A Vibrio cholerae serogroup O1 vaccine candidate against CTX ET Phi infection

Cholera is a severe diarrheal disease that may spread rapidly. Vaccination is considered a valid measure against it. We developed a new vaccine candidate, IEM109, against Vibrio cholerae. To generate this candidate, a chromosomal fragment containing the TLC element, attB of the CTX Phi integration site, and RTX cluster responsible for the cytotoxic activity for mammalian cells was deleted through homologous recombination from the previously described El Tor biotype, IEM101. The protective genes ctxB and rstR, which establish resistance to CTX Phi infections, were inserted into that same location on the chromosome of IEM109 to enhance the safety and genetic stability of the vaccine candidate and to prevent horizontal gene transfer. In in vivo tests, cell cultures showed that the cytotoxic effect of IEM109 on Hep-2 was negative. Furthermore, the infection rate of El Tor biotype CTX Phi to that of IEM109 in the rabbit intestine is 3000-fold lower than that of IEM101. Intraintestinal vaccination of rabbits with a single dose of IEM109 elicits high titers of anti-CTB IgG and vibriocidal antibodies. When challenged with 0.5-2 microg CT and 10(5) to 10(8)CFU of four wild toxigenic strains of different biotypes and serogroups, IEM109 conferred full protection. Thus, IEM109 is a stable vaccine candidate that evokes not only antitoxic and vibriocidal immunities, but also resistance to the El Tor biotype CTX Phi infection.

Peru-15, a live attenuated oral cholera vaccine, is safe and immunogenic in Bangladeshi toddlers and infants

A live oral Vibrio cholerae O1 El Tor vaccine, Peru-15 was tested in a double-blind, randomized placebo controlled study for safety and immunogenicity in Phase I and Phase II studies in 240 Bangladeshi children aged 9 months-5 years of age. Two different doses (2x10(7) and 2x10(8)cfu) were tested. Vaccination did not elicit adverse events and the strain was genetically stable. Vibriocidal antibody responses developed in 42/50 (84%) toddlers (2-5 years) and 35/50 (70%) of younger children (9-23 months) and overall 77/100 (77%) who received the high dose. LPS-IgA-antibody responses were seen in 60% of toddlers and 34% of infants; 40% responded with IgA antibodies to cholera toxin. The responses to the reduced dose was lower. These studies demonstrate that Peru-15 at a dose of 2x10(8)cfu is safe and immunogenic in children in Bangladesh.

Traffic of antibody-secreting cells after immunization with a liposome-associated, CpG-ODN-adjuvanted oral cholera vaccine

An oral cholera vaccine made up of heat-treated recombinant cholera toxin (rCT), V. cholerae lipopolysaccharide (LPS), and recombinant toxin-co-regulated pili subunit A (rTcpA), entrapped in liposomes in the presence of unmethylated bacterial CpG-DNA (ODN#1826) was used to orally immunize a group of eight week old rats. A booster dose was given 14 days later. Control rats received placebo (vaccine diluent). The kinetics of the immune response were investigated by enumerating the antigen specific-antibody secreting cells (ASC) in the blood circulation and intestinal lamina propria using the ELISPOT assay and a histo-immunofluorescence assay (IFA), respectively. ASC of all antigenic specificities were detected in the blood of the vaccinated rats as early as two days after the booster dose. The numbers of LPS-ASC and TcpA-ASC in the blood were at their peak at day 3 post booster while the number of CT-ASC was highest at day 4 after the booster immunization. At day 13 post immunization, no ASC were detected in the blood. A several fold increase in the number of ASC of all antigenic specificities in the lamina propria above the background numbers of the control animals were found in all vaccinated rats at days 6 and 13 post booster (earlier and later time points were not studied). Vibriocidal antibody and specific antibodies to CT, LPS and TcpA were detected in 57.1% and 52.4%, 14.3%, and 19.0% of the orally vaccinated rats, respectively. The data indicated that rats orally primed with the vaccine could produce a rapid anamnestic response after re-exposure to the V. cholerae antigens. Thus, a single dose of the vaccine is expected to elicit a similar anamnestic immune response in people from cholera endemic areas who have been naturally primed to V. cholerae antigens, while two doses at a 14 day interval should be adequate for a traveler to a disease endemicarea.

Transcutaneous immunization with toxin-coregulated pilin A induces protective immunity against Vibrio cholerae O1 El Tor challenge in mice

Toxin-coregulated pilin A (TcpA) is the main structural subunit of a type IV bundle-forming pilus of Vibrio cholerae, the cause of cholera. Toxin-coregulated pilus is involved in formation of microcolonies of V. cholerae at the intestinal surface, and strains of V. cholerae deficient in TcpA are attenuated and unable to colonize intestinal surfaces. Anti-TcpA immunity is common in humans recovering from cholera in Bangladesh, and immunization against TcpA is protective in murine V. cholerae models. To evaluate whether transcutaneously applied TcpA is immunogenic, we transcutaneously immunized mice with 100 mug of TcpA or TcpA with an immunoadjuvant (cholera toxin [CT], 50 mug) on days 0, 19, and 40. Mice immunized with TcpA alone did not develop anti-TcpA responses. Mice that received transcutaneously applied TcpA and CT developed prominent anti-TcpA immunoglobulin G (IgG) serum responses but minimal anti-TcpA IgA. Transcutaneous immunization with CT induced prominent IgG and IgA anti-CT serum responses. In an infant mouse model, offspring born to dams transcutaneously immunized either with TcpA and CT or with CT alone were challenged with 10(6) CFU (one 50% lethal dose) wild-type V. cholerae O1 El Tor strain N16961. At 48 h, mice born to females transcutaneously immunized with CT alone had 36% +/- 10% (mean +/- standard error of the mean) survival, while mice born to females transcutaneously immunized with TcpA and CT had 69% +/- 6% survival (P < 0.001). Our results suggest that transcutaneous immunization with TcpA and an immunoadjuvant induces protective anti-TcpA immune responses. Anti-TcpA responses may contribute to an optimal cholera vaccine.

Immunogenicity of synthetic saccharide fragments of Vibrio cholerae O1 (Ogawa and Inaba) bound to Exotoxin A

Recombinant exotoxin A (rEPA) from Pseudomonas aeruginosa conjugated to Vibrio cholerae O1 serotype-specific polysaccharides (mono-, di- and hexasaccharide) were immunogenic in mice. Monosaccharide conjugates boosted the humoral responses to the hexasaccharide conjugates. Prior exposure to purified Ogawa lipopolysaccharide (LPS) enabled contra-serotype hexasaccharide conjugates to boost the vibriocidal response, but Inaba LPS did not prime for an enhanced vibriocidal response by a contra-serotype conjugate. Prior exposure to the carrier, and priming B cells with the LPS of either serotype, resulted in enhanced vibriocidal titers if the Ogawa hexasaccharides were used, but a diminished response to the Inaba LPS. These studies demonstrate that the 'functional' B cell epitopes on the LPS differ from those of the neoglycoconjugates and that the order of immunization and the serotype of the boosting conjugate can influence the epitope specificity and function of the antisera.

Safety and immunogenicity of a reformulated Vietnamese bivalent killed, whole-cell, oral cholera vaccine in adults

Vietnam currently produces an orally administered, bivalent (O1 and O139) killed whole-cell vaccine and is the only country in the world with endemic cholera to use an oral cholera vaccine in public health practice. In order to allow international use, the vaccine had to be reformulated to meet World Health Organization (WHO) requirements. We performed a randomized, placebo controlled, safety and immunogenicity studies of this reformulated vaccine among Vietnamese adults. One hundred and forty-four subjects received the two-dose regimen and 143 had two blood samples obtained for analysis. We found that this reformulated oral killed whole-cell cholera vaccine was safe, well tolerated and highly immunogenic.

Immunological properties of complex conjugates based on Vibrio cholerae O1 Ogawa lipopolysaccharide antigen

Host protection by humoral immunity against Vibrio cholerae O1 confers lipopolysaccharide (LPS)-specific vibriocidal antibodies. Levels of relevant specific antibodies are closely related to complement-mediated inactivation of the vibrios inoculum, especially on the mucosal surface of intestine. We have tested complex V. cholerae O1 Ogawa-detoxified lipopolysaccharide (dLPS) conjugates. The first conjugate contained glucan both as the immunomodulator and the matrix; the second conjugate contained immunologically inert amylose as matrix. Both d-LPS conjugates contain multiply attached dLPS antigen. These conjugates elicited a statistically significant increase of antigen-specific IgG levels in mice (P<0.001 and P<0.05, respectively). The specific anti-conjugate IgG and IgA response after the second (booster) dose were significantly higher compared to pre-immune and whole-cell response. The most effective vibriocidal activity was observed in the case of conjugate, with glucan as the matrix. The highest correlation was found between vibriocidal activity and specific IgG2b (r=0.765) and IgA (r=0.887) sera levels. The determination of specific IgG subclasses and IgG2a + 2b/IgG1 ratio revealed a dominant T(H)1 cell response crucial for effective vaccine candidate.

Oral cholera vaccines: use in clinical practice

Cholera continues to occur globally, particularly in sub-Saharan Africa and Asia. Oral cholera vaccines have been developed and have now been used for several years, primarily in traveller populations. The licensure in the European Union of a killed whole cell cholera vaccine combined with the recombinant B subunit of cholera toxin (rCTB-WC) has stimulated interest in protection against cholera. Because of the similarity between cholera toxin and the heat-labile toxin of Escherichia coli, a cause of travellers' diarrhoea, it has been proposed that the rCTB-WC vaccine may be used against travellers' diarrhoea. An analysis of trials of this vaccine against cholera (serotype O1) shows that for 4-6 months it will protect 61-86% of people living in cholera-endemic regions; lower levels of protection continue for 3 years. Protection wanes rapidly in young children. Because the risk of cholera for most travellers is extremely low, vaccination should be considered only for those working in relief or refugee settings or for those who will be travelling in cholera-epidemic areas and who will be unable to obtain prompt medical care. The vaccine can be expected to prevent 7% or less of cases of travellers' diarrhoea and should not be used for this purpose.

Length of the linker and the interval between immunizations influences the efficacy ofVibrio choleraeO1, Ogawa hexasaccharide neoglycoconjugates

Ogawa hexasaccharide neoglycoconjugates induce protective antibodies in mice. Similar Ogawa conjugates but with a longer linker that connects the carrier to shorter saccharides are immunogenic, but generally ineffective at inducing vibriocidal or protective antibodies. The efficacy of Ogawa hexasaccharide neoglycoconjugates of different linker lengths were tested. The majority of mice given immunizations separated by a 14-day gap did not produce vibriocidal or protective antibodies. Mice immunized 28 days apart with immunogens containing the shortest or medium length linker, but not the longest, produced vibriocidal and protective antibodies. A nonprotective, priming dose of purified Ogawa LPS followed 5 days later with a booster of the Ogawa neoglycoconjugates (di-, tetra-, or hexasaccharide) resulted in vibriocidal antibodies at day 10.

Process development for a Cuban cholera vaccine based on the attenuated strain Vibrio cholerae 638

Genetically modified Vibrio cholerae strain 638 (biotype El Tor, serotype Ogawa) has previously been shown to be immunogenic in animal models and in human trials. Our objective in the work reported herein was to describe the process development methods for the production of the 638 attenuated cholera vaccine. Cell seed bank, culture of biomass, lyophilization and final formulation were processes were developed. The results show kinetics of culture that fulfils a logistical model. The microbiological properties, colonizing capability, immunogenicity and non-toxigenicity of the final product were indistinguishable from the properties of the working seed lot. We conclude that the non-reactogenic, immunogenic and protective strain 638 is robust and can withstand the fermentation processes required for large-scale production of a vaccine.

[Expression and immunogenicity analysis of a recombinant fusion protein of V. Cholera ctB and H. pylori ure I]

AIM

To express fusion protein of the cholera toxin B subunit (ctB) and the urea membrane channel gene (ure I) of H. pylori in E. coli, and analyze its immunogenicity.

METHODS

The prokaryotic expression vector pET32a+/ctB/ure I was constructed by inserting ctB gene amplified by PCR into the 5' terminus of ure I gene of expression vector pET32a+/ure I. The fusion gene was verified by endonuclease digestion and sequence analysis. The fusion protein ctB/ure I was expressed in E. coli BL21(DE3), purified by His-HP affinity chromatography, and analyzed by SDS-PAGE, Western blot and Pro-gel analyzer 4.0. The mice were immunized with purified ctB/ure I, and the immunoreactivity with ctB and ure I of the murine sera was analyzed by indirect ELISA.

RESULTS

The pET32a+/ctB/ure I expression vector was constructed successfully and confirmed by endonuclease digestion and sequence analysis. The expressed ctB/ure I protein with molecular weight about 58,000 was shown when induced with 1 mmol/L IPTG for 4 h at 22 degrees C, and the protein could react with horse anti-ctB and human anti-ure I sera when detected with Western blot, and the purity of the purified protein was about 94.3%. The sera from mice immunized with purified ctB/ure I protein could react with ctB, ure I, and ctB/ure I when detected with indirect ELISA.

CONCLUSION

The fusion protein expression vector pET32a+/ctB/ure I was constructed successfully. The fusion protein ctB/ure I was shown to have immunoreactivity with both anti-ctB and anti-ure I anti-sera, and could evoke production of anti-ctB and anti-ure I antibody in mice. Our work established a good foundation for further study on the new and effective H. pylori vaccines.

Construction and evaluation of a O139 Vibrio cholerae vaccine candidate based on a hemA gene mutation

In this paper, we describe the development of VCUSM2, a live metabolic auxotroph of Vibrio cholerae O139. Auxotrophy was achieved by mutating a house keeping gene, hemA, that encodes for glutamyl-tRNA reductase, an important enzyme in the C5 pathway for delta-aminolevulenic acid (ALA) biosynthesis, which renders this strain dependent on exogenous ALA for survival. Experiments using the infant mouse and adult rabbit models show that VCUSM2 is a good colonizer of the small intestine and elicits greater than a four-fold rise in vibriocidal antibodies in vaccinated rabbits. Rabbits vaccinated with VCUSM2 were fully protected against subsequent challenge with 1 x 10(11) CFU of the virulent wild type (WT) strain. Experiments using ligated ileal loops of rabbits show that VCUSM2 is 2.5-fold less toxic at the dose of 1 x 10(6) CFU compared to the WT strain. Shedding of VCUSM2 in rabbits were found to occur for no longer than 4 days and its maximum survival rate in environmental waters is 8 days compared to the greater than 20 days for the WT strain. VCUSM2 is thus a potential vaccine candidate against infection by V. cholerae O139.

Biosafety evaluation of recombinant live oral bacterial vaccines in the context of European regulation

Live bacterial vaccines represent a highly valid preventive strategy in the fight against infectious disease. However, the road from research to market is peppered with hurdles, one of which is the requirement for high biosafety characteristics, which the candidate vaccine has to display. In Europe, the European Agency for the evaluation of medicinal products (EMEA) is the relevant authority regulating the licensure of genetically engineered vaccines. For this purpose, the agency may rely on several directives and guidelines defined in the past 15 years. As for live vaccines containing genetically modified organisms (GMOs) susceptible to be released into the environment, Directive 2001/18/EC determines the framework and principles of an environmental risk assessment (ERA) process, the results of which constitute an important section of the vaccine registration package submitted to registration authorities. In this article, we address the implications of current European regulations for the approval of live oral bacterial vaccines with emphasis on the assessment of potential risks associated with environmental release. Biosafety aspects of already registered and some promising live bacterial vaccine strains will be briefly discussed.

Dendritic cell-mediated induction of mucosal cytotoxic responses following intravaginal immunization with the nontoxic B subunit of cholera toxin

The use of the nontoxic B subunit of cholera toxin (CTB) as mucosal adjuvant and carrier-delivery system for inducing secretory Ab responses has been documented previously with different soluble Ags. In this study, we have evaluated this approach for inducing CTL responses against a prototype Ag, OVA, in the female genital mucosa. We report here the ability of an immunogen comprised of CTB conjugated to OVA (CTB-OVA) given by intravaginal (ivag) route to induce genital OVA-specific CTLs in mice. Using adoptive transfer models, we demonstrate that ivag application of CTB-OVA activates OVA-specific IFN-gamma-producing CD4 and CD8 T cells in draining lymph nodes (DLN). Moreover, ivag CTB induces an expansion of IFN-gamma-secreting CD8+ T cells in DLN and genital mucosa and promotes Ab responses to OVA. In contrast, ivag administration of OVA alone or coadministered with CTB failed to induce such responses. Importantly, we demonstrate that ivag CTB-OVA generates OVA-specific CTLs in DLN and the genital mucosa. Furthermore, genital CD11b+ CD11c+ dendritic cells (DCs), but not CD8+ CD11c+ or CD11c- APCs, present MHC class I epitopes acquired after ivag CTB-OVA, suggesting a critical role of this DC subset in the priming of genital CTLs. Inhibition studies indicate that the presentation of OVA MHC class I epitopes by DCs conditioned with CTB-OVA involves a proteasome-dependent and chloroquine-sensitive mechanism. These results demonstrate that CTB is an efficient adjuvant-delivery system for DC-mediated induction of genital CTL responses and may have implications for the design of vaccines against sexually transmitted infections.

Formulation in tablets of a cholera whole cells inactivated vaccine candidate

Licensed as well as candidate cholera vaccines available at the present requires the dose preparation (included buffer) at the moment of application. The aim of this work was to evaluate the presentation in oral tablets of an inactivated cholera vaccine to avoid that inconveniences during application. We have therefore compared inactivated cultures of Vibrio cholerae with tablets formulation vaccine. We obtained that antigenic activity (ELISA) and immunogenicity in animal model (ELISA and vibriocidal tests) of V. cholerae inactivated cell remained unaltered in the final tablet formulation. The results suggest that the oral tablet formulation could be a useful pharmaceutical form in order to produce a new and affordable cholera vaccine.

Long-term effectiveness against cholera of oral killed whole-cell vaccine produced in Vietnam

We assessed the long-term protection afforded by a killed whole-cell oral cholera vaccine produced in Vietnam. A mass immunization of children and adults with the killed whole-cell oral cholera vaccine was undertaken in half of the communes of Hue, Vietnam, in 1998; the remaining communes were immunized in 2000. No cholera was observed in Hue until 2003, when an outbreak of El Tor cholera made it possible to conduct a case-control study. The overall vaccine effectiveness 3-5 years after vaccination was 50% (9-63%). This low-cost, easily administered vaccine should be considered as a tool for the control of cholera.

Oral cholera vaccine—for whom, when, and why?

The search for a safe, effective, well tolerated, low cost vaccine against the ancient cholera enemy has been ongoing since the 19th century and has been revitalized in the past two decades since the advent of recombinant technology. Large-scale field trials have readily demonstrated the tolerability and safety of oral cholera vaccine in various forms. Variable levels of protection have been shown and one challenge has been to demonstrate whether this is a cost effective treatment in differing environments including its use in endemic and epidemic areas as well as for travelers. A review of recent literature was undertaken to assess the effectiveness and uses of currently available oral cholera vaccine. While the evidence does not support the creation of formal guidelines, some clear recommendations can be made. There is undoubtedly the potential to reduce the burden of illness both in endemic and epidemic situations. For travelers, certain higher risk groups may benefit from protection against cholera. More significantly, the short term cross-protection afforded by whole cell, B subunit (WC BS) oral cholera vaccine formulations against enterotoxigenic E. coli, (ETEC), the commonest causative agent of traveler's diarrhoea, may prove to be the most important raison d'être.

Reduction in capsular content and enhanced bacterial susceptibility to serum killing of Vibrio cholerae O139 associated with the 2002 cholera epidemic in Bangladesh

Vibrio cholerae O139 emerged in 1992 as a major cause of epidemic cholera. However, the incidence of disease due to this new serogroup subsequently decreased for almost a decade. In April 2002, there was a dramatic resurgence of V. cholerae O139 in Bangladesh. We compared the phenotypic properties of the bacterial isolates and the immunological responses in patients with disease due to V. cholerae O139 during the 2002 epidemic with those dating to the emergence of this disease in 1993 to 1995. Strains isolated from patients in the two time periods were compared with respect to capsular polysaccharide, their resistance to the bactericidal effect of serum, and their capacity to be used as target strains in complement-mediated vibriocidal assays. Phase-contrast microscopy showed that strains isolated in 2002 had less capsular material than those isolated from 1993 to 1995 (P = <0.001), a finding confirmed by electron microscopic studies. Strains isolated in 2002 were more susceptible to the bactericidal activity of serum compared to strains from 1993 to 1995 (P = 0.013). Compared to results using a standard O139 strain, a modified vibriocidal assay utilizing a 2002 strain, CIRS 134, as the target organism detected higher vibriocidal responses in both O139-infected cholera patients as well as O139 vaccine recipients. The vibriocidal assay utilizing the less encapsulated 2002 strain, CIRS 134, is a more sensitive indicator of adaptive immune responses to recent infection with V. cholerae O139. Consequently, this assay may be useful in studies of both O139-infected patients and recipients of O139 vaccines.

Role of toll-like receptor 4 in the proinflammatory response to Vibrio cholerae O1 El tor strains deficient in production of cholera toxin and accessory toxins

Following intranasal inoculation, Vibrio cholerae KFV101 (DeltactxAB DeltahapA DeltahlyA DeltartxA) colonizes and stimulates tumor necrosis factor alpha and interleukin 1beta (IL-1beta) in mice, similar to what occurs with isogenic strain P4 (DeltactxAB), but is less virulent and stimulates reduced levels of IL-6, demonstrating a role for accessory toxins in pathogenesis. Morbidity is enhanced in C3H/HeJ mice, indicating that Toll-like receptor 4 is important for infection containment.

Analysis of efficacy of CVD 103-HgR live oral cholera vaccine against all-cause travellers’ diarrhoea in a randomised, double-blind, placebo-controlled study

Enterotoxigenic Escherichia coli (ETEC), which produces heat labile toxin (LT) and/or heat stable toxin (ST), is considered to be the most common known cause of travellers' diarrhoea (TD). Owing to the antigenic similarity between cholera toxin and LT, immunization with inactivated oral B-subunit/whole-cell cholera vaccine (BS-WC) offers short term (3 months) but significant (>67%) protection against TD caused by LT-related ETEC. Since it expresses the cholera toxin B (CTB) subunit, the live attenuated oral cholera vaccine strain CVD 103-HgR, may induce similar protection. A trial was performed to determine if CVD 103-HgR live oral cholera vaccine would provide a protective efficacy of at least 50% against TD. In addition, the protective efficacy of the vaccine against TD specifically due to LT-ETEC and LT/ST-ETEC was determined. Volunteers (n=134) travelling to Indonesia, India, Thailand or West-Africa were randomised to receive either a placebo (n=65) or the vaccine (n=69). In the placebo group, 46% reported an episode of diarrhoea, compared to 52% in the vaccine group. No significant group differences were found with regard to incidence, duration or severity of all caused TD or ETEC-associated TD. However, ETEC-associated TD occurred earlier in the placebo group (median 5 days), compared to the vaccine group (median 15 days). In conclusion, CVD 103-HgR live oral cholera vaccine failed to provide a 50% protection against TD. This study does not exclude that the vaccine may offer a short-lived protection against ETEC-associated TD. However, the power of the study was limited by the unexpected low incidence of LT-ETEC-associated diarrhoea (9% of all TD) compared to ST-associated TD (24% of all TD).

Randomized, controlled study of the safety and immunogenicity of Peru-15, a live attenuated oral vaccine candidate for cholera, in adult volunteers in Bangladesh

BACKGROUND

A live oral Vibrio cholerae O1 El Tor vaccine candidate, Peru-15, was studied for safety, immunogenicity, and excretion in phase 1 (inpatient) and phase 2 (outpatient) studies of Bangladeshi adults.METHODs. The study was conducted among adults, by use of a double-blind, randomized, placebo-controlled design. A single dose of Peru-15 (approximately 2 x 108 cfu) or placebo (buffer only) was given in standard bicarbonate and ascorbic acid buffer.RESULTS. Study treatment did not elicit any major adverse events in the volunteers, during either the inpatient or the outpatient phases, and there were no reports of diarrhea. V. cholerae was isolated from the stool of only 1 volunteer and was found to be genetically identical to the vaccine strain. Vibriocidal antibody responses were seen in 30 (75%) of 40 vaccine recipients and in 3 (10%) of 30 placebo recipients. Peripheral blood immunoglobulin (Ig) A and IgM antibody-secreting cell responses to lipopolysaccharide were seen in the majority of vaccine recipients (response rate, 78%--88%). Seroconversion for lipopolysaccharide-specific IgA antibodies was seen in 88% of vaccine recipients. The response in vaccine recipients was significantly higher than that in placebo recipients, in all of the immunological assays (P=.036 to <.001). A lower immunological response against cholera toxin B subunit was detected.CONCLUSIONS. The safety and immunogenicity of this Peru-15 vaccine candidate indicates the usefulness of future studies in Bangladesh, where cholera is endemic.

Herd immunity conferred by killed oral cholera vaccines in Bangladesh: a reanalysis

BACKGROUND

Decisions about the use of killed oral cholera vaccines, which confer moderate levels of direct protection to vaccinees, can depend on whether the vaccines also provide indirect (herd) protection when high levels of vaccine coverage are attained. We reanalysed data from a field trial in Bangladesh to ascertain whether there is evidence of indirect protection from killed oral cholera vaccines.

METHODS

We analysed the first year of surveillance data from a placebo-controlled trial of B subunit-killed whole-cell and killed whole-cell-only oral cholera vaccines in children and adult women in Bangladesh. We calculated whether there was an inverse, monotonic trend for the relation between the level of vaccine coverage in a residential cluster and the incidence of cholera in individual vaccine recipients or placebo recipients residing in the cluster after controlling for potential confounding variables.

FINDINGS

Vaccine coverage of the targeted population ranged from 4% to 65%. Incidence rates of cholera among placebo recipients were inversely related to levels of vaccine coverage (7.01 cases per 1000 in the lowest quintile of coverage vs 1.47 cases per 1000 in the highest quintile; p<0.0001 for trend). Receipt of vaccine by an individual and the level of vaccine coverage of the individual's cluster were independently related to a reduced risk of cholera. Moreover, after adjustment for the level of vaccine coverage of the cluster, vaccine protective efficacy remained significant (55% [95% CI 41-66], p<0.0001).

INTERPRETATION

In addition to providing direct protection to vaccine recipients, killed oral cholera vaccines confer significant herd protection to neighbouring non-vaccinated individuals. Use of these vaccines could have a major effect on the burden of cholera in endemic settings.

The vaccine candidate Vibrio cholerae 638 is protective against cholera in healthy volunteers

Vibrio cholerae 638 is a living candidate cholera vaccine strain attenuated by deletion of the CTXPhi prophage from C7258 (O1, El Tor Ogawa) and by insertion of the Clostridium thermocellum endoglucanase A gene into the hemagglutinin/protease coding sequence. This vaccine candidate was previously found to be well tolerated and immunogenic in volunteers. This article reports a randomized, double-blind, placebo-controlled trial conducted to test short-term protection conferred by 638 against subsequent V. cholerae infection and disease in volunteers in Cuba. A total of 45 subjects were enrolled and assigned to receive vaccine or placebo. The vaccine contained 10(9) CFU of freshly harvested 638 buffered with 1.3% NaHCO(3), while the placebo was buffer alone. After vaccine but not after placebo intake, 96% of volunteers had at least a fourfold increase in vibriocidal antibody titers, and 50% showed a doubling of at least the lipopolysaccharide-specific immunoglobulin A titers in serum. At 1 month after vaccination, five volunteers from the vaccine group and five from the placebo group underwent an exploratory challenge study with 10(9) CFU of DeltaCTXPhi attenuated mutant strain V. cholerae 81. Only two volunteers from the vaccine group shed strain 81 in their feces, but none of them experienced diarrhea; in the placebo group, all volunteers excreted the challenge strain, and three had reactogenic diarrhea. An additional 12 vaccinees and 9 placebo recipients underwent challenge with 7 x 10(5) CFU of virulent strain V. cholerae 3008 freshly harvested from a brain heart infusion agar plate and buffered with 1.3% NaHCO(3). Three volunteers (25%) from the vaccine group and all from the placebo group shed the challenge agent in their feces. None of the 12 vaccinees but 7 volunteers from the placebo group had diarrhea, and 2 of the latter exhibited severe cholera (>5,000 g of diarrheal stool). These results indicate that at 1 month after ingestion of a single oral dose (10(9) CFU) of strain 638, volunteers remained protected against cholera infection and disease provoked by the wild-type challenge agent V. cholerae 3008. We recommend that additional vaccine lots of 638 be prepared under good manufacturing practices for further evaluation.

Policymakers' views regarding the introduction of new-generation vaccines against typhoid fever, shigellosis and cholera in Asia

Face-to-face interviews and meetings with more than 160 policymakers and other influential professionals in seven large Asian countries (Bangladesh, China, India, Indonesia, Pakistan, Thailand and Vietnam) were conducted to survey opinions regarding the need for, and potential uses of new-generation vaccines against cholera, typhoid fever and shigellosis. Despite several barriers to their uptake--notably uncertainty of the burden of enteric diseases; preference for water, sanitation and other environmental improvements over vaccination for disease control; and high prices of the current vaccines relative to basic EPI vaccines, and their moderate protection levels--considerable interest was found in the targeted use of Vi typhoid vaccine in most countries, followed by (future) Shigella and oral cholera vaccines. The introduction of these vaccines in Asia could be greatly facilitated by country-specific evidence of disease burden, local or regional vaccine production, field studies demonstrating their safety and efficacy in local populations, evidence of potential economic savings from vaccination, and effective dissemination of research results to all those who make or influence immunization policy.

[Selection of attenuated Vibrio cholerae strains to obtain oral attenuated candidate vaccines against cholera]

A methodology was developed for the selection of genetically modified strains of Vibrio cholerae 01 and 0139 aimed at obtaining oral attenuated candidate vaccines against cholera. The modified strains underwent microbiological characterization, bacterial susceptibility and different biological tests (mean lethal dose, colonizing capacity, adherence in mice, ligated intestine and intraduodenal inoculation in rabbits as virulence and potency tests. The strains 81, 638, 638T and 1333 were evaluated in clinical trials to determine their reactogenicity and immunogenicity. All the strains were sensitive to tetracycline and doxoclycine. They showed their attenuation and immunogenicity in animal models. The strains 638 and 1333 proved to be immunogenic and non reactogenic in volunteers.

Construction and Characterization of a thyA Mutant Derived From Cholera Vaccine Candidate IEM101

A naturally cholera toxin gene negative Vibrio cholerae (O1, El Tor, Ogawa) strain, named IEM101, was isolated in China. The human volunteer tests showed that this strain was safe, able to colonize the intestinal mucosa, and able to induce a strong immune response. Also other studies indicated that it was an efficient live vector to deliver heterologous antigens. In this article, a thymidylate synthase gene (thyA)-defined mutant was constructed using homologous recombination. Except for the morphological changes in minimal medium and slightly reduced colonization capacity, mutant strain IEM101-T maintained most of the desirable features as the wild-type strain IEM101 in terms of growth rate and immunogenicity. However, the mutant was more biosafe than its parent strain. In conclusion, IEM101-T may be a promising strain to develop live vaccine candidate of cholera or an attractive vaccine vector to deliver heterologous antigens in vivo.

[Comparative analysis of the major protective antigens production in Vibrio cholerae recombinant and producer strains of the classical biovar]

The comparative study of 4 constructed protective antigen producing strains of the classical biovar and V. cholerae strains 569 B Inaba and M41 Ogawa, used in manufacturing the cholera chemical vaccine "cholerogen-toxoid", was carried out. The study revealed that V. cholerae plasmid strains 2414 Ogawa, 2415 Inaba and nonplasmid strains 2416 Ogawa, 2417 Inaba had a higher level of production of the main protective antrigens in comparison with producer strains. They also synthesized much more (4-5 fold) cholera toxin, toxin co-regulated adhesion pili, contained protein OmpU in their outer membrane, exceeded 2- to 3-fold in the synthesis of pathogenicity enzymes (proteases, phospholipases) and synthesized the same amounts of 01 antigen, serovars Inaba and Ogawa. The use of the newly created protective-antigen producing strains in vaccine manufacturing could facilitate the preparation of a more effective cholera chemical vaccine "cholerogen-toxoid".

A Vibrio cholerae classical TcpA amino acid sequence induces protective antibody that binds an area hypothesized to be important for toxin-coregulated pilus structure

Vibrio cholerae is a gram-negative bacterium that has been associated with cholera pandemics since the early 1800s. Whole-cell, killed, and live-attenuated oral cholera vaccines are in use. We and others have focused on the development of a subunit cholera vaccine that features standardized epitopes from various V. cholerae macromolecules that are known to induce protective antibody responses. TcpA protein is assembled into toxin-coregulated pilus (TCP), a type IVb pilus required for V. cholerae colonization, and thus is a strong candidate for a cholera subunit vaccine. Polypeptides (24 to 26 amino acids) in TcpA that can induce protective antibody responses have been reported, but further characterization of their amino acid targets relative to tertiary or quaternary TCP structures has not been done. We report a refinement of the TcpA sequences that can induce protective antibody. One sequence, TcpA 15 (residues 170 to 183), induces antibodies that bind linear TcpA in a Western blot as well as weakly bind soluble TcpA in solution. These antibodies bind assembled pili at high density and provide 80 to 100% protection in the infant mouse protection assay. This is in sharp contrast to other anti-TcpA peptide sera (TcpA 11, TcpA 13, and TcpA 17) that bind very strongly in Western blot and solution assays yet do not provide protection or effectively bind TCP, as evidenced by immunoelectron microscopy. The sequences of TcpA 15 that induce protective antibody were localized on a model of assembled TCP. These sequences are centered on a site that is predicted to be important for TCP structure.

Vaccines against diarrheal diseases

At least 2 million persons succumb annually to enteric infection, and in countless other patients, diarrheal disease aggravates malnutrition and susceptibility to other infections. Prevention of enteric illness by virtue of improved hygiene and provision of sanitation and water treatment is impractical in most developing countries, where morbidity and mortality rates are highest. For this reason, development of vaccines against the most important gastrointestinal infections remains a high priority.

The Cholera Toxin-Derived CTA1-DD Vaccine Adjuvant Administered Intranasally Does Not Cause Inflammation or Accumulate in the Nervous Tissues

Although highly effective, the use of GM1-receptor binding holotoxins as nasal mucosal adjuvants has recently been cautioned due to the risk for their accumulation in the brain and other nervous tissues. Therefore we have explored the efficacy of the CTA1-DD adjuvant for its ability to enhance nasal immune responses in mice. We found that despite the lack of a mucosal binding element, the B cell-targeted CTA1-DD molecule was an equally strong adjuvant as cholera toxin (CT). The potency of CTA1-DD was not a result of endotoxin contamination because more than a 50-fold higher dose of LPS was needed to achieve a similar enhancement. Moreover, the adjuvant effect was TLR4-independent and absent in mutant CTA1-E112K-DD, lacking enzymatic activity. The CTA1-DD adjuvant augmented germinal center formations and T cell priming in the draining lymph nodes, and contrary to CT, promoted a balanced Th1/Th2 response with little effect on IgE Ab production. CTA1-DD did not induce inflammatory changes in the nasal mucosa, and most importantly did not bind to or accumulate in the nervous tissues of the olfactory bulb, whereas CT bound avidly to the nervous tissues. We believe that the nontoxic CTA1-DD adjuvant is an attractive solution to the current dilemma between efficacy and toxicity encountered in CT-holotoxin adjuvant or Escherichia coli heat-labile toxin-holotoxin adjuvant strategies and provides a safe and promising candidate to be included in future vaccines for intranasal administration.

Can oral cholera vaccination play a role in controlling a cholera outbreak?

Control measures to limit the spread of a cholera outbreak in Pohnpei Island (Micronesia), included mass vaccination with the single-dose live-attenuated oral cholera vaccine CVD 103-HgR as a potential adjunct measure. The outbreak provided a unique opportunity to evaluate the practicality of use and effectiveness of this vaccine. Under field conditions encountered in Pohnpei, crude vaccine efficacy was estimated at 79.2% (95% CI: 71.9-84.6%) in the target population. Retrospective analysis suggests that mass vaccination with oral cholera vaccines can be a useful adjunct tool for controlling outbreaks, particularly if implemented early in association with other standard control measures.

Experimental immunisation and protection of guinea pigs with Vibrio cholerae toxoid and mucinases, neuraminidase and proteinase

As measured by fluid accumulation in ileal loops, Vibrio cholerae mucinase complex, with or without toxoid, protected guinea pigs from challenges with V. cholerae live organisms and enterotoxin. The neuraminidase and proteinases of the complex were combined in modified oil emulsion or aluminum hydroxide adjuvants and the resultant vaccines given by the parenteral or oral routes. There was little difference between the two types of adjuvant. Control of stomach acidity improved oral vaccination. Animals injected intramuscularly (i.m.) with toxoid-containing vaccines were protected from challenge with cholera toxin (CT) whereas those given oral doses were not. Toxoid plus killed V. cholerae cells elicited a more effective protection against toxin challenge than killed V. cholerae cells alone. Vaccines containing mucinases, with or without toxoid, protected the animals from a live V. cholerae challenge. The anti-mucinase immune response may prevent adhesion of the V. cholerae cells and hence reduce delivery of toxin to receptors. These mucinases, neuraminidase and proteinases, may be useful components of acellular, toxoided cholera vaccines for human immunisation.

Biosafety aspects of the recombinant live oral Vibrio cholerae vaccine strain CVD 103-HgR

The development of live attenuated vaccines, allowing for the safe and effective immunisation at mucosal surfaces, is a strategy of great interest for vaccinologists. The main advantage of this approach over conventional parenteral vaccines is the induction of strong mucosal immune responses, allowing targeting of the pathogen at the initial point of contact with the host. Further advantages include the ease of administration, high acceptance by vaccines, and relatively low production costs. Finally, well-characterised, safe and immunogenic vaccine strains are well suited as vectors for the mucosal delivery of foreign vaccine antigens and of DNA vaccines. However, such vaccines, when based on or containing genetically modified organisms (GMOs), are facing new and specific regulatory hurdles, particularly regarding the potential risks for humans and the environment. In this contribution we address selected aspects of the risk assessment of live attenuated bacterial vaccines covered in the course of the registration of vaccine strain CVD 103-HgR as a recombinant live oral vaccine against cholera.

Suppressive effect of zinc on antibody response to cholera toxin in children given the killed, B subunit-whole cell, oral cholera vaccine

In a previous study, children aged 2-5 years old in Bangladesh were supplemented orally with a single dose of Vitamin A (200,000 IU) and a placebo for zinc (zinc equivalent to 20 mg of elemental zinc) everyday for 42 days (group A), zinc and a placebo for Vitamin A (group Z), zinc and Vitamin A (group AZ) or both placebos (group P). All children were orally immunised with two doses of the killed cholera vaccine containing whole cells and a recombinant B subunit of cholera toxin (CT). The number of children who responded with > or = 4-fold vibriocidal antibody (a proxy indicator of protection against cholera) was significantly greater among the zinc-supplemented groups than among the non-zinc-supplemented groups, while Vitamin A supplementation did not appear to have any effect. The sera from these children were assayed for antibody to CT. Antibody to CT is known to exert a synergistic protective effect against cholera in animal studies, and offer significantly higher short-term protection against cholera and significant short-term protection against enterotoxigenic Escherichia coli diarrhoea in humans on oral immunisation with the cholera vaccine. Children who received zinc had significantly reduced levels of serum antibodies to CT than children who received placebos only. Factorial analysis showed a trend for zinc showing a reduction in the number of children responding with CT-antibody, while Vitamin A did not appear to have any effect. Thus, zinc enhanced vibriocidal antibody response, but suppressed CT-antibody response, suggesting that zinc supplementation has different modulating effects on vibriocidal antibody response and CT-antibody response.

Mucosal vaccination increases endothelial expression of mucosal addressin cell adhesion molecule 1 in the human gastrointestinal tract

Homing of leukocytes to various tissues is dependent on the interaction between homing receptors on leukocytes and their ligands, addressins, on endothelial cells. Mucosal immunization results in homing of antigen-specific lymphocytes back to the mucosa where they first encountered the antigen. However, it is unknown whether this homing of antigen-specific cells is mediated by an altered endothelial addressin expression after vaccination. Using different immunization routes with an oral cholera vaccine, we show that the endothelial expression of mucosal addressin cell adhesion molecule 1 (MAdCAM-1) is increased in the gastric and upper small intestinal mucosae after immunization through various local routes in the upper gastrointestinal tract. In contrast, rectal immunization did not influence the levels of MAdCAM-1 in the gastric or duodenal mucosa. Furthermore, we show that MAdCAM-1 can be induced on human endothelial cells by tumor necrosis factor alpha (TNF-alpha) and gamma interferon. The vaccine component cholera toxin B subunit (CTB) increased MAdCAM-1 expression on endothelial cells in cultured human gastric explants, an effect that seemed to be mediated by TNF-alpha. In conclusion, MAdCAM-1 expression is increased in the upper gastrointestinal tract after local immunizations with a vaccine containing CTB. This strongly suggests the involvement of MAdCAM-1 in the preferential homing of mucosal lymphocytes to their original site of activation.

Comparison of different routes of vaccination for eliciting antibody responses in the human stomach

Determination of optimal routes to induce mucosal immune responses locally in the stomach and duodenum are important steps in the development of vaccines against Helicobacter pylori infection. In this study, we immunized H. pylori-infected individuals either nasally or rectally with a model antigen, i.e. cholera toxin B subunit, and compared the immune responses after these routes with the responses after oral or intrajejunal vaccination. Specific antibody levels in serum as well as specific antibody levels and antibody-secreting cells in biopsies from antrum and duodenum were determined by ELISA and ELISPOT methods. In contrast to oral vaccination, nasal and rectal vaccination did not induce significant increases in specific antibody-secreting cells either in the antrum or duodenum. Furthermore, when analyzing the antibody levels in saponin extracted biopsies, intrajejunal vaccination was superior to both nasal and rectal vaccination in inducing antigen-specific IgA levels in the stomach. We conclude that oral vaccination is the optimal route for induction of antigen-specific IgA antibody responses in the stomach and duodenum of humans, while nasal or rectal vaccination is less suitable for this purpose.

Dynamics of intestinal flora after oral vaccination with inactivated whole-cell/recombinant B subunit O139 cholera vaccine

OBJECTIVE

To investigate the change of intestinal flora in subjects receiving oral vaccination with inactivated whole-cell/recombinant B subunit (WC/rBS) O139 cholera vaccine made in China.

METHODS

The fecal smears of 5 groups of subjects receiving the vaccine were collected before and 2 and 3 months after the vaccination to examine the distribution of the intestinal flora.

RESULTS

In the 458 specimens examined, the total amount of bacteria and percentages of G+b, G+c and G-c were decreased whereas the amount of G-b significantly increased after vaccination. Compared with the placebo control group, the vaccinated groups exhibited significant changes in G+b and G-c, which also varied significantly between the group receiving 3 doses of WC/rBS vaccine and the other vaccinated groups. The vaccination produced distinct changes in the percentage of the intestinal flora at different time points, showing the most obvious effect on G-b. Oral vaccination was shown to affect the percentage of the intestinal flora very likely through its effect on the amount of G-b. The percentages of G+b, G-b and G-c varied significantly between male and female subjects after vaccination.

CONCLUSION

Oral vaccination with WC/rBS affects the intestinal flora in human, and the mechanism as well as the implications needs to be further explored.

Studies on the immunogenic potential of plant-expressed cholera toxin B subunit

Nicotiana tabacum var. Samsun was transformed via Agrobacterium-mediated transformation with a gene encoding the cholera toxin B subunit (CTB) of Vibrio cholerae, modified to contain a sequence coding for an endoplasmic reticulum retention signal (SEKDEL), under the control of the cauliflower mosaic virus 35S promoter. Total protein from the transgenic leaf tissue was isolated and an aliquot containing 5 microg recombinant CTB was injected intradermally into Balb/c (H2K(d)) mice. CTB-specific serum IgG was detected in animals that had been administered plant-expressed or native purified CTB. A T-cell proliferation study using splenocytes and cytokine estimations in supernatants generated by in vitro stimulation of macrophages isolated from the immuno-primed animals was carried out. Inhibition of proliferation of T lymphocytes was observed in splenic T lymphocytes isolated from animals injected with either native or plant-expressed CTB. Macrophages isolated from mice immunised with native or plant-expressed CTB showed enhanced secretion of interleukin-10 but secretion of lipopolysaccharide-induced interleukin-12 and tumor necrosis factor alpha was inhibited. These studies suggest that plant-expressed protein behaved like native CTB with regards to effects on T-cell proliferation and cytokine levels, indicating the suitability of plant expression systems for the production of bacterial antigens, which could be used as edible vaccine. The transgene was found to be inherited in the progeny and was expressed to yield a pentameric form of CTB as evident by its interaction with G(M1) ganglioside.

Cholera vaccine candidate 638: intranasal immunogenicity and expression of a foreign antigen from the pulmonary pathogen Coccidioides immitis

Vibrio cholerae strain 638 is a live genetically attenuated candidate cholera vaccine in which the CTXPhi prophage encoding cholera toxin has been deleted and hapA, encoding an extracellular Zn-dependent metalloprotease, was insertionally inactivated. Strain 638 was highly immunogenic when inoculated to adult Swiss mice by the intranasal route as judged by the induction of a strong serum vibriocidal antibody response. A side-by-side comparison of strain 638 with its isogenic hapA(+) precursor (strain 81) in the above model indicated that inactivation of hapA does not affect immunogenicity. The spherule-associated antigen 2/proline-rich antigen (Ag2/PRA) of Coccidioides immitis has been shown to protect mice against coccidioidomycosis to an extent dependent on the modes of antigen presentation and challenge with C. immitis arthrospores. In this work, we demonstrate the use of a live genetically attenuated V. cholerae strain to deliver Ag2/PRA. Ag2/PRA was expressed in 638 as a fusion protein with the Escherichia coli heat labile toxin B subunit leader peptide using the strong Tac promoter. The recombinant Ag2/PRA was efficiently expressed, processed and secreted to the periplasmic space. Intranasal immunizations of adult mice with strain 638 expressing Ag2/PRA induced serum vibriocidal antibody response to the vector strain and serum total IgG response to Ag2/PRA. Strain 638 expressing PRA could be recovered from trachea and lung up to 20h after immunization but was effectively cleared 72h post-inoculation.

CpG DNA, liposome and refined antigen oral cholera vaccine

An oral cholera vaccine made up of three Vibrio cholerae antigens, i.e. lipopolysaccharide (LPS), recombinant toxin co-regulated pili (rTcpA) and heat-treated cholera toxin (H-CT) has been developed in six different formulations. Eight-week-old Wistar rats were divided into nine groups and immunized as follows: the first group received the oral vaccine 1 consisting of the three antigens (LPS, rTcpA and H-CT) associated with a liposome (L) and bacterial CpG-DNA (ODN#1826). The rats of groups 2 and 3 received oral vaccines 2 and 3 consisting of the liposome-associated three antigens with and without non-bacterial CpG-DNA (ODN#1982), respectively. Rats of groups 4 received oral vaccine 4 consisting of the three antigens mixed with the ODN#1826, similar to vaccine 1, but without liposome. Rats of groups 5 and 6 received oral vaccines 5 and 6 consisting of the three antigens with and without ODN#1982, respectively, similar to vaccines 2 and 3, but without liposome. Rats of groups 7, 8 and 9 received oral placebos, namely liposomes (L), ODN#1826 (CpG), and vaccine diluent, i.e. 5% NaHCO3 solution, respectively. All vaccines were given in three doses at 14-day intervals. It was found that the combination of liposome and ODN#1826 in vaccine 1 evoked the highest immune response to V. cholerae antigen compared to other vaccine formulations and placebos, as measured by the appearance of antigen-specific antibody-producing cells in the intestinal lamina propria. The immunogenicity according to the magnitude of the immune response was: V1>V2=V3>V4>V5=V6>V7=V8=V9. The results of this study indicate that CpG-DNA and liposome are effective mucosal adjuvants for an oral cholera vaccine prepared from refined V. cholerae antigens and their combination seems to be synergistic. The potential role of liposome as a vaccine delivery vehicle has been confirmed.

Evaluation of the protective efficacy of Vibrio cholerae ghost (VCG) candidate vaccines in rabbits

An effective Vibrio cholerae vaccine is needed to reduce the morbidity and mortality caused by this pathogen. Despite the availability of current oral vaccines with measurable efficacy, there is need for more effective vaccines with broad-spectrum efficacy in target populations. Recent studies have shown that bacterial ghosts, produced by the expression of cloned lysis gene E, possess adjuvant properties and are immunogenic. In this study, ghosts were prepared from V. cholerae O1 or O139 and evaluated as vaccines in the reversible intestinal tie adult rabbit diarrhea (RITARD) model. Rabbits were orally immunized with different doses of V. cholerae ghost (VCG) formulations. The vaccine formulations elicited high levels of serum vibriocidal titers against indicator strains. The magnitude of the response was measured as the geometric mean titer (GMT) increase for all rabbits in relation to prevaccination titers. The induction of cross protection was evidenced by the ability of serum from VCG-immunized rabbits to mediate complement-dependent killing of both the homologous and the heterologous strains. Immunized rabbits were protected against intraduodenal challenge 30 days after primary immunization. Protective immunity against challenge appeared to be dose dependent and was associated with marked inhibition of colonization. These results indicate that VCGs represent a novel approach to cholera vaccine development and constitute an effective vaccine delivery vehicle.

Intestinal and systemic immune responses to an oral cholera toxoid B subunit whole-cell vaccine administered during zinc supplementation

Zinc plays a critical role in the normal functioning of the immune system. We investigated whether zinc sulfate administered orally to adult zinc-replete volunteers modulates systemic and intestinal immune responses to an oral killed cholera toxoid B subunit (CTB) whole-cell cholera vaccine. The 30 participants were immunized twice, with a 17-day interval. The vaccinees in the intervention group ingested 45 mg of elemental zinc thrice daily for 9 days starting 2 days before each vaccine dose. The median serum anti-CTB immunoglobulin A (IgA) and IgG responses from day 0 to day 30, i.e. after two vaccine doses, were 13-fold lower (P value for identical distribution, <0.005) in the zinc-supplemented compared to the nonsupplemented vaccinees. The median serum vibriocidal responses from baseline to after one (day 0 to day 17) and two (day 0 to day 30) vaccine doses were at least sixfold (P = 0.033) and fourfold (P = 0.091) higher, while the median fecal anti-CTB IgA response after two doses was estimated to be fourfold higher (P = 0.084) in the zinc-supplemented vaccinees. These observations show that zinc reduces the antitoxin and may enhance the antibacterial responses in serum. Zinc may also improve the intestinal antitoxin immune response. Oral zinc administration has the potential to modify critical immune responses to antigens applied to mucosal surfaces.