Multi-parameter flow cytometry as a process analytical technology (PAT) approach for the assessment of bacterial ghost production.

Flow cytometry (FCM) is a tool for the analysis of single-cell properties in a cell suspension. In this contribution, we present an improved FCM method for the assessment of E-lysis in Enterobacteriaceae. The result of the E-lysis process is empty bacterial envelopes-called bacterial ghosts (BGs)-that constitute potential products in the pharmaceutical field. BGs have reduced light scattering properties when compared with intact cells. In combination with viability information obtained from staining samples with the membrane potential-sensitive fluorescent dye bis-(1,3-dibutylarbituric acid) trimethine oxonol (DiBAC4(3)), the presented method allows to differentiate between populations of viable cells, dead cells, and BGs. Using a second fluorescent dye RH414 as a membrane marker, non-cellular background was excluded from the data which greatly improved the quality of the results. Using true volumetric absolute counting, the FCM data correlated well with cell count data obtained from colony-forming units (CFU) for viable populations. Applicability of the method to several Enterobacteriaceae (different Escherichia coli strains, Salmonella typhimurium, Shigella flexneri 2a) could be shown. The method was validated as a resilient process analytical technology (PAT) tool for the assessment of E-lysis and for particle counting during 20-l batch processes for the production of Escherichia coli Nissle 1917 BGs.

Protection against Shiga-Toxigenic Escherichia coli by Non-Genetically Modified Organism Receptor Mimic Bacterial Ghosts.

Shiga-toxigenic Escherichia coli (STEC) causes severe gastrointestinal infections in humans that may lead to life-threatening systemic sequelae, such as the hemolytic uremic syndrome (HUS). Rapid diagnosis of STEC infection early in the course of disease opens a window of opportunity for therapeutic intervention, for example, by administration of agents that neutralize Shiga toxin (Stx) in the gut lumen. We previously developed a recombinant bacterium that expresses a mimic of the Stx receptor globotriaosyl ceramide (Gb3) on its surface through modification of the lipopolysaccharide (A. W. Paton, R. Morona, and J. C. Paton, Nat Med 6:265-270, 2000, http://dx.doi.org/10.1038/73111). This construct was highly efficacious in vivo, protecting mice from otherwise fatal STEC disease, but the fact that it is a genetically modified organism (GMO) has been a barrier to clinical development. In the present study, we have overcome this issue by development of Gb3 receptor mimic bacterial ghosts (BGs) that are not classified as GMOs. Gb3-BGs neutralized Stx1 and Stx2 in vitro with high efficiency, whereas alternative Gb3-expressing non-GMO subbacterial particles (minicells and outer membrane blebs) were ineffective. Gb3-BGs were highly efficacious in a murine model of STEC disease. All mice (10/10) treated with Gb3-BGs survived challenge with a highly virulent O113:H21 STEC strain and showed no pathological signs of renal injury. In contrast, 6/10 mice treated with control BGs succumbed to STEC challenge, and survivors exhibited significant weight loss, neutrophilia, and histopathological evidence of renal damage. Thus, Gb3-BGs offer a non-GMO approach to treatment of STEC infection in humans, particularly in an outbreak setting.

Escherichia coli ghosts promote innate immune responses in human keratinocytes.

Bacterial ghosts (BGs) as non-living bacterial envelopes devoid of cytoplasmic content with preserved and intact inner and outer membrane structures of their living counterparts have been used to study the ability of their surface components for the induction of antimicrobial peptides and pro-inflammatory cytokines in human primary keratinocytes (KCs). Quantitative real-time PCR analysis revealed that incubation of KCs with BGs generated from wild-type Escherichia coli induced the mRNA expression of antimicrobial psoriasin (S100A7c) in a BGs particle concentration-dependent manner. Using immunoblot analysis we showed that BGs generated from the flagellin-deficient (ΔFliC) E. coli strain NK9375 were as effective as its isogenic wild-type (wt) E. coli strain NK9373 to induce psoriasin expression when normalized to BG particles being taken up by KCs. However, results obtained from endocytic activity of KCs reflect that internalization of BGs is greatly dependent on the presence of flagellin on the surface of BGs. Moreover, BGs derived from wt E. coli NK9373 strongly induced the release of the pro-inflammatory cytokines IL-6 and IL-8, compared to ΔFliC E. coli NK9375 BGs. Taken together, obtained data demonstrate that non-living BGs possessing all bacterial bio-adhesive surface properties in their original state while not posing any infectious threat have the capacity to induce the expression of innate immune modulators and that these responses are partially dependent on the presence of flagellin.

Applications of bacterial ghosts in biomedicine.

Bacterial Ghosts (BG) are empty cell envelopes of Gram-negative bacteria which have been produced by E-mediated lysis. BG are devoid of cytoplasmic content and in combination with the expression of the nuclease SNUC, BG are also devoid of chromosomal and plasmid DNA. Proof of concept and proof of principle studies showed that BG candidate vaccines are highly immunogenic and in many instances induce protective immunity against lethal challenge in animal models. Due to their nature of being bacterial envelope complexes, BG are endowed with intrinsic natural adjuvant activity. BG are able to stimulate the innate and adaptive immune system without any addition of exogenous adjuvants. Although the use of plasmid encoded genetic information is essential for the final make up of BG, BG are not to be considered as genetically manipulated organisms (GMO), as they are nonliving and devoid of genetic information. The latter aspect is of great importance for safety, as no pathogenic islands or antibiotic resistance cassettes can be transferred to other bacteria by horizontal gene transfer. This is an important difference to other chemical-, heat- and pressure- or radiation-inactivated vaccine candidates, which also very often need artificial adjuvants to be added to improve their immunogenicity. The final BG vaccine preparations are freeze dried and are stable for many years at ambient temperature. BG can also be used as carrier and delivery vehicles for drugs or active substances in tumor therapy and due to specific targeting of tumor cells allow a higher specificity of treatment and a reduction of the total amount of drug per application. As carrier of enzymatic activity BG can be used for a new concept of probiotics which can synthesise active compounds from substrates of the environment where they are applied with a certain preference for the gut system. Thus, BG represent a promising technology platform for novel vaccines including combination or DNA vaccines, as drug carriers for therapeutic approaches in tumor treatment and as novel probiotics.

Improving Intensive Care Unit and Ward Utilization by Adapting Master Surgery Schedules.

With increasing organizational and financial pressure on hospitals, each individual surgical treatment has to be reviewed and planned thoroughly. Apart from the expensive operating room facilities, proper staffing and planning of downstream units, like the wards or the intensive care units (ICUs), should be considered as well. In this article, we outline the relationship between a master surgery schedule (MSS), i.e., the assignment of surgical blocks to medical specialties, and the bed demand in the downstream units using an analytical model. By using historical data retrieved from the clinical information system and a patient flow model, we applied a recently developed algorithm for predicting bed demand based on the MSSs for patients of 3 surgical subspecialties of a hospital. Simulations with 3 different MSSs were performed. The impact on the required amount of beds in the downstream units was analyzed. We show the potential improvements of the current MSS considering 2 main goals: leveling workload among days and reduction of weekend utilization. We discuss 2 different MSSs, one decreasing the weekend ICU utilization by 20% and the other one reducing maximum ward bed demand by 7%. A test with 12 months of real-life data validates the results. The application of the algorithm provides detailed insights for the hospital into the impact of MSS designs on the bed demand in downstream units. It allowed creating MSSs that avoid peaks in bed demand and high weekend occupancy levels in the ICU and the ward.

Bacterial ghosts as antigen delivery vehicles.

The bacterial ghost system is a novel vaccine delivery system unusual in that it combines excellent natural intrinsic adjuvant properties with versatile carrier functions for foreign antigens. The efficient tropism of bacterial ghosts (BG) for antigen presenting cells promotes the generation of both cellular and humoral responses to heterologous antigens and carrier envelope structures. The simplicity of both BG production and packaging of (multiple) target antigens makes them particularly suitable for use as combination vaccines. Further advantages of BG vaccines include a long shelf-life without the need of cold-chain storage due to their freeze-dried status, they are safe as they do not involve host DNA or live organisms, they exhibit improved potency with regard to target antigens compared to conventional approaches, they are versatile with regards to DNA or protein antigen choice and size, and as a delivery system they offer high bioavailability.

Essential role of calcium in vascular endothelial growth factor A-induced signaling: mechanism of the antiangiogenic effect of carboxyamidotriazole.

Vascular endothelial growth factor-A (VEGF-A) plays a major role in tumor angiogenesis and raises the concentration of intracellular free calcium ([Ca2+]i). Carboxyamidotriazole (CAI), an inhibitor of calcium influx and of angiogenesis, is under investigation as a tumoristatic agent. We studied the effect of CAI and the role of [Ca2+]i in VEGF-A signaling in human endothelial cells. VEGF-A induced a biphasic [Ca2+]i signal. VEGF-A increased the level of intracellular inositol 1,4,5-trisphosphate (IP3), which suggests that VEGF-A releases Ca2+ from IP3-sensitive stores and induces store-operated calcium influx. Reduction of either extracellular or intracellular free Ca2+ inhibited VEGF-A-induced proliferation. CAI inhibited IP3 formation, both phases of the calcium signal, nitric oxide (NO) release, and proliferation induced by VEGF-A. CAI prevented neither activation of VEGF receptor-2 (VEGFR-2) (KDR/Flk-1), phospholipase C-g, or mitogen-activated protein kinase (MAP kinase) nor translocation of nuclear factor of activated T cells (NFAT). We conclude that calcium signaling is necessary for VEGF-A-induced proliferation. MAP kinase activation occurs independently of [Ca2+]i but is not sufficient to induce proliferation in the absence of calcium signaling. Inhibition of the VEGF-A-induced [Ca2+]i signal and proliferation by CAI can be explained by inhibition of IP3 formation and may contribute to the antiangiogenic action of CAI. Calcium-dependent NO formation may represent a link between calcium signaling and proliferation.

Bacterial ghosts--biological particles as delivery systems for antigens, nucleic acids and drugs.

Despite the exponential rate of discovery of new antigens and DNA vaccines resulting from modern molecular biology and proteomics, the lack of effective delivery technology is a major limiting factor in their application. The bacterial ghost system represents a platform technology for antigen, nucleic acid and drug delivery. Bacterial ghosts have significant advantages over other engineered biological delivery particles, owing to their intrinsic cellular and tissue tropic abilities, ease of production and the fact that they can be stored and processed without the need for refrigeration. These particles have found both veterinary and medical applications for the vaccination and treatment of tumors and various infectious diseases.

Escherichia coli Nissle 1917 bacterial ghosts retain crucial surface properties and express chlamydial antigen: an imaging study of a delivery system for the ocular surface.

To target chronic inflammatory ocular surface diseases, a drug delivery platform is needed that is safe, possesses immunomodulatory properties, and can be used either for drug delivery, or as a foreign antigen carrier. A new therapeutic approach that we have previously proposed uses nonliving bacterial ghosts (BGs) as a carrier-delivery system which can be engineered to carry foreign antigens and/or be loaded with therapeutic drugs. The parent strain chosen for development of our BG delivery system is the probiotic Escherichia coli strain Nissle 1917 (EcN), whose intrinsic properties trigger the innate immune system with the flagella and fimbriae used to attach and stimulate epithelial cells. In previous studies, we have shown that EcN BGs are safe for the ocular surface route, but evidence that EcN BGs retain flagella and fimbriae after transformation, has never been visually confirmed. In this study, we used different visualization techniques to determine whether flagella and fimbriae are retained on EcN BGs engineered either for drug delivery or as a foreign antigen carrier. We have also shown by immunoelectron microscopy that EcN retains two foreign antigens after processing to become EcN BGs. Furthermore, we demonstrated that BGs derived from EcN and expressing a foreign antigen attachment to conjunctival epithelial cells in vitro without causing reduced cell viability. These results are an important step in constructing a delivery system based on a nonliving probiotic that is suitable for use in ocular surface diseases pairing immunomodulation and targeted delivery.

Delivery of a Chlamydial Adhesin N-PmpC Subunit Vaccine to the Ocular Mucosa Using Particulate Carriers.

Trachoma, caused by the intracellular bacterium Chlamydia trachomatis (Ct), remains the world's leading preventable infectious cause of blindness. Recent attempts to develop effective vaccines rely on modified chlamydial antigen delivery platforms. As the mechanisms engaged in the pathology of the disease are not fully understood, designing a subunit vaccine specific to chlamydial antigens could improve safety for human use. We propose the delivery of chlamydia-specific antigens to the ocular mucosa using particulate carriers, bacterial ghosts (BGs). We therefore characterized humoral and cellular immune responses after conjunctival and subcutaneous immunization with a N-terminal portion (amino acid 1-893) of the chlamydial polymorphic membrane protein C (PmpC) of Ct serovar B, expressed in probiotic Escherichia coli Nissle 1917 bacterial ghosts (EcN BGs) in BALB/c mice. Three immunizations were performed at two-week intervals, and the immune responses were evaluated two weeks after the final immunization in mice. In a guinea pig model of ocular infection animals were immunized in the same manner as the mice, and protection against challenge was assessed two weeks after the last immunization. N-PmpC was successfully expressed within BGs and delivery to the ocular mucosa was well tolerated without signs of inflammation. N-PmpC-specific mucosal IgA levels in tears yielded significantly increased levels in the group immunized via the conjunctiva compared with the subcutaneously immunized mice. Immunization with N-PmpC EcN BGs via both immunization routes prompted the establishment of an N-PmpC-specific IFNγ immune response. Immunization via the conjunctiva resulted in a decrease in intensity of the transitional inflammatory reaction in conjunctiva of challenged guinea pigs compared with subcutaneously and non-immunized animals. The delivery of the chlamydial subunit vaccine to the ocular mucosa using a particulate carrier, such as BGs, induced both humoral and cellular immune responses. Further investigations are needed to improve the immunization scheme and dosage.

In vitro and in vivo uptake study of Escherichia coli Nissle 1917 bacterial ghosts: cell-based delivery system to target ocular surface diseases.

PURPOSE: For the successful topical administration of drugs or vaccines to treat ocular surface diseases, efficient and well-tolerated delivery systems/carriers for conjunctival delivery are crucial in the development of new treatment strategies. The present study investigated the efficiency of internalization of bacterial ghosts (BGs) produced from probiotic Escherichia coli Nissle 1917 (EcN) by human conjunctival epithelial (HCjE) cell line, the EcN BGs cytotoxicity for HCjE cells, and in vivo uptake of EcN BGs by conjunctival guinea pig epithelial cells. METHODS: The uptake of EcN BGs by HCjE cells was analyzed by laser scanning microscopy and flow cytometry. Immunohistochemistry was used to localize the EcN BGs in the guinea pig conjunctival tissue. Cytotoxicity of EcN BGs on HCjE cells was evaluated by measurement of LDH. RESULTS: Laser scanning microscopy and flow cytometry revealed that EcN BGs internalization by HCjE cells was time- and dose dependent. No cytotoxic effect on HCjE cells was observed after EcN BGs inoculation for 30 and 120 minutes, as well as 24 hours. In addition, the uptake of EcN BGs was detected in the conjunctival cells after in vivo administration of EcN BGs into the eye of the guinea pig. CONCLUSIONS: The findings that EcN BGs are nontoxic and effectively internalized in vitro by human and in vivo by guinea pig conjunctival cells comprise an important contribution to the future use of BGs as a system for conjunctival delivery of drugs and vaccines, either to treat or prevent ocular surface diseases.

Bacterial ghosts as carriers of protein subunit and DNA-encoded antigens for vaccine applications.

Bacterial ghosts (BGs) represent vaccine delivery systems gifted with outstanding natural adjuvant properties. BGs are empty cell envelopes of Gram-negative bacteria lacking cytoplasmic content yet retaining all unaltered morphological and structural features of their living counterparts. The intact surface make-up of BGs is easily recognized by professional APCs through pattern-recognition receptors, making them ideal for mucosal administration through oral, ocular, intranasal or aerogenic routes, which represent the most desirable methods of application in advanced vaccine use. BGs have been designed to be used as carriers of active substances and foreign antigens (protein and/or DNA) for vaccine development. This review highlights the salient features of the BGs' versatile multipurpose vaccine platform for application in a wide range of human and veterinary medicines.

Rectal single dose immunization of mice with Escherichia coli O157:H7 bacterial ghosts induces efficient humoral and cellular immune responses and protects against the lethal heterologous challenge.

Bacterial ghosts (BGs) have been applied through oral, aerogenic, intraocular or intranasal routes for mucosal immunization using a wide range of experimental animals. All these applications required a booster after primary immunization to achieve protective immunity against the lethal challenge. Here we report for the first time that a single rectal dose of BGs produced from enterohaemorrhagic Escherichia coli (EHEC) O157:H7 fully protects mice against a 50% lethal challenge with a heterologous EHEC strain given at day 55. BGs from EHEC O157:H7 were prepared by a combination of protein E-mediated cell lysis and expression of staphylococcal nuclease A guaranteeing the complete degradation of pathogen residual DNA. The lack of genetic material in the EHEC BGs vaccine abolished any potential hazard for horizontal gene transfer of plasmid encoded antibiotic resistance genes or pathogenic islands to the recipient's gut flora. Single rectal immunization using EHEC O157:H7 BGs without any addition of adjuvant significantly stimulated efficient humoral and cellular immune responses, and was equally protective as two immunizations, which indicates the possibility to develop a novel efficacious single dose mucosal EHEC O157:H7 BGs vaccine using a simplified immunization regimen.

Bacterial Ghosts as antigen and drug delivery system for ocular surface diseases: Effective internalization of Bacterial Ghosts by human conjunctival epithelial cells.

The purpose of the presented investigation was to examine the efficiency of the novel carrier system Bacterial Ghosts (BGs), which are empty bacterial cell envelopes of Gram-negative bacteria to target human conjunctival epithelial cells, as well as to test the endocytic capacity of conjunctival cells after co-incubation with BGs generated from different bacterial species, and to foreclose potential cytotoxic effects caused by BGs. The efficiency of conjunctival cells to internalize BGs was investigated using the Chang conjunctival epithelial cell line and primary human conjunctiva-derived epithelial cells (HCDECs) as in vitro model. A high capacity of HCDECs to functionally internalize BGs was detected with the level of internalization depending on the type of species used for BGs generation. Detailed analysis showed no cytotoxic effect of BGs on HCDECs independently of the used bacterial species. Moreover, co-incubation with BGs did not enhance expression of both MHC class I and class II molecules by HCDECs, but increased expression of ICAM-1. The high rates of BG's internalization by HCDECs with no BG-mediated cytotoxic impact designate this carrier system to be a promising candidate for an ocular surface drug delivery system. BGs could be useful for future therapeutic ocular surface applications and eye-specific disease vaccine development including DNA transfer.

The Bacterial Ghost platform system: production and applications.

The Bacterial Ghost (BG) platform technology is an innovative system for vaccine, drug or active substance delivery and for technical applications in white biotechnology. BGs are cell envelopes derived from Gram-negative bacteria. BGs are devoid of all cytoplasmic content but have a preserved cellular morphology including all cell surface structures. Using BGs as delivery vehicles for subunit or DNA-vaccines the particle structure and surface properties of BGs are targeting the carrier itself to primary antigen-presenting cells. Furthermore, BGs exhibit intrinsic adjuvant properties and trigger an enhanced humoral and cellular immune response to the target antigen. Multiple antigens of the native BG envelope and recombinant protein or DNA antigens can be combined in a single type of BG. Antigens can be presented on the inner or outer membrane of the BG as well as in the periplasm that is sealed during BG formation. Drugs or supplements can also be loaded to the internal lumen or periplasmic space of the carrier. BGs are produced by batch fermentation with subsequent product recovery and purification via tangential flow filtration. For safety reasons all residual bacterial DNA is inactivated during the BG production process by the use of staphylococcal nuclease A and/or the treatment with ß-propiolactone. After purification BGs can be stored long-term at ambient room temperature as lyophilized product. The production cycle from the inoculation of the pre-culture to the purified BG concentrate ready for lyophilization does not take longer than a day and thus meets modern criteria of rapid vaccine production rather than keeping large stocks of vaccines. The broad spectrum of possible applications in combination with the comparably low production costs make the BG platform technology a safe and sophisticated product for the targeted delivery of vaccines and active agents as well as carrier of immobilized enzymes for applications in white biotechnology.

Effective gene transfer to melanoma cells using bacterial ghosts.

Bacterial ghosts (BG) are cell envelopes preparations of Gram-negative bacteria devoid of cytoplasmic content produced by controlled expression of PhiX174 plasmid-encoded lysis gene E. Eight melanoma cell lines were investigated for their capacity to bind and phagocyte BG derived from Escherichia coli NM522 and Mannheimia haemolytica A23. High capability to bind BG was observed in almost all of the analyzed cell lines, furthermore cells were able to take up BG independently of the used bacterial species. Further, transfection efficiency of BG loaded with DNA in vitro was measured. The Bowes cells exhibited a high expression level of GFP and the incubation of cells with plasmid loaded BG led up to 82% transfection efficiency.

Proteomics and bioinformatics strategies to design countermeasures against infectious threat agents.

The potential devastation resulting from an intentional outbreak caused by biological warfare agents such as Brucella abortus and Bacillus anthracis underscores the need for next generation vaccines. Proteomics, genomics, and systems biology approaches coupled with the bacterial ghost (BG) vaccine delivery strategy offer an ideal approach for developing safer, cost-effective, and efficacious vaccines for human use in a relatively rapid time frame. Critical to any subunit vaccine development strategy is the identification of a pathogen's proteins with the greatest potential of eliciting a protective immune response. These proteins are collectively referred to as the pathogen's immunome. Proteomics provides high-resolution identification of these immunogenic proteins using standard proteomic technologies, Western blots probed with antisera from infected patients, and the pathogen's sequenced and annotated genome. Selected immunoreactive proteins can be then cloned and expressed in nonpathogenic Gram-negative bacteria. Subsequently, a temperature shift or chemical induction process is initiated to induce expression of the PhiX174 E-lysis gene, whose protein product forms an E tunnel between the inner and outer membrane of the bacteria, expelling all intracellular contents. The BG vaccine system is a proven strategy developed for many different pathogens and tested in a complete array of animal models. The BG vaccine system also has great potential for producing multiagent vaccines for protection to multiple species in a single formulation.

Bacterial ghosts as an oral vaccine: a single dose of Escherichia coli O157:H7 bacterial ghosts protects mice against lethal challenge.

Enterohemorrhagic Escherichia coli (EHEC) is a bacterial pathogen that is associated with several life-threatening diseases for humans. The combination of protein E-mediated cell lysis to produce EHEC ghosts and staphylococcal nuclease A to degrade DNA was used for the development of an oral EHEC vaccine. The lack of genetic material in the oral EHEC bacterial-ghost vaccine abolished any hazard of horizontal gene transfer of resistance genes or pathogenic islands to resident gut flora. Intragastric immunization of mice with EHEC ghosts without the addition of any adjuvant induced cellular and humoral immunity. Immunized mice challenged at day 55 showed 86% protection against lethal challenge with a heterologous EHEC strain after single-dose oral immunization and 93.3% protection after one booster at day 28, whereas the controls showed 26.7% and 30% survival, respectively. These results indicate that it is possible to develop an efficacious single-dose oral EHEC bacterial-ghost vaccine.

Bacterial ghosts as novel efficient targeting vehicles for DNA delivery to the human monocyte-derived dendritic cells.

Recombinant bacterial ghosts loaded with plasmids were tested as an antigen delivery system and as a potential mediator of maturation for human monocyte-derived dendritic cells (DCs). Bacterial ghosts are cell envelopes derived from Gram-negative bacteria; the intracellular content is released by the controlled expression of plasmid-encoded lysis gene E of PhiX174. All the cell surface structures of the native bacteria, including the outer membrane proteins, adhesins, LPS, lipid A, and peptidoglycans, are preserved. Co-incubation of immature DCs with ghosts resulted in decreased expression of CD1a, CD80, and CD83 molecules, while addition of maturation mix (TNF-alpha, IL-1 beta, IL-6, and PGE2) to the cultures enhanced expression of these molecules. No marked changes were observed in the expression of the CD11c, CD40, and CD86 surface molecules. The exposure of DCs to ghosts in combination with maturation mix resulted in a nonsignificant increase in their ability to activate T cells. DCs co-incubated with bacterial ghosts carrying plasmids encoding GFP in combination with maturation mix exhibited high expression levels of GFP (up to 85%). These results indicate that in addition to their well-established use as vaccines, bacterial ghosts can also be used as carriers of nucleic acid-encoded antigens.

Antigen discovery and delivery of subunit vaccines by nonliving bacterial ghost vectors.

The bacterial ghost (BG) platform system is a novel vaccine delivery system endowed with intrinsic adjuvant properties. BGs are nonliving Gram-negative bacterial cell envelopes which are devoid of their cytoplasmic contents, yet maintain their cellular morphology and antigenic structures, including bioadhesive properties. The main advantages of BGs as carriers of subunit vaccines include their ability to stimulate a high immune response and to target the carrier itself to primary antigen-presenting cells. The intrinsic adjuvant properties of BGs enhance the immune response to target antigens, including T-cell activation and mucosal immunity. Since native and foreign antigens can be carried in the envelope complex of BGs, combination vaccines with multiple antigens of diverse origin can be presented to the immune system simultaneously. Beside the capacity of BGs to function as carriers of protein antigens, they also have a high loading capacity for DNA. Thus, loading BGs with recombinant DNA takes advantage of the excellent bioavailability for DNA-based vaccines and the high expression rates of the DNA-encoded antigens in target cell types such as macrophages and dendritic cells. There are many spaces within BGs including the inner and outer membranes, the periplasmic space and the internal lumen which can carry antigens, DNA or mediators of the immune response. All can be used for subunit antigen to design new vaccine candidates with particle presentation technology. In addition, the fact that BGs can also carry piggyback large-size foreign antigen particles, increases the technologic usefulness of BGs as combination vaccines against viral and bacterial pathogens. Furthermore, the BG antigen carriers can be stored as freeze-dried preparations at room temperature for extended periods without loss of efficacy. The potency, safety and relatively low production cost of BGs offer a significant technical advantage over currently utilized vaccine technologies.