Intransal or intragastric immunization with proteosome-Shigella lipopolysaccharide vaccines protects against lethal pneumonia in a murine model of Shigella infection

Development of the Shigella flexneri 2a, 3a, 6, and S. sonnei artificial Invaplex (InvaplexAR) vaccines

The Shigella artificial invasin complex (InvaplexAR) vaccine is a subunit approach that effectively induces robust immunogenicity directed to serotype-specific lipopolysaccharide and the broadly conserved IpaB and IpaC proteins. One advantage of the vaccine approach is the ability to adjust the constituents to address suboptimal immunogenicity and to change the Shigella serotype targeted by the vaccine. As the vaccine moves through the product development pipeline, substantial modifications have been made to address manufacturing feasibility, acceptability to regulatory authorities, and developing immunogenic and effective products for an expanded list of Shigella serotypes. Modifications of the recombinant clones used to express affinity tag-free proteins using well-established purification methods, changes to detergents utilized in the assembly process, and in vitro and in vivo evaluation of different Invaplex formulations have led to the establishment of a scalable, reproducible manufacturing process and enhanced immunogenicity of Invaplex products designed to protect against four of the most predominant Shigella serotypes responsible for global morbidity and mortality. These adjustments and improvements provide the pathway for the manufacture and clinical testing of a multivalent Invaplex vaccine. IMPORTANCE Shigella species are a major global health concern that cause severe diarrhea and dysentery in children and travelers to endemic areas of the world. Despite significant advancements in access to clean water, the increases in antimicrobial resistance and the risk of post-infection sequelae, including cognitive and physical stunting in children, highlight the urgent need for an efficacious vaccine. One promising vaccine approach, artificial Invaplex, delivers key antigens recognized by the immune system during infection, which results in increased resistance to re-infection. The work presented here describes novel modifications to a previously described vaccine approach resulting in improved methods for manufacturing and regulatory approvals, expansion of the breadth of coverage to all major Shigella serotypes, and an increase in the potency of artificial Invaplex.

Intranasal immunization with a proteosome-adjuvanted SARS-CoV-2 spike protein-based vaccine is immunogenic and efficacious in mice and hamsters

With the persistence of the SARS-CoV-2 pandemic and the emergence of novel variants, the development of novel vaccine formulations with enhanced immunogenicity profiles could help reduce disease burden in the future. Intranasally delivered vaccines offer a new modality to prevent SARS-CoV-2 infections through the induction of protective immune responses at the mucosal surface where viral entry occurs. Herein, we evaluated a novel protein subunit vaccine formulation containing a resistin-trimerized prefusion Spike antigen (SmT1v3) and a proteosome-based mucosal adjuvant (BDX301) formulated to enable intranasal immunization. In mice, the formulation induced robust antigen-specific IgG and IgA titers, in the blood and lungs, respectively. In addition, the formulations were highly efficacious in a hamster challenge model, reducing viral load and body weight loss. In both models, the serum antibodies had strong neutralizing activity, preventing the cellular binding of the viral Spike protein based on the ancestral reference strain, the Beta (B.1.351) and Delta (B.1.617.2) variants of concern. As such, this intranasal vaccine formulation warrants further development as a novel SARS-CoV-2 vaccine.

From Concept to Clinical Product: A Brief History of the Novel Shigella Invaplex Vaccine’s Refinement and Evolution

The Shigella invasin complex or Invaplex vaccine is a unique subunit approach to generate a protective immune response. Invaplex is a large, macromolecular complex consisting of the major Shigella antigens: lipopolysaccharide (LPS) and the invasion plasmid antigen (Ipa) proteins B and C. Over the past several decades, the vaccine has progressed from initial observations through pre-clinical studies to cGMP manufacture and clinical evaluations. The Invaplex product maintains unique biological properties associated with the invasiveness of virulent shigellae and also presents both serotype-specific epitopes, as well as highly conserved invasin protein epitopes, to the immunized host. The vaccine product has evolved from a native product isolated from wild-type shigellae (native Invaplex) to a more defined vaccine produced from purified LPS and recombinant IpaB and IpaC (artificial Invaplex). Each successive “generation” of the vaccine is derived from earlier versions, resulting in improved immunogenicity, homogeneity and effectiveness. The current vaccine, detoxified artificial Invaplex (Invaplex_AR-Detox), was developed for parenteral administration by incorporating LPS with under-acylated lipid A. Invaplex_AR-Detox has demonstrated an excellent safety and immunogenicity profile in initial clinical studies and is advancing toward evaluations in the target populations of children and travelers to endemic countries.

Potential adjuvants for the development of a SARS-CoV-2 vaccine based on experimental results from similar coronaviruses

The extensive efforts around the globe are being made to develop a suitable vaccine against COVID-19 (Coronavirus Disease-19) caused by SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus-2). An effective vaccine should be able to induce high titers of neutralizing antibodies to prevent the virus from attaching to the host cell receptors. However, to elicit the protective levels of antibodies, a vaccine may require multiple doses or assistance from other immunostimulatory molecules. Further, the vaccine should be able to induce protective levels of antibodies rapidly with the least amount of antigen used. This decreases the cost of a vaccine and makes it affordable. As the pandemic has hit most countries across the globe, there will be an overwhelming demand for the vaccine in a quick time. Incorporating a suitable adjuvant in a SARS-CoV-2 vaccine may address these requirements. This review paper will discuss the experimental results of the adjuvanted vaccine studies with similar coronaviruses (CoVs) which might be useful to select an appropriate adjuvant for a vaccine against rapidly emergingSARS-CoV-2. We also discuss the current progress in the development of adjuvanted vaccines against the disease.

The Galleria mellonella larvae as an in vivo model for evaluation of Shigella virulence

Shigella spp. causing bacterial diarrhea and dysentery are human enteroinvasive bacterial pathogens that are orally transmitted through contaminated food and water and cause bacillary dysentery. Although natural Shigella infections are restricted to humans and primates, several smaller animal models are used to analyze individual steps in pathogenesis. No animal model fully duplicates the human response and sustaining the models requires expensive animals, costly maintenance of animal facilities, veterinary services and approved animal protocols. This study proposes the development of the caterpillar larvae of Galleria mellonella as a simple, inexpensive, informative, and rapid in-vivo model for evaluating virulence and the interaction of Shigella with cells of the insect innate immunity. Virulent Shigella injected through the forelegs causes larvae death. The mortality rates were dependent on the Shigella strain, the infectious dose, and the presence of the virulence plasmid. Wild-type S. flexneri 2a, persisted and replicated within the larvae, resulting in haemocyte cell death, whereas plasmid-cured mutants were rapidly cleared. Histology of the infected larvae in conjunction with fluorescence, immunofluorescence, and transmission electron microscopy indicate that S. flexneri reside within a vacuole of the insect haemocytes that ultrastructurally resembles vacuoles described in studies with mouse and human macrophage cell lines. Some of these bacteria-laden vacuoles had double-membranes characteristic of autophagosomes. These results suggest that G. mellonella larvae can be used as an easy-to-use animal model to understand Shigella pathogenesis that requires none of the time and labor-consuming procedures typical of other systems.

Shigellosis murine model established by intraperitoneal and intranasal route of administration: a comparative comprehension overview

Shigellosis, a major cause of mortality and morbidity, requires development of effective intervention strategy for which animal model mimicking human pathology is essential. Among various animal models for shigellosis, mice being more convenient have been used wherein intraperitoneal and intranasal routes are preferred. With the aim to comprehend the comparative pathophysiological indicators, we have examined relatively high and low dose of Shigella flexneri administered through intraperitoneal and intranasal routes in mice. Characterization of these two models along with the resulting pathophysiology of shigellosis adds to our understanding and offers suitable models appropriate to the objectives of the study.

Shigella IpaB and IpaD displayed on L. lactis bacterium-like particles induce protective immunity in adult and infant mice

Shigella spp. are among the enteric pathogens with the highest attributable incidence of moderate-to-severe diarrhea in children under 5 years of age living in endemic areas. There are no vaccines available to prevent this disease. In this work, we investigated a new Shigella vaccine concept consisting of non-living, self-adjuvanted, Lactococcus lactis bacterium-like particles (BLP) displaying Shigella invasion plasmid antigen (Ipa) B and IpaD and examined its immunogenicity and protective efficacy in adult and newborn/infant mice immunized via the nasal route. Unique advantages of this approach include the potential for broad protection due to the highly conserved structure of the Ipas and the safety and practicality of a probiotic-based mucosal/adjuvant delivery platform. Immunization of adult mice with BLP-IpaB and BLP-IpaD (BLP-IpaB/D) induced high levels of Ipa-specific serum IgG and stool IgA in a dose-dependent manner. Immune responses and protection were enhanced by BLP delivery. Vaccine-induced serum antibodies exhibited opsonophagocytic and cytotoxic neutralizing activity, and IpaB/D IgG titers correlated with increased survival post-challenge. Ipa-specific antibody secreting cells were detected in nasal tissue and lungs, as well as IgG in bronchoalveolar lavage. Bone marrow cells produced IpaB/D-specific antibodies and contributed to protection after adoptive transfer. The BLP-IpaB/D vaccine conferred 90% and 80% protection against S. flexneri and S. sonnei, respectively. Mice immunized with BLP-IpaB/D as newborns also developed IpaB and IpaD serum antibodies; 90% were protected against S. flexneri and 44% against S. sonnei. The BLP-IpaB/D vaccine is a promising candidate for safe, practical and potentially effective immunization of children against shigellosis.

Gut-Homing Conventional Plasmablasts and CD27(-) Plasmablasts Elicited after a Short Time of Exposure to an Oral Live-Attenuated Shigella Vaccine Candidate in Humans

Currently, there is no licensed Shigella vaccine; however, various promising live-attenuated vaccine candidates have emerged, including CVD1208S (ΔguaBA, Δset, Δsen S. flexneri 2a), which was shown to be safe and immunogenic in Phase 1 clinical trials. Here, we report the immune responses elicited in an outpatient Phase 2 clinical trial in which subjects were vaccinated with CVD 1208S. Oral immunization with CVD 1208S elicited high anti-S. flexneri 2a LPS and IpaB antibody responses as well as an acute plasmablast (PB) infiltration in peripheral blood 7 days after immunization. PB sorted based on their expression of homing molecules confirmed that cells expressing integrin α4β7 alone or in combination with CD62L were responsible for antibody production (as measured by ELISpot). Furthermore, using high-color flow-cytometry, on day 7 after immunization, we observed the appearance of conventional PB (CPB, CD19^dim CD20⁻ CD27^+high CD38^+high CD3⁻), as well as a PB population that did not express CD27 (CD27⁻ PB; pre-plasmablasts). The pattern of individual or simultaneous expression of homing markers (integrin α4β7, CD62L, CXCR3, and CXCR4) suggested that CPB cells homed preferentially to the inflamed gut mucosa. In contrast, ~50% CD27⁻ PB cells appear to home to yet to be identified peripheral lymphoid organs or were in a transition state preceding integrin α4β7 upregulation. In sum, these observations demonstrate that strong immune responses, including distinct PB subsets with the potential to home to the gut and other secondary lymphoid organs, can be elicited after a short time of exposure to a shigella oral vaccine.

The route less taken: pulmonary models of enteric Gram-negative infection

Many pathogens are capable of causing a fulminant infection in pulmonary tissues of mammals. Animal models have provided an extensive understanding of the genetic and molecular mechanisms of bacterial pathogenesis as well as host immune response in the lungs. Many clinically relevant Gram-negative bacteria are host-restricted. Thus, the powerful, informative tools of mouse models are not available for study with these organisms. However, over the past 30 years, enterprising work has demonstrated the utility of pulmonary infection with enteric pathogens. Such infection models have increased our understanding host-pathogen interactions in these organisms. Here, we provide a review and comparison of lung models of infection with enteric, Gram-negative bacteria relative to naturally occurring lung pathogens.

Immunologic characterization of a novel inactivated nasal mumps virus vaccine adjuvanted with Protollin

An inactivated, mucosal mumps virus (MuV) vaccine would address many of the problems associated with current live-attenuated formulations. Protollin (Prl)-based adjuvants (containing TLR2 and TLR4 ligands) are well-suited for nasal administration. We sought to develop an inactivated whole-virus nasal vaccine for MuV using the Prl adjuvant/delivery vehicle and to test tolerability and immunogenicity in a mouse model. BALB/c mice exhibited signs of transient reactogenicity (hunched posture, erect fur, weight loss ≤10% of total body weight) following administration of intranasal MuV-Prl vaccines, though most of these manifestations resolved within 24h. Compared to high-dose unadjuvanted vaccine (8μgMuV), administration of high-dose adjuvanted formulation (8μgMuV-Prl) induced greater MuV-specific serum IgG (3.26E6ng/mL vs. 2.2E5ng/mL, 8μgMuV-Prl vs. 8μgMuV, p<0.001) and mucosal IgA (128ng/mL vs. 45ng/mL, 8μgMuV-Prl vs. 8μgMuV, p<0.05). Serum IgG isotypes and splenocyte cytokine secretion induced by MuV-Prl suggested a predominant T helper cell (Th)1-type immune response. This response was characterized by: (1) ≥four-fold increase of IgG2a levels compared to IgG1; and (2) high IL-2 (644pg/mL)/IFN-γ (228pg/mL) and low IL-5 (31pg/mL) secretion in MuV-restimulated splenocytes from animals receiving MuV-Prl formulations. MuV-Prl vaccination induced higher levels of serum antibodies capable of neutralizing MuV in vitro than MuV alone, particularly for high-dose 8μg formulations (357 neutralizing units (NU)/mL vs. 32NU/mL, 8μgMuV-Prl vs. 8μgMuV, p<0.001). Thus, nasal MuV-Prl vaccines are fairly well-tolerated and highly immunogenic in mice.

Recent progress towards development of a Shigella vaccine

The burden of dysentery due to shigellosis among children in the developing world is still a major concern. A safe and efficacious vaccine against this disease is a priority, since no licensed vaccine is available. This review provides an update of vaccine achievements focusing on subunit vaccine strategies and the forthcoming strategies surrounding this approach. In particular, this review explores several aspects of the pathogenesis of shigellosis and the elicited immune response as being the basis of vaccine requirements. The use of appropriate Shigella antigens, together with the right adjuvants, may offer safety, efficacy and more convenient delivery methods for massive worldwide vaccination campaigns.

Evaluation of virulent and live Shigella sonnei vaccine candidates in a gnotobiotic piglet model

Newborn gnotobiotic (GB) piglets given virulent Shigella orally develop many of the clinical symptoms and gastrointestinal (GI) manifestations that mimic human shigellosis. Shigella sonnei virulent strain Moseley, a mutant ShET2-1,2, lacking enterotoxin SenA and its paralog SenB, and vaccine candidates WRSS1 and WRSs3 were evaluated in this model for rates of diarrhea, colonization and other GI symptoms and pathology. Moseley-infected piglets developed diarrhea from 1 to 7 days, with the highest rates seen on days 2-4 after inoculation. In contrast, WRSs3-infected piglets did not have diarrhea over the entire experimental period. Compared to the Moseley group, lower diarrheal rates were observed in the double enterotoxin mutant and significantly lower in the WRSS1 group. Moseley infection also caused marked mucosal damage in the GI tissues at PID1 to PID8, and induced predominantly proinflammatory cytokine secretion. IL-8 and to a lesser extent IL-6 and IL-1β were observed early after inoculation and IL-12 secretion could be measured till late in infection. The ShET2-1,2 mutant, WRSS1 and WRSs3 also colonized the GI tract in a manner similar to Moseley; however, both vaccine candidates developed milder histopathological indices and cytokine responses. WRSs3-infected animals showed the least pathology. Furthermore, unlike the other strains, WRSs3 was rarely detected in organs outside the gastrointestinal tract. These results support the development of the GB piglet model as a sensitive in vivo oral model for the evaluation of virulence of different Shigella strains which could be applied to other oral vaccine candidates.

Effects of different adjuvants in the context of intramuscular and intranasal routes on humoral and cellular immune responses induced by detergent-split A/H3N2 influenza vaccines in mice

Influenza A/H3N2 viruses have caused the most severe epidemics since 1968 despite current immunization programs with inactivated vaccines. We undertook a side-by-side preclinical evaluation of different adjuvants (Alum, AS03, and Protollin) and routes of administration (intramuscular [i.m.] and intranasal [i.n.]) for assessing their effect on the immunogenicity and cross-reactivity of inactivated split vaccines (A/H3N2/New York/55/2004). Humoral and T cell-mediated immune responses against the homologous virus and a heterologous drifted strain (A/H3N2/Wisconsin/67/2005) were measured in BALB/c mice at 2, 6, and 19 weeks postboost. The AS03- and Alum-adjuvanted i.m. vaccines induced at least an 8-fold increase over the nonadjuvanted vaccine in functional antibody titers against both the homotypic and heterotypic strains and low IgG2a and high IgG1 levels, suggesting a mixed Th1/Th2 response with a Th2 trend. The Protollin-adjuvanted i.n. vaccine induced the lowest IgG1/IgG2a ratio, which is indicative of a mixed Th1/Th2-type profile with a Th1 trend. This adjuvanted vaccine was the only vaccine to stimulate a mucosal IgA response. Whatever the timing after the boost, both hemagglutination inhibition (HAI) and microneutralization (MN) titers were higher with the AS03-adjuvanted i.m. vaccine than with the protollin-adjuvanted i.n. vaccine. Finally, the Alum-adjuvanted i.m. vaccine and the lower-dose Protollin-adjuvanted i.n. vaccine elicited significantly higher CD4(+) Th1 and Th2 responses and more gamma interferon (IFN-γ)-producing CD8(+) T cells than the nonadjuvanted vaccine. Our data indicate that the adjuvanted vaccines tested in this study can elicit stronger, more persistent, and broader immune responses against A/H3N2 strains than nonadjuvanted inactivated influenza vaccines.

Mucosal immunization with Shigella flexneri outer membrane vesicles induced protection in mice

Vaccination appears to be the only rational prophylactic approach to control shigellosis. Unfortunately, there is still no safe and efficacious vaccine available. We investigated the protection conferred by a new vaccine containing outer membrane vesicles (OMVs) from Shigella flexneri with an adjuvant based on nanoparticles in an experimental model of shigellosis in mice. OMVs were encapsulated in poly(anhydride) nanoparticles prepared by a solvent displacement method with the copolymer PMV/MA. OMVs loaded into NPs (NP-OMVs) were homogeneous and spherical in shape, with a size of 197nm (PdI=0.06). BALB/c mice (females, 9-week-old, 20±1g) were immunized by intradermal, nasal, ocular (20μg) or oral route (100μg) with free or encapsulated OMV. Thirty-five days after administration, mice were infected intranasally with a lethal dose of S. flexneri (1×10(7)CFU). The new vaccine was able to protect fully against infection when it was administered via mucosa. By intradermal route the NP-OMVs formulation increased the protection from 20%, obtained with free extract, to 100%. Interestingly, both OMVs and OMV-NP induced full protection when administered by the nasal and conjuntival route. A strong association between the ratio of IL-12p40/IL-10 and protection was found. Moreover, low levels of IFN-γ correlate with protection. Under the experimental conditions used, the adjuvant did not induce any adverse effects. These results place OMVs among promising candidates to be used for vaccination against Shigellosis.

Outer membrane protein A (OmpA) of Shigella flexneri 2a, induces protective immune response in a mouse model

Background

In our earlier studies 34 kDa outer membrane protein (OMP) of Shigella flexneri 2a has been identified as an efficient immunostimulant.

Key Results

In the present study MALDI-TOF MS analysis of the purified 34 kDa OMP of Shigella flexneri 2a shows considerable sequence homology (Identity 65%) with the OmpA of S. flexneri 2a. By using the specific primers, the gene of interest has been amplified from S. flexneri 2a (N.Y-962/92) genomic DNA, cloned in pET100/D-TOPO® vector and expressed using induction with isopropyl thiogalactoside (IPTG) for the first time. Immunogenicity and protective efficacy of the recombinant OmpA has been evaluated in an intranasally immunized murine pulmonary model. The recombinant protein induces significantly enhanced protein specific IgG and IgA Abs in both mucosal and systemic compartments and IgA secreting cells in the systemic compartment (spleen). The mice immunized with OmpA have been protected completely from systemic challenge with a lethal dose of virulent S. flexneri 2a. Immunization with the protein causes mild polymorphonuclear neutrophil infiltration in the lung, without inducing the release of large amounts of proinflammatory cytokines.

Conclusion

These results suggest that the OmpA of S. flexneri 2a can be an efficacious mucosal immunogen inducing protective immune responses. Our findings also demonstrate that antibodies and Th1 immune response may be associated with the marked protective efficacy of immunized mice after intranasal shigellae infection.

Development of a new guinea-pig model of shigellosis

Shigellosis is a major form of bacillary dysentery caused by Shigella spp. To date, there is no suitable animal model to evaluate the protective efficacy of vaccine candidates against this pathogen. Here, we describe a successful experimental shigellosis in the guinea-pig model, which has shown the characteristic features of human shigellosis. This model yielded reproducible results without any preparatory treatment besides cecal ligation. In this study, guinea-pigs were discretely infected with virulent Shigella dysenteriae type 1 and Shigella flexneri type 2a into the cecocolic junction after ligation of the distal cecum. All the experimental animals lost ∼10% of their body weight and developed typical dysentery within 24-h postinfection. In the histological analysis, distal colon showed edema, hemorrhage, exudation and inflammatory infiltrations in the lamina propria. Orally immunized animals with heat-killed S. dysenteriae type 1 and S. flexneri type 2a strains showed high levels of serum immunoglobulin G (IgG) and mucosal IgA antibodies and conferred significant homologous protective immunity against subsequent challenges with the live strains. The direct administration of shigellae into the cecocolic junction induces acute inflammation, making this animal model useful for assessing shigellosis and evaluating the protective immunity of Shigella vaccine candidates.

Inactivated and subunit vaccines to prevent shigellosis

Shigellosis remains a formidable disease globally, with children of the developing world bearing the greatest number of infections. The need for an affordable, safe and efficacious vaccine has persisted for decades. Vaccines to prevent shigellosis can be divided into living and nonliving approaches. Several nonliving Shigella vaccines are currently at different stages of development and show substantial promise. Outlined here is an overview of multiple nonliving vaccine technologies, highlighting their current status and recent advances in testing. In addition, gaps in the knowledge base regarding immune mechanisms of protection are explored.

A challenge model for Shigella dysenteriae 1 in cynomolgus monkeys (Macaca fascicularis)

Shigella dysenteriae type 1 can cause devastating pandemics with high case fatality rates; a vaccine for Shigella is unavailable currently. Because of the risks associated with performing challenge studies with wild-type S. dysenteriae 1 in human clinical trials to advance vaccine development, an improved nonhuman primate model is needed urgently. In the present study, cynomolgus macaques (Macaca fascicularis) were challenged with various doses of S. dysenteriae 1 strain 1617 to establish a dose that would produce shigellosis. Further, different routes of delivery of S. dysenteriae 1 were compared to establish the most appropriate route for infection. Animals receiving 10(11) cfu S. dysenteriae 1 intragastrically consistently developed signs of shigellosis characterized by the onset of diarrhea and dysentery within 2 to 3 d. Administration of as many as 10(9) cfu S. dysenteriae 1 intraduodenally did not elicit signs characteristic of infection in macaques despite fecal shedding of bacteria for as long as 10 d. S. dysenteriae 1 administered intraduodenally at 10(9) cfu or intragastrically at 10(11) cfu elicited robust IgG and IgA antibody responses to LPS. We have developed a reliable challenge model of infection with wild-type S. dysenteriae 1 in cynomolgus macaques that reproducibly induces disease and elicits robust immune responses. We believe that this animal model may provide unique insights into the immunologic mechanisms of protection to S. dysenteriae 1 infection and in advancing development of a vaccine against shigellosis.

Shigellosis: the current status of vaccine development

PURPOSE OF REVIEW

Shigellosis, a major form of bacillary dysentery, is caused by infection with Shigella organisms. In poor countries, Shigella-caused dysentery is endemic and causes an estimated 163 million illness episodes annually and more than one million deaths. Although several strategies have been used to develop vaccines targeting shigellosis, none has been licensed for use outside China. Owing to the wide range of Shigella serotypes and subtypes, there is a need for a multivalent vaccine representing prevalent species and serotypes.

RECENT FINDINGS

Vaccine development has been limited by the lack of a suitable animal model for vaccine testing. This review discusses the most advanced strategies for Shigella vaccine development including live attenuated, conjugate, broad spectrum, and proteosome-based vaccines and describes current animal models under study.

SUMMARY

The greatest barrier to the use of vaccine against shigellosis in developing areas is poor immune responses to oral vaccines in children who have minimal maternal antibodies. Clinical studies of promising shigellosis vaccine candidates are urgently needed after confirmation of safety, immunogenicity, and protection in volunteer challenge models.

A proteoliposome based formulation administered by the nasal route produces vibriocidal antibodies against El Tor Ogawa Vibrio cholerae O1 in BALB/c mice

A vaccine candidate against the enteric pathogen Vibrio cholerae was developed based on a proteoliposome (PL) formulation using a wild type strain C7258, V. cholerae O1, El Tor Ogawa as part of strategy to develop a combined formulation against enteric diseases preventable by the stimulation of the mucosal immune system. A detergent extraction method was applied to obtain the PL. Scanning electron microscopy and molecular exclusion chromatography showed the presence of two PL populations. Photon correlation spectroscopy studies were then carried out to evaluate the size (169.27+/-3.85nm), polydispersity (0.410) and zeta potential (-23.28+/-1.21mV) of the PL. SDS-PAGE and Western blot analysis revealed the presence of lipopolysaccharide (LPS), mannose-sensitive haemagglutinin (MSHA) and a range of outer membrane proteins, including OmpU. BALB/c mice were immunized intranasally with two doses of PL containing 25mug of LPS each 28 days apart. The mice showed high anti-LPS IgG titres (3.36+/-0.235) and vibriocidal antibodies (3.70+/-0.23) after two weeks from last dose. These results show for the first time that PL can be obtained from V. cholerae O1 and when administer by intranasal route has the potential to protect against this pathogen.

Histopathological and ultrastructural studies of a mouse lung model of Campylobacter jejuni infection

Campylobacter jejuni is a major cause of diarrhoea in humans. However, the pathogenesis of C. jejuni diarrhoea is poorly understood due to the lack of a good animal model of infection. Many animals have been tried with limited success, but a mouse lung model of infection has been found to be satisfactory previously; however, the lung pathology of this model has not been studied. For the purpose of characterizing the histopathological and ultrastructural lesions in the lung of the mouse pulmonary model of C. jejuni infection, C. jejuni strain 81-176 or sterile PBS was intranasally inoculated into BALB/c mice. The infection resulted in a mild illness only, and in an initial predominance of polymorphonuclear cells, followed by the accumulation of macrophages and later the prominence of epithelioid cells. Focal peribronchial pneumonia appeared on day 3, granuloma-like reaction on day 4 and bronchopneumonia on day 5 post-infection. These features developed until day 5 post-infection, but were less consistent afterwards when histopathology was monitored up to 9 days post-infection. Intracellular structures resembling bacteria were observed on days 3 and 5 post-infection, but not on day 7 post-infection. On days 3 and 5 post-infection, degenerative changes were also observed by transmission electron microscopy. The histological changes were not associated with acid-fast bacteria or any fungal elements. The infection was systemic as C. jejuni was isolated from blood and all organ homogenates (lung, spleen, liver, and small and large intestines) at 24 h post-infection. Thereafter, the organism was recovered from the intestine only, thus indicating its predilection for this location. This characterization of pathology should contribute to a better understanding of the animal model and pathogenesis of C. jejuni infection.

Immunogenicity and efficacy of highly purified invasin complex vaccine from Shigella flexneri 2a

Development of a subunit vaccine for shigellosis requires identification of protective antigens and delivering these antigens in a manner that stimulates immunity comparable to that induced by natural infection. The Shigella invasin complex (Invaplex) vaccine is an ion-exchange-purified extract from virulent Shigella that consists of LPS and several other proteins, including the invasins IpaB and IpaC. Intranasal delivery of Invaplex stimulates protective immunity in small animal models for shigellosis. To identify the active component(s) of Invaplex responsible for its immunogenicity and efficacy, size-exclusion chromatography (SEC) was used to separate Invaplex into several different fractions. A high-molecular mass complex with a molecular mass between 669 MDa and 2 MDa consisted primarily of LPS, IpaB and IpaC and was considered to be a highly purified (HP) form of Invaplex. Using the mouse lung model to evaluate the immunogenicity and efficacy of the SEC fractions it was clearly demonstrated that the high-molecular mass complex of the invasins and LPS was responsible for the protective capacity of parent native Invaplex. Other smaller mass SEC fractions were mostly non-immunogenic and did not stimulate solid protection. In guinea pigs, the HP Invaplex stimulated an enhanced immune response as compared to the parent Invaplex and was fully protective. Isolation and characterization of the immunogenic and protective moiety within Invaplex will allow better standardization of the Invaplex product and may allow future development of an Invaplex assembled from purified components.

Intranasal Protollin-formulated recombinant SARS S-protein elicits respiratory and serum neutralizing antibodies and protection in mice

The feasibility of developing a prophylactic vaccine against SARS was assessed by comparing the immune responses elicited by immunizing mice with a recombinant SARS spike glycoprotein (S-protein) formulated with different adjuvants, given by different routes. In both young and aged mice, an intranasal Protollin-formulated S-protein vaccine elicited high levels of antigen-specific IgG in serum, comparable to those elicited by an intramuscular Alum-adsorbed S-protein vaccine. Serum antibodies were shown to be virus neutralizing. Intranasal immunization of young mice with the Protollin-formulated vaccine elicited significant levels of antigen-specific lung IgA in contrast to mice immunized with the intramuscular vaccine in which no antigen-specific lung IgA was detected. Following live virus challenge of aged mice, no virus was detected in the lungs of intranasally immunized mice, in contrast to intramuscularly immunized mice whose lung virus titers were comparable to those observed in control mice.

Immunogenicity and protective efficacy offered by a ribosomal-based vaccine from Shigella flexneri 2a

Shigellosis is a major form of bacillary dysentery caused by Shigella infection. Shigella ribosome-based vaccines (SRV), considered among the potent vaccine candidates, are composed of O-antigen and ribosome isolated from S. flexneri 2a. To investigate the immunogenicity and protective efficacy of SRV, mice were vaccinated with SRV via the intranasal (i.n.) route. Interestingly, robust levels of Shigella-derived LPS-specific IgG and IgA Abs and antibody-forming cells were elicited in systemic and mucosal compartments following two i.n. administrations of SRV. Groups of mice receiving i.n. SRV developed milder pulmonary pneumonia upon challenge with virulent S. flexneri 2a than did those receiving parenteral SRV. We further found that the MyD88-dependent TLR2 signal partially mediates SRV-induced mucosal immunity, with the exception of TLR4- and TLR5-governed innate immunity. Most importantly, polymeric immunoglobulin receptor knockout (pIgR-/-) mice, which lack secretory IgA Ab, were afforded less protective efficacy than were wild-type mice. It can be concluded then that SRV is immunogenic and provides protective efficacy in mice. It can also be surmised that a mucosal SRV vaccine would be particularly relevant in targeting shigellosis, which provokes inflammation in the human colon.

C57Bl/6 mice are protected from respiratory syncytial virus (RSV) challenge and IL-5 associated pulmonary eosinophilic infiltrates following intranasal immunization with Protollin-eRSV vaccine

The protective efficacy of an intranasal (IN) Protollin-eRSV vaccine has recently been demonstrated in the RSV-susceptible BALB/c mouse model. Here, we report the safety, immunogenicity and efficacy of Protollin-eRSV vaccine in the relatively resistant C57Bl/6 mouse model. C57Bl/6 mice immunized IN with either two or three doses of Protollin-eRSV produced significant systemic and mucosal RSV-specific antibodies. Mice immunized with the Protollin vaccine displayed polarized Th1 responses with augmented IFNgamma/IL-5 ratios in RSV-restimulated lung and spleen cell preparations compared with animals that received antigen alone. The Protollin-eRSV immunized C57Bl/6 mice were fully protected against challenge without eosinophilic pulmonary pathology observed in the animals immunized with the formalin-inactivated RSV vaccine. This new model will permit us to dissect the respective roles of the TLR2 and TLR4 ligands contained in the vaccine using TLR knock-out animals established on the C57Bl/6 background.

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

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

New Animal Model of Shigellosis in the Guinea Pig: Its Usefulness for Protective Efficacy Studies

It has been difficult to evaluate the protective efficacy of vaccine candidates against shigellosis, a major form of bacillary dysentery caused by Shigella spp. infection, because of the lack of suitable animal models. To develop a proper animal model representing human bacillary dysentery, guinea pigs were challenged with virulent Shigella flexneri serotype 2a (strains 2457T or YSH6000) or S. flexneri 5a (strain M90T) by the intrarectal (i.r.) route. Interestingly, all guinea pigs administered these Shigella strains developed severe and acute rectocolitis. They lost approximately 20% of their body weight and developed tenesmus by 24 h after Shigella infection. Shigella invasion and colonization of the distal colon were seen at 24 h but disappeared by 48 h following i.r. infection. Histopathological approaches demonstrated significant damage and destruction of mucosal and submucosal layers, thickened intestinal wall, edema, erosion, infiltration of neutrophils, and depletion of goblet cells in the distal colon. Furthermore, robust expression of IL-8, IL-1beta, and inducible NO synthase mRNA was detected in the colon from 6 to 24 h following Shigella infection. Most importantly, in our new shigellosis model, guinea pigs vaccinated with an attenuated S. flexneri 2a SC602 strain possessing high levels of mucosal IgA Abs showed milder symptoms of bacillary dysentery than did animals receiving PBS alone after Shigella infection. In the guinea pig, administration of Shigella by i.r. route induces acute inflammation, making this animal model useful for assessing the protective efficacy of Shigella vaccine candidates.

Intranasal inoculation of mice with Yersinia pseudotuberculosis causes a lethal lung infection that is dependent on Yersinia outer proteins and PhoP

Yersinia pseudotuberculosis infects many mammals and birds including humans, livestock, and wild rodents and can be recovered from the lungs of infected animals. To determine the Y. pseudotuberculosis factors important for growth during lung infection, we developed an intranasal model of infection in mice. Following intranasal inoculation, we monitored both bacterial growth in lungs and dissemination to systemic tissues. Intranasal inoculation with as few as 18 CFU of Y. pseudotuberculosis caused a lethal lung infection in some mice. Over the course of 7 days, wild-type Y. pseudotuberculosis replicated to nearly 1 x 10(8) CFU/g of lung in BALB/c mice, induced histopathology in lungs consistent with pneumonia, but disseminated sporadically to other tissues. In contrast, a Delta yopB deletion strain was attenuated in this model, indicating that translocation of Yersinia outer proteins (Yops) is essential for virulence. Additionally, a Delta yopH null mutant failed to grow to wild-type levels by 4 days postintranasal inoculation, but deletions of any other single effector YOP did not attenuate lung colonization 4 days postinfection. Strains with deletions in yopH and any one of the other known effector yop genes were more attenuated that the Delta yopH strain, indicating a unique role for yopH in lungs. In summary, we have characterized the progression of a lung infection with an enteric Yersinia pathogen and shown that YopB and YopH are important in lung colonization and dissemination. Furthermore, this lung infection model with Y. pseudotuberculosis can be used to test potential therapeutics against Yersinia and other gram-negative infections in lungs.

Development and evaluation of a Shigella flexneri 2a and S. sonnei bivalent invasin complex (Invaplex) vaccine

Over 160 million cases of shigellosis occur annually worldwide, with the two most prevalent species being Shigella flexneri and S. sonnei. Protective immunity against Shigella infection is primarily directed at the lipopolysaccharide (LPS) of the homologous serotype, so it may be necessary to combine monovalent vaccines for multiple Shigella serotypes to construct a multivalent vaccine against predominant serotypes. Recently, we described a subcellular vaccine isolated from virulent S. flexneri, consisting of proteins (including the invasins IpaB and IpaC) and LPS, that protected mice and guinea pigs from homologous challenge. In the present study, a bivalent Invaplex vaccine consisting of S. flexneri 2a and S. sonnei Invaplex was used to intranasally immunize mice and guinea pigs to determine the bivalent vaccine's immunogenicity and protective capacity against challenge with either strain. Mice and guinea pigs immunized with the bivalent S. flexneri 2a/S. sonnei Invaplex vaccine produced serum IgA and IgG antibodies to S. flexneri LPS, S. sonnei LPS, the homologous Invaplex and the water extract antigens (invasins) as determined by ELISA. The immune responses in animals immunized with the bivalent vaccine were similar to responses in animals immunized with the monovalent Invaplex vaccines. Mice and guinea pigs immunized with the bivalent vaccine were protected from a lethal lung challenge (mice, P<0.001) or severe keratoconjunctivitis (guinea pigs, P< or = 0.002) after challenge with either S. flexneri 2a or S. sonnei. Animals immunized with monovalent Invaplex vaccines were protected (P<0.001) against the homologous agent at levels comparable to the bivalent vaccine. After challenge, immunized animals demonstrated boosts in antibody titers to LPS, water extract antigens and Invaplex. These studies indicate that the subcellular Invaplex vaccine will be readily adaptable to a multivalent vaccine approach for shigellosis.

A novel intranasal Protollin-based measles vaccine induces mucosal and systemic neutralizing antibody responses and cell-mediated immunity in mice

Protollin-MV is a vaccine produced by mixing split measles virus (MV) antigen with the novel adjuvant Protollin (Neisseria meningitidis outer membrane proteins non-covalently complexed with Shigella flexneri 2a lipopolysaccharide). Intranasal immunization of mice with two or three doses of Protollin-MV induces both serum IgG and mucosal IgA with strong neutralizing activity. There is a dose-dependent shift towards lower IgG1:IgG2a ratios and MV-specific IFNgamma production in splenocytes. Intranasal Protollin-MV can therefore induce systemic and mucosal neutralizing antibody responses as well as elicit a balanced TH1/TH2-type response.

Delivery of plant-derived vaccines

Many protein subunit vaccine candidates have been expressed in transgenic plants, and in a few cases the recombinant material has entered early phase clinical or target animal trials. The expressed protein can be purified prior to formulation for any preferred delivery approach. However, there are major cost advantages associated with avoiding protein purification and pursuing the oral delivery of a processed plant product containing the recombinant protein. Grains and dry products that are processed from fresh plant tissues can stably store expressed proteins for extended periods of time at room temperature, making refridgeration unnecessary during storage and distribution. Encapsulation of recombinant proteins in plant tissues guards against their rapid degradation in the gut, therefore facilitating the uptake and induction of appropriate immune responses. Early trial data with plant-based vaccine candidates has shown promising safety and efficacy.

Role of anti-CD3 in modulation of Th1-type immune response in Shigella dysenteriae infection

A murine model was used to evaluate the role of anti-CD3 in modulating a Th1-type response by restimulation of T-cells after immunization with the 57 kDa immunodominant antigen of Shigella dysenteriae 1 outer-membrane proteins (OMPs), followed by Shigella infection after immunization. To observe the effect of anti-CD3, other T-cell cultures were also established following anti-CD1, anti-IL2 and phytohaemagglutinin stimulation. Anti-CD3 stimulation of reconstituted T-cells showed 'mean' levels of CD4 and CD25 were enhanced by 34.5 and 31.1 % in immunized mice, which was comparable to 53.2 and 50.7 %, respectively, in challenged-immunized mice, and were dominant over CD8+ T-cells. Levels of IL2 generated by anti-CD3-stimulated T-cells of immunized mice were greater than those of unstimulated T-cells and were significantly elevated in challenged-immunized mice. The reactivity of T-cells indicated their complete responsiveness, as anti-CD3 antibody might not inhibit the migration of the macrophages but rather inhibit IL4. These macrophage factors synergistically act with anions towards an activated response, which in turn provokes IL2 secretion with a low degree of internalization of its receptor. Thus, sharing of IL2 to form a high-affinity receptor complex with CD4+ T-cells through motive signals suggested a generalized T-cell activation with increased humoral responses. Macrophage migration inhibition factor (MIF) and IL4 responses during anti-CD3 stimulation of immunized mice indicated that the role of anti-CD3 in generation of O2- is due to a synergistic effect by Th1 subsets of Th0 cells. The above findings should have implications for understanding the immunoregulatory role of anti-CD3 associated with 57 kDa antigen in immunoprophylactic measures.

Vaccines against Infections Caused by Salmonella, Shigella, and Pathogenic Escherichia coli

Infectious diseases represent one of the most common causes of death worldwide, with the enteropathogenic bacteria Salmonella and Shigella and pathogenic Escherichia coli being among the most detrimental. Currently, vaccination represents the preferred method of preventing such infections. For stimulating the adaptive immune response, immunizations are frequently based on formulations which include inactivated whole-cell vaccines, live attenuated vaccines, or subunit vaccines. These can be administered via a parenteral or mucosal route, the latter having the advantage that it most closely mimics the actual course of infection. In addition to the type of vaccine and method of application, important consideration needs to be paid to safety, efficacy, and cost, which are often major bottlenecks in the successful implementation of vaccines. In this chapter we take a limited look at the history surrounding vaccinations involving Salmonella, Shigella, and pathogenic E. coli. Salmonella infections, which can lead to typhoid fever, are becoming increasing difficult to treat with antibiotics due to multi-drug-resistant strains. At present, the parenteral Vi-based subunit vaccines and the live attenuated oral vaccine Ty21a have proven to be the vaccines of choice, with high levels of protective efficacy and limited side effects. Shigella infections are responsible for the diarrheal disease shigellosis. Various live and nonliving mucosal and parenteral vaccines have been tested, with the most promising candidates evolving around those that stimulate the production of O-antigen-specific antibodies. Pathogenic Escherichia coli infections can lead to severe diseases due to the bacterium's production of several specific toxins. Vaccines against this bacterium target its toxins, as well as surface-exposed antigens, all of which have been found to be effective as immunogens.

Role of 57 kDa major antigenic component of Shigella dysenteriae outer membrane proteins in induction of major histocompatibility complex II-restricted T-cell response

BACKGROUND

In the past, many Shigella surface antigens were used to activate both T and B lymphocytes but failed to induce antigen-specific responses in Shigellosis. Our objective was to identify in vitro T-cell components using 57 kDa major antigenic fraction of Shigella dysenteriae 1 (IPC-31) outer membrane proteins (OMPs) in modulating specific T-cell subset responses against Shigellosis.

METHODS

Antigen-specific T- and B-cell activation was studied in immunized Balb/c mice against 57 kDa antigen by proliferative responses using [3H]-thymidine incorporation and avidin-biotin complex (ABC) peroxidase staining for CD4, CD8, CD3, CD22, and CD25 followed by IL-2 and IL-4 estimation. Macrophage functional assays for migration inhibition factors (MIF) and superoxide (O2-) anions were also performed against 57 kDa antigen, whole OMPs, and phytohemagglutinin (PHA) stimulation.

RESULTS

Greater increase of lymphocyte proliferation was observed after 57 kDa antigen stimulation than post-OMP and -PHA stimulation. Proportionately, CD4+ and CD25+ expression of total CD3+ T-cells was significantly dominant (p >0.05) over CD8+ T-cells. On day 7 of this stimulation, it was found to increase % MIF and O2- anions with decrease of IL-2 leading to activation of MHC-II antigens. Later, on day 28 of immunization, IL-2 levels were more increased than on days 7 and 14 but insignificant with non-immunized mice stimulated with 57 kDa. Levels of IL-2 were also noted with low degree of internalization to its IL-2R receptors rather than to IL-4 receptors. In parallel, expression of CD22 was also recorded higher in this stimulation than in PHA, indicating a T-cell-dependent humoral response.

CONCLUSIONS

Our results suggested that 57 kDa major antigenic OMP is immunogenic for MHC II-restricted T-cell response to acquire host defense against Shigella infection.

Protollin™: a novel adjuvant for intranasal vaccines

Protollin is a novel adjuvant comprising Proteosomes non-covalently complexed with LPS. Intranasal immunization of mice with Protollin combined with detergent-split influenza antigens (HA) or recombinant influenza hemagglutinin (rHA) enhanced serum IgG and mucosal IgA levels by up to 250-fold compared with immunization with the antigens alone. IFN-gamma responses were also enhanced compared to the levels produced by splenocytes from mice immunized with antigen alone, while production of IL-5 was abrogated. Mice immunized with Protollin-rHA were completely protected against lethal challenge with influenza virus, demonstrating that Protollin is an effective mucosal adjuvant for prophylactic vaccines.

A nasal Proteosome influenza vaccine containing baculovirus-derived hemagglutinin induces protective mucosal and systemic immunity

The potential for enhancing the immunogenicity of recombinant (baculovirus-derived) influenza hemagglutinin (rHA) was investigated by comparing the immune responses elicited in mice by an intranasal (i.n.) rHA formulated with Proteosomes, with those induced by intramuscular (i.m.) or i.n. rHA alone. The Proteosome-rHA vaccine induced mucosal responses in the respiratory tract, as well as high serum IgG and hemagglutination inhibition (HAI) titers. In contrast, rHA alone given i.m. induced serum IgG without mucosal responses and was ineffective at inducing either mucosal or systemic responses when given i.n. Only mice immunized with the Proteosome-rHA vaccine were completely protected from both death and acute morbidity following live virus challenge, indicating that the i.n. Proteosome-rHA vaccine induced more complete protective immunity than the same doses of unformulated rHA given i.n. or i.m.

Lipid and carbohydrate based adjuvant/carriers in immunology

This review discusses various issues regarding vaccines; what are they and how they work, safety aspects, the role of adjuvants and carriers in vaccination, synthetic peptides as immunogens, and new technologies for vaccine development and delivery including the identification of novel adjuvants for mucosal vaccine delivery. There has been a recent increase of interest in the use of lipids and carbohydrates as adjuvants, and so a particular emphasis is placed on adjuvants derived from lipids or carbohydrates, or from both.

Plant-based vaccines

Plant systems are reviewed with regard to their ability to express and produce subunit vaccines. Examples of different types of expression systems producing a variety of vaccine candidates are illustrated. Many of these subunit vaccines have been purified and shown to elicit an immune response when injected into animal models. This review also includes vaccines that have been administered orally in a non-purified form as a food or feed product. Cases are highlighted which demonstrate that orally delivered plant-based vaccines can elicit immune responses and in some case studies, confer protection. Examples are used to illustrate some of the inherent advantages of a plant-based system, such as cost, ease of scale-up and convenience of delivery. Also, some of the key steps are identified that will be necessary to bring these new vaccines to the market.

Nasal immunization with subunit proteosome influenza vaccines induces serum HAI, mucosal IgA and protection against influenza challenge

The immunogenicity of a mucosally delivered subunit influenza vaccine was assessed in mice. Split influenza virus vaccine (sFlu) was formulated with proteosomes (Pr-sFlu), administered intranasally, and the induced immunity was compared with the responses elicited by sFlu alone given either intramuscularly or intranasally. Intranasal (i.n.) immunization with Pr-sFlu induced specific serum IgG and hemagglutination inhibition (HAI) titers comparable to or better than those induced by intramuscular (i.m.) sFlu, and in contrast to sFlu alone, i.n. Pr-sFlu also induced high levels of influenza-specific IgA in lung and nasal washes. Mice receiving i.n. Pr-sFlu were completely protected against live virus challenge, as were mice immunized by injection with sFlu alone. The i.n. Pr-sFlu elicited cytokine responses polarized towards a type 1 phenotype whereas those elicited by sFlu alone were of a mixed type 1/type 2 phenotype. The data strongly suggest that i.n. proteosome-formulated influenza antigens are highly effective and are excellent candidates for a non-invasive human vaccine.

Safety and immunogenicity of a proteosome-Shigella flexneri 2a lipopolysaccharide vaccine administered intranasally to healthy adults

We studied the safety and immunogenicity of a Shigella flexneri 2a vaccine comprising native S. flexneri 2a lipopolysaccharide (LPS) complexed to meningococcal outer membrane proteins-proteosomes-in normal, healthy adults. A two-dose series of immunizations was given by intranasal spray, and doses of 0.1, 0.4, 1.0, and 1.5 mg (based on protein) were studied in a dose-escalating design. The vaccine was generally well tolerated. The most common reactions included rhinorrhea and nasal stuffiness, which were clearly dose related (P < or = 0.05). These reactions were self-limited and generally mild. The vaccine elicited S. flexneri 2a LPS-specific immunoglobulin A (IgA), IgG, and IgM antibody-secreting cells (ASCs) in a dose-responsive manner. At doses of 1.0 or 1.5 mg, highly significant (P < 0.001) increases in ASCs of all antibody isotypes occurred and 95% of subjects had an ASC response in at least one antibody isotype. Dose-related serum antibody responses were observed, with geometric mean two- to fivefold rises in specific serum IgA and IgG titers and two- to threefold rises in IgM in the 1.0- and 1.5-mg-dose groups (P < 0.0001 for each isotype). Elevated serum antibody levels persisted through day 70. Increases in fecal IgG and IgA and also in urinary IgA specific for S. flexneri 2a LPS were demonstrated. These were most consistent and approached statistical significance (P = 0.02 to 0.12 for various measures) on day 70 after the first dose. The magnitude of immune responses to intranasally administered proteosome-S. flexneri 2a LPS vaccine is similar to those reported for live vaccine candidates associated with protective efficacy in human challenge models, and further evaluation of this product is warranted.

Attenuated Shigella flexneri 2a Delta guaBA strain CVD 1204 expressing enterotoxigenic Escherichia coli (ETEC) CS2 and CS3 fimbriae as a live mucosal vaccine against Shigella and ETEC infection

To construct a prototype hybrid vaccine against Shigella and enterotoxigenic Escherichia coli (ETEC), the genes encoding the production of ETEC CS2 and CS3 fimbriae were isolated and expressed in attenuated Shigella flexneri 2a guaBA strain CVD 1204. The CS2 cotA to -D genes, isolated from ETEC strain C91F, and the CS3 cstA to -H genes, subcloned from plasmid pCS100, were cloned into ~15-copy-number-stabilized pGA1 behind the osmotically regulated ompC promoter, resulting in high expression of both fimbriae. Under nonselective in vitro growth conditions, pGA1-CS2 and pGA1-CS3 were stable in CVD 1204, exhibiting a plasmid loss of only approximately 1% per duplication. Expression of CS2 and CS3 reduced the invasiveness of Shigella for HeLa cells and slowed the intracellular growth rate. Guinea pigs immunized intranasally with CVD 1204(pGA1-CS2) or CVD 1204(pGA1-CS3), or with a mixture of these strains, developed secretory immunoglobulin A (IgA) in tears and serum IgG antibodies against Shigella lipopolysaccharide, CS2, and CS3 antigens. Moreover, the animals were protected against keratoconjunctivitis following conjunctival challenge with virulent S. flexneri 2a strain 2457T. Animals immunized with Shigella expressing CS2 or CS3 developed serum antibodies that agglutinated Shigella as well as an ETEC strain bearing the homologous fimbriae, whereas animals immunized with combined CVD 1204(pGA1-CS2) and CVD 1204(pGA1-CS3) developed antibodies that agglutinated all three test strains. These observations support the feasibility of a multivalent vaccine against shigellosis and ETEC diarrhea consisting of multiple Shigella live vectors expressing relevant ETEC antigens.

Parameters underlying successful protection with live attenuated mutants in experimental shigellosis

Because the use of live attenuated mutants of Shigella spp. represents a promising approach to protection against bacillary dysentery (M. E. Etherridge, A. T. M. Shamsul Hoque, and D. A. Sack, Lab. Anim. Sci. 46:61-66, 1996), it becomes essential to rationalize this approach in animal models in order to optimize attenuation of virulence in the vaccine candidates, as well as their route and mode of administration, and to define the correlates of protection. In this study, we have compared three strains of Shigella flexneri 5--the wild-type M90T, an aroC mutant, and a double purE aroC mutant--for their pathogenicity, immunogenicity, and protective capacity. Protection against keratoconjunctivitis, induced by wild-type M90T, was used as the protection read out in guinea pigs that were inoculated either intranasally or intragastrically. Following intranasal immunization, the aroC mutant elicited weak nasal tissue destruction compared to M90T and achieved protection correlated with high levels of local anti-lipopolysaccharide immunoglobulin A (IgA), whereas the purE aroC double mutant, which also elicited weak tissue destruction, was not protective and elicited a low IgA response. Conversely, following intragastric immunization, only the M90T purE aroC double mutant elicited protection compared to both the aroC mutant and the wild-type strain. This mutant caused mild inflammatory destruction, particularly at the level of Peyer's patches, but it persisted much longer within the tissues. This could represent an essential parameter of the protective response that, in this case, did not clearly correlate with high anti-lipopolysaccharide IgA titers.

Isolation and characterization of a Shigella flexneri invasin complex subunit vaccine

The invasiveness and virulence of Shigella spp. are largely due to the expression of plasmid-encoded virulence factors, among which are the invasion plasmid antigens (Ipa proteins). After infection, the host immune response is directed primarily against lipopolysaccharide (LPS) and the virulence proteins (IpaB, IpaC, and IpaD). Recent observations have indicated that the Ipa proteins (IpaB, IpaC, and possibly IpaD) form a multiprotein complex capable of inducing the phagocytic event which internalizes the bacterium. We have isolated a complex of invasins and LPS from water-extractable antigens of virulent shigellae by ion-exchange chromatography. Western blot analysis of the complex indicates that all of the major virulence antigens of Shigella, including IpaB, IpaC, and IpaD, and LPS are components of this macromolecular complex. Mice or guinea pigs immunized intranasally with purified invasin complex (invaplex), without any additional adjuvant, mounted a significant immunoglobulin G (IgG) and IgA antibody response against the Shigella virulence antigens and LPS. The virulence-specific response was very similar to that previously noted in primates infected with shigellae. Guinea pigs (keratoconjunctivitis model) or mice (lethal lung model) immunized intranasally on days 0, 14, and 28 and challenged 3 weeks later with virulent shigellae were protected from disease (P<0.01 for both animal models).

Outer membrane vesicles from group B meningococci are strongly immunogenic when given intranasally to mice

Outer membrane vesicles (OMVs) from group B meningococci induced both serum and mucosal antibodies when given as a nasal and rectal vaccine to mice. Cholera toxin (CT) enhanced the antibody responses in serum both after nasal and rectal immunizations, and the mucosal responses after rectal immunizations only. Nasal immunizations, however, were most effective, with mucosal responses which were not dependent on the use of CT. The serum bactericidal activity was similarly not enhanced by CT, indicating that the positive effect of CT on the serum IgG level was not including bactericidal activity. A small nasal booster dose induced antibody responses in serum as far as eight months after intranasal and subcutaneous immunizations, and in saliva after intranasal immunizations. Nasal vaccines may thus be favorably combined with parenteral vaccines.