The cholera toxin B subunit is a mucosal adjuvant for oral tolerance induction in type 1 diabetes

Oral Administration of Silkworm-Produced GAD65 and Insulin Bi-Autoantigens against Type 1 Diabetes

Induction of mucosal tolerance by oral administration of protein antigens is a potential therapeutic strategy for preventing and treating type 1 diabetes (T1D); however, the requirement for a large dosage of protein limits clinical applications because of the low efficacy. In this study, we generated a fusion protein CTB-Ins-GAD composed of CTB (cholera toxin B subunit), insulin, and three copies of GAD65 peptide 531–545, which were efficiently produced in silkworm pupae, to evaluate its protective effect against T1D. We demonstrate that oral administration of CTB-Ins-GAD suppressed T1D by up to 78%, which is much more effective than GAD65 single-antigen treatment. Strikingly, CTB-Ins-GAD enhance insulin- and GAD65-specific Th2-like immune responses, which repairs the Th1/Th2 imbalance and increases the number of CD4⁺CD25⁺Foxp3⁺ T cell and suppresses insulin- and GAD65-reactive spleen T lymphocyte proliferation and migration. Our results strongly suggest that the combined dual antigens promote the induction of oral tolerance, thus providing an effective and economic immunotherapy against T1D in combination with a silkworm bioreactor.

Plant-based vaccines: novel and low-cost possible route for Mediterranean innovative vaccination strategies

A plant bioreactor has enormous capability as a system that supports many biological activities, that is, production of plant bodies, virus-like particles (VLPs), and vaccines. Foreign gene expression is an efficient mechanism for getting protein vaccines against different human viral and nonviral diseases. Plants make it easy to deal with safe, inexpensive, and provide trouble-free storage. The broad spectrum of safe gene promoters is being used to avoid risk assessments. Engineered virus-based vectors have no side effect. The process can be manipulated as follows: (a) retrieve and select gene encoding, use an antigenic protein from GenBank and/or from a viral-genome sequence, (b) design and construct hybrid-virus vectors (viral vector with a gene of interest) eventually flanked by plant-specific genetic regulatory elements for constitutive expression for obtaining chimeric virus, (c) gene transformation and/or transfection, for transient expression, into a plant-host model, that is, tobacco, to get protocols processed positively, and then moving into edible host plants, (d) confirmation of protein expression by bioassay, PCR-associated tests (RT-PCR), Northern and Western blotting analysis, and serological assay (ELISA), (e) expression for adjuvant recombinant protein seeking better antigenicity, (f) extraction and purification of expressed protein for identification and dosing, (g) antigenicity capability evaluated using parental or oral delivery in animal models (mice and/or rabbit immunization), and (h) growing of construct-treated edible crops in protective green houses. Some successful cases of heterologous gene-expressed protein, as edible vaccine, are being discussed, that is, hepatitis C virus (HCV). R9 mimotope, also named hypervariable region 1 (HVR1), was derived from the HVR1 of HCV. It was used as a potential neutralizing epitope of HCV. The mimotope was expressed using cucumber mosaic virus coat protein (CP), alfalfa mosaic virus CP P3/RNA3, and tobacco mosaic virus (TMV) CP-tobacco mild green mosaic virus (TMGMV) CP as expression vectors into tobacco plants. Expressed recombinant protein has not only been confirmed as a therapeutic but also as a diagnostic tool. Herpes simplex virus 2 (HSV-2), HSV-2 gD, and HSV-2 VP16 subunits were transfected into tobacco plants, using TMV CP-TMGMV CP expression vectors.

Persistent suppression of type 1 diabetes by a multicomponent vaccine containing a cholera toxin B subunit-autoantigen fusion protein and complete Freund's adjuvant

Data presented here demonstrate multifunctional vaccination strategies that harness vaccinia virus mediated delivery of a gene encoding an immunoenhanced diabetes autoantigen in combination with complete Freund's adjuvant (CFA) that can maintain safe and durable immunologic homeostasis in NOD mice. Systemic coinoculation of prediabetic mice with recombinant vaccinia virus rVV-CTB::GAD and undiluted or 10-fold diluted CFA demonstrated a significant decrease in hyperglycemia and pancreatic islet inflammation in comparison with control animals during 17–61 and 17–105 weeks of age, respectively. Synergy in these beneficial effects was observed during 43–61 and 61–105 wks of age, respectively. Inflammatory cytokine and chemokine levels in GAD-stimulated splenocytes isolated from vaccinated mice were generally lower than those detected in unvaccinated mice. The overall health and humoral immune responses of the vaccinated animals remained normal throughout the duration of the experiments.

Cholera toxin subunit B peptide fusion proteins reveal impaired oral tolerance induction in diabetes-prone but not in diabetes-resistant mice

The cholera toxin B subunit (CTB) has been used as adjuvant to improve oral vaccine delivery in type 1 diabetes. The effect of CTB/peptide formulations on Ag-specific CD4(+) T cells has remained largely unexplored. Here, using tetramer analysis, we investigated how oral delivery of CTB fused to two CD4(+) T-cell epitopes, the BDC-2.5 T-cell 2.5 mi mimotope and glutamic acid decarboxylase (GAD) 286-300, affected diabetogenic CD4(+) T cells in nonobese diabetic (NOD) mice. When administered i.p., CTB-2.5 mi activated 2.5 mi(+) T cells and following intragastric delivery generated Ag-specific Foxp3(+) Treg and Th2 cells. While 2.5 mi(+) and GAD-specific T cells were tolerized in diabetes-resistant NODxB6.Foxp3(EGFP) F1 and nonobese resistant (NOR) mice, this did not occur in NOD mice. This indicated that NOD mice had a recessive genetic resistance to induce oral tolerance to both CTB-fused epitopes. In contrast to NODxB6.Foxp3(EGFP) F1 mice, oral treatment in NOD mice lead to strong 2.5 mi(+) T-cell activation and the sequestration of these cells to the effector-memory pool. Oral treatment of NOD mice with CTB-2.5 mi failed to prevent diabetes. These findings underline the importance of investigating the effect of oral vaccine formulations on diabetogenic T cells as in selected cases they may have counterproductive consequences in human patients.

Prolonged survival time of allografts by the oral administration of RDP58 linked to the cholera toxin B subunit

Oral administration, which has been identified as a tool for boosting physiological immunoregulatory mechanisms in an antigen-specific manner, is a more convenient way than classical parenteral injection methods. RDP58 is derived from specific regions of class-I MHC molecules and is known to have immunomodulatory effects after intraperitoneal injection or intravenous administration. To determine whether the oral administration of RDP58 conjugated to the cholera toxin B subunit (CTB) can better induce peripheral tolerance than the use of traditional methods, we used various feeding regimens and methods of administration using equivalent doses of antigen during rat kidney transplantation. The results showed that RDP58-GC/CTB treatment increased the activity of Haem oxygenase-1 (HO-1) in vivo and significantly improved the survival and histopathology of allograft kidney tissue relative to the oral administration of RDP58 alone. These results suggest that the administration of RDP58 linked to CTB outweighs the benefits of oral administration of RDP58 alone for prolonging the survival time of kidney transplantation. This study supports the potential therapeutic use of oral administration of RDP58 linked to CTB as a platform molecule in the treatment of allograft rejection.

Autoantigens plus interleukin-10 suppress diabetes autoimmunity

BACKGROUND

Recombinant vaccinia virus (rVV) strains expressing the immunomodulatory cholera toxin B subunit (CTB) fused to the autoantigen glutamic acid decarboxylase (GAD) or the immunosuppressive cytokine interleukin-10 (IL-10) were independently able to generate only low levels of immune suppression of type 1 diabetes mellitus (T1DM). Here we suggest that a vaccinia virus (VV)-mediated combination of CTB::GAD fusion and IL-10 proteins promises a effective and durable immunotherapeutic strategy for T1DM.

METHODS

To explore this hypothesis, a CTB::GAD fusion gene was co-delivered with a gene encoding IL-10 by rVV infection (rVV-CTB::GAD + rVV-IL10) into 5-7-week-old non-obese diabetic (NOD) mice. The mice were assessed for vaccine protection against development of hyperglycemia from 12 to 64 weeks of age by assessment of pancreatic inflammation (insulitis) and splenocyte-secreted interferon-gamma and IL-10 cytokine levels.

RESULTS

By 36 weeks of age, from 54% to 80% of the mice in the negative control animal groups (either mock-infected or inoculated with unrelated plasmid or VV) had developed hyperglycemia. Similarly, no statistically significant improvement in protection against diabetes onset was achieved by inoculation with VV expressing CTB::GAD or IL-10 independently. Surprisingly, only 20% of mice co-inoculated with rVV-CTB::GAD + rVV-IL10 developed hyperglycemia by 28 weeks of age. Other treatment groups developed hyperglycemia by 32-36 weeks. After 36 weeks, diabetes incidence no longer increased in any groups until the end of experiment at 64 weeks of age. Histological analysis of pancreatic tissues of hyperglycemic mice revealed high levels of intra-islet insulitis. Analysis of insulitis at termination of the experiment showed that euglycemic mice co-inoculated with VV expressing CTB::GAD and IL-10 had more effectively reduced inflammation in comparison with the other groups.

CONCLUSIONS

A combinatorial vaccination strategy based on VV co-delivery of genes encoding the immunoenhanced autoantigen CTB::GAD and the anti-inflammatory cytokine IL-10 can maintain effective and durable euglycemia and immunological homeostasis in NOD mice with prediabetes.

Gene therapy in diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease, whereby auto-reactive cytotoxic T cells target and destroy insulin-secreting β-cells in pancreatic islets leading to insulin deficiency and subsequent hyperglycemia. These individuals require multiple daily insulin injections every day of their life without which they will develop life-threatening diabetic ketoacidosis (DKA) and die. Gene therapy by viral vector and non-viral transduction may be useful techniques to treat T1D as it can be applied from many different angles; such as the suppression of autoreactive T cells to prevent islet destruction (prophylactic) or the replacement of the insulin gene (post-disease). The need for a better method for providing euglycemia arose from insufficient numbers of cadaver islets for transplantation and the immunosuppression required post-transplant. Ectopic expression of insulin or islet modification have been examined, but not perfected. This review examines the various gene transfer methods, gene therapy techniques used to date and promising novel techniques for the maintenance of euglycemia in the treatment of T1D.

Expression of a ricin toxin B subunit: insulin fusion protein in edible plant tissues

Onset of juvenile Type 1 diabetes (T1D) occurs when autoreactive lymphocytes progressively destroy the insulin-producing beta-cells in the pancreatic Islets of Langerhans. The increasing lack of insulin and subsequent onset of hyperglycemia results in increased damage to nerves, blood vessels, and tissues leading to the development of a host of severe disease symptoms resulting in premature morbidity and mortality. To enhance restoration of normoglycemia and immunological homeostasis generated by lymphocytes that mediate the suppression of autoimmunity, the non-toxic B chain of the plant AB enterotoxin ricin (RTB), a castor bean lectin binding a variety of epidermal cell receptors, was genetically linked to the coding region of the proinsulin gene (INS) and expressed as a fusion protein (INS-RTB) in transformed potato plants. This study is the first documented example of a plant enterotoxin B subunit linked to an autoantigen and expressed in transgenic plants for enhanced immunological suppression of T1D autoimmunity.

Type II collagen oral tolerance; mechanism and role in collagen-induced arthritis and rheumatoid arthritis. Mod Rheumatol. 2009;19:581-589. [PMID: 19697097 DOI: 10.1007/s10165-009-0210-0]

Oral tolerance means a diminished immune response to previously fed antigens. Repeated oral administrations of type II collagen (CII) induce oral tolerance and inhibit the development of collagen-induced arthritis (CIA). Dendritic cells (DCs) in the gut-associated lymphoid tissue (GALT) take up the CII and then present it to T cells to generate regulatory T cells (Tregs), which induce systemic immune tolerance to CII. Inhibitory cytokines, such as transforming growth factor (TGF)-beta and interleukin (IL)-10, and several immune regulatory molecules, including indoleamine 2,3-dioxygenase (IDO) and retinoic acid, play an important role in Treg generation. Each DC subset may play different roles, and CD11c+CD11b+DCs and IDO+DCs are important in the generation of antigen-inducible Tregs in CII oral tolerance. Upon stimulation with the antigen involved in its generation, Treg is activated and regulates the immune response through inhibitory cytokine production, cell-to-cell contact-dependent mechanisms, DC modification, and bystander suppression. The DCs and Tregs are deeply involved in oral tolerance through reciprocal interactions. Several clinical trials have been conducted in RA patients to examine the efficacy of CII oral tolerance. An understanding the mechanism of oral tolerance to CII would give clinicians new insights into the development of natural immune tolerance and new therapeutic approaches for the treatment of autoimmune diseases.

Cloning, expression, purification and characterization of the cholera toxin B subunit and triple glutamic acid decarboxylase epitopes fusion protein in Escherichia coli

Induction of specific immunological unresponsiveness by oral autoantigens such as glutamic acid decarboxylase 65 (GAD65) is termed oral tolerance and may be a potential therapy for autoimmune diabetes. However, the requirement for large amounts of protein will limit clinical testing of autoantigens, which are difficult to produce. Mucosal adjuvants such as cholera toxin B subunit (CTB) may lower the level of autoantigens required. Here we describe cloning, expression, purification and identification study of the CTB and triple GAD(531-545) epitopes fusion gene. The fusion gene was ligated via a flexible hinge tetrapeptide and expressed as a soluble protein in Escherichia coli BL21 (DE3) driven by the T7 promoter. We purified the recombination protein from the cell lysate and obtained approximately 2.5mg of CTB-GAD((531-545)3) per liter of culture with greater than 90% purity by a Ni-NTA resin column. The bacteria produced this protein as the pentameric form, which retained the GM1-ganglioside binding affinity and the native antigenicity of CTB and GAD65. Further studies revealed that oral administration of bacterial CTB-GAD((531-545)3) fusion protein showed the prominent reduction in pancreatic islet inflammation in non-obese diabetic mice. The results presented here demonstrate that the bacteria bioreactor is an ideal production system for an oral protein vaccine designed to develop immunological tolerance against autoimmune diabetes.

Cholera toxin B subunit promotes the induction of regulatory T cells by preventing human dendritic cell maturation

Cholera toxin B subunit (CTB) is an efficient mucosal carrier molecule for the generation of immune responses to linked antigens. There is also good evidence that CTB acts as an immunosuppressant, as it is able to down-modulate human monocyte/macrophage cell line activation and to suppress Th1-type responses. In the present study, we examined the possibility that recombinant CTB (rCTB) may affect human dendritic cell (DC) functions in response to LPS stimulation and may induce the generation of DC with the capacity to generate CD4(+) regulatory T cells (Tregs). Our findings show that rCTB partially prevents the LPS-induced maturation process of monocyte-derived DC (MDDC) and decreases their IL-12 production with no relevant effect on IL-10 production. LPS-stimulated MDDC pretreated with rCTB are able to promote the induction of low proliferating T cells, which show an enhanced IL-10 production associated with a reduced IFN-gamma production and the same high levels of TGF-beta as the control. These T cells suppress proliferation of activated autologous T cells. Transwell experiments and blockade of IL-10R and TGF-beta showed that the immunomodulatory effect is mediated by soluble factors. Thus, T cells induced by rCTB-conditioned MDDC acquire a regulatory phenotype and activity similar to those described for type 1 Tregs.

Suppression of hyperglycemia in NOD mice after inoculation with recombinant vaccinia viruses

In autoimmune (type 1) diabetes, autoreactive lymphocytes destroy pancreatic beta-cells responsible for insulin synthesis. To assess the feasibility of gene therapy for type 1 diabetes, recombinant vaccinia virus (rVV) vectors were constructed expressing pancreatic islet autoantigens proinsulin (INS) and a 55-kDa immunogenic peptide from glutamic acid decarboxylase (GAD), and the immunomodulatory cytokine interleukin (IL)-10. To augment the beneficial effects of recombinant virus therapy, the INS and GAD genes were fused to the C terminus of the cholera toxin B subunit (CTB). Five-week-old non-obese diabetic (NOD) mice were injected once with rVV. Humoral antibody immune responses and hyperglycemia in the infected mice were analyzed. Only 20% of the mice inoculated with rVV expressing the CTB::INS fusion protein developed hyperglycemia, in comparison to 70% of the mice in the uninoculated animal group. Islets from pancreatic tissues isolated from euglycemic mice from this animal group showed no sign of inflammatory lymphocyte invasion. Inoculation with rVV producing CTB::GAD or IL-10 was somewhat less effective in reducing diabetes. Humoral antibody isotypes of hyperglycemic and euglycemic mice from all treated groups possessed similar IgG1/IgG2c antibody titer ratios from 19 to 32 wk after virus inoculation. In comparison with uninoculated mice, 11-wk-old NOD mice injected with virus expressing CTB::INS were delayed in diabetes onset by more than 4 wk. The experimental results demonstrate the feasibility of using rVV expressing CTB::INS fusion protein to generate significant protection and therapy against type 1 diabetes onset and progression.

Mucosal exposure to antigen: cause or cure of type 1 diabetes?

The human gut offers more than 200 m2 of mucosal surface, where direct interactions between the immune system and foreign antigens take place to eliminate pathogens or induce immune tolerance toward food antigens or normal gut flora. Therefore, mucosally administered antigens can induce tolerance under certain circumstances. In autoimmune diabetes, mucosal vaccination with autoantigens elicits some efficacy in restoring tolerance in mice, but it never succeeded in humans. Furthermore, in some instances autoimmunity can be precipitated upon oral or intranasal autoantigen administration. Therefore, it is difficult to predict the effect of mucosal vaccination on autoimmunity and much effort should be put into establishing better assays to reduce the risk for possible adverse events in humans and enable a rapid and smooth translation.

Lost in translation: barriers to implementing clinical immunotherapeutics for autoimmunity

Induction of selective, autoantigen-specific tolerance is the “holy grail” for the treatment and prevention of autoimmune diseases. Despite successes in many differential murine models, rational and efficient translation to the clinic has been difficult. During the 5th Annual Federation of Clinical Immunological Societies (FOCIS) Meeting, May 12–16, 2005, in Boston, MA, a Kirin-sponsored “Ideashop” was convened to discuss this theme amongst scientists, clinicians, industry partners, and funding agencies.

Protection of NOD mice from type 1 diabetes after oral inoculation with vaccinia viruses expressing adjuvanted islet autoantigens

Oral administration of autoantigens and allergens can delay or suppress clinical disease in experimental autoimmune and allergic disorders. However, repeated feeding of large amounts of the tolerogens is required over long periods and is only partially effective in animals systemically sensitized to the ingested antigen. Enhanced suppression of type 1 autoimmune diabetes insulitis and hyperglycemia was demonstrated in both naive and immune animals following oral inoculation with plant-based antigens coupled to the cholera toxin B subunit (CTB). Thus, plant-synthesized antigens linked to the CTB adjuvant, can enhance suppression of inflammatory TH1 lymphocyte-mediated autoreactivity in both naive and immune animals. To stimulate adjuvant-autoantigen fusion protein biosynthesis in the gut mucosae, the authors evaluated oral inoculation of juvenile non-obese diabetic (NOD) mice with recombinant vaccinia virus (rVV) expressing fusion genes encoding CTB linked to the pancreatic islet autoantigens proinsulin (INS) and a 55-kDa C-terminal peptide from glutamate decarboxylase (GAD55). Hyperglycemia in both rVV-CTB:: INS and rVV-CTB:: GAD inoculated mice was substantially reduced in comparison with the uninoculated mouse control. Oral inoculation with rVV carrying the CTB::INS fusion gene generated a significant reduction in insulitis. An increase in IgG1 in comparison with IgG2c antibody isotype titers in rVV-CTB::INS infected mice suggested possible activation of autoantigen specific Th2 lymphocytes. The experimental results demonstrate feasibility of using vaccinia virus oral delivery of adjuvanted autoantigens to the mucosae of prediabetic mice for suppression and therapy of type 1 autoimmune diabetes.

Induction and recall of immune memory by mucosal immunization with a non-toxic recombinant enterotoxin-based chimeric protein

Previous reports have suggested that peroral delivery of antigens chemically coupled to non-toxic recombinant enterotoxin B subunits, such as the cholera toxin B subunit (CTB), induces tolerance to the antigen that may be abrogated by the toxic enzyme activity of intact enterotoxins, such as cholera toxin (CT). The aim of this study was to examine the immunogenicity of a genetically coupled protein composed of the saliva-binding region (SBR) of the Streptococcus mutans surface antigen AgI/II and the non-toxic A2 and B subunits of CT (SBR-CTA2/B) compared with that of recombinant SBR admixed with CT (SBR + CT) and SBR chemically coupled to recombinant CTB (SBR-CTB) following peroral delivery by intragastric (i.g.) immunization. The results showed that i.g. immunization with SBR-CTA2/B, like SBR + CT, induced antigen-specific serum immunoglobulin G (IgG) and salivary IgA antibodies, and sensitized splenic T cells. Comparison studies with SBR-CTB produced serum IgG but not salivary IgA titres and failed to sensitize splenic cells. Immunization with SBR-CTA2/B via the intranasal route also primed for the recall of antigen-specific memory antibody responses 6 months later. These findings show that SBR-CTA2/B is an immunogenic, not tolerogenic, chimeric protein that can induce and recall antigen-specific memory responses upon mucosal immunization.

Expression of Cholera Toxin B Subunit and Assembly as Functional Oligomers in Silkworm

The nontoxic B subunit of cholera toxin (CTB) can significantly increase the ability of proteins to induce immunological tolerance after oral administration, when it was conjugated to various proteins. Recombinant CTB offers great potential for treatment of autoimmune disease. Here we firstly investigated the feasibility of silkworm baculovirus expression vector system for the cost-effective production of CTB under the control of a strong polyhedrin promoter. Higher expression was achieved via introducing the partial non-coding and coding sequences (ATAAAT and ATGCCGAAT) of polyhedrin to the 5' end of the native CTB gene, with the maximal accumulation being approximately 54.4 mg/L of hemolymph. The silkworm bioreactor produced this protein vaccine as the glycoslated pentameric form, which retained the GM1-ganglioside binding affinity and the native antigenicity of CTB. Further studies revealed that mixing with silkworm-derived CTB increases the tolerogenic potential of insulin. In the nonconjugated form, an insulin : CTB ratio of 100 : 1 was optimal for the prominent reduction in pancreatic islet inflammation. The data presented here demonstrate that the silkworm bioreactor is an ideal production and delivery system for an oral protein vaccine designed to develop immunological tolerance against autoimmune diabetes and CTB functions as an effective mucosal adjuvant for oral tolerance induction.

Oral tolerance

Multiple mechanisms of tolerance are induced by oral antigen. Low doses favor active suppression, whereas higher doses favor clonal anergy/deletion. Oral antigen induces T-helper 2 [interleukin (IL)-4/IL-10] and Th3 [transforming growth factor (TGF)-beta] T cells plus CD4+CD25+ regulatory cells and latency-associated peptide+ T cells. Induction of oral tolerance is enhanced by IL-4, IL-10, anti-IL-12, TGF-beta, cholera toxin B subunit, Flt-3 ligand, and anti-CD40 ligand. Oral (and nasal) antigen administration suppresses animal models of autoimmune diseases including experimental autoimmune encephalitis, uveitis, thyroiditis, myasthenia, arthritis, and diabetes in the non-obese diabetic (NOD) mouse, plus non-autoimmune diseases such as asthma, atherosclerosis, graft rejection, allergy, colitis, stroke, and models of Alzheimer's disease. Oral tolerance has been tested in human autoimmune diseases including multiple sclerosis (MS), arthritis, uveitis, and diabetes and in allergy, contact sensitivity to dinitrochlorobenzene (DNCB), and nickel allergy. Although positive results have been observed in phase II trials, no effect was observed in phase III trials of CII in rheumatoid arthritis or oral myelin and glatiramer acetate (GA) in MS. Large placebo effects were observed, and new trials of oral GA are underway. Oral insulin has recently been shown to delay onset of diabetes in at-risk populations, and confirmatory trials of oral insulin are being planned. Mucosal tolerance is an attractive approach for treatment of autoimmune and inflammatory diseases because of lack of toxicity, ease of administration over time, and antigen-specific mechanisms of action. The successful application of oral tolerance for the treatment of human diseases will depend on dose, developing immune markers to assess immunologic effects, route (nasal versus oral), formulation, mucosal adjuvants, combination therapy, and early therapy.

An HIV-1 tat-autoantigen fusion protein suppresses insulitis in NOD mice

To assess the immunomodulatory activity of the HIV Tat transduction peptide for enhancement of suppression of Type 1 autoimmune diabetes, the 11 amino acid HIV-1 Tat transduction peptide was genetically linked to the major islet autoantigens proinsulin (INS) and glutamic acid decarboxylase (GAD). The Tat-autoantigen fusion proteins were synthesized in Escherichia coli and characterized by acrylamide gel separation and immunoblot analysis. Histological examination of pancreatic islets isolated from juvenile NOD mice inoculated orally with the Tat-autoantigen conjugates revealed a significant reduction in islet inflammation (insulitis) in comparison with islets from unimmunized mice. Increased serum IgG1 antibody isotype titers detected in Tat-autoantigen inoculated mice suggest that the transduction peptide-autoantigen fusion proteins stimulate Th2 lymphocyte mediated bystander suppression. The reduction of islet insulitis observed in Tat-autoantigen inoculated mice suggests that the adjuvant effect of the Tat transduction peptide resides in Tat enhanced delivery of linked autoantigens through enterocytes to lymphocytes in the gut-associated lymphoid tissues.

Effects of cholera toxin on innate and adaptive immunity and its application as an immunomodulatory agent

Cholera toxin (CT) is a potent vaccine adjuvant when administered via parenteral, mucosal, or transcutaneous routes. It also inhibits innate inflammatory responses induced by pathogen-derived molecules, such as lipopolysaccharide (LPS). We demonstrated previously that CT promotes the induction of regulatory type 1 T cells (Tr1) as well as T helper type 2 cells (Th2). T cells from mice immunized with antigen in the presence of CT produced high levels of interleukin (IL)-10 and IL-5 and low levels of IL-4 and interferon-gamma (IFN-gamma). Here, we demonstrate that immunization with antigen in the presence of CT induced a population of antigen-specific CD4(+) T cells that produced IL-10 in the absence of IL-4, in addition to cells that coexpressed IL-4 and IL-10 or produced IL-4 only. CT-generated Tr1 cells inhibited antigen-specific proliferation as well as IFN-gamma production by Th1 cells, and this suppression was cell contact-independent. It is interesting that coincubation with Th1 cells significantly enhanced IL-10 production by the Tr1 cells. As IL-10 can promote the differentiation of Tr1 cells, we investigated cytokine production by dendritic cells (DC) following exposure to CT. Previous data showed that CT can modulate the expression of costimulatory molecules and inhibit the production of chemokines and cytokines, including IL-12 and tumor necrosis factor alpha and enhance IL-10 production. Here, we show that CT synergizes with LPS to induce IL-6 and IL-1beta in addition to IL-10 production by immature DC. Therefore, CT may promote the induction of Th2 and Tr1 cells in part via selective modulation of DC cytokine production and costimulatory molecule expression.

The cholera toxin B subunit directly costimulates antigen-primed CD4+ T cells ex vivo

The nontoxic B subunit of cholera toxin (CTB) has been used as an adjuvant in experimental systems of mucosal vaccination. However, the mechanisms behind its adjuvant effects remain unclear. Here, we have used an ex vivo system to elucidate these mechanisms in antigen-specific T cells. Using splenocytes from keyhole limpet haemocyanin (KLH)-immunized mice, initial experiments showed that recombinant CTB (rCTB) did not affect the KLH-specific proliferation of splenocytes isolated from mice immunized 2 weeks earlier. However, rCTB strongly enhanced the KLH-specific proliferation of splenocytes from mice immunized with KLH 4 weeks prior. This adjuvant effect was dose-dependent, with maximum at 30-300 ng/ml rCTB. At higher doses of CTB this effect declined because of the induction of apoptosis. Using antibody depletion and coculture systems, we show that rCTB directly costimulates KLH-specific CD4+ and CD8+ T-cell proliferation but not B cells. Enzyme-linked immunospot (ELISPOT) assays revealed that rCTB also enhanced the KLH-specific CD4+ T-cell-mediated production of interleukin-2 (IL-2), IL-4 and interferon-gamma(IFN-gamma) by four to fivefold. Characterizing the adjuvant effect of rCTB in vivo confirmed the results above, i.e. rCTB mediated a twofold increase in the ex vivo T-cell response when used as a classical adjuvant in a secondary, but not in a primary KLH-immunization regimen. Together these data show that rCTB can act as a strong adjuvant, by directly costimulating antigen-primed CD4+ and CD8+ T cell in a dose-dependent manner. This new insight might be valuable in the future rational design of bacterial toxin-based vaccines.