Rotavirus vp7 antigen produced by Lactococcus lactis induces neutralizing antibodies in mice

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

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

Double-Labeling Method for Visualization and Quantification of Membrane-Associated Proteins in Lactococcus lactis

Lactococcus lactis displaying recombinant proteins on its surface can be used as a potential drug delivery vector in prophylactic medication and therapeutic treatments for many diseases. These applications enable live-cell mucosal and oral administration, providing painless, needle-free solutions and triggering robust immune response at the site of pathogen entry. Immunization requires quantitative control of antigens and, ideally, a complete understanding of the bacterial processing mechanism applied to the target proteins. In this study, we propose a double-labeling method based on a conjugated dye specific for a recombinantly introduced polyhistidine tag (to visualize surface-exposed proteins) and a membrane-permeable dye specific for a tetra-cysteine tag (to visualize cytoplasmic proteins), combined with a method to block the labeling of surface-exposed tetra-cysteine tags, to clearly obtain location-specific signals of the two dyes. This allows simultaneous detection and quantification of targeted proteins on the cell surface and in the cytoplasm. Using this method, we were able to detect full-length peptide chains for the model proteins HtrA and BmpA in L. lactis, which are associated with the cell membrane by two different attachment modes, and thus confirm that membrane-associated proteins in L. lactis are secreted using the Sec-dependent post-translational pathway. We were able to quantitatively follow cytoplasmic protein production and accumulation and subsequent export and surface attachment, which provides a convenient tool for monitoring these processes for cell surface display applications.

Lactic Acid Bacteria as Mucosal Immunity Enhancers and Antivirals through Oral Delivery

Mucosal vaccination offer an advantage over systemic inoculation from the immunological viewpoint. The development of an efficient vaccine is now a priority for emerging diseases such as COVID-19, that was declared a pandemic in 2020 and caused millions of deaths globally. Lactic acid bacteria (LAB) especially Lactobacillus are the vital microbiota of the gut, which is observed as having valuable effects on animals’ and human health. LAB produce lactic acid as the major by-product of carbohydrate degradation and play a significant role in innate immunity enhancement. LAB have significant characteristics to mimic pathogen infections and intrinsically possess adjuvant properties to enhance mucosal immunity. Increasing demand and deliberations are being substantially focused on probiotic organisms that can enhance mucosal immunity against viral diseases. LAB can also strengthen their host’s antiviral defense system by producing antiviral peptides, and releasing metabolites that prevent viral infections and adhesion to mucosal surfaces. From the perspectives of “one health” and the use of probiotics, conventional belief has opened up a new horizon on the use of LAB as antivirals. The major interest of this review is to depict the beneficial use of LAB as antivirals and mucosal immunity enhancers against viral diseases.

Induction of Immunogenic Response in BALB/c Mice by Live and Killed Form of Recombinant Lactococcus lactis Displaying EG95 of Echinococcus granulosus

Background:

CE is a zoonotic parasitic infection caused by Echinococcus granulosus worldwide and is associated with economic losses among livestock animals. EG95 is an immunogenic antigen from the E. granulosus.Lactococcus lactis has been prested as a safe vehicle for antigen delivery. The goal of this study was to design a novel L. lactis strain displaying EG95 as a vaccine delivery system.

Methods:

The eg95 encoding gene fragment fused to the M6 anchoring protein was cloned into the pNZ7021 vector, and L. lactis NZ9000 displaying recombinant EG95 was constructed. The expression of an approximately 32-kDa EG95 protein was confirmed by Western blotting and immunofluorescence analysis. The immune responses were evaluated in BALB/c mice immunized orally and subcutaneously with the live and killed recombinant L. lactis, respectively.

Results:

Total IgG level in mice immunized with heat-killed recombinant L. lactis (pNZ7021-eg95) significantly increased compared to the control group. sIgA was significantly higher in mice received live recombinant L. lactis (pNZ7021-eg95) compared to the control mice. Splenic lymphocytes from immunized mice represented the high levels of IFN-γ and the low-levels of IL-4 and IL-10.

Conclusion:

Our results indicate that immunization with EG95-expressing L. lactis can induce both specific humoral and cellular immune responses in mice.

Cytoplasmic expression of a model antigen with M Cell-Targeting moiety in lactic acid bacteria and implication of the mechanism as a mucosal vaccine via oral route

Lactic acid bacteria (LAB) have been widely studied as mucosal vaccine delivery carriers against many infectious diseases for heterologous expression of protein antigens. There are three antigen expression strategies for LAB: cytoplasmic expression (CE), cell surface display (SD), and extracellular secretion (ES). Despite the generally higher protein expression level and many observations of antigen-specific immunogenicity in CE, its application as a mucosal vaccine has been overlooked relative to SD and ES because of the antigens enclosed by the LAB cell wall. We hypothesized that the antigens in CE could be released from the LAB into the intestinal lumen before host bacterial access to gut-associated lymphoid tissue (GALT), which could contribute to antigen-specific immune responses after oral administration. To elucidate this hypothesis, three recombinant Lactobacillus plantarum (LP) strains were constructed to produce a model antigen, BmpB, with or without an M cell-targeting moiety, and their immunogenicities were analyzed comparatively as oral vaccines in mouse model. The data indicated that the recombinant LPs producing BmpBs with different conformations could induce mucosal immunity differentially. This suggests that the cytoplasmic antigens in LAB could be released into the intestinal lumen, subsequently translocated through M cells, and stimulate the GALT to generate antigen-specific immune responses. Therefore, the CE strategy has great potential, especially in the application of oral LAB vaccines as well as SD and ES strategies. This research provides a better understanding of the mechanism for recombinant oral LAB vaccines and gives insight to the future design of LAB vaccines and oral delivery applications for useful therapeutic proteins.

Combined use of lactic-acid-producing bacteria as probiotics and rotavirus vaccine candidates expressing virus-specific proteins

Due to the lower efficacy of currently approved live attenuated rotavirus (RV) vaccines in developing countries, a new approach to the development of safe mucosally administered live bacterial vectors is being considered, using probiotic bacteria as an efficient delivery platform for heterologous RV antigens. Lactic acid bacteria (LAB), which are considered food-grade bacteria and normal microbiota, have been utilized throughout history as probiotics and developed since the 1990s as a delivery system for recombinant heterologous proteins. Over the last decade, LAB have frequently been used as a platform for the delivery of various RV antigens to the mucosa. Given the appropriate safety profile for neonates and providing the benefits of probiotics, recombinant LAB-based vaccines could potentially address the need for a subunit RV vaccine. The present review focuses mainly on different recombinant LAB vaccine constructs for RV and their potential as an alternative recombinant vaccine against RV disease.

Protective Immunity Against Enterotoxigenic Escherichia coli by Oral Vaccination of Engineered Lactococcus lactis

Enterotoxigenic Escherichia coli (ETEC) is one of the leading causes of diarrhea in children globally, and thus suitable vaccines are desired. Antigen display on lactic acid bacteria is a reliable approach for efficient oral vaccination and preventing bowel diseases. To develop an oral vaccine against ETEC, the gene of the binding domain from heat-labile toxin (LTB), a key ETEC virulence factor, was codon-optimized and cloned into a construct containing a signal peptide and an anchor for display on L. lactis. Bioinformatics analysis showed a codon adaptation index of 0.95 for the codon-optimized gene. Cell surface expression of LTB was confirmed by transmission electron microscopy and blotting. White New Zealand rabbits were immunized per os (PO) with the recombinant L. lactis, and the antibody titers were assayed with ELISA. In vitro neutralization assay was performed using mouse adrenal tumor cells and rabbit ileal loop test was performed as the in vivo assay. ELISA results indicated that oral administration of the engineered L. lactis elicited a significant production of IgA in the intestine. In vitro neutralization assay showed that the effect of the toxin could be neutralized with 500 µg/ml of IgG isolated from the oral vaccine group. Furthermore, the dose of ETEC causing fluid accumulation in the ileal loop test showed a tenfold increase in rabbits immunized with either recombinant L. lactis or LTB protein compared to other groups. Our results imply that recombinant L. lactis could potentially be an effective live oral vaccine against ETEC toxicity.

Preparation of mouse anti-human rotavirus VP7 monoclonal antibody and its protective effect on rotavirus infection

The aim of the current study was to prepare and identify mouse anti-human rotavirus (RV) VP7 monoclonal antibodies and explore their protective effects on RV infection. The mouse anti-human RV VP7 monoclonal antibody was produced using the ascites method and identified via western blot analysis. In vitro neutralization of mouse anti-human RV VP7 monoclonal antibodies was detected by performing an MTT assay. The TCID₅₀ value was calculated to obtain antibody neutralization titers. A mouse RV infection model was generated to assess the protective effect of the mouse anti-human RV VP7 monoclonal antibody in experimental animals. Monoclonal antibodies were successfully prepared and their purity reached ≥90%. Western blotting demonstrated that monoclonal antibodies specifically bound to the purified Wa RV strain, with a specific reaction band at ~40 kDa. Monoclonal antibody in vitro neutralization results demonstrated that cell survival rate in the virus + monoclonal antibody group was higher than that in virus + maintenance fluid group (P<0.05). Monoclonal antibody neutralization titer detection revealed that the cytopathic effect did not extend beyond 4 days. In addition, the calculated monoclonal antibody neutralization titer was 1:446. The results revealed that the positive rate of colloidal gold RV in the 100 µl monoclonal antibody group was significantly lower than that in the control group (P<0.05). Furthermore, the protection rate of the 100 µl monoclonal antibody group was 71.4%, whereas the 50 µl monoclonal antibody group was 42.9% and the ribavirin group was 57.1%. In conclusion, the results of the current study demonstrated that mouse anti-human RV VP7 monoclonal antibodies can be successfully prepared using ascites method. These antibodies also effectively neutralize the cytotoxic effects of the human RV Wa strain in vitro and mouse anti-human RV VP7 monoclonal antibodies also exhibited a good protective role in mice. Furthermore, greater protective effects were observed at a higher dose and the protective effects of these high dose treatments were superior to that of ribavirin.

Current issues regarding the application of recombinant lactic acid bacteria to mucosal vaccine carriers

Over the past two decades, lactic acid bacteria (LAB) have been intensively studied as potential bacterial carriers for therapeutic materials, such as vaccine antigens, to the mucosal tissues. LAB have several attractive advantages as carriers of mucosal vaccines, and the effectiveness of LAB vaccines has been demonstrated in numerous studies. Research on LAB vaccines to date has focused on whether antigen-specific immunity, particularly antibody responses, can be induced. However, with recent developments in immunology, microbiology, and vaccinology, more detailed analyses of the underlying mechanisms, especially, of the induction of cell-mediated immunity and memory cells, have been required for vaccine development and licensure. In this mini-review, we will discuss the issues, including (i) immune responses other than antibody production, (ii) persistence of LAB vaccine immunity, (iii) comparative evaluation of LAB vaccines with any existing or reference vaccines, (iv) strategies for increasing the effectiveness of LAB vaccines, and (iv) effects of microbiota on the efficacy of LAB vaccines. Although these issues have been rarely studied or discussed to date in relation to LAB vaccine research, further understanding of them is critical for the practical application of LAB vaccine systems.

Oral immunization with LacVax® OmpA induces protective immune response against Shigella flexneri 2a ATCC 12022 in a murine model

Shigellosis is an acute invasive disease of the lower intestine, which afflicts millions of people worldwide with an estimated one million fatalities per annum. Despite of extensive research during the last two decades, a vaccine against multi-drug resistant Shigella is not yet available in the market. To provide a safe, effective and broad-spectrum vaccine against Shigella, we explored food grade bacteria Lactococcus lactis (L. lactis) for the delivery of conserved antigenic protein; Outer membrane protein A (OmpA) to the mucosal sites for effective elicitation of systemic and mucosal immunity. We have previously confirmed the immunogenic potential of recombinant L. lactis expressing OmpA (LacVax® OmpA) in BALB/c mice. In the present study, we have characterized the humoral and cellular immune profile of LacVax® OmpA and assessed its protective efficacy using a newly developed human like murine shigellosis model. The significant increase in OmpA specific serum IgG, fecal sIgA and a Th1 dominant immune response (indicated by high INF-γ/IL-4 ratio) in LacVax® OmpA immunized mice revealed successful activation of humoral and cellular immunity. The LacVax® OmpA immunized animals were also protected from human-like shigellosis when challenged with S. flexneri 2a ATCC 12022. The antigen specific serum IgG, fecal sIgA, INF-γ and IL-10 levels were found to be the significant correlates of protection. Collectively these results suggest that the LacVax® OmpA is a promising prophylactic candidate against shigellosis. However, the protective efficacy of LacVax® OmpA in the higher animals would further strengthen its future application in humans.

Rotavirus VP6 protein mucosally delivered by cell wall-derived particles from Lactococcus lactis induces protection against infection in a murine model

Rotaviruses are the primary cause of acute gastroenteritis in children worldwide. Although the implementation of live attenuated vaccines has reduced the number of rotavirus-associated deaths, variance in their effectiveness has been reported in different countries. This fact, among other concerns, leads to continuous efforts for the development of new generation of vaccines against rotavirus.In this work, we describe the obtention of cell wall-derived particles from a recombinant Lactococcus lactis expressing a cell wall-anchored version of the rotavirus VP6 protein. After confirming by SDS-PAGE, Western blot, flow cytometry and electronic immunomicroscopy that these particles were carrying the VP6 protein, their immunogenic potential was evaluated in adult BALB/c mice. For that, mucosal immunizations (oral or intranasal), with or without the dmLT [(double mutant Escherichia coli heat labile toxin LT(R192G/L211A)] adjuvant were performed. The results showed that these cell wall-derived particles were able to generate anti-rotavirus IgG and IgA antibodies only when administered intranasally, whether the adjuvant was present or not. However, the presence of dmLT was necessary to confer protection against rotavirus infection, which was evidenced by a 79.5 percent viral shedding reduction.In summary, this work describes the production of cell wall-derived particles which were able to induce a protective immune response after intranasal immunization. Further studies are needed to characterize the immune response elicited by these particles as well as to determine their potential as an alternative to the use of live L. lactis for mucosal antigen delivery.

Oral immunization with rotavirus VP7-CTB fusion expressed in transgenic Arabidopsis thaliana induces antigen-specific IgA and IgG and passive protection in mice

Human rotavirus (HRV) is the primary cause of severe gastroenteritis in children. However, there is currently no protective virus for rotavirus available. In the present study, an HRVVP7-cholera toxin B subunit (CTB) fusion protein was expressed in Arabidopsis thaliana. To determine the adjuvant effect of HRVVP7-CTB, HRVVP7 without CTB was expressed in the same manner. HRVVP7-CTB accounted for 0.39% of the total soluble protein (TSP) in the transgenic seeds and 52.65 µg/g of HRVVP7 protein was expressed in these seeds. Mice were immunized with TSP from the transformed seeds and produced serum immunoglobulin G (IgG) and mucosal IgA specifically directed against HRVVP7. Antibody titers were highest in mice orally immunized with the plant-expressed HRVVP7-CTB protein, whereas HRVVP7-CTB-specific IgG neutralized the rotavirus. Suckling pups born from dams immunized with the HRVVP7-CTB fusion protein were protected against challenge with virulent rotavirus. The results of the present study suggest that the HRVVP7-CTB fusion protein produced in A. thaliana may be a rotaviral-specific candidate subunit vaccine.

Immunization with r-Lactococcus lactis expressing outer membrane protein A of Shigella dysenteriae type-1: evaluation of oral and intranasal route of administration

AIMS

To evaluate the comparative immunogenic potential of food grade Lactococcus lactis expressing outer membrane protein A (OmpA) of Shigella dysenteriae type-1 (SD-1) when administered either orally or intranasally.

METHODS AND RESULTS

OmpA of SD-1 was cloned and expressed first in Escherichia coli and then in L. lactis. Presence of recombinant gene was confirmed by restriction enzyme digestion and immunoblot analysis. Using immobilized metal affinity chromatography, OmpA was purified from recombinant E. coliBL21 (DE3) and subcutaneously administered in BALB/c mice. Detection of OmpA-specific IgG antibodies by enzyme-linked immunosorbent assay (ELISA) confirmed the immunogenicity of OmpA. In order to establish r-L. lactis as a mucosal delivery vehicle, it was administered orally and nasally in BALB/c mice. Serum IgG and faecal IgA were assessed through ELISA to compare the relative potential of immunization routes and immunogenic potential of r-L. lactis. Immunization via the oral route proved superior to intranasal exposure.

CONCLUSION

Recombinant L. lactis expressing OmpA of SD-1 was found to be immunogenic. Oral administration of r-L. lactis elicited higher systemic and mucosal immune response when compared with the nasal route.

SIGNIFICANCE AND IMPACT OF THE STUDY

Using food grade recombinant L. lactis has implications in the development of a prophylactic against multidrug-resistant Shigella, which can be used as a prospective vaccine candidate. Evaluating mucosal routes of immunization demonstrated that the oral route of administration elicited better immune response against OmpA of Shigella.

Display of recombinant proteins at the surface of lactic acid bacteria: strategies and applications

Lactic acid bacteria (LAB) are promising vectors of choice to deliver active molecules to mucosal tissues. They are recognized as safe by the World Health Organization and some strains have probiotic properties. The wide range of potential applications of LAB-driven mucosal delivery includes control of inflammatory bowel disease, vaccine delivery, and management of auto-immune diseases. Because of this potential, strategies for the display of proteins at the surface of LAB are gaining interest. To display a protein at the surface of LAB, a signal peptide and an anchor domain are necessary. The recombinant protein can be attached to the membrane layer, using a transmembrane anchor or a lipoprotein-anchor, or to the cell wall, by a covalent link using sortase mediated anchoring via the LPXTG motif, or by non-covalent liaisons employing binding domains such as LysM or WxL. Both the stability and functionality of the displayed proteins will be affected by the kind of anchor used. The most commonly surfaced exposed recombinant proteins produced in LAB are antigens and antibodies and the most commonly used LAB are lactococci and lactobacilli. Although it is not necessarily so that surface-display is the preferred localization in all cases, it has been shown that for certain applications, such as delivery of the human papillomavirus E7 antigen, surface-display elicits better biological responses, compared to cytosolic expression or secretion. Recent developments include the display of peptides and proteins targeting host cell receptors, for the purpose of enhancing the interactions between LAB and host. Surface-display technologies have other potential applications, such as degradation of biomass, which is of importance for some potential industrial applications of LAB.

Lactic acid bacteria--20 years exploring their potential as live vectors for mucosal vaccination

Lactic acid bacteria (LAB) are a diverse group of Gram-positive, nonsporulating, low G + C content bacteria. Many of them have been given generally regarded as safe status. Over the past two decades, intensive genetic and molecular research carried out on LAB, mainly Lactococcus lactis and some species of the Lactobacillus genus, has revealed new, potential biomedical LAB applications, including the use of LAB as adjuvants, immunostimulators, or therapeutic drug delivery systems, or as factories to produce therapeutic molecules. LAB enable immunization via the mucosal route, which increases effectiveness against pathogens that use the mucosa as the major route of entry into the human body. In this review, we concentrate on the encouraging application of Lactococcus and Lactobacillus genera for the development of live mucosal vaccines. First, we present the progress that has recently been made in the field of developing tools for LAB genetic manipulations, which has resulted in the successful expression of many bacterial, parasitic, and viral antigens in LAB strains. Next, we discuss the factors influencing the efficacy of the constructed vaccine prototypes that have been tested in various animal models. Apart from the research focused on an application of live LABs as carriers of foreign antigens, a lot of work has been recently done on the potential usage of nonliving, nonrecombinant L. lactis designated as Gram-positive enhancer matrix (GEM), as a delivery system for mucosal vaccination. The advantages and disadvantages of both strategies are also presented.

Modulation of peanut-induced allergic immune responses by oral lactic acid bacteria-based vaccines in mice

Peanut allergy (PNA) has becoming a non-negligible health concern worldwide. Thus far, allergen-specific immunotherapy aimed at inducing mucosal tolerance has widely been regarded as a major management strategy for PNA. The safety profiles and the intrinsic probiotic properties of lactic acid bacteria (LAB) render them attractive delivery vehicles for mucosal vaccines. In the present study, we exploited genetically modified Lactococcus lactis to produce peanut allergen Ara h 2 via different protein-targeting systems and their immunomodulatory potency for allergic immune responses in mice were investigated. By comparison with the strain expressing the cytoplasmic form of Ara h 2 (LL1), the strains expressing the secreted and anchored forms of Ara h 2 (LL2 and LL3) were more potent in redirecting a Th2-polarized to a non-allergic Th1 immune responses. Induction of SIgA and regulatory T cells were also observed at the local levels by orally administration of recombinant L. lactis. Our results indicate that allergen-producing L. lactis strains modulated allergic immune responses and may be developed as promising mucosal vaccines for managing allergic diseases.

Pushing the Bacterial Envelope

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

Antigenicity and immunogenicity of rotavirus VP6 protein expressed on the surface of Lactococcus lactis

Group A rotaviruses are the major etiologic agents of acute gastroenteritis worldwide in children and young animals. Among its structural proteins, VP6 is the most immunogenic and is highly conserved within this group. Lactococcus lactis is a food-grade, Gram-positive, and nonpathogenic lactic acid bacteria that has already been explored as a mucosal delivery system of heterologous antigens. In this work, the nisin-controlled expression system was used to display the VP6 protein at the cell surface of L. lactis. Conditions for optimal gene expression were established by testing different nisin concentrations, cell density at induction, and incubation times after induction. Cytoplasmic and cell wall protein extracts were analyzed by Western blot and surface expression was confirmed by flow cytometry. Both analysis provided evidence that VP6 was efficiently expressed and displayed on the cell surface of L. lactis. Furthermore, the humoral response of mice immunized with recombinant L. lactis was evaluated and the displayed recombinant VP6 protein proved to be immunogenic. In conclusion, this is the first report of displaying VP6 protein on the surface of L. lactis to induce a specific immune response against rotavirus. These results provide the basis for further evaluation of this VP6-displaying L. lactis as a mucosal delivery vector in a mouse model of rotavirus infection.

A Novel Lactococcal Vaccine Expressing a Peptide from the M2 Antigen of H5N2 Highly Pathogenic Avian Influenza A Virus Prolongs Survival of Vaccinated Chickens

A cost-effective and efficacious influenza vaccine for use in commercial poultry farms would help protect against avian influenza outbreaks. Current influenza vaccines for poultry are expensive and subtype specific, and therefore there is an urgent need to develop a universal avian influenza vaccine. We have constructed a live bacterial vaccine against avian influenza by expressing a conserved peptide from the ectodomain of M2 antigen (M2e) on the surface of Lactococcus lactis (LL). Chickens were vaccinated intranasally with the lactococcal vaccine (LL-M2e) or subcutaneously with keyhole-limpet-hemocyanin conjugated M2e (KLH-M2e). Vaccinated and nonvaccinated birds were challenged with high pathogenic avian influenza virus A subtype H5N2. Birds vaccinated with LL-M2e or KLH-M2e had median survival times of 5.5 and 6.0 days, respectively, which were significantly longer than non-vaccinated birds (3.5 days). Birds vaccinated subcutaneously with KLH-M2e had a lower mean viral burden than either of the other two groups. However, there was a significant correlation between the time of survival and M2e-specific serum IgG. The results of these trials show that birds in both vaccinated groups had significantly (P < 0.05) higher median survival times than non-vaccinated birds and that this protection could be due to M2e-specific serum IgG.

Mucosal Lactobacillus vectored vaccines

Traditional non-gastrointestinal vaccines can prevent effectively the invasion of pathogens; however, these vaccines are less effective against mucosal infections because there is not a sufficient immune response at the mucosa. Most pathogens invade via a mucosal pathway (oral, intranasal, or vaginal). It is widely accepted that Lactobacillus species play a critical role as commensals in the gastrointestinal (GI) tract. Their ability to survive in the digestive tract, their close association with the intestinal epithelium, their immunomodulatory properties and their safety even when consumed in large amounts make lactobacilli attractive candidates for live vehicles for the delivery of immunogens to the intestinal mucosa. The oral or intranasal administration of Lactobacillus-based vaccines is a promising method to control mucosal infection because these vaccines could induce strong humoral and cellular immune responses both in the blood and at mucosal sites.

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.

Mucosal vaccination and therapy with genetically modified lactic acid bacteria

Lactic acid bacteria (LAB) have proved to be effective mucosal delivery vehicles that overcome the problem of delivering functional proteins to the mucosal tissues. By the intranasal route, both live and killed LAB vaccine strains have been shown to elicit mucosal and systemic immune responses that afford protection against infectious challenges. To be effective via oral administration, frequent dosing over several weeks is required but new targeting and adjuvant strategies have clearly demonstrated the potential to increase the immunogenicity and protective immunity of LAB vaccines. Oral administration of Lactococcus lactis has been shown to induce antigen-specific oral tolerance (OT) to secreted recombinant antigens. LAB delivery is more efficient at inducing OT than the purified antigen, thus avoiding the need for purification of large quantities of antigen. This approach holds promise for new therapeutic interventions in allergies and antigen-induced autoimmune diseases. Several clinical and research reports demonstrate considerable progress in the application of genetically modified L. lactis for the treatment of inflammatory bowel disease (IBD). New medical targets are on the horizon, and the approval by several health authorities and biosafety committees of a containment system for a genetically modified L. lactis that secretes Il-10 should pave the way for new LAB delivery applications in the future.

Modern approaches in probiotics research to control foodborne pathogens

Foodborne illness is a serious public health concern. There are over 200 known microbial, chemical, and physical agents that are known to cause foodborne illness. Efforts are made for improved detection, control and prevention of foodborne pathogen in food, and pathogen associated diseases in the host. Several commonly used approaches to control foodborne pathogens include antibiotics, natural antimicrobials, bacteriophages, bacteriocins, ionizing radiations, and heat. In addition, probiotics offer a potential intervention strategy for the prevention and control of foodborne infections. This review focuses on the use of probiotics and bioengineered probiotics to control foodborne pathogens, their antimicrobial actions, and their delivery strategies. Although probiotics have been demonstrated to be effective in antagonizing foodborne pathogens, challenges exist in the characterization and elucidation of underlying molecular mechanisms of action and in the development of potential delivery strategies that could maintain the viability and functionality of the probiotic in the target organ.

Lactococcus lactis-based vaccines from laboratory bench to human use: an overview

Developing effective vaccines is an important weapon in the battle against potential pathogens and their evolving antibiotic resistance trends. Several vaccine delivery vectors have been investigated among which the generally regarded as safe (GRAS) Lactococcus lactis has a distinguished position. In this review, different factors affecting the efficacy of L. lactis-based vaccines are discussed. In addition, the issues of biological containment and pharmaceutical quality assurance of L. lactis vaccines are highlighted. These issues are critical for the success of medical translation of L. lactis-based vaccines from research laboratories to clinical use by ensuring consistent manufacturing of safe and efficacious vaccines.

Dissimilar properties of two recombinant Lactobacillus acidophilus strains displaying Salmonella FliC with different anchoring motifs

Display of heterologous antigens on the cell surface is considered a useful technique for vaccine delivery by recombinant lactobacilli. In this study, two recombinant Lactobacillus acidophilus derivatives displaying Salmonella flagellin (FliC) were constructed using different anchor motifs. In one instance, the FliC protein was fused to the C-terminal region of a cell envelope proteinase (PrtP) and was bound to the cell wall by electrostatic bonds. In the other case, the same antigen was conjugated to the anchor region of mucus binding protein (Mub) and was covalently associated with the cell wall by an LPXTG motif. These two recombinant L. acidophilus cell surface displays resulted in dissimilar maturation and cytokine production by human myeloid dendritic cells. The surface-associated antigen was highly sensitive to simulated gastric and small intestinal juices. By supplementation with bicarbonate buffer and soybean trypsin inhibitor, the cell surface antigen was protected from proteolytic enzymes during gastric challenge in vitro. The protective reagents also increased the viability of the L. acidophilus cells upon challenge with simulated digestive juices. These results demonstrate the importance of protecting cells and their surface-associated antigens during oral immunization.

Lactococci and lactobacilli as mucosal delivery vectors for therapeutic proteins and DNA vaccines

Food-grade Lactic Acid Bacteria (LAB) have been safely consumed for centuries by humans in fermented foods. Thus, they are good candidates to develop novel oral vectors, constituting attractive alternatives to attenuated pathogens, for mucosal delivery strategies. Herein, this review summarizes our research, up until now, on the use of LAB as mucosal delivery vectors for therapeutic proteins and DNA vaccines. Most of our work has been based on the model LAB Lactococcus lactis, for which we have developed efficient genetic tools, including expression signals and host strains, for the heterologous expression of therapeutic proteins such as antigens, cytokines and enzymes. Resulting recombinant lactococci strains have been tested successfully for their prophylactic and therapeutic effects in different animal models: i) against human papillomavirus type 16 (HPV-16)-induced tumors in mice, ii) to partially prevent a bovine β-lactoglobulin (BLG)-allergic reaction in mice and iii) to regulate body weight and food consumption in obese mice. Strikingly, all of these tools have been successfully transposed to the Lactobacillus genus, in recent years, within our laboratory. Notably, anti-oxidative Lactobacillus casei strains were constructed and tested in two chemically-induced colitis models. In parallel, we also developed a strategy based on the use of L. lactis to deliver DNA at the mucosal level, and were able to show that L. lactis is able to modulate the host response through DNA delivery. Today, we consider that all of our consistent data, together with those obtained by other groups, demonstrate and reinforce the interest of using LAB, particularly lactococci and lactobacilli strains, to develop novel therapeutic protein mucosal delivery vectors which should be tested now in human clinical trials.

Lactococcus lactis as a live vector: heterologous protein production and DNA delivery systems

Lactic acid bacteria (LAB), widely used in the food industry, are present in the intestine of most animals, including humans. The potential use of these bacteria as mucosal delivery vehicles for vaccinal, medical or technological use has been extensively investigated. Lactococcus lactis, a LAB species, is a potential candidate for the production of biologically useful proteins and for plasmid DNA delivery to eukaryotic cells. Several delivery systems have been developed to target heterologous proteins to a specific cell location (i.e., cytoplasm, cell wall or extracellular medium) and more recently to efficiently transfer DNA to eukaryotic cells. A promising application of L. lactis is its use for the development of live mucosal vaccines. Here, we have reviewed the expression of heterologous protein and the various delivery systems developed for L. lactis, as well as its use as an oral vaccine carrier.

Development of a Bacillus subtilis-based rotavirus vaccine

Bacillus subtilis vaccine strains engineered to express either group A bovine or murine rotavirus VP6 were tested in adult mice for their ability to induce immune responses and provide protection against rotavirus challenge. Mice were inoculated intranasally with spores or vegetative cells of the recombinant strains of B. subtilis. To enhance mucosal immunity, whole cholera toxin (CT) or a mutant form (R192G) of Escherichia coli heat-labile toxin (mLT) were included as adjuvants. To evaluate vaccine efficacy, the immunized mice were challenged orally with EDIM EW murine rotavirus and monitored daily for 7 days for virus shedding in feces. Mice immunized with either VP6 spore or VP6 vegetative cell vaccines raised serum anti-VP6 IgG enzyme-linked immunosorbent assay (ELISA) titers, whereas only the VP6 spore vaccines generated fecal anti-VP6 IgA ELISA titers. Mice in groups that were immunized with VP6 spore vaccines plus CT or mLT showed significant reductions in virus shedding, whereas the groups of mice immunized with VP6 vegetative cell vaccines showed no difference in virus shedding compared with mice immunized with control spores or cells. These results demonstrate that intranasal inoculation with B. subtilis spore-based rotavirus vaccines is effective in generating protective immunity against rotavirus challenge in mice.

Utilisation des bactéries lactiques comme vecteurs vaccinaux

Aujourd’hui, nous disposons de données suffisantes qui confortent l’intérêt d’utiliser des bactéries lactiques (BL), notamment des souches des lactocoques et lactobacilles, pour le développement de nouvelles stratégies de vaccination mucosale. Les BL sont des bactéries à Gram positif utilisées depuis des millénaires dans la production d’aliments fermentés. Elles sont donc de bonnes candidates pour le développement de nouvelles stratégies de vectorisation orale et constituent des alternatives attractives aux stratégies vaccinales basées sur des bactéries pathogènes atténuées dont l’utilisation présente des risques sanitaires. Ce chapitre passe en revue la recherche et les progrès les plus récents dans l’utilisation des BL comme vecteurs de délivrance de protéines d’intérêt médical pour développer de nouveaux vaccins.

Development of Mucosal Vaccines Based on Lactic Acid Bacteria

Today, sufficient data are available to support the use of lactic acid bacteria (LAB), notably lactococci and lactobacilli, as delivery vehicles for the development of new mucosal vaccines. These non-pathogenic Gram-positive bacteria have been safely consumed by humans for centuries in fermented foods. They thus constitute an attractive alternative to the attenuated pathogens (most popular live vectors actually studied) which could recover their pathogenic potential and are thus not totally safe for use in humans. This chapter reviews the current research and advances in the use of LAB as live delivery vectors of proteins of interest for the development of new safe mucosal vaccines. The use of LAB as DNA vaccine vehicles to deliver DNA directly to antigen-presenting cells of the immune system is also discussed.

Mucosal delivery of therapeutic and prophylactic molecules using lactic acid bacteria

Important developments in the design of recombinant lactic acid bacteria (LAB) as mucosal carriers for a range of health-beneficial compounds, such as antigens, allergens, immune modulators, antimicrobial and trefoil peptides, single-chain antibodies and a few enzymes, have taken place in the past decade. The different approaches, strategies and proof-of-concept studies that have been conducted in animal models are reviewed in this article.

The rationale for the use of lactic acid bacteria as mucosal delivery vehicles and key aspects of their interaction with the host mucosal surfaces are discussed.

An overview of the progress in the field of LAB-based mucosal vaccines and a discussion of protection studies that have been conducted in rodents, mainly by intranasal and intragastric immunization, are provided.

The latest developments in the use of LAB as vechicles for DNA vaccination are described.

Studies that deal with successful delivery of cytokines or trefoil peptides to treat experimental colitis in rodents are reviewed. Notably, the first Phase I trial has been conducted with patients that suffer from inflammatory bowel disease using safe biologically contained recombinant lactococci that secrete human interleukin-10.

Efforts to induce oral tolerance and develop preventive strategies against type I allergies using LAB are highlighted.

Anti-infective strategies that are based on the delivery of microbicidal peptides are discussed, with a special emphasis on the prevention of HIV-1 infection.

The concluding section captures the key learning points in the field, identifies major questions that remain to be answered and highlights challenges for the future.

The development of lactic acid bacteria as delivery vehicles for therapeutics, anti-infectives and vaccines at mucosa is discussed in this Review. Engineered LAB could be deployed to treat conditions such as allergy and inflammatory bowel disease, and might also be adopted in the fight against pathogens, including HIV-1 infection.

Studies of lactic acid bacteria (LAB) as delivery vehicles have focused mainly on the development of mucosal vaccines, with much effort being devoted to the generation of genetic tools for antigen expression in different bacterial locations. Subsequently, interleukins have been co-expressed with antigens in LAB to enhance the immune response that is raised against the antigen. LAB have also been used as a delivery system for a range of molecules that have different applications, including anti-infectives, therapies for allergic diseases and therapies for gastrointestinal diseases. Now that the first human trial with a Lactococcus strain that expresses recombinant interleukin-10 has been completed, we discuss what we have learnt, what we do not yet understand and what the future holds for therapy and prophylaxis with LAB.

Targeting mucosal dendritic cells with microbial antigens from probiotic lactic acid bacteria

The use of vaccines against infectious microbes has been critical to the advancement of medicine. Vaccine strategies combined with, or without, adjuvants have been established to eradicate various bacterial and viral pathogens. A new generation of vaccines is being developed using specific strains of Gram-positive, lactic acid bacteria and, notably, some probiotic lactobacilli. These bacteria have been safely consumed by humans for centuries in fermented foods. Thus, they can be orally administered, are well tolerated by recipients and could be easily and economically provided to large populations. In this overview, we focus on mucosal immunity and how its cellular component(s), particularly dendritic cells, can be specifically targeted to deliver immunogenic subunits, such as the protective antigen from Bacillus anthracis (the causative agent of anthrax). An antigen-specific immune response can be elicited using specific strains of Lactobacillus acidophilus expressing the protective antigen. A mucosal, dendritic cell-targeted approach increases the bioavailability of an immunogen of interest when delivered orally by L. acidophilus. This provides an efficiently elegant natural strategy and serves a dual function as an immune-stimulating adjuvant in vivo.

Induction of neutralizing antibodies against dengue virus type 2 upon mucosal administration of a recombinant Lactococcus lactis strain expressing envelope domain III antigen

Mucosal vaccines present several advantages over conventional parenteral vaccines including their ease of administration and low cost, both criteria being priorities for developing countries plagued by infectious diseases. A recombinant Lactococcus lactis strain producing the envelope domain III (EDIII) antigen from dengue virus serotype 2 was engineered, and the ability of the live recombinant bacteria to trigger a systemic anti-EDIII IgG antibody response upon nasal or oral administration to BALB/c and C57BL/6 mice was investigated. Results showed that the antibody response depended on the route of administration and on the mouse strain inoculated. Out of six, two and three C57BL/6 mice orally and nasally inoculated with the recombinant bacteria, respectively, displayed anti-EDIII antibody responses higher than that obtained in the mouse group intraperitoneally (i.p.) immunized with heat-inactivated dengue 2 virus. The protective potential of the immune sera was measured using the plaque reduction neutralizing test (PRNT) and results indicated that high anti-EDIII antibody levels did not correlate directly with high neutralizing activities. Immune sera from orally inoculated mice were found the most potent to neutralize in vitro dengue infection with neutralizing antibody activities in some cases higher than that obtained with the immune sera from mice i.p. injected with heat-inactivated virus.

Intragastric immunization with recombinant Lactobacillus casei expressing flagellar antigen confers antibody-independent protective immunity against Salmonella enterica serovar Enteritidis

A recombinant Lactobacillus casei expressing a flagellar antigen from Salmonella enterica serovar Enteritidis was constructed and evaluated as a mucosal vaccine. Intragastric immunization of the recombinant strain conferred protective immunity against Salmonella infection in mice. This immunization did not result in antigen-specific antibody in either feces or sera but induced the release of IFN-γ on restimulation of primed lymphocytes ex vivo. The results suggested that the protective efficacy provided by flagellin-expressing L. casei is mainly attributable to cell-mediated immune responses. In addition, an adjuvant-type effect of the antigen delivery system with L. casei was also observed.

Live bacterial vaccines--a review and identification of potential hazards

The use of live bacteria to induce an immune response to itself or to a carried vaccine component is an attractive vaccine strategy. Advantages of live bacterial vaccines include their mimicry of a natural infection, intrinsic adjuvant properties and their possibility to be administered orally. Derivatives of pathogenic and non-pathogenic food related bacteria are currently being evaluated as live vaccines. However, pathogenic bacteria demands for attenuation to weaken its virulence. The use of bacteria as vaccine delivery vehicles implies construction of recombinant strains that contain the gene cassette encoding the antigen. With the increased knowledge of mucosal immunity and the availability of genetic tools for heterologous gene expression the concept of live vaccine vehicles gains renewed interest. However, administration of live bacterial vaccines poses some risks. In addition, vaccination using recombinant bacteria results in the release of live recombinant organisms into nature. This places these vaccines in the debate on application of genetically modified organisms. In this review we give an overview of live bacterial vaccines on the market and describe the development of new live vaccines with a focus on attenuated bacteria and food-related lactic acid bacteria. Furthermore, we outline the safety concerns and identify the hazards associated with live bacterial vaccines and try to give some suggestions of what to consider during their development.