺ T cell proliferation and IFNγ production are strongly inhibited by CD4⁺CD25⁺ T cells pre-treated with cAMP-elevating agents. Furthermore, we found that CD4⁺CD25⁺ T lymphocytes pre-treated with cAMP-elevating agents induce the upregulation of CD80 and CD86 co-stimulatory molecules on immature dendritic cells (DCs) in the absence of antigenic stimulation, however without leading to full DC maturation. These data show that the increase of intracellular cAMP modulates the phenotype and function of human CD4⁺CD25⁺ T cells.

Cocoa Diet Prevents Antibody Synthesis and Modifies Lymph Node Composition and Functionality in a Rat Oral Sensitization Model

Cocoa powder, a rich source of polyphenols, has shown immunomodulatory properties in both the intestinal and systemic immune compartments of rats. The aim of the current study was to establish the effect of a cocoa diet in a rat oral sensitization model and also to gain insight into the mesenteric lymph nodes (MLN) activities induced by this diet. To achieve this, three-week-old Lewis rats were fed either a standard diet or a diet with 10% cocoa and were orally sensitized with ovalbumin (OVA) and with cholera toxin as a mucosal adjuvant. Specific antibodies were quantified, and lymphocyte composition, gene expression, and cytokine release were established in MLN. The development of anti-OVA antibodies was almost totally prevented in cocoa-fed rats. In addition, this diet increased the proportion of TCRγδ+ and CD103+CD8+ cells and decreased the proportion of CD62L+CD4+ and CD62L+CD8+ cells in MLN, whereas it upregulated the gene expression of OX40L, CD11c, and IL-1β and downregulated the gene expression of IL-17α. In conclusion, the cocoa diet induced tolerance in an oral sensitization model accompanied by changes in MLN that could contribute to this effect, suggesting its potential implication in the prevention of food allergies.

Development of safe, effective and immunogenic vaccine candidate for diarrheagenic Escherichia coli main pathotypes in a mouse model

Background

Enteric and diarrheal diseases are important causes of childhood death in the developing world. These diseases are responsible for more than 750 thousand deaths in children under 5 years old worldwide, ranking second cause of death, after lower respiratory diseases, in this age group. Among the major causative agents of diarrhea is Escherichia coli. There are several vaccine trials for diarrheagenic E. coli. However, diarrheagenic E. coli has seven pathotypes and vaccines are directed for one or two of the five main pathotypes-causing diarrhea. Currently, there are no combined vaccines available in the market for all five diarrheagenic E. coli pathotypes. Therefore, we aimed to develop a low-cost vaccine candidate combining the five main diarrheagenic E. coli to offer wide-spectrum protection. We formulated a formalin-killed whole-cell mixture of enteroaggregative, enteropathogenic, enteroinvasive, enterohemorrhagic, and enterotoxigenic E. coli pathotypes as a combined vaccine candidate.

Results

We immunized Balb/C mice subcutaneously with 10⁹ CFU of combined vaccine candidate and found a significant increase in survival rate post challenge compared to unimmunized controls (100 % survival). Next we aimed to determine the immunological response of mice to the combined vaccine candidate compared to each pathotype immunization. To do so, we immunized mice groups with combined vaccine candidate and monitored biomarkers levels over 6 weeks as well as measured responses post challenge with relevant living E. coli. We found significant increase in specific systemic antibodies (IgG), interferon gamma (IFNγ) and interleukin 6 (IL-6) levels elicited by combined vaccine candidate especially in the first 2 weeks after mice immunization compared to controls (p < 0.05). We also evaluated alum and cholera toxin B subunit (CTB) as potential adjuvant systems for our candidate vaccine. We found that CTB-adjuvanted combined vaccine candidate showed significantly higher IgG and IFNγ levels than alum.

Conclusions

Overall, our combined vaccine candidate offered protection against the five main diarrheagenic E. coli pathotypes in a single vaccine using mouse model. To the best of our knowledge, this is the first combined vaccine against the five main diarrheagenic E. coli pathotypes that is cost-effective with promise for further testing in humans.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-016-1891-z) contains supplementary material, which is available to authorized users.

Cholera toxin B induced activation of murine macrophages exposed to a fixed bacterial immunogen

OBJECTIVES

Previous studies have demonstrated that intranasal administration of inactivated (fixed) Francisella tularensis (iFt) live vaccine strain (LVS) in conjunction with the mucosal adjuvant, cholera toxin B (CTB), provides full protection against subsequent lethal challenge with Ft LVS and partial protection against the more virulent Ft SchuS4 strain. Understanding the mechanisms of CTB-induced immune stimulation that confer protection against Ft will be valuable to the development of an effective vaccine against this highly virulent fatal pathogen. In this study, an in vitro system was utilized to further elucidate the immunologic adjuvant effect of CTB when administered with the fixed bacterial immunogen iFt.

METHODS

The murine macrophage cell line (RAW264.7) was treated with combinations of iFt and CTB. The treated RAW264.7 cells and their supernatants were collected and assessed for cell surface marker expression and cytokine secretion. In addition, the ability of RAW264.7 cells to present bacterial antigens (iFt or LVS) to an Ft-specific T-cell hybridoma cell line, following exposure to CTB, was analyzed.

RESULTS

We found that RAW264.7 cells responded to treatment with iFt + CTB by an increased secretion of the proinflammatory cytokines interleukin 6 and tumor necrosis factor α and upregulation of the surface expression of toll-like receptor 4 and the costimulatory molecules CD80 and CD86. Furthermore, the experimental vaccine treatment iFt + CTB enhanced the ability of macrophages to present iFt antigens to an FT-specific T-cell hybridoma cell line, although they failed to do so with LVS.

CONCLUSION

The adjuvant CTB administered in conjunction with iFt showed evidence of enhancing an antigen-specific proinflammatory response in vitro. These observations allow us to define, in part, the mechanisms of immune activation conferred by mucosal administration of iFt + CTB against lethal F. tularensis challenge.

Subcutaneous cholera toxin exposure induces potent CD103⁺ dermal dendritic cell activation and migration

CD103⁺ dermal dendritic cells (dDCs) are a recently described DC subset of the skin shown to be the principal migratory DCs capable of efficiently cross-presenting antigens and activating CD8⁺ T cells. Harnessing their activity would promote vaccine efficacy, but it has been unclear how this can be achieved. We tested a panel of adjuvants for their ability to affect dDCs. In comparison to the other adjuvants tested, the capacity of cholera toxin (CT) to induce the migration of dDCs was unique. Within 24 h of CT injection, large numbers of highly activated dDCs (including CD103⁺ dDCs) migrated to the draining lymph nodes and cross-presented coinjected antigens, potently activating naïve CD8⁺ T cells. Peptide vaccines adjuvanted with CT induced T-cell responses uniquely characterized by dynamic cytokine responses including the production of IL-2, and such vaccines were protective in situations reliant on CD8⁺ T-cell responses, including liver-stage Plasmodium challenge, or tumor challenge. This study is the first to examine the effects of adjuvants on CD103⁺ dDCs and identifies CT as a prototypical adjuvant for the activation of CD103⁺ dDCs, opening the way to development of vaccines and adjuvants that specifically target dDCs and generate effective CD8⁺ T-cell responses.

Intestinal epithelial barrier dysfunction in food hypersensitivity

Intestinal epithelial barrier plays a critical role in the maintenance of gut homeostasis by limiting the penetration of luminal bacteria and dietary allergens, yet allowing antigen sampling for the generation of tolerance. Undigested proteins normally do not gain access to the lamina propria due to physical exclusion by tight junctions at the cell-cell contact sites and intracellular degradation by lysosomal enzymes in enterocytes. An intriguing question then arises: how do macromolecular food antigens cross the epithelial barrier? This review discusses the epithelial barrier dysfunction in sensitized intestine with special emphasis on the molecular mechanism of the enhanced transcytotic rates of allergens. The sensitization phase of allergy is characterized by antigen-induced cross-linking of IgE bound to high affinity FcεRI on mast cell surface, leading to anaphylactic responses. Recent studies have demonstrated that prior to mast cell activation, food allergens are transported in large quantity across the epithelium and are protected from lysosomal degradation by binding to cell surface IgE and low-affinity receptor CD23/FcεRII. Improved immunotherapies are currently under study including anti-IgE and anti-CD23 antibodies for the management of atopic disorders.

Cholera toxin impairs the differentiation of monocytes into dendritic cells, inducing professional antigen-presenting myeloid cells

Cholera toxin (CT) is a potent adjuvant for mucosal vaccination; however, its mechanism of action has not been clarified completely. It is well established that peripheral monocytes differentiate into dendritic cells (DCs) both in vitro and in vivo and that monocytes are the in vivo precursors of mucosal CD103(-) proinflammatory DCs. In this study, we asked whether CT had any effects on the differentiation of monocytes into DCs. We found that CT-treated monocytes, in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4), failed to differentiate into classical DCs (CD14(low) CD1a(high)) and acquired a macrophage-like phenotype (CD14(high) CD1a(low)). Cells differentiated in the presence of CT expressed high levels of major histocompatibility complex class I (MHC-I) and MHC-II and CD80 and CD86 costimulatory molecules and produced larger amounts of IL-1β, IL-6, and IL-10 but smaller amounts of tumor necrosis factor alpha (TNF-α) and IL-12 than did monocytes differentiated into DCs in the absence of CT. The enzymatic activity of CT was found to be important for the skewing of monocytes toward a macrophage-like phenotype (Ma-DCs) with enhanced antigen-presenting functions. Indeed, treatment of monocytes with scalar doses of forskolin (FSK), an activator of adenylate cyclase, induced them to differentiate in a dose-dependent manner into a population with phenotype and functions similar to those found after CT treatment. Monocytes differentiated in the presence of CT induced the differentiation of naïve T lymphocytes toward a Th2 phenotype. Interestingly, we found that CT interferes with the differentiation of monocytes into DCs in vivo and promotes the induction of activated antigen-presenting cells (APCs) following systemic immunization.

Human CD4+ T lymphocytes with increased intracellular cAMP levels exert regulatory functions by releasing extracellular cAMP

We have previously shown that cholera toxin (CT) and other cAMP-elevating agents induce up-regulation of the inhibitory molecule CTLA-4 on human resting T lymphocytes. In this study, we evaluated the function of these cells. We found that purified human CD4(+) T lymphocytes pretreated with CT were able to inhibit proliferation of autologous PBMC in a dose-dependent manner. It is interesting that this phenomenon was not mediated by inhibitory cytokines such as IL-10, IL-4, or TGF-beta but was in part caused by the release of extracellular cAMP by the CD4(+) T lymphocytes. Purified CD4(+) T cells pretreated with forskolin, a transient cAMP inducer, or with dibutyryl cAMP, an analog of cAMP, did not exert suppressive functions, suggesting that a sustained production of cAMP, such as that induced by CT, was required to identify a novel regulatory function mediated by CD4(+) T cells. Our results show that CD4(+) T lymphocytes can exert regulatory functions through the release of extracellular cAMP and that the cyclic nucleotide acts as a primary messenger, which could play a biological role in the modulation of immune responses.

Protective immune responses to meningococcal C conjugate vaccine after intranasal immunization of mice with the LTK63 mutant plus chitosan or trimethyl chitosan chloride as novel delivery platform

Chitosan and its derivative N-trimethyl chitosan chloride (TMC), given as microparticles or powder suspensions, and the non-toxic mucosal adjuvant LTK63, were evaluated for intranasal immunization with the group C meningococcal conjugated vaccine (CRM-MenC). Mice immunized intranasally with CRM-MenC formulated with chitosan or TMC and the LTK63 mutant, showed high titers of serum and mucosal antibodies specific for the MenC polysaccharide. Neither significant differences were observed between microparticle formulations and powder suspensions nor when LTK63 was pre-associated to the delivery system or not. The bactericidal activity measured in serum of mice immunized intranasally with the conjugated vaccine formulated with the delivery systems and the LT mutant was superior to the activity in serum of mice immunized sub-cutaneously. Importantly, intranasal but not parenteral immunization, induced bactericidal antibodies at the nasal level, when formulated with both delivery system and adjuvant.

Bacillus anthracis edema toxin acts as an adjuvant for mucosal immune responses to nasally administered vaccine antigens

Anthrax edema toxin (EdTx) is an AB-type toxin that binds to anthrax toxin receptors on target cells via the binding subunit, protective Ag (PA). Edema factor, the enzymatic A subunit of EdTx, is an adenylate cyclase. We found that nasal delivery of EdTx enhanced systemic immunity to nasally coadministered OVA and resulted in high OVA-specific plasma IgA and IgG (mainly IgG1 and IgG2b). The edema factor also enhanced immunity to the binding PA subunit itself and promoted high levels of plasma IgG and IgA responses as well as neutralizing PA Abs. Mice given OVA and EdTx also exhibited both PA- and OVA-specific IgA and IgG Ab responses in saliva as well as IgA Ab responses in vaginal washes. EdTx as adjuvant triggered OVA- and PA-specific + T cells which secreted IFN-gamma and selected Th2-type cytokines. The EdTx up-regulated costimulatory molecule expression by APCs but was less effective than cholera toxin for inducing IL-6 responses either by APCs in vitro or in nasal washes in vivo. Finally, nasally administered EdTx did not target CNS tissues and did not induce IL-1 mRNA responses in the nasopharyngeal-associated lymphoepithelial tissue or in the olfactory bulb epithelium. Thus, EdTx derivatives could represent an alternative to the ganglioside-binding enterotoxin adjuvants and provide new tools for inducing protective immunity to PA-based anthrax vaccines.

Dynamics of dendritic cell phenotype and interactions with CD4+ T cells in airway inflammation and tolerance

An emerging concept is that different types of dendritic cells (DCs) initiate different immune outcomes, such as tolerance vs inflammation. In this study, we have characterized the DCs from the lung draining lymph nodes of mice immunized for allergic airway inflammation or tolerance and examined their interactions with CD4(+) T cells. The DC population derived from tolerized mice was predominantly CD11c(+), B220(+), Gr-1(+), CD11b(-), and MHC class II(low), which resembled plasmacytoid-type DCs whereas DCs from the inflammatory condition were largely CD11c(+), B220(-), Gr-1(-), CD11b(+), and MHC class II(high) resembling myeloid-type DCs. The DCs from the tolerogenic condition were poor inducers of T cell proliferation. DCs from both conditions induced T cell IL-4 production but the T cells cultured with tolerogenic DCs were unresponsive to IL-4 as indicated by inhibition of STAT6 activation and expression of growth factor-independent 1, which has been recently shown to be important for STAT6-activated Th2 cell expansion. Our data suggest that airway tolerance vs inflammation is determined by the DC phenotype in lung draining lymph nodes.

Adjuvant synergy: The effects of nasal coadministration of adjuvants

Modern peptide and protein subunit vaccines suffer from poor immunogenicity and require the use of adjuvants. However, none of the currently licensed adjuvants can elicit cell-mediated immunity or are suitable for mucosal immunization. In this study we explored the immunological effect of nasal co-administration of adjuvants with distinct functions: cholera toxin subunit B, a potent mucosal adjuvant that induces strong humoral responses, muramy di-peptide (MDP), an adjuvant known to elicit cell mediated immunity but rarely used nasally, and chitosan, an adjuvant that achieves specific physiological effects on mucosal membranes that improve antigen uptake. Groups of five female BALB/c mice received on days 1 and 56 nasal instillations of the recombinant Helicobacter pylori antigen urease admixed to single or multiple adjuvant combinations. Serum IgG kinetics were followed over 24 weeks. At the conclusion of the experiment, local antibody responses were determined and antigen-specific recall responses in splenocyte cultures were assayed for proliferation and cytokine production. The combination of adjuvants was shown to further contribute to the increased antigenicity of recombinant H. pylori urease. The data presented here outline and support facilitation of increased immunomodulation by an adjuvant previously defined as an effective mucosal adjuvant (chitosan) for another adjuvant (MDP) that is not normally effective via this route.

Vaccination with dendritic cells pulsed in vitro with tumor antigen conjugated to cholera toxin efficiently induces specific tumoricidal CD8+ cytotoxic lymphocytes dependent on cyclic AMP activation of dendritic cells

We investigated the development of CD8+ tumor-specific cytotoxic lymphocytes (CTL) and protection against tumor growth after vaccination with bone marrow-derived dendritic cells (DC) pulsed with a model protein ovalbumin conjugated to cholera toxin (OVA-CT) in B6 mice using E.G7 tumor cells expressing OVA(257-264) peptide (SIINFEKL) as target cells in vitro and in vivo. Vaccination with OVA-CT-pulsed DC concurrently induced strong CTL in vitro activity and anti-E.G7 tumor protection in vivo in WT, NK-depleted and CD4-deficient mice as well as in IL-12-/- and IFN-gamma-/- mice but not in CD8-deficient mice. Importantly, activation of CTL by OVA-CT-pulsed DC was dependent on CT-induced activation of adenylate cyclase and increased cAMP production by DC associated with increased expression of MHC class I and co-stimulatory molecules (CD80, CD86 and CD40). These results show that vaccination with DC pulsed with antigens (Ag) conjugated to CT induces a strong CTL response and suggest that conjugation of tumor Ag to CT for DC vaccination represents a promising approach for tumor vaccination and immunotherapy.

Enhanced mucosal and systemic immune responses following intravaginal immunization with human papillomavirus 16 L1 virus-like particle vaccine in thermosensitive mucoadhesive delivery systems

To develop more potent and convenient mucosal human papillomavirus (HPV) vaccines, we tested the effect of thermosensitive mucoadhesive vaginal vaccine delivery systems on the local and systemic antibody responses to HPV 16 L1 virus-like particles (VLP). HPV 16 L1 VLP expressed from recombinant baculovirus-infected Sf21 insect cells were delivered in phosphate-buffered saline (PBS) or thermosensitive mucoadhesive delivery systems, composed of poloxamers (Pol) and varying amounts of polyethylene oxide (PEO). Pol/PEO-based vaginal vaccine delivery systems existed in liquid form at room temperature, but gelled at 37 degrees C. The mucoadhesiveness of Pol/PEO-based delivery systems increased with PEO, but the formulations with PEO higher than 1.0% were too viscous to be administered into the vagina. Vaccine vehicles affected the vaginal and salivary immune responses to HPV 16 L1 VLP intravaginally administered into mice. At 42 days after the first intravaginal immunization of HPV 16 L1 VLP with cholera toxin, vaginal and salivary IgA titers were the highest in the group given in Pol/PEO 1.0% vehicle followed by Pol/PEO 0.4% and PBS vehicles. Intravaginal coadministration of HPV 16 L1 VLP and cholera toxin in Pol/PEO 1.0% showed 31- and 39-fold higher titers compared to the PBS-based HPV 16 L1 VLP groups administered by intravaginal and intramuscular routes, respectively. Following intravaginal administration, Pol/PEO 1.0%, but not Pol/PEO 0.4%, showed significantly higher HPV 16 L1 VLP-specific serum IgG titers as compared to the PBS vehicle. Our results indicate that the use of in situ-gelling vaginal vaccine delivery systems with increased mucoadhesiveness would be beneficial for more effective induction of mucosal and systemic immune responses to intravaginally administered HPV 16 L1 VLP vaccines.

Mucosal immunisation and adjuvants: a brief overview of recent advances and challenges

Mucosal immunisation may be used both to prevent mucosal infections through the activation of anti-microbial immunity and to treat selected autoimmune, allergic or infectious-immunopathological disorders through the induction of antigen-specific tolerance. The development of mucosal vaccines, whether for prevention of infectious diseases or for immunotherapy, requires antigen delivery and adjuvant systems that can efficiently help to present vaccine or immunotherapy antigens to the mucosal immune system. Promising advances have recently been made in the design of more efficient mucosal adjuvants based on detoxified bacterial toxin derivatives or CpG motif-containing DNA, and perhaps even more striking progress has been done in the use of virus-like particles as mucosal delivery systems for vaccines and of cholera toxin B subunit as antigen vector for immunotherapeutic tolerance induction. However, it is a memento that two recently developed mucosal vaccines for human use against rotavirus diarrhoea and influenza were withdrawn after a short period in the market because of adverse reactions among the vaccinees, thus emphasising the difficult and challenging task also for mucosal immunisation of combining vaccine and adjuvant efficacy with safety and acceptability.

Maturation of human dendritic cells induced by the adjuvant cholera toxin: role of cAMP on chemokine receptor expression

Cholera toxin (CT) is a very effective adjuvant for mucosal vaccination. It binds to cells through its B subunit and induces intracellular increase of cAMP through the A subunit. We previously showed that CT induces maturation of human dendritic cells (DCs) and this may account for its adjuvant property. Here, we investigated the role of the A subunit on DCs maturation by using forskolin, a cAMP inducer. The results show that although cAMP does not stimulate full maturation of DCs it induces upregulation of the chemokine receptors CXCR4 and CCR7.