Protection against tetanus toxin in mice nasally immunized with recombinant Lactococcus lactis expressing tetanus toxin fragment C

Evaluation of a subunit vaccine candidate (Biotech Vac Cox) against Eimeria spp. in broiler chickens

This study evaluated growth performance and cross-protection against Eimeria spp. using a subunit coccidia vaccine in 2 independent challenge experiments. In both trials, chickens were challenged with E. acervulina, E. maxima, and E. tenella oocysts. In Exp 1, 1000-day-old chickens were allocated in one of 2 treatments 1) Control group; 2) Biotech Vac Cox group. The vaccine was orally gavaged on d 2 and 16 of life and coccidia challenge was on d 21. Performance parameters were evaluated on d 21, 35, and 42. On d 34, coccidia lesions were scored. Oocysts per gram of feces (OPG) were evaluated on d 28, 35, and 42. In Exp 2, 900-day-old chickens were assigned in one of 2 treatments 1) Control group; 2) Biotech Vac Cox group. The vaccine was orally gavaged on d 2 and 16 of life and coccidia challenge was on d 21. Performance parameters were evaluated on d 21, 27, 35, and 42, and lesion scores and OPG at d 27. In Exp 1, chickens vaccinated had significantly lower feed intake (FI) at d 21 and feed conversion ratio (FCR) at d 35 compared to control chickens (P < 0.05). Vaccinated chickens showed a significant reduction (P ≤ 0.05) in OPG for E. maxima to nondetectable levels and for all coccidian species at d 42 compared to control chickens. In Exp 2, the chickens vaccinated showed a significant increase in BW, BW gain (BWG) and reduction in FCR on d 27, 35, and 42 (P ≤ 0.05). Vaccinated chickens had significantly lower (P ≤ 0.05) lesion scores for all 3 Eimeria species. Moreover, vaccinated chickens had a reduction in total OPG of 35.50% (P = 0.0739). Studies to evaluate the serological and mucosal immune response are currently being evaluated. This inactivated, orally delivered subunit vaccine offers significant cross-protection to Eimeria spp. and eliminates the needs to treat broilers with live oocysts, enhanced ease of use, and greater biosecurity to producers.

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.

Expression of Helicobacter pylori hspA Gene in Lactococcus lactis NICE System and Experimental Study on Its Immunoreactivity

Aim. The aim of this study was to develop an oral Lactococcus lactis (L. lactis) vaccine against Helicobacter pylori (H. pylori). Methods. After L. lactis NZ3900/pNZ8110-hspA was constructed, growth curves were plotted to study whether the growth of recombinant L. lactis was affected after hspA was cloned into L. lactis and whether the growth of empty bacteria, empty plasmid bacteria, and recombinant L. lactis was affected by different concentrations of Nisin; SDS-PAGE and Western blot were adopted, respectively, to detect the HspA expressed by recombinant L. lactis and its immunoreactivity. Results. There was no effect observed from the growth curve after exogenous gene hspA was cloned into L. lactis NZ3900; different concentrations of Nisin did not affect the growth of NZ3900 and NZ3900/pNZ8110, while different concentrations of Nisin inhibited the growth of NZ3900/pNZ8110-hspA except 10 ng/mL Nisin. No HspA strip was observed from SDS-PAGE. Western blot analysis showed that HspA expressed by recombinant bacteria had favorable immunoreactivity. Conclusion. The growth of recombinant L. lactis was suppressed even though a small amount of HspA had been induced to express. Therefore recombinant L. lactis only express HspA which was not suitable to be oral vaccine against Helicobacter pylori.

Tetanus toxin fragment C fused to flagellin makes a potent mucosal vaccine

PURPOSE

Recombinant subunit vaccines provide safe and targeted protection against microbial infections. However, the protective efficacy of recombinant subunit vaccines tends to be less potent than the whole cell vaccines, especially when they are administered through mucosal routes. We have reported that a bacterial flagellin has strong mucosal adjuvant activity to induce protective immune responses. In this study, we tested whether FlaB could be used as a fusion partner of subunit vaccine for tetanus.

MATERIALS AND METHODS

We constructed fusion proteins consisted with tetanus toxin fragment C (TTFC), the nontoxic C-terminal portion of tetanus toxin, and a Toll-like receptor 5 agonist from Vibrio vulnificus (FlaB). Mice were intranasally administered with fusion protein and protective immune responses of the vaccinated mice were analyzed.

RESULTS

FlaB-TTFC recombinant protein induced strong tetanus-specific antibody responses in both systemic and mucosal compartments and prolonged the survival of mice after challenge with a supra-lethal dose of tetanus toxin.

CONCLUSION

This study establishes FlaB as a successful fusion partner for recombinant subunit tetanus vaccine applicable through mucosal route, and it further endorses our previous observations that FlaB could be a stable adjuvant partner for mucosal vaccines.

Progress toward development of an inhalation vaccine against botulinum toxin

The looming threat of bioterrorism has enhanced interest in the development of vaccines against agents such as botulinum toxin. This in turn has stimulated efforts to create vaccines that are effective by the oral and inhalation routes. Recently, considerable progress has been made in creating an inhalation vaccine against botulism. This work stems from the discovery that a polypeptide that represents a third of the toxin molecule retains the ability to be adsorbed from the airway and to evoke an immune response but retains none of the adverse effects of the native toxin. Interestingly, this polypeptide can also serve as a carrier molecule in the creation of inhalation vaccines against other pathogens.

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.

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.

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.

Immune responses elicited in mice with recombinant Lactococcus lactis expressing F4 fimbrial adhesin FaeG by oral immunization

Enterotoxigenic Escherichia coli (ETEC) is a major pathogenic agent causing piglet diarrhea. The major subunit and adhesin FaeG of F4(+) ETEC is an important virulence factor with strong immunogenicity. To determine whether Lactococcus lactis (L. lactis) could effectively deliver FaeG to the mucosal immune system, recombinant L. lactis expressing FaeG was constructed, and immune responses in mice following oral route delivery of recombinant L. lactis were explored. The production of FaeG expressed in L. lactis was up to approximately 10% of soluble whole-cell proteins, and recombinant FaeG (rFaeG) possessed good immunoreactivity by Western blot analysis. Oral immunization with recombinant L. lactis expressing FaeG induced F4-specific mucosal and systemic immune responses in the mice. In addition, high dose recombinant L. lactis or co-administration of high dose recombinant L. lactis with CTB enhanced the immune responses. These results suggested that L. lactis expressing FaeG was a promising candidate vaccine against ETEC.

Expression of hepatitis B virus surface antigen determinants in Lactococcus lactis for oral vaccination

Lactococcus lactis with non-pathogenic and non-colonizing properties is an attractive candidate for delivering biologically active proteins by mucosal routes. In this report we described recombinant L. lactis applicable for the development of live mucosal vaccine against hepatitis B virus (HBV). The PreS region of the HBV surface antigen alone or combined with "a" determinant of S region (PreSa) was cloned and expressed in the food grade bacterium L. lactis using a nisin-controlled expression (NICE) system. Western blot analysis indicated that both PreS and PreSa fusion proteins were successfully expressed in L. lactis after nisin induction. Oral immunization of BALB/c mice with PreS and PreSa-producing strains induced both mucosal (intestinal IgA) and systemic (serum IgG) immune responses against HBV at the same magnitude. Two additional groups of mice given L. lactis expressing human interferon-alpha 2b as an adjuvant with the PreS or PreSa-producing strains produced higher IgG but not IgA antibody responses. These results indicated that the lactococci-derived vaccines could be promising candidates as alternative HBV vaccines for preventing hepatitis B.

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.

Current prophylactic and therapeutic uses of a recombinant Lactococcus lactis strain secreting biologically active interleukin-12

The noninvasive and food-grade Gram-positive bacterium Lactococcus lactis is well adapted to deliver medical proteins to the mucosal immune system. In the last decade, the potential of live recombinant lactococci to deliver such proteins to the mucosal immune system has been investigated. This approach offers several advantages over the traditional systemic injection, such as easy administration and the ability to elicit both systemic and mucosal immune responses. This paper reviews the current research and advances made with recombinant L. lactis as live vector for the in situ delivery of biologically active interleukin-12, a potent pleiotropic cytokine with adjuvant properties when co-delivered with vaccinal antigens, at mucosal surfaces. Three well-illustrated examples demonstrate the high potential of interleukin-12-secreting lactococci strains for future prophylactic and therapeutic uses.

Display of heterologous proteins on the surface of Lactococcus lactis using the H and W domain of PrtB from Lactobacillus delburueckii subsp. bulgaricus as an anchoring matrix

AIMS

The aim of this study was to develop a cell-surface display system for foreign antigens on the surface of a Lactococcus lactis strain using an H and W domain of PrtB from Lactobacillus delburueckii subsp. bulgaricus as an anchoring matrix.

METHODS AND RESULTS

To construct a cell-surface display pACL1 vector, a derivative of pSECE1 vector, we amplified the H and W domain of the cell-surface proteinase Prt B from Lact. bulgaricus using specific primers and then cloned it into a site downstream of the secretion signal sequence in the pSECE1 vector. The new system, designed for cell-surface display of recombinant proteins on L. lactis, was evaluated by the expression and display of the FliC protein of Salmonella enterica serovar Enteritidis as a reporter gene (pALC1:FliC). The expression of the FliC protein by the transformed cells was analysed by Western blot analysis, and the localization of FliC on the cell surface was confirmed by immunofluorescence microscopy and flow cytometry analysis. A specific band corresponding in size (approx. 110 kDa) to FliC plus the anchor residues was detected by anti-FliC antibody in the cell extract of L. lactis H61 harbouring pALC1:FliC, but not L. lactis H61 harbouring pALC1. In addition, flow cytometry and immunofluorescence microscopy revealed FliC-specific positive signals and a significant increase of fluorescence, respectively, in cells harbouring pALC1:FliC compared with that in control cells harbouring the parental pALC1 plasmid. These findings demonstrated that FliC was successfully displayed on the cell surface by the anchor domain of PrtB.

CONCLUSIONS

A pALC1 vector using the H and W domain of PrtB from Lact. bulgaricus as an anchoring matrix can be used to successfully display the FliC protein on the surface of L. lactis.

SIGNIFICANCE AND IMPACT OF THE STUDY

This novel way of displaying heterologous proteins on the cell surface of L. lactis using the PrtB anchor domain should prove useful for the delivery of antigens and other proteins.

Mucosal immunisation of mice with malaria protein on lactic acid bacterial cell walls

Mice were orally and nasally immunised with a malaria parasite protein, MSA2, expressed in Lactococcus lactis, covalently attached to the peptidoglycan (MSA2cP), or non-covalently rebound to L. lactis cell walls, live Lactobacillus reuteri and Lb. salivarius (MSA2cA). Although there was marked variation within mice of the same inbred strain, the data suggest that the characteristics of serum IgG antibodies formed against MSA2 are influenced by the mouse strain and mode of MSA2 presentation. MSA2-specific IgA antibodies in sera and faecal pellets, and IFNgamma-secreting spleen cells were detectable in some immunised animals. MSA2cA on lactobacilli, although not effective in eliciting serum IgG antibodies, showed a potential for eliciting IgA antibodies in the gut. The presence of MSA2 in L. lactis tended to divert the antibody response from lactococcal antigens. The data suggest that anti-MSA2 and anti-lactococcal antibody responses are not necessarily associated in the mice. The findings are related to the use of lactic acid bacteria expressing heterologous proteins for therapy and vaccination.

Therapeutic drug delivery by genetically modified Lactococcus lactis

Food-grade bacteria have been consumed throughout history without associated pathologies and are, therefore, absolutely safe to ingest. Unexpectedly, Lactococcus lactis (L. lactis), known from cheese production, can be genetically engineered to constantly secrete satisfactory amounts of bioactive cytokines. Both of these features enabled the development of a new kind of topical delivery system: topical and active delivery of therapeutic proteins by genetically modified micro-organisms. The host organism's record inspired the development of applications that target intestinal diseases. In a variety of mouse models, chronic colon inflammation can be successfully treated with (interleukin) IL-10-secreting L. lactis. Trefoil factor (TFF) producer strains have also been shown to be very effective in the treatment of acute colitis. Such novel therapeutic strains are textbook examples of genetically modified (GM) organisms. There are legitimate concerns with regard to the deliberate release of GM micro-organisms. On development of these applications, therefore, we have engineered these bacteria in such a way that biological containment is guaranteed. The essential gene thyA, encoding thymidylate synthase, has been exchanged for IL-10. This makes the GM strain critically dependent on thymidine. Lack of thymidine, for example, resulting from thymidine consumption by thyA-deficient strains-will irreversibly lead to induced "thymidine-less death." This accomplishment has created the possibility of using this strategy for application in human medicine.

Development of lactococcal GEM-based pneumococcal vaccines

We report the development of a novel protein-based nasal vaccine against Streptococcus pneumoniae, in which three pneumococcal proteins were displayed on the surface of a non-recombinant, killed Lactococcus lactis-derived delivery system, called Gram-positive Enhancer Matrix (GEM). The GEM particles induced the production of the proinflammatory cytokine tumour necrosis factor-alpha (TNF-alpha) by macrophages as well as the maturation of dendritic cells. The pneumococcal proteins IgA1 protease (IgA1p), putative proteinase maturation protein A (PpmA) and streptococcal lipoprotein A (SlrA) were anchored in trans to the surface of the GEM particles after recombinant production of the antigens in L. lactis as hybrids with a lactococcal cell wall binding domain, named Protein Anchor domain (PA). Intranasal immunisation with the SlrA-IgA1p or trivalent vaccine combinations without additional adjuvants showed significant protection against fatal pneumococcal pneumonia in mice. The GEM-based trivalent vaccine is a potential pneumococcal vaccine candidate that is expected to be easy to administer, safe and affordable to produce.

Expression of the Giardia lamblia cyst wall protein 2 in Lactococcus lactis

In this study, Lactococcus lactis was engineered to express Giardia lamblia cyst wall protein 2 (CWP2) at three different subcellular locations, intracellular, secreted or cell-surface-anchored, using nisin as an inducing agent. CWP2 expression did not appear to be detrimental to L. lactis viability. No particular subcellular location of CWP2 expression offered any advantages over the others with respect to decreased toxicity towards the bacteria. All recombinant lactococci experienced a similar reduction in growth rate when induced. It was determined whether recombinant lactococcal cells engineered for cell surface expression of CWP2 were capable of inducing a CWP2-specific mucosal IgA antibody response. Recombinant lactococci were successful at inducing CWP2-specific IgA antibodies. Moreover, in a pilot challenge experiment, mice immunized with these recombinant lactococci demonstrated a significant (63 %) reduction in cyst output. Thus, it has been demonstrated that G. lamblia CWP2 may be expressed in L. lactis and that recombinant lactococcal cells elicit Giardia-specific antibodies which reduce cyst shedding in a murine model.

Green fluorescent protein is a reliable reporter for screening signal peptides functional in Lactobacillus reuteri

A signal peptide (SP)-probe vector pNICE-gfpSP, which employed a green fluorescent protein (Gfp) as the SP-selection marker, was constructed for use in Lactobacillus reuteri. This chimerical plasmid allowed cloning and screening DNA fragments with the SP function by direct visualization of the expressed fluorescence activity around cells. Assay of fluorescent intensity in their culture supernatant with spectrofluorometry further enabled quantifying the secretion efficiency of the identified SP fragment.

Lactococcus lactis GEM particles displaying pneumococcal antigens induce local and systemic immune responses following intranasal immunization

The present work reports the use of non-living non-recombinant bacteria as a delivery system for mucosal vaccination. Antigens are bound to the cell-wall of pretreated Lactococcus lactis, designated as Gram-positive enhancer matrix (GEM), by means of a peptidoglycan binding domain. The influence of the GEM particles on the antigen-specific serum antibody response was studied. Following nasal immunization with the GEM-based vaccines, antibody responses were induced at systemic and local levels. Furthermore, different GEM-based vaccines could be used consecutively in the same mice without adverse effects or loss of activity. Taken together, the results evidence the adjuvant properties of the GEM particles and indicate that GEM-based vaccines can be used repeatedly and are particularly suitable for nasal immunization purposes.

Immunogenicity of a malaria parasite antigen displayed by Lactococcus lactis in oral immunisations

A putative protective protein from Plasmodium falciparum merozoites, MSA2, was expressed in two different ways on the cell surface of the Gram-positive food-grade bacterium, Lactococcus lactis. The first display format exploits an LPXTG-type anchoring motif of the lactococcal proteinase PrtP to covalently anchor MSA2 to the genetically modified producer cells. In a second display format, MSA2 was fused to the peptidoglycan-binding domain (Protein Anchor) of the lactococcal cell wall hydrolase AcmA and was non-covalently rebound to the surface of non-genetically modified, non-living high-binder L. lactis cells, termed Gram-positive enhancer matrix (GEM) particles. The L. lactis recombinants carrying covalently bound MSA2 were used to immunise rabbits through nasal and oral routes. The highest levels of IgG antibodies reacting with near-native MSA2 on merozoites was elicited by oral administration. Intestinal antibodies to MSA2 were produced only after oral immunisation. MSA2-specific T(h)-cell activation could be demonstrated. Based on these results, the immunogenicity in oral immunisations of MSA2, bound non-covalently to non-genetically modified L. lactis GEM particles, was compared with MSA2 that was bound covalently to genetically modified L. lactis. These two forms elicited similar titres of serum antibodies. The results illustrate the potential of using non-genetically modified L. lactis as a safe vaccine delivery vehicle to elicit systemic antibodies, thereby avoiding the dissemination of recombinant DNA into the environment.

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

AIMS

To determine if live recombinant Lactococcus lactis strains expressing rotavirus VP7 antigen are immunogenic in mice.

METHODS AND RESULTS

Using the food-grade lactic acid bacterium L. lactis as a carrier, we expressed VP7, the major rotavirus outer shell protein and one of the main components of the infective particle, as a cytoplasmic, secreted or cell wall anchored forms. Our results showed that recombinant L. lactis strains secreting VP7 proved to be more immunogenic than strains containing the antigen in the cytoplasm or anchored to the cell wall.

CONCLUSIONS

This is the first demonstration that recombinant L. lactis producing VP7 can induce the production of a neutralizing antibody response against rotavirus by the intragastric route.

SIGNIFICANCE AND IMPACT OF THE STUDY

Rotaviruses are the single most important aetiological agents of severe diarrhoea of infants and young children worldwide and have been estimated to be responsible for 650 000-800 000 deaths per year of children younger than 5 years old in development countries. Thus, the development of a safe and effective vaccine has been a global public health goal. Although two of five mice orally inoculated with L. lactis strains secreting VP7 elicited a specific-antibody response, these strains could be very useful to be used as a prototype to develop a new generation of protective rotavirus vaccines.

A novel mucosal vaccine based on live Lactococci expressing E7 antigen and IL-12 induces systemic and mucosal immune responses and protects mice against human papillomavirus type 16-induced tumors

Current strategies to prevent or treat human papillomavirus type 16 (HPV-16) infection are promising, but remain costly. More economical but efficient vaccines are thus needed. In this study, we evaluated the protective effects of mucosally coadministered live Lactococcus lactis strains expressing cell wall-anchored E7 Ag and a secreted form of IL-12 to treat HPV-16-induced tumors in a murine model. When challenged with lethal levels of tumor cell line TC-1 expressing E7, immunized mice showed full prevention of TC-1-induced tumors, even after a second challenge, suggesting that this prophylactic immunization can provide long-lasting immunity. Therapeutic immunization with L. lactis recombinant strains, i.e., 7 days after TC-1 injection, induced regression of palpable tumors in treated mice. The antitumor effects of vaccination occurred through a CTL response, which is CD4+ and CD8+ dependent. Furthermore, immunized mice developed an E7-specific mucosal immune response. These preclinical results suggest the feasibility of the low-cost mucosal vaccination and/or immunotherapy strategies against HPV-related cervical cancer in humans.

Delivery of therapeutic proteins to the mucosa using genetically modified microflora

Drug delivery through mucosal surfaces offers a panorama of opportunities. The advantages are clear and include safety, ease of administration and higher social acceptance, although the major disadvantages are drug availability and appropriate drug targeting. Most mucosa are well equipped to manage the presence of bacteria and many are actually permanently colonised with a specific microflora. Such microbiota may become attractive tools for the delivery of a specific niche of protein therapeutics. These proteins can be produced from genetically modified microbes that are common to the mucosa, and their delivery to the host tissues has been demonstrated. This concept is being developed for the delivery of proteins to the intestine, but has also been applied in delivery to the vagina, nose and mouth.

Fermented functional foods based on probiotics and their biogenic metabolites

The claimed health benefits of fermented functional foods are expressed either directly through the interaction of ingested live microorganisms, bacteria or yeast with the host (probiotic effect) or indirectly as a result of ingestion of microbial metabolites produced during the fermentation process (biogenic effect). Although still far from fully understood, several probiotic mechanisms of action have been proposed, including competitive exclusion, competition for nutrients and/or stimulation of an immune response. The biogenic properties of fermented functional foods result from the microbial production of bioactive metabolites such as certain vitamins, bioactive peptides, organic acids or fatty acids during fermentation.

Cell surface display system for Lactococcus lactis: a novel development for oral vaccine

The food-grade Lactococcus lactis is a potential vector to be used as a live vehicle for the delivery of heterologous proteins for vaccine and pharmaceutical purposes. We constructed a plasmid vector pSVac that harbors a 255-bp single-repeat sequence of the cell wall-binding protein region of the AcmA protein. The recombinant plasmid was transformed into Escherichia coli and expression of the gene fragment was driven by the T7 promoter of the plasmid. SDS-PAGE showed the presence of the putative AcmA' fragment and this was confirmed by Western blot analysis. The protein was isolated and purified using a His-tag affinity column. When mixed with a culture of L. lactis MG1363, ELISA and immunofluorescence assays showed that the cell wall-binding fragment was anchored onto the outer surface of the bacteria. This indicated that the AcmA' repeat unit retained the active site for binding onto the cell wall surface of the L. lactis cells. Stability assays showed that the fusion proteins (AcmA/A1, AcmA/A3) were stably docked onto the surface for at least 5 days. The AcmA' fragment was also shown to be able to strongly bind onto the cell surface of naturally occurring lactococcal strains and Lactobacillus and, with less strength, the cell surface of Bacillus sphericus. The new system designed for cell surface display of recombinant proteins on L. lactis was evaluated for the expression and display of A1 and A3 regions of the VP1 protein of enterovirus 71 (EV71). The A1 and A3 regions of the VP1 protein of EV71 were cloned upstream to the cell wall-binding domains of AcmA protein and successfully expressed as AcmA/A1 and AcmA/A3. Whole-cell ELISA showed the successful display of VP1 protein epitopes of EV71 on the surface of L. lactis. The success of the anchoring system developed in this study for docking the A1 and A3 epitopes of VP1 onto the surface of L. lactis cells opens up the possibilities of peptide and protein display for not only Lactococcus but also for other gram-positive bacteria. This novel way of displaying epitopes on the cell surface of L. lactis and other related organisms should be very useful in the delivery of vaccines and other useful proteins.

Receptor binding domain of Escherichia coli F18 fimbrial adhesin FedF can be both efficiently secreted and surface displayed in a functional form in Lactococcus lactis

Adherence of F18 fimbrial Escherichia coli to porcine intestinal epithelial cells is mediated by the adhesin (FedF) of F18 fimbriae. In a previous study, we demonstrated the specificity of the amino acid residues between 60 and 109 as the receptor binding domain of FedF. In this study, different expression, secretion, and anchoring systems for the receptor binding domain of the FedF adhesin in Lactococcus lactis were evaluated. Two partially overlapping receptor binding domains (42 and 62 amino acid residues) were expressed as fusions with L. lactis subsp. cremoris protein PrtP for evaluation of secretion efficiency. To evaluate the cell surface display of these FedF-PrtP fusions, they were further combined with different lengths of PrtP spacers fused with either the L. lactis AcmA anchor or the PrtP cell wall binding domain. An HtrA-defective L. lactis NZ9000 mutant was constructed to determine its effect on the level of secreted or anchored fusion proteins. Recombinant L. lactis clones secreting the receptor binding domain of F18 fimbriae as a fusion with the H domains of L. lactis protein PrtP were first constructed by using two different signal peptides. FedF-PrtP fusions, directed by the signal sequence of L. brevis SlpA, were throughout found to be secreted at significantly higher quantities than corresponding fusions with the signal peptide of L. lactis Usp45. In the surface display systems tested, the L. lactis AcmA anchor performed significantly better, particularly in the L. lactis NZ9000DeltahtrA strain, compared to the L. lactis PrtP anchor region. Of the cell surface display constructs with the AcmA anchor, only those with the longest PrtP spacer regions resulted in efficient binding of recombinant L. lactis cells to porcine intestinal epithelial cells. These results confirmed that it is possible to efficiently produce the receptor binding domain of the F18 adhesin in a functionally active form in L. lactis.

Enhanced mucosal delivery of antigen with cell wall mutants of lactic acid bacteria

The potential of recombinant lactic acid bacteria (LAB) to deliver heterologous antigens to the immune system and to induce protective immunity has been best demonstrated by using the C subunit of tetanus toxin (TTFC) as a model antigen. Two types of LAB carriers have mainly been used, Lactobacillus plantarum and Lactococcus lactis, which differ substantially in their abilities to resist passage through the stomach and to persist in the mouse gastrointestinal tract. Here we analyzed the effect of a deficiency in alanine racemase, an enzyme that participates in cell wall synthesis, in each of these bacterial carriers. Recombinant wild-type and mutant strains of L. plantarum NCIMB8826 and L. lactis MG1363 producing TTFC intracellularly were constructed and used in mouse immunization experiments. Remarkably, we observed that the two cell wall mutant strains were far more immunogenic than their wild-type counterparts when the intragastric route was used. However, intestinal TTFC-specific immunoglobulin A was induced only after immunization with the recombinant L. plantarum mutant strain. Moreover, the alanine racemase mutant of either LAB strain allowed induction of a much stronger serum TTFC-specific immune response after immunization via the vagina, which is a quite different ecosystem than the gastrointestinal tract. The design and use of these mutants thus resulted in a major improvement in the mucosal delivery of antigens exhibiting vaccine properties.

Mucosal and cellular immune responses elicited by recombinant Lactococcus lactis strains expressing tetanus toxin fragment C

The mucosal and cellular responses of mice were studied, following mucosal-route administration of recombinant Lactococcus lactis expressing tetanus toxin fragment C (TTFC), which is a known immunogen protective against tetanus. A TTFC-specific T-cell response with a mixed profile of T-helper (Th) subset-associated cytokines was elicited in the intestine, with a Th2 bias characteristic of a mucosal response. These results correlated with the humoral response, where equivalent titers of anti-TTFC immunoglobulin G1 (IgG1) and IgG2a in serum were accompanied by an elevated IgA-specific response at more than one mucosal site. The route of vaccination had an important role in determining the immune response phenotype, as evidenced by the fact that an IgG1-biased subclass profile was obtained when lactococci were administered parenterally. Stimulation of splenic or mesenteric lymph node cells with lactococci resulted in their proliferation and the secretion of gamma interferon via antigen-specific and innate immune mechanisms. The data therefore provide further evidence of the potential of recombinant lactococcal vaccines for inducing systemic and mucosal immune responses.

Characterization of a Lactococcus lactis strain that secretes a major epitope of bovine beta-lactoglobulin and evaluation of its immunogenicity in mice

Bovine beta-lactoglobulin (Blg) is one of the major cow's milk allergens. Peptide 41-60 of Blg (Blg41-60) was described as a murine T-cell determinant and a murine, rat, and human immunoglobulin E (IgE) epitope. The aim of this study was the expression of Blg41-60 as a fusion protein in the food-grade bacterium Lactococcus lactis and the characterization of its immunogenicity in mice. We constructed a recombinant strain of L. lactis capable of inducible production and secretion of Blg41-60::Nuc, a fusion protein between Blg41-60 and the mature part of the staphylococcal nuclease (Nuc). The highest production yield of Blg41-60::Nuc (32.5 mg/liter) was reached 4 h after induction. At this time, up to 75% of Blg41-60::Nuc was secreted. When monoclonal antibodies specific for Blg41-60 were used, purified Blg41-60::Nuc and synthetic Blg41-60 exhibited very similar immunoreactivities. Subcutaneous coadministration of purified Blg41-60::Nuc and killed nonrecombinant L. lactis resulted in the induction of specific anti-Blg41-60 IgG2a and IgG1. The IgG1/IgG2a ratio and the lack of specific IgE suggest a Th1-type immune response, i.e., a nonallergic response. Similar administrations of the killed Blg41-60::Nuc-producing L. lactis strain did not elicit a specific immune response, whereas a transitory mucosal IgA-specific immune response was induced in mice after oral administration of the live Blg41-60::Nuc-producing L. lactis strain.

Genetically modified lactic acid bacteria: applications to food or health and risk assessment

Lactic acid bacteria have a long history of use in fermented food products. Progress in gene technology allows their modification by introducing new genes or by modifying their metabolic functions. These modifications may lead to improvements in food technology (bacteria better fitted to technological processes, leading to improved organoleptic properties em leader ), or to new applications including bacteria producing therapeutic molecules that could be delivered by mouth. Examples in these two fields will be discussed, at the same time evaluating their potential benefit to society and the possible risks associated with their use. Risk assessment and expected benefits will determine the future use of modified bacteria in the domains of food technology and health.

Production and targeting of the Brucella abortus antigen L7/L12 in Lactococcus lactis: a first step towards food-grade live vaccines against brucellosis

Brucella abortus is a facultative intracellular gram-negative bacterial pathogen that infects humans and animals by entry mainly through the digestive tract. B. abortus causes abortion in pregnant cattle and undulant fever in humans. The immunogenic B. abortus ribosomal protein L7/L12 is a promising candidate antigen for the development of oral live vaccines against brucellosis, using food-grade lactic acid bacteria (LAB) as a carrier. The L7/L12 gene was expressed in Lactococcus lactis, the model LAB, under the nisin-inducible promoter. Using different signals, L7/L12 was produced in cytoplasmic, cell-wall-anchored, and secreted forms. Cytoplasmic production of L7/L12 gave a low yield, estimated at 0.5 mg/liter. Interestingly, a secretable form of this normally cytoplasmic protein via fusion with a signal peptide resulted in increased yield of L7/L12 to 3 mg/liter; secretion efficiency (SE) was 35%. A fusion between the mature moiety of the staphylococcal nuclease (Nuc) and L7/L12 further increased yield to 8 mg/liter. Fusion with a synthetic propeptide (LEISSTCDA) previously described as an enhancer for heterologous protein secretion in L. lactis (Y. Le Loir, A. Gruss, S. D. Ehrlich, and P. Langella, J. Bacteriol. 180:1895-1903, 1998) raised the yield to 8 mg/liter and SE to 50%. A surface-anchored L7/L12 form in L. lactis was obtained by fusing the cell wall anchor of Streptococcus pyogenes M6 protein to the C-terminal end of L7/L12. The fusions described allow the production and targeting of L7/L12 in three different locations in L. lactis. This is the first example of a B. abortus antigen produced in a food-grade bacterium and opens new perspectives for alternative vaccine strategies against brucellosis.

Surface expression of the conserved C repeat region of streptococcal M6 protein within the Pip bacteriophage receptor of Lactococcus lactis

The C repeat region of the M6 protein (M6c) from Streptococcus pyogenes was expressed within the Pip bacteriophage receptor on the surface of Lactococcus lactis. M6c was also detected in the culture medium. The pip-emm6c allele was integrated into the chromosome and stably expressed without antibiotic selection. The level of cell-associated surface expression of PipM6c was 0.015% of total cellular protein. The amount of PipM6c on the cell surface was increased about 17-fold by expressing pip-emm6c from a high-copy-number plasmid. Replacing the native pip promoter with stronger promoters isolated previously from Lactobacillus acidophilus increased surface expression of PipM6c from the high-copy-number plasmid up to 27-fold. Concomitantly, the amount of PipM6c in the medium increased 113-fold. The amount of PipM6c did not vary greatly between exponential- and stationary-phase cultures. Western blots indicated that the full-length PipM6c protein and most of the numerous proteolytic products were found only on the cell surface, whereas only one proteolytic fragment was found in the culture medium.

Nasal vaccination using live bacterial vectors

Live recombinant bacteria represent an attractive means to induce both mucosal and systemic immune responses against heterologous antigens. Several models have now been developed and shown to be highly efficient following intranasal immunization. In this review, we describe the two main classes of live recombinant bacteria: generally recognized as safe bacteria and attenuated strains derived from pathogenic bacteria. Among the latter, we have differentiated the bacteria, which do not usually colonize the respiratory tract from those that are especially adapted to respiratory tissues. The strategies of expression of the heterologous antigens, the invasiveness and the immunogenicity of the recombinant bacteria are discussed.

Nasal vaccines

The nasal route for vaccination offers some important opportunities, especially for the prophylaxis of respiratory diseases. Vaccination via the respiratory tract is reviewed and the deposition and clearance of antigens in the deep lung and nose are described and contrasted. Lymphoid structures in the respiratory tract differ according to species; the rat and mouse have a well developed nose-associated lymphoid tissue, while in man, the structure known as Waldeyer's ring (that includes the tonsils), is important as an induction site. The immune response following intranasal administration can provide protection at the administration site and at various effector sites as part of the common mucosal immune system. A number of formulation considerations are important when designing novel systems for nasal administration as are physiological factors such as mucociliary clearance.

Induction of mucosal immune response after intranasal or oral inoculation of mice with Lactococcus lactis producing bovine beta-lactoglobulin

The bovine beta-lactoglobulin (BLG) is a major cow's milk allergen. Here, we evaluated the immune response against BLG induced in mice, using the organism Lactococcus lactis, which has GRAS ("generally regarded as safe") status, as a delivery vehicle. The cDNA of the blg gene, encoding BLG, was expressed and engineered for either intra- or extracellular expression in L. lactis. Using a constitutive promoter, the yield of intracellular recombinant BLG (rBLG) was about 20 ng per ml of culture. To increase the quantity of rBLG, the nisin-inducible expression system was used to produce rBLG in the cytoplasmic and extracellular locations. Although the majority of rBLG remained in the cytoplasm, the highest yield (2 microg per ml of culture) was obtained with a secreting strain that encodes a fusion between a lactococcal signal peptide and rBLG. Whatever the expression system, the rBLG is produced mostly in a soluble, intracellular, and denatured form. The BLG-producing strains were then administered either orally or intranasally to mice, and the immune response to BLG was examined. Specific anti-BLG immunoglobulin A (IgA) antibodies were detected 3 weeks after the immunization protocol in the feces of mice immunized with the secreting lactococcal strain. Specific anti-BLG IgA detected in mice immunized with lactococci was higher than that obtained in mice immunized with the same quantity of pure BLG. No specific anti-BLG IgE, IgA, IgG1, or IgG2a was detected in sera of mice. These recombinant lactococcal strains constitute good vehicles to induce a mucosal immune response to a model allergen and to better understand the mechanism of allergy induced by BLG.

Mucosal immune responses and protection against tetanus toxin after intranasal immunization with recombinant Lactobacillus plantarum

The use of live microorganisms as an antigen delivery system is an effective means to elicit local immune responses and thus represents a promising strategy for mucosal vaccination. In this respect, lactic acid bacteria represent an original and attractive approach, as they are safe organisms that are used as food starters and probiotics. To determine whether an immune response could be elicited by intranasal delivery of recombinant lactobacilli, a Lactobacillus plantarum strain of human origin (NCIMB8826) was selected as the expression host. Cytoplasmic production of the 47-kDa fragment C of tetanus toxin (TTFC) was achieved at different levels depending on the plasmid construct. All recombinant strains proved to be immunogenic by the intranasal route in mice and able to elicit very high systemic immunoglobulin G (IgG1, IgG2b, and IgG2a) responses which correlated to the antigen dose. No significant differences in enzyme-linked immunosorbent assay IgG titers were observed when mice were immunized with live or mitomycin C-treated recombinant lactobacilli. Nevertheless, protection against the lethal effect of tetanus toxin was obtained only with the strains producing the highest dose of antigen and was greater following immunization with live bacteria. Significant TTFC-specific mucosal IgA responses were measured in bronchoalveolar lavage fluids, and antigen-specific T-cell responses were detected in cervical lymph nodes, both responses being higher in mice receiving a double dose of bacteria (at a 24-h interval) at each administration. These results demonstrate that recombinant lactobacilli can induce specific humoral (protective) and mucosal antibodies and cellular immune response against protective antigens upon nasal administration.

Antimicrobial peptides of lactic acid bacteria: mode of action, genetics and biosynthesis

A survey is given of the main classes of bacteriocins, produced by lactic acid bacteria: I. lantibiotics II. small heat-stable non-lanthionine containing membrane-active peptides and III. large heat-labile proteins. First, their mode of action is detailed, with emphasis on pore formation in the cytoplasmatic membrane. Subsequently, the molecular genetics of several classes of bacteriocins are described in detail, with special attention to nisin as the most prominent example of the lantibiotic-class. Of the small non-lanthionine bacteriocin class, the Lactococcus lactococcins, and the Lactobacillus sakacin A and plantaricin A-bacteriocins are discussed. The principles and mechanisms of immunity and resistance towards bacteriocins are also briefly reported. The biosynthesis of bacteriocins is treated in depth with emphasis on response regulation, post-translational modification, secretion and proteolytic activation of bacteriocin precursors. To conclude, the role of the leader peptides is outlined and a conceptual model for bacteriocin maturation is proposed.

Partial protection to respiratory syncytial virus (RSV) elicited in mice by intranasal immunization using live staphylococci with surface-displayed RSV-peptides

A live bacterial vaccine-delivery system based on the food-grade bacterium Staphylococcus carnosus was used for delivery of peptides from the G glycoprotein of human respiratory syncytial virus, subtype A (RSV-A). Three peptides, corresponding to the G protein amino acids, 144-159 (denoted G5), 190-203 (G9) and 171-188 (G4 S), the latter with four cysteine residues substituted for serines, were expressed by recombinant means as surface-exposed on three different bacteria, and their surface accessibility on the bacteria was verified by fluorescence-activated cell sorting (FACS). Intranasal immunization of mice with the live recombinant staphylococci elicited significant anti-peptide as well as anti-virus serum IgG responses of balanced IgG1/IgG2a isotype profiles, and upon viral challenge with 10(5) tissue culture infectious doses(50) (TCID(50)), lung protection was demonstrated for approximately half of the mice in the G9 and G4 S immunization groups. To our knowledge, this is the first study in which protective immunity to a viral pathogen has been evoked using food-grade bacteria as vaccine-delivery vehicles.

The effects of tetanus toxin on the orbicularis oculi muscle

PURPOSE

Tetanus toxin can cause localized neuromuscular weakness, but it also can produce systemic tetany. The action of tetanus toxin on the orbicularis muscle has not been studied in animals immunized to prevent systemic tetany. Our objective was to determine whether tetanus toxin could be used to treat orbicularis oculi muscle spasms.

METHODS

We analyzed the clinical, electrophysiologic, and histopathologic effects of tetanus toxin injected into the orbicularis oculi muscle of rabbits with passive immunity to tetanus toxin. In six rabbits, the orbicularis oculi function in both eyes was assessed clinically, and the baseline orbicularis oculi muscle action potential was measured physiologically with electromyography (EMG). The rabbits then were immunized against tetanus toxin with tetanus immunoglobulin for immediate and definitive immunity. Tetanus toxin was injected into the left orbicularis oculi muscles, leaving the right eyes as controls. Ten days later, the rabbits were again assessed by clinical examination and with EMGs on both the injected side and the noninjected side. The animals were killed at 14 days, and the orbicularis muscle was removed from both sides. The injected and control tissues were examined microscopically for signs of neuromuscular denervation.

RESULTS

All six rabbits showed weakness in eye closure on the side injected with tetanus toxin. In addition, four rabbits developed complete ear ptosis on the tetanus toxin injected side because of spread of the toxin to adjacent ear muscles. EMGs showed both a denervation of the orbicularis oculi muscle and a poor blink potential on the side injected with tetanus toxin. Histopathologic studies of the orbicularis oculi muscle injected with tetanus toxin showed angulation of both slow and fast types of muscle fibers compatible with neuromuscular denervation.

CONCLUSIONS

Tetanus toxin can cause localized orbicularis oculi weakness, as documented clinically, physiologically, and microscopically, without producing systemic tetany in immunized rabbits. Tetanus toxin may have a potential application in the treatment of blepharospasm and hemifacial spasm.

Production of recombinant subunit vaccines: protein immunogens, live delivery systems and nucleic acid vaccines

The first scientific attempts to control an infectious disease can be attributed to Edward Jenner, who, in 1796 inoculated an 8-year-old boy with cowpox (vaccinia), giving the boy protection against subsequent challenge with virulent smallpox. Thanks to the successful development of vaccines, many major diseases, such as diphtheria, poliomyelitis and measles, are nowadays kept under control, and in the case of smallpox, the dream of eradication has been fulfilled. Yet, there is a growing need for improvements of existing vaccines in terms of increased efficacy and improved safety, besides the development of completely new vaccines. Better technological possibilities, combined with increased knowledge in related fields, such as immunology and molecular biology, allow for new vaccination strategies. Besides the classical whole-cell vaccines, consisting of killed or attenuated pathogens, new vaccines based on the subunit principle, have been developed, e.g. the Hepatitis B surface protein vaccine and the Haemophilus influenzae type b vaccine. Recombinant techniques are now dominating in the strive for an ideal vaccine, being safe and cheap, heat-stable and easy to administer, preferably single-dose, and capable of inducing broad immune response with life-long memory both in adults and in infants. This review will describe different recombinant approaches used in the development of novel subunit vaccines, including design and production of protein immunogens, the development of live delivery systems and the state-of-the-art for nucleic acids vaccines.