Production of a recombinant hybrid molecule of cholera toxin-B-subunit and proteolipid-protein-peptide for the treatment of experimental encephalomyelitis

Oral MucoRice-CTB vaccine is safe and immunogenic in healthy US adults

MucoRice-CTB is a promising cold-chain-free oral cholera vaccine candidate. Here, we report a double-blind, randomized, placebo-controlled, phase I study conducted in the USA in which vaccination with the 6-g dose of MucoRice-CTB induced cross-reactive antigen-specific antibodies against the B subunit of cholera toxin (CTB) and enterotoxigenic Escherichia coli heat-labile enterotoxin without inducing serious adverse events. This dosage was acceptably safe and tolerable in healthy men and women. In addition, it induced a CTB-specific IgA response in the saliva of two of the nine treated subjects; in one subject, the immunological kinetics of the salivary IgA were similar to those of the serum CTB-specific IgA. Antibodies from three of the five responders to the vaccine prevented CTB from binding its GM1 ganglioside receptor. These results are consistent with those of the phase I study in Japan, suggesting that oral MucoRice-CTB induces neutralizing antibodies against diarrheal toxins regardless of ethnicity.

Eyedrop vaccination: an immunization route with promises for effective responses to pandemics

INTRODUCTION

Mucosal vaccines have several advantages over parenteral vaccines. They induce both systemic and mucosal antigen-specific immune responses, allow easy administration, and bypass the need for trained medical personnel.

AREAS COVERED

Eye mucosa is a novel route of mucosal vaccine administration. Eyedrop vaccination induces systemic and mucosal immune responses similar to other forms of mucosal vaccines such as oral and intranasal vaccines.

EXPERT OPINION

Eyedrop vaccines are free of serious adverse side effects like the infiltration of CNS by pathogens. Studies over the years have shown promising results for eye drop vaccines against infectious agents like the influenza virus, Salmonella typhi, and Escherichia coli in animal models. Such efficacy and safety of eyedrop vaccination enable the application of eyedrop vaccines against other infectious diseases as well as chronic diseases. In this review of published literature, we examine the mechanism, efficacy, and safety of eyedrop vaccines and contemplate their role in times of a pandemic.

Antigen-Specific Treatment Modalities in MS: The Past, the Present, and the Future

Antigen-specific therapy for multiple sclerosis may lead to a more effective therapy by induction of tolerance to a wide range of myelin-derived antigens without hampering the normal surveillance and effector function of the immune system. Numerous attempts to restore tolerance toward myelin-derived antigens have been made over the past decades, both in animal models of multiple sclerosis and in clinical trials for multiple sclerosis patients. In this review, we will give an overview of the current approaches for antigen-specific therapy that are in clinical development for multiple sclerosis as well provide an insight into the challenges for future antigen-specific treatment strategies for multiple sclerosis.

Nasal Administration of Cholera Toxin as a Mucosal Adjuvant Damages the Olfactory System in Mice

Cholera toxin (CT) induces severe diarrhea in humans but acts as an adjuvant to enhance immune responses to vaccines when administered orally. Nasally administered CT also acts as an adjuvant, but CT and CT derivatives, including the B subunit of CT (CTB), are taken up from the olfactory epithelium and transported to the olfactory bulbs and therefore may be toxic to the central nervous system. To assess the toxicity, we investigated whether nasally administered CT or CT derivatives impair the olfactory system. In mice, nasal administration of CT, but not CTB or a non-toxic CT derivative, reduced the expression of olfactory marker protein (OMP) in the olfactory epithelium and olfactory bulbs and impaired odor responses, as determined with behavioral tests and optical imaging. Thus, nasally administered CT, like orally administered CT, is toxic and damages the olfactory system in mice. However, CTB and a non-toxic CT derivative, do not damage the olfactory system. The optical imaging we used here will be useful for assessing the safety of nasal vaccines and adjuvants during their development for human use and CT can be used as a positive control in this test.

Intranasal delivery: circumventing the iron curtain to treat neurological disorders

INTRODUCTION

The blood-brain barrier (BBB) is like an iron curtain that prevents exogenous substances, including most drugs, from entering the CNS. Intranasal delivery has been demonstrated to circumvent the BBB due to the special anatomy of the olfactory and trigeminal neural pathways that connect the nasal mucosa with the brain and the perivascular pathway within the CNS. In the last two decades, the concepts, mechanisms and pathways of intranasal delivery to the CNS have led to great success both in preclinical and clinical studies. More researchers have translated results from bench to bedside, and a number of publications have reported the clinical application of intranasal delivery.

AREAS COVERED

This review summarizes results from recent clinical trials utilizing intranasal delivery of therapeutics to explore its pharmacokinetics and application to treating neurological disorders. Moreover, existing problems with the methods and possible solutions have also been discussed. The promising results from clinical trials have demonstrated that intranasal delivery provides an extraordinary approach for circumventing the BBB. Many drugs, including high-molecular-weight molecules, could potentially improve the treatment of neurological disorders via intranasal administration.

EXPERT OPINION

Intranasal delivery is a novel method with great potential for delivering and targeting therapeutics to the CNS to treat neurological disorders.

RNAi-mediated suppression of endogenous storage proteins leads to a change in localization of overexpressed cholera toxin B-subunit and the allergen protein RAG2 in rice seeds

RNAi-mediated suppression of the endogenous storage proteins in MucoRice-CTB-RNAi seeds affects not only the levels of overexpressed CTB and RAG2 allergen, but also the localization of CTB and RAG2. A purification-free rice-based oral cholera vaccine (MucoRice-CTB) was previously developed by our laboratories using a cholera toxin B-subunit (CTB) overexpression system. Recently, an advanced version of MucoRice-CTB was developed (MucoRice-CTB-RNAi) through the use of RNAi to suppress the production of the endogenous storage proteins 13-kDa prolamin and glutelin, so as to increase CTB expression. The level of the α-amylase/trypsin inhibitor-like protein RAG2 (a major rice allergen) was reduced in MucoRice-CTB-RNAi seeds in comparison with wild-type (WT) rice. To investigate whether RNAi-mediated suppression of storage proteins affects the localization of overexpressed CTB and major rice allergens, we generated an RNAi line without CTB (MucoRice-RNAi) and investigated gene expression, and protein production and localization of two storage proteins, CTB, and five major allergens in MucoRice-CTB, MucoRice-CTB-RNAi, MucoRice-RNAi, and WT rice. In all lines, glyoxalase I was detected in the cytoplasm, and 52- and 63-kDa globulin-like proteins were found in the aleurone particles. In WT, RAG2 and 19-kDa globulin were localized mainly in protein bodies II (PB-II) of the endosperm cells. Knockdown of glutelin A led to a partial destruction of PB-II and was accompanied by RAG2 relocation to the plasma membrane/cell wall and cytoplasm. In MucoRice-CTB, CTB was localized in the cytoplasm and PB-II. In MucoRice-CTB-RNAi, CTB was produced at a level six times that in MucoRice-CTB and was localized, similar to RAG2, in the plasma membrane/cell wall and cytoplasm. Our findings indicate that the relocation of CTB in MucoRice-CTB-RNAi may contribute to down-regulation of RAG2.

Induction of toxin-specific neutralizing immunity by molecularly uniform rice-based oral cholera toxin B subunit vaccine without plant-associated sugar modification

Plants have been used as expression systems for a number of vaccines. However, the expression of vaccines in plants sometimes results in unexpected modification of the vaccines by N-terminal blocking and sugar-chain attachment. Although MucoRice-CTB was thought to be the first cold-chain-free and unpurified oral vaccine, the molecular heterogeneity of MucoRice-CTB, together with plant-based sugar modifications of the CTB protein, has made it difficult to assess immunological activity of vaccine and yield from rice seed. Using a T-DNA vector driven by a prolamin promoter and a signal peptide added to an overexpression vaccine cassette, we established MucoRice-CTB/Q as a new generation oral cholera vaccine for humans use. We confirmed that MucoRice-CTB/Q produces a single CTB monomer with an Asn to Gln substitution at the 4th glycosylation position. The complete amino acid sequence of MucoRice-CTB/Q was determined by MS/MS analysis and the exact amount of expressed CTB was determined by SDS-PAGE densitometric analysis to be an average of 2.35 mg of CTB/g of seed. To compare the immunogenicity of MucoRice-CTB/Q, which has no plant-based glycosylation modifications, with that of the original MucoRice-CTB/N, which is modified with a plant N-glycan, we orally immunized mice and macaques with the two preparations. Similar levels of CTB-specific systemic IgG and mucosal IgA antibodies with toxin-neutralizing activity were induced in mice and macaques orally immunized with MucoRice-CTB/Q or MucoRice-CTB/N. These results show that the molecular uniformed MucoRice-CTB/Q vaccine without plant N-glycan has potential as a safe and efficacious oral vaccine candidate for human use.

MucoRice-cholera toxin B-subunit, a rice-based oral cholera vaccine, down-regulates the expression of α-amylase/trypsin inhibitor-like protein family as major rice allergens

To develop a cold chain- and needle/syringe-free rice-based cholera vaccine (MucoRice-CTB) for human use, we previously advanced the MucoRice system by introducing antisense genes specific for endogenous rice storage proteins and produced a molecularly uniform, human-applicable, high-yield MucoRice-CTB devoid of plant-associated sugar. To maintain the cold chain-free property of this vaccine for clinical application, we wanted to use a polished rice powder preparation of MucoRice-CTB without further purification but wondered whether this might cause an unexpected increase in rice allergen protein expression levels in MucoRice-CTB and prompt safety concerns. Therefore, we used two-dimensional fluorescence difference gel electrophoresis and shotgun MS/MS proteomics to compare rice allergen protein expression levels in MucoRice-CTB and wild-type (WT) rice. Both proteomics analyses showed that the only notable change in the expression levels of rice allergen protein in MucoRice-CTB, compared with those in WT rice, was a decrease in the expression levels of α-amylase/trypsin inhibitor-like protein family such as the seed allergen protein RAG2. Real-time PCR analysis showed mRNA of RAG2 reduced in MucoRice-CTB seed. These results demonstrate that no known rice allergens appear to be up-reregulated by genetic modification of MucoRice-CTB, suggesting that MucoRice-CTB has potential as a safe oral cholera vaccine for clinical application.

Functional pentameric formation via coexpression of the Escherichia coli heat-labile enterotoxin B subunit and its fusion protein subunit with a neutralizing epitope of ApxIIA exotoxin improves the mucosal immunogenicity and protection against challenge by Actinobacillus pleuropneumoniae

A coexpression strategy in Saccharomyces cerevisiae using episomal and integrative vectors for the Escherichia coli heat-labile enterotoxin B subunit (LTB) and a fusion protein of an ApxIIA toxin epitope produced by Actinobacillus pleuropneumoniae coupled to LTB, respectively, was adapted for the hetero-oligomerization of LTB and the LTB fusion construct. Enzyme-linked immunosorbent assay (ELISA) with GM1 ganglioside indicated that the LTB fusion construct, along with LTB, was oligomerized to make the functional heteropentameric form, which can bind to receptors on the mucosal epithelium. The antigen-specific antibody titer of mice orally administered antigen was increased when using recombinant yeast coexpressing the pentameric form instead of recombinant yeast expressing either the LTB fusion form or antigen alone. Better protection against challenge infection with A. pleuropneumoniae was also observed for coexpression in recombinant yeast compared with others. The present study clearly indicated that the coexpression strategy enabled the LTB fusion construct to participate in the pentameric formation, resulting in an improved induction of systemic and mucosal immune responses.

Intranasal delivery of stem cells to the brain

INTRODUCTION

Stem cell-based therapy has proved to be a promising treatment option for neurological disorders. However, there are difficulties in successfully administrating these stem cells. For example, the brain-blood barrier impedes the entrance of stem cells into the CNS after systemic administration. Direct transplantation or injection may result in brain injury, and these strategies are clinically less feasible. Intranasal administration is a non-invasive and effective alternative for the delivery of drugs, vector-encoded viruses or even phages to the CNS. Recent studies have in fact demonstrated that stem cells may enter the CNS after intranasal administration. These results suggest that intranasal delivery may provide an alternative strategy for stem cell-based therapy.

AREAS COVERED

This review summarizes current studies that have applied the intranasal delivery of stem cells into the brain. In addition, the distribution and fate of stem cells in the brain and the potential opportunities as well as challenges of intranasal stem cell delivery are also discussed.

EXPERT OPINION

Intranasal delivery of stem cells is a new method with great potential for the transplantation of stem cells into the brain, and it may provide an extraordinary approach to overcoming the existing barriers of stem cell delivery for the treatment of many neurological disorders. This potential benefit emphasizes the importance of future research into intranasal delivery of stem cells.

Active immunization using a single dose immunotherapeutic abates established EAE via IL-10 and regulatory T cells

Stimulation of Ag-specific inducible Treg can enhance resolution of autoimmune disease. Conventional methods to induce Treg often require induction of autoimmune disease or subjection to infection. Reovirus adhesin, protein σ1 (pσ1), can successfully facilitate tolerance when fused to a tolerogen. We tested whether myelin oligodendrocyte glycoprotein (MOG) fused to pσ1 (MOG-pσ1) can stimulate Ag-specific Treg. We show that C57BL/6 mice treated nasally with MOG-pσ1 fail to induce MOG-specific Abs and delayed-type hypersensitivity (DTH) responses and resist EAE. Such resistance was attributed to stimulation of Foxp3(+) Treg, as well as Th2 cells. MOG-pσ1's protective capacity was abrogated in IL-10(-/-) mice, but restored when adoptively transferred with MOG-pσ1-induced Treg. As a therapeutic, MOG-pσ1 diminished EAE within 24 h of nasal application, unlike recombinant MOG (rMOG), pσ1, or pσ1+rMOG, implicating the importance of Ag specificity by pσ1-based therapeutics. MOG-pσ1-treated mice showed elevated IL-4, IL-10, and IL-28 production by CD4(+) T cells, unlike rMOG treated or control mice that produced elevated IFN-γ or IL-17, respectively. These data show the feasibility of using pσ1 as a tolerogen platform for Ag-specific tolerance induction and highlight its potential use as an immunotherapeutic for autoimmunity.

Nanogel antigenic protein-delivery system for adjuvant-free intranasal vaccines

Nanotechnology is an innovative method of freely controlling nanometre-sized materials. Recent outbreaks of mucosal infectious diseases have increased the demands for development of mucosal vaccines because they induce both systemic and mucosal antigen-specific immune responses. Here we developed an intranasal vaccine-delivery system with a nanometre-sized hydrogel ('nanogel') consisting of a cationic type of cholesteryl-group-bearing pullulan (cCHP). A non-toxic subunit fragment of Clostridium botulinum type-A neurotoxin BoHc/A administered intranasally with cCHP nanogel (cCHP-BoHc/A) continuously adhered to the nasal epithelium and was effectively taken up by mucosal dendritic cells after its release from the cCHP nanogel. Vigorous botulinum-neurotoxin-A-neutralizing serum IgG and secretory IgA antibody responses were induced without co-administration of mucosal adjuvant. Importantly, intranasally administered cCHP-BoHc/A did not accumulate in the olfactory bulbs or brain. Moreover, intranasally immunized tetanus toxoid with cCHP nanogel induced strong tetanus-toxoid-specific systemic and mucosal immune responses. These results indicate that cCHP nanogel can be used as a universal protein-based antigen-delivery vehicle for adjuvant-free intranasal vaccination.

Secretory IgA-mediated protection against V. cholerae and heat-labile enterotoxin-producing enterotoxigenic Escherichia coli by rice-based vaccine

Cholera and enterotoxigenic Escherichia coli (ETEC) are among the most common causes of acute infantile gastroenteritis globally. We previously developed a rice-based vaccine that expressed cholera toxin B subunit (MucoRice-CTB) and had the advantages of being cold chain-free and providing protection against cholera toxin (CT)-induced diarrhea. To advance the development of MucoRice-CTB for human clinical application, we investigated whether the CTB-specific secretory IgA (SIgA) induced by MucoRice-CTB gives longstanding protection against diarrhea induced by Vibrio cholerae and heat-labile enterotoxin (LT)-producing ETEC (LT-ETEC) in mice. Oral immunization with MucoRice-CTB stored at room temperature for more than 3 y provided effective SIgA-mediated protection against CT- or LT-induced diarrhea, but the protection was impaired in polymeric Ig receptor-deficient mice lacking SIgA. The vaccine gave longstanding protection against CT- or LT-induced diarrhea (for > or = 6 months after primary immunization), and a single booster immunization extended the duration of protective immunity by at least 4 months. Furthermore, MucoRice-CTB vaccination prevented diarrhea in the event of V. cholerae and LT-ETEC challenges. Thus, MucoRice-CTB is an effective long-term cold chain-free oral vaccine that induces CTB-specific SIgA-mediated longstanding protection against V. cholerae- or LT-ETEC-induced diarrhea.

IL-28 supplants requirement for T(reg) cells in protein sigma1-mediated protection against murine experimental autoimmune encephalomyelitis (EAE)

Conventional methods to induce tolerance in humans have met with limited success. Hence, efforts to redirect tolerogen uptake using reovirus adhesin, protein sigma 1 (pσ1), may circumvent these shortcomings based upon the recent finding that when reovirus pσ1 is engineered to deliver chicken ovalbumin (OVA) mucosally, tolerance is obtained, even with a single dose. To test whether single-dose tolerance can be induced to treat EAE, proteolipid protein (PLP_130–151) was genetically fused to OVA to pσ1 (PLP:OVA-pσ1) and shown to significantly ameliorate EAE, suppressing proinflammatory cytokines by IL-10⁺ forkhead box P3 (FoxP3)⁺ CD25⁺CD4⁺ T_reg and IL-4⁺CD25⁻CD4⁺ Th2 cells. IL-10R or IL-4 neutralization reversed protection to EAE conferred by PLP:OVA-pσ1, and adoptive transfer of Ag-specific T_reg or Th2 cells restored protection against EAE in recipients. Upon assessment of each relative participant, functional inactivation of CD25 impaired PLP:OVA-pσ1's protective capacity, triggering TGF-β-mediated inflammation; however, concomitant inactivation of TGF-β and CD25 reestablished PLP:OVA-pσ1-mediated protection by IL-28-producing FoxP3⁺CD25⁻CD4⁺ T cells. Thus, pσ1-based therapy can resolve EAE independently of or dependently upon CD25 and assigns IL-28 as an alternative therapy for autoimmunity.

Mucosally induced immunological tolerance, regulatory T cells and the adjuvant effect by cholera toxin B subunit

Induction of peripheral immunological tolerance by mucosal administration of selected antigens (Ags) ('oral tolerance') is an attractive, yet medically little developed, approach to prevent or treat selected autoimmune or allergic disorders. A highly effective way to maximize oral tolerance induction for immunotherapeutic purposes is to administer the relevant Ag together with, and preferably linked to the non-toxic B subunit protein of cholera toxin (CTB). Oral, nasal or sublingual administration of such Ag/CTB conjugates or gene fusion proteins have been found to induce tolerance with superior efficiency compared with administration of Ag alone, including the suppression of various autoimmune disorders and allergies in animal models. In a proof-of-concept clinical trial in patients with Behcet's disease, this was extended with highly promising results to prevent relapse of autoimmune uveitis. Tolerization by mucosal Ag/CTB administration results in a strong increase in Ag-specific regulatory CD4(+) T cells, apparently via two separate pathways: one using B cells as APCs and leading to a strong expansion of Foxp3(+) Treg cells which can both suppress and mediate apoptotic depletion of effector T cells, and one being B cell-independent and associated with development of Foxp3(-) regulatory T cells that express membrane latency-associated peptide and transforming growth factor (TGF-beta) and/or IL-10. The ability of CTB to dramatically increase mucosal Ag uptake and presentation by different APCs through binding to GM1 ganglioside (which makes most B cells effective APCs irrespective of their Ag specificity), together with CTB-mediated stimulation of TGF-beta and IL-10 production and inhibition of IL-6 formation may explain the dramatic potentiation of oral tolerance by mucosal Ags presented with CTB.

A rice-based oral cholera vaccine induces macaque-specific systemic neutralizing antibodies but does not influence pre-existing intestinal immunity

We previously showed that oral immunization of mice with a rice-based vaccine expressing cholera toxin (CT) B subunit (MucoRice-CT-B) induced CT-specific immune responses with toxin-neutralizing activity in both systemic and mucosal compartments. In this study, we examined whether the vaccine can induce CT-specific Ab responses in nonhuman primates. Orally administered MucoRice-CT-B induced high levels of CT-neutralizing serum IgG Abs in the three cynomolgus macaques we immunized. Although the Ab level gradually decreased, detectable levels were maintained for at least 6 mo, and high titers were rapidly recovered after an oral booster dose of the rice-based vaccine. In contrast, no serum IgE Abs against rice storage protein were induced even after multiple immunizations. Additionally, before immunization the macaques harbored intestinal secretory IgA (SIgA) Abs that reacted with both CT and homologous heat-labile enterotoxin produced by enterotoxigenic Escherichia coli and had toxin-neutralizing activity. The SIgA Abs were present in macaques 1 mo to 29 years old, and the level was not enhanced after oral vaccination with MucoRice-CT-B or after subsequent oral administration of the native form of CT. These results show that oral MucoRice-CT-B can effectively induce CT-specific, neutralizing, serum IgG Ab responses even in the presence of pre-existing CT- and heat-labile enterotoxin-reactive intestinal SIgA Abs in nonhuman primates.

Low-dose tolerance is mediated by the microfold cell ligand, reovirus protein sigma1

Mucosal tolerance induction generally requires multiple or large Ag doses. Because microfold (M) cells have been implicated as being important for mucosal tolerance induction and because reovirus attachment protein sigma1 (psigma1) is capable of binding M cells, we postulated that targeting a model Ag to M cells via psigma1 could induce a state of unresponsiveness. Accordingly, a genetic fusion between OVA and the M cell ligand, reovirus psigma1, termed OVA-psigma1, was developed to enhance tolerogen uptake. When applied nasally, not parenterally, as little as a single dose of OVA-psigma1 failed to induce OVA-specific Abs even in the presence of adjuvant. Moreover, the mice remained unresponsive to peripheral OVA challenge, unlike mice given multiple nasal OVA doses that rendered them responsive to OVA. The observed unresponsiveness to OVA-psigma1 could be adoptively transferred using cervical lymph node CD4(+) T cells, which failed to undergo proliferative or delayed-type hypersensitivity responses in recipients. To discern the cytokines responsible as a mechanism for this unresponsiveness, restimulation assays revealed increased production of regulatory cytokines, IL-4, IL-10, and TGF-beta1, with greatly reduced IL-17 and IFN-gamma. The induced IL-10 was derived predominantly from FoxP3(+)CD25(+)CD4(+) T cells. No FoxP3(+)CD25(+)CD4(+) T cells were induced in OVA-psigma1-dosed IL-10-deficient (IL-10(-/-)) mice, and despite showing increased TGF-beta1 synthesis, these mice were responsive to OVA. These data demonstrate the feasibility of using psigma1 as a mucosal delivery platform specifically for low-dose tolerance induction.

Expression of a bioactive fusion protein of Escherichia coli heat-labile toxin B subunit to a synapsin peptide

The B subunit of Escherichia coli heat-labile toxin (LTB) may function as an efficient carrier molecule for the delivery of genetically coupled antigens across the mucosal barrier. We constructed vectors for the expression of LTB and LTBSC proteins. LTBSC is a fusion protein that comprises the amino acid sequence from the C-domain of rat synapsin fused to the C-terminal end of LTB. Both constructions have a coding sequence for a 6His-tag fused in-frame. LTBSC was expressed in E. coli as inclusion bodies. The inclusion bodies were isolated and purified by Ni2+-chelating affinity chromatography under denaturing condition. Purified LTBSC was diluted in several refolding buffers to gain a soluble and biologically active protein. Refolded LTBSC assembled as an active oligomer which binds to the GM1 receptor in an enzyme-linked immunosorbent assay (ELISA). Soluble LTB in the E. coli lysate was also purified by Ni2+-chelating affinity chromatography and the assembled pentamer was able to bind with high affinity to GM1 in vitro. LTBSC and LTB were fed to rats and the ability to induce antigen-specific tolerance was tested. LTBSC inhibited the specific delayed-type hypersensitivity (DTH) response and induced decreased antigen-specific in vivo and in vitro cell proliferation more efficiently than LTB. Thus, the novel hybrid molecule LTBSC when orally delivered was able to elicit a systemic immune response. These results suggest that LTBSC could be suitable for exploring further therapeutic treatment of autoimmune inflammatory diseases involving antigens from central nervous system.

Cancer immunotherapy based on recombinant Salmonella enterica serovar Typhimurium aroA strains secreting prostate-specific antigen and cholera toxin subunit B

Prostate cancer is the most common malignant tumor in men and is normally associated with increased serum levels of prostate-specific antigen (PSA). Therefore, PSA is one potential target for a prostate cancer vaccine. In this study we analyzed the functionality of new bacterial PSA vaccines, expressed and secreted via the hemolysin (HlyA) secretion system of Escherichia coli, the prototype of Type I secretion systems (T1SS) using an attenuated Salmonella enterica serovar Typhimurium aroA strain as carrier. The data demonstrate that a bacterial live vaccine encompassing T1SS in combination with cholera toxin subunit B can be successfully used for delivery of PSA to induce cytotoxic CD8+ T-cell responses resulting in an efficient prevention of tumor growth in mice.

Rice-based mucosal vaccine as a global strategy for cold-chain- and needle-free vaccination

Capable of inducing antigen-specific immune responses in both systemic and mucosal compartments without the use of syringe and needle, mucosal vaccination is considered ideal for the global control of infectious diseases. In this study, we developed a rice-based oral vaccine expressing cholera toxin B subunit (CTB) under the control of the endosperm-specific expression promoter 2.3-kb glutelin GluB-1 with codon usage optimization for expression in rice seed. An average of 30 mug of CTB per seed was stored in the protein bodies, which are storage organelles in rice. When mucosally fed, rice seeds expressing CTB were taken up by the M cells covering the Peyer's patches and induced CTB-specific serum IgG and mucosal IgA antibodies with neutralizing activity. When expressed in rice, CTB was protected from pepsin digestion in vitro. Rice-expressed CTB also remained stable and thus maintained immunogenicity at room temperature for >1.5 years, meaning that antigen-specific mucosal immune responses were induced at much lower doses than were necessary with purified recombinant CTB. Because they require neither refrigeration (cold-chain management) nor a needle, these rice-based mucosal vaccines offer a highly practical and cost-effective strategy for orally vaccinating large populations against mucosal infections, including those that may result from an act of bioterrorism.

Recent developments in mucosal vaccines against prion diseases

Bovine spongiform encephalopathy in cattle is highly suspected to be orally transmitted to humans through contaminated food, causing new variant Creutzfeldt-Jakob disease. However, no prophylactic procedures against these diseases, such as vaccines, in particular those stimulating mucosal protective immunity, have been established. The causative agents of these diseases, termed prions, consist of the host-encoded prion protein (PrP). Therefore, prions are immunologically tolerated, inducing no host antibody responses. This immune tolerance to PrP has hampered the development of vaccines against prions. We and others recently reported that the immune tolerance could be successfully broken and mucosal immunity could be stimulated by mucosal immunization of mice with PrP fused with bacterial enterotoxin or delivered using an attenuated Salmonella strain, eliciting significantly higher immunoglobulin A and G antibody responses against PrP. In this review, we will discuss these reports.

Heteropentameric cholera toxin B subunit chimeric molecules genetically fused to a vaccine antigen induce systemic and mucosal immune responses: a potential new strategy to target recombinant vaccine antigens to mucosal immune systems

Noninvasive mucosal vaccines are attractive alternatives to parenteral vaccines. Although the conjugation of vaccine antigens with the B subunit of cholera toxin (CTB) is one of the most promising strategies for vaccine delivery to mucosal immune systems, the molecule cannot tolerate large-protein fusion, as it severely impairs pentamerization and loses affinity for GM1-ganglioside. Here we report a new strategy, in which steric hindrance between CTB-antigen fusion subunits is significantly reduced through the integration of unfused CTB "molecular buffers" into the pentamer unit, making them more efficiently self-assemble into biologically active pentamers. In addition, the chimeric protein took a compact configuration, becoming small enough to be secreted, and one-step affinity-purified proteins, when administered through a mucosal route, induced specific immune responses in mice. Since our results are not dependent on the use of a particular expression system or vaccine antigen, this strategy could be broadly applicable to bacterial enterotoxin-based vaccine design.

A novel method for the rational construction of well-defined immunogens: the use of oximation to conjugate cholera toxin B subunit to a peptide-polyoxime complex

Cholera toxin B subunit (CTB), capable of binding to all mucous membranes in its pentameric form, is a potential carrier of mucosal vaccines. In our previous work we reported that the N-terminus of CTB, a threonine, could in principle undergo oxidation and oximation to form conjugates with a cascade of immunogenic peptides. In this study, we set up a model by chemically coupling CTB to a polyoxime that possessed five copies of influenza virus-derived peptides displayed in comblike form. The construct was reconstituted into pentameric form when eluted from a Superdex column after conjugation, and the pentameric nature of this CTB-viral peptide complex was confirmed by SDS-PAGE. GM(1)-ELISA assay showed that the binding properties of CTB-viral peptide complex were increased 4-5-fold over native CTB.

Permeability issues in nasal drug delivery

The nasal route is one of the most permeable and highly vascularized site for drug administration ensuring rapid absorption and onset of therapeutic action. It has been potentially explored as an alternative route for drugs with poor bioavailability and for the delivery of biosensitive and high molecular weight (MW) compounds such as proteins, peptides, steroids, vaccines, and so on. This review discusses the major factors affecting the permeability of drugs or biomolecules through the nasal mucosa, including biological, formulation and device-related factors. This information could potentially help to achieve desired plasma concentrations of drugs without compromising or altering the normal physiology of the nasal cavity.