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

Mechanism study of cross presentation of exogenous antigen induced by cholera toxin-like chimeric protein

Tumor subunit vaccines have great potential in personalized cancer immunotherapy. They are usually administered with adjuvant owing to their low immunogenicity. Cholera toxin (CT) is a biological adjuvant with diverse biological functions and a long history of use. Our earlier study revealed that a CT-like chimeric protein co-delivered with murine granulocyte-macrophage colony stimulating factor (mGM-CSF) and prostate cancer antigen epitope could co-stimulate dendritic cells (DCs) and enhance cross presentation of tumor epitope. To further study the molecular mechanism of CT-like chimeric protein in cross presentation, major histocompatibility complex class I (MHC I)-restricted epitope 257-264 of ovalbumin (OVAT) was used as a model antigen peptide in this study. Recombinant A subunit and pentameric B subunit of CT protein were respectively genetically constructed and purified. Then both assembled into AB5 chimeric protein in vitro. Three different chimeric biomacromolecules containing mGM-CSF and OVAT were constructed according to the different fusion sites and whether the endoplasmic reticulum (ER) retention sequence was included. It was found that A2 domain and B subunit of CT were both available for loading epitopes and retaining GM1 affinity. The binding activity of GM1 was positively correlated with antigen endocytosis. Once internalized, DCs became mature and cross-presented antigen. KDEL helped the whole molecule to be retained in the ER, and this improved the cross presentation of antigen on MHC I molecules. In conclusion, hexameric CT-like chimeric protein with dual effects of GM1 affinity and ER retention sequence were potential in improvement of cross presentation. The results laid a foundation for designing personalized tumor vaccine based on CT-like chimeric protein molecular structure.

Advances in Infectious Disease Vaccine Adjuvants

Vaccines are one of the most significant medical interventions in the fight against infectious diseases. Since their discovery by Edward Jenner in 1796, vaccines have reduced the worldwide transmission to eradication levels of infectious diseases, including smallpox, diphtheria, hepatitis, malaria, and influenza. However, the complexity of developing safe and effective vaccines remains a barrier for combating many more infectious diseases. Immune stimulants (or adjuvants) are an indispensable factor in vaccine development, especially for inactivated and subunit-based vaccines due to their decreased immunogenicity compared to whole pathogen vaccines. Adjuvants are widely diverse in structure; however, their overall function in vaccine constructs is the same: to enhance and/or prolong an immunological response. The potential for adverse effects as a result of adjuvant use, though, must be acknowledged and carefully managed. Understanding the specific mechanisms of adjuvant efficacy and safety is a key prerequisite for adjuvant use in vaccination. Therefore, rigorous pre-clinical and clinical research into adjuvant development is essential. Overall, the incorporation of adjuvants allows for greater opportunities in advancing vaccine development and the importance of immune stimulants drives the emergence of novel and more effective adjuvants. This article highlights recent advances in vaccine adjuvant development and provides detailed data from pre-clinical and clinical studies specific to infectious diseases. Future perspectives into vaccine adjuvant development are also highlighted.

Adjuvant effect of enterotoxigenic Escherichia coli (ETEC) double-mutant heat-labile toxin (dmLT) on systemic immunogenicity induced by the CFA/I/II/IV MEFA ETEC vaccine: Dose-related enhancement of antibody responses to seven ETEC adhesins (CFA/I, CS1-CS6)

Double-mutant heat-labile toxin (dmLT, LT_R192G/L211A) of enterotoxigenic Escherichia coli (ETEC) is an effective mucosal adjuvant. Recent studies have shown that dmLT also exhibits adjuvanticity for antigens administered parenterally. In this study, we subcutaneously (SC) immunized mice with the ETEC adhesin-based vaccine, CFA/I/II/IV MEFA (multiepitope fusion antigen), adjuvanted with dmLT and examined the impact of dmLT on antibody responses specific to the seven adhesins in the vaccine construction [CFA/I, CFA/II (CS1, CS2, CS3) and CFA/IV (CS4, CS5, CS6)]. Mice were immunized with a fixed dose of CFA/I/II/IV MEFA and ascending doses of dmLT adjuvant (0, 0.05, 0.1, 0.5 or 1.0 µg) to assess the potential dmLT dose response relationship. Data showed that dmLT enhanced systemic antibody responses to all seven antigens (CFA/I, CS1-CS6) targeted by MEFA in a dose-dependent way. The adjuvant effect of dmLT on the MEFA construct plateaued at a dose of 0.1 µg. Results also indicated that dmLT is an effective parenteral adjuvant when given by the SC route with the ETEC adhesin MEFA vaccine and that antibody enhancement was achieved with relatively low doses. These observations suggest the potential usefulness of dmLT for parenteral ETEC vaccine candidates and also perhaps for vaccines against other pathogens.

Requirement for Cyclic AMP/Protein Kinase A-Dependent Canonical NFκB Signaling in the Adjuvant Action of Cholera Toxin and Its Non-toxic Derivative mmCT

Cholera toxin (CT) is widely used as an effective adjuvant in experimental immunology for inducing mucosal immune responses; yet its mechanisms of adjuvant action remain incompletely defined. Here, we demonstrate that mice lacking NFκB, compared to wild-type (WT) mice, had a 90% reduction in their systemic and mucosal immune responses to oral immunization with a model protein antigen [Ovalbumin (OVA)] given together with CT. Further, NFκB^−/− mouse dendritic cells (DCs) stimulated in vitro with CT showed reduced expression of MHCII and co-stimulatory molecules, such as CD80 and CD86, as well as of IL-1β, and other pro-inflammatory cytokines compared to WT DCs. Using a human monocyte cell line THP1 with an NFκB activation reporter system, we show that CT induced NFκB signaling in human monocytes, and that inhibition of the cyclic AMP—protein kinase A (cAMP-PKA) pathway abrogated the activation and nuclear translocation of NFκB. In a human monocyte-CD4⁺ T cell co-culture system we further show that the strong Th17 response induced by CT treatment of monocytes was abolished by blocking the classical but not the alternative NFκB signaling pathway of monocytes. Our results indicate that activation of classical (canonical) NFκB pathway signaling in antigen-presenting cells (APCs) by CT is important for CT's adjuvant enhancement of Th17 responses. Similar findings were obtained using the almost completely detoxified mmCT mutant protein as adjuvant. Altogether, our results demonstrate that activation of the classical NFκB signal transduction pathway in APCs is important for the adjuvant action of both CT and mmCT.

Sublingual targeting of STING with 3'3'-cGAMP promotes systemic and mucosal immunity against anthrax toxins

Anthrax is caused by Bacillus anthracis, a zoonotic bacterial pathogen affecting humans and livestock worldwide. The current human anthrax vaccine, anthrax vaccine adsorbed (AVA), is an injected vaccine with a cumbersome administration schedule and fails to promote mucosal immunity. Bacterial enterotoxins, which stimulate production of the cyclic nucleotide cAMP are effective experimental mucosal vaccine adjuvants, but their inherent toxicity has precluded their use in humans. We investigated whether cyclic dinucleotides that target Stimulator of Interferon Gamma Genes (STING) in mammalian cells could represent an alternative to bacterial enterotoxins as adjuvant for sublingual immunization and promotion of mucosal immunity and secretory IgA responses in addition to systemic immunity. We found that sublingual immunization of mice with Bacillus anthracis protective antigen (PA) and the STING ligand 3'3'-cGAMP promotes PA-specific serum IgG Ab responses of the same magnitude as those induced after immunization with PA and the experimental adjuvant cholera toxin (CT). Interestingly, this STING ligand also promoted serum anti-PA IgA and IgA-producing cells in the bone marrow. Furthermore, the saliva of mice immunized with the STING ligand exhibited similar levels of PA-specific IgA Abs as groups immunized with CT as adjuvant. The adjuvant activity of 3'3'-cGAMP was associated with mixed Th1, Th2, and Th17 responses. This STING ligand also induced rapid IFN-β and IL-10 responses in sublingual tissues and cervical lymph nodes, and TGF-β responses in the cervical lymph nodes, which could contribute to promoting IgA responses after sublingual immunization.

Enterotoxigenic Escherichia coli heat-stable toxin and heat-labile toxin toxoid fusion 3xSTaN12S-dmLT induces neutralizing anti-STa antibodies in subcutaneously immunized mice

Enterotoxigenic Escherichia coli (ETEC) bacteria producing heat-stable toxin (STa) and/or heat-labile toxin (LT) are among top causes of children's diarrhea and travelers' diarrhea. Currently no vaccines are available for ETEC associated diarrhea. A major challenge in developing ETEC vaccines is the inability to stimulate protective antibodies against the key STa toxin that is potently toxic and also poorly immunogenic. A recent study suggested toxoid fusion 3xSTaN12S-dmLT, which consists of a monomer LT toxoid (LTR192G/L211A) and three copies of STa toxoid STaN12S, may represent an optimal immunogen inducing neutralizing antibodies against STa toxin [IAI 2014, 82(5):1823-32]. In this study, we immunized mice with this fusion protein following a different parenteral route and using different adjuvants to further characterize immunogenicity of this toxoid fusion. Data from this study showed that 3xSTaN12S-dmLT toxoid fusion induced neutralizing anti-STa antibodies in the mice following subcutaneous immunization, as effectively as in the mice under intraperitoneal route. Data also indicated that double mutant LT (dmLT) can be an effective adjuvant for this toxoid fusion in mice subcutaneous immunization. Results from this study affirmed that toxoid fusion 3xSTaN12S-dmLT induces neutralizing antibodies against STa toxin, suggesting this toxoid fusion is potentially a promising immunogen for ETEC vaccine development.

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.

"Cystic fibrotics could survive cholera, choleraics could survive cystic fibrosis"; hypothesis that explores new horizons in treatment of cystic fibrosis

Cystic fibrosis, the most common inherited disease of white population, is a disease of CFTR channels, in which mucosal function of many organs especially respiratory tract is impaired. Decreased mucociliary clearance and accumulation of mucus in airways facilitates colonization of infectious microorganisms, followed by infection. Following chronic infection, persistent inflammation ensues, which results in airway remodeling and deterioration of mucociliary clearance and result in a vicious cycle. Here, it is hypothesized that cholera toxin (CT) could ameliorate symptoms of cystic fibrosis as CT could dilute the thickened mucus, improve mucociliary clearance and alleviate airway obstruction. CT strengthens immunity of airway mucosa and it could attenuates bacterial growth and reduce persistency of infection. CT also modulates cellular immune response and it could decrease airway inflammation, hinder airway remodeling and prevent respiratory deterioration. Thereby it is hypothesized that CT could target and ameliorate many of pathophysiologic steps of the disease and it explores new horizons in treatment of CF.

Crosstalk between PKA and Epac regulates the phenotypic maturation and function of human dendritic cells

The cAMP-dependent signaling pathways that orchestrate dendritic cell (DC) maturation remain to be defined in detail. Although cAMP was previously thought to signal exclusively through protein kinase A (PKA), it is now clear that cAMP also activates exchange protein activated by cAMP (Epac), a second major cAMP effector. Whether cAMP signaling via PKA is sufficient to drive DC maturation or whether Epac plays a role has not been examined. In this study, we used cAMP analogs to selectively activate PKA or Epac in human monocyte-derived DCs and examined the effect of these signaling pathways on several hallmarks of DC maturation. We show that PKA activation induces DC maturation as evidenced by the increased cell-surface expression of MHC class II, costimulatory molecules, and the maturation marker CD83. PKA activation also reduces DC endocytosis and stimulates chemotaxis to the lymph node-associated chemokines CXCL12 and CCL21. Although PKA signaling largely suppresses cytokine production, the net effect of PKA activation translates to enhanced DC activation of allogeneic T cells. In contrast to the stimulatory effects of PKA, Epac signaling has no effect on DC maturation or function. Rather, Epac suppresses the effects of PKA when both pathways are activated simultaneously. These data reveal a previously unrecognized crosstalk between the PKA and Epac signaling pathways in DCs and raise the possibility that therapeutics targeting PKA may generate immunogenic DCs, whereas those that activate Epac may produce tolerogenic DCs capable of attenuating allergic or autoimmune disease.

Gene expression profiling identifies STAT3 as a novel pathway for immunomodulation by cholera toxin adjuvant

Earlier studies have reported on both proinflammatory and anti-inflammatory activities of cholera toxin (CT). As CT is a powerful adjuvant, we were interested in identifying genes with a possible involvement in these functions. A global gene expression analysis in mouse B cells showed that CT regulated <100 annotated genes, which encoded transcription factors, G proteins, cell-cycle regulators, and immunoregulating molecules. Interestingly, CT regulated the expression of the signal transducer and activator of transcription (STAT)3 gene and influenced the level and activation of both isoforms STAT3 alpha and STAT3 beta, in vitro in a B-cell line and in Peyer's patch (PP) B cells and in vivo in freshly isolated splenic B cells from CT-treated mice. This effect was cAMP dependent and was not seen with CTB. B cells pre-exposed to CT were significantly more susceptible to the activation of STAT3 by interleukin (IL)-6 and IL-10. This exerted a stronger inhibitory effect of IL-10 on lipopolysaccharide (LPS)-stimulated B-cell proliferation and cytokine production (IL-6). Moreover, IgG1 and IgA production induced by LPS and IL-10 were enhanced by the addition of CT to cultures of PP or splenic B cells. This is the first study to provide a molecular mechanism that can reconcile previous findings of proinflammatory and anti-inflammatory effects by CT adjuvant.

Toxins-useful biochemical tools for leukocyte research

Leukocytes are a heterogeneous group of cells that display differences in anatomic localization, cell surface phenotype, and function. The different subtypes include e.g., granulocytes, monocytes, dendritic cells, T cells, B cells and NK cells. These different cell types represent the cellular component of innate and adaptive immunity. Using certain toxins such as pertussis toxin, cholera toxin or clostridium difficile toxin, the regulatory functions of Gα_i, Gαs and small GTPases of the Rho family in leukocytes have been reported. A summary of these reports is discussed in this review.

Primary porcine CD11R1+ antigen-presenting cells isolated from small intestinal mucosa mature but lose their T cell stimulatory function in response to cholera toxin treatment

Antigen-presenting cells (APCs) in the small intestinal mucosa perform dual functions of maintaining tissue homeostasis and of protecting against intestinal pathogens as key inducers of both innate and adaptive immune responses. Intestinal APCs are thus important regulators of intestinal immunity and also potential target cells for mucosal adjuvants such as cholera toxin (Ctx), which was used successfully in several oral vaccination studies in pigs. The aims of the present study were (1) to isolate porcine small intestinal APCs and evaluate the feasibility of using these cells for functional in vitro studies and (2) to determine the response of intestinal APCs to Ctx. Microscopic and flow cytometric analyses using antibodies to CD1, CD11R1, CD16, and SIRPalpha (SWC3) revealed the presence of multiple subsets of MHC-II(++) APCs in porcine small intestinal mucosa. The alpha-integrin subunit CD11R1 was most frequently expressed and therefore chosen as a selection marker. CD11R1(+) cells were enriched from total lamina propria cells to >90% purity by immunomagnetic separation. Within the CD11R1 cells, we identified two populations with distinct forward and side scatter characteristics: (1) APCs identified by their high expression of MHC-II and consisting of SIRPalpha(+) and SIRPalpha(-) subsets, and (2) contaminating eosinophils. In culture, intestinal APCs spontaneously matured, as shown by significant (>5-fold) increase in CD80/CD86 expression. The SIRPalpha(+) APCs quickly disappeared from the cultures, likely due to increased apoptotic cell death. However, the observed spontaneous changes in the isolated cell population did not mask the effects of stimulation with Ctx, which resulted in a 2.5-fold increase in the expression of maturation markers CD80/CD86, but significant loss of T cell stimulatory function, corroborating previous results obtained with MoDC.

Cholera toxin and Escherichia coli heat-labile enterotoxin, but not their nontoxic counterparts, improve the antigen-presenting cell function of human B lymphocytes

B lymphocytes play an important role in the immune response induced by mucosal adjuvants. In this study we investigated the in vitro antigen-presenting cell (APC) properties of human B cells upon treatment with cholera toxin (CT) and Escherichia coli heat-labile enterotoxin (LT) and nontoxic counterparts of these toxins, such as the B subunit of CT (CT-B) and the mutant of LT lacking ADP ribosyltransferase activity (LTK63). Furthermore, forskolin (FSK), a direct activator of adenylate cyclase, and cyclic AMP (cAMP) analogues were used to investigate the role of the increase in intracellular cAMP caused by the A subunit of CT and LT. B lymphocytes were cultured with adjuvants and polyclonal stimuli necessary for activation of B cells in the absence of CD4 T cells. Data indicated that treatment with CT, LT, FSK, or cAMP analogues, but not treatment with CT-B or LTK63, upregulated surface activation markers on B cells, such as CD86 and HLA-DR, and induced inhibition of the proliferation of B cells at early time points, while it increased cell death in long-term cultures. Importantly, B cells treated with CT, LT, or FSK were able to induce pronounced proliferation of both CD4(+) and CD8(+) allogeneic T cells compared with untreated B cells and B cells treated with CT-B and LTK63. Finally, only treatment with toxins or FSK induced antigen-specific T-cell proliferation in Mycobacterium tuberculosis purified protein derivative or tetanus toxoid responder donors. Taken together, these results indicated that the in vitro effects of CT and LT on human B cells are mediated by cAMP.

Starch Microparticles as Oral Vaccine Adjuvant: Antigen-dependent Uptake in Mouse Intestinal Mucosa

An oral vaccine formulation comprised of starch microparticles with conjugated antigens is being developed. In this report we have examined the uptake of such microparticles by the intestinal mucosa and examined whether the conjugated antigen can influence the uptake. Two model antigens were used: recombinant cholera toxin B subunit (rCTB), which is known to bind to the ubiquitous GM1-receptor, and human serum albumin (HSA) which is not known to have any specific binding properties. The uptake was studied in mouse ligated intestinal loops into which the microparticles were injected. The intestinal loops were excised, fixed in ice-cold 95% ethanol. Entire specimens were mounted, exposed to fluorescence-labeled reagents staining the cytoskeleton, the particles and/or M cells and examined in a confocal laser-scanning microscope. A qualitative difference in the uptake of the rCTB- and HSA-conjugated microparticles was seen. The rCTB-conjugated microparticles were found both in villi and in the follicles of the Peyer's patches. HSA-conjugated microparticles could only be detected in the follicles of the Peyer's patches and not in villi. The rCTB conjugated to the microparticles did not lose its ability to bind the GM1-receptor, as shown with a GM1-ELISA, and the uptake of rCTB-conjugated microparticles in villi is most probably facilitated by the rCTB binding to the GM1-receptor. The qualitative difference in uptake could be of importance for the development of an immune response as the cytokine and chemokine microenvironment during antigen presentation will decide the differentiation of the immune response induced.

Cholera toxin promotes the generation of semi-mature porcine monocyte-derived dendritic cells that are unable to stimulate T cells

Cholera toxin (Ctx) is a powerful mucosal adjuvant with potential applications for oral vaccination of swine. Dendritic cells (DC) play a key role in the decision between immunity and tolerance, and are likely target cells for mediating Ctx functions in vivo. Therefore, we examined the capacity of Ctx to enhance stimulatory activity of porcine monocyte-derived DC (MoDC). Ctx promoted the development of a semi-mature DC phenotype, with decreased levels of MHC class II and CD40, but increased CD80/86 expression. These changes were associated with activation of extracellular signal-regulated kinase (ERK), but not NFkappaB or c-Jun N-terminal kinase (JNK). Functionally, Ctx-priming greatly diminished T cell stimulatory capacity both in antigen-specific and superantigen-induced proliferation assays. The lower proliferation rate was not due to increased apoptosis of either DC or T cells. Ctx suppressed TNFalpha secretion by MoDC, but induced IL-10 production. The observed effects on T cell proliferation could only be partially mimicked by IL-10 alone. However, addition of recombinant TNFalpha to co-cultures of Ctx-primed MoDC and lymphocytes restored lymphocyte proliferation in a concentration-dependent manner. Ctx-primed DC were not actively tolerogenic, since they could not suppress proliferative T cell reactions induced by untreated DC.

Bordetella pertussis inhibition of interleukin-12 (IL-12) p70 in human monocyte-derived dendritic cells blocks IL-12 p35 through adenylate cyclase toxin-dependent cyclic AMP induction

Bordetella pertussis, the causative agent of whooping cough, possesses an array of virulence factors, including adenylate cyclase toxin (ACT), relevant in the establishment of infection. Here we better define the impact of cyclic AMP (cAMP) intoxication due to the action of ACT on dendritic cell (DC)-driven immune response, by infecting monocyte-derived DC (MDDC) with an ACT-deficient B. pertussis mutant (ACT- 18HS19) or its parental strain (WT18323). Both strains induced MDDC maturation and antigen-presenting cell functions; however, only ACT- 18HS19 infected MDDC-induced production of interleukin-12 (IL-12) p70. Gene expression analysis of the IL-12 cytokine family subunits revealed that both strains induced high levels of p40 (protein chain communal to IL-12 p70 and IL-23) as well as p19, a subunit of IL-23. Conversely only ACT- 18HS19 infection induced consistent transcription of IL-12 p35, a subunit of IL-12 p70. Addition of the cAMP analogous D-butyril-cAMP (D-cAMP) abolished IL-12 p70 production and IL-12 p35 expression in ACT- 18HS19-infected MDDC. ACT- 18HS19 infection induced the expression of the transcription factors interferon regulatory factor 1 (IRF-1) and IRF-8 and of beta interferon, involved in IL-12 p35 regulation, and the expression of these genes was inhibited by D-cAMP addition and in WT18323-infected MDDC. The concomitant expression of IL-12 p70 and IL-23 allowed ACT- 18HS19 to trigger a more pronounced T helper 1 polarization compared to WT18323. The present study suggests that ACT-dependent cAMP induction leads to the inhibition of pathways ultimately leading to IL-12 p35 production, thus representing a mechanism for B. pertussis to escape the host immune response.

Adjuvants modulating mucosal immune responses or directing systemic responses towards the mucosa

In developing veterinary mucosal vaccines and vaccination strategies, mucosal adjuvants are one of the key players for inducing protective immune responses. Most of the mucosal adjuvants seem to exert their effect via binding to a receptor/or target cells and these properties were used to classify the mucosal adjuvants reviewed in the present paper: (1) ganglioside receptor-binding toxins (cholera toxin, LT enterotoxin, their B subunits and mutants); (2) surface immunoglobulin binding complex CTA1-DD; (3) TLR4 binding lipopolysaccharide; (4) TLR2-binding muramyl dipeptide; (5) Mannose receptor-binding mannan; (6) Dectin-1-binding ss 1,3/1,6 glucans; (7) TLR9-binding CpG-oligodeoxynucleotides; (8) Cytokines and chemokines; (9) Antigen-presenting cell targeting ISCOMATRIX and ISCOM. In addition, attention is given to two adjuvants able to prime the mucosal immune system following a systemic immunization, namely 1alpha, 25(OH)2D3 and cholera toxin.

cAMP-induced PKCzeta activation increases functional CXCR4 expression on human CD34+ hematopoietic progenitors

Chemokines are key regulators of hematopoiesis and host defense. We report here that functional expression of the chemokine receptor CXCR4 on human immature CD34+ hematopoietic progenitors was increased as a result of sustained elevation in cellular cAMP by dbcAMP and prostaglandin E2. This effect of cAMP was specifically mediated by PKCzeta activity. CXCR4 expression and PKCzeta activation by cAMP were decreased after the inhibition of cAMP effector-Rap1 by Spa1 overexpression. Interference with the activation of Rac1, a downstream target of Rap1, prevented the cAMP-induced increase in PKCzeta activity and CXCR4 levels. Functional manifestation of the effects of cAMP-elevating agents revealed an increased ability of human CD34+ cells to transmigrate the bone marrow (BM) endothelial layer and adhere to BM stroma in vitro, and it augmented the homing potential to the BM and spleens of immunodeficient mice in a Rac1- and a PKCzeta-dependent manner. cAMP- and TNFalpha-stimulated pathways converged in PKCzeta-activated CXCR4 expression and MMP-2/MMP-9 secretion. cAMP treatment had a beneficial effect on CD34+ cell survival in a PKCzeta-mediated fashion. Taken together, our data reveal major roles for cAMP-induced PKCzeta activation in signaling governing the motility and development of CD34+ cells.

Expression of CXCR4 and Its Down-Regulation by IFN-γ in Head and Neck Squamous Cell Carcinoma

PURPOSE

The functional expression of CXCR4, which plays roles in cell migration and proliferation in response to its unique ligand stromal cell-derived factor-1 (SDF-1), has been reported in variety of carcinomas. However, CXCR4 expression and its functional role in head and neck squamous cell carcinomas (HNSCC) remain unclear. In this study, we investigated CXCR4 expression and analyzed its functions in HNSCC cell lines. We also attempted to regulate CXCR4 expression using cytokines, such as interleukin-1beta, tumor necrosis factor-alpha, and IFN-gamma. Finally, we investigated correlation between CXCR4 expression and clinical features in patients with HNSCC.

EXPERIMENTAL DESIGN

Six HNSCC cell lines were used in this study. Reverse transcription-PCR and flow cytometry analysis were shown for CXCR4 expressions with or without stimulations of cytokines. SDF-1-mediated cell migration was assayed in Matrigel-coated chemotaxis chamber. The SDF-1-mediated cell proliferation was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The SDF-1-mediated signaling pathways were analyzed by Western blot analysis. Biopsy specimens from 56 patients with HNSCC were used for immunohistologic analysis.

RESULTS

The significant CXCR4 expression was found in HSQ-89, IMC-3, and Nakamura cells. The SDF-1-mediated cell migration and proliferation were observed in CXCR4-positive cells. SDF-1 also promoted rapid phosphorylation of extracellular signal-regulated kinase 1/2 and Akt signaling pathways in CXCR4-positive cells. The SDF-1-mediated cell migration and proliferation of CXCR4-positive cells were inhibited by neutralization of CXCR4. Among three cytokines tested, IFN-gamma significantly reduced CXCR4 expression and SDF-1-induced cell migration and proliferation of CXCR4-positive cells. Immunohistologic analysis revealed that patients with advanced neck status and patients who developed distant metastases showed significantly higher CXCR4 expression, and the cause-specific survival of patients with CXCR4-expression was significantly shorter. Furthermore, multivariate analysis confirmed that CXCR4 positive was the independent factor for cause-specific death.

CONCLUSION

Our results may provide an insight into future therapeutic agent that inhibits tumor metastasis and progression via down-regulating CXCR4 expression in patients with HNSCC.

From toxin to adjuvant: basic mechanisms for the control of mucosal IgA immunity and tolerance

We provide compelling evidence that delivery of Ag in the absence of ADP-ribosylation can promote tolerance, whereas ADP-ribosyltransferase activity induces IgA immunity and prevents tolerance. By linking Ag to the ADP-ribosylating enzyme, cholera toxin subunit A1 (CTA1), we could show that the combination of targeting to antigen-presenting cells (APC) and enzymatic activity is a highly effective means of controlling the induction of tolerance or immunity. Firstly, we demonstrated that cholera toxin (CT), although potentially binding to all nucleated cells, in fact, bound preferentially to dendritic cells (DC) in vivo. Following injection of CT-conjugated Ag, we found that DC in the marginal zone (MZ) of the spleen accumulated Ag, a process that was GM1-ganglioside receptor dependent. Contrary to CTB, which also delivered Ag to the MZ DC, CT matured and activated co-stimulatory functions in the targeted DC and greatly augmented immune responses to Ag. Secondly, when Ag was incorporated into the CTA1-DD fusion protein, which equals the CT in adjuvant function but lacks GM1-ganglioside-binding ability, we greatly augmented specific responses to Ag. The DD-bound Ag was distinctly targeted to B cells and probably also to follicular dendritic cells (FDC) in vivo. Thus, in both constructs Ag was targeted to APC and associated with an ADP-ribosylating enzyme, which resulted in greatly enhanced immunogenicity. When the enzymatic activity was absent, as in CT B-subunit (CTB) or in the inactive CTA1R7K-DD mutant, Ag largely failed to stimulate an active immune response. Rather, this type of Ag exposure resulted in Ag-specific tolerance, especially when mucosal delivery of Ag was attempted. Therefore, targeting to APC in the absence or presence of the CTA1-enzyme appears to be an effective means to control tolerance and active protective IgA immunity.

Cholera toxin improves the F4(K88)-specific immune response following oral immunization of pigs with recombinant FaeG

Oral immunization of both humans and animals with non-replicating soluble antigens often results in the induction of oral tolerance. However, receptor-dependent uptake of orally administered soluble antigens can lead to the induction of an antigen-specific immune response. Indeed, oral immunization of pigs with recombinant FaeG (rFaeG), the adhesin of the F4(K88) fimbriae of enterotoxigenic Escherichia coli (ETEC), induces an F4-specific humoral and cellular immune response. This response is accompanied with a reduction in the excretion of F4(+)E. coli following challenge. To improve the immune response against F4, rFaeG was orally co-administered with the mucosal adjuvant cholera toxin (CT). Oral immunization of pigs with rFaeG and CT significantly improved the induction of an F4-specific humoral and cellular immune response and also significantly reduced the faecal F4(+)E. coli excretion following F4(+) ETEC challenge as compared to rFaeG-immunized pigs. Therefore, the present study demonstrates that CT can act in pigs as a mucosal adjuvant for antigens that bind to the intestinal epithelium by a CT-receptor-independent mechanism.

Mucosal adjuvants and anti-infection and anti-immunopathology vaccines based on cholera toxin, cholera toxin B subunit and CpG DNA

Mucosal immunisation may be used both to protect the mucosal surfaces against infections and as a means for immunological treatment of peripheral immunopathological disorders through the induction of systemic antigen-specific tolerance ('oral tolerance'). The development of mucosal vaccines, whether for prevention of infectious diseases or for oral tolerance immunotherapy, requires efficient antigen delivery and adjuvant systems that can help to present the appropriate vaccine or immunotherapy antigens to the mucosal immune system. The most potent (but also toxic) mucosal adjuvants are cholera toxin (CT) and the closely related Escherichia coli heat-labile enterotoxin (LT), and much effort and significant progress have been made recently to generate toxicologically acceptable derivatives of these toxins with retained adjuvant activity. Among these are the non-toxic, recombinantly produced cholera toxin B-subunit (CTB). CTB is a specific protective antigen component of a widely registered oral cholera vaccine as well as a promising vector for either giving rise to mucosal anti-infective immunity or for inducing peripheral anti-inflammatory tolerance to chemically or genetically linked foreign antigens administered mucosally. CT and CTB have also recently been used as combined vectors and adjuvants for markedly promoting ex vivo dendritic cell (DC) vaccination with different antigens and also steering the immune response to the in vivo-reinfused DCs towards either broad Th1 + Th2 + CTL immunity (CT) or Th2 or tolerance (CTB). Another type of mucosal adjuvants is represented by bacterial DNA or synthetic oligodeoxynucleotides containing CpG-motifs, which especially when linked to CTB have been found to effectively stimulate both innate and adaptive mucosal immune responses. The properties and clinical potential of these different classes of adjuvants are being discussed.

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.

Activation and suppression of the proinflammatory immune response by Vibrio cholerae toxins

Vibrio cholerae induces either non-inflammatory diarrhea or inflammatory gastroenteritis, depending on the presence of cholera toxin, a fluid secretion inducer and a modulator of host immunity. In the absence of cholera toxin, other toxins induce inflammation, resulting in gastroenteritis. Thus, multiple toxins likely affect the safety of live attenuated vaccines.