Expression of a Porphyromonas gingivalis hemagglutinin on the surface of a Salmonella vaccine vector

Comparison of the immune effects of the Chlamydia abortus MOMP antigen displayed in different parts of bacterial ghosts

Bacterial ghosts (BGs) are promising vaccine platforms owing to their high adjuvant properties and delivery efficiency. Heterologous antigens can be anchored to different parts of BGs using genetic engineering strategies to prepare vaccines. However, several key issues need to be resolved, including the efficient preparation of BGs and determining the optimal anchoring position of exogenous antigens in the BGs. Here, we prepared an efficient temperature-controlled lysis system using lysis gene E of phage PhiX174 and used the major outer membrane protein (MOMP) of Chlamydia abortus (C. abortus) as a model antigen to explore the optimal display location of exogenous antigens in BGs. We demonstrated that the constructed recombinant temperature-controlled lysis plasmid can still stably inhibit E gene expression at 37°C, and the lysis efficiency of E. coli can reach above 99.9%. Four recombinant MOMP Escherichia coli (E. coli) ghost vaccines were constructed using different anchor sequences. These vaccines all induced strong specific antibody responses and secrete high levels of IFN-γ in immunized mice and significantly increased the clearance of C. abortus in a mouse infection model. Notably, the strongest immune effect was observed when MOMP was displayed on the surface of E. coli ghosts (rECG-InpN-M), which resulted in the clearance of C. abortus in mice 6 days earlier than that with the recombinant MOMP vaccine. Altogether, we constructed an efficient BG temperature-controlled lysis system and provided a feasible strategy for developing a BG delivery platform with enhanced immune effects.

C500 variants conveying complete mucosal immunity against fatal infections of pigs with Salmonella enterica serovar Choleraesuis C78-1 or F18+ Shiga toxin-producing Escherichia coli

Salmonella enterica serovar Choleraesuis (S. Choleraesuis) C500 strain is a live, attenuated vaccine strain that has been used in China for over 40 years to prevent piglet paratyphoid. However, this vaccine is limited by its toxicity and does not offer protection against diseases caused by F18+ Shiga toxin-producing Escherichia coli (STEC), which accounts for substantial economic losses in the swine industry. We recently generated a less toxic derivative of C500 strain with both asd and crp deletion (S. Choleraesuis C520) and assessed its efficacy in mice. In addition, we demonstrate that C520 is also less toxic in pigs and is effective in protecting pigs against S. Choleraesuis when administered orally. To develop a vaccine with a broader range of protection, we prepared a variant of C520 (S. Choleraesuis C522), which expresses rSF, a fusion protein comprised of the fimbriae adhesin domain FedF and the Shiga toxin-producing IIe B domain antigen. For comparison, we also prepared a control vector strain (S. Choleraesuis C521). After oral vaccination of pigs, these strains contributed to persistent colonization of the intestinal mucosa and lymphoid tissues and elicited both cytokine expression and humoral immune responses. Furthermore, oral immunization with C522 elicited both S. Choleraesuis and rSF-specific immunoglobulin G (IgG) and IgA antibodies in the sera and gut mucosa, respectively. To further evaluate the feasibility and efficacy of these strains as mucosal delivery vectors via oral vaccination, we evaluated their protective efficacy against fatal infection with S. Choleraesuis C78-1, as well as the F18+ Shiga toxin-producing Escherichia coli field strain Ee, which elicits acute edema disease. C521 conferred complete protection against fatal infection with C78-1; and C522 conferred complete protection against fatal infection with both C78-1 and Ee. Our results suggest that C520, C521, and C522 are competent to provide complete mucosal immune protection against fatal infection with S. Choleraesuis in swine and that C522 equally qualifies as an oral vaccine vector for protection against F18+ Shiga toxin-producing Escherichia coli.

Mucosal Vaccination Against Periodontal Disease: Current Status and Opportunities

Approximately 9 out of 10 adults have some form of periodontal disease, an infection-induced inflammatory disease of the tooth-supporting tissues. The initial form, gingivitis, often remains asymptomatic, but this can evolve into periodontitis, which is typically associated with halitosis, oral pain or discomfort, and tooth loss. Furthermore, periodontitis may contribute to systemic disorders like cardiovascular disease and type 2 diabetes mellitus. Control options remain nonspecific, time-consuming, and costly; largely relying on the removal of dental plaque and calculus by mechanical debridement. However, while dental plaque bacteria trigger periodontal disease, it is the host-specific inflammatory response that acts as main driver of tissue destruction and disease progression. Therefore, periodontal disease control should aim to alter the host's inflammatory response as well as to reduce the bacterial triggers. Vaccines may provide a potent adjunct to mechanical debridement for periodontal disease prevention and treatment. However, the immunopathogenic complexity and polymicrobial aspect of PD appear to complicate the development of periodontal vaccines. Moreover, a successful periodontal vaccine should induce protective immunity in the oral cavity, which proves difficult with traditional vaccination methods. Recent advances in mucosal vaccination may bridge the gap in periodontal vaccine development. In this review, we offer a comprehensive overview of mucosal vaccination strategies to induce protective immunity in the oral cavity for periodontal disease control. Furthermore, we highlight the need for additional research with appropriate and clinically relevant animal models. Finally, we discuss several opportunities in periodontal vaccine development such as multivalency, vaccine formulations, and delivery systems.

Developing a Virus-Binding Bacterium Expressing Mx Protein on the Bacterial Surface to Prevent Grouper Nervous Necrosis Virus Infection

Grouper nervous necrosis virus (GNNV) infection causes mass grouper mortality, leading to substantial economic loss in Taiwan. Traditional methods of controlling GNNV infections involve the challenge of controlling disinfectant doses; low doses are ineffective, whereas high doses may cause environmental damage. Identifying potential methods to safely control GNNV infection to prevent viral outbreaks is essential. We engineered a virus-binding bacterium expressing a myxovirus resistance (Mx) protein on its surface for GNNV removal from phosphate-buffered saline (PBS), thus increasing the survival of grouper fin (GF-1) cells. We fused the grouper Mx protein (which recognizes and binds to the coat protein of GNNV) to the C-terminus of outer membrane lipoprotein A (lpp-Mx) and to the N-terminus of a bacterial autotransporter adhesin (Mx-AIDA); these constructs were expressed on the surfaces of Escherichia coli BL21 (BL21/lpp-Mx and BL21/Mx-AIDA). We examined bacterial surface expression capacity and GNNV binding activity through enzyme-linked immunosorbent assay; we also evaluated the GNNV removal efficacy of the bacteria and viral cytotoxicity after bacterial adsorption treatment. Although both constructs were successfully expressed, only BL21/lpp-Mx exhibited GNNV binding activity; BL21/lpp-Mx cells removed GNNV and protected GF-1 cells from GNNV infection more efficiently. Moreover, salinity affected the GNNV removal efficacy of BL21/lpp-Mx. Thus, our GNNV-binding bacterium is an efficient microparticle for removing GNNV from 10‰ brackish water and for preventing GNNV infection in groupers.

Live-Attenuated Bacterial Vectors for Delivery of Mucosal Vaccines, DNA Vaccines, and Cancer Immunotherapy

Vaccines save millions of lives each year from various life-threatening infectious diseases, and there are more than 20 vaccines currently licensed for human use worldwide. Moreover, in recent decades immunotherapy has become the mainstream therapy, which highlights the tremendous potential of immune response mediators, including vaccines for prevention and treatment of various forms of cancer. However, despite the tremendous advances in microbiology and immunology, there are several vaccine preventable diseases which still lack effective vaccines. Classically, weakened forms (attenuated) of pathogenic microbes were used as vaccines. Although the attenuated microbes induce effective immune response, a significant risk of reversion to pathogenic forms remains. While in the twenty-first century, with the advent of genetic engineering, microbes can be tailored with desired properties.

In this review, I have focused on the use of genetically modified bacteria for the delivery of vaccine antigens. More specifically, the live-attenuated bacteria, derived from pathogenic bacteria, possess many features that make them highly suitable vectors for the delivery of vaccine antigens. Bacteria can theoretically express any heterologous gene or can deliver mammalian expression vectors harboring vaccine antigens (DNA vaccines). These properties of live-attenuated microbes are being harnessed to make vaccines against several infectious and noninfectious diseases. In this regard, I have described the desired features of live-attenuated bacterial vectors and the mechanisms of immune responses manifested by live-attenuated bacterial vectors. Interestingly anaerobic bacteria are naturally attracted to tumors, which make them suitable vehicles to deliver tumor-associated antigens thus I have discussed important studies investigating the role of bacterial vectors in immunotherapy. Finally, I have provided important discussion on novel approaches for improvement and tailoring of live-attenuated bacterial vectors for the generation of desired immune responses.

Salmonella Vaccines: Conduits for Protective Antigens

Vaccines afford a better and more cost-effective approach to combatting infectious diseases than continued reliance on antibiotics or antiviral or antiparasite drugs in the current era of increasing incidences of diseases caused by drug-resistant pathogens. Recombinant attenuated Salmonella vaccines (RASVs) have been significantly improved to exhibit the same or better attributes than wild-type parental strains to colonize internal lymphoid tissues and persist there to serve as factories to continuously synthesize and deliver rAgs. Encoded by codon-optimized pathogen genes, Ags are selected to induce protective immunity to infection by that pathogen. After immunization through a mucosal surface, the RASV attributes maximize their abilities to elicit mucosal and systemic Ab responses and cell-mediated immune responses. This article summarizes many of the numerous innovative technologies and discoveries that have resulted in RASV platforms that will enable development of safe efficacious RASVs to protect animals and humans against a diversity of infectious disease agents.

Antigen Delivery System II

This chapter reviews papers mostly written since 2005 that report results using live attenuated bacterial vectors to deliver after administration through mucosal surfaces, protective antigens, and DNA vaccines, encoding protective antigens to induce immune responses and/or protective immunity to pathogens that colonize on or invade through mucosal surfaces. Papers that report use of such vaccine vector systems for parenteral vaccination or to deal with nonmucosal pathogens or do not address induction of mucosal antibody and/or cellular immune responses are not reviewed.

Pushing the Bacterial Envelope

Over the past three decades, a powerful array of techniques has been developed for expressing heterologous proteins and saccharides on the surface of bacteria. Surface-engineered bacteria, in turn, have proven useful in a variety of settings, including high-throughput screening, biofuel production, and vaccinology. In this chapter, we provide a comprehensive review of methods for displaying polypeptides and sugars on the bacterial cell surface, and discuss the many innovative applications these methods have found to date. While already an important biotechnological tool, we believe bacterial surface display may be further improved through integration with emerging methodology in other fields, such as protein engineering and synthetic chemistry. Ultimately, we envision bacterial display becoming a multidisciplinary platform with the potential to transform basic and applied research in bacteriology, biotechnology, and biomedicine.

Fermentation preparation of recombinant Vibrio anguillarum vaccine with heterogeneous antigen display

In the design of recombinant bacterial vector vaccine, heterogeneous antigen is displayed on the outer membrane of the vector strain to evoke polyvalent immunological protection. Thus, the expression of heterogeneous antigen in cells and its display on the outer membrane are of great concern for vaccine preparation. In our previous work, a multivalent bacterial vector vaccine MVAV6203A-1 was constructed by displaying the protective antigen GAPDH from Aeromonas hydrophila on the surface of an attenuated Vibrio anguillarum MVAV6203. In this work, a new fermentation medium was designed by a four-step method to improve the cell growth and antigen display of V. anguillarum MVAV6203A-1. First, suitable carbon and nitrogen sources were selected by a component swapping method. Second, the initial concentrations of carbon and nitrogen sources were determined by orthogonal design. Then three main factors to significantly affect cell growth and antigen expression were screened by a Plackett-Burman design. Finally, the three main factors were meticulously optimized by response surface methodology. Based on this medium, a fed-batch fermentation process was established in a 5-L bioreactor, and the dry cell weight, the antigen expression in cells, and its display on outer membrane reached 5.98 g/L, 2.82 mg/g DCW, and 0.119 mg/g DCW, respectively.

Comparative immunological evaluation of recombinant Salmonella Typhimurium strains expressing model antigens as live oral vaccines

Background

Despite the development of various systems to generate live recombinant Salmonella Typhimurium vaccine strains, little work has been performed to systematically evaluate and compare their relative immunogenicity. Such information would provide invaluable guidance for the future rational design of live recombinant Salmonella oral vaccines.

Result

To compare vaccine strains encoded with different antigen delivery and expression strategies, a series of recombinant Salmonella Typhimurium strains were constructed that expressed either the enhanced green fluorescent protein (EGFP) or a fragment of the hemagglutinin (HA) protein from the H5N1 influenza virus, as model antigens. The antigens were expressed from the chromosome, from high or low-copy plasmids, or encoded on a eukaryotic expression plasmid. Antigens were targeted for expression in either the cytoplasm or the outer membrane. Combinations of strategies were employed to evaluate the efficacy of combined delivery/expression approaches. After investigating in vitro and in vivo antigen expression, growth and infection abilities; the immunogenicity of the constructed recombinant Salmonella strains was evaluated in mice. Using the soluble model antigen EGFP, our results indicated that vaccine strains with high and stable antigen expression exhibited high B cell responses, whilst eukaryotic expression or colonization with good construct stability was critical for T cell responses. For the insoluble model antigen HA, an outer membrane expression strategy induced better B cell and T cell responses than a cytoplasmic strategy. Most notably, the combination of two different expression strategies did not increase the immune response elicited.

Conclusion

Through systematically evaluating and comparing the immunogenicity of the constructed recombinant Salmonella strains in mice, we identified their respective advantages and deleterious or synergistic effects. Different construction strategies were optimally-required for soluble versus insoluble forms of the protein antigens. If an antigen, such as EGFP, is soluble and expressed at high levels, a low-copy plasmid-cytoplasmic expression strategy is recommended; since it provokes the highest B cell responses and also induces good T cell responses. If a T cell response is preferred, a eukaryotic expression plasmid or a chromosome-based, cytoplasmic-expression strategy is more effective. For insoluble antigens such as HA, an outer membrane expression strategy is recommended.

Iron-regulated lysis of recombinant Escherichia coli in host releases protective antigen and confers biological containment

The use of a recombinant bacterial vector vaccine is an attractive vaccination strategy to induce an immune response to a carried protective antigen. The superiorities of live bacterial vectors include mimicry of a natural infection, intrinsic adjuvant properties, and the potential for administration by mucosal routes. Escherichia coli is a simple and efficient vector system for production of exogenous proteins. In addition, many strains are nonpathogenic and avirulent, making it a good candidate for use in recombinant vaccine design. In this study, we screened 23 different iron-regulated promoters in an E. coli BL21(DE3) vector and found one, P(viuB), with characteristics suitable for our use. We fused P(viuB) with lysis gene E, establishing an in vivo inducible lysis circuit. The resulting in vivo lysis circuit was introduced into a strain also carrying an IPTG (isopropyl-β-d-thiogalactopyranoside)-inducible P(T7)-controlled protein synthesis circuit, forming a novel E. coli-based protein delivery system. The recombinant E. coli produced a large amount of antigen in vitro and could deliver the antigen into zebrafish after vaccination via injection. The strain subsequently lysed in response to the iron-limiting signal in vivo, implementing antigen release and biological containment. The gapA gene, encoding the protective antigen GAPDH (glyceraldehyde-3-phosphate dehydrogenase) from the fish pathogen Aeromonas hydrophila LSA34, was introduced into the E. coli-based protein delivery system, and the resultant recombinant vector vaccine was evaluated in turbot (Scophtalmus maximus). Over 80% of the vaccinated fish survived challenge with A. hydrophila LSA34, suggesting that the E. coli-based antigen delivery system has great potential in bacterial vector vaccine applications.

Salmonella vaccine vectors displaying delayed antigen synthesis in vivo to enhance immunogenicity

We have developed a regulated delayed antigen synthesis (RDAS) system for use in recombinant attenuated Salmonella vaccine (RASV) strains to enhance immune responses by reducing the adverse effects of high-level antigen synthesis. This system includes a chromosomal repressor gene, lacI, expressed from the arabinose-regulated araC PBAD promoter. LacI serves to regulate expression from a plasmid promoter, Ptrc, that directs antigen synthesis. In the presence of arabinose LacI is produced, which binds to Ptrc, blocking antigen synthesis. In vivo, an arabinose-poor environment, the concentration of LacI decreases with each cell division, allowing increased antigen synthesis. To optimize the system and for comparison, we altered the lacI ribosome-binding site, start codon, and/or codon content to construct RDAS strains chi9095, chi9959, and chi9241, synthesizing from low to high levels of LacI, respectively, and non-RDAS strain chi9555 as a control. We evaluated this system with two test antigens, the green fluorescent protein for initial in vitro assessment and the Streptococcus pneumoniae PspA protein for validation of our system in mice. All RASV strains expressing PspA generated high antilipopolysaccharide antibody titers, indicating that expression of lacI did not interfere with the capacity to induce an immune response. Strain chi9241 induced significantly higher anti-PspA IgG and IgA antibody titers than strain chi9555, which expressed PspA constitutively. Anti-PspA antibody titers were inversely correlated to the level of LacI synthesis. Strain chi9241 also induced significantly greater protective efficacy against challenge with virulent S. pneumoniae. These results suggest that regulated delayed antigen synthesis is useful for improving immunogenicity of RASV strains.

Oral vaccination with attenuated Salmonella enterica strains encoding T-cell epitopes from tumor antigen NY-ESO-1 induces specific cytotoxic T-lymphocyte responses

Bacterial fimbriae can accept foreign peptides and display them on the cell surface. A highly efficient gene replacement method was used to generate peptide vaccines based on Salmonella enterica serovar Typhimurium SL3261. The T-cell epitopes (NY-ESO-1 p157-165 and p157-167) from NY-ESO-1, which is a promising target antigen in patients for the specific immune recognition of cancer, were incorporated into the gene encoding AgfA (the major subunit protein of thin aggregative fimbriae of Salmonella) by replacing an equal length of the DNA segment. To improve cytotoxic T-lymphocyte recognition, both termini of the peptide were flanked by double alanine (AA) residues. Immunofluorescence microscopy with AgfA-specific antiserum verified the expression of chimeric AgfA, which was also proved by a Congo red binding assay. Oral immunizations of HLA-A*0201 transgenic mice with recombinant SL3261 strains encoding NY-ESO-1 p157-165 or p157-167 induced NY-ESO-1 p157-165-specific CD8(+) T cells, detected by an HLA-A*0201 pentamer, and induced a T-cell response detected by an enzyme-linked immunospot assay. The Salmonella fimbrial display system was efficient at the induction of an antitumor cellular immune response in vivo, providing a new strategy for the development of efficient cancer vaccinations.

Feasibility and therapeutic strategies of vaccines against Porphyromonas gingivalis

Periodontitis is a chronic infectious disease that is highly prevalent worldwide and is characterized by inflammation of the gums, and loss of connective tissue and bone support. The Gram-negative anerobic bacterium Porphyromonas gingivalis is generally accepted as the main etiological agent for chronic periodontitis. The objective of this paper is to elucidate the feasibility of achieving protection against periodontitis though immunization against P. gingivalis. Until now, animal studies have showed no complete protection against P. gingivalis. However, current knowledge about P. gingivalis structures could be applicable for further research to develop a successful licensed vaccine and alternative therapeutic strategies. This review reveals that a multicomponent vaccine against P. gingivalis, which includes structures shared among P. gingivalis serotypes, will be feasible to induce broad and complete protection.

Salmonella expressing a T-cell epitope from Sendai virus are able to induce anti-infection immunity

Bacterial fimbriae can accept foreign peptides and display them on the cell surface. A highly efficient gene replacement method was used to generate peptide vaccines based on Salmonella enterica subsp. enterica serovar Typhimurium LT2. DNA encoding an epitope from Sendai virus, SV9 (Sendai virus nucleoprotein peptide 324–332, FAPGNYPAL), which is known to induce cytotoxic T lymphocytes, was incorporated into the gene encoding AgfA (the major subunit protein of thin aggregative fimbriae of Salmonella) by replacing an equal length DNA segment. To improve cytotoxic T lymphocyte recognition, both termini of the peptide were flanked by double alanine (AA) or arginine (RR) residues. Western blotting and immunofluorescence microscopy using AgfA-specific antiserum verified the expression of chimeric AgfA; expression was also proved by a Congo red binding assay. Oral immunizations of C57BL/6 mice with the four strains induced an epitope-specific T-cell response (detected by enzyme-linked immunosorbent spot assay). When the mice were challenged with the Sendai virus, the magnitude of the infection was significantly reduced in the immunized groups compared with the controls. The Salmonella fimbrial display system efficiently induces a cellular immune response and anti-infection immunity in vivo, providing a new strategy for the development of efficient peptide vaccination.

Effect of expression level on immune responses to recombinant oral Salmonella enterica serovar Typhimurium vaccines

Live, attenuated Salmonella has been used to express heterologous antigens for development of oral vaccines. Often, expression must be regulated because of deleterious effects on the Salmonella vector. The effect of varying expression levels on immune response parameters has not been well defined. In this study we introduced mutations in the -10 region of the trc promoter in the expression plasmid to generate series of vaccine strains with different levels of expression of a model antigen, the hemagglutinin HagB from Porphyromonas gingivalis. There was no difference in growth rates of the Salmonella vaccine strains containing the wild-type, the mutant plasmids or the empty expression vector. The primary IgG response in serum in mice orally immunized with the wild-type strain peaked 3-4 weeks earlier than the intermediate expression level strains, suggesting that high expression levels may favor an earlier response. While there was a trend for anti-HagB recall responses to correlate with higher expression level, the peak levels were not significantly different even for expression levels as low as 33% of wild-type. A similar trend in terms of response level was seen with serum and salivary IgA. The subclass of the IgG response was predominately IgG2a regardless of expression level, consistent with a Th1 response. These data suggest that isotype distribution, immune response level and T helper cell profile are largely unaffected over a wide range of expression levels.

Novel bacterial surface display systems based on outer membrane anchoring elements from the marine bacterium Vibrio anguillarum

Surface display of heterologous peptides and proteins such as receptors, antigens, and enzymes on live bacterial cells is of considerable value for various biotechnological and industrial applications. In this study, a series of novel cell surface display systems were examined by using Vibrio anguillarum outer membrane protein and outer membrane lipoprotein as anchoring motifs. These display systems consist of (i) the signal sequence and first 11 N-terminal amino acids of V. anguillarum outer membrane lipoprotein Wza, or the signal sequence and first 9 N-terminal amino acids of the mature major Escherichia coli lipoprotein Lpp, and (ii) transmembrane domains of V. anguillarum outer membrane proteins Omporf1, OmpU, or Omp26La. In order to assay the translocation efficiency of constructed display systems in bacteria, green fluorescent protein (GFP) was inserted to the systems and the results of GFP surface localization confirmed that four of the six surface display systems could successfully display GFP on the E. coli surface. For assaying its potential application in live bacteria carrier vaccines, an excellent display system Wza-Omporf1 was fused with the major capsid protein (MCP) of large yellow croaker iridovirus and introduced into attenuated V. anguillarum strain MVAV6203, and subsequent analysis of MCP surface localization proved that the novel display system Wza-Omporf1 could function as a strong tool in V. anguillarum carrier vaccine development.