Antibody responses in volunteers induced by nasal influenza vaccine combined with Escherichia coli heat-labile enterotoxin B subunit containing a trace amount of the holotoxin

Safety, tolerability, and efficacy of intranasally-administered detoxified LTh(αK) in mild-to-moderate COVID-19 patients: A randomized, double-blinded, placebo-controlled phase 2 study

The objective of the study was to assess the safety, tolerability, and potential efficacy of intranasally administered AD17002, a detoxified form of Escherichia coli heat-labile enterotoxin, in treating individuals with mild-to-moderate coronavirus disease of 2019 (COVID-19). In this randomized, double-blinded, and placebo-controlled phase 2a study, a total of 30 adults aged 20-70 years with mild-to-moderate COVID-19 were recruited from three medical centers in Taiwan in 2022-2023. The trial comprised two cohorts, and participants were randomly assigned to receive intranasal administrations of either three doses of AD17002 immunomodulator or a placebo formulation buffer. Outcome analyses were conducted on the intention-to-treat set, and the safety set that included all randomized participants exposed to the AD17002. The proportion of cycle threshold (Ct) ≥30 and time to the recovery of key symptoms were assessed. An exploratory study was conducted to analyze the integrity of the viral genome after treatment. Administering 20 μg of AD17002 three times, either at 1-week or 1-day intervals, proved to be safe and well tolerated in subjects with mild-to-moderate COVID-19. AD17002 demonstrated a rapid and positive outcome in reducing the viral load in patients receiving the treatment. Impact of AD17002 treatment was further supported by the analysis of viral genome integrity following the treatment. The enhancement in clinical recovery by AD17002 within 5 days after symptom onset was observed but did not achieve statistical significance. According to the results, intranasal administration of AD17002 was safe, well-tolerated, and potentially effective for treating mild-to-moderate COVID-19.

Intranasal booster with SARS-CoV-2 RBD protein fused to E. coli enterotoxin a subunit after primary mRNA vaccination in mice

The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 2019 led to the coronavirus infection diseases 2019 (COVID-19) pandemic, significantly impacting global public health and the economy. Numerous COVID-19 vaccines based on the receptor binding domain (RBD) of SARS-CoV-2 spike protein have been developed, utilizing various protein expression platforms and adjuvant systems. In a previous study, we reported using the direct fusion of the A subunit of type IIb E. coli heat-labile enterotoxin with the SARS-CoV-2 RBD protein (RBD-LTA) as an intranasal vaccine candidate (Hsieh et al., 2023). In this study, we investigated the effects of an intranasal booster of RBD-LTA/RBD mixture proteins after one or two doses of intramuscular bivalent BA.4/5 mRNA vaccination over 17 and 35 weeks. Our results indicate that the intranasal RBD-LTA/RBD mixture proteins booster maintains high levels of anti-RBD IgG and neutralizing antibodies, comparable to those elicited by a two-dose mRNA vaccination regimen. An additional RBD-LTA/RBD mixture proteins booster significantly increased antibody titers, demonstrating the potential of this approach for long-term immunity against SARS-CoV-2. Our findings suggest that combining primary mRNA vaccination with an intranasal RBD-LTA/RBD mixture proteins booster can effectively sustain antibody levels over extended periods, providing a promising strategy for long-term protection against SARS-CoV-2 and its variants.

Recombinant adenovirus carrying a core neutralizing epitope of porcine epidemic diarrhea virus and heat-labile enterotoxin B of Escherichia coli as a mucosal vaccine

Porcine epidemic diarrhea virus (PEDV) targets the intestinal mucosa in pigs. To protect against PEDV invasion, a mucosal vaccine is utilized effectively. In this study, we generated a recombinant adenovirus vaccine encoding the heat-labile enterotoxin B (LTB) and the core neutralizing epitope (COE) of PEDV (rAd-LTB-COE). The fusion protein LTB-COE was successfully expressed by the recombinant adenovirus in HEK293 cells, and the immunogenicity of the vaccine candidate was assessed in BALB/c mice and piglets. Three intramuscular or oral vaccinations with rAd-LTB-COE at two-week intervals induced robust humoral and mucosal immune responses. Moreover, a cell-mediated immune response was promoted in immunized mice, and the neutralizing antibody inhibited both the vaccine strain and the emerging PEDV isolate. Immunization experiments in piglets revealed that rAd-LTB-COE was immunogenic and induced good immune responses in piglets. Further studies are required to evaluate the efficacy of rAd-LTB-COE against a highly virulent PEDV challenge.

A double-blind, randomized controlled trial to evaluate the safety and immunogenicity of an intranasally administered trivalent inactivated influenza vaccine with the adjuvant LTh(αK): A phase II study

BACKGROUND

Intranasal influenza vaccines may provide protective efficacy by inducing both systemic antibodies and local secretory IgA. Live attenuated intranasal vaccines are not feasible for high-risk groups. A previously constructed inactivated vaccine with adjuvant revealed an association with neurological events in some studies. In this phase II trial, we aimed to evaluate the safety and immunogenicity of an intranasal influenza vaccine with a novel adjuvant, heat-labile enterotoxin (LT)-derived from E. coli (LTh(αK)).

METHODS

This study is a multicenter, randomized controlled, double-blind, phase II trial of an intranasal influenza vaccine containing 22.5 μg of the hemagglutinin (HA) antigen of three influenza strains in combination with 2 different LTh(αK) adjuvant doses (group 1: 30 μg; group 2: 45 μg) in subjects 20-70 years old. The control vaccine was 22.5 μg of influenza HA antigen alone (group 3). The vaccine was intranasally administered on days 1 and 8. Serum anti-HA antibody and nasal secretory IgA were measured, and adverse events (AEs) were recorded prevaccination and 29 (±2) days postvaccination.

RESULTS

Of 354 participants randomized in the study, 340 received two vaccine doses. AEs were mostly mild, and there was no discontinuation related to the vaccine. Only a higher frequency of diarrhea after the first dose was noted among group 2 (11.5%) than among group 3 (2.8%), and there was no significant difference after the second dose. The three groups had comparable serum anti-HA antibody immunogenicity. However, the adjuvanted vaccines induced greater mucosal IgA antibody production than the control vaccine. In a subgroup analysis, group 1 participants achieved adequate immunogenicity among both 20- to 60- and 61- to 70-year-old participants.

CONCLUSION

The intranasal influenza vaccine adjuvanted with LTh(αK) is generally safe and could provide systemic and local antibody responses. Adjuvanted vaccines were significantly more immunogenic than the nonadjuvanted control vaccine in mucosal immunity. ClinicalTrials.gov Identifier: NCT03784885.

Recent Approaches for Solid Dose Vaccine Delivery

Recent studies on vaccine delivery systems are exploring the possibility of replacing liquid vaccines with solid dose vaccines due to the many advantages that solid dose vaccines can offer. These include the prospect of a needle-free vaccine delivery system leading to better patient compliance, cold chain storage, less-trained vaccinators and fewer chances for needle stick injury hazards. Some studies also indicate that vaccines in a solid dosage form can result in a higher level of immunogenicity compared to the liquid form, thus providing a dose-sparing effect. This review outlines the different approaches in solid vaccine delivery using various routes of administration including, oral, pulmonary, intranasal, buccal, sublingual, and transdermal routes. The various techniques and their current advancements will provide a knowledge base for future work to be carried out in this arena.

Intranasal immunization with aluminum salt-adjuvanted dry powder vaccine

Intranasal vaccination using dry powder vaccine formulation represents an attractive, non-invasive vaccination modality with better storage stability and added protection at the mucosal surfaces. Herein we report that it is feasible to induce specific mucosal and systemic antibody responses by intranasal immunization with a dry powder vaccine adjuvanted with an insoluble aluminum salt. The dry powder vaccine was prepared by thin-film freeze-drying of a model antigen, ovalbumin, adsorbed on aluminum (oxy)hydroxide as an adjuvant. Special emphasis was placed on the characterization of the dry powder vaccine formulation that can be realistically used in humans by a nasal dry powder delivery device. The vaccine powder was found to have "passable" to "good" flow properties, and the vaccine was uniformly distributed in the dry powder. An in vitro nasal deposition study using nasal casts of adult humans showed that around 90% of the powder was deposited in the nasal cavity. Intranasal immunization of rats with the dry powder vaccine elicited a specific serum antibody response as well as specific IgA responses in the nose and lung secretions of the rats. This study demonstrates the generation of systemic and mucosal immune responses by intranasal immunization using a dry powder vaccine adjuvanted with an aluminum salt.

Intranasal Inactivated Influenza Vaccines: a Reasonable Approach to Improve the Efficacy of Influenza Vaccine?

Influenza is a contagious, acute respiratory disease caused by the influenza virus. The mucosal lining in the host respiratory tract is not only the site of virus infection, but also the site of defense; it is at this site that the host immune response targets the virus and protects against reinfection. One of the most effective methods to prevent influenza is to induce specific antibody (Ab) responses in the respiratory tract by vaccination. Two types of influenza vaccines, intranasal live attenuated influenza virus (LAIV) vaccines and parenteral (injectable) inactivated vaccines, are currently used worldwide. These vaccines are approved by the European Medicines Agency (EMA) and the US Food and Drug Administration. Live attenuated vaccines induce both secretory IgA (S-IgA) and serum IgG antibodies (Abs), whereas parenteral vaccines induce only serum IgG Abs. However, intranasal administration of inactivated vaccines together with an appropriate adjuvant induces both S-IgA and IgG Abs. Several preclinical studies on adjuvant-combined, nasal-inactivated vaccines revealed that nasal S-IgA Abs, a major immune component in the upper respiratory tract, reacted with homologous virus hemagglutinin (HA) and were highly cross-reactive with viral HA variants, resulting in protection and cross-protection against infection by both homologous and variant viruses, respectively. Serum-derived IgG Abs, which are present mainly in the lower respiratory tract, are less cross-reactive and cross-protective. In addition, our own clinical trials have shown that nasal-inactivated whole virus vaccines, including a built-in adjuvant (single-stranded RNA), induced serum hemagglutination inhibition (HI) Ab titers that fulfilled the EMA criteria for vaccine efficacy. The nasal-inactivated whole virus vaccines also induced high levels of nasal HI and neutralizing Ab titers, although we have not yet evaluated the nasal HI titers due to the lack of official criteria to establish efficacy based on this parameter. Data suggest that adjuvant-combined nasal-inactivated vaccines have advantages over the current injectable vaccine because the former induce both S-IgA and serum IgG Abs. In addition, nasal-inactivated vaccines seem to be superior to the LAIV vaccines, because non-infectious preparations could be used in high-risk groups. Thus, the development of intranasal inactivated vaccines is recommended, because such vaccines are expected to improve the efficacy of influenza vaccines.

Cross-reactivity of immunoglobulin A secreted on the nasal mucosa in mice nasally inoculated with inactivated H1N1 influenza A viruses in the presence of D-octaarginine-linked polymers

We evaluated cross-reactivity of immunoglobulin A (IgA) secreted on the nasal mucosa in mice that were nasally inoculated 4 times with a mixture of inactivated H1N1 influenza A viruses and poly(N-vinylacetamide-co-acrylic acid) (PNVA-co-AA) bearing d-octaarginine at 7-day intervals. Three viral strains (A/Puerto Rico/8/34, A/New Caledonia/20/99 IVR116, and A/Solomon Islands/03/2006) and D-octaarginine-linked polymers with different molecular weights were used as antigens and their carriers, respectively. Secretion of intranasal IgA was barely observed when the inactivated virus alone was administered. The polymer induced the production of intranasal IgA specific to the inoculated viruses, irrespective of the viral strain and molecular weight of the polymer. The respective antibodies cross-reacted to recombinant hemagglutinin proteins of not only the viral strain used for immunization but also other H1N1 strains, including A/Puerto Rico/8/34 strain whose hemagglutinin proteins are diverse from those of other strains. Mice with high reactivity of IgA to the inoculated viruses tended to acquire clear cross-reactivity to other viral strains. Notably, IgA induced by inactivated H1N1 A/New Caledonia/20/99 IVR116 strain with the strongest immunogenicity between 3 antigens in the presence of the polymer cross-reacted to recombinant hemagglutinin proteins of the A/Brisbane/10/2007 and A/Viet Nam/1194/2004 strains, which are categorized into H3N2 and H5N1, respectively. Our polymer is a potential candidate for an efficient antigen carrier that induces mucosal IgA having cross-reactivity to antigenically drifted variants, irrespective of the subtype of viral strains.

Induction of protective immunity against H1N1 influenza A(H1N1)pdm09 with spray-dried and electron-beam sterilised vaccines in non-human primates

Currently, the need for cooled storage and the impossibility of terminal sterilisation are major drawbacks in vaccine manufacturing and distribution. To overcome current restrictions a preclinical safety and efficacy study was conducted to evaluate new influenza A vaccine formulations regarding thermal resistance, resistance against irradiation-mediated damage and storage stability. We evaluated the efficacy of novel antigen stabilizing and protecting solutions (SPS) to protect influenza A(H1N1)pdm09 split virus antigen under experimental conditions in vitro and in vivo. Original or SPS re-buffered vaccine (Pandemrix) was spray-dried and terminally sterilised by irradiation with 25 kGy (e-beam). Antigen integrity was monitored by SDS-PAGE, dynamic light scattering, size exclusion chromatography and functional haemagglutination assays. In vitro screening experiments revealed a number of highly stable compositions containing glycyrrhizinic acid (GA) and/or chitosan. The most stable composition was selected for storage tests and in vivo assessment of seroconversion in non-human primates (Macaca fascicularis) using a prime-boost strategy. Redispersed formulations with original adjuvant were administered intramuscularly. Storage data revealed high stability of protected vaccines at 4°C and 25°C, 60% relative humidity, for at least three months. Animals receiving original Pandemrix exhibited expected levels of seroconversion after 21 days (prime) and 48 days (boost) as assessed by haemagglutination inhibition and microneutralisation assays. Animals vaccinated with spray-dried and irradiated Pandemrix failed to exhibit seroconversion after 21 days whereas spray-dried and irradiated, SPS-protected vaccines elicited similar seroconversion levels to those vaccinated with original Pandemrix. Boost immunisation with SPS-protected vaccine resulted in a strong increase in seroconversion but had only minor effects in animals treated with non SPS-protected vaccine. In conclusion, utilising the SPS formulation technology, spray-drying and terminal sterilisation of influenza A(H1N1)pdm09 split virus vaccine is feasible. Findings indicate the potential utility of such formulated vaccines e.g. for needle-free vaccination routes and delivery to countries with uncertain cold chain facilities.

Intranasal vaccination with an inactivated whole influenza virus vaccine induces strong antibody responses in serum and nasal mucus of healthy adults

Haemagglutination inhibition (HI) and neutralization (NT) titers as well as haemagglutinin (HA) specific antibody responses were examined in 50 healthy adults aged between 22 and 69 y old after two intranasal administrations of an inactivated whole virus vaccine derived from A/Victoria/210/2009 virus (45 μg HA per dose) at 3 week intervals. Serum HI titers after two-doses of the nasal vaccine showed >2.5-fold rise in the ratio of geometric mean titer upon vaccination, >40% of subjects with a ≥4-fold increase in titer and >70% of subjects with a titer of ≥1:40, all parameters associated with an effective outcome of vaccination in the criteria defined by the European Medicines Agency. Serum neutralizing antibody responses correlated with HI antibody responses, although NT titers were about 2-fold higher than HI titers. These high levels of serum responses were accompanied by high levels of HI and neutralizing antibody responses in nasal mucus as measured in concentrated nasal wash samples that were about 10 times diluted compared with natural nasal mucus. Serum and nasal HI and neutralizing antibody responses consisted of HA-specific IgG and IgA antibody responses, with IgG and IgA antibodies being dominant in serum and nasal responses, respectively.

Intranasal administration of influenza vaccines: current status

AbstractThis review article focuses on intranasal immunisation against influenza,although it also encompasses antigen uptake and processing in the nasopharyngealpassages, host defence from influenza and current influenza vaccination practices.Improvement of current vaccination strategies is clearly required; current proceduresinvolve repeated annual injections that sometimes fail to protect the recipient. It isenvisaged that nonpercutaneous immunisation would be more attractive to potentialvaccinees, thus improving uptake and coverage. As well as satisfying noninvasivecriteria, intranasal influenza immunisation has a number of perceived immunologicaladvantages over current procedures. Perhaps one of the greatest attributes of thisapproach is its potential to evoke the secretion of haemagglutinin-specific IgAantibodies in the upper respiratory tract, the main site of viral infection. Inactivated influenza vaccines have the advantage that they have a long historyof good tolerability as injected immunogens, and in this respect are possibly morelikely to be licensed than attenuated viruses. Inert influenza vaccines are poormucosal immunogens, requiring several administrations, or prior immunologicalpriming, in order to engender significant antibody responses. The use of vaccinedelivery systems or mucosal adjuvants serves to appreciably improve theimmunogenicity of mucosally applied inactivated influenza vaccines. As is the casewhen they are introduced parenterally, inactivated influenza vaccines are relativelypoor stimulators of virus-specific cytotoxic T lymphocyte activity following nasalinoculation. Live attenuated intranasal influenza vaccines are at a far moreadvanced stage of clinical readiness (phase III versus phase I). With the use of liveattenuated vaccines, it is possible to stimulate mucosal and cell-mediatedimmunological responses of a similar kind to those elicited by natural influenzainfection. In children, recombinant live attenuated cold-adapted influenza viruses arewell tolerated. Moreover, cold-adapted influenza viruses usually stimulate protectiveimmunity following only a single nasal inoculation. Safety of recombinant liveattenuated cold-adapted influenza viruses has also been demonstrated in high riskindividuals with cystic fibrosis, asthma, cardiovascular disease and diabetes mellitus.They are not suitable for immunising immunocompromised patients, however, andare poorly efficacious in individuals with pre-existing immunity to strains closelyantigenically matched with the recombinant virus. According to the reviewedliterature, it is apparent that intranasal administration of vaccine as an aerosol issuperior to administration as nose drops. The information reviewed in this papersuggests that nasally administered influenza vaccines could make a substantialimpact on the human and economic cost of influenza.

Cell-penetrating peptide-linked polymers as carriers for mucosal vaccine delivery

We evaluated the potential of poly(N-vinylacetamide-co-acrylic acid) modified with d-octaarginine, which is a typical cell-penetrating peptide, as a carrier for mucosal vaccine delivery. Mice were nasally inoculated four times every seventh day with PBS containing ovalbumin with or without the d-octaarginine-linked polymer. The polymer enhanced the production of ovalbumin-specific immunoglobulin G (IgG) and secreted immunoglobulin A (IgA) in the serum and the nasal cavity, respectively. Ovalbumin internalized into nasal epithelial cells appeared to stimulate IgA production. Ovalbumin transferred to systemic circulation possibly enhanced IgG production. An equivalent dose of the cholera toxin B subunit (CTB), which was used as a positive control, was superior to the polymer in enhancing antibody production; however, dose escalation of the polymer overcame this disadvantage. A similar immunization profile was also observed when ovalbumin was replaced with influenza virus HA vaccines. The polymer induced a vaccine-specific immune response identical to that induced by CTB, irrespective of the antibody type, when its dose was 10 times that of CTB. Our cell-penetrating peptide-linked polymer is a potential candidate for antigen carriers that induce humoral immunity on the mucosal surface and in systemic circulation when nasally coadministered with antigens.

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.

Characterization of immune responses elicited in mice by intranasal co-immunization with HIV-1 Tat, gp140 DeltaV2Env and/or SIV Gag proteins and the nontoxicogenic heat-labile Escherichia coli enterotoxin

The development of a vaccine against HIV/AIDS capable of inducing broad humoral and cellular responses at both systemic and mucosal sites, able to stop or reduce viral infection at the portal of entry, represents the only realistic way to control the infection caused by HIV world-wide. The promising results obtained with the HIV-1 Tat-based vaccines in preclinical and clinical settings, the evidence that a broad immunity against HIV correlates with reduced viral load or virus control, as well as the availability of novel gp140 V2-loop deleted HIV-1 Env (DeltaV2Env) immunogens capable of inducing cross-reactive neutralizing antibodies, have led to the design of new vaccine strategies based on the combination of non-structural and structural proteins. In this study, we demonstrate that immunization with a biologically active HIV-1 Tat protein in combination with the oligomeric HIV-1 gp140 DeltaV2Env and/or SIV Gag proteins, delivered intranasally with the detoxified LTK63 mucosal adjuvant, whose safety has been recently shown in humans, elicits long-lasting local and systemic antibody and cellular immune responses against the co-administered antigens in a fashion similar to immune responses induced by vaccination with Tat, DeltaV2Env and Gag proteins alone. The results indicate lack of antigen interference implying that HIV-1 Tat is an optimal co-antigen for combined vaccine strategies employing DeltaV2Env and/or Gag proteins.

Mucosal vaccine development for botulinum intoxication

Botulism has classically been considered to be a food- and water-borne disease. However, it was recently classified by the US National Institute of Allergy and Infectious Diseases (National Institute of Health) and the US Centers for Disease Control and Prevention as a Category A agent. Thus, the botulinum exotoxin, a neurotoxin, could be easily disseminated by bioterrorists through the air-borne route with a high morbidity and mortality rate. In this regard, a high priority should be given to the development of a safe and effective mucosal vaccine to protect against botulinum neurotoxins (BoNTs) since it is well known that the mucosal immune system is the first line of defense against major pathogens. Further, mucosal immunization has been shown to induce both mucosal and systemic immunity to pathogens. By contrast, the current injection-type vaccine only provides protective immunity in the systemic compartment. Clearly, the development of a safe and effective mucosal vaccine against this toxin should be a high priority. In this regard, it has been shown that both nasal and oral immunization approaches have been taken in order to protect from BoNT intoxication. In this article, we will discuss the importance of the development of a mucosal vaccine against botulinum and introduce current aspects of BoNT mucosal vaccines, which show that they effectively prevent mucosal BoNT intoxication.

Phase I evaluation of intranasal trivalent inactivated influenza vaccine with nontoxigenic Escherichia coli enterotoxin and novel biovector as mucosal adjuvants, using adult volunteers

Trivalent influenza virus A/Duck/Singapore (H5N3), A/Panama (H3N2), and B/Guandong vaccine preparations were used in a randomized, controlled, dose-ranging phase I study. The vaccines were prepared from highly purified hemagglutinin and neuraminidase from influenza viruses propagated in embryonated chicken eggs and inactivated with formaldehyde. We assigned 100 participants to six vaccine groups, as follows. Three intranasally vaccinated groups received 7.5-microg doses of hemagglutinin from each virus strain with either 3, 10, or 30 microg of heat-labile Escherichia coli enterotoxin (LTK63) and 990 microg of a supramolecular biovector; one intranasally vaccinated group was given 7.5-microg doses of hemagglutinin with 30 microg of LTK63 without the biovector; and another intranasally vaccinated group received saline solution as a placebo. The final group received an intramuscular vaccine containing 15 microg hemagglutinin from each strain with MF59 adjuvant. The immunogenicity of two intranasal doses, delivered by syringe as drops into both nostrils with an interval of 1 week between, was compared with that of two inoculations by intramuscular delivery 3 weeks apart. The intramuscular and intranasal vaccine formulations were both immunogenic but stimulated different limbs of the immune system. The largest increase in circulating antibodies occurred in response to intramuscular vaccination; the largest mucosal immunoglobulin A (IgA) response occurred in response to mucosal vaccination. Current licensing criteria for influenza vaccines in the European Union were satisfied by serum hemagglutination inhibition responses to A/Panama and B/Guandong hemagglutinins given with MF59 adjuvant by injection and to B/Guandong hemagglutinin given intranasally with the highest dose of LTK63 and the biovector. Geometric mean serum antibody titers by hemagglutination inhibition and microneutralization were significantly higher for each virus strain at 3 and 6 weeks in recipients of the intramuscular vaccine than in recipients of the intranasal vaccine. The immunogenicity of the intranasally delivered experimental vaccine varied by influenza virus strain. Mucosal IgA responses to A/Duck/Singapore (H5N3), A/Panama (H3N2), and B/Guandong were highest in participants given 30 microg LTK63 with the biovector, occurring in 7/15 (47%; P=0.0103), 8/15 (53%; P=0.0362), and 14/15 (93%; P=0.0033) participants, respectively, compared to the placebo group. The addition of the biovector to the vaccine given with 30 microg LTK63 enhanced mucosal IgA responses to A/Duck/Singapore (H5N3) (P=0.0491) and B/Guandong (P=0.0028) but not to A/Panama (H3N2). All vaccines were well tolerated.

Enterotoxin-based mucosal adjuvants alter antigen trafficking and induce inflammatory responses in the nasal tract

The safety of nasal vaccines containing enterotoxin-based mucosal adjuvants has not been studied in detail. Previous studies have indicated that native cholera toxin (nCT) can alter antigen trafficking when applied nasally. In this study, we determined the enterotoxin-based variables that alter antigen trafficking. To measure the influence of enterotoxin-based mucosal adjuvants on antigen trafficking in the nasal tract, native and mutant enterotoxins were coadministered with radiolabeled tetanus toxoid (TT). The nCT and heat-labile enterotoxin type 1 (LTh-1) redirected TT into the olfactory neuroepithelium (ON/E). Antigen redirection occurred mainly across the nasal epithelium without subsequent transport along olfactory neurons into the olfactory bulbs (OB). Thus, no significant accumulation of the vaccine antigen TT was observed in the OB when coadministered with nCT. In contrast, neither mutant CT nor mutant LTh-1, which lack ADP-ribosyltransferase activity, redirected TT antigen into the ON/E. Thus, ADP-ribosyltransferase activity was essential for antigen trafficking across the olfactory epithelium. Accumulation of TT in the ON/E was also due to B-subunit binding to GM1 gangliosides, as was demonstrated (i) by redirection of TT by LTh-1 in a dose-dependent manner, (ii) by ganglioside inhibition of the antigen redirection by LTh-1 and nCT, and (iii) by the use of LT-IIb, a toxin that binds to gangliosides other than GM1. Redirection of TT into the ON/E coincided with elevated production of interleukin 6 (IL-6) but not IL-1beta or tumor necrosis factor alpha in the nasal mucosa. Thus, redirection of TT is dependent on ADP-ribosyltransferase activity and GM1 binding and is associated with production of the inflammatory cytokine IL-6.

Effective nasal influenza vaccine delivery using chitosan

Nasal influenza vaccination may prove to be a good alternative to parenteral injection because of the enhancement of the mucosal immune response and the ease of vaccine administration. This study investigated the use of chitosan, a bioadhesive polymer, as a nasal delivery system with inactivated, subunit influenza vaccine. Subjects received nasally 15 or 7.5 microg of the standard inactivated trivalent influenza vaccine with chitosan or 15 microg of the same vaccine intramuscularly. Serum haemagglutination inhibition (HI) titres for all three vaccine components were measured prior to, and at time points up to 14 weeks after dosing. Serum HI titres following intranasal vaccination with the nasal chitosan-influenza vaccine met the criteria set by the Committee for Proprietary Medicinal Products in terms of seroprotection rate, seroconversion rate and mean fold increase of HI titre for at least one of the three antigens in the vaccination schedules used. These data show that nasal immunisation with chitosan plus trivalent inactivated influenza is a potentially effective, easily-administered form of vaccination.

Mucosal adjuvants

Induction of immune responses following oral immunization is frequently dependent upon the co-administration of appropriate adjuvants that can initiate and support the transition from innate to adaptive immunity. The three bacterial products with the greatest potential to function as mucosal adjuvants are the ADP-ribosylating enterotoxins (cholera toxin and the heat-labile enterotoxin of Escherichia coli), synthetic oligodeoxynucleotides containing unmethylated CpG dinucleotides (CpG ODN), and monophosphoryl lipid A (MPL). The mechanism of adjuvanticity of the ADP-ribosylating enterotoxins is the subject of considerable debate. Our own view is that adjuvanticity is an outcome and not an event. It is likely that these molecules exert their adjuvant function by interacting with a variety of cell types, including epithelial cells, dendritic cells, macrophages, and possibly B- and T-lymphocytes. The adjuvant activities of CpG and MPL are due to several different effects they have on innate and adaptive immune responses and both MPL and CpG act through MyD88-dependent and -independent pathways. This presentation will summarize the probable mechanisms of action of these diverse mucosal adjuvants and discuss potential synergy between these molecules for use in conjunction with plant-derived vaccines.

A novel dry powder influenza vaccine and intranasal delivery technology: induction of systemic and mucosal immune responses in rats

Intranasal (i.n.) vaccination represents an attractive non-invasive alternative to needle-based injection and provides superior protection at mucosal surfaces. However, new formulations are needed to improve efficacy and reduce the refrigerated storage and distribution requirements associated with standard liquid vaccines. Here, we describe a powder formulation of whole inactivated influenza virus and a novel i.n. delivery platform. The powder-formulated vaccine elicited a significant serum antibody response in rats that was at least as strong as that provided by the liquid vaccine administered i.n. or via intramuscular (i.m.) injection. Significant nasal IgA responses were also observed solely after i.n. delivery. This study demonstrates for the first time the generation of potent nasal mucosal and systemic immune responses using an i.n. delivered influenza vaccine powder and suggests an alternative approach to vaccination against influenza and other infectious diseases.

Characterization of protective immune responses induced by nasal influenza vaccine containing mutant cholera toxin as a safe adjuvant (CT112K)

Immune responses induced by a nasal influenza vaccine with a mutant cholera toxin (CT112K), known to be a safe adjuvant, were characterized in BALB/c mice to confirm the most suitable regimen of this vaccine for humans. Mice received a primary intranasal administration of the adjuvant (0.1 micro g)-combined PR8 vaccine (0.1 micro g) and a secondary administration of the PR8 vaccine alone (0.1 micro g) 4 weeks later. Two weeks after the secondary immunization, the mice were infected with a nonlethal or a lethal dose of PR8 viruses. Nasal and lung wash virus titers 1 or 3 days after infection indicated that complete protection could be provided by secondary immune responses, which had an immediate effect of preventing infection 2 weeks after the secondary immunization. In this two-dose regimen, high levels of secondary IgA, IgG and IgM antibody-forming cell (AFC) responses were induced in the nasal-associated lymphoid tissue and the spleen. In parallel with the AFC responses, high levels of nasal wash anti-PR8 HA IgA, and lung and serum IgG antibody (Ab) responses were induced 2 weeks after the secondary immunization. The two-dose regimen also induced accelerated delayed-type hypersensitivity responses, which exhibited almost the same peak height as that in the case of the primary response. In addition, the two-dose regimen induced a low memory cell activity of cytotoxic T lymphocytes, detected by in vitro culture of spleen cells. Thus, the immediate effect of preventing infection was mainly provided by the secondary Ab responses. Moreover, the levels of nasal wash IgA Abs correlated well with cross-protection against infection with variant viruses in the upper respiratory tract (RT). These results suggest that the major protective factors among Ab and T cell-mediated immune responses, which are induced by the two-dose regimen using CT112K-combined vaccines, are the cross-reactive IgA Abs in the upper RT and the less cross-reactive IgG Abs in the lower RT, and that the two-dose regimen is a suitable vaccination condition for humans.

Intranasal immunotherapy for the treatment of Alzheimer's disease: Escherichia coli LT and LT(R192G) as mucosal adjuvants

Alzheimer's disease (AD) is the most common form of dementia worldwide, yet there is currently no effective treatment or cure. Extracellular deposition of amyloid-beta protein (Abeta) in brain is a key neuropathological characteristic of AD. In 1999, Schenk et al. first reported that an injected Abeta vaccine given to PDAPP mice, an AD mouse model displaying Abeta deposition in brain, led to the lowering of Abeta levels in brain. In 2000, we demonstrated that intranasal (i.n.) immunization with human synthetic Abeta1-40 peptide for 7 months led to a 50-60% reduction in cerebral Abeta burden in PDAPP mice; serum Abeta antibody titers were low (approximately 26 microg/ml). More recently, we have optimized our i.n. Abeta immunization protocol in wild-type (WT) mice. When low doses Escherichia coli heat-labile enterotoxin (LT) were given as a mucosal adjuvant with Abeta i.n., there was a dramatic 12-fold increase in Abeta antibody titers in WT B6D2F1 mice treated two times per week for 8 weeks compared to those of mice receiving i.n. Abeta without adjuvant. A non-toxic form of LT, designated LT(R192G), showed even better adjuvanticity; anti-Abeta antibody titers were 16-fold higher than those seen in mice given i.n. Abeta without adjuvant. In both cases, the serum Abeta antibodies recognized epitopes within Abeta1-15 and were of the immunoglobulin (Ig) isotypes IgG2b, IgG1, IgG2a and low levels of IgA. This new and improved Abeta vaccine protocol is now being tested in AD mouse models with the expectation that higher Abeta antibody titers may be more effective in reducing cerebral Abeta levels.

Intranasal immunization against influenza

Nasalflu is a novel influenza subunit vaccine, which is administered by the intranasal route using a spray device. Nasalflu is based on the virosomal concept which is registered in the EU as Epaxal Berna, a vaccine against Hepatitis A, and Inflexal Berna V, a subunit influenza vaccine. The virosome is a carrier system which delivers antigens to cells and is able to induce both B- and T-cell immunity. When virosomal vaccines are given parenterally, an immune response is elicited fast and sufficiently.

Can nonliving nasal vaccines be made to work?

Nasal vaccines consisting of nonliving particulate formulations can induce immune responses of importance for protection against infection. The most promising results have been obtained with vaccines against influenza, pertussis and group B meningococcal disease. So far, however, the results do not challenge the standing of corresponding injectable vaccines, although results of experiments in animals do indicate that effective nonliving nasal vaccines may soon be developed. This will depend on refined immunization schedules to benefit from immunological memory and on formulations to make the vaccines more accessible to the immune system by way of mucosal adjuvants or immune modulators.

Cold-adapted live influenza vaccine versus inactivated vaccine: systemic vaccine reactions, local and systemic antibody response, and vaccine efficacy. A meta-analysis

Since the 1940s, influenza vaccines are inactivated and purified virus or virus subunit preparations (IIV) administered by the intramuscular route. Since decades, attempts have been made to construct, as an alternative, attenuated live influenza vaccines (LIV) for intranasal administration. Presently, the most successful LIV is derived from the cold-adapted master strains A/Ann Arbor/6/60 (H2N2) and B/Ann Arbor/1/66 (AA-LIV, for Ann-Arbor-derived live influenza vaccine). It has been claimed that AA-LIV is more efficacious than IIV. In order to assess differences between the two vaccines with respect to systemic reactogenicity, antibody response, and efficacy, we performed a meta-analysis on eighteen randomised comparative clinical trials involving a total of 5000 vaccinees of all ages. Pooled odds ratios (AA-LIV versus IIV) were calculated according to the random effects model. The two vaccines were associated with similarly low frequencies of systemic vaccine reactions (pooled odds ratio: 0.96, 95% confidence interval: 0.74-1.24). AA-LIV induced significantly lower levels of serum haemagglutination inhibiting antibody and significantly greater levels of local IgA antibody (influenza virus-specific respiratory IgA assayed by ELISA in nasal wash specimens) than IIV. Yet, although they predominantly stimulate different antibody compartments, the two vaccines were similarly efficacious in preventing culture-positive influenza illness. In all trials assessing clinical efficacy, the odds ratios were not significantly different from one (point of equivalence). The pooled odds ratio for influenza A-H3N2 was 1.50 (95% CI: 0.80-2.82), and for A-H1N1, 1.03 (95% CI: 0.58-1.82). The choice between the two vaccine types should be based on weighing the advantage of the attractive non-invasive mode of administration of AA-LIV, against serious concerns about the biological risks inherent to large-scale use of infectious influenza virus, in particular the hazard of gene reassortment with non-human influenza virus strains.

Mutant Escherichia coli heat-labile enterotoxin [LT(R192G)] enhances protective humoral and cellular immune responses to orally administered inactivated influenza vaccine

Influenza vaccines capable of inducing both systemic and mucosal antibody responses are highly desirable. Optimal induction of mucosal IgA is accomplished by mucosal delivery of vaccine. Mucosal adjuvants may improve the immunogenicity and efficacy of vaccines delivered by this route. Here, we compare the adjuvant activities of a mutant of heat-labile enterotoxin from Escherichia coli [LT(R192G)] with those of the wildtype LT (wtLT) for oral vaccination with inactivated influenza vaccine in BALB/c mice. Compared with administration of oral influenza vaccine alone, co-administration of vaccine with LT(R192G) provided enhanced protection from infection in the upper and lower respiratory tract equivalent to and at similar doses as that obtained with wtLT. Likewise, LT(R192G) augmented virus-specific IgG and IgA responses in serum, lung and nasal washes and the numbers of virus-specific antibody-forming cells in spleen, lung and Peyer's patches in a manner comparable to wtLT. Virus-specific splenic CD4(+) cells from mice administered oral vaccine with either adjuvant produced a mixed Th1- and Th2-type cytokine response pattern. Taken together, these results indicate that LT(R192G), like wtLT, is a potent adjuvant for oral vaccination of mice with influenza vaccine.

An open-label comparison of the immunogenicity and tolerability of intranasal and intramuscular formulations of virosomal influenza vaccine in healthy adults

BACKGROUND

Many intramuscular inactivated influenza vaccines achieve suboptimal results in the prevention of respiratory disease and influenza complications. This has led to the current interest in developing effective oral or intranasal preparations.

OBJECTIVE

This study compared the immunogenicity and tolerability of intranasal and intramuscular formulations of virosomal subunit influenza vaccine in healthy adults. It also assessed the immunogenicity and tolerability of 3 different production lots of the intranasal vaccine containing Escherichia coli heat-labile toxin adjuvant.

METHODS

This was a multicenter, Phase I, randomized, open-label pilot study in which the primary end point was immunogenicity (hemagglutination-inhibition [HI] antibody assay on days 1 and 29). The secondary end point was the frequency of adverse events (AEs). Subjects were assigned to 4 vaccination groups: groups AI, AII, and AIII received intranasal influenza vaccine from batches that differed in the hemagglutinin and neuraminidase strains used, and group B received intramuscular virosomal subunit vaccine. Assessments of health status, hematology, biochemistry, body temperature, heart rate, blood pressure, and incidence of AEs were made on days 1, 8, and 29, and serology was assessed on days 1 and 29.

RESULTS

The study enrolled 88 subjects. All 3 production lots of intranasal vaccine induced an immune response to most of the viral strains administered (A/Singapore, A/Texas, A/Wuhan, B/Beijing), with no notable immunogenic differences between lots. After intranasal vaccination, geometric mean titers (GMT) increased 2.7-fold against A/Singapore (group AI); 1.8- and 3.1-fold against A/Texas (groups AII and AIII, respectively); 1.9- to 2.4-fold against A/Wuhan; and 1.5- to 1.7-fold against B/Beijing. After intramuscular vaccination. GMT increased 11.3-, 6.3-, and 2.7-fold against A/Texas, A/Wuhan, and B/Beijing, respectively. Seroprotection (HI antibody titers > or = 1:40 in > 70% of those vaccinated) was achieved against all strains in the group that received intramuscular vaccination, against A/Wuhan in all groups that received intranasal vaccination, and against A/Texas in group AII. Both vaccine formulations were well tolerated. Intranasal vaccination was associated with a low incidence ( < 20%) of nasal AEs.

CONCLUSIONS

Both the intranasal and intramuscular vaccinations elicited a systemic immune response and were well tolerated. The different batches of intranasal vaccine showed a similar immunogenic profile. Intranasal administration may be preferred to intramuscular administration by some patients.

Review of intranasal influenza vaccine

Influenza viruses cause costly recurrent annual epidemics. Current efforts to control the morbidity and mortality associated with influenza outbreaks are based on the use of annual intramuscularly administered inactivated vaccines which are not only painful to administer, but are suboptimal in efficacy. This paper reviews the composition, safety analysis, rates of adverse events, immune response and protective efficacy of a new inactivated intranasal influenza vaccine.

Mucosal immunization of mice using CpG DNA and/or mutants of the heat-labile enterotoxin of Escherichia coli as adjuvants

Cholera toxin (CT) and the Escherichia coli heat-labile enterotoxin (LT) are potent mucosal adjuvants in animals associated, at least in part, with their ability to induce cAMP. While toxicity generally precludes their use in humans, a number of different subunit or genetically detoxified mutants of CT and LT have been developed. Another type of adjuvant that has been shown to be effective at mucosal surfaces comprises synthetic oligodeoxynucleotides (ODN) containing immunostimulatory CpG motifs (CpG ODN). We have previously demonstrated a synergy between CpG ODN and native toxins after intranasal (IN) administration to mice, and herein have examined whether this synergy is linked to the cAMP activity. The adjuvanticity of CpG ODN was evaluated with IN and oral delivery of tetanus toxoid or the hepatitis B surface antigen, relative to and in combination with native LT holotoxin (LTh), three active site mutants (LTS61F, LTA69G, LTE112K), a protease site mutant (LTR192G), and the B subunit of LT (LTB). At an equivalent dose, the adjuvants could generally be divided into two groups: one that included CpG ODN, LTh, LTR192G, and LTA69G which acted as strong adjuvants; and the second which comprised LTB, LTS61F, and LTE112K, which produced significantly weaker immune responses. When CpG ODN was co-administered with bacterial toxin-derivatives, in most cases, no synergy between CpG and the LT derivatives was found for strength of the humoral response. Nevertheless, for both routes and antigens, CpG ODN combined with any LT derivative induced a more Type 1-like response than LT derivative alone. These results suggest that while the synergy seen previously with native toxins may have been due in part to inherent cAMP activity, it may have also depended on the particular antigen used and the route of immunization.

Understanding mucosal responsiveness: lessons from enteric bacterial pathogens

Mucosal immune responses must discriminate between commensal flora within the lumen and potential pathogens. These responses are highly adapted to induce protection without excessive inflammation. The balances that regulate mucosal immune and inflammatory responses have to be understood if effective mucosal immunity is to be induced through local immunization. This review will summarize some of the lessons learnt from studies of antigens derived from enteric bacterial pathogens and discuss how the gastrointestinal epithelia can 'fight back' when it encounters pathogens.

Effectiveness and safety of mutant Escherichia coli heat-labile enterotoxin (LT H44A) as an adjuvant for nasal influenza vaccine

The effectiveness and safety of mutant Escherichia coli heat-labile enterotoxin, LT H44A (His to Arg substitution at position 44 from the N-terminus of the A1 fragment of the A subunit) as an adjuvant for nasal influenza vaccine were examined. (1) When 0.2 microg of LT H44A, together with 0.2 microg of influenza A/PR/8/34 virus (PR8, H1N1) vaccine, was administered intranasally into BALB/c mice (twice, 4 weeks apart), anti-PR8 hemagglutinin (HA) IgA and IgG antibody (Ab) responses were induced at levels that were sufficient to provide either complete protection against infection with a small volume of PR8 virus suspension or partial protection against infection with a lethal dose of the suspension. The dose of the mutant LT and vaccine used here (0.2 microg/ 20 g doses mouse) corresponded to the estimated dose per person, i.e. 0.1 mg/10 kg body weight. (2) Using these vaccination conditions, no additional total IgE Ab responses were induced. (3) The mutant was confirmed to be less toxic than the native LT when the toxicity was analyzed either using Y1 adrenal cells in vitro (1/483 EC(50)) or by an ileal loop test. (4) One hundred micrograms of the mutant, administered intranasally or intraperitoneally into guinea-pigs (Heartley strain, 0.3-0.4 kg), caused no body-weight changes 7 days after administration, although 100 microg of the native LT administered intraperitoneally caused death in all guinea-pigs due to diarrhea within 2 days. The intranasal administration of 100 microg of the mutant resulted in almost no pathological changes in the nasal mucosa 3 days after administration. These results suggest that LT H44A, which can be produced in high yields in an E. coli culture (about 5 mg/l), could be used as one of the effective and safe adjuvants for nasal influenza vaccine in humans.

Effects of intranasal administration of cholera toxin (or Escherichia coli heat-labile enterotoxin) B subunits supplemented with a trace amount of the holotoxin on the brain

Effects of intranasal administration of cholera toxin (CT) [or Escherichia coli heat-labile enterotoxin (LT)] B subunits supplemented with a trace amount of the holotoxin, CTB* or LTB*, on the brain were examined in BALB/c mice by comparing with those of the intracerebral injection. Intracerebral injection of CTB* at doses more than 10 microg/mouse caused significant body weight loss and dose-dependent death within 7 days, with localization of conjugates of horseradish peroxidase with CTB (HRP-CTB) in the ventricular system and in the perineural space of olfactory nerves of the nasal mucosa 3 h after injection. Intracerebral injection of CTB* at doses less than 3 microg/mouse (or LTB* at doses less than 22.7 microg/mouse) did not cause any significant body weight loss for 7 days, with localization of HRP-CTB in the brain but not in the nasal mucosa. On the other hand, intranasal administration of 10 microg of CTB* caused localization of HRP-CTB in the nasal mucosa but not in the brain 3 h after administration and caused body weight loss even after 30 administrations. Neither any histological changes of brain tissues nor marked changes in serum biochemical parameters were found in mice after the 30 administrations of CTB* or LTB*. These results suggest that 0.1 microg of CTB* or LTB*, which is known to be close to the minimal effective dose as an adjuvant for nasal influenza vaccine in mice and corresponds to 100 microg per person, can be used as a safe nasal adjuvant without adversely affecting the brain.

Generation of female genital tract antibody responses by local or central (common) mucosal immunization

Genital antibody responses were compared in female mice immunized intravaginally (i.vag.) or intranasally (i.n.) with a bacterial protein antigen (AgI/II of Streptococcus mutans) coupled to the B subunit of cholera toxin. Serum and salivary antibodies were also evaluated as measures of disseminated mucosal and systemic responses. Although i.vag. immunization induced local vaginal immunoglobulin A (IgA) and IgG antibody responses, these were not disseminated to a remote secretion, the saliva, and only modest levels of serum antibodies were generated. In contrast, i.n. immunization was substantially more effective at inducing IgA and IgG antibody responses in the genital tract and in the circulation, as well as at inducing IgA antibodies in the saliva. Moreover, mucosal and systemic antibodies induced by i.n. immunization persisted for at least 12 months. Analysis of the molecular form of genital IgA indicated that the majority of both total IgA and specific IgA antibody was polymeric, and likely derived from the common mucosal immune system.

Safety and immunogenicity of adjuvanted and unadjuvanted subunit influenza vaccines administered intranasally to healthy adults

Antigen-specific mucosal immunity is thought to be important for protection against influenza virus infection. Currently licensed parenteral influenza vaccines stimulate the production of serum antibodies, but are poor inducers of mucosal immunity. The adjuvant MF59 has been shown to enhance the humoral immune response to parenteral influenza vaccine in humans and the mucosal immune response to intranasally-administered influenza vaccine in mice. We conducted an open-label safety study followed by an observer-blind, randomized trial comparing the immune response to intranasally-administered subunit influenza vaccine adjuvanted with MF59, unadjuvanted subunit influenza vaccine, and placebo. Adverse reactions did not occur significantly more frequently in vaccinees than placebo recipients. Of 31 subjects receiving 2 doses of MF59-adjuvanted influenza vaccine, 19 (61%), 8 (26%), and 11 (35%) developed a mucosal IgA response to influenza A/H1N1, A/H3N2, and B, respectively. The percentage of subjects with a serum antibody response was slightly lower. The immune responses to adjuvanted vaccine were not significantly different from those to unadjuvanted vaccine. Both vaccines gave more frequent responses than seen in placebo recipients, indicating the potential of intranasal inactivated vaccines to stimulate local IgA responses.

Immunology of Helicobacter pylori and prospects for vaccine

Since the initial discovery of H. pylori by Marshall and Warren 17 years ago, much progress has been made in treating this infection. However, as we enter the millennium, H. pylori infection continues to be one of the most common infections of mankind. In addition, eradication of H. pylori still requires multiple antimicrobial agents. A better understanding of the host immune response to H. pylori infection should allow investigators to develop immunotherapies to prevent the acquisition of infection and eradicate existing chronic H. pylori infection.

Parenteral adjuvant activities of Escherichia coli heat-labile toxin and its B subunit for immunization of mice against gastric Helicobacter pylori infection

The heat-labile toxin (LT) of Escherichia coli is a potent mucosal adjuvant that has been used to induce protective immunity against Helicobacter felis and Helicobacter pylori infection in mice. We studied whether recombinant LT or its B subunit (LTB) has adjuvant activity in mice when delivered with H. pylori urease antigen via the parenteral route. Mice were immunized subcutaneously or intradermally with urease plus LT, recombinant LTB, or a combination of LT and LTB prior to intragastric challenge with H. pylori. Control mice were immunized orally with urease plus LT, a regimen shown previously to protect against H. pylori gastric infection. Parenteral immunization using either LT or LTB as adjuvant protected mice against H. pylori challenge as effectively as oral immunization and enhanced urease-specific immunoglobulin G (IgG) responses in serum as effectively as aluminum hydroxide adjuvant. LT and LTB had adjuvant activity at subtoxic doses and induced more consistent antibody responses than those observed with oral immunization. A mixture of a low dose of LT and a high dose of LTB stimulated the highest levels of protection and specific IgG in serum. Urease-specific IgG1 and IgG2a antibody subclass responses were stimulated by all immunization regimens tested, but relative levels were dependent on the adjuvant used. Compared to parenteral immunization with urease alone, LT preferentially enhanced IgG1, while LTB or the LT-LTB mixture preferentially enhanced IgG2a. Parenteral immunization using LT or LTB as adjuvant also induced IgA to urease in the saliva of some mice. These results show that LT and LTB stimulate qualitatively different humoral immune responses to urease but are both effective parenteral adjuvants for immunization of mice against H. pylori infection.

New approaches to mucosal immunization

Every year more than 17 million deaths worldwide are caused by infectious diseases. The great majority of these deaths occur in underdeveloped countries and are attributed to diseases preventable by existing vaccines, or diseases that could potentially be prevented with new vaccines. The fact that most human and veterinary pathogens establish infection in the host by initiating contact at a mucosal surface, provide the rationale for the development of mucosal vaccines. An increasing number of strategies have been proposed to facilitate mucosal immunization. Among the most widely investigated strategies are the use of attenuated microorganisms; the inclusion of immunizing antigens in lipid-based carriers, the genetic creation of transgenic plants and the use of mucosal adjuvants derived from bacterial toxins. This review provides a brief summary of the most recent advances in the field of mucosal immunization with an special emphasis on a promising genetically detoxified mucosal adjuvant, LT(R192G), derived from the heat-labile toxin of enterotoxigenic E. coli. We present evidence regarding the safety, immunogenicity, and efficacy of LT(R192G) for the development of a new generation of mucosal vaccines.

Effectiveness of intranasal immunization with HIV-gp160 and an HIV-1 env CTL epitope peptide (E7) in combination with the mucosal adjuvant LT(R192G)

LT(R192G) is a novel mucosal adjuvant that induces protective immunity when co-administered with certain whole inactivated bacteria or viruses or with subunits of relevant virulence determinants from these pathogens. LT(R192G) stimulates antigen-specific humoral and cellular immune responses, both systemically and in mucosal compartments, and is safe and nontoxic at adjuvant effective doses. Intranasal (IN) immunization of mice with LT(R192G) in conjunction with oligomeric HIV-1 gp160 elevates antigen-specific systemic and mucosal IgG and IgA production and Th1- and Th2-type cytokine responses. Isotype characterization of induced IgG reveals that gp160 alone fails to stimulate IgG2a responses in the absence of adjuvant. Both IgG1 and IgG2a are induced by immunization in the presence of LT(R192G). Additionally, intranasal immunization with a 15-amino acid peptide corresponding to an HIV-1 Env CTL determinant and LT(R192G) induces systemic, peptide-specific CTL activity and Th1 and Th2 cytokine responses that are absent when the adjuvant is excluded from the immunizations. These studies show that LT(R192G) quantitatively and qualitatively enhances cellular and humoral HIV-specific immune responses and that this adjuvant may offer significant advantages toward vaccine development against HIV.

Inactivated meningococci and pertussis bacteria are immunogenic and act as mucosal adjuvants for a nasal inactivated influenza virus vaccine

Whole killed meningococci (Nm) and pertussis bacteria (Bp) were tested for mucosal immunogenicity and as mucosal adjuvants for an inactivated influenza virus vaccine given intranasally to unanaesthetized mice. Virus was given alone, or simply mixed with one of the bacterial preparations, in four doses at weekly intervals. The virus alone induced low but significant increases of influenza-specific IgG antibodies in serum measured by ELISA, whereas IgA responses in serum and saliva were insignificant compared to non-immunized controls. With Bp or Nm admixed, serum IgG and IgA and salivary IgA responses to the influenza virus were substantially augmented (P<0.005). However, this adjuvant effect of the bacterial preparations was not significant for responses in the intestine as measured by antibodies in faeces. Antibody responses to Bp itself, but not to Nm, were inhibited by the admixture of the virus vaccine. Moreover, the pertussis preparation induced salivary antibodies which cross-reacted with Nm. Whole-cell bacteria with inherent strong mucosal immunogenicity may also possess mucosal adjuvanticity for admixed particulate antigens which are weakly immunogenic by the nasal route.

Efficient extracellular production of recombinant Escherichia coli heat-labile enterotoxin B subunit by using the expression/secretion system of Bacillus brevis and its mucosal immunoadjuvanticity

A gene encoding the mature Escherichia coli heat-labile enterotoxin B subunit (LTB) was introduced in a vector pNU212 and expressed at high levels in Bacillus brevis HPD31. The maximum amount of recombinant LTB (rLTB) secreted into the modified 5PY medium containing erythromycin was about 350 mg l(-1) when cultivated at 30 degrees C for 8 days. The rLTB purified directly from the culture supernatant by using D-galactose immobilized agarose was identical to the native LTB with respect to the molecular weight determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and the amino terminal amino acid sequence. Western blot analysis with antiserum to cholera toxin B subunit (CTB) indicated that rLTB had cross-reactivity to native CTB and its GM1 binding ability was almost the same as that of the CTB. The rLTB predominantly showed the pentameric form when non-boiled samples were applied to SDS-PAGE. When rLTB was administered intranasally to mice with diphtheria toxoid (D(T)), it resulted in the substantial stimulation of D(T)-specific serum IgG antibody, and in the induction of moderate levels of D(T)-specific mucosal IgA antibody responses in the nasal cavities and in the lung, suggesting that purified rLTB acts as a promising immunoadjuvant on mucosal immunizations.

Approaches to improved influenza vaccination

Inactivated influenza vaccine (Ivac) has had an important impact on reducing attack rates of influenza and reducing the severity of illness amongst the vaccinees who still acquire infection. Ivac is most efficacious amongst young, otherwise healthy subjects and least effective against elderly at high risk. This is in part because Ivac does not appear to significantly reduce infection rates and in part because response rate and final antibody titer are lower in the elderly. Therefore Ivac does not eliminate disease in the elderly who are prone to complications when any virus replication occurs. Simultaneous administration of intra-nasal live attenuated influenza vaccine (Livac) and Ivac reduces the infection rate and thus illness rate amongst high-risk elderly. Presumably this is because of the ability of Livac to stimulate secretory antibody which neutralizes virus at the mucosal surface. Other approaches are examining the benefit of baculovirus recombinant vaccine or adjuvanted Ivac to determine if the higher serum antibody these vaccines produce compared to Ivac, will diffuse onto the mucosal surfaces and in a similar fashion, neutralize virus at that site.

Intranasal immunization with inactivated influenza vaccine

The development of improved vaccines against epidemic and pandemic influenza virus infection remains a priority in vaccine research. Killed vaccines given by injection are both cost-effective and induce immunity; however, their limitations are well known. Live vaccines have been in development for many years, but difficulties and safety concerns have prohibited their licensing in Western countries. However, the newer technologies of vaccine development, including DNA vaccines and attenuated virus vaccines produced by reverse genetics, remain a hope for the future. With these problems in mind, emphasis has been given to the development of inactivated vaccines that are administered intranasally, either as repeated doses of saline vaccine or in conjunction with suitable carriers or adjuvants. This review describes these latter developments and concludes that this approach offers advantages and should be vigorously researched.

Is there a role for a mucosal influenza vaccine in the elderly?

Influenza infection is an acute respiratory disease with a high morbidity and significant mortality, particularly among the elderly and individuals with chronic diseases. The majority of countries now recommend annual influenza vaccination for all people aged 65 years or older, and for those with high risk conditions. Most commercially available influenza vaccines are administered systemically and while these are effective in children and young adults, efficacy levels in elderly individuals have been reported to be much lower. Mucosal vaccines may offer an improved vaccine strategy for protection of the elderly. As the influenza virus causes a respiratory infection, it is potentially more beneficial to administer a vaccine that will boost protection in the mucosal surfaces of the upper and lower respiratory tract. Mucosal influenza vaccines are aimed at stimulating protective immunity in the respiratory tract via oral or intranasal immunisation. This review examines our present knowledge of mucosal immunity and current strategies for mucosal vaccination. It also stresses that the use of serum antibody levels as a 'surrogate marker' for protection against influenza is potentially misleading; serum antibody, for example, may be a quite inappropriate marker to assess a mucosal vaccine. This marker does not reflect other immune responses to vaccination that are crucial for protection.