Oral, intrarectal and intranasal immunizations using CpG and non-CpG oligodeoxynucleotides as adjuvants

Development of a safe and effective novel synthetic mucosal adjuvant SF-10 derived from physiological metabolic pathways and function of human pulmonary surfactant

A safe and effective mucosal adjuvant is required for vaccination against influenza A virus (IAV) infection. Previously, we described that intranasally administration of surfacten®, a medicine derived from bovine pulmonary surfactant (PS), with IAV vaccine can induce IAV-specific IgA in the respiratory tract mucosa and IgG in serum. PS is secreted by alveolar type II cells and Clara cells and serves to reduce lung surface tension. PS finished its rules is incorporated by antigen presenting cells (APCs), such as alveolar macrophages and dendritic cells, and alveolar type II cells and rapidly metabolized. We focused on the metabolic pathways and rapid metabolic turnover of PS and developed a PS-based mucosal adjuvant. First, we determined the essential components of PS adjuvanticity and found that the complex of three PS lipids and surfactant protein-C can enhance to deliver the vaccine antigen and activate APCs. Later, we improved the safety, efficacy and ease of manufacture and finally succeeded in developing SF-10. The use of SF-10 with influenza split vaccine (HAv) (HAv-SF-10) enhances HAv incorporation into APCs both in vitro and in vivo, and intranasal instillation of HAv-SF-10 induced systemic and mucosal HAv-specific immunities in not only mice but also cynomolgus monkeys. The report that PS has physiological effects on the gastrointestinal mucosa prompted us develop a new SF-10-based vaccine that can be administered orally. In this review, We summarize our work on the development of clinically effective PS-based nasal and oral mucosal adjuvants for influenza vaccine.

Potential of the Escherichia coli LT(R192G/L211A) toxoid as a mucosal adjuvant for rainbow trout (Oncorhynchus mykiss)

Oral vaccines are highly demanded by aquaculture sector that requires alternatives to injectable vaccines, involving fish handling, stress-related immunosuppression and mortalities. However, most previous attempts to obtain effective oral vaccines have failed due to a restricted tolerance mechanisms in intestine, whose mucosa is at the frontline of antigen encounter and has to balance the equilibrium between tolerance and immunity in a microbe-rich environment. Thus, the search for oral adjuvants that could augment immune responses triggered by antigens allowing them to circumvent intestinal tolerance is of great relevance. The present work focuses on the adjuvant potential of the Escherichia coli LT(R192G/L211A) toxoid (dmLT). To undertake an initial screening of the potential that dmLT has as an oral adjuvant in rainbow trout (Oncorhynchus mykiss), we have analyzed its transcriptional effects alone or in combination with Aeromonas salmonicida subsp. salmonicida or viral hemorrhagic septicemia virus (VHSV) on rainbow trout intestinal epithelial cell line RTgutGC and gut explants. Our results show that although dmLT provoked no significant effects by itself, it increased the transcription of pro-inflammatory cytokines and antimicrobial genes induced by the bacteria. In contrast, when combined with VHSV, dmLT only increased the transcription of Mx and the intracellular adhesion molecule 1 (ICAM1). Therefore, the protocol designed is an effective method to initially evaluate the effects of potential oral adjuvants, and points to dmLT as an effective adjuvant for oral antibacterial vaccines.

Lipid-Based Particles: Versatile Delivery Systems for Mucosal Vaccination against Infection

Vaccination is the process of administering immunogenic formulations in order to induce or harness antigen (Ag)-specific antibody and T cell responses in order to protect against infections. Important successes have been obtained in protecting individuals against many deleterious pathological situations after parenteral vaccination. However, one of the major limitations of the current vaccination strategies is the administration route that may not be optimal for the induction of immunity at the site of pathogen entry, i.e., mucosal surfaces. It is now well documented that immune responses along the genital, respiratory, or gastrointestinal tracts have to be elicited locally to ensure efficient trafficking of effector and memory B and T cells to mucosal tissues. Moreover, needle-free mucosal delivery of vaccines is advantageous in terms of safety, compliance, and ease of administration. However, the quest for mucosal vaccines is challenging due to (1) the fact that Ag sampling has to be performed across the epithelium through a relatively limited number of portals of entry; (2) the deleterious acidic and proteolytic environment of the mucosae that affect the stability, integrity, and retention time of the applied Ags; and (3) the tolerogenic environment of mucosae, which requires the addition of adjuvants to elicit efficient effector immune responses. Until now, only few mucosally applicable vaccine formulations have been developed and successfully tested. In animal models and clinical trials, the use of lipidic structures such as liposomes, virosomes, immune stimulating complexes, gas-filled microbubbles and emulsions has proven efficient for the mucosal delivery of associated Ags and the induction of local and systemic immune reponses. Such particles are suitable for mucosal delivery because they protect the associated payload from degradation and deliver concentrated amounts of Ags via specialized sampling cells (microfold cells) within the mucosal epithelium to underlying antigen-presenting cells. The review aims at summarizing recent development in the field of mucosal vaccination using lipid-based particles. The modularity ensured by tailoring the lipidic design and content of particles, and their known safety as already established in humans, make the continuing appraisal of these vaccine candidates a promising development in the field of targeted mucosal vaccination.

Hepatitis B core antigen based novel vaccine against porcine epidemic diarrhea virus

Porcine epidemic diarrhea Virus (PEDV) is the causative agent of porcine epidemic diarrhea, which is a devastating viral disease and causes severe economic loss to the swine industry. Current vaccine options for PEDV include modified live viruses and killed live viruses. Though these vaccines have shown efficacy, some have side effects including viral shedding. This report details an E. coli based expression and purification process of multiple vaccine candidates for PEDV using Hepatitis B Core Antigen (HBcAg) as a backbone protein. Short linear peptide sequences from PEDV were inserted into the immunodominant region of HBcAg in a novel recombinant vaccine design against PEDV. These peptide sequences were successfully inserted individually as well as all together in a multivalent strategy. Each vaccine candidate was tested in vivo in an intranasal as well as an intraperitoneal administration. Although each candidate was able to elicit a strong immunogenic response specific for the inserted peptide sequences, only two out of five of the test candidates demonstrated an ability to elicit an immune response capable of virus neutralization when delivered via intraperitoneal administration in mice.

Vaccines for the Prevention of Melioidosis and Glanders

Purpose of review

Burkholderia pseudomallei's and Burkholderia mallei's high rate of infectivity, limited treatment options, and potential use as biological warfare agents underscore the need for development of effective vaccines against these bacteria. Research efforts focused on vaccines against these bacteria are in pre-clinical stages, with no approved formulations currently on the market.

Recent findings

Several live attenuated and subunit vaccine formulations have been evaluated in animal studies, with no reports of significant long term survival after lethal challenge.

Summary

This review encompasses the most current vaccine strategies to prevent B. pseudomallei and B. mallei infections while providing insight for successful vaccines moving forward.

Adjuvant effects of a sequence-engineered mRNA vaccine: translational profiling demonstrates similar human and murine innate response

Background

Prophylactic and therapeutic vaccines often depend upon a strong activation of the innate immune system to drive a potent adaptive immune response, often mediated by a strong adjuvant. For a number of adjuvants immunological readouts may not be consistent across species.

Methods

In this study, we evaluated the innate immunostimulatory potential of mRNA vaccines in both humans and mice, using a novel mRNA-based vaccine encoding influenza A hemagglutinin of the pandemic strain H1N1pdm09 as a model. This evaluation was performed using an in vitro model of human innate immunity and in vivo in mice after intradermal injection.

Results

Results suggest that immunostimulation from the mRNA vaccine in humans is similar to that in mice and acts through cellular RNA sensors, with genes for RLRs [ddx58 (RIG-1) and ifih1 (MDA-5)], TLRs (tlr3, tlr7, and tlr8-human only), and CLRs (clec4gp1, clec2d, cledl1) all significantly up-regulated by the mRNA vaccine. The up-regulation of TLR8 and TLR7 points to the involvement of both mDCs and pDCs in the response to the mRNA vaccine in humans. In both humans and mice activation of these pathways drove maturation and activation of immune cells as well as production of cytokines and chemokines known to attract and activate key players of the innate and adaptive immune system.

Conclusion

This translational approach not only allowed for identification of the basic mechanisms of self-adjuvantation from the mRNA vaccine but also for comparison of the response across species, a response that appears relatively conserved or at least convergent between the in vitro human and in vivo mouse models.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-1111-6) contains supplementary material, which is available to authorized users.

Comparison of the protective effects of killed Burkholderia pseudomallei and CpG oligodeoxynucleotide against live challenge

Melioidosis is a fatal disease caused by Burkholderia pseudomallei. Currently there is no vaccine available. Synthetic oligodeoxynucleotides with unmethylated CpG dinucleotide motifs (CpG ODN) can stimulate vertebrate immune cells and clear certain pathogens that are susceptible to a strong Th1 response. In our previous study, pretreatment with CpG ODN alone or CpG-ODN with cationic liposomes for 2-10 or 30 days before B. pseudomallei infection in mice conferred 80-100% protection. In the present study we investigated the protective effect of CpG-ODN together with heat-killed (HK) or paraformaldehyde-killed B. pseudomallei (PP). HK or PP were used to immunize BALB/c mice twice at 15-day intervals before intra-peritoneal challenge with 5LD50 of B. pseudomallei and observed for 30 days. We found that PP could significantly protect mice (60%) with an increased survival time (24.8±11.63 days) while in the HK and PBS groups, all infected mice died within 6 days. Although either CpG ODN or PP conferred significant protection, giving them in combination did not enhance it further. Serum IFN-γ levels on day-5 (before challenge) of the PP and PP+CpG ODN groups were significantly higher than those of the PBS control group. The results further support the importance of IFN-γ in host protection against B. pseudomallei and suggest further study on paraformaldehyde-killed bacteria as a component of a future B. pseudomallei vaccine.

Progress toward development of an inhalation vaccine against botulinum toxin

The looming threat of bioterrorism has enhanced interest in the development of vaccines against agents such as botulinum toxin. This in turn has stimulated efforts to create vaccines that are effective by the oral and inhalation routes. Recently, considerable progress has been made in creating an inhalation vaccine against botulism. This work stems from the discovery that a polypeptide that represents a third of the toxin molecule retains the ability to be adsorbed from the airway and to evoke an immune response but retains none of the adverse effects of the native toxin. Interestingly, this polypeptide can also serve as a carrier molecule in the creation of inhalation vaccines against other pathogens.

Reduced severity of peanut-induced anaphylaxis in TLR9-deficient mice is associated with selective defects in humoral immunity

Signaling through the innate immune system can promote or suppress allergic sensitization. Toll-like receptor 9 (TLR9) has modulatory effects on the mucosal immune system, and we hypothesized that TLR9 would influence susceptibility to allergic sensitization to foods. We observed that TLR9-/- mice were resistant to peanut-induced anaphylaxis. This was associated with a significant impairment in total immunoglobulin E (IgE) and peanut-specific IgE and IgA, but not IgG1 or Th2 cytokine production. TLR9-/- mice had reduced development of Peyer's patches, but resistance to sensitization was not restricted to oral routes. Rag1-deficient mice were reconstituted with TLR9+/+ or -/- B cells plus CD4+ T cells. TLR9-/- B cells regained the ability to produce IgE in the presence of a wild-type environment. Our results demonstrate that TLR9 on an unknown cell type is required for the development of IgE-producing B cells, and we conclude that TLR9 signaling indirectly shapes the immune response for optimal IgE production.

Nasal immunization with different forms of heat shock protein-65 reduced high-cholesterol-diet-driven rabbit atherosclerosis

Heat shock protein-65 (Hsp65) is an important pro-atherogenic factor, but nasal immunization of Hsp65 can induce immune tolerance and reduce atherosclerotic inflammation. Here, we describe the effects of different forms of Hsp65 antigen inoculated, i.e. Hsp65 DNA, Hsp65 protein, Hsp65 DNA prime combined with Hsp65 protein boost, on high-cholesterol-diet-driven rabbit atherosclerosis lesions. The results showed that sera anti-Hsp65 IgG antibodies were lower induced and protective anti-Hsp65 IgA in nasal cavity and lung were induced after rabbits were immunized with different forms of Hsp65. However, the avidity between Hsp65 IgG antibody and antigen is different. Hsp65 DNA prime-protein boost could further improve the avidity compared with Hsp65 DNA immunization alone, but only immunization with Hsp65 protein alone obtain the best avidity. In addition, more protective IL-10 and less adverse IFN-γ were produced and sera TC and LDL-C were decreased obviously at different extents in immunized groups. As a result, atherosclerosis lesions were significantly attenuated, but only nasal immunization with Hsp65 protein alone may be the best effective form of Hsp65 antigen to control atherosclerotic lesions. The results demonstrated that different forms of Hsp65 antigen could produce different effects in the treatment of atherosclerosis. Immunization mucosally with Hsp65 protein could be a promising therapeutic method for atherosclerosis.

Cationic liposomes extend the immunostimulatory effect of CpG oligodeoxynucleotide against Burkholderia pseudomallei infection in BALB/c mice

Melioidosis is a severe disease caused by the Gram-negative bacterium Burkholderia pseudomallei. Previously we showed that pretreatment of mice with CpG oligodeoxynucleotide (CpG ODN) 2 to 10 days prior to B. pseudomallei challenge conferred as high as 90% protection, but this window of protection was rather short. In the present study, we therefore aimed to prolong this protective window and to gain further insight into the mechanisms underlying the protection induced by CpG ODN against B. pseudomallei infection. It was found that the CpG ODN incorporated with cationic liposomes (DOTAP) but not zwitterionic liposomes (DOPC) provided complete protection against bacterial challenge. Although marked elevation of gamma interferon (IFN-γ) was found in the infected animals 2 days postinfection, it was significantly lowered by the DOTAP-plus-CpG ODN pretreatment. When appropriately activated, the phagocytic index and oxidative burst responses of neutrophils appeared not to be elevated. However, macrophages from stimulated mice showed higher levels of nitric oxide production and exhibited higher levels of antimicrobial activities, judging from lower numbers of viable intracellular bacteria. Taken together, our results demonstrate that DOTAP can enhance the protective window period of CpG ODN to at least 30 days and provide 100% protection against B. pseudomallei infection. The protective effect of DOTAP plus CpG ODN could provide an alternative approach to preventing this lethal infection, for which no vaccine is yet available.

Co-administration of attenuated Mycoplasma hyopneumoniae 168 strain with bacterial DNA enhances the local and systemic immune response after intranasal vaccination in pigs

Mycoplasma hyopneumoniae, the primary pathogen of enzootic pneumonia, occurs worldwide and causes major economic losses to the pig industry. M. hyopneumoniae infects pigs at mucosal surfaces of respiratory tract. The aim of the present study was to investigate if the protection rate against M. hyopneumoniae infection following intranasal immunization with attenuated M. hyopneumoniae 168 strain is improved by administration of bacterial DNA containing CpG motifs. Thirty pigs were immunized intranasally or intramuscularly and the levels of local respiratory tract and systemic immune responses were detected. The results showed that the number of intraepithelial lymphocytes in the tracheal fork, the levels of cytokine IL-6, and M. hyopneumoniae specific SIgA in local nasal cavity increased respectively after intranasal vaccination with the attenuated M. hyopneumoniae 168 strain alone. However, the levels of IL-10 and IFN-γ in local nasal cavity, the number of intraepithelial lymphocytes in trachea, CD4(+) and CD8(+) T lymphocytes in the lung and hilar lymph nodes, the specific IgG antibody level in serum on 35 day post immunization were all increased significantly after intranasal vaccination of the attenuated M. hyopneumoniae 168 strain adjuvanted with bacterial DNA. We concluded that intranasal administration of attenuated M. hyopneumoniae 168 strain adjuvanted with bacterial DNA may be effective in evoking the local cellular and humoral immune response in the respiratory tract and the systemic immune response. Intranasal vaccination will be effective in prevention of the transmission and prevalence of MPS.

Formulation design considerations for oral vaccines

Whilst oral vaccination is a potentially preferred route in terms of patient adherence and mass vaccination, the ability to formulate effective oral vaccines remains a challenge. The primary barrier to oral vaccination is effective delivery of the vaccine through the GI tract owing to the many obstacles it presents, including low pH, enzyme degradation and bile-salt solubilization, which can result in breakdown/deactivation of a vaccine. For effective immune responses after oral administration, particulates need to be taken up by the M cells however, these are few in number. To enhance M-cell uptake, particle characteristics can be optimized with particle size, surface charge, targeting groups and bioadhesive properties all being considerations. Yet improved uptake may not translate into enhanced immune responses and formulating particulates with inherent adjuvant properties can offer advantages. Within this article, we establish the options available for consideration when building effective oral particulate vaccines.

TLR-based immune adjuvants

This work describes the nature and strength of the immune response induced by various Toll-like receptor ligands and their ability to act as vaccine adjuvants. It reviews the various ligands capable of triggering individual TLRs, and then focuses on the efficacy and safety of those agents for which clinical results are available.

Dietary deoxynucleic acid induces type 2 T-helper immune response through toll-like receptor 9 in mice

BACKGROUND

It has been shown that dietary nucleotides modulate immune response. Due to their unique properties in immune responses, nucleotides are used as immunonutrition in the field of clinical nutrition.

AIM OF THE STUDY

In this study, we examined the effect of dietary deoxynucleic acid (DNA) on antigen (Ag)-specific immune response in ovalbumin (OVA)-immunized BALB/c mice and determined the mechanism using toll-like receptor 9 (TLR9) knock-out (KO) mice.

METHODS

BALB/c or TLR9 KO mice were fed control and 1% DNA diets and immunized with OVA. Spleen cells from OVA-immunized mice were stimulated with OVA in vitro, and the contents of IFN-γ and IL-4 in supernatants were measured by an ex vivo system. CD11c(+) dendritic cells were purified, and ability of cytokine induction to CD4(+) cells was examined.

RESULTS

The level of OVA-specific IL-4 production in the DNA group was significantly higher than that in the control group. In contrast, the level of OVA-specific IFN-γ production in the DNA group was lower than that in the control group. The DNA diet decreased Ag-specific IL-4 production and enhanced Ag-specific IFN-γ production in TLR9 KO mice. CD11c(+) DCs from mice fed the DNA diet had a greater ability than CD11c(+) DCs from mice fed the control diet to induce the production of IL-4 from DO11.10 CD4(+) T cells.

CONCLUSIONS

Dietary DNA increases Ag-specific IL-4 production and decreases IFN-γ production through a TLR9-dependent pathway. CD11c(+) dendritic cells are target cells in dietary DNA-induced immune regulation.

Progress towards a needle-free hepatitis B vaccine

Hepatitis B virus (HBV) infection is a worldwide public health problem. Vaccination is the most efficient way to prevent hepatitis B. Despite the success of the currently available vaccine, there is a clear need for the development of new generation of HBV vaccines. Needle-free immunization is an attractive approach for mass immunization campaigns, since avoiding the use of needles reduces the risk of needle-borne diseases and prevents needle-stick injuries and pain, thus augmenting patient compliance and eliminating the need for trained medical personnel. Moreover, this kind of immunization was shown to induce good systemic as well as mucosal immunological responses, which is important for the creation of both a prophylactic and therapeutic vaccine. In order to produce a better, safer, more efficient and more suitable vaccine, adjuvants have been used. In this article, several adjuvants tested over the years for their potential to help create a needle-free vaccine against HBV are reviewed.

Needle-free influenza vaccination

Vaccination is the cornerstone of influenza control in epidemic and pandemic situations. Influenza vaccines are typically given by intramuscular injection. However, needle-free vaccinations could offer several distinct advantages over intramuscular injections: they are pain-free, easier to distribute, and easier to give to patients, and their use could reduce vaccination costs. Moreover, vaccine delivery via the respiratory tract, alimentary tract, or skin might elicit mucosal immune responses at the site of virus entry and better cellular immunity, thus improving effectiveness. Although various needle-free vaccination methods for influenza have shown preclinical promise, few have progressed to clinical trials-only live attenuated intranasal vaccines have received approval, and only in some countries. Further clinical investigation is needed to help realise the potential of needle-free vaccination for influenza.

Transgenic plant-based oral vaccines

Oral vaccines offer significant advantages over needle-based vaccines for achieving universal childhood vaccination goals. The expression of vaccine antigens in transgenic plants has the potential to provide a convenient, safe approach for oral vaccination and thus a feasible alternative to traditional parenteral vaccines. Many developments in the field have ushered in improvements such as enhanced protein antigen expression for the use of plants as factories for vaccine production, and facilitated studies pertaining to immunogenicity of candidate vaccines. Oral delivery of plant-based vaccines offers the benefit of antigen protection within the harsh intestinal environment. Within the gut, mucosal immune cells are poised to respond to pathogens, but can also be exploited to elicit protective immune responses to oral vaccines. Inclusion of mucosal adjuvants during immunization with the vaccine antigen has been an important step towards the success of plant-based vaccines. This review discusses the mechanisms that control mucosal immune responses and highlights some of the studies and the results achieved following immunization with transgenic plants.

Intranasal CpG therapy attenuated experimental fungal asthma in a TLR9-dependent and -independent manner

BACKGROUND

CpG administration abolishes airway inflammation and remodeling in acute models of allergic airway disease.

METHODS

Herein, we investigated the therapeutic effect of CpG in a chronic fungal model of asthma. TLR9+/+ and TLR9-/- mice were sensitized to soluble Aspergillus fumigatus antigens and challenged with live A. fumigatus conidia. Mice were treated with intraperitoneal (IP) or intranasal (IN) CpG, or left untreated 14-28 days after conidium challenge. All features of allergic airway disease were attenuated in TLR9+/+ mice treated with IN CpG, including airway hyperresponsiveness (AHR), mucus production, and peribronchial fibrosis.

RESULTS

TLR9-/- mice treated with IN CpG exhibited attenuated airway remodeling but not AHR. Whole-lung IL-12 levels were significantly elevated in both TLR9+/+ and TLR9-/- mice receiving IN CpG but not in either group receiving IP CpG. Whole-lung IL-10 levels were significantly elevated in IN CpG-treated TLR9+/+ mice but not in TLR9-/- mice receiving IN CpG. Increased whole-lung transcript and protein levels of the scavenger receptors SR-A and MARCO were observed in TLR9-/- mice compared with TLR9+/+ mice, possibly accounting for the CpG responsiveness in the knockout group.

CONCLUSIONS

Together, these data show that IN CpG has a therapeutic effect during established fungal asthma, which is TLR9 dependent and independent.

Mucosal vaccines: recent progress in understanding the natural barriers

It has long been known that protection against pathogens invading the organism via mucosal surfaces correlates better with the presence of specific antibodies in local secretions than with serum antibodies. The most effective way to induce mucosal immunity is to administer antigens directly to the mucosal surface. The development of vaccines for mucosal application requires antigen delivery systems and immunopotentiators that efficiently facilitate the presentation of the antigen to the mucosal immune system. This review provides an overview of the events within mucosal tissues that lead to protective mucosal immune responses. The understanding of those biological mechanisms, together with knowledge of the technology of vaccines and adjuvants, provides guidance on important technical aspects of mucosal vaccine design. Not being exhaustive, this review also provides information related to modern adjuvants, including polymeric delivery systems and immunopotentiators.

Non-viral vectors in cystic fibrosis gene therapy: recent developments and future prospects

Gene therapy has been proposed for a wide range of human diseases but few have received the level of attention over such a prolonged period as cystic fibrosis (CF) with over 20 clinical studies undertaken. Following a 10-year interval, clinical trials of an aerosolisable non-viral gene transfer agent have recently been initiated by researchers in the United Kingdom. Here we review the rationale and requirements for effective gene therapy for CF lung disease. The previous non-viral gene therapy trials are discussed and the prospects for the current leading non-viral formulations for CF gene therapy are considered. Factors affecting the selection and design of the plasmid DNA molecule, likely to be of central importance to clinical efficacy, are reviewed and we describe the potential merits of the formulation that has been selected for the forthcoming UK trials.

Contrasting effects of type I interferon as a mucosal adjuvant for influenza vaccine in mice and humans

To identify an adjuvant that enhances antibody responses in respiratory secretions to inactivated influenza virus vaccine (IVV), a comparison was made of responses to intranasal vaccinations of mice with IVV containing monophosphoryl lipid A (MPL), type I interferon (IFN) or cholera toxin B (CTB). Antibody in nasal secretions and lung wash fluids from mice was increased after vaccination and lung virus was significantly reduced after challenge to a similar level in each adjuvant group. Interferon was selected for a trial in humans. Trivalent inactivated influenza vaccine was given intranasally to healthy adult volunteers alone or with 1 million units (Mu) or 10 Mu of alpha interferon. Vaccinations were well tolerated but neither serum hemagglutination-inhibiting nor neutralizing antibody responses among the vaccine groups were significantly different. Similarly, neither neutralizing nor IgA antibody responses in nasal secretions were significantly different. Thus, despite exhibiting a significant adjuvant effect in mice, interferon did not exhibit an adjuvant effect for induction of antibody in respiratory secretions of humans to inactivated influenza virus vaccine given intranasally.

Induction of mucosal and systemic humoral immune responses in murine system by intranasal immunization with peptide antigens of P. vivax and CpG oligodeoxynucleotide (ODN) in microparticle delivery

In the present study we have investigated the immunomodulatory effects of two adjuvants, CpG 1826 (two copies of CpG motifs) and CpG 2006 (three copies of CpG motifs) to the five peptide antigens of Plasmodium vivax derived from circumsporozoite protein (CSP), merozoite surface protein-1 (MSP1#1, MSP1#23), apical membrane antigen-1 (AMA-1) and gametocyte surface antigen (Pvs24) in alum and microparticle formulations, using intramuscular and intranasal routes of immunization. Alum formulation without CpG ODN generated low serum IgG and IgA antibody titers and the predominant IgG isotypes were IgG1 but with the addition of CpG ODN (1826 or 2006), the antibody titers were increased by four fold with the predominance of IgG2a/2b isotypes. The SIgA peak titers in lung and intestinal washes were significantly increased with the intranasal mode of administration. Specific activity measurement was done to calculate for the accurate amounts of total serum IgG, IgA and SIgA in washes and showed direct correlation between antibody titer and its concentration. High titer anti-Pvs24 antibodies have significant inhibitory effects on parasite development in the mosquito midgut when tested in membrane feeding assays. The immunofluorescence results show that the peptide specific antisera reacted with the air-dried parasite antigens isolated from P. vivax patients. The present study demonstrates that intranasal route of immunization appears to be an alternate mode of inducing protective immunity in P. vivax malaria.

CpG DNA: Trigger of Sepsis, Mediator of Protection, or Both?

Unmethylated CpG motifs are prevalent in bacterial but not vertebrate genomic DNAs and activate immune cells that express the TLR9 receptor. This triggers the production of reactive oxygen species and the secretion of proinflammatory cytokines and chemokines. Under some conditions these effects can result in the systemic inflammatory response syndrome. Under other conditions, the immune stimulatory effects of CpG motifs can protect against pathogen challenge and initiate prophylactic and therapeutic innate and adaptive immune responses.

Immunogenicity of Recombinant Helicobacter pylori Urease B Administered by Various Routes and with Different Adjuvants

Because of the high prevalence of Helicobacter pylori infection and the morbidity and mortality associated to the disease, development of a preventive vaccine has become a priority. To this goal, we produced recombinant H. pylori urease B (rUreB) and tested its immunogenicity in BALB/c mice when administered as 3 doses (week 0, 4 and 6) by either parenteral (intramuscular) or mucosal routes (intragastric, intranasal, intrarectal) and with the use of various adjuvants (none, CpG, alum or Freund's). The intramuscular route was more immunogenic than any mucosal route; of the mucosas, only intranasal induced modest levels of serum IgG. All adjuvants improved the seroresponse to plain rUreB and, of them, Freund's and alum were equally good and better than CpG ODN 1826. Stool IgA was barely detected by any immunization strategy.

Immunotherapeutic applications of CpG oligodeoxynucleotide TLR9 agonists

Toll-like receptor 9 (TLR9) agonists have demonstrated substantial potential as vaccine adjuvants, and as mono- or combination therapies for the treatment of cancer and infectious and allergic diseases. Commonly referred to as CpG oligodeoxynucleotides (ODN), TLR9 agonists directly induce the activation and maturation of plasmacytoid dendritic cells and enhance differentiation of B cells into antibody-secreting plasma cells. Preclinical and early clinical data support the use of TLR9 agonists as vaccine adjuvants, where they can enhance both the humoral and cellular responses to diverse antigens. In mouse tumor models TLR9 agonists have shown activity not only as monotherapy, but also in combination with multiple other therapies including vaccines, antibodies, cellular therapies, other immunotherapies, antiangiogenic agents, radiotherapy, cryotherapy, and some chemotherapies. Phase I and II clinical trials have indicated that these agents have antitumor activity as single agents and enhance the development of antitumor T-cell responses when used as therapeutic vaccine adjuvants. CpG ODN have shown benefit in multiple rodent and primate models of asthma and other allergic diseases, with encouraging results in some early human clinical trials. Although their potential clinical contributions are enormous, the safety and efficacy of these TLR9 agonists in humans remain to be determined.

CpG oligonucleotides as adjuvants for vaccines targeting infectious diseases

Synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs act as immune adjuvants, accelerating and boosting antigen-specific immune responses. CpG motifs promote the induction of Th1 and pro-inflammatory cytokines and support the maturation/activation of professional antigen presenting cells (particularly plasmacytoid dendritic cells). These effects are optimized by maintaining close physical contact between the CpG ODN and the immunogen. Co-administering CpG ODN with a variety of vaccines has improved the resultant humoral and/or cellular immune responses, culminating in enhanced protective immunity in rodent and primate challenge models. Ongoing clinical studies indicate that CpG ODN are safe and well-tolerated when administered as adjuvants to humans, and that they can support increased vaccine-specific immune responses.

The mucosal adjuvanticity of the oligodeoxynucleotides containing a non-methylated CpG motif on BCG and diphtheria toxoid

CpG-DNA is currently attracting attention as an effective and safe vaccine adjuvant to prevent from microbial infections. In this report, we examined the effects of oligo B, which is a synthetic CpG-DNA, in mucosal administration of Bacillus Calmette-Guérin (BCG) and diphtheria toxoid (DT). Co-administration with oligo B enhanced BCG-induced delayed type hypersensitivity to purified protein derivative (PPD) in guinea pigs. The titers of anti-DT serum IgG, IgA and mucosal IgA antibodies induced by intranasal administration with DT plus oligo B were significantly higher than that with DT alone. In both C57BL/6 and BALB/c mice, intranasal administration of DT with oligo B induced enough level of antibodies to prevent onset of diphtheria. The analysis of antibody subclasses showed that intranasal administration of oligo B induced not only IgG1 but also IgG2a, IgG2c and IgA anti-DT antibodies. In contrast, there was no or little production of the anti-DT serum IgE. Taken together our data suggest that oligo B is a powerful adjuvant in 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.

Broad-spectrum drugs against viral agents

Development of antivirals has focused primarily on vaccines and on treatments for specific viral agents. Although effective, these approaches may be limited in situations where the etiologic agent is unknown or when the target virus has undergone mutation, recombination or reassortment. Augmentation of the innate immune response may be an effective alternative for disease amelioration. Nonspecific, broad-spectrum immune responses can be induced by double-stranded (ds)RNAs such as poly (ICLC), or oligonucleotides (ODNs) containing unmethylated deocycytidyl-deoxyguanosinyl (CpG) motifs. These may offer protection against various bacterial and viral pathogens regardless of their genetic makeup, zoonotic origin or drug resistance.

Effects of different immunization protocols and adjuvant on antibody responses to inactivated SARS-CoV vaccine

Severe acute respiratory syndrome (SARS) is a deadly and highly infectious disease caused by SARS Coronavirus (SARS-CoV). Inactivated SARS-CoV has been explored as a vaccine against SARS-CoV; however, current knowledge of inactivated SARS-CoV vaccine is quite limited. We attempted to investigate the effects of different immunization protocols and adjuvant on the antibody responses to inactivated SARS-CoV vaccine. With an intraperitoneal (IP) immunization protocol, inactivated SARS-CoV alone induced significant amounts of SARS-CoV-specific IgG antibodies in sera and a small quantity of SARS-CoV-specific IgA antibodies in the genital tract and feces, but failed to induce any detectable SARS-CoV-specific IgA antibodies in sera, saliva, lung, and intestine, and the addition of CpG ODN 2006 had only a marginal effect on antibody production. In contrast, with an intranasal (IN) immunization protocol, inactivated SARS-CoV alone failed to induce any detectable SARS-CoV-specific IgA antibodies in sera, saliva, lung, and intestine, except for a small quantity of IgA antibodies in fecal extracts and the genital tract, along with IgG antibodies in sera, but when given with adjuvant CpG ODN 2006, inactivated SARS-CoV induced significant amounts of SARS-CoV-specific IgG antibodies in sera, and a detectable amount of SARS-CoV-specific IgA antibodies in sera and all tested mucosal secretions and tissues (i.e., saliva, the genital tract, fecal extract, lung, and intestine). On a neutralization assay, neutralizing activity with the IP immunization protocol was detected in sera and mucosal secretions (from the saliva and genital tract), but sera from the IN protocol failed to show any neutralizing activity. Our study demonstrated that inactivated SARS-CoV vaccine is promising, and our data provide a sound foundation for the development of an effective inactivated SARS-CoV vaccine.

Mouse models for the study of mucosal vaccination against otitis media

Otitis media (OM) is one of the most common infectious diseases in humans. The pathogenesis of OM involves nasopharyngeal (NP) colonization and retrograde ascension of the pathogen up the Eustachian tube into the middle ear (ME). Due to increasing rates of antibiotic resistance, there is an urgent need for vaccines to prevent infections caused by the most common causes of bacterial OM, including nontypeable Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis. Current vaccine strategies aim to diminish bacterial NP carriage, thereby reducing the likelihood of developing acute OM. To be effective, vaccination should induce local mucosal immunity both in the ME and in the NP. Studies in animal models have demonstrated that the intranasal route of vaccination is particularly effective at inducing immune responses in the nasal passage and ME for protection against OM. The mouse is increasingly used in these models, because of the availability of murine reagents and the existence of technology to manipulate murine models of disease immunologically and genetically. Previous studies confirmed the suitability of the mouse as a model for inflammatory processes in acute OM. Here, we discuss various murine models of OM and review the applicability of these models to assess the efficacy of mucosal vaccination and the mechanisms responsible for protection. In addition, we discuss various mucosal vaccine antigens, mucosal adjuvants and mucosal delivery systems.

Intranasal immunization of mice with a formalin-inactivated bovine respiratory syncytial virus vaccine co-formulated with CpG oligodeoxynucleotides and polyphosphazenes results in enhanced protection

As respiratory syncytial virus (RSV) targets the mucosal surfaces of the respiratory tract, induction of both systemic and mucosal immunity will be critical for optimal protection. In this study, the ability of an intranasally delivered, formalin-inactivated bovine RSV (FI-BRSV) vaccine co-formulated with CpG oligodeoxynucleotides (ODN) and polyphosphazenes (PP) to induce systemic and mucosal immunity, as well as protection from BRSV challenge, was evaluated. Intranasal immunization of mice with FI-BRSV formulated with CpG ODN and PP resulted in both humoral and cell-mediated immunity, characterized by enhanced production of BRSV-specific serum IgG, as well as increased gamma interferon and decreased interleukin-5 production by in vitro-restimulated splenocytes. These mice also developed mucosal immune responses, as was evident from increased production of BRSV-specific IgG and IgA in lung-fragment cultures. Indeed, the increases in serum and mucosal IgG, and in particular mucosal IgA and virus-neutralizing antibodies, were the most critical differences observed between FI-BRSV formulated with both CpG ODN and PP in comparison to formulations with CpG ODN, non-CpG ODN or PP individually. Finally, FI-BRSV/CpG/PP was the only formulation that resulted in a significant reduction in viral replication upon BRSV challenge. Co-formulation of CpG ODN and PP is a promising new vaccine platform technology that may have applications in mucosal immunization in humans.

Immunization with adenovirus at the large intestinal mucosa as an effective vaccination strategy against sexually transmitted viral infection

The large intestinal mucosa contains immunological structures that may potentially serve as a site for induction of mucosal immunity against infections. Adenovirus (Ad), which is effective in gene transfer to epithelia, may be an ideal antigen delivery system for vaccination at the large intestinal mucosa. To investigate this potential, we immunized mice with recombinant replication-deficient Ad through a single intracolorectal (ICR) administration. Effective transfer of encoded genes was found in both the epithelial layer and lamina propria of the colorectal mucosa. Dendritic cells were able to transfer antigen to the draining lymph nodes, where antigen-specific CD8(+) T cells were primed. Functional antigen-specific CD8(+) T cells and IgA-specific antibodies were detected during the effector phase in the large intestine. Compared to other immunization routes (intranasal, subcutaneous), ICR immunization induced stronger colorectal immune responses and more potent protection against rectal challenge with pathogenic viruses. Further, this immunization strategy provided vaginal protection, more potent than that induced by vaccination in the nose or skin. Therefore, large intestine mucosal immunization using Ad represents an effective vaccination strategy against virus infection at both rectal and vaginal mucosal tissue sites.

In vivo oral administration effects of various oligodeoxynucleotides containing synthetic immunostimulatory motifs in the immune response to pseudorabies attenuated virus vaccine in newborn piglets

Numerous studies have demonstrated that oligonucleotides containing CpG motifs (CpG ODN) are efficient immunoadjuvants to various antigens administered by parenteral routes to mice. Recently, it has been found that CpG ODNs also is a promising mucosal adjuvant in mice. To date, there have been no studies to screen the optimal CpG sequence and modified ODN backbone to piglets in vivo, when delivered by oral route. We have previously demonstrated that human-specific CpG ODN is a potent adjuvant to pseudorabies live attenuated virus (PRV) vaccine when administered subcutaneously (SC) or ocularly in piglets. In this study, we screened and evaluated the optimal CpG sequences (porcine-specific, human-specific, mouse-specific ODN) and optimal backbone (SOS-backbone consisting of a nuclease-resistant phosphorothioate guanosines at the 5' and the 3'-end and with a phosphodiester (O) in the center and phosphorothioate (S) backbone (S-backbone)) to PRV vaccine delivered orally in piglets. The proliferation of peripheral blood mononuclear cells (PBMCs), IFN-gamma and IL-4 in serum, and the titre of IgG, IgG2/IgG1 isotype in serum and IgA in intestinal washings and feces to PRV vaccine were tested at different time-points. The results suggested that, CpG ODNs augmented systemic (IgG in serum, T-cell proliferation) and mucosal (IgA in intestinal washings and feces) immune responses against antigen. CpG ODNs stimulated both T-helper type1 (Th1) (IgG2) and Th2 (IgA) responses when delivered orally. With the same backbone, the porcine-specific ODN-induced responses were comparable with human-specific ODNs, but stronger than mouse-specific CpG ODNs. SOS-backbone induced a stronger IFN-gamma and proliferative responses than S-backbone, while antibody responses induced by SOS-backbones were slightly less or similar with S-backbone. The in vivo data demonstrate for the first time that porcine-specific and human-specific ODNs both are optimal sequences for mucosal system in piglets.

The potential of topical DNA vaccines adjuvanted by cytokines

To improve the efficacy of DNA immunization epidermal Langerhans cells are attractive targets to deliver antigen-encoding plasmid DNA. Topical vaccination with naked plasmid DNA has been shown to induce immune responses, and their potency might be improved by chemical and physical methods aimed to enhance the efficiency of plasmid DNA delivery into the skin. Cytokines have also been evaluated as adjuvants for DNA vaccines because they influence the host immune response. This review focuses on the action of several cytokines tested as molecular adjuvants for DNA vaccines and the combination of them with the DermaVir Patch vaccine. DermaVir vaccine, topically administered under a patch, consists of a plasmid DNA that is chemically formulated into a nanoparticle to support vaccine delivery into epidermal Langerhans cells and to induce antigen-specific memory T cells.

Oral vaccination: where we are?

As early as 900 years ago, the Bedouins of the Negev desert were reported to kill a rabid dog, roast its liver and feed it to a dog-bitten person for three to five days according to the size and number of bites [1] . In sixteenth century China, physicians routinely prescribed pills made from the fleas collected from sick cows, which purportedly prevented smallpox. One may dismiss the wisdom of the Bedouins or Chinese but the Nobel laureate, Charles Richet, demonstrated in 1900 that feeding raw meat can cure tuberculous dogs - an approach he termed zomotherapy. Despite historical clues indicating the feasibility of oral vaccination, this particular field is notoriously infamous for the abundance of dead-end leads. Today, most commercial vaccines are delivered by injection, which has the principal limitation that recipients do not like needles. In the last few years, there has been a sharp increase in interest in needle-free vaccine delivery; new data emerges almost daily in the literature. So far, there are very few licensed oral vaccines, but many more vaccine candidates are in development. Vaccines delivered orally have the potential to take immunization to a fundamentally new level. In this review, the authors summarize the recent progress in the area of oral vaccines.

Evaluation of the immune response following a short oral vaccination schedule with hepatitis B antigen encapsulated into alginate-coated chitosan nanoparticles

The purpose of this work was to assess the ability of recombinant hepatitis B vaccine, encapsulated in alginate-coated chitosan nanoparticles, to induce local and systemic immune responses following oral vaccination. The antigen was administered either alone or in combination with the immunopotentiator, synthetic oligodeoxynucleotide containing immunostimulatory CpG motif (CpG ODN) as adjuvant, and associated or not with the alginate-coated chitosan nanoparticles. After two immunizations the group I (HBsAg associated with nanoparticles) and the group VI (HBsAg and CpG, both associated with nanoparticles) showed enhanced immune responses. Both groups showed significant higher values of the CD69 expression in CD4+ and CD8+ T-lymphocytes and lower values of this marker in B lymphocytes. Moreover, a strongest proliferative response of the splenocytes, ex vivo stimulated with concanavalin A, was observed in the same groups. Although with a presence of non-responder mice within the groups, only mice of the groups I and VI elicited the generation of anti-HBsAg antibodies detected in serum (IgG) and in the intestinal washings (sIgA). The results demonstrated that coated chitosan nanoparticles might have potential for being used as a deliver system for oral vaccination with the recombinant hepatitis B surface antigen.

Effects of a Th1- versus a Th2-biased immune response in protection against Helicobacter pylori challenge in mice

The roles that T helper type 1 (Th1) and T helper type 2 (Th2) Helicobacter pylori-specific immune responses play in protection from H. pylori challenge are poorly understood. It is expected that Th2 immune responses are required for protection against extracellular bacteria, such as H. pylori. However, recent studies have suggested that Th1 immunity is required for protection. The mechanisms by which this might occur are unknown. Our goal in this study was to more clearly define the effects of a Th1- versus a Th2-promoting H. pylori vaccine on immunity and protection. Therefore, we tested a Th1 vaccine consisting of an H. pylori sonicate and CpG oligonucleotides (CpG) and a Th2 vaccine consisting of a lipopolysaccharide (LPS)-depleted H. pylori sonicate combined with cholera toxin (CT). We demonstrate that although the Th2-promoting vaccine induced stronger systemic and local immune responses, only the Th1-promoting vaccine was protective.

Intranasal immunization with a recombinant truncated FimH adhesin adjuvanted with CpG oligodeoxynucleotides protects mice against uropathogenic Escherichia coli challenge

In this work, we assessed the efficacy of an experimental intranasal vaccine against urinary-tract infections. The vaccine contained a recombinant truncated FimH (rFimHt) adhesin plus CpG oligodeoxynucleotides. The efficacy of the vaccine was compared with that of an intramuscular vaccine that was formulated with the same immunogen plus Freund's adjuvant. Our results show that serum immunoglobulin G titers of vaccinated animals were similarly enhanced in both cases. However, the intranasal vaccine elicited higher vaginal-wash-specific immunoglobulin A titers against rFimHt than the intramuscular route. Both vaccines reduced the in vivo colonization of the bladder by uropathogenic Escherichia coli more than 100-fold in a murine cystitis model. Our results indicate that a recombinant truncated FimH adhesin plus CpG oligodeoxynucleotides is a suitable immunogenic combination that can contribute to the development of a highly efficacious urinary tract infection vaccine.

Delivery systems and adjuvants for oral vaccines

The oral route is the ideal means of delivering prophylactic and therapeutic vaccines, offering significant advantages over systemic delivery. Most notably, oral delivery is associated with simple administration and improved safety. In addition, unlike systemic immunisation, oral delivery can induce mucosal immune responses. However, the oral route of vaccine delivery is the most difficult because of the numerous barriers posed by the gastrointestinal tract. To facilitate effective immunisation with peptide and protein vaccines, antigens must be protected, uptake enhanced and the innate immune response activated. Numerous delivery systems and adjuvants have been evaluated for oral vaccine delivery, including live vectors, inert particles and bacterial toxins. Although developments in oral vaccines have been disappointing so far, in terms of the generation of products, the availability of a range of novel delivery systems offers much greater hope for the future development of improved oral vaccines.

Enhancement of infectious disease vaccines through TLR9-dependent recognition of CpG DNA

The adaptive immune system-with its remarkable ability to generate antigen-specific antibodies and T lymphocytes against pathogens never before "seen" by an organism-is one of the marvels of evolution. However, to generate these responses, the adaptive immune system requires activation by the innate immune system. Toll-like receptors (TLRs) are perhaps the best-understood family of innate immune receptors for detecting infections and stimulating adaptive immune responses. TLR9 appears to have evolved to recognize infections by a subtle structural difference between eukaryotic and prokaryotic/viral DNA; only the former frequently methylates CpG dinucleotides. Used as vaccine adjuvants, synthetic oligodeoxynucleotide (ODN) ligands for TLR9--CpG ODN--greatly enhance the speed and strength of the immune responses to vaccination.

The role of adjuvants in the development of mucosal vaccines

It is well-established that most pathogens that cause infectious diseases enter the host via mucosal membranes of the respiratory, digestive and genital tracts. Some parenterally administered vaccines induce protection against mucosal pathogens. However, there is increasing evidence that mucosal protection is better afforded by mucosal vaccination, particularly for the induction of memory responses. Mucosal vaccines must pass several difficult hurdles before entering the host and inducing an effective and protective immune response. This review deals with present and past efforts in devising effective mucosal vaccines using delivery systems and immunopotentiating adjuvants for protein-based vaccines. The paper will conclude with the authors' opinion on how the field will or should progress in the future and what will be the required components of ideal future mucosal vaccines that can induce immunological memory.

TLR9 in health and disease

Toll-like receptor 9 (TLR9) is specialized for the recognition of pathogenic nucleic acids. TLR9 is expressed in intracellular compartments where it responds specifically to pathogen DNA. Several factors contribute to the ability of TLR9 to discriminate between self and foreign DNA. Regulatory mechanisms of the innate and adaptive immune system exist that balance the immune responses mediated by TLR9. Short synthetic CpG oligodeoxynucleotides are used to induce controlled and directed TLR9-dependent stimulation and are effective immune modulators in preclinical and clinical studies. This review will summarize the interplay between TLR9-dependent opposing stimulatory and regulatory effects in innate and adaptive immunity.