Immunogenicity and efficacy against lethal aerosol staphylococcal enterotoxin B challenge in monkeys by intramuscular and respiratory delivery of proteosome-toxoid vaccines

Effective Treatment of Staphylococcal Enterotoxin B Aerosol Intoxication in Rhesus Macaques by Using Two Parenterally Administered High-Affinity Monoclonal Antibodies

Staphylococcal enterotoxin B (SEB) is a protein exotoxin found on the cell surface of Staphylococcus aureus that is the source for multiple pathologies in humans. When purified and concentrated in aerosol form, SEB can cause an acute and often fatal intoxication and thus is considered a biological threat agent.

Staphylococcal enterotoxin B (SEB) is a protein exotoxin found on the cell surface of Staphylococcus aureus that is the source for multiple pathologies in humans. When purified and concentrated in aerosol form, SEB can cause an acute and often fatal intoxication and thus is considered a biological threat agent. There are currently no vaccines or treatments approved for human use. Studies with rodent models of SEB intoxication show that antibody therapy may be a promising treatment strategy; however, many have used antibodies only prophylactically or well before any clinical signs of intoxication are apparent. We assessed and compared the protective efficacies of two monoclonal antibodies, Ig121 and c19F1, when administered after aerosol exposure in a uniformly lethal nonhuman primate model of SEB intoxication. Rhesus macaques were challenged using small-particle aerosols of SEB and then were infused intravenously with a single dose of either Ig121 or c19F1 (10 mg/kg of body weight) at either 0.5, 2, or 4 h postexposure. Onset of clinical signs and hematological and cytokine response in untreated controls confirmed the acute onset and potency of the toxin used in the challenge. All animals administered either Ig121 or c19F1 survived SEB challenge, whereas the untreated controls succumbed to SEB intoxication 30 to 48 h postexposure. These results represent the successful therapeutic in vivo protection by two investigational drugs against SEB in a severe nonhuman primate disease model and punctuate the therapeutic value of monoclonal antibodies when faced with treatment options for SEB-induced toxicity in a postexposure setting.

Potent Neutralization of Staphylococcal Enterotoxin B In Vivo by Antibodies that Block Binding to the T-Cell Receptor

To develop an antibody (Ab) therapeutic against staphylococcal enterotoxin B (SEB), a potential incapacitating bioterrorism agent and a major cause of food poisoning, we developed a "class T" anti-SEB neutralizing Ab (GC132) targeting an epitope on SEB distinct from that of previously developed "class M" Abs. A systematic engineering approach was applied to affinity-mature Ab GC132 to yield an optimized therapeutic candidate (GC132a) with sub-nanomolar binding affinity. Mapping of the binding interface by hydrogen-deuterium exchange coupled to mass spectrometry revealed that the class T epitope on SEB overlapped with the T-cell receptor binding site, whereas other evidence suggested that the class M epitope overlapped with the binding site for the major histocompatibility complex. In the IgG format, GC132a showed ∼50-fold more potent toxin-neutralizing efficacy than the best class M Ab in vitro, and fully protected mice from lethal challenge in a toxic shock post-exposure model. We also engineered bispecific Abs (bsAbs) that bound tetravalently by utilizing two class M binding sites and two class T binding sites. The bsAbs displayed enhanced toxin neutralization efficacy compared with the respective monospecific Ab subunits as well as a mixture of the two, indicating that enhanced efficacy was due to heterotypic tetravalent binding to two non-overlapping epitopes on SEB. Together, these results suggest that class T anti-SEB Ab GC132a is an excellent candidate for clinical development and for bsAb engineering.

Adaptive Immunity Against Staphylococcus aureus

A complex interplay between host and bacterial factors allows Staphylococcus aureus to occupy its niche as a human commensal and a major human pathogen. The role of neutrophils as a critical component of the innate immune response against S. aureus, particularly for control of systemic infection, has been established in both animal models and in humans with acquired and congenital neutrophil dysfunction. The role of the adaptive immune system is less clear. Although deficiencies in adaptive immunity do not result in the marked susceptibility to S. aureus infection that neutrophil dysfunction imparts, emerging evidence suggests both T cell- and B cell-mediated adaptive immunity can influence host susceptibility and control of S. aureus. The contribution of adaptive immunity depends on the context and site of infection and can be either beneficial or detrimental to the host. Furthermore, S. aureus has evolved mechanisms to manipulate adaptive immune responses to its advantage. In this chapter, we will review the evidence for the role of adaptive immunity during S. aureus infections. Further elucidation of this role will be important to understand how it influences susceptibility to infection and to appropriately design vaccines that elicit adaptive immune responses to protect against subsequent infections.

Pulmonary vaccine delivery

This review will discuss developments in the field of pulmonary vaccine delivery. The possibilities of adopting aerosol-generation technology and specific pharmaceutical formulations for the purpose of pulmonary immunization are described. Aerosol-generation systems might offer advantages with respect to vaccine stability and antigenicity. Adjuvants and their inclusion in vaccine-delivery systems are described. Other formulation components, such as surfactants, particulate systems and dispersion of the aerosols are detailed in this paper. The noninvasive, relatively safe and low-cost nature of pulmonary delivery may provide great benefits to the public health vaccination campaign.

Protective effect of recombinant staphylococcal enterotoxin A entrapped in polylactic-co-glycolic acid microspheres against Staphylococcus aureus infection

Staphylococcus aureus is an important cause of nosocomial and community-acquired infections in humans and animals, as well as the cause of mastitis in dairy cattle. Vaccines aimed at preventing S. aureus infection in bovine mastitis have been studied for many years, but have so far been unsuccessful due to the complexity of the bacteria, and the lack of suitable vaccine delivery vehicles. The current study developed an Escherichia coli protein expression system that produced a recombinant staphylococcal enterotoxin A (rSEA) encapsulated into biodegradable microparticles generated by polylactic-co-glycolic acid (PLGA) dissolved in methylene chloride and stabilized with polyvinyl acetate. Antigen loading and surface properties of the microparticles were investigated to optimize particle preparation protocols. The prepared PLGA-rSEA microspheres had a diameter of approximately 5 μm with a smooth and regular surface. The immunogenicity of the PLGA-rSEA vaccine was assessed using mice as an animal model and showed that the vaccine induced a strong humoral immune response and increased the percent survival of challenged mice and bacterial clearance. Histological analysis showed moderate impairment caused by the pathogen upon challenge afforded by immunization with PLGA-rSEA microspheres. Antibody titer in the sera of mice immunized with PLGA-rSEA microparticles was higher than in vaccinated mice with rSEA. In conclusion, the PLGA-rSEA microparticle vaccine developed here could potentially be used as a vaccine against enterotoxigenic S. aureus.

Chimeric anti-staphylococcal enterotoxin B antibodies and lovastatin act synergistically to provide in vivo protection against lethal doses of SEB

Staphylococcal enterotoxin B (SEB) is one of a family of toxins secreted by Staphylococcus aureus that act as superantigens, activating a large fraction of the T-cell population and inducing production of high levels of inflammatory cytokines that can cause toxic shock syndrome (TSS) and death. Extracellular engagement of the TCR of T-cells and class II MHC of antigen presenting cells by SEB triggers the activation of many intracellular signaling processes. We engineered chimeric antibodies to block the extracellular engagement of cellular receptors by SEB and used a statin to inhibit intracellular signaling. Chimeric human-mouse antibodies directed against different neutralizing epitopes of SEB synergistically inhibited its activation of human T-cells in vitro. In the in vivo model of lethal toxic shock syndrome (TSS) in HLA-DR3 transgenic mice, two of these antibodies conferred significant partial protection when administered individually, but offered complete protection in a synergistic manner when given together. Similarly, in vivo, lovastatin alone conferred only partial protection from TSS similar to single anti-SEB antibodies. However, used in combination with one chimeric neutralizing anti-SEB antibody, lovastatin provided complete protection against lethal TSS in HLA-DR3 transgenic mice. These experiments demonstrate that in vivo protection against lethal doses of SEB can be achieved by a statin of proven clinical safety and chimeric human-mouse antibodies, agents now widely used and known to be of low immunogenicity in human hosts.

Antibodies for biodefense

Potential bioweapons are biological agents (bacteria, viruses, and toxins) at risk of intentional dissemination. Biodefense, defined as development of therapeutics and vaccines against these agents, has seen an increase, particularly in the US following the 2001 anthrax attack. This review focuses on recombinant antibodies and polyclonal antibodies for biodefense that have been accepted for clinical use. These antibodies aim to protect against primary potential bioweapons, or category A agents as defined by the Centers for Disease Control and Prevention (Bacillus anthracis, Yersinia pestis, Francisella tularensis, botulinum neurotoxins, smallpox virus, and certain others causing viral hemorrhagic fevers) and certain category B agents. Potential for prophylactic use is presented, as well as frequent use of oligoclonal antibodies or synergistic effect with other molecules. Capacities and limitations of antibodies for use in biodefense are discussed, and are generally applicable to the field of infectious diseases.

Immunotherapeutic approaches against Staphylococcus aureus

Staphylococcus aureus is a major cause of life-threatening infections such as bacteremia and endocarditis. Unfortunately, many strains of this bacterial species have become resistant to certain antibiotics, including methicillin and amoxicillin. These strains are known as methicillin-resistant S. aureus (MRSA). Therefore, the prophylactic and therapeutic potential of antistaphylococcal vaccines is currently being explored with priority. In animal models, (passive) immunization with (antibodies directed against) certain S. aureus surface components, staphylococcal toxins and capsular polysaccharides protects against S. aureus colonization or infection. However, immunization studies performed in humans show less promising results. So far, not a single antistaphylococcal vaccine successfully passed clinical trials. This article focuses on the results that were obtained with immunotherapeutic approaches directed against S. aureus in animal and human studies. In addition, it is discussed whether effective immunization approaches against S. aureus are feasible in humans.

Progress in the development of effective vaccines to prevent selected gram-positive bacterial infections

Infections caused by virulent Gram-positive bacteria, such as Staphylococcus aureus, group B streptococci and group A streptococci, remain significant causes of morbidity and mortality despite progress in antimicrobial therapy. Despite significant advances in the understanding of the pathogenesis of infection caused by these organisms, there are only limited strategies to prevent infection. In this article, we review efforts to develop safe and effective vaccines that would prevent infections caused by these 3 pathogens.

Novel targeted immunotherapy approaches for staphylococcal infection

IMPORTANCE OF THE FIELD

Staphylococcus aureus is a leading human pathogen in the hospital and the community. Many S. aureus strains are resistant to antibiotics, making treatment of S. aureus infections often very complicated. In contrast to many other bacterial pathogens, a working vaccine has never been found for S. aureus despite considerable efforts in academia and pharmaceutical companies.

AREAS COVERED IN THIS REVIEW

The latest strategies aimed at finding a working vaccine against S. aureus, including active and passive immunization efforts in pre-clinical and clinical stages, and the molecular reasons for why it may be difficult to develop a vaccine are discussed.

WHAT THE READER WILL GAIN

In addition to receiving an overview of current efforts in S. aureus vaccine research, the reader will understand that vaccine development for S. aureus may be difficult owing to the facts that S. aureus is a commensal microorganism and produces toxins that lyse white blood cells, thereby undermining a vaccine's role as a facilitator of opsonophagocytosis.

TAKE HOME MESSAGE

As a result of failed clinical trials with monovalent traditional vaccines, recent developments include a shift towards the potential use of polyvalent formulas and therapeutic antibodies and more systematic selection of optimal antigens.

Potent neutralization of staphylococcal enterotoxin B by synergistic action of chimeric antibodies

Staphylococcal enterotoxin B (SEB), a shock-inducing exotoxin synthesized by Staphylococcus aureus, is an important cause of food poisoning and is a class B bioterrorism agent. SEB mediates antigen-independent activation of a major subset of the T-cell population by cross-linking T-cell receptors (TCRs) with class II major histocompatibility complex (MHC-II) molecules of antigen-presenting cells, resulting in the induction of antigen independent proliferation and cytokine secretion by a significant fraction of the T-cell population. Neutralizing antibodies inhibit SEB-mediated T-cell activation by blocking the toxin's interaction with the TCR or MHC-II and provide protection against the debilitating effects of this superantigen. We derived and searched a set of monoclonal mouse anti-SEB antibodies to identify neutralizing anti-SEB antibodies that bind to different sites on the toxin. A pair of non-cross-reactive, neutralizing anti-SEB monoclonal antibodies (MAbs) was found, and a combination of these antibodies inhibited SEB-induced T-cell proliferation in a synergistic rather than merely additive manner. In order to engineer antibodies more suitable than mouse MAbs for use in humans, the genes encoding the VL and VH gene segments of a synergistically acting pair of mouse MAbs were grafted, respectively, onto genes encoding the constant regions of human Igkappa and human IgG1, transfected into mammalian cells, and used to generate chimeric versions of these antibodies that had affinity and neutralization profiles essentially identical to their mouse counterparts. When tested in cultures of human peripheral blood mononuclear cells or splenocytes derived from HLA-DR3 transgenic mice, the chimeric human-mouse antibodies synergistically neutralized SEB-induced T-cell activation and cytokine production.

Staphylococcal vaccines and immunotherapies

Staphylococcus aureus is an important pathogen in the hospital and in the community, and it is increasingly resistant to multiple antibiotics. A nonantimicrobial approach to controlling S aureus is needed. The most extensively tested vaccine against S aureus, which is a capsular polysaccharide-based vaccine known as StaphVAX, showed promise in an initial phase 3 trial, but was found to be ineffective in a confirmatory trial, leading to its development being halted. Likewise, a human IgG preparation known as INH-A21 (Veronate) with elevated levels of antibodies to the staphylococcal surface adhesins ClfA and SdrG made it into phase 3 testing, where it failed to show a clinical benefit. Several novel antigens are being tested for potential inclusion in a staphylococcal vaccine, including cell wall-anchored adhesin proteins and exotoxins. Given the multiple and sometimes redundant virulence factors of S aureus that enable it to be such a crafty pathogen, if a vaccine is to prove effective, it will have to be multicomponent, incorporating several surface proteins, toxoids, and surface polysaccharides.

Protective effects of recombinant staphylococcal enterotoxin type C mutant vaccine against experimental bovine infection by a strain of Staphylococcus aureus isolated from subclinical mastitis in dairy cattle

Staphylococcus aureus is one of the main etiological agents of bovine mastitis; however, antibiotics that are effective against bovine strains of S. aureus are not currently available. Staphylococcal enterotoxin type C (SEC), a superantigen, is the enterotoxin most frequently expressed by bovine strains of S. aureus and one of immunogenic determinants. The purpose of this study was to evaluate the protective effectiveness of recombinant SEC mutant vaccine (MastaVactrade mark) against experimentally induced bovine infection. Three representative SEC secreting strains were selected from 9 candidate isolates that showed various intensities of pathogenicity on mice and inoculated into 5 lactating dairy cattle at a concentration of 50-5.0x10(8) CFU per quarter. The optimal experimental bovine subclinical mastitis model was produced by inoculation with 50 CFU of S. aureus 409 per quarter, a level which was not lethal to mice. After the experimental model was determined, other 3 cattle were intramuscularly administered three doses of vaccine at day 0, at 2 wks and at 6 wks. Nine quarters of 3 vaccinated cattle and 8 quarters of 3 control cattle were then challenged with S. aureus 409. An SEC-specific ELISA test conducted at 4 wks post-immunization confirmed the presence of a high antibody titer against SEC in all vaccinated cattle. The somatic cell counts from the vaccinated group remained relatively low, whereas those of control group increased significantly after challenge with S. aureus. After challenge, S. aureus was not isolated from any cattle in the vaccinated group, whereas it was isolated from 75% of the cattle in the control group. These results indicate that recombinant SEC mutant vaccine had a protective effect against S. aureus intramammary infection in lactating cattle.

Staphylococcus aureus enterotoxin D is secreted in milk and stimulates specific antibody responses in cows in the course of experimental intramammary infection

An enterotoxin D (SED)-producing strain of Staphylococcus aureus was used to infect one mammary gland of each of 17 lactating dairy cows. All glands became infected and shed bacteria over a sampling period of 3 weeks. Serum and milk antibodies specific for SED were monitored by an enzyme-linked immunosorbent assay for 12 weeks. Elevated anti-SED antibodies were detected in all cows after infection, and immunoglobulin of the G2 subclass comprised most of the specific serum response. SED was detected in mastitic milk samples from two cows at levels of 5 to 10 ng/ml. An in vitro lymphocyte proliferation assay showed that SED at levels below 10 pg/ml induced proliferation of bovine lymphocytes and that sheep antiserum specific for SED neutralized this proliferative response. Sera obtained from the cows pre- and postinfection inhibited lymphocyte proliferation at SED concentrations of 10 and 50 ng/ml, respectively. The addition of SED to whole blood or to isolated neutrophils had no significant effect on neutrophil function in vitro. The results show that SED is secreted during mammary gland infection, is mitogenic for bovine lymphocytes, and stimulates the production of specific antibodies.

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.

Immunization with glutathioneS-transferase and mutant toxic shock syndrome toxin 1 fusion protein protects againstStaphylococcus aureusinfection

To investigate whether immunization with glutathione S-transferase (GST) and mutant toxic shock syndrome toxin 1 (mTSST-1) fusion protein can protect against Staphylococcus aureus infection, we purified a non-toxic mutant GST-mTSST-1 fusion protein. Mice were immunized with the GST-mTSST-1 plus alum adjuvant and then challenged with viable S. aureus. The results showed that the survival rate of GST-mTSST-1-immunized group was higher and the bacteria counts in the organs were significantly lower than those of the non-immunized mice. Immunization with GST-mTSST-1 induced strongly the production of TSST-1 specific antibodies, especially immunoglobulin G1 and immunoglobulin G2b. Furthermore, the serum samples from GST-mTSST-1-immunized mice also significantly inhibited interferon-gamma and tumor necrosis factor-alpha production from murine spleen cells by TSST-1. These results suggest that vaccination with GST-mTSST-1 provides protection against S. aureus infection and that the protection might be mediated by TSST-1-neutralizing antibody.

Vaccines against the category B toxins: Staphylococcal enterotoxin B, epsilon toxin and ricin

The threat of bioterrorism worldwide has accelerated the demand for the development of therapies and vaccines against the Category B toxins: staphylococcal enterotoxin B (SEB), epsilon toxin (ETX) produced by Clostridium perfringens types B and D, and ricin, a natural product of the castor bean. The diverse and unique nature of these toxins poses a challenge to vaccinologists. While formalin-inactivated toxins can successfully induce antibody-mediated protection in animals, their usefulness in humans is limited because of potential safety concerns. For this reason, research is now aimed at developing recombinant, attenuated vaccines based on a detailed understanding of the molecular mechanisms by which these toxins function. Vaccine development is further complicated by the fact that as bioterrorism agents, SEB, ETX and ricin would most likely be disseminated as aerosols or in food/water supplies. Our understanding of the mechanisms by which these toxins cross mucosal surfaces, and importance of mucosal immunity in preventing toxin uptake is only rudimentary.

A mutant of staphylococcal enterotoxin C devoid of bacterial superantigenic activity elicits a Th2 immune response for protection against Staphylococcus aureus infection

Staphylococcal enterotoxin C (SEC), a bacterial superantigenic exotoxin, is commonly produced by invasive Staphylococcus aureus isolates, especially methicillin-resistant strains and isolates from animal diseases. We constructed and expressed a nontoxic mutant SEC (mSEC) and investigated whether immunization with mSEC, which is devoid of superantigenic activity, can protect against S. aureus infection. Mice were immunized with mSEC and challenged with viable S. aureus. The bacterial counts in the organs of mSEC-immunized mice were significantly lower and the survival rate was higher than the corresponding values for the control group. Immunization with mSEC strongly induced the production of T-helper 2 type antibodies, immunoglobulin G1, and immunoglobulin G2b. The production of interleukin-10 (IL-10) and IL-4 was significantly greater in immunized mice challenged with S. aureus than in the control mice, whereas the production of gamma interferon (IFN-gamma) was significantly decreased in the immunized mice. The cytokine response in a spleen cell culture that was stimulated with heat-killed S. aureus or SEC showed that immunization with mSEC inhibited IFN-gamma production and up-regulated IL-10 production in vitro. Furthermore, IFN-gamma and tumor necrosis factor alpha production in vitro was significantly inhibited by sera from mSEC-immunized mice but not by sera from control mice. These results suggest that immunization with mSEC devoid of superantigenic properties provides protection against S. aureus infection and that the protection might be mediated by SEC-specific neutralizing antibodies.

Suitability of a recombinant Staphylococcus aureus enterotoxin C bovine variant for immunodiagnostics and therapeutic vaccine development

Recombinant bovine variant of staphylococcal enterotoxin C (SECbovine), produced as a NH2-terminal histidine hexamer fusion protein (His6-tagged SECbovine), expressed at high levels (25%) in Escherichia coli and affinity purified to homogeneity (99.9%), was tested for its diagnostic and therapeutic potentials. His6-tagged SECbovine is antigenically authentic to native SECbovine across host species, as confirmed by antibody-based capture detection assays using human, mouse, rabbit and chicken hyperimmune sera. His6-tagged SECbovine showed significant T-cell stimulation activity in vitro. His6-tagged SECbovine was immunogenic for IgG in mice (intragastric and intravenous routes) and rabbits (intramuscular and subcutaneous routes), dispensing immunoadjuvant coadministration. The formation of neutralizing antibodies reduced the severity of intoxication symptoms in immunized rabbits. Purified anti-recombinant SECbovine rabbit polyclonal IgG neutralized the pyrexic and diarrhoeagenic effects of native SEC/SED and recombinant SEC, tested by the kitten and rabbit bioassays, respectively.

Vaccine development strategies for improving immunization: the role of modern immunology

An ideal vaccine has certain biological and physical characteristics. Technological advances have provided new strategies that may help the design of such a vaccine.

The automated bioaerosol exposure system: Preclinical platform development and a respiratory dosimetry application with nonhuman primates

INTRODUCTION

Well-characterized inhalation exposure systems are critical for preclinical testing and pathogenesis studies. The automated bioaerosol exposure system (ABES) provides a microprocessor-driven inhalation platform that provides exquisite data acquisition and control over all aspects of inhalation exposures. Because this represents a new technology, the development and characteristics of the ABES are thoroughly discussed. In addition to control over homeostatic and aerosol conditions, the ABES incorporates a dosimetry function based on respiratory performance of the test animal during inhalation.

METHODS

To test the system, rhesus macaques were initially sham-exposed using the ABES in a head-only inhalation configuration. The ABES was subsequently used under biosafety level (BSL)-III conditions in a vaccine efficacy challenge using aerosolized staphylococcal enterotoxin B (SEB) toxin, again using the real-time dosimetry function of the system.

RESULTS

Sham exposure results indicated significant departures from corresponding whole-body plethysmography (WBP) respiratory function estimates taken before the inhalation procedure. The results of the SEB exposure demonstrated the utility of using the ABES to generate consistently accurate and precise inhalation dose.

DISCUSSION

Taken together, the results of the sham and toxin challenge experiments demonstrate that the dosimetry function of the ABES improves the precision and accuracy of inhaled dose delivery and calculation as compared to predictive WBP conducted before the exposure. The ABES represents a highly adaptable platform for the design of inhalation systems to suit the requirements of a variety of animal models.

Toxicity of the staphylococcal enterotoxin B mutants with histidine-to-tyrosine substitutions

In this study we made a series of site-directed mutants of staphylococcal enterotoxin B (SEB), in which histidine residues in the molecule were replaced by tyrosine. The mutant genes were cloned and expressed, and the corresponding proteins were purified. These mutant proteins were tested for binding to human HLA-DR4 and for mitogenetic activity in mouse splenocyte culture. Toxicity of the proteins in vivo was evaluated in the actinomycin D-primed C3H/HeJ mouse model. We found that SEB mutant proteins with fewer than four histidine-to-tyrosine (his-to-tyr) substitutions retained toxic properties similar to wild-type SEB. However, studies showed that his-to-tyr substitution of four consecutive histidine residues eliminated SEB toxicity. Our results clearly show that this genetically modified SEB protein is non-toxic and justifies its further development as a component of a new, safer vaccine to prevent SEB intoxication.

Corneal ulceration in pediatric patients: a brief overview of progress in topical treatment

Pediatric microbial keratitis is a rare but potentially devastating condition. The condition is similar to adult microbial keratitis, but is often characterized by a more severe inflammatory response. The micro-organisms that cause microbial keratitis in children are similar to the causative agents in adults, with herpes simplex and bacteria being the predominant causative agents, and fungi being less frequent. Of the bacterial pathogens, Pseudomonas aeruginosa, Staphylococcus aureus and alpha-hemolytic streptococci are common. The risk factors for pediatric keratitis include colonization of the eyes during birth and trauma to the cornea. Certain microbial factors involved in microbial keratitis are common to all micro-organisms, including adhesion to the cornea, penetration into the cornea, destruction of the corneal stroma (usually by microbial and/or host proteases), and recruitment of white blood cells to help defend the eye. Specific inflammatory responses that occur during pediatric microbial keratitis are not known in detail, but it is likely that cytokines and polymorphonuclear leucocytes are major factors, as they are in adult microbial keratitis. Treatment for pediatric microbial keratitis is usually the same as treatment for adult microbial keratitis; topical application of antimicrobial agents initially, followed by application of anti-inflammatory agents. With pediatric microbial keratitis, extra care must be taken to ensure nontoxicity due to blood adsorption. New microbial keratitis treatments are being developed and these mainly focus on new antimicrobials, antivirulence agents (such as vaccination against microbial toxins) or specific anti-inflammatory agents. There remains a clear need for increased research into the specific responses during microbial keratitis in children which will help progress new therapies as well as the development of new antimicrobials, especially new antifungal therapies.

Identification of a transcytosis epitope on staphylococcal enterotoxins

Staphylococcal enterotoxins (SE) are exoproteins produced by Staphylococcus aureus that act as superantigens and have been implicated as a leading cause of food-borne disease and toxic shock. Little is known about how these molecules penetrate the gut lining and gain access to both local and systemic immune tissues. To model movement in vitro of staphylococcal enterotoxins, we have employed a monolayer system composed of crypt-like human colonic T-84 cells. SEB and SEA showed comparable dose-dependent transcytosis in vitro, while toxic shock syndrome toxin (TSST-1) exhibited increased movement at lower doses. Synthetic peptides corresponding to specific regions of the SEB molecule were tested in vitro to identify the domain of the protein involved in the transcytosis of SE. A toxin peptide of particular interest contains the amino acid sequence KKKVTAQELD, which is highly conserved across all SE. At a toxin-to-peptide ratio of 1:10, movement of SEB across the monolayers was reduced by 85%. Antisera made against the SEB peptide recognized native SEB and also inhibited SEB transcytosis. Finally, the conserved 10-amino-acid peptide inhibited transcytosis of multiple staphylococcal enterotoxins, SEA, SEE, and TSST-1. These data demonstrate that this region of the staphylococcal enterotoxins plays a distinct role in toxin movement across epithelial cells. It has implications for the prevention of staphylococcal enterotoxin-mediated disease by design of a peptide vaccine that could reduce systemic exposure to oral or inhaled superantigens. Since the sequence identified is highly conserved, it allows for a single epitope blocking the transcytosis of multiple SE.

Development of Antistaphylococcal Vaccines

Staphylococcus aureus is frequently isolated from both hospital-acquired and community-acquired infections, and the emergence of antibiotic resistance among clinical isolates has made treatment of staphylococcal infections difficult. This scenario has sparked renewed interest in the development of a vaccine for individuals at high risk for staphylococcal infections. As part of the effort to develop a multicomponent vaccine against S. aureus, several vaccine candidates are currently being evaluated in animal models of staphylococcal infection or in human clinical trials. The most promising candidates to date include adhesins (fibronectin-binding protein, collagen-binding protein, and fibrinogen-binding protein ), a nontoxic alpha toxin mutant, and capsular polysaccharides type 5 and 8.

Mucosal vaccination with recombinantly attenuated staphylococcal enterotoxin B and protection in a murine model

Previous work in our laboratory revealed that mice parenterally vaccinated with recombinantly attenuated staphylococcal enterotoxin (SE) or toxic shock syndrome toxin 1 develop protective antibodies against a lethal intraperitoneal (i.p.) toxin challenge. This study investigated the efficacy of nasal and oral immunizations with an SEB vaccine (SEBv) toward an i.p. or mucosal (via an aerosol) toxin challenge. Both vaccination routes, with the immunoadjuvant cholera toxin (CT), elicited comparable SEB-specific immunoglobulin A (IgA) and IgG levels in saliva. Nasal or oral inoculations also generated SEB-specific IgA, IgG, and IgM in the serum, but the nasal route yielded higher specific IgG titers. SEBv alone, when given nasally or orally, did not induce any detectable SEB-specific antibody. Mice vaccinated mucosally were protected against a 50% lethal dose of wild-type SEB given i.p. or mucosally, thus demonstrating that nasal or oral administration of this SEBv, with CT, elicits systemic and mucosal antibodies to SEB that protect against SEB-induced lethal shock.

Immunization with alpha-toxin toxoid protects the cornea against tissue damage during experimental Staphylococcus aureus keratitis

Alpha-toxin is a major virulence factor in Staphylococcus aureus keratitis. Active or passive immunization with alpha-toxin toxoid could protect against corneal damage. Results show that either form of immunization did not kill bacteria but did significantly protect against corneal pathology, especially epithelial erosion.

Recombinant expression and neutralizing activity of an MHC class II binding epitope of toxic shock syndrome toxin-1

Toxic shock syndrome (TSS) is caused by the staphylococcal superantigen, TSST-1. The MHC class II binding domain of TSST-1 containing a conserved sequence with other related staphylococcal enterotoxins, comprising TSST-1 residues 47-64 [(T(47-64)], was expressed as a fusion protein with either glutathione-S-transferase (GST(47-64)), filamentous phage coat protein (pIII(47-64)), or E. coli outer membrane porin protein (OprF(47-64)), or synthesized as a peptide conjugated to bovine serum albumin, BSA(47-64). GST(47-64), OprF(47-64) and BSA(47-64), but not pIII(47-64), all induced high-titer T(47-64)-specific antibodies in Balb/c mice. However, only anti-GST(47-64) antibodies inhibited (125)I-TSST-1 binding to MHC class II and abrogated TSST-1-induced T cell mitogenesis and TNFalpha secretion in human peripheral blood mononuclear cells. Purified GST(47-64) also inhibited (125)I-TSST-1 binding in a dose-dependent manner. These findings suggest that GST(47-64) may have potential as a recombinant peptide vaccine or TSST-1 receptor inhibitor against TSS.

New approaches to mucosal immunization

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

The structural basis of T cell activation by superantigens

Superantigens (SAGs) are a class of immunostimulatory and disease-causing proteins of bacterial or viral origin with the ability to activate large fractions (5-20%) of the T cell population. Activation requires simultaneous interaction of the SAG with the V beta domain of the T cell receptor (TCR) and with major histocompatibility complex (MHC) class II molecules on the surface of an antigen-presenting cell. Recent advances in knowledge of the three-dimensional structure of bacterial SAGs, and of their complexes with MHC class II molecules and the TCR beta chain, provide a framework for understanding the molecular basis of T cell activation by these potent mitogens. These structures along with those of TCR-peptide/MHC complexes reveal how SAGs circumvent the normal mechanism for T cell activation by peptide/MHC and how they stimulate T cells expressing TCR beta chains from a number of different families, resulting in polyclonal T cell activation. The crystal structures also provide insights into the basis for the specificity of different SAGs for particular TCR beta chains, and for the observed influence of the TCR alpha chain on SAG reactivity. These studies open the way to the design of SAG variants with altered binding properties for TCR and MHC for use as tools in dissecting structure-activity relationships in this system.

HIV-1 Neutralizing Antibodies in the Genital and Respiratory Tracts of Mice Intranasally Immunized with Oligomeric gp160

Because mucosal surfaces are a primary route of HIV-1 infection, we evaluated the mucosal immunogenicity of a candidate HIV-1 vaccine, oligomeric gp160 (o-gp160). In prior studies, parenteral immunization of rabbits with o-gp160 elicited broad neutralizing serum Ab responses against both T cell line-adapted HIV-1 and some primary HIV-1 isolates. In this study, nasal immunization of mice with o-gp160, formulated with liposomes containing monophosphoryl lipid A (MPL), MPL-AF, proteosomes, emulsomes, or proteosomes with emulsomes elicited strong gp160-specific IgG and IgA responses in serum as well as vaginal, lung, and intestinal washes and fecal pellets. The genital, respiratory, and intestinal Abs were determined to be locally produced. No mucosal immune responses were measurable when the immunogen was given s.c. Abs from sera and from vaginal and lung washes preferentially recognized native forms of monomeric gp120, suggesting no substantial loss in protein tertiary conformation after vaccine formulation and mucosal administration. Inhibition of HIV-1MN infection of H9 cells was found in sera from mice immunized intranasally with o-gp160 formulated with liposomes plus MPL, proteosomes, and proteosomes plus emulsomes. Formulations of o-gp160 with MPL-AF, proteosomes, emulsomes, or proteosomes plus emulsomes elicited HIV-1MN-neutralizing Ab in lung wash, and formulations with proteosomes, emulsomes, or proteosomes plus emulsomes elicited HIV-1MN-neutralizing Ab in vaginal wash. These data demonstrate the feasibility of inducing both systemic and mucosal HIV-1-neutralizing Ab by intranasal immunization with an oligomeric gp160 protein.