Vaginal immunization with recombinant gram-positive bacteria

Recombinant lactic acid bacteria as promising vectors for mucosal vaccination

Lactic acid bacteria (LAB), a diverse family of gram-positive bacteria, has been proven effective in delivering varieties of therapeutic and prophylactic molecules such as antigens and cytokines. Featuring the properties of acid-resistant, high uptake into Peyer's patches, and superior capacity for inducing secretory IgA antibodies, LAB have good potential to be used as vaccine vectors for mucosal vaccination. Mucosal immunization enables both mucosal and systemic immune responses, which are critical for resisting pathogens that invade the host through the mucosal surfaces. With the development of genetic engineering, LAB strains, primarily Lactococcus and Lactobacillus have been exploited to express a range of heterologous antigens. Numerous studies have demonstrated that LAB mucosal vaccines can stimulate all arms of the immune system to provide adequate protection against pathogen infections. Additionally, several LAB-based human papillomavirus vaccines have entered the clinical trial studies, which suggest the great promise of LAB vaccines for new interventions in mucosal transport diseases. Herein, we will discuss the factors that influence the immunogenicity of LAB vaccines, including LAB strains, the location of antigens, and administration routes, and focus on the current strategies that have been reported for optimizing LAB vaccines.

Intrauterine vaccination induces a dose-sensitive primary humoral response with limited evidence of recall potential

PROBLEM

Induction of the local mucosal immune system within the reproductive tract is widely considered to be a key component in the development of effective prophylactic vaccines to control the spread of sexually transmitted infections. Here, we examine the capacity of the upper reproductive tract to act as a site of immune induction following.

METHOD OF STUDY

Two vaccines formulated with a triple adjuvant combination and either recombinant bovine herpesvirus (tgD) protein or ovalbumin (OVA) were delivered at varying doses to the uterine lumen of rabbits and the resulting immune response evaluated after 32 days.

RESULTS

Intrauterine vaccination produced a dose-dependent induction of both antigen-specific IgG and IgA in serum. Both uterine and broncheoalveolar lavage of the high and medium-dose vaccine group contained a significant increase in both anti-OVA and anti-tgD IgG, but no significant quantities of antigen-specific IgA were observed. The restimulation of splenocytes from the high-dose vaccine group with ovalbumin (OVA) only resulted in a small but significant increase in gene expression of the Th1 cytokines (IL2/IFNγ) in the absence of an observable increase in proliferation.

CONCLUSION

Collectively, the results confirm the capacity of the uterine immune system to generate a primary response following stimulation.

Oral administration of LPS and lipoteichoic acid prepartum modulated reactants of innate and humoral immunity in periparturient dairy cows

The study evaluated the effects of repeated oral exposure to LPS and lipoteichoic acid (LTA) on immune responses of dairy cows. Thirty pregnant Holstein cows were randomly assigned to two treatment groups. Cows received orally either 2 ml of 0.85% sterile saline solution (control group), or 2 ml of sterile saline solution containing three doses of LPS from Escherichia coli 0111 : B4 along with a flat dose of LTA from Bacillus subtilis. Blood and saliva samples were collected and analyzed for serum amyloid A (SAA); LPS-binding protein (LBP); anti-LPS plasma IgA, IgG and IgM; TNF-α; and IL-1. Results showed greater concentrations of IgA in the saliva of treated cows compared with the controls (P < 0.01). Treated cows had lower plasma concentrations of anti-LPS IgA, IgG and IgM Abs, and TNF-α than the controls (P < 0.05). There was a tendency for the concentrations of plasma LBP (P = 0.06) and haptoglobin (P = 0.10) to be lesser in the treatment group, although no differences were found in the concentration of plasma SAA and IL-1 (P > 0.10). Overall, the results of this study indicate that repeated oral administration with LPS and LTA stimulates innate and humoral immune responses in periparturient dairy cows.

IL-1Ra and its delivery strategies: inserting the association in perspective

Interleukin-1 receptor antagonist (IL-1Ra) is a naturally occurring anti-inflammatory antagonist of interleukin-1 family of pro-inflammatory cytokines. The broad spectrum anti-inflammatory effects of IL-1Ra have been investigated against various auto-immune diseases such as diabetes mellitus, rheumatoid arthritis. Despite of its outstanding broad spectrum anti-inflammatory effects, IL-1Ra has short biological half-life (4-6 h) and to cope with this problem, up till now, many delivery strategies have been applied either to extend the half-life and/or prolong the steady-state sustained release of IL-1Ra from its target site. Here in our present paper, we have provided an overview of all approaches attempted to prolong the duration of therapeutic effects of IL-1Ra either by fusing IL-1Ra using fusion protein technology to extend the half-life and/or development of new dosage forms using various biodegradable polymers to prolong its steady-state sustained release at the site of administration. These approaches have been characterized by their intended impact on either in vitro release characteristics and/or pharmacokinetic and pharmacodynamic parameters of IL-1Ra. We have also compared these delivery strategies with each other on the basis of bioactivity of IL-1Ra after fusion with fusion protein partner and/or encapsulation with biodegradable polymer.

Primary activation of antigen-specific naive CD4+ and CD8+ T cells following intranasal vaccination with recombinant bacteria

The primary activation of T-helper and T-cytotoxic cells following mucosal immunization with recombinant Streptococcus gordonii was studied in vivo by adoptive transfer of ovalbumin (OVA)-specific transgenic CD8(+) (OT-I) and CD4(+) (OT-II) T cells. A recombinant strain, expressing on the surface the vaccine antigen Ag85B-ESAT-6 from Mycobacterium tuberculosis fused to OVA T-helper and T-cytotoxic epitopes (peptides 323 to 339 and 257 to 264), was constructed and used to immunize C57BL/6 mice by the intranasal route. Recombinant, but not wild-type, bacteria induced OVA-specific CD4(+) and CD8(+) T-cell clonal expansion in cervical lymph nodes, lung, and spleen. OVA-specific CD4(+) and CD8(+) T-cell proliferation appeared first in cervical lymph nodes and later in the spleen, suggesting a possible migration of activated cells from the inductive site to the systemic district. A significant correlation between the percentages of CD4(+) and CD8(+) proliferating T cells was observed for each animal. The expression of CD69, CD44, and CD45RB on proliferating T lymphocytes changed as a function of the cell division number, confirming T-cell activation following the antigen encounter. These data indicate that intranasal immunization with recombinant S. gordonii is capable of inducing primary activation of naive antigen-specific CD4(+) and CD8(+) T cells, both locally and systemically.

Probiotics: potential to prevent HIV and sexually transmitted infections in women

Women are at significant risk of human immunodeficiency virus (HIV) and sexually transmitted infection (STI) acquisition with the genital mucosa serving as the main portal of infection. Exogenously supplied lactobacillus used as a probiotic may prove a cost-effective, female-initiated method to prevent HIV and STI infection in women. A probiotic may act indirectly through treating and preventing recurrent bacterial vaginosis or directly by secreting endogenous (e.g., hydrogen peroxide) and exogenous substances that block HIV and STI transmission. This review summarizes the preclinical and clinical studies that have been conducted so far to test probiotic bacteria for these purposes. Although significant progress has been made in this field, more fundamental research is required to better understand vaginal ecology to maximize probiotic formulations. Once identified, a suitable product will require testing in a well-designed, randomized, placebo-controlled trial to measure its effectiveness in augmenting antibiotic treatment to prevent bacterial vaginosis. If results from such a trial demonstrate efficacy, future studies should be designed to determine whether a probiotic can significantly lower the risk for HIV and STIs in at-risk female populations.

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.

Stimulation of human monocytes with the gram-positive vaccine vector Streptococcus gordonii

Streptococcus gordonii is a bacterial vaccine vector which has previously been shown to activate dendritic cells in vitro and to induce local and systemic immune responses in vivo. In the present study, human monocytes (THP-1 cell line and peripheral blood monocytes) were characterized following interaction with S. gordonii. Treatment of human monocytes with S. gordonii but not latex beads induced a clear up-regulation of CD83, CD40, CD80, and CD54 and the down-regulation of CD14. Furthermore, bacterial treatment stimulated an increased expression of Toll-like receptor 5 (TLR5), TLR6, and TLR7, production of the proinflammatory cytokines tumor necrosis factor alpha and interleukin 1 beta, and reduction of the phagocytic activity. This work shows that the immunostimulatory activity of S. gordonii is not restricted to induction of dendritic-cell maturation but also affects the differentiation process of human monocytes.

Oral immunization of BALB/c mice by intragastric delivery of Streptococcus gordonii-expressing Giardia cyst wall protein 2 decreases cyst shedding in challenged mice

Giardia lamblia (Giardia duodenalis or Giardia intestinalis) is a protozoan parasite of vertebrates with broad host specificity. Specific antibodies directed against cyst antigens can interfere with the cyst wall-building process. In this study, we engineered Streptococcus gordonii to express a 26 kDa fragment of cyst wall protein 2 (CWP2), containing a relevant B cell epitope, on the cell surface. This is the first report of S. gordonii expressing a protein of parasite origin. As S. gordonii was intended for intestinal delivery of CWP2, it was determined that this oral commensal bacterium is able to persist in the murine intestine for 30 days. Immunization with recombinant streptococci expressing the 26 kDa fragment resulted in higher antibody levels. Specific anti-CWP2 IgA antibodies were detected in fecal samples and anti-CWP2 IgG antibodies were detected in serum demonstrating the efficacy of S. gordonii for intragastric antigen delivery. In a pilot challenge experiment, immunized mice demonstrated a significant 70% reduction in cyst output.

In vivo activation of naive CD4+ T cells in nasal mucosa-associated lymphoid tissue following intranasal immunization with recombinant Streptococcus gordonii

The antigen-specific primary activation of CD4+ T cells was studied in vivo by adoptive transfer of ovalbumin-specific transgenic T cells (KJ1-26+ CD4+) following intranasal immunization with recombinant Streptococcus gordonii. A strain of S. gordonii expressing on its surface a model vaccine antigen fused to the ovalbumin (OVA) peptide from position 323 to 339 was constructed and used to study the OVA-specific T-cell activation in nasal mucosa-associated lymphoid tissue (NALT), lymph nodes, and spleens of mice immunized by the intranasal route. The recombinant strain, but not the wild type, activated the OVA-specific CD4+ T-cell population in the NALT (89% of KJ1-26+ CD4+ T cells) just 3 days following immunization. In the cervical lymph nodes and in the spleen, the percentage of proliferating cells was initially low, but it reached the peak of activation at day 5 (90%). This antigen-specific clonal expansion of KJ1-26+ CD4+ T cells after intranasal immunization was obtained with live and inactivated recombinant bacteria, and it indicates that the NALT is the site of antigen-specific T-cell priming.

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.

Mucosal delivery of anti-inflammatory IL-1Ra by sporulating recombinant bacteria

BACKGROUND

Mucosal delivery of therapeutic protein drugs or vaccines is actively investigated, in order to improve bioavailability and avoid side effects associated with systemic administration. Orally administered bacteria, engineered to produce anti-inflammatory cytokines (IL-10, IL-1Ra), have shown localised ameliorating effects in inflammatory gastro-intestinal conditions. However, the possible systemic effects of mucosally delivered recombinant bacteria have not been investigated.

RESULTS

B. subtilis was engineered to produce the mature human IL-1 receptor antagonist (IL-1Ra). When recombinant B. subtilis was instilled in the distal colon of rats or rabbits, human IL-1Ra was found both in the intestinal lavage and in the serum of treated animals. The IL-1Ra protein in serum was intact and biologically active. IL-1-induced fever, neutrophilia, hypoglycemia and hypoferremia were inhibited in a dose-dependent fashion by intra-colon administration of IL-1Ra-producing B. subtilis. In the mouse, intra-peritoneal treatment with recombinant B. subtilis could inhibit endotoxin-induced shock and death. Instillation in the rabbit colon of another recombinant B. subtilis strain, which releases bioactive human recombinant IL-1beta upon autolysis, could induce fever and eventually death, similarly to parenteral administration of high doses of IL-1beta.

CONCLUSIONS

A novel system of controlled release of pharmacologically active proteins is described, which exploits bacterial autolysis in a non-permissive environment. Mucosal administration of recombinant B. subtilis causes the release of cytoplasmic recombinant proteins, which can then be found in serum and exert their biological activity in vivo systemically.

Reduced experimental autoimmune encephalomyelitis after intranasal and oral administration of recombinant lactobacilli expressing myelin antigens

Oral administration of autoantigens is a safe and convenient way to induce peripheral T-cell tolerance in autoimmune diseases like multiple sclerosis (MS). To increase the efficacy of oral tolerance induction and obviate the need for large-scale purification of human myelin proteins, we use genetically modified lactobacilli expressing myelin antigens. A panel of recombinant lactobacilli was constructed producing myelin proteins and peptides, including human and guinea pig myelin basic protein (MBP) and proteolipid protein peptide 139-151 (PLP(139-151)). In this study we examined whether these Lactobacillus recombinants are able to induce oral and intranasal tolerance in an animal model for multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). Lewis rats received soluble cell extracts of Lactobacillus transformants intranasally three times prior to induction of EAE. For the induction of oral tolerance, rats were fed live transformed lactobacilli for 20 days. Ten days after the first oral administration EAE was induced. Intranasal administration of extracts containing guinea pig MBP (gpMBP) or MBP(72-85) significantly inhibited EAE in Lewis rats. Extracts of control transformants did not reduce EAE. Live lactobacilli expressing guinea pig MBP(72-85) fused to the marker enzyme beta-glucuronidase (beta-gluc) were also able to significantly reduce disease when administered orally. In conclusion, these experiments provide proof of principle that lactobacilli expressing myelin antigens reduce EAE after mucosal (intranasal and oral) administration. This novel method of mucosal tolerance induction by mucosal administration of recombinant lactobacilli expressing relevant autoantigens could find applications in autoimmune disease in general, such as multiple sclerosis, rheumatoid arthritis and uveitis.

Genetically engineered probiotics

Probiotic micro-organisms have been used for many years. Originating as food supplements, they are now most often administered orally and offer an attractive alternative for treating of intestinal disorders. A better understanding of the mechanisms by which these micro-organisms act has now opened up possibilities for designing new probiotic strains. Through genetic engineering, it is possible not only to strengthen the effects of existing strains, but also to create completely new probiotics. These need not necessarily be composed only of bacterial products but can also include elements of regulatory systems or enzymes derived from a foreign-human-source. If designed carefully and with absolute attention to biological safety in its broadest sense, the development of genetically modified probiotics has the potential to revolutionize alimentary health.

In vivo mucosal delivery of bioactive human interleukin 1 receptor antagonist produced by Streptococcus gordonii

BACKGROUND

Interleukin-1 (IL-1) is a cytokine involved in the initiation and amplification of the defence response in infectious and inflammatory diseases. IL-1 receptor antagonist (IL-1ra) is an inactive member of the IL-1 family and represents one of the most potent mechanisms for controlling IL-1-dependent inflammation. IL-1ra has proven effective in the therapy of acute and chronic inflammatory diseases in experimental animal models and also in preliminary clinical trials. However, optimisation of therapeutic schedules is still needed. For instance, the use of drug delivery systems targeting specific mucosal sites may be useful to improve topical bioavailability and avoid side effects associated with systemic administration.

RESULTS

In order to develop systems for the delivery of IL-1ra to mucosal target sites, a Streptococcus gordonii strain secreting human IL-1ra was constructed. The recombinant IL-1ra produced by S. gordonii was composed of the four amino acid residues RVFP of the fusion partner at the N-terminus, followed by the mature human IL-1ra protein. RFVP/IL-1ra displayed full biological activity in vitro in assays of inhibition of IL-1beta-induced lymphocyte proliferation and was released by recombinant S. gordonii in vivo both at the vaginal and the gastrointestinal mucosa of mice. RFVP/IL-1ra appeared beneficial in the model of ulcerative colitis represented by IL-2-/- mice (knock-out for the interleukin-2 gene), as shown by the body weight increase of IL-2-/- mice locally treated with S. gordonii producing RFVP/IL-1ra.

CONCLUSIONS

These results indicate that recombinant S. gordonii can be successfully used as a delivery system for the selective targeting of mucosal surfaces with therapeutic proteins.

Validation of a high sensitive immunoenzymatic assay to establish the origin of immunoglobulins in female genital secretions

Several studies were carried out to characterize the humoral immune response on mucosal genital surfaces. However, the results obtained so far were particularly conflicting due to the absence of validation methods. The aim of this study was to develop and validate a quantitative ELISA method, which is sensitive and reproducible, to measure immunoglobulin and secretory immunoglobulin concentrations in various biological fluids. This quantitative, sensitive (detection limit = 1 microg/L) and reproducible (coefficient of variation < 15%) method could be of interest to study the effects of viral infections on mucosal non-specific immune response in genital tract. To explore the humoral response, serum, saliva, vaginal secretions, and cervicovaginal secretions from 18 women, 20-45 years old, were evaluated for total-IgA, secretory IgA, IgM, and IgG. Albumin level was also evaluated by immuno-nephelometry. The secretion rates of immunoglobulins were measured by calculating their relative coefficients of excretion by reference to albumin. Despite large individual variations, median immunoglobulin levels were higher in the endocervical secretions than in the cervicovaginal secretions. When we compared the rates of immunoglobulins in genital fluids, IgG prevalence was higher (80%) in cervicovaginal and endocervical secretions than IgA prevalence (12%). In contrast, digestive mucosal secretions, such as saliva, contained mostly IgA (80%). In cervicovaginal and endocervical secretions, IgG and IgM originated mainly from serum, whereas a local synthesis provided total-IgA and secretory IgA. These results allowed us to raise a possible hypothesis for the origin of immunoglobulins in the genital tract. They illustrated the peculiar feature of the female reproductive tract and the difficulty for this tissue to contribute in the mucosal associated lymphoid tissue. The low secretory-IgA and total-IgA levels could explain the particular sensitivity of the vagina and the cervix to infections.

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.

Recombinant Streptococcus gordonii for mucosal delivery of a scFv microbicidal antibody

The gram-positive bacterium Streptococcus gordonii was engineered to express the microbicidal molecule H6, which is an antiidiotypic single chain antibody mimicking a yeast killer toxin. S. gordonii is a human commensal which we developed as a model system for mucosal delivery of heterologous proteins. The in vivo candidacidal activity of both H6-secreting and H6-surface-displaying streptococcal strains were assayed in a well-established rat model of vaginal candidiasis. At day 21 full clearance of Candida albicans infection was observed in 75% of animals treated with the H6-secreting strain, and in 37.5% of animals treated with the strain expressing H6 on the surface, while all animals treated with the control strain were still infected. The observed candidacidal effect was comparable with that observed with the antimycotic drug fluconazole. These data confirm the potential of H6 as a candidacidal agent and show how promising is the approach of using recombinant bacteria for mucosal delivery of biologically active molecules.

Edible genetically modified microorganisms and plants for improved health

The development of new strategies for the delivery of vaccine antigens or immune modulators to the mucosal tissue includes innovative approaches such as the use of genetically modified food microorganisms and plants. Even though the 'proof-of-concept' has recently been established for these two systems, key questions mainly related to efficacy and risk of breaking oral tolerance remain to be critically addressed in the immediate future.

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.

Probiotic agents and infectious diseases: a modern perspective on a traditional therapy

There is an increasing scientific and commercial interest in the use of beneficial microorganisms, or "probiotics," for the prevention and treatment of disease. The microorganisms most frequently used as probiotic agents are lactic-acid bacteria such as Lactobacillus rhamnosus GG (LGG), which has been extensively studied in recent literature. Multiple mechanisms of action have been postulated, including lactose digestion, production of antimicrobial agents, competition for space or nutrients, and immunomodulation. We have reviewed recent studies of probiotics for the treatment and control of infectious diseases. Studies of pediatric diarrhea show substantial evidence of clinical benefits from probiotic therapy in patients with viral gastroenteritis, and data on LGG treatment for Clostridium difficile diarrhea appear promising. However, data to support use of probiotics for prevention of traveler's diarrhea are more limited. New research suggests potential applications in vaccine development and prevention of sexually transmitted diseases. Further studies are needed to take full advantage of this traditional medical approach and to apply it to the infectious diseases of the new millennium.

Oral immunization with recombinant Streptococcus gordonii expressing porphyromonas gingivalis FimA domains

Porphyromonas gingivalis, a gram-negative anaerobe, is implicated in the etiology of adult periodontitis. P. gingivalis fimbriae are one of several critical surface virulence factors involved in both bacterial adherence and inflammation. P. gingivalis fimbrillin (FimA), the major subunit protein of fimbriae, is considered an important antigen for vaccine development against P. gingivalis-associated periodontitis. We have previously shown that biologically active domains of P. gingivalis fimbrillin can be expressed on the surface of the human commensal bacterium Streptococcus gordonii. In this study, we examined the effects of oral coimmunization of germfree rats with two S. gordonii recombinants expressing N (residues 55 to 145)- and C (residues 226 to 337)-terminal epitopes of P. gingivalis FimA to elicit FimA-specific immune responses. The effectiveness of immunization in protecting against alveolar bone loss following P. gingivalis infection was also evaluated. The results of this study show that the oral delivery of P. gingivalis FimA epitopes via S. gordonii vectors resulted in the induction of FimA-specific serum (immunoglobulin G [IgG] and IgA) and salivary (IgA) antibody responses and that the immune responses were protective against subsequent P. gingivalis-induced alveolar bone loss. These results support the potential usefulness of the S. gordonii vectors expressing P. gingivalis fimbrillin as a mucosal vaccine against adult periodontitis.

Immunoglobulin-binding domains of peptostreptococcal protein L enhance vaginal colonization of mice by Streptococcus gordonii

Protein L, an immunoglobulin-binding protein of some strains of the anaerobic bacterium Peptostreptococcus magnus, has been hypothesized to be a virulence determinant in bacterial vaginosis. In order to investigate the role of protein L in peptostreptococcal virulence, the Ig-binding domains of protein L were expressed at the surface of the human oral commensal Streptococcus gordonii. Recombinant streptococci were used in vaginal colonization experiments, and protein L-expressing S. gordonii demonstrated enhanced ability to colonize the vaginal mucosa. Compared to the control strain, they also persisted for a longer period in the murine vagina.

Immunization with recombinant Streptococcus gordonii expressing tetanus toxin fragment C confers protection from lethal challenge in mice

Tetanus toxin fragment C (TTFC) was expressed on the surface of the vaccine vector Streptococcus gordonii, a Gram-positive commensal bacterium of the human oral cavity. The immunogenicity of recombinant S. gordonii expressing TTFC was assayed in mice immunized by the parenteral and mucosal routes. High serum TTFC-specific IgG responses were induced in both BALB/c and C57BL/6 mice immunized subcutaneously. A total of 82% of vaccinated BALB/c mice were protected from the lethal challenge with 50 LD(50) of tetanus toxin (TT) and a direct correlation between the serum TTFC-specific IgG concentration and survival time of unprotected animals was observed. Intranasal immunization of BALB/c mice was also effective in inducing TTFC-specific serum IgG and local IgA in lung washes. Furthermore, 38% of animals immunized intranasally were protected from the lethal challenge with 10 LD(50) of TT while all control animals died within 24 h. Analysis of the serum IgG subclasses showed that the IgG1 subclass was predominant after parenteral immunization in BALB/c mice (IgG1/IgG2a ratio congruent with6) while following mucosal immunization a mixed IgG1 and IgG2a pattern (IgG1/IgG2a ratio congruent with1) was observed. These data show that TTFC expressed on the surface of S. gordonii is immunogenic by the subcutaneous and mucosal routes and the immune response induced is capable of conferring protection from the lethal challenge with TT.

Therapy of mucosal candidiasis by expression of an anti-idiotype in human commensal bacteria

Two recombinant strains of Streptococcus gordonii, secreting or displaying a microbicidal single-chain antibody (H6), and stably colonizing rat vagina, were used to treat an experimental vaginitis caused by Candida albicans. A post-challenge intravaginal delivery of the H6-secreting strain was as efficacious as fluconazole in rapidly abating the fungal burden. Three weeks after challenge, 75% and 37.5% of the rats treated with the H6-secreting or displaying bacteria, respectively, were cured of the infection, which persisted in 100% of the animals treated with a S. gordonii strain expressing an irrelevant single-chain antibody. Thus, a human commensal bacterium can be suitably engineered to locally release a therapeutic antibody fragment.

Antibody responses to a mucosally delivered HIV-1 gp120-derived C4/V3 peptide

T1-SP10MN(A) is a synthetic peptide containing a T-helper (Th), cytotoxic T cell (CTL) and a B-cell epitope derived from the HIV-1 gp120 envelope protein. This peptide can elicit both systemic and mucosal antibody responses following nasal immunization in various species. In the present study, three different mucosal immunization strategies were performed in rabbits to determine which induced a more vigorous antibody response to T1-SP10MN(A). Nasal immunization followed by nasal boosting was found to be superior at inducing both serum IgG and vaginal secretory IgA (S-IgA) when compared to nasal followed by vaginal boosting. Conversely, vaginal priming followed by vaginal boosting elicited minimal serum IgG and vaginal S-IgA responses to T1-SP10MN(A), but moderate levels of vaginal IgG were detected. This study further demonstrates that vaginal immune responses can be elicited by immunization at distant and local mucosal sites.

Engineering the gram-positive cell surface for construction of bacterial vaccine vectors

A genetic system for surface display of heterologous proteins has been developed in Streptococcus gordonii, a gram-positive human oral commensal that is naturally competent for genetic transformation. Our approach is based on chromosomal integration downstream from a resident promoter and translational fusion to an M6 protein. Using this strategy a variety of proteins, of different origin and size, were displayed on the cell surface and were shown to be stably expressed both in vitro and in vivo. Animal models of mucosal colonization (oral and vaginal) and intragastric immunization with recombinant S. gordonii were developed and the local and systemic immune responses were studied. Here we report the techniques for the construction of recombinant bacteria, use of animal models, and analysis of the immune response.

The use of vaccines in treating cervical cancer: present status and future prospects

HPV types are carcinogenic agents in cervical cancer. This view is supported by epidemiological and biological evidence. The oncogenic products and capsid proteins of high risk HPV types are potential targets against which effective immunity may be generated by vaccination. Both therapeutic and prophlylactic immunisation are potential strategies to deal with the widespread problem of HPV infection and possibly established cervical neoplasia. Clinical trials are now underway to evaluate candidate vaccines.

Antigenicity and immunogenicity of the V3 domain of HIV type 1 glycoprotein 120 expressed on the surface of Streptococcus gordonii

Five different V3 domains of HIV-1 gp120 were expressed on the surface of the gram-positive bacterium Streptococcus gordonii, a model live vector for vaccine delivery. Sera of HIV-1-infected individuals and human monoclonal antibodies specifically recognized the gp120 sequences on the bacterial surface. Recombinant V3 from the reference HIV-1 strain MN was also shown to retain a conformation that allowed reaction with a conformation-specific monoclonal antibody. A V3-specific serum antibody response was detected in mice immunized both by subcutaneous injection and by vaginal colonization. V3-specific IgG2a antibodies, suggestive of a Th1 response, were found in the sera of mice colonized by recombinant bacteria.

Surface proteins of gram-positive bacteria and mechanisms of their targeting to the cell wall envelope

The cell wall envelope of gram-positive bacteria is a macromolecular, exoskeletal organelle that is assembled and turned over at designated sites. The cell wall also functions as a surface organelle that allows gram-positive pathogens to interact with their environment, in particular the tissues of the infected host. All of these functions require that surface proteins and enzymes be properly targeted to the cell wall envelope. Two basic mechanisms, cell wall sorting and targeting, have been identified. Cell well sorting is the covalent attachment of surface proteins to the peptidoglycan via a C-terminal sorting signal that contains a consensus LPXTG sequence. More than 100 proteins that possess cell wall-sorting signals, including the M proteins of Streptococcus pyogenes, protein A of Staphylococcus aureus, and several internalins of Listeria monocytogenes, have been identified. Cell wall targeting involves the noncovalent attachment of proteins to the cell surface via specialized binding domains. Several of these wall-binding domains appear to interact with secondary wall polymers that are associated with the peptidoglycan, for example teichoic acids and polysaccharides. Proteins that are targeted to the cell surface include muralytic enzymes such as autolysins, lysostaphin, and phage lytic enzymes. Other examples for targeted proteins are the surface S-layer proteins of bacilli and clostridia, as well as virulence factors required for the pathogenesis of L. monocytogenes (internalin B) and Streptococcus pneumoniae (PspA) infections. In this review we describe the mechanisms for both sorting and targeting of proteins to the envelope of gram-positive bacteria and review the functions of known surface proteins.