Immunomodulators and delivery systems for vaccination by mucosal routes

Novel approaches to oral immunization for hepatitis B

Hepatitis B is a necroinflammatory liver disease manifested with subacute to acute symptoms, liver cirrhosis, and mortality. Parenteral alum-adsorbed hepatitis B surface antigenic (HBsAg) vaccination, although available, poses serious concerns regarding inability to induce both cell-mediated and mucosal immune response. In this context, oral delivery may be a prospective solution to the issues associated with conventional vaccination. However, the strategy is detrimental to the antigenic substances, suffers various physical/chemical barriers, and impedes poor transcytosis via mucosal route. Therefore, surface-engineered novel carrier-based approaches are reportedly promising for effective HBsAg oral vaccine delivery. This review focuses on the efforts for developing oral mucosal vaccine against hepatitis B, with considerable attention on novel drug delivery systems for spatial distribution of antigenic substance to the immune effector cells and organs.

Intranasal immunization with an archaeal lipid mucosal vaccine adjuvant and delivery formulation protects against a respiratory pathogen challenge

Archaeal lipid mucosal vaccine adjuvant and delivery (AMVAD) is a safe mucosal adjuvant that elicits long lasting and memory boostable mucosal and systemic immune responses to model antigens such as ovalbumin. In this study, we evaluated the potential of the AMVAD system for eliciting protective immunity against mucosal bacterial infections, using a mouse model of intranasal Francisella tularensis LVS (LVS) challenge. Intranasal immunization of mice with cell free extract of LVS (LVSCE) adjuvanted with the AMVAD system (LVSCE/AMVAD) induced F. tularensis-specific antibody responses in sera and bronchoalveolar lavage fluids, as well as antigen-specific splenocyte proliferation and IL-17 production. More importantly, the AMVAD vaccine partially protected the mice against a lethal intranasal challenge with LVS. Compared to LVSCE immunized and naïve mice, the LVSCE/AMVAD immunized mice showed substantial to significant reduction in pathogen burdens in the lungs and spleens, reduced serum and pulmonary levels of proinflammatory cytokines/chemokines, and longer mean time to death as well as significantly higher survival rates (p<0.05). These results suggest that the AMVAD system is a promising mucosal adjuvant and vaccine delivery technology, and should be explored further for its applications in combating mucosal infectious diseases.

Molecular basis of the mucosal immune system: from fundamental concepts to advances in liposome-based vaccines

The mucosal immune system, the primary portal for entry of most prevalent and devastating pathogens, is guarded by the special lymphoid tissues (mucosally associated lymphoid tissues) for immunity. Mucosal immune infection results in induction of IgA-manifested humoral immunity. Cell-mediated immunity may also be generated, marked by the presence of CD4+ Th1 and CD8+ cells. Furthermore, the immunity generated at the mucosal site is transported to the distal mucosal site as well as to systemic tissues. An understanding of the molecular basis of the mucosal immune system provides a unique platform for designing a mucosal vaccine. Coadministration of immunostimulatory molecules further accelerates functioning of the immune system. Mimicking receptor-mediated binding of the pathogen may be achieved by direct conjugation of antigen with an immunostimulatory molecule or encapsulation in a carrier followed by anchoring of a ligand having affinity to the cells of the mucosal immune system. Nanotechnology has played a significant role in mucosal vaccine development and among the available options liposomes are the most promising. Liposomes are phospholipid bilayered vesicles that can encapsulate protein as well as DNA-based vaccines and offer coencapsulation of adjuvant along with the antigen. At the same, time ligand-conjugated liposomes augment interaction of antigen with the cells of the mucosal immune system and thereby serve as suitable candidates for the mucosal delivery of vaccines. This article exhaustively explores strategies involved in the generation of mucosal immunity and also provides an insight to the progress that has been made in the development of liposome-based mucosal vaccine.

The M cell-targeting ligand promotes antigen delivery and induces antigen-specific immune responses in mucosal vaccination

Oral mucosal immunization can induce protective immunity in both systemic compartments and the mucosa. Successful mucosal immunization depends on Ag delivery to the mucosal immune induction site. The high transcytotic activity of M cells within the mucosa makes these cells attractive targets for mucosal Ag delivery, although it remains unclear whether delivery of Ag to M cells only can guarantee the induction of effective immune responses. In this study, we evaluated the ability of an M cell-targeting ligand with adjuvant activity to induce immunity against ligand-fused Ag. We selected M cell-targeting ligands through biopanning of a phage display library against differentiated in vitro M-like cells and produced the recombinant Ags fused to the selected ligands using the model Ag. One of the selected peptide ligands, Co1, promoted the binding of ligand-fused Ag to mouse Peyer's patch M cells and human M-like cells that had been defined by binding with the M cell-specific and anti-GP2 Abs. In addition, Co1 ligand enhanced the uptake of fused Ag by immunogenic tissue in an ex vivo loop assay and in vivo oral administration experiments. After oral administration, the ligand-fused Ag enhanced immune responses against the fused Ag compared with those of the control Ag without ligand. In addition, this use of the ligand supported a skewed Th2-type immune response against the fused Ag. Collectively, these results suggest that the ligand selected through biopanning against cultured M-like cells could be used as an adjuvant for targeted Ag delivery into the mucosal immune system to enhance immune induction.

Mucosal vaccination using claudin-4-targeting

Mucosa-associated lymphoid tissue (MALT) plays pivotal roles in mucosal immune responses. Efficient delivery of antigens to MALT is a critical issue for the development of mucosal vaccines. Although claudin-4 is preferentially expressed in MALT in the gut, a claudin-4-targeting approach for mucosal vaccination has never been developed. In the present study, we found that claudin-4 is expressed in nasal MALT, and we prepared a fusion protein of ovalbumin (OVA) as a model antigen with a claudin-4-binder, the C-terminal fragment of Clostridium perfringens enterotoxin (C-CPE) (OVA-C-CPE). Nasal immunization with OVA-C-CPE, but not a mixture of OVA and C-CPE, induced the production of OVA-specific serum IgG and nasal, vaginal and fecal IgA. Deletion of the claudin-4-binding region in OVA-C-CPE attenuated the induction of the immune responses. OVA-C-CPE immunization activated both Th1 and Th2 responses, and nasal immunization with OVA-C-CPE showed anti-tumor activity in mice inoculated with OVA-expressing thymoma cells. These results indicate that the claudin-4-targeting may be a potent strategy for nasal vaccination.

Oral vaccine formulations stimulate mucosal and systemic antibody responses against staphylococcal enterotoxin B in a piglet model

Despite the potential for its use as an agent of biowarfare or bioterrorism, no approved vaccine against staphylococcal enterotoxin B (SEB) exists. Nontoxic, mutant forms of SEB have been developed; however, it has been difficult to determine the efficacy of such subunit vaccine candidates due to the lack of superantigen activity of native SEB in rodents and due to the limitations of primate models. Since pigs respond to SEB in a manner similar to that of human subjects, we utilized this relevant animal model to investigate the safety and immunogenicity of a triple mutant of SEB carrying the amino acid changes L45R, Y89A, and Y94A. This recombinant mutant SEB (rmSEB) did not possess superantigen activity in pig lymphocyte cultures. Furthermore, rmSEB was unable to compete with native SEB for binding to pig leukocytes. These in vitro studies suggested that rmSEB could be a safe subunit vaccine. To test this possibility, piglets immunized orally with rmSEB formulations experienced no significant decrease in food consumption and no weight loss during the vaccination regimen. Oral vaccination with 1-mg doses of rmSEB on days 0, 7, 14, and 24 resulted in serum IgG and fecal IgA levels by day 36 that cross-reacted with native SEB. Surprisingly, the inclusion of cholera toxin adjuvant in vaccine formulations containing rmSEB did not result in increased antibody responses compared to formulations using the immunogen alone. Taken together, these studies provide additional evidence for the potential use of nontoxic forms of SEB as vaccines.

Striking activation of NALT and nasal passages lymphocytes induced by intranasal immunization with Cry1Ac protoxin

Cry1Ac protoxin from Bacillus thuringiensis is a potent mucosal immunogen and adjuvant. When delivered intranasally (i.n.) Cry1Ac elicits significant antibody response and is able to improve vaccination against Naegleria fowleri infection, but the functional effects occurring in nasal lymphocytes when this protein is administered alone have not been determined. Here, we investigated the effects of i.n. immunization with Cry1Ac on antibody production, lymphocyte activation and cytokine production in lymphocytes from nasal-associated lymphoid tissue (NALT) and nasal passages (NP). Our results show that i.n. immunization with Cry1Ac induced significant specific IgA and IgG cell responses, especially in NP. Besides, it increased the proportion of lymphocytes expressing the activation markers CD25 and CD69 in both nasal tissues, but differently. CD25 was increased in B cells along with CD4 and CD8 T cells from NALT and NP, while CD69 was increased in B cells from both tissues but only in CD4 T cells from NP. Finally, we found that Cry1Ac augmented especially a Th2 profile of cytokines, as the proportion of T cells that spontaneously produced IL-4, IL-5 and IL-10 was increased and this effect was higher in NP than in NALT. These data contribute to explain the potent immunogenicity of Cry1Ac via i.n. route.

The potential of 3',5'-cyclic diguanylic acid (c-di-GMP) as an effective vaccine adjuvant

3', 5'-Cyclic diguanylic acid (c-di-GMP) is a bacterial intracellular signaling molecule that plays a crucial role in the regulation of bacterial motility, adhesion, cell-to-cell communication, exopolysaccharide synthesis, biofilm formation and virulence. The recent finding that c-di-GMP can act as a danger signal on eukaryotic cells has prompted the study of the immunostimulatory and immunomodulatory properties of c-di-GMP in an effort to determine whether c-di-GMP might be further developed as a potential vaccine adjuvant. In this review, we discussed the recent in vitro and in vivo studies of the immunostimulatory properties of c-di-GMP and the progress that has been made in the preclinical development of c-di-GMP as a potential vaccine adjuvant for systemic and mucosal vaccination.

ADP-ribosylation controls the outcome of tolerance or enhanced priming following mucosal immunization

Accumulating evidence suggests that the dichotomy between tolerance and active IgA immunity in mucosal immune responses is regulated at the APC level. Therefore, immunomodulation of the APC could be an effective mechanism to control the two response patterns. In this study, we demonstrate that ADP-ribosylation controls the outcome of tolerance or active effector T cell immunity to an internal peptide p323-339 from OVA inserted into the cholera toxin (CT)-derived CTA1-OVA-DD adjuvant. We found that a single point mutation, CTA1R7K-OVA-DD, resulting in lack of enzymatic activity, promoted peptide-specific tolerance in TCR transgenic CD4(+) T cells following a single intranasal (i.n.) treatment. The CTA1R7K-OVA-DD-induced tolerance was strong, long-lasting, and impaired the ability of adoptively transferred naive peptide-specific CD4(+) T cells to respond to Ag-challenge, irrespective if this was given i.p or i.n. The tolerance correlated with induction of regulatory T cells of the regulatory T type 1 characterized by CD25(-)Foxp3(-)CD4(+) T cells producing IL-10. In contrast, in IL-10-deficient mice, no peptide-specific tolerance was observed, and these mice exhibited unimpaired CD4(+) T cell responsiveness to recall Ag irrespective of if they were untreated (PBS) or treated i.n. with CTA1R7K-OVA-DD. Thus, for the first time, we can provide unequivocal proof that ADP-ribosylation can control the outcome of mucosal Ag exposure from tolerance to an enhanced effector CD4(+) T cell response. The exploitation of this system for clinical treatment of autoimmune diseases is discussed.

Immunogenicity of self-adjuvanticity oral vaccine candidate based on use of Bacillus subtilis spore displaying Schistosoma japonicum 26 KDa GST protein

One of the promising approaches in mucosal immunization relies on live recombinant vaccine carriers. In this study, we used a six-extracellular protease-deficient Bacillus subtilis strain WB600 to express Schistosoma japonicum 26 kDa glutathione S-transferase (GST). Western blot, immunofluorescence, and flow cytometry analyses were used to identify SjGST expression on spore surface. SjGST recombinant spores were used for oral vaccination in mice and were shown to generate mucosal and systemic response. Both SjGST-specific secretory IgA in feces and IgG in serum augmented significantly on day 33 after oral administration. It seemed that surface display of recombinant S. japonicum SjGST on B. subtilis WB600 spores showed good immunogenicity, and B. subtilis spores could be used as potential mucosal delivery vehicles to provide more effective vaccination strategies for parasite prevention and control in the future.

M-cell targeted delivery of recombinant hepatitis B surface antigen using cholera toxin B subunit conjugated bilosomes

The present study aims to improve upon our earlier findings with bilosomes as potential delivery vehicle through oral route for recombinant hepatitis B surface antigen (HBsAg). The work entails the conjugation of bilosomal system with cholera toxin B subunit (CTB) to increase transmucosal uptake via M-cell specific delivery approach. The study encompasses the development and characterization of HBsAg-loaded CTB-conjugated system for percent antigen entrapment, size, shape, and stability in SGF (USP, pH 1.2), SIF (USP, pH 7.5) and in bile salt solutions. Biological activity of CTB, subsequent to conjugation, was verified by hemagglutination test. Anti-HBsAg IgG response in serum and anti-HBsAg sIgA in various body secretions were estimated using ELISA, following oral immunization with 10 microg dose-loaded CTB-conjugated bilosomes (CTB2) and 20 microg dose-loaded CTB-conjugated bilosomes (CTB1) in BALB/c mice. The results showed that CTB1 produced anti-HBsAg IgG antibody titre response comparable to that of the intramuscular (i.m.) injection of 10 microg of alum-adsorbed HBsAg. Moreover, all the bilosomal preparations elicited measurable sIgA vis-à-vis negligible response with i.m. administered HBsAg. Thus, HBsAg-loaded CTB-conjugated bilosomes provide a promising potential for targeted oral immunization against hepatitis B.

Production of Ascaris suum As14 protein and its fusion protein with cholera toxin B subunit in rice seeds

Plants are attractive vaccine production and oral delivery systems. Cereals are excellent candidate for edible vaccines, which can express and store high levels of proteins for extended periods of time without degradation. In this study, we produced a 14-kDa protective surface antigen of Ascaris suum L3 larvae and its fusion chimera with a mucosal carrier molecule cholera toxin B subunit (CTB) in rice (Oryza sativa L.) under the control of the endosperm-specific glutelin-B promoter. We found that the recombinant protein expression levels reached 1.5 microg per seed, a comparably high amount as compared to previously reported transgenic rice expression experiments. Potentials of transgenic rice plants as a source of oral vaccines against swine roundworm are discussed.

Mucosal immunization using proteoliposome and cochleate structures from Neisseria meningitidis serogroup B induce mucosal and systemic responses

Most pathogens either invade the body or establish infection in mucosal tissues and represent an enormous challenge for vaccine development by the absence of good mucosal adjuvants. A proteoliposome-derived adjuvant from Neisseria meningitidis serogroup B (AFPL1, Adjuvant Finlay Proteoliposome 1) and its derived cochleate form (Co, AFCo1) contain multiple pathogen-associated molecular patterns as immunopotentiators, and can also serve as delivery systems to elicit a Th1-type immune response. The present studies demonstrate the ability of AFPL1and AFCo1 to induce mucosal and systemic immune responses by different mucosal immunizations routes and significant adjuvant activity for antibody responses of both structures: a microparticle and a nanoparticle with a heterologous antigen. Therefore, we used female mice immunized by intragastric, intravaginal, intranasal or intramuscular routes with both structures alone or incorporated with ovalbumin (OVA). High levels of specific IgG antibody were detected in all sera and in vaginal washes, but specific IgA antibody in external secretions was only detected in mucosally immunized mice. Furthermore, antigen specific IgG1 and IgG2a isotypes were all induced. AFPL1 and AFCo1 are capable of inducing IFN-gamma responses, and chemokine secretions, like MIP-1alpha and MIP-1beta. However, AFCo1 is a better alternative to induce immune responses at mucosal level. Even when we use a heterologous antigen, the AFCo1 response was better than with AFPL1 in inducing mucosal and systemic immune responses. These results support the use of AFCo1 as a potent Th1 inducing adjuvant particularly suitable for mucosal immunization.

Adjuvant Effect of Lemnan, Pectic Polysaccharide of Callus Culture ofLemna minorL. at Oral Administration

A pectic polysaccharide, lemnan LMC, was extracted from the callus of duckweed Lemna minor L. and was tested for adjuvant properties at oral administration with protein antigen. Mice were orally immunized thrice with weekly interval with free hen's egg lysozyme or lysozyme with LMC. Lemnan LMC was shown to increase delayed type hypersensitivity and serum antilysozyme IgG responses. LMC was established to increase levels of both serum IgG1 and IgG2a subclasses. The concentration of malondialdehyde and myeloperoxidase activity were found to be higher in the tissue samples obtained from small intestine of mice immunized with mixture of lysozyme/LMC than those immunized with lysozyme only. Thus, lemnan appeared to be useful as the adjuvant for oral immunization.

Glycopeptide dendrimers, part III: a review. Use of glycopeptide dendrimers in immunotherapy and diagnosis of cancer and viral diseases

Glycopeptide dendrimers containing different types of tumor associated-carbohydrate antigens (T(N), TF, sialyl-T(N), sialyl-TF, sialyl-Le(x), sialyl-Le(a) etc.) were used in diagnosis and therapy of different sorts of cancer. These dendrimeric structures with incorporated T-cell epitopes and adjuvants can be used as antitumor vaccines. Best results were obtained with multiantigenic vaccines, containing, e.g. five or six different TAAs. The topic of TAAs and their dendrimeric forms at molecular level are reviewed, including structure, syntheses, and biological activities. Use of glycopeptide dendrimers as antiviral vaccines against HIV and influenza is also described. Their syntheses, physico-chemical properties, and biological activities are given with many examples.

Stimulation of respiratory immunity by oral administration of Lactococcus lactis

This work demostrates that nonrecombinant Lactococcus lactis NZ, administered by the oral route at the proper dose, is able to improve resistance against pneumococcal infection. Lactococcus lactis NZ oral administration was able to improve pathogen lung clearance, increased survival of infected mice, and reduced lung injuries. This effect was related to an upregulation of the respiratory innate and specific immune responses. Administration of L. lactis NZ improved production of bronchoalveolar lavage (BAL) fluid TNF-α, enhanced recruitment of neutrophils into the alveolar spaces, and induced a higher activation of BAL phagocytes compared with the control group. Lactococcus lactis NZ administered orally stimulated the IgA cycle, increased IgA+ cells in intestine and bronchus, and improved production of BAL IL-4 and IL-10 during infection. Moreover, mice treated with L. lactis NZ showed higher levels of BAL anti-pneumococcal IgA and IgG. Taking into consideration that orally administered L. lactis NZ stimulates both the innate and the specific immune responses in the respiratory tract and that bacterial and viral antigens have been efficiently produced in this strain, L. lactis NZ is an excellent candidate for the development of an effective pneumococcal oral vaccine.

Safety of Intranasally Administered Archaeal Lipid Mucosal Vaccine Adjuvant and Delivery (AMVAD) Vaccine in Mice

The safety profile of a recently described novel archaeal lipid mucosal vaccine adjuvant and delivery (AMVAD) system capable of eliciting robust antigen-specific mucosal and systemic immune responses was evaluated in female Balb/c mice (10/group) using ovalbumin (OVA) antigen. Mice were intranasally immunized (0, 7, and 21 days) with a vaccine comprising 1 μg OVA (0.05 mg/kg body weight) formulated in 0.04 mg total polar lipids extract (2.17 mg/kg body weight) of Methanobrevibacter smithii constituting the AMVAD system. Control groups were similarly immunized with 10-fold higher AMVAD vaccine dose (0.54 mg OVA and 21.7 mg lipid per kg), saline, 10 μg OVA in saline, or 0.04 or 0.4 mg lipid constituting empty AMVAD (no OVA) in saline, or were naïve mice. Clinical signs, rectal temperature, and body weight were monitored once daily or as appropriate. Half the mice in each group were euthanized at 2 days after the first immunization. Blood was collected for clinical chemistry analyses. Major organs (heart, lungs, kidneys, liver, spleen, thymus, and brain) were examined macroscopically and histologically. The remaining mice were euthanized at 29 days and blood and organs collected for analyses as done at 2 days. Feces collected at 27 days, and sera, bile, and nasal lavage at 29 days, were assayed for antibody responses. Based on clinical symptoms, temperature, body weight changes, serum clinical chemistry, and tissue histopathology, there were no overt toxicities associated with OVA/AMVAD or empty AMVAD vaccines. There were no antibodies elicited against the lipids comprising the AMVAD system. These results demonstrate that at 10-fold excess dose of that required for vaccine efficacy, intranasally administered AMVAD vaccine appears to be relatively safe.

Intranasal immunization with Naegleria fowleri lysates and Cry1Ac induces metaplasia in the olfactory epithelium and increases IgA secretion

According to previous reports, intranasal administration of the Cry1Ac protein alone or with amoebic lysates increases protection against Naegleria fowleri meningoencephalitis in mice, apparently by eliciting IgA responses in the nasal mucosa. In the current study, we performed an immunohistochemical analysis of IgA in the nasal mucosa of mice immunized intranasally with Cry1Ac, and amoebic lysates or a combination of both. The animals were sacrificed 24 h after the last immunization or after an intranasal lethal challenge with N. fowleri. Our results indicate that all of the intranasal immunizations provoked an increase in areas with metaplasia in the olfactory epithelium, allowing for secretion of IgA. As a result, IgA antibodies were found interacting with trophozoites in the nasal lumen, and there was a marked increase of IgA in the metaplasic epithelium. On the other hand in nonimmunized mice trophozoites were observed invading the nasal mucosa, which was not the case for immunized mice. Our results suggest that intranasal immunization provokes cellular changes in the olfactory epithelium, leading to greater protection against N. fowleri that is probably caused by an increased secretion of IgA. The increased IgA response induced in the nasal mucosa by immunization probably impedes both amoebic adhesion and subsequent invasion of the parasite to the nasal epithelium.

Actinobacillus pleuropneumoniaevaccines: from bacterins to new insights into vaccination strategies

With the growing emergence of antibiotic resistance and rising consumer demands concerning food safety, vaccination to prevent bacterial infections is of increasing relevance.Actinobacillus pleuropneumoniaeis the etiological agent of porcine pleuropneumonia, a respiratory disease leading to severe economic losses in the swine industry. Despite all the research and trials that were performed withA. pleuropneumoniaevaccination in the past, a safe vaccine that offers complete protection against all serotypes has yet not reached the market. However, recent advances made in the identification of new potential vaccine candidates and in the targeting of specific immune responses, give encouraging vaccination perspectives. Here, we review past and current knowledge onA. pleuropneumoniaevaccines as well as the newly available genomic tools and vaccination strategies that could be useful in the design of an efficient vaccine againstA. pleuropneumoniaeinfection.

Stimulation of mucosal and systemic antibody responses against recombinant transferrin-binding protein B of Actinobacillus pleuropneumoniae with chitosan after tracheal administration in piglets

This study evaluated the suitability of using a chitosan formulation as an adjuvant to enhance both the mucosal and systemic immune responses against recombinant transferrin-binding protein B (rTbp B) of Actinobacillus pleuropneumoniae via direct tracheal administration. The chitosan formulation was found to enhance mucosal immune response, as measured by the secretory IgA level in lung lavage fluid and lung homogenate extracts, and systemic immune response, as measured by the serum IgG level.

Attachment of the outer membrane lipoprotein (OprI) of Pseudomonas aeruginosa to the mucosal surfaces of the respiratory and digestive tract of chickens

The development of mucosal vaccines requires antigen delivery and adjuvant systems that can efficiently help in presenting vaccine antigens to the mucosal immune system. The outer membrane lipoprotein I (OprI) of Pseudomonas aeruginosa seems to possess both the quality to induce a non-specific immune response (adjuvant effect through its lipid tail) as well as the quality to facilitate uptake of the vaccine antigen by interacting with Toll-like receptor 2/4 (TLR2/4) on antigen-presenting cells (APC) and epithelial cells (adhesion effect). Here, we show for the first time the adhesion of OprI to epithelial cells of the trachea and small intestine of chickens. Adhesion could be seen on cryosections after in vitro as well as after in vivo incubation of the trachea and intestine. This proves the value of OprI as a fusion partner in mucosal protein vaccine development, which is especially important for poultry where mass vaccination is only possible by the respiratory or oral route.

Mucosal and systemic immune responses by intranasal immunization using archaeal lipid-adjuvanted vaccines

The utility of archaeal polar lipids as an adjuvant/delivery system for elicitation of antigen-specific mucosal immune responses in intranasally administered vaccines was investigated. Although unilamellar archaeosomes (liposomes made from archaeal polar lipids) with encapsulated ovalbumin (OVA/archaeosomes) induced anti-OVA IgG antibody responses in sera, they failed to induce anti-OVA IgA antibody responses at mucosal sites. However, the addition of CaCl2 to convert OVA/archaeosomes into an archaeal lipid mucosal vaccine adjuvant and delivery (AMVAD) vaccine (OVA/AMVAD) consisting of larger, particulate, aggregated structures resulted in an efficacious intranasal (i.n.) vaccine. Intranasal immunization of mice with OVA/AMVAD vaccines prepared from various archaeal polar lipid compositions elicited anti-OVA IgA antibody responses in sera, feces, bile, vaginal and nasal wash samples. The i.n. immunization also induced anti-OVA IgG, IgG1 and IgG2a antibody responses in sera, as well as cytotoxic T lymphocyte responses. The mucosal and systemic immune responses induced by OVA/AMVAD immunization were generally sustained over several months, and were subject to memory boost responses. Thus, polar archaeal lipids appear to be promising for developing a non-replicating mucosal adjuvant and vaccine delivery system.

TLR2 activation by proteosomes promotes uptake of particulate vaccines at mucosal surfaces

Proteosome-based vaccines have TLR2-based adjuvant activity and show promise for mucosal immunization. We examined the effects of proteosomes on mucosal uptake in Peyer's patches in vivo. Proteosomes accelerated transepithelial transport of microparticles by M cells and induced migration of dendritic cells (DCs) into the follicle-associated epithelium (FAE); both effects were dependent on TLR2. Proteosomes induced the release of the DC-attracting chemokine MIP3alpha from Caco-2 epithelial cells in vitro. In HEK cells, proteosome-mediated MIP3alpha release was dependent on TLR2 expression and matrix metalloproteinase activation. Thus, TLR2 activation by proteosomes may promote mucosal uptake of particulate vaccines, and this may contribute to their adjuvanticity.

Clarification of how HIV-1 DNA and protein immunizations may be better used to obtain HIV-1-specific mucosal and systemic immunity

More focused research on a mucosal HIV-1 vaccine is needed urgently. An increasing amount of collected data, using heterologous multimodality prime-booster strategies, suggest that an efficient and protective HIV-1 vaccine must generate broad, long-lasting HIV-specific CD8(+) cytotoxic T-lymphocyte and neutralizing antibody responses. In the mucosa, these responses would be most effective if a preferential stimulus of HIV-1 neutralizing secretory immunoglobulin A and G were obtained. The attractive property of mucosal immunization is the obtained mucosal and systemic immunity, whereas systemic immunization induces a more limited immunity, predominantly in systemic sites. These objectives will require new vaccine regimens, such as multiclade HIV DNA and protein vaccines (nef, tat, gag and env expressed in DNA plasmids) delivered onto mucosal surfaces with needle-free delivery methods, such as nasal drop, as well as oral and rectal/vaginal delivery, and should merit clinical trials.

Nasal immunization with Burkholderia multivorans outer membrane proteins and the mucosal adjuvant adamantylamide dipeptide confers efficient protection against experimental lung infections with B. multivorans and B. cenocepacia

Chronic lung infection by opportunistic pathogens, such as Pseudomonas aeruginosa and members of the Burkholderia cepacia complex, is a major cause of morbidity and mortality in patients with cystic fibrosis. Outer membrane proteins (OMPs) of gram-negative bacteria are promising vaccine antigen candidates. In this study, we evaluated the immunogenicity, protection, and cross-protection conferred by intranasal vaccination of mice with OMPs from B. multivorans plus the mucosal adjuvant adamantylamide dipeptide (AdDP). Robust mucosal and systemic immune responses were stimulated by vaccination of naive animals with OMPs from B. multivorans and B. cenocepacia plus AdDP. Using a mouse model of chronic pulmonary infection, we observed enhanced clearance of B. multivorans from the lungs of vaccinated animals, which correlated with OMP-specific secretory immunoglobulin A responses. Furthermore, OMP-immunized mice showed rapid resolution of the pulmonary infection with virtually no lung pathology after bacterial challenge with B. multivorans. In addition, we demonstrated that administration of B. multivorans OMP vaccine conferred protection against B. cenocepacia challenge in this mouse infection model, suggesting that OMPs provide cross-protection against the B. cepacia complex. Therefore, we concluded that mucosal immunity to B. multivorans elicited by intranasal vaccination with OMPs plus AdDP could prevent early steps of colonization and infection with B. multivorans and also ameliorate lung tissue damage, while eliciting cross-protection against B. cenocepacia. These results support the notion that therapies leading to increased mucosal immunity in the airways may help patients with cystic fibrosis.

Characterisation of the oral adjuvant effect of lemnan, a pectic polysaccharide of Lemna minor L

Lemnan LM, apiogalacturonanic pectin of duckweed Lemna minor L. was tested for adjuvant properties following oral administration with protein antigen. Male Swiss mice were orally immunized thrice with weekly intervals with free OVA or OVA with lemnan (LM). Lemnan LM was shown to increase delayed type hypersensitivity (DTH) and serum anti OVA IgG responses. LM was established to increase levels of both serum IgG1 and IgG2a subclasses, intestinal IgA and failed to elevate levels of serum IgE. Lemnan was found to increase the adhesion of macrophages and to enhance the generation of oxygen radicals by macrophages in response to phorbol 12-myristate 13-acetate. Serum OVA levels were four-fold higher in mice immunized with the mixture of OVA and LM in comparison with those in mice immunized with OVA only. Thus, substantial systemic and local mucosal immune responses were attained by oral immunization with the mixture of OVA and lemnan. Lemnan appeared to elicit adjuvant activity via induction of both Th1- and Th2-type responses. The immunopotentiating effect of lemnan may result from enhanced antigen ingestion and stimulation of macrophage activity.

B subunit of E. coli enterotoxin as adjuvant and carrier in oral and skin vaccination

Mucosal sites are one of the main natural ports of entry into the body. Stimulation of a local response by antibodies as the systemic protection may enhance the efficacy of non-living vaccines, and allow for vaccination by subunit vaccines without the need for injection. Mucosal or skin vaccination necessitates a suitable adjuvant and carrier. Escherichia coli heat-labile enterotoxin (LT) and its B subunit (LTB) have been found to be effective adjuvants. The aim of this study was to efficiently produce and purify recombinant LTB (brLTB), and examine its adjuvant and carrier properties. The gene encoding LTB was cloned and expressed in E. coli, and the product was found to have a pentameric form with the ability to bind the cell receptor, GM1 ganglioside. A one-step method for efficient purification and concentration of brLTB was developed. Both oral and intramuscular vaccination with purified brLTB yielded high antibody titers, which detected the whole toxin. In an attempt to test its adjuvant characteristics, brLTB was mixed with either BSA or a recombinant protein (rKnob of egg drop syndrome adenovirus) and delivered intramuscularly, orally or transcutaneously. The addition of brLTB significantly elevated the antibody response in groups vaccinated orally and transcutaneously, but had no influence in injected groups. Vaccination with another recombinant protein, (viral protein 2 of infectious bursal disease virus) supplemented with brLTB did not elevate the antibody response, as compared to vaccination with the antigen alone. These results demonstrate that the addition of brLTB makes oral and transcutaneous vaccination with protein antigens possible.

Mucosal vaccines: the promise and the challenge

Most infectious agents enter the body at mucosal surfaces and therefore mucosal immune responses function as a first line of defence. Protective mucosal immune responses are most effectively induced by mucosal immunization through oral, nasal, rectal or vaginal routes, but the vast majority of vaccines in use today are administered by injection. As discussed in this Review, current research is providing new insights into the function of mucosal tissues and the interplay of innate and adaptive immune responses that results in immune protection at mucosal surfaces. These advances promise to accelerate the development and testing of new mucosal vaccines against many human diseases including HIV/AIDS.

Oral administration of human papillomavirus type 16 E7 displayed onLactobacillus casei induces E7-specific antitumor effects in C57/BL6 mice

The mounting of a specific immune response against the human papillomavirus type 16 E7 protein (HPV16 E7) is important for eradication of HPV16 E7-expressing cancer cells from the cervical mucosa. To induce a mucosal immune response by oral delivery of the E7 antigen, we expressed the HPV16 E7 antigen on the surface of Lactobacillus casei by employing a novel display system in which the poly-gamma-glutamic acid (gamma-PGA) synthetase complex A (PgsA) from Bacillus subtilis (chungkookjang) was used as an anchoring motif. After surface expression of the HPV16 E7 protein was confirmed by Western blot, flow cytometry and immunofluorescence microscopy, mice were orally inoculated with L. casei-PgsA-E7. E7-specific serum IgG and mucosal IgA productions were enhanced after oral administration and significantly enhanced after boosting. Systemic and local cellular immunities were significantly increased after boosting, as shown by increased counts of lymphocytes (SI = 9.7 +/- 1.8) and IFN-gamma secreting cells [510 +/- 86 spot-forming cells/10(6)cells] among splenocytes and increased IFN-gamma in supernatants of vaginal lymphocytes. Furthermore, in an E7-based mouse tumor model, animals receiving orally administered L. casei-PgsA-E7 showed reduced tumor size and increased survival rate versus mice receiving control (L. casei-PgsA) immunization. These results collectively indicate that the oral administration of E7 displayed on lactobacillus induces cellular immunity and antitumor effects in mice.

Mucosal and systemic immunization elicited by Newcastle disease virus (NDV) transgenic plants as antigens

As a step towards developing a safe and effective edible vaccine against Newcastle disease virus (NDV), we have explored the use of plants genetically engineered to express viral proteins. We report the construction of transgenic potato plants expressing the genes coding for immunogenic proteins of NDV under the regulation of CaMV 35S promoter and its immunogenicity in mice. All mice receiving transgenic plant extracts in incomplete Freund adjuvant produced specific anti-NDV antibodies. Animals fed with transgenic leaves showed a specific response against NDV. Detection of IgA released from in vitro-cultured intestinal tissue fragments indicated the presence of IgA-secreting cells in the gut.

Starch microparticles as vaccine adjuvant

The demand for new vaccine adjuvants is well documented. New purified antigens from parasites, bacterial or viral pathogens, as well as recombinant subunit antigens and synthetic peptides, are often inherently weak immunogens; therefore, they need some kind of adjuvant to help initiate an immune response. In addition, there are very few adjuvants using the potential of the mucosal immune system, which may play an important role in the defence against air- and food-borne infections. Starch is a natural biocompatible and biodegradable polymer that is suitable for the production of various particulate adjuvant formulations, which can induce mucosal as well as systemic immune responses. This review gives an account of the different starch adjuvants used in immunisation studies. In particular, the properties of polyacryl starch microparticles as an oral vaccine adjuvant that induce protective immune responses in mice challenge experiments are summarised. In addition, a diphtheria booster vaccine has been proposed to be used to proving the concept in man and the possibilities to design an efficient vaccine formulation for human use are discussed.

Vaccine and adjuvant activity of recombinant subunit B of E. coli enterotoxin produced in yeast

Escherichia coli heat-labile enterotoxin (LT) and cholera toxin (CT) have been studied intensively as vaccines against diseases caused by those bacteria and as adjuvants for mucosal vaccination. Two major problems interfere with the use of these promising adjuvants: their toxicity and the residual bacterial endotoxins mixed with the desired LT. In this study, subunit B of LT was expressed in Pichia pastoris yeast cells (yrLTB) and the recombinant protein was purified and concentrated by ion-exchange chromatography. The final yield of the recombinant protein was 5-8 mg/l induction medium. The molecule is in pentameric form and binds to GM1 gangliosides. When given orally to chickens, anti-LTB antibodies were produced, exhibiting its ability to cross the digestive system and induce an immune response. The adjuvant activity of yrLTB was proven by fusing it to viral protein 2 (VP2) of infectious bursal disease virus. Birds intramuscularly vaccinated with this molecule exhibit 70-100% protection, in a dose-response-dependent manner. This method eliminated the bacterial endotoxins and enabled the production of large quantities of LTB. Expression in a eukaryotic system allows the production of fusion proteins that require post-translational modifications. This may allow oral vaccination with a protein fused to yrLTB. The approach described in this study will enable the efficient production of a non-toxic, eukaryotically expressed enterotoxin as a vaccine against the toxin itself or as a carrier or adjuvant for foreign vaccine molecules.

Oronasal vaccination with classical swine fever virus (CSFV) replicon particles with either partial or complete deletion of the E2 gene induces partial protection against lethal challenge with highly virulent CSFV

A cDNA clone of the classical swine fever virus (CSFV) strain Alfort/187 [Ruggli N, Tratschin JD, Mittelholzer C, Hofmann MA. Nucleotide sequence of classical swine fever virus strain Alfort/187 and transcription of infectious RNA from stably cloned full-length cDNA. J Virol 1996;70(6):3478-87] was used to construct two E2 deletion mutants lacking either the complete E2 gene or, alternatively, a stretch of 204 nucleotides encoding 68 amino acids located in the C-terminal region of the E2 glycoprotein. The respective in vitro synthesized mutant RNAs replicated in SK-6 cells but no infectious virus was generated. Both replicons could be packaged into virus particles in SK-6 cells constitutively expressing E2 of CSFV. For the resulting CSF virus replicon particles (CSF-VRP) A187-E2del373 and A187-E2del68 titers of 10(6) and 10(7) TCID(50)/ml, respectively, were obtained. Oronasal vaccination with 10(7) TCID(50) of either of the two CSF-VRP protected pigs against a challenge with a lethal dose of CSFV strain Eystrup. In contrast, after intradermal vaccination VRP A187-E2del68 but not VRP A187-E2del373 lacking the complete E2 gene induced a protective immune response. We conclude that E2-complemented CSF-VRP have the potential to be used as live-attenuated non-transmissible oral vaccines for pigs. In addition, our data suggest that E2 of CSFV is dispensable for the induction of mucosal but not of parenteral immunity.

Modulation of protective immunity, eosinophilia, and cytokine responses by selective mutagenesis of a recombinant G protein vaccine against respiratory syncytial virus

Using an Escherichia coli-grown plasmid vector encoding a fragment of thioredoxin (Trx) fused to a central region (amino acids 128 to 229) of the respiratory syncytial virus (RSV) (Long strain) G protein, we employed site-directed mutagenesis to investigate the importance of selected amino acids to vaccine efficacy. Mice were immunized with a total of 10 wild-type or mutant Trx-G proteins and challenged intranasally with RSV. Striking differences in the induction of RSV G-protein-specific antibodies, protection against RSV challenge, cytokine RNA responses, and induction of RSV-associated eosinophilic inflammation were observed among the mutant proteins examined. Taken together, the results identify a critical role for specific amino acids in the induction of protective immunity and priming for eosinophilia against RSV.

Characterization of the porcine neonatal Fc receptor--potential use for trans-epithelial protein delivery

The neonatal Fc receptor transports maternal immunoglobulin across the gut wall and has the potential to deliver genetically engineered proteins bearing immunoglobulin Fc domains across the gut to the mucosal immune system. Here we have characterized the porcine neonatal Fc receptor and tested its utility as a model system to study this kind of protein delivery. The complete DNA sequence obtained from an EST revealed 70-80% homology to mouse and human receptors, respectively, and tyrptophan and di-leucine endocytosis motifs were identified in the cytoplasmic tail. Reverse transcription-polymerase chain reaction analysis showed expression of the receptor mRNA in gut, liver, kidney and spleen tissue, aortic endothelial cells and monocytes. Pig kidney cell lines showed saturable pH-dependent binding and uptake of porcine immunoglobulin G (IgG) and also bovine, mouse and human IgG. Polyclonal antibodies raised against the receptor immunoprecipitated a protein of 40,000 MW when the cDNA was expressed in cells and the receptor required assembly with porcine beta2-microglobulin for transport from the endoplasmic reticulum to recycling and early endosomes. Immunohistochemical analysis showed the receptor expressed in epithelial cells of the gut of young and adult animals. The ability of the receptor to deliver immunoglobulin across the gut was demonstrated by feeding piglets bovine colostrum as a source of bovine IgG. Bovine IgG was delivered into the pig circulation. Pigs express the neonatal Fc receptor and the receptor has the potential to deliver protein antigens to the pig immune system.

Development of a single-dose stabilized poly(D,L-lactic-co-glycolic acid) microspheres-based vaccine against hepatitis B

The purpose of this study was to develop a stable single-dose vaccine based on recombinant hepatitis B surface antigen (HBsAg) in poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres, in which HBsAg was stabilized by a protein stabilizer (trehalose) and an antacid (Mg(OH)2). The microspheres were prepared by the double emulsion method and characterized by scanning electron microscopy. To neutralize the acids liberated by the biodegradable lactic/glycolic acid based polymer, we coincorporated into the polymer an antacid, Mg(OH)2, which neutralized the acidity during degradation of the polymer and also prevented HBsAg structural losses and aggregation. The antigen integrity after encapsulation was examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis followed by silver staining, isoelectric focusing and Western blotting techniques, which confirmed that antigen remained intact after encapsulation. In-vitro release experiments were performed in phosphate-buffered saline (pH 7.4) and the release of antigen was found to be improved by the protein stabilizer (trehalose). In stability studies, performed at 37 degrees C, the microspheres were found to be stable for 16 days. The immunogenicity of stable microsphere formulations bearing HBsAg was compared with the conventional alum-absorbed HBsAg vaccine in a guinea-pig model. The antibody titre indicated that a single injection of stabilized HBsAg-PLGA microspheres produced a better immune response than two injections of alum-formulated HBsAg vaccine. The findings suggest that recombinant HBsAg can be stabilized by use of a protein stabilizer and antacid during entrapment, and this stabilized preparation can be useful for antigen delivery.

Effects of infection with transmissible gastroenteritis virus on concomitant immune responses to dietary and injected antigens

Normal piglets weaned onto soy- or egg-based diets generated antibody responses to fed protein. Concurrent infection with transmissible gastroenteritis virus (TGEV) did not affect the responses to dietary antigens at weaning, nor did it affect the subsequent development of tolerance. However, TGEV infection did enhance the primary immunoglobulin M (IgM) and IgG1, but not IgG2, antibody responses to injected soy in comparison to those of uninfected animals. Paradoxically, TGEV-infected animals showed an enhanced primary IgG1 antibody response to injected soy at 4 weeks of age, but they subsequently showed a reduced secondary response after an intraperitoneal challenge at 9 weeks of age in comparison to uninfected animals. The results suggest that an enteric virus, either used as a vaccine vector or present as a subclinical infection, may not have significant effects on the development of dietary allergies but may have effects both on the primary response and on the subsequent recall response to systemic antigens to which the animal is exposed concurrently with virus antigens.

Intranasal immunization with genetically detoxified diphtheria toxin induces T cell responses in humans: enhancement of Th2 responses and toxin-neutralizing antibodies by formulation with chitosan

We previously reported that intranasal immunization with a non-toxic mutant cross-reacting material (CRM)197 of diphtheria toxin, formulated with chitosan, generated protective neutralizing antibodies in mice and guinea pigs. Furthermore, we demonstrated that intranasal delivery of a powder formulation of the CRM197-based vaccine was well tolerated and significantly boosted antibody responses in adult volunteers. Here we report that intranasal booster immunization with CRM197 alone or with chitosan induced systemic T cell responses. We addressed for the first time the induction of T cell subtypes following intranasal vaccination in humans. Intranasal vaccination with CRM197, like parenteral immunization with a conventional diphtheria toxoid vaccine, enhanced antigen-specific IFN-gamma production. However, formulation of the nasal diphtheria vaccine with chitosan significantly augmented Th2-type responses, which correlated with protective levels of toxin-neutralizing antibodies in intranasally boosted individuals. The results suggest that vaccines capable of inducing strong Th2-type responses, such as CRM197 formulated with chitosan, have potential for the development of a protective mucosal vaccine against diphtheria in humans. Furthermore, our findings demonstrate that mucosal subunit vaccines with appropriate delivery systems have considerable potential for booster immunization of adults.

Intranasal coadministration of the Cry1Ac protoxin with amoebal lysates increases protection against Naegleria fowleri meningoencephalitis

Cry1Ac protoxin has potent mucosal and systemic adjuvant effects on antibody responses to proteins or polysaccharides. In this work, we examined whether Cry1Ac increased protective immunity against fatal Naegleria fowleri infection in mice, which resembles human primary amoebic meningoencephalitis. Higher immunoglobulin G (IgG) than IgA anti-N. fowleri responses were elicited in the serum and tracheopulmonary fluids of mice immunized by the intranasal or intraperitoneal route with N. fowleri lysates either alone or with Cry1Ac or cholera toxin. Superior protection against a lethal challenge with 5 x 10(4) live N. fowleri trophozoites was achieved for immunization by the intranasal route. Intranasal immunization of N. fowleri lysates coadministered with Cry1Ac increased survival to 100%; interestingly, immunization with Cry1Ac alone conferred similar protection to that achieved with amoebal lysates alone (60%). When mice intranasally immunized with Cry1Ac plus lysates were challenged with amoebae, both IgG and IgA mucosal responses were rapidly increased, but only the increased IgG response persisted until day 60 in surviving mice. The brief rise in the level of specific mucosal IgA does not exclude the role that this isotype may play in the early defense against this parasite, since higher IgA responses were detected in nasal fluids of mice intranasally immunized with lysates plus either Cry1Ac or cholera toxin, which, indeed, were the treatments that provided the major protection levels. In contrast, serum antibody responses do not seem to be related to the protection level achieved. Both acquired and innate immune systems seem to play a role in host defense against N. fowleri infection, but further studies are required to elucidate the mechanisms involved in protective effects conferred by Cry1Ac, which may be a valuable tool to improve mucosal vaccines.

Adenylate cyclase toxin from Bordetella pertussis synergizes with lipopolysaccharide to promote innate interleukin-10 production and enhances the induction of Th2 and regulatory T cells

Adenylate cyclase toxin (CyaA) from Bordetella pertussis can subvert host immune responses allowing bacterial colonization. Here we have examined its adjuvant and immunomodulatory properties and the possible contribution of lipopolysaccharide (LPS), known to be present in purified CyaA preparations. CyaA enhanced antigen-specific interleukin-5 (IL-5) and IL-10 production and immunoglobulin G1 antibodies to coadministered antigen in vivo. Antigen-specific CD4(+)-T-cell clones generated from mice immunized with antigen and CyaA had cytokine profiles characteristic of Th2 or type 1 regulatory T (Tr1) cells. Since innate immune cells direct the induction of T-cell subtypes, we examined the influence of CyaA on activation of dendritic cells (DC) and macrophages. CyaA significantly augmented LPS-induced IL-6 and IL-10 and inhibited LPS-driven tumor necrosis factor alpha and IL-12p70 production from bone marrow-derived DC and macrophages. CyaA also enhanced cell surface expression of CD80, CD86, and major histocompatibility class II on immature DC. The stimulatory activity of our CyaA preparation for IL-10 production and CD80, CD86, and major histocompatibility complex class II expression was attenuated following the addition of polymyxin B or with the use of DC from Toll-like receptor (TLR) 4-defective mice. However, treatment of DC with LPS alone at the concentration present in the CyaA preparation (0.2 ng/ml) failed to activate DC in vitro. Our findings demonstrate that activation of innate cells in vitro by CyaA is dependent on a second signal through a TLR and that CyaA can promote Th2/Tr1-cell responses by inhibiting IL-12 and promoting IL-10 production by DC and macrophages.

Alternative routes of mucosal immunization in large animals

Mucosal immunization regimes that employ the oral route of delivery are often compromised by antigen degradation in the stomach. Moreover, tolerance or immunological unresponsiveness to orally delivered vaccine antigens is also a major problem associated with this route of immunization. Immunization by alternative routes including intrarectal (i.r.) and intranasal (i.n.) is becoming increasingly recognized in large animals for generating protective antibody responses at mucosal surfaces. These approaches are particularly useful in ruminant species which have four stomachs that can potentially interfere with antigen presentation to mucosal inductive sites of the gut. Modifications to enhance existing mucosal immunization regimes have also been explored through the use of alternative antigen delivery systems and mucosal adjuvants. The combination of alternative immunization routes and the use of appropriate antigen delivery systems appear to be a rational approach for providing protective immunity at mucosal surfaces. There has been a considerable amount of research conducted on evaluating the efficacy of emerging antigen delivery systems and novel adjuvants for improved immunity to mucosal immunization but very little of this work has been specific to the mucosal compartment of large animals. The aim of this review is therefore to assess the feasibility and practicality of using large animals (particularly sheep, cattle and pigs) for inducing and detecting specific immune responses to alternative mucosal routes of immunization.

T cell targeted immune enhancement yields effective T cell adjuvants

Given the critical role of cell-mediated immunity (CMI) in defense against attack from pathogens that establish chronic infections, it has become abundantly clear that current vaccine methodology will not be sufficient to develop the appropriate immune response for protection and/or clearance of infection. By extension, this logic also applies to cancer vaccines where T cell immune-mediated destruction is a critical mechanism for control of the disease. This review describes our current thoughts on the events associated with immune activation and evaluates the various approaches to achieve successful immune activation with defined or targeted antigens as opposed to using inactivated or attenuated organisms. The advantages and disadvantages of the current adjuvants for antigens that focus on mimicking the infection events via the innate immune system or antigen uptake are described in the context of generation of T cell specific responses. A central theme of the discussions is the importance of cytokines in modulating the immune response towards T cell immunity, either by adjuvant modulation or use of natural cytokine mixtures targeted towards the site of immune activation. Also discussed is the possibility that thymomimetic agents such as thymosin alpha1, levamisole and methyl inosine monophosphate (MIMP) may be useful in enhancing the T cell mediated arm of the immune response.

Use of Bordetella bronchiseptica and Bordetella pertussis as live vaccines and vectors for heterologous antigens

Bordetella pertussis and Bordetella bronchiseptica are respiratory pathogens of humans and animals respectively. Unlike many bacteria, they are able to efficiently colonise healthy ciliated respiratory mucosa. This characteristic of Bordetella spp. can potentially be exploited to develop efficient live vaccines and vectors for delivery of heterologous antigens to the respiratory tract. Here we review the progress in this area.

A single amino acid substitution in a recombinant G protein vaccine drastically curtails protective immunity against respiratory syncytial virus (RSV)

Recent studies have indicated a dominant T cell epitope located approximately between amino acids 184 and 203 on the respiratory syncytial virus (RSV) G protein. Using an Escherichia coli-grown plasmid vector encoding a fragment of thioredoxin (Trx) fused to a central region (amino acids 128-229) of the RSV G protein, we employed site-directed mutagenesis to investigate the importance of selected amino acids on vaccine efficacy. By changing two amino acids Arg 188 and Lys 192 to alanine, the ability of the Trx-G 128-229 fusion protein to protect mice against RSV challenge was virtually abolished. Mice immunized with the double mutant protein showed low levels of neutralizing antibodies and no pulmonary eosinophilic infiltrate, in contrast to that observed in mice immunized with wild type protein prior to RSV challenge. While less effective than the double mutant, mutation of either Arg 188 or Lys 192 to Ala drastically impaired the ability of immunized Trx-G 128-229 to induce neutralizing antibodies and to elicit pulmonary eosinophilia associated with RSV challenge. Despite low levels of virus-neutralizing antibodies, G protein-specific antibodies were detected by Western blotting in the sera from mice immunized with either of the single mutants (Arg 188 or Lys 192) but not the double mutant. Finally, immunization of mice with truncated forms of the Trx-G protein, showed partial protection against RSV challenge with Trx-G 128-188 but not with Trx-G 189-229. Taken together, the results indicate an important role for Arg 188 and Lys 192 in the induction of protective immunity and priming for eosinophilia against RSV. Furthermore, while the dominant protective linear epitope on the RSV G protein requires an intact sequence around Arg 188, there are additional, but less potent, protective epitopes upstream of Arg 188.