Bacterial infectious disease control by vaccine development

A novel vaccine strategy using quick and easy conversion of bacterial pathogens to unnatural amino acid-auxotrophic suicide derivatives

We propose a novel strategy for quick and easy preparation of suicide live vaccine candidates against bacterial pathogens. This method requires only the transformation of one or more plasmids carrying genes encoding for two types of biological devices, an unnatural amino acid (uAA) incorporation system and toxin-antitoxin systems in which translation of the antitoxins requires the uAA incorporation. Escherichia coli BL21-AI laboratory strains carrying the plasmids were viable in the presence of the uAA, whereas the free toxins killed these strains after the removal of the uAA. The survival time after uAA removal could be controlled by the choice of the uAA incorporation system and toxin-antitoxin systems. Multilayered toxin-antitoxin systems suppressed escape frequency to less than 1 escape per 109 generations in the best case. This conditional suicide system also worked in Salmonella enterica and E. coli clinical isolates. The S. enterica vaccine strains were attenuated with a >105 fold lethal dose. Serum IgG response and protection against the parental pathogenic strain were confirmed. In addition, the live E. coli vaccine strain was significantly more immunogenic and provided greater protection than a formalin-inactivated vaccine. The live E. coli vaccine was not detected after inoculation, presumably because the uAA is not present in the host animals or the natural environment. These results suggest that this strategy provides a novel way to rapidly produce safe and highly immunogenic live bacterial vaccine candidates.

IMPORTANCE

Live vaccines are the oldest vaccines with a history of more than 200 years. Due to their strong immunogenicity, live vaccines are still an important category of vaccines today. However, the development of live vaccines has been challenging due to the difficulties in achieving a balance between safety and immunogenicity. In recent decades, the frequent emergence of various new and old pathogens at risk of causing pandemics has highlighted the need for rapid vaccine development processes. We have pioneered the use of uAAs to control gene expression and to conditionally kill host bacteria as a biological containment system. This report proposes a quick and easy conversion of bacterial pathogens into live vaccine candidates using this containment system. The balance between safety and immunogenicity can be modulated by the selection of the genetic devices used. Moreover, the uAA-auxotrophy can prevent the vaccine from infecting other individuals or establishing the environment.

MAIT cells in bacterial infectious diseases: heroes, villains, or both?

Due to the aggravation of bacterial drug resistance and the lag in the development of new antibiotics, it is crucial to develop novel therapeutic regimens for bacterial infectious diseases. Currently, immunotherapy is a promising regimen for the treatment of infectious diseases. Mucosal-associated invariant T (MAIT) cells, a subpopulation of innate-like T cells, are abundant in humans and can mount a rapid immune response to pathogens, thus becoming a potential target of immunotherapy for infectious diseases. At the site of infection, activated MAIT cells perform complex biological functions by secreting a variety of cytokines and cytotoxic substances. Many studies have shown that MAIT cells have immunoprotective effects because they can bridge innate and adaptive immune responses, leading to bacterial clearance, tissue repair, and homeostasis maintenance. MAIT cells also participate in cytokine storm generation, tissue fibrosis, and cancer progression, indicating that they play a role in immunopathology. In this article, we review recent studies of MAIT cells, discuss their dual roles in bacterial infectious diseases and provide some promising MAIT cell-targeting strategies for the treatment of bacterial infectious diseases.

Immunogenicity of a freeze-dried combined vaccine against Rift Valley fever and bovine ephemeral fever in cattle

Background

The target of vaccination is to encourage a strong, covering and long-lasting immune response against antigens. For achieving these objectives; effective adjuvant and new vaccine strategies are demanded to make the vaccine sufficiently immunogenic to instigate a powerful immune response.

Aim

This study was completed for elaboration and evaluation of freeze-dried combined vaccine against both Rift Valley fever (RVF) and bovine ephemeral fever (BEF) viruses using different stabilizers.

Methods

Three formulae were prepared from such vaccine including: formula (1): stabilized with a mixture of 5% Lactalbumin Hydrolysate and 2.5% sucrose, formula (2): stabilized with a mixture of 50% the previous stabilizer and 50% of 1% Carbopol and formula (3): stabilized with 1% Carbopol solution. Samples of the three vaccine formulae were reconstituted on the time of experimental animal vaccination using saponin diluent which acts as an adjuvant for both RVFv and BEFv and as an inactivator BEF virus. The ratio between both viruses in all vaccine formulae was 1:1.

Results

All vaccine batches were proved to be free of any foreign contaminants and unharmed for experimentally vaccinated animals. Each of the three groups of calves was vaccinated S/C with 2 ml of a reconstituted vaccine formula and their immune response was evaluated using serum neutralization test. The gained results revealed that the prepared combined freeze-dried vaccine with Carbopol elicited a better humoral immune response than the other two vaccine formulae.

Conclusion

It could be recommended to use Carbopol as a stabilizer for the preparation of the aimed vaccine.

Mucosal delivery of ESX-1-expressing BCG strains provides superior immunity against tuberculosis in murine type 2 diabetes

Tuberculosis (TB) claims 1.5 million lives per year. This situation is largely due to the low efficacy of the only licensed TB vaccine, Bacillus Calmette-Guérin (BCG) against pulmonary TB. The metabolic disease type 2 diabetes (T2D) is a risk factor for TB and the mechanisms underlying increased TB susceptibility in T2D are not well understood. Furthermore, it is unknown if new TB vaccines will provide protection in the context of T2D. Here we used a diet-induced murine model of T2D to investigate the underlying mechanisms of TB/T2D comorbidity and to evaluate the protective capacity of two experimental TB vaccines in comparison to conventional BCG. Our data reveal a distinct immune dysfunction that is associated with diminished recognition of mycobacterial antigens in T2D. More importantly, we provide compelling evidence that mucosal delivery of recombinant BCG strains expressing the Mycobacterium tuberculosis (Mtb) ESX-1 secretion system (BCG::RD1 and BCG::RD1 ESAT-6 ∆92-95) are safe and confer superior immunity against aerosol Mtb infection in the context of T2D. Our findings suggest that the remarkable anti-TB immunity by these recombinant BCG strains is achieved via augmenting the numbers and functional capacity of antigen presenting cells in the lungs of diabetic mice.

Phage proteins are expressed on the surface of Neisseria gonorrhoeae and are potential vaccine candidates

All Neisseria gonorrhoeae strains whose DNA sequences have been determined possess filamentous phage sequences representing their full genomes. The presence of filamentous phage DNA sequences in all sequenced N. gonorrhoeae strains suggest that purified phage particles might be used as a gonococcal vaccine. To test this hypothesis, we purified filamentous NgoΦfil phages and immunized rabbits subcutaneously. The elicited sera contained large quantities of anti-phage IgG and IgA antibodies that bound to the surface of N. gonorrhoeae cells, as shown by ELISA and flow cytometry. The elicited sera bound to the structural NgoΦ6fil proteins present in phage particles and to N. gonorrhoeae cells. The sera did not react with gonococcal outer membrane proteins. The sera also had bactericidal activity and blocked adhesion of gonococci to tissue culture cells. These data demonstrate that NgoΦfil phage particles can induce antibodies with anti-gonococcal activity and may be a candidate for vaccine development.

Synthetic Immunobiotics: A Future Success Story in Small Molecule-Based Immunotherapy?

Drug resistance to our current stock of antibiotics is projected to increase to levels that threaten our ability to reduce and eliminate bacterial infections, which is now considered one of the primary health care crises of the 21st century. Traditional antibiotic agents (e.g., penicillin) paved the way for massive advances in human health, but we need novel strategies to maintain the upper hand in the battle against pathogenic bacteria. Nontraditional strategies, such as targeted immunotherapies, could prove fruitful in complementing our antibiotic arsenal.

Salmonella enterica serovar Choleraesuis vector delivering SaoA antigen confers protection against Streptococcus suis serotypes 2 and 7 in mice and pigs

Streptococcus suis is one of the major pathogens that cause economic losses in the swine industry worldwide. However, current bacterins only provide limited prophylactic protection in the field. An ideal vaccine against S. suis should protect pigs against the clinical diseases caused by multiple serotypes, or at least protect against the dominant serotype in a given geographic region. A new recombinant Salmonella enterica serotype Choleraesuis vaccine vector, rSC0011, that is based on the regulated delayed attenuation system and regulated delayed antigen synthesis system, was developed recently. In this study, an improved recombinant attenuated Salmonella Choleraesuis vector, rSC0016, was developed by incorporating a sopB mutation to ensure adequate safety and maximal immunogenicity. In the spleens of mice, rSC0016 colonized less than rSC0011. rSC0016 and rSC0011 colonized similarly in Peyer's patches of mice. The recombinant vaccine rSC0016(pS-SaoA) induced stronger cellular, humoral, and mucosal immune responses in mice and swine against SaoA, a conserved surface protein that is present in many S. suis serotypes, than did rSC0011(pS-SaoA) without sopB or rSC0018(pS-SaoA), which is an avirulent, chemically attenuated vaccine strain. rSC0016(pS-SaoA) provided 100% protection against S. suis serotype 2 in mice and pigs, and full cross-protection against SS7 in pigs. This new vaccine vector provides a foundation for the development of a universal vaccine against multiple serotypes of S. suis in pigs.

Regulated delayed synthesis of lipopolysaccharide and enterobacterial common antigen of Salmonella Typhimurium enhances immunogenicity and cross-protective efficacy against heterologous Salmonella challenge

Lipopolysaccharide (LPS) O-antigen and enterobacterial common antigen (ECA) are two major polysaccharide structures on the surface of Salmonella enterica serovar Typhimurium. Previous studies have demonstrated that regulated truncation of LPS enhances the cross-reaction against conserved outer membrane proteins (OMPs) from enteric bacteria. We speculate that the regulation of both O-antigen and ECA may enhance the induction of immune responses against conserved OMPs from enteric bacteria. In this work we targeted rfbB and rffG genes which encode dTDP-glucose 4,6-dehydratases and share the same function in regulating O-antigen and ECA synthesis. We constructed a mutant, S496 (ΔrfbB6 ΔrffG7 ΔpagL73::TT araC PBADrfbB-3), in which rfbB gene expression was dependent on exogenously supplied arabinose during in vitro growth and achieved the simultaneous tight regulation of both LPS and ECA synthesis, as demonstrated by the LPS profile and Western blotting using antisera against LPS and ECA. When administered orally, S. Typhimurium S496 was completely attenuated for virulence but still retained the capacity to colonize and disseminate in mice. In addition, we found that oral immunization with S496 resulted in increased immune responses against OMPs from enteric bacteria and enhanced survival compared with immunization with S492 possessing ΔrfbB6 ΔrffG8 mutations when challenged with lethal doses of Salmonella Choleraesuis or Salmonella Enteritidis. These results indicate that S. Typhimurium arabinose-regulated rfbB strain S496 is a good vaccine candidate, conferring cross-protection against lethal challenge with heterologous Salmonella.

Design of live attenuated bacterial vaccines based on D-glutamate auxotrophy

Vaccine development is a priority for global health due to the growing multidrug resistance in bacteria. D-glutamate synthesis is essential for bacterial cell wall formation. Here we present a strategy for generating effective bacterial whole-cell vaccines auxotrophic for D-glutamate. We apply this strategy to generate D-glutamate auxotrophic vaccines for three major pathogens, Acinetobacter baumannii, Pseudomonas aeruginosa and Staphylococcus aureus. These bacterial vaccines show virulence attenuation and self-limited growth in mice, and elicit functional and cross-reactive antibodies, and cellular immunity. These responses correlate with protection against acute lethal infection with other strains of the same species, including multidrug resistant, virulent and/or high-risk clones such as A. baumannii AbH12O-A2 and Ab307-0294, P. aeruginosa PA14, and community-acquired methicillin-resistant S. aureus USA300LAC. This approach can potentially be applied for the development of live-attenuated vaccines for virtually any other bacterial pathogens, and does not require the identification of virulence determinants, which are often pathogen-specific.

Deletion of ssnA Attenuates the Pathogenicity of Streptococcus suis and Confers Protection against Serovar 2 Strain Challenge

Streptococcus suis serotype 2 (SS2) is a major porcine and human pathogen which causes arthritis, meningitis, and septicemia. Streptococcus suis nuclease A (SsnA) is a recently discovered deoxyribonuclease (DNase), which has been demonstrated to contribute to escape killing in neutrophil extracellular traps (NETs). To further determine the effects of ssnA on virulence, the ssnA deletion mutant (ΔssnA) and its complemented strain (C-ΔssnA) were constructed. The ability of ΔssnA mutant to interact with human laryngeal epithelial cell (Hep-2) was evaluated and it exhibited dramatically decreased ability to adhere to and invade Hep-2 cells. This mutation was found to exhibit significant attenuation of virulence when evaluated in CD1 mice, suggesting ssnA plays a critical role in the pathogenesis of SS2. Finally, we found that immunization with the ΔssnA mutant triggered both antibody responses and cell-mediated immunity, and conferred 80% protection against virulent SS2 challenge in mice. Taken together, our results suggest that ΔssnA represents an attractive candidate for designing an attenuated live vaccine against SS2.

Outer membrane vesicles from flagellin-deficient Salmonella enterica serovar Typhimurium induce cross-reactive immunity and provide cross-protection against heterologous Salmonella challenge

Outer membrane vesicles (OMVs) isolated from Salmonella Typhimurium are potentially useful for developing subunit vaccines because of high immunogenicity and protective efficacy. However, flagella might remain in OMV pellets following OMV purification, resulting in non-essential immune responses and counteraction of bacterial protective immune responses when developing a vaccine against infection of multiple serotypes Salmonella. In this study, a flagellin-deficient S. Typhimurium mutant was constructed. Lipopolysaccharide profiles, protein profiles and cryo-electron microscopy revealed that there were no significant differences between the wild-type and mutant OMVs, with the exception of a large amount of flagellin in the wild-type OMVs. Neither the wild-type OMVs nor the non-flagellin OMVs were toxic to macrophages. Mice immunized with the non-flagellin OMVs produced high concentrations of IgG. The non-flagellin OMVs elicited strong mucosal antibody responses in mice when administered via the intranasal route in addition to provoking higher cross-reactive immune responses against OMPs isolated from S. Choleraesuis and S. Enteritidis. Both intranasal and intraperitoneal immunization with the non-flagellin OMVs provided efficient protection against heterologous S. Choleraesuis and S. Enteritidis challenge. Our results indicate that the flagellin-deficient OMVs may represent a new vaccine platform that could be exploited to facilitate the production of a broadly protective vaccine.

Vaccination with Bivalent DNA Vaccine of α1-Giardin and CWP2 Delivered by Attenuated Salmonella typhimurium Reduces Trophozoites and Cysts in the Feces of Mice Infected with Giardia lamblia

Background

Giardia lamblia is one of the most common infectious protozoans in human that may cause diarrhea in travelers. Searching for antigens that induced effectively protective immunity has become a key point in the development of vaccine against giardiasis.

Methodology/Principal Findings

Mice vaccinated with G. lamblia trophozozite-specific α1-giardin DNA vaccine delivered orally by attenuated Salmonella typhimurium SL7027 elicited 74.2% trophozoite reduction, but only 28% reduction in cyst shedding compared with PBS buffer control. Oral vaccination with Salmonella-delivered cyst-specific CWP2 DNA produced 89% reduction in cysts shedding in feces of vaccinated mice. Significantly, the mice vaccinated with Salmonella-delivered bivalent α1-giardin and CWP2 DNA vaccines produced significant reduction in both trophozoite (79%) and cyst (93%) in feces of vaccinated mice. This parasite reduction is associated with the strong local mucosal IgA secretion and the IgG2a-dominant systemic immune responses in vaccinated mice.

Conclusions

The results demonstrate that bivalent vaccines targeting α1-giardin and CWP2 can protect mice against the colonization of Giardia trophozoite and block the transformation of cyst in host at the same time, and can be used to prevent Giardia infection and block the transmission of giardiasis.

Generation of influenza virus from avian cells infected by Salmonella carrying the viral genome

Domestic poultry serve as intermediates for transmission of influenza A virus from the wild aquatic bird reservoir to humans, resulting in influenza outbreaks in poultry and potential epidemics/pandemics among human beings. To combat emerging avian influenza virus, an inexpensive, heat-stable, and orally administered influenza vaccine would be useful to vaccinate large commercial poultry flocks and even migratory birds. Our hypothesized vaccine is a recombinant attenuated bacterial strain able to mediate production of attenuated influenza virus in vivo to induce protective immunity against influenza. Here we report the feasibility and technical limitations toward such an ideal vaccine based on our exploratory study. Five 8-unit plasmids carrying a chloramphenicol resistance gene or free of an antibiotic resistance marker were constructed. Influenza virus was successfully generated in avian cells transfected by each of the plasmids. The Salmonella carrier was engineered to allow stable maintenance and conditional release of the 8-unit plasmid into the avian cells for recovery of influenza virus. Influenza A virus up to 10⁷ 50% tissue culture infective doses (TCID50)/ml were recovered from 11 out of 26 co-cultures of chicken embryonic fibroblasts (CEF) and Madin-Darby canine kidney (MDCK) cells upon infection by the recombinant Salmonella carrying the 8-unit plasmid. Our data prove that a bacterial carrier can mediate generation of influenza virus by delivering its DNA cargoes into permissive host cells. Although we have made progress in developing this Salmonella influenza virus vaccine delivery system, further improvements are necessary to achieve efficient virus production, especially in vivo.

Nanomedicine in the Management of Microbial Infection - Overview and Perspectives

For more than 2 billion years, microbes have reigned on our planet, evolving or outlasting many obstacles they have encountered. In the 20th century, this trend took a dramatic turn with the introduction of antibiotics and vaccines. Nevertheless, since then, microbes have progressively eroded the effectiveness of previously successful antibiotics by developing resistance, and many infections have eluded conventional vaccine design approaches. Moreover, the emergence of resistant and more virulent strains of bacteria has outpaced the development of new antibiotics over the last few decades. These trends have had major economic and health impacts at all levels of the socioeconomic spectrum - we need breakthrough innovations that could effectively manage microbial infections and deliver solutions that stand the test of time. The application of nanotechnologies to medicine, or nanomedicine, which has already demonstrated its tremendous impact on the pharmaceutical and biotechnology industries, is rapidly becoming a major driving force behind ongoing changes in the antimicrobial field. Here we provide an overview on the current progress of nanomedicine in the management of microbial infection, including diagnosis, antimicrobial therapy, drug delivery, medical devices, and vaccines, as well as perspectives on the opportunities and challenges in antimicrobial nanomedicine.

Regulatory T-cell vaccination independent of auto-antigen

To date, efforts to treat autoimmune diseases have primarily focused on the disease symptoms rather than on the cause of the disease. In large part, this is attributed to not knowing the responsible auto-antigens (auto-Ags) for driving the self-reactivity coupled with the poor success of treating autoimmune diseases using oral tolerance methods. Nonetheless, if tolerogenic approaches or methods that stimulate regulatory T (T_reg) cells can be devised, these could subdue autoimmune diseases. To forward such efforts, our approach with colonization factor antigen I (CFA/I) fimbriae is to establish bystander immunity to ultimately drive the development of auto-Ag-specific T_reg cells. Using an attenuated Salmonella vaccine expressing CFA/I fimbriae, fimbriae-specific T_reg cells were induced without compromising the vaccine's capacity to protect against travelers' diarrhea or salmonellosis. By adapting the vaccine's anti-inflammatory properties, it was found that it could also dampen experimental inflammatory diseases resembling multiple sclerosis (MS) and rheumatoid arthritis. Because of this bystander effect, disease-specific T_reg cells are eventually induced to resolve disease. Interestingly, this same vaccine could elicit the required T_reg cell subset for each disease. For MS-like disease, conventional CD25⁺ T_reg cells are stimulated, but for arthritis CD39⁺ T_reg cells are induced instead. This review article will examine the potential of treating autoimmune diseases without having previous knowledge of the auto-Ag using an innocuous antigen to stimulate T_reg cells via the production of transforming growth factor-β and interleukin-10.

New technologies in developing recombinant attenuated Salmonella vaccine vectors

Recombinant attenuated Salmonella vaccine (RASV) vectors producing recombinant gene-encoded protective antigens should have special traits. These features ensure that the vaccines survive stresses encountered in the gastrointestinal tract following oral vaccination to colonize lymphoid tissues without causing disease symptoms and to result in induction of long-lasting protective immune responses. We recently described ways to achieve these goals by using regulated delayed in vivo attenuation and regulated delayed in vivo antigen synthesis, enabling RASVs to efficiently colonize effector lymphoid tissues and to serve as factories to synthesize protective antigens that induce higher protective immune responses. We also developed some additional new strategies to increase vaccine safety and efficiency. Modification of lipid A can reduce the inflammatory responses without compromising the vaccine efficiency. Outer membrane vesicles (OMVs) from Salmonella-containing heterologous protective antigens can be used to increase vaccine efficiency. A dual-plasmid system, possessing Asd+ and DadB+ selection markers, each specifying a different protective antigen, can be used to develop multivalent live vaccines. These new technologies have been adopted to develop a novel, low-cost RASV synthesizing multiple protective pneumococcal protein antigens that could be safe for newborns/infants and induce protective immunity to diverse Streptococcus pneumoniae serotypes after oral immunization.

Development of vaccine delivery vehicles based on lactic acid bacteria

Live recombinant bacteria represent attractive antigen delivery systems able to induce both mucosal and systemic immune responses against heterologous antigens. The first live recombinant bacterial vectors developed were derived from attenuated pathogenic microorganisms. In addition to the difficulties often encountered in the construction of stable attenuated mutants of pathogenic organisms, attenuated pathogens may retain a residual virulence level that renders them unsuitable for the vaccination of partially immunocompetent individuals such as infants, the elderly or immunocompromised patients. As an alternative to this strategy, non-pathogenic food-grade lactic acid bacteria (LAB) maybe used as live antigen carriers. This article reviews LAB vaccines constructed using antigens other than tetanus toxin fragment C, against bacterial, viral, and parasitic infective agents, for which protection studies have been performed. The antigens utilized for the development of LAB vaccines are briefly described, along with the efficiency of these systems in protection studies. Moreover, the key factors affecting the performance of these systems are highlighted.

Live attenuated Salmonella vaccines against Mycobacterium tuberculosis with antigen delivery via the type III secretion system

Tuberculosis remains a global health threat, and there is dire need to develop a vaccine that is safe and efficacious and confers long-lasting protection. In this study, we constructed recombinant attenuated Salmonella vaccine (RASV) strains with plasmids expressing fusion proteins consisting of the 80 amino-terminal amino acids of the type 3 secretion system effector SopE of Salmonella and the Mycobacterium tuberculosis antigens early secreted antigenic target 6-kDa (ESAT-6) protein and culture filtrate protein 10 (CFP-10). We demonstrated that the SopE-mycobacterial antigen fusion proteins were translocated into the cytoplasm of INT-407 cells in cell culture assays. Oral immunization of mice with RASV strains synthesizing SopE-ESAT-6-CFP-10 fusion proteins resulted in significant protection of the mice against aerosol challenge with M. tuberculosis H37Rv that was similar to the protection afforded by immunization with Mycobacterium bovis bacillus Calmette-Guérin (BCG) administered subcutaneously. In addition, oral immunization with the RASV strains specifying these mycobacterial antigens elicited production of significant antibody titers to ESAT-6 and production of ESAT-6- or CFP-10-specific gamma interferon (IFN-γ)-secreting and tumor necrosis factor alpha (TNF-α)-secreting splenocytes.

Α1-giardin based live heterologous vaccine protects against Giardia lamblia infection in a murine model

Giardia lamblia is a leading protozoan cause of diarrheal disease worldwide, yet preventive medical strategies are not available. A crude veterinary vaccine has been licensed for cats and dogs, but no defined human vaccine is available. We tested the vaccine potential of three conserved antigens previously identified in human and murine giardiasis, α1-giardin, α-enolase, and ornithine carbamoyl transferase, in a murine model of G. lamblia infection. Live recombinant attenuated Salmonella enterica Serovar Typhimurium vaccine strains were constructed that stably expressed each antigen, maintained colonization capacity, and sustained total attenuation in the host. Oral administration of the vaccine strains induced antigen-specific serum IgG, particularly IgG(2A), and mucosal IgA for α1-giardin and α-enolase, but not for ornithine carbamoyl transferase. Immunization with the α1-giardin vaccine induced significant protection against subsequent G. lamblia challenge, which was further enhanced by boosting with cholera toxin or sublingual α1-giardin administration. The α-enolase vaccine afforded no protection. Analysis of α1-giardin from divergent assemblage A and B isolates of G. lamblia revealed >97% amino acid sequence conservation and immunological cross-reactivity, further supporting the potential utility of this antigen in vaccine development. Together. These results indicate that α1-giardin is a suitable candidate antigen for a vaccine against giardiasis.

Effect of deletion of genes involved in lipopolysaccharide core and O-antigen synthesis on virulence and immunogenicity of Salmonella enterica serovar typhimurium

Lipopolysaccharide (LPS) is a major virulence factor of Salmonella enterica serovar Typhimurium and is composed of lipid A, core oligosaccharide (C-OS), and O-antigen polysaccharide (O-PS). While the functions of the gene products involved in synthesis of core and O-antigen have been elucidated, the effect of removing O-antigen and core sugars on the virulence and immunogenicity of Salmonella enterica serovar Typhimurium has not been systematically studied. We introduced nonpolar, defined deletion mutations in waaG (rfaG), waaI (rfaI), rfaH, waaJ (rfaJ), wbaP (rfbP), waaL (rfaL), or wzy (rfc) into wild-type S. Typhimurium. The LPS structure was confirmed, and a number of in vitro and in vivo properties of each mutant were analyzed. All mutants were significantly attenuated compared to the wild-type parent when administered orally to BALB/c mice and were less invasive in host tissues. Strains with ΔwaaG and ΔwaaI mutations, in particular, were deficient in colonization of Peyer's patches and liver. This deficiency could be partially overcome in the ΔwaaI mutant when it was administered intranasally. In the context of an attenuated vaccine strain delivering the pneumococcal antigen PspA, all of the mutations tested resulted in reduced immune responses against PspA and Salmonella antigens. Our results indicate that nonreversible truncation of the outer core is not a viable option for developing a live oral Salmonella vaccine, while a wzy mutant that retains one O-antigen unit is adequate for stimulating the optimal protective immunity to homologous or heterologous antigens by oral, intranasal, or intraperitoneal routes of administration.

Improving Salmonella vector with rec mutation to stabilize the DNA cargoes

BACKGROUND

Salmonella has been employed to deliver therapeutic molecules against cancer and infectious diseases. As the carrier for target gene(s), the cargo plasmid should be stable in the bacterial vector. Plasmid recombination has been reduced in E. coli by mutating several genes including the recA, recE, recF and recJ. However, to our knowledge, there have been no published studies of the effect of these or any other genes that play a role in plasmid recombination in Salmonella enterica.

RESULTS

The effect of recA, recF and recJ deletions on DNA recombination was examined in three serotypes of Salmonella enterica. We found that (1) intraplasmid recombination between direct duplications was RecF-independent in Typhimurium and Paratyphi A, but could be significantly reduced in Typhi by a ΔrecA or ΔrecF mutation; (2) in all three Salmonella serotypes, both ΔrecA and ΔrecF mutations reduced intraplasmid recombination when a 1041 bp intervening sequence was present between the duplications; (3) ΔrecA and ΔrecF mutations resulted in lower frequencies of interplasmid recombination in Typhimurium and Paratyphi A, but not in Typhi; (4) in some cases, a ΔrecJ mutation could reduce plasmid recombination but was less effective than ΔrecA and ΔrecF mutations. We also examined chromosome-related recombination. The frequencies of intrachromosomal recombination and plasmid integration into the chromosome were 2 and 3 logs lower than plasmid recombination frequencies in Rec+ strains. A ΔrecA mutation reduced both intrachromosomal recombination and plasmid integration frequencies.

CONCLUSIONS

The ΔrecA and ΔrecF mutations can reduce plasmid recombination frequencies in Salmonella enterica, but the effect can vary between serovars. This information will be useful for developing Salmonella delivery vectors able to stably maintain plasmid cargoes for vaccine development and gene therapy.

Evaluation of Psn, HmuR and a modified LcrV protein delivered to mice by live attenuated Salmonella as a vaccine against bubonic and pneumonic Yersinia pestis challenge

We evaluated the ability of Yersinia pestis antigens HmuR, Psn and modified forms of LcrV delivered by live attenuated Salmonella strains to stimulate a protective immune response against subcutaneous or intranasal challenge with Y. pestis CO92. LcrV196 is a previously described truncated protein that includes aa 131-326 of LcrV and LcrV5214 has been modified to replace five key amino acids required for interaction with the TLR2 receptor. Psn is the outer membrane receptor for the siderophore, yersiniabactin, and the bacteriocin, pesticin. Mice immunized with Salmonella synthesizing Psn, LcrV196 or LcrV5214 developed serum IgG responses to the respective Yersinia antigen and were protected against pneumonic challenge with Y. pestis. Immunization with Salmonella synthesizing Psn or LcrV196 was sufficient to afford nearly full protection against bubonic challenge, while immunization with the strain synthesizing LcrV5214 was not protective. Immunization with Salmonella synthesizing HmuR, an outer membrane protein involved in heme acquisition in Y. pestis, was poorly immunogenic and did not elicit a protective response against either challenge route. These findings indicate that both Psn and LcrV196 delivered by Salmonella provide protection against both bubonic and pneumonic plague.

Regulated delayed expression of rfc enhances the immunogenicity and protective efficacy of a heterologous antigen delivered by live attenuated Salmonella enterica vaccines

The Salmonella rfc gene encodes the O-antigen polymerase. We constructed three strains in which we replaced the native rfc promoter with the arabinose-dependent araC P(BAD) promoter so that rfc expression was dependent on exogenously supplied arabinose provided during in vitro growth. The three mutant strains were designed to synthesize different amounts of Rfc by altering the ribosome-binding sequence and start codon. We examined these strains for a number of in vitro characteristics compared to an isogenic Deltarfc mutant and the wild-type parent strain. One promoter-replacement mutation, DeltaP(rfc174), yielded an optimal profile, exhibiting wild-type characteristics when grown with arabinose, and Deltarfc characteristics when grown without arabinose. In addition, when administered orally, the DeltaP(rfc174) strain was completely attenuated in for virulence in mice. The DeltaP(rfc174) mutation was introduced into attenuated Salmonella vaccine strain chi9241 (DeltapabA DeltapabB DeltaasdA) followed by introduction of an Asd(+) balanced-lethal plasmid to designed for expression of the pneumococcal surface protein PspA. Mice immunized with either chi9241 or its DeltaP(rfc174) derivative expressing pspA were protected against S. pneumoniae challenge.

Live recombinant Salmonella Typhi vaccines constructed to investigate the role of rpoS in eliciting immunity to a heterologous antigen

We hypothesized that the immunogenicity of live Salmonella enterica serovar Typhi vaccines expressing heterologous antigens depends, at least in part, on its rpoS status. As part of our project to develop a recombinant attenuated S. Typhi vaccine (RASTyV) to prevent pneumococcal diseases in infants and children, we constructed three RASTyV strains synthesizing the Streptococcus pneumoniae surface protein PspA to test this hypothesis. Each vector strain carried ten engineered mutations designed to optimize safety and immunogenicity. Two S. Typhi vector strains (chi9639 and chi9640) were derived from the rpoS mutant strain Ty2 and one (chi9633) from the RpoS(+) strain ISP1820. In chi9640, the nonfunctional rpoS gene was replaced with the functional rpoS gene from ISP1820. Plasmid pYA4088, encoding a secreted form of PspA, was moved into the three vector strains. The resulting RASTyV strains were evaluated for safety in vitro and for immunogenicity in mice. All three RASTyV strains were similar to the live attenuated typhoid vaccine Ty21a in their ability to survive in human blood and human monocytes. They were more sensitive to complement and were less able to survive and persist in sewage and surface water than their wild-type counterparts. Adult mice intranasally immunized with any of the RASTyV strains developed immune responses against PspA and Salmonella antigens. The RpoS(+) vaccines induced a balanced Th1/Th2 immune response while the RpoS(-) strain chi9639(pYA4088) induced a strong Th2 immune response. Immunization with any RASTyV provided protection against S. pneumoniae challenge; the RpoS(+) strain chi9640(pYA4088) provided significantly greater protection than the ISP1820 derivative, chi9633(pYA4088). In the pre-clinical setting, these strains exhibited a desirable balance between safety and immunogenicity and are currently being evaluated in a Phase 1 clinical trial to determine which of the three RASTyVs has the optimal safety and immunogenicity profile in human hosts.

A live oral recombinant Salmonella enterica serovar typhimurium vaccine expressing Clostridium perfringens antigens confers protection against necrotic enteritis in broiler chickens

Necrotic enteritis (NE) in broiler chickens is caused by Clostridium perfringens, and there is currently no effective vaccine for NE. We previously showed that in broiler chickens protection against NE can be achieved through intramuscular immunization with alpha toxin (AT) and hypothetical protein (HP), and we subsequently identified B-cell epitopes in HP. In the present study, we identified B-cell epitopes in AT recognized by chickens immune to NE. The gene fragments encoding immunodominant epitopes of AT as well as those of HP were codon optimized for Salmonella and cloned into pYA3493, and the resultant plasmid constructs were introduced into an attenuated Salmonella enterica serovar Typhimurium chi9352 vaccine vehicle. The expression of these Clostridium perfringens proteins, alpha toxoid (ATd) and truncated HP (HPt), was confirmed by immunoblotting. The protection of broiler chickens against experimentally induced NE was assessed at both the moderate and the severe levels of challenge. Birds immunized orally with Salmonella expressing ATd were significantly protected against moderate NE, and there was a nonsignificant trend for protection against severe challenge, whereas HPt-immunized birds were significantly protected against both severities of challenge. Immunized birds developed serum IgY and mucosal IgA and IgY antibody responses against Clostridium and Salmonella antigens. In conclusion, this study identified, for the first time, the B-cell epitopes in AT from an NE isolate recognized by chickens and showed the partial protective ability of codon-optimized ATd and HPt against NE in broiler chickens when they were delivered orally by using a Salmonella vaccine vehicle.

Regulated delayed expression of rfaH in an attenuated Salmonella enterica serovar typhimurium vaccine enhances immunogenicity of outer membrane proteins and a heterologous antigen

RfaH is a transcriptional antiterminator that reduces the polarity of long operons encoding secreted and surface-associated cell components of Salmonella enterica serovar Typhimurium, including O antigen and lipopolysaccharide core sugars. A DeltarfaH mutant strain is attenuated in mice (50% lethal dose [LD(50)], >10(8) CFU). To examine the potential for using rfaH in conjunction with other attenuating mutations, we designed a series of strains in which we replaced the native rfaH promoter with the tightly regulated arabinose-dependent araC P(BAD) promoter so that rfaH expression was dependent on exogenously supplied arabinose provided during in vitro growth. Following colonization of host lymphoid tissues, where arabinose was not available, the P(BAD) promoter was no longer active and rfaH was not expressed. In the absence of RfaH, O antigen and core sugars were not synthesized. We constructed three mutant strains that expressed different levels of RfaH by altering the ribosome-binding sequence and start codon. One mutation, DeltaP(rfaH178), was introduced into the attenuated vaccine strain chi9241 (DeltapabA DeltapabB DeltaasdA) expressing the pneumococcal surface protein PspA from an Asd(+) balanced-lethal plasmid. Mice immunized with this strain and boosted 4 weeks later induced higher levels of serum immunoglobulin G specific for PspA and for outer membrane proteins from other enteric bacteria than either an isogenic DeltarfaH derivative or the isogenic RfaH(+) parent. Eight weeks after primary oral immunization, mice were challenged with 200 LD(50) of virulent Streptococcus pneumoniae WU2. Immunization with DeltaP(rfaH178) mutant strains led to increased levels of protection compared to that of the parent chi9241 and of a DeltarfaH derivative of chi9241.

Characterisation of a live Salmonella vaccine stably expressing the Mycobacterium tuberculosis Ag85B-ESAT6 fusion protein

A recombinant Salmonella enterica serovar Typhimurium (S. Typhimurium) vaccine strain was constructed that stably expressed the Mycobacterium tuberculosis fusion antigen Ag85B–ESAT6 from the chromosome. Live oral vaccination of mice with the Salmonella/Ag85B–ESAT6 strain generated a potent anti-Ag85B–ESAT6 T_H1 response with high antibody titres with a IgG2a-bias and significant IFN-γ production lasting over a 120-day period. When mice primed with the Salmonella/Ag85B–ESAT6 vaccine were mucosally boosted with the Ag85B–ESAT6 antigen and adjuvant the IFN-γ responses increased markedly. To determine the protective efficacy of this vaccine strain, guinea pigs were immunised and followed for a 30-week period after aerosol challenge with M. tuberculosis. The heterologous prime-boost strategy of live Salmonella vaccine followed by a systemic boost of antigen and adjuvant reduced the levels of M. tuberculosis bacteria in the lungs and spleen to the same extent as BCG. Additionally, this vaccination regimen was observed to be statistically equivalent in terms of protection to immunisation with BCG. Thus, live oral priming with the recombinant Salmonella/Ag85B–ESAT6 and boosting with Ag85B–ESAT6 plus the adjuvant LTK63 represents an effective mucosal vaccination regimen.

An oral recombinant Salmonella enterica serovar Typhimurium mutant elicits systemic antigen-specific CD8+ T cell cytokine responses in mice

Background

The induction of antigen-specific CD8+ T cell cytokine responses against an attenuated, oral recombinant Salmonella enterica serovar Typhimurium vaccine expressing a green fluorescent protein (GFP) model antigen was investigated. A GFP expression plasmid was constructed in which the gfp gene was fused in-frame with the 5' domain of the Escherichia coli β-galactosidase α-gene fragment with expression under the lac promoter. Groups of mice were orally immunized three times with the bacteria and systemic CD8+ T cell cytokine responses were evaluated.

Results

High level of the GFP model antigen was expressed by the recombinant Salmonella vaccine vector. Systemic GFP-specific CD8+ T cell cytokine (IFN-γ and IL-4) immune responses were detected after mice were orally vaccinated with the bacteria. It was shown that 226 net IFN-γ and 132 net IL-4 GFP-specific SFUs/10e6 splenocytes were formed in an ELISPOT assay. The level of IFN-γ produced by GFP peptide-stimulated cells was 65.2-fold above background (p < 0.05). The level of IL-4 produced by the cells was 10.4-fold above background (p < 0.05).

Conclusion

These results suggested that a high expressing recombinant Salmonella vaccine given orally to mice would elicit antigen-specific CD8+ T cell responses in the spleen. Salmonella bacteria may, therefore, be used as potential mucosal vaccine vectors.

MyD88 signaling is not essential for induction of antigen-specific B cell responses but is indispensable for protection against Streptococcus pneumoniae infection following oral vaccination with attenuated Salmonella expressing PspA antigen

TLRs directly induce innate host defense responses, but the mechanisms of TLR-mediated adaptive immunity remain subject to debate. In this study, we clarified a role of TLR-mediated innate immunity for induction of adaptive immunity by oral vaccination with a live recombinant attenuated Salmonella enteric serovar Typhimurium vaccine (RASV) strain expressing Streptococcus pneumoniae surface protein A (PspA) Ag. Of note, oral or intranasal vaccination with RASV expressing PspA resulted in identical or even significantly higher levels of PspA-specific IgG and IgA responses in the systemic and mucosal compartments of MyD88(-/-) mice of either BALB/c or C57BL/6 background when compared with those of wild-type mice. Although PspA-specific CD4(+) T cell proliferation in the MyD88(-/-) mice was minimal, depletion of CD4(+) T cells abolished PspA-specific IgG and IgA responses in the MyD88(-/-) mice of BALB/c background. Of the greatest interest, MyD88(-/-) mice that possessed high levels of PspA-specific IgG and IgA responses but minimal levels of CD4(+) T cell responses died earlier than nonvaccinated and vaccinated wild-type mice following i.v. or intranasal challenge with virulent S. pneumoniae. Taken together, these results suggest that innate immunity activated by MyD88 signals might not be necessary for Ag-specific Ab induction in both systemic and mucosal sites but is critical for protection following oral vaccination with attenuated Salmonella expressing PspA.

Regulation of Vi capsular polysaccharide synthesis in Salmonella enterica serotype Typhi

The synthesis of Vi polysaccharide, a major virulence determinant in Salmonella enterica serotype Typhi (S. Typhi), is under the control of two regulatory systems, ompR-envZ and rscB-rscC, which respond to changes in osmolarity. Some S. Typhi isolates exhibit over-expression of Vi polysaccharide, which masks clinical detection of LPS O-antigen. This variation in Vi polysaccharide and O-antigen display (VW variation) has been observed since the initial studies of S. Typhi. We have reported that the status of the rpoS gene is responsible for this phenomenon. We review the regulatory network of the Vi polysaccharide, linking osmolarity and RpoS expression. Also, we discuss how this may impact live attenuated Salmonella vaccine development.

Regulated programmed lysis of recombinant Salmonella in host tissues to release protective antigens and confer biological containment

We have devised and constructed a biological containment system designed to cause programmed bacterial cell lysis with no survivors. We have validated this system, using Salmonella enterica serovar Typhimurium vaccines for antigen delivery after colonization of host lymphoid tissues. The system is composed of two parts. The first component is Salmonella typhimurium strain chi8937, with deletions of asdA and arabinose-regulated expression of murA, two genes required for peptidoglycan synthesis and additional mutations to enhance complete lysis and antigen delivery. The second component is plasmid pYA3681, which encodes arabinose-regulated murA and asdA expression and C2-regulated synthesis of antisense asdA and murA mRNA transcribed from the P22 P(R) promoter. An arabinose-regulated c2 gene is present in the chromosome. chi8937(pYA3681) exhibits arabinose-dependent growth. Upon invasion of host tissues, an arabinose-free environment, transcription of asdA, murA, and c2 ceases, and concentrations of their gene products decrease because of cell division. The drop in C2 concentration results in activation of P(R), driving synthesis of antisense mRNA to block translation of any residual asdA and murA mRNA. A highly antigenic alpha-helical domain of Streptococcus pneumoniae Rx1 PspA was cloned into pYA3681, resulting in pYA3685 to test antigen delivery. Mice orally immunized with chi8937(pYA3685) developed antibody responses to PspA and Salmonella outer membrane proteins. No viable vaccine strain cells were detected in host tissues after 21 days. This system has potential applications with other Gram-negative bacteria in which biological containment would be desirable.

Tolerance in the absence of autoantigen

Regulatory T (T(reg)) cells show promise for treating autoimmune diseases, but their induction to elevated potency has been problematic when the most optimally derived cells are from diseased animals. To circumvent reliance on auto-antigen reactive T(reg) cells, stimulation to vaccine antigens (Ags) may offer a viable alternative while maintaining potency to protect against proinflammatory diseases. Our Salmonella vaccine expressing colonization factor Ag I (CFA/I) possesses anti-inflammatory properties, evident by elevated Th2 cell responses, reduced inflammatory cell infiltrates in the Peyer's patches, and an absence of proinflammatory cytokine production by infected macrophages. Given these findings, we hypothesized whether this vaccine would be protective against experimental autoimmune encephalomyelitis (EAE). As such, Salmonella-CFA/I protected in both prophylactic and therapeutic paradigms against proteolipid protein (PLP(139-151))-mediated EAE in SJL mice. The protected mice showed significantly reduced clinical disease and subsequent resolution when compared to PBS-treated controls. Histopathological studies showed reduced demyelination and no inflammation of spinal cords when compared to PBS- or Salmonella vector-treated mice. To ascertain whether the observed immune deviation was in part supported by T(reg) cells, analysis revealed involvement of FoxP3(+) CD25(+) CD4(+) T cells. Adoptive transfer of induced TGF-beta (+) T(reg) cells from vaccinated mice showed complete protection against PLP(139-151) challenge, but not by naive T(reg) cells. Partial protection to EAE was also achieved by the adoptive transfer of CD25(-) CD4(+) T cells, suggesting that Th2 cells also contributed. Thus, these data show that T(reg) cells are induced by oral vaccination with Salmonella-CFA/I contributing to the efficacious treatment of autoimmune disease.

The pyrH gene of Vibrio vulnificus is an essential in vivo survival factor

We have suggested an important role of the pyrH gene during the infectious process of Vibrio vulnificus. Previously, we have identified 12 genes expressed preferentially during human infections by using in vivo-induced antigen technology. Among the in vivo-expressed genes, pyrH encodes UMP kinase catalyzing UMP phosphorylation. Introduction of a deletion mutation to the pyrH gene was lethal to V. vulnificus, and an insertional mutant showed a high frequency of curing. We constructed a site-directed mutant strain (R62H/D77N) on Arg-62 and Asp-77, both predicted to be involved in UMP binding, and characterized the R62H/D77N strain compared with the previously reported insertional mutant. We further investigated the essential role of the pyrH gene in the establishment of infection using the R62H/D77N strain. Cytotoxicity was decreased in the R62H/D77N strain, and the defect was restored by an in trans complementation. The intraperitoneal 50% lethal dose of the R62H/D77N strain increased by 26- and 238,000-fold in normal and iron-overloaded mice, respectively. The growth of the R62H/D77N strain in 50% HeLa cell lysate, 100% human ascitic fluid, and 50% human serum was significantly retarded compared to that of the isogenic wild-type strain. The R62H/D77N mutant also had a critical defect in the ability to survive and replicate even in iron-overloaded mice. These results demonstrate that pyrH is essential for the in vivo survival and growth of V. vulnificus and should be an attractive new target for the development of antibacterial drugs and replication-controllable live attenuated vaccines.

Adjuvant effects of saponins on animal immune responses

Vaccines require optimal adjuvants including immunopotentiator and delivery systems to offer long term protection from infectious diseases in animals and man. Initially it was believed that adjuvants are responsible for promoting strong and sustainable antibody responses. Now it has been shown that adjuvants influence the isotype and avidity of antibody and also affect the properties of cell-mediated immunity. Mostly oil emulsions, lipopolysaccharides, polymers, saponins, liposomes, cytokines, ISCOMs (immunostimulating complexes), Freund's complete adjuvant, Freund's incomplete adjuvant, alums, bacterial toxins etc., are common adjuvants under investigation. Saponin based adjuvants have the ability to stimulate the cell mediated immune system as well as to enhance antibody production and have the advantage that only a low dose is needed for adjuvant activity. In the present study the importance of adjuvants, their role and the effect of saponin in immune system is reviewed.

Role of RpoS in fine-tuning the synthesis of Vi capsular polysaccharide in Salmonella enterica serotype Typhi

Regulation of the synthesis of Vi polysaccharide, a major virulence determinant in Salmonella enterica serotype Typhi, is under the control of two regulatory systems, ompR-envZ and rscB-rscC, which respond to changes in osmolarity. Some serotype Typhi strains exhibit overexpression of Vi polysaccharide, which masks clinical detection of lipopolysaccharide O antigen. This variation in Vi polysaccharide and O antigen display (VW variation) has been observed since the initial studies of serotype Typhi. In this study, we report that rpoS plays a role in this increased expression in Vi polysaccharide. We constructed a variety of isogenic serotype Typhi mutants that differed in their expression levels of RpoS and examined the role of the rpoS product in synthesis of Vi polysaccharide under different osmolarity conditions. Vi polysaccharide synthesis was also examined in serotype Typhi mutants in which the native promoter of the rpoS was replaced by an araCP(BAD) cassette, so that the expression of rpoS was arabinose dependent. The RpoS(-) strains showed increased syntheses of Vi polysaccharide, which at low and medium osmolarities masked O antigen detection. In contrast, RpoS(+) strains showed lower syntheses of Vi polysaccharide, and an increased detection of O antigen was observed. During exponential growth, when rpoS is unstable or present at low levels, serotype Typhi RpoS(+) strains overexpress the Vi polysaccharide at levels comparable to those for RpoS(-) strains. Our results show that RpoS is another regulator of Vi polysaccharide synthesis and contributes to VW variation in serotype Typhi, which has implications for the development of recombinant attenuated Salmonella vaccines in humans.

Optimization of the delivery of heterologous proteins by the Salmonella enterica serovar Typhimurium type III secretion system for vaccine development

Type III protein secretion systems, which are organelles with the capacity to deliver bacterial proteins into host cells, have been adapted to deliver heterologous antigens for vaccine development. A limitation of these antigen delivery systems is that some proteins are not amenable to secretion through this pathway. We show here that proteins from the simian and human immunodeficiency viruses that are not permissive for secretion through a Salmonella enterica serovar Typhimurium type III secretion system can be modified to travel this secretion pathway by introduction of discrete mutations. Proteins optimized for secretion were presented more efficiently via the major histocompatibility complex class I pathway and were able to induce a better immune response.

Flagellin fusion proteins as adjuvants or vaccines induce specific immune responses

Vaccination is the most efficient prophylaxis against a variety of infectious diseases. New vaccination strategies rely on the incorporation of effective adjuvants, which stimulate the innate immune response and, in turn, activate the adaptive immune response. It is well established that flagellin induces inflammatory responses through the activation of antigen-presenting cells (APCs). In order to evaluate whether flagellin can serve as a carrier for the development of adjuvants or vaccines, we prepared a flagellin-enhanced green fluorescent protein (EGFP) fusion protein. Our results demonstrate that a flagellin-EGFP fusion protein is capable of stimulating APCs, resulting in the maturation of these cells and secretion of proinflammatory cytokines. Furthermore, APCs pulsed with the flagellin-EGFP fusion protein effectively process and present EGFP antigens. More importantly, animals immunized with the flagellin-EGFP fusion protein developed specific anti-EGFP T-cell responses. In contrast, recombinant EGFP was not able to stimulate APCs, nor did it induce a T-cell response. Thus, recombinant-flagellin fusion proteins may be suitable carriers as adjuvants or vaccines for the development of new vaccination strategies to induce and boost immune responses against infectious diseases and cancer.

Modern veterinary vaccines and the Shaman's apprentice

This paper is an overview and assessment of new, commercially available veterinary vaccines placed in a historical context. The authors critically evaluate the current state of the field of veterinary vaccines in both food and companion animals and the promises for future vaccine development. The authors maintain that there is considerable variability in safety and sustained efficacy among veterinary vaccines, especially those developed for companion animals. It is proposed that establishment of an international vaccine advisory committee be supported which would function to apprise the veterinary profession of the current status of vaccines and their use.