Intranasal vaccination of mice against infection with Mycobacterium tuberculosis

Changes in the Immune Phenotype and Gene Expression Profile Driven by a Novel Tuberculosis Nanovaccine: Short and Long-Term Post-immunization

Deciphering protection mechanisms against Mycobacterium tuberculosis (Mtb) remains a critical challenge for the development of new vaccines and therapies. We analyze the phenotypic and transcriptomic profile in lung of a novel tuberculosis (TB) nanoparticle-based boosting mucosal vaccine Nano-FP1, which combined to BCG priming conferred enhanced protection in mice challenged with low-dose Mtb. We analyzed the vaccine profile and efficacy at short (2 weeks), medium (7 weeks) and long term (11 weeks) post-vaccination, and compared it to ineffective Nano-FP2 vaccine. We observed several changes in the mouse lung environment by both nanovaccines, which are lost shortly after boosting. Additional boosting at long-term (14 weeks) recovered partially cell populations and transcriptomic profile, but not enough to enhance protection to infection. An increase in both total and resident memory CD4 and CD8 T cells, but no pro-inflammatory cytokine levels, were correlated with better protection. A unique gene expression pattern with differentially expressed genes revealed potential pathways associated to the immune defense against Mtb. Our findings provide an insight into the critical immune responses that need to be considered when assessing the effectiveness of a novel TB vaccine.

Vaccines Against Tuberculosis: Problems and Prospects (Review)

Despite the efforts of the global medical and scientific community, tuberculosis remains the leading cause of death from infectious diseases. The expectation of success associated with the development of new anti-TB drugs was not justified, and the attention of researchers was largely drawn to the creation of new mycobacterial strains for vaccination against tuberculosis. The proposed review contains current information on the existing vaccine strains and the development of new, genetically engineered strains for the prevention of tuberculosis and the prevention and treatment of other diseases. The review includes relevant information on the correlation between BCG vaccination and the frequency and severity of COVID-19 infection.

The Humoral Immune Response to BCG Vaccination

Bacillus Calmette Guérin (BCG) is the only currently available vaccine against tuberculosis (TB), but it confers incomplete and variable protection against pulmonary TB in humans and bovine TB (bTB) in cattle. Insights into the immune response induced by BCG offer an underexploited opportunity to gain knowledge that may inform the design of a more efficacious vaccine, which is urgently needed to control these major global epidemics. Humoral immunity in TB and bTB has been neglected, but recent studies supporting a role for antibodies in protection against TB has driven a growing interest in determining their relevance to vaccine development. In this manuscript we review what is known about the humoral immune response to BCG vaccination and re-vaccination across species, including evidence for the induction of specific B cells and antibodies; and how these may relate to protection from TB or bTB. We discuss potential explanations for often conflicting findings and consider how factors such as BCG strain, manufacturing methodology and route of administration influence the humoral response. As novel vaccination strategies include BCG prime-boost regimens, the literature regarding off-target immunomodulatory effects of BCG vaccination on non-specific humoral immunity is also reviewed. Overall, reported outcomes to date are inconsistent, but indicate that humoral responses are heterogeneous and may play different roles in different species, populations, or individual hosts. Further study is warranted to determine whether a new TB vaccine could benefit from the targeting of humoral as well as cell-mediated immunity.

Evaluation of a temperature-restricted, mucosal tuberculosis vaccine in guinea pigs

Tuberculosis (TB) is currently the leading cause of death in humans by a single infectious agent, Mycobacterium tuberculosis. The Bacillus Calmette-Guérin (BCG) vaccine prevents pulmonary TB with variable efficacy, but can cause life-threatening systemic infection in HIV-infected infants. In this study, TBvac85, a derivative of Mycobacterium shottsii expressing M. tuberculosis Antigen 85B, was examined as a safer alternative to BCG. Intranasal vaccination of guinea pigs with TBvac85, a naturally temperature-restricted species, resulted in serum Ag85B-specific IgG antibodies. Delivery of the vaccine by this route also induced protection equivalent to intradermal BCG based on organ bacterial burdens and lung pathology six weeks after aerosol challenge with M. tuberculosis strain Erdman. These results support the potential of TBvac85 as the basis of an effective TB vaccine. Next-generation derivatives expressing multiple M. tuberculosis immunogens are in development.

Enhanced effect of BCG vaccine against pulmonary Mycobacterium tuberculosis infection in mice with lung Th17 response to mycobacterial heparin-binding hemagglutinin adhesin antigen

Although the BCG vaccine can prevent tuberculosis (TB) in infants, its ability to prevent adult pulmonary TB is reportedly limited. Therefore, development of a novel effective vaccine against pulmonary TB has become an international research priority. We have previously reported that intranasal vaccination of mice with a mycobacterial heparin-binding hemagglutinin adhesin (HBHA) plus mucosal adjuvant cholera toxin (CT) enhances production of IFN-γ and anti-HBHA antibody and suppresses extrapulmonary bacterial dissemination after intranasal infection with BCG. In the present study, the effects of intranasal HBHA + CT vaccine on murine pulmonary Mycobacterium tuberculosis (Mtb) infection were examined. Intranasal HBHA + CT vaccination alone failed to reduce the bacterial burden in the infected lung. However, a combination vaccine consisting of s.c. BCG priming and an intranasal HBHA + CT booster significantly enhanced protective immunity against pulmonary Mtb infection on day 14 compared with BCG vaccine alone. Further, it was found that intranasal HBHA + CT vaccine enhanced not only IFN-γ but also IL-17A production by HBHA-specific T cells in the lung after pulmonary Mtb infection. Therefore, this combination vaccine may be a good candidate for a new vaccine strategy against pulmonary TB.

Crystal structure of the phosphate-binding protein (PBP-1) of an ABC-type phosphate transporter from Clostridium perfringens

Phosphate limitation is an important environmental stress that affects the metabolism of various organisms and, in particular, can trigger the virulence of numerous bacterial pathogens. Clostridium perfringens, a human pathogen, is one of the most common causes of enteritis necroticans, gas gangrene and food poisoning. Here, we focused on the high affinity phosphate-binding protein (PBP-1) of an ABC-type transporter, responsible for cellular phosphate uptake. We report the crystal structure (1.65 Å resolution) of the protein in complex with phosphate. Interestingly, PBP-1 does not form the short, low-barrier hydrogen bond with phosphate that is typical of previously characterized phosphate-binding proteins, but rather a canonical hydrogen bond. In its unique binding configuration, PBP-1 forms an unusually high number of hydrogen bonds (14) with the phosphate anion. Discrimination experiments reveal that PBP-1 is the least selective PBP characterised so far and is able to discriminate phosphate from its close competing anion, arsenate, by ~150-fold.

Pulmonary vaccine delivery

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

IgA response to ESAT-6/CFP-10 and Rv2031 antigens varies in patients with culture-confirmed pulmonary tuberculosis, healthy Mycobacterium tuberculosis-infected and non-infected individuals in a tuberculosis endemic setting, Ethiopia

Little attention has been given to the role of antibodies against Mycobacterium tuberculosis (Mtb) infection. We have compared the levels of IgA and IgG against ESAT-6/CFP-10 and Rv2031c antigens in sera of patients with culture-confirmed pulmonary tuberculosis (PTB), healthy Mtb-infected and non-infected individuals in endemic TB settings. Venous blood samples were collected from 166 study participants; sera were separated and assayed by an enzyme-linked immunosorbent assay (ELISA). QuantiFERON-TB Gold In-Tube (QFTGIT) assay was used for the screening of latent TB infection. The mean optical density (OD) values of IgA against ESAT-6/CFP-10 and Rv2031 were significantly higher in sera of patients with culture-confirmed PTB compared with healthy Mtb-infected and non-infected individuals (P < 0.001). The mean OD values of IgG against ESAT-6/CFP-10 and Rv2031 were also significantly higher in sera of patients with culture-confirmed PTB compared with healthy Mtb-infected and non-infected individuals (P < 0.05). The mean OD values of IgA against both antigens were also higher in sera of healthy Mtb-infected cases compared with non-infected individuals. There were positive correlations (P < 0.05) between the level of IFN-γ induced in QFTGIT assay and the OD values of serum IgA against both antigens in healthy Mtb-infected subjects. This study shows the potential of IgA response against ESAT-6/CFP-10 and Rv2031 antigens in discriminating clinical TB from healthy Mtb-infected and non-infected cases. Nevertheless, further well-designed cohort study is needed to fully realize the full potential of this diagnostic marker.

Effects of Recombinant Cholera Toxin B Subunit (rCTB) on Cellular Immune Responses: Enhancement of Delayed-Type Hypersensitivity Following Intranasal Co-Administration ofMycobacterium bovis-BCG with rCTB

Recombinant cholera toxin B subunit (rCTB) is a safe and potent mucosal adjuvant. To gain insight into the mechanism underlying the adjuvant effect of rCTB, the effects of rCTB on cell-mediated immune responses of mice and guinea pigs were examined after intranasal administration of Mycobacterium bovis -bacillus Calmette-Guérin (BCG) with and without rCTB. Delayed-type hypersensitivity, for skin reactions in guinea pigs and for footpad swelling reactions in mice, to purified protein derivative (PPD) were enhanced by intranasal co-administration of BCG and rCTB, as compared to giving BCG alone to these animals. Moreover, tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma production of spleen cells and antigen specific spleen cell proliferation, stimulated with PPD, were enhanced in the presence of rCTB. These results strongly suggest that rCTB enhances cellular as well as humoral immune responses.

Passive administration of purified secretory IgA from human colostrum induces protection against Mycobacterium tuberculosis in a murine model of progressive pulmonary infection

BACKGROUND

Immunoglobulin A is the most abundant isotype in secretions from mucosal surfaces of the gastrointestinal, respiratory and genitourinary tracts and in external secretions such as colostrum, breast milk, tears and saliva. The high concentration of human secretory IgA (hsIgA) in human colostrum strongly suggests that it should play an important role in the passive immune protection against gastrointestinal and respiratory infections.

MATERIALS AND METHODS

Human secretory IgA was purified from colostrum. The reactivity of hsIgA against mycobacterial antigens and its protective capacity against mycobacterial infection was evaluated.

RESULTS

The passive administration of hsIgA reduces the pneumonic area before challenge with M. tuberculosis. The intratracheal administration of M. tuberculosis preincubated with hsIgA to mice greatly reduced the bacterial load in the lungs and diminished lung tissue injury.

CONCLUSIONS

HsIgA purified from colostrum protects against M. tuberculosis infection in an experimental mouse model.

Cholera toxin induces a shift from inactive to active cyclooxygenase 2 in alveolar macrophages activated by Mycobacterium bovis BCG

Intranasal vaccination stimulates formation of cyclooxygenases (COX) and release of prostaglandin E(2) (PGE(2)) by lung cells, including alveolar macrophages. PGE(2) plays complex pro- or anti-inflammatory roles in facilitating mucosal immune responses, but the relative contributions of COX-1 and COX-2 remain unclear. Previously, we found that Mycobacterium bovis BCG, a human tuberculosis vaccine, stimulated increased release of PGE(2) by macrophages activated in vitro; in contrast, intranasal BCG activated no PGE(2) release in the lungs, because COX-1 and COX-2 in alveolar macrophages were subcellularly dissociated from the nuclear envelope (NE) and catalytically inactive. This study tested the hypothesis that intranasal administration of BCG with cholera toxin (CT), a mucosal vaccine component, would shift the inactive, NE-dissociated COX-1/COX-2 to active, NE-associated forms. The results showed increased PGE(2) release in the lungs and NE-associated COX-2 in the majority of COX-2(+) macrophages. These COX-2(+) macrophages were the primary source of PGE(2) release in the lungs, since there was only slight enhancement of NE-associated COX-1 and there was no change in COX-1/COX-2 levels in alveolar epithelial cells following treatment with CT and/or BCG. To further understand the effect of CT, we investigated the timing of BCG versus CT administration for in vivo and in vitro macrophage activations. When CT followed BCG treatment, macrophages in vitro had elevated COX-2-mediated PGE(2) release, but macrophages in vivo exhibited less activation of NE-associated COX-2. Our results indicate that inclusion of CT in the intranasal BCG vaccination enhances COX-2-mediated PGE(2) release by alveolar macrophages and further suggest that the effect of CT in vivo is mediated by other lung cells.

Roles of Mucosal Immunity against Mycobacterium tuberculosis Infection

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is one of the world's leading infectious causes of morbidity and mortality. As a mucosal-transmitted pathogen, Mtb infects humans and animals mainly through the mucosal tissue of the respiratory tract. Apart from providing a physical barrier against the invasion of pathogen, the major function of the respiratory mucosa may be to serve as the inductive sites to initiate mucosal immune responses and sequentially provide the first line of defense for the host to defend against this pathogen. A large body of studies in the animals and humans have demonstrated that the mucosal immune system, rather than the systemic immune system, plays fundamental roles in the host's defense against Mtb infection. Therefore, the development of new vaccines and novel delivery routes capable of directly inducing respiratory mucosal immunity is emphasized for achieving enhanced protection from Mtb infection. In this paper, we outline the current state of knowledge regarding the mucosal immunity against Mtb infection, including the development of TB vaccines, and respiratory delivery routes to enhance mucosal immunity are discussed.

Cellular immune responses to nine Mycobacterium tuberculosis vaccine candidates following intranasal vaccination

BACKGROUND

The identification of Mycobacterium tuberculosis vaccines that elicit a protective immune response in the lungs is important for the development of an effective vaccine against tuberculosis.

METHODS AND PRINCIPAL FINDINGS

In this study, a comparison of intranasal (i.n.) and subcutaneous (s.c.) vaccination with the BCG vaccine demonstrated that a single moderate dose delivered intranasally induced a stronger and sustained M. tuberculosis-specific T-cell response in lung parenchyma and cervical lymph nodes of BALB/c mice than vaccine delivered subcutaneously. Both BCG and a multicomponent subunit vaccine composed of nine M. tuberculosis recombinant proteins induced strong antigen-specific T-cell responses in various local and peripheral immune compartments. Among the nine recombinant proteins evaluated, the alanine proline rich antigen (Apa, Rv1860) was highly antigenic following i.n. BCG and immunogenic after vaccination with a combination of the nine recombinant antigens. The Apa-induced responses included induction of both type 1 and type 2 cytokines in the lungs as evaluated by ELISPOT and a multiplexed microsphere-based cytokine immunoassay. Of importance, i.n. subunit vaccination with Apa imparted significant protection in the lungs and spleen of mice against M. tuberculosis challenge. Despite observed differences in the frequencies and location of specific cytokine secreting T cells both BCG vaccination routes afforded comparable levels of protection in our study.

CONCLUSION AND SIGNIFICANCE

Overall, our findings support consideration and further evaluation of an intranasally targeted Apa-based vaccine to prevent tuberculosis.

Adjuvants in tuberculosis vaccine development

Tuberculosis remains a major public health problem around the world. Because the Mycobacterium bovis Bacilli-Calmette-Guerin (BCG) vaccine fails to protect adults from pulmonary tuberculosis, there is an urgent need for improved vaccine formulations. Unlike BCG, recombinant vaccines purified from bacterial expression vectors, as well as naked DNA, require an additional adjuvant. Recent improvements in our understanding of disease immunopathology, together with advances in biochemical and molecular techniques, have permitted the successful development of promising tuberculosis vaccine delivery and adjuvant combinations for human use. Here, we summarize the current state of adjuvant development and its impact on tuberculosis vaccine progress.

Immunogenicity and protective efficacy of "Mycobacterium w" against Mycobacterium tuberculosis in mice immunized with live versus heat-killed M. w by the aerosol or parenteral route

As the disease caused by Mycobacterium tuberculosis continues to be a burden, there is a concerted effort to find new vaccines to combat this problem. One of the important vaccine strategies is whole bacterial vaccines. This approach relies on multiple antigens and built-in adjuvanticity. Other mycobacterial strains which share cross-reactive antigens with M. tuberculosis have been considered as alternatives to M. bovis for vaccine use. One such strain, "Mycobacterium w", had been evaluated for its immunomodulatory properties in leprosy. A vaccine against leprosy based on killed M. w is approved for human use, where it has resulted in clinical improvement, accelerated bacterial clearance, and increased immune responses to Mycobacterium leprae antigens. M. w shares antigens not only with M. leprae but also with M. tuberculosis, and initial studies have shown that vaccination with killed M. w induces protection against tuberculosis in Mycobacterium bovis BCG responder, as well as BCG nonresponder, strains of mice. Hence, we further studied the protective potential of M. w and the underlying immune responses in the mouse model of tuberculosis. We analyzed the protective efficacy of M. w immunization in both live and killed forms through the parenteral route and by aerosol immunization, compared with that of BCG. Our findings provide evidence that M. w has potential protective efficacy against M. tuberculosis. M. w activates macrophage activity, as well as lymphocytes. M. w immunization by both the parenteral route and aerosol administration gives higher protection than BCG given by the parenteral route in the mouse model of tuberculosis.

Protection against tuberculosis induced by oral prime with Mycobacterium bovis BCG and intranasal subunit boost based on the vaccine candidate Ag85B-ESAT-6 does not correlate with circulating IFN-gamma producing T-cells

The potent IFN-gamma inducing fusion antigen Ag85B-ESAT-6 (85B6) is a lead subunit candidate to improve current vaccination against Mycobacterium tuberculosis (Mtb). The recombinant M. bovis BCG strain Myc3504 was constructed to secrete 85B6. It was based on commercial BCG strain Moreau Rio de Janeiro (BCG(MoWT)) which remains available for human oral administration. Myc 3504 induced higher levels of 85B6-specific IFN-gamma circulating T-cells as compared to BCG(MoWT). A novel needle-free mucosal immunization regimen combining oral prime with Myc3504 or BCG(MoWT) with intranasal boost with LTK-63-adjuvanted 85B6 was compared to subcutaneous prime-boost immunization. Strikingly whereas parenteral immunization induced sustained levels of 85B6-specific IFN-gamma secretion by circulating T-cells, mucosal regimens induced barely detectable IFN-gamma. Despite this, mice and guinea pigs immunized with the mucosal regimens were as efficiently protected against aerosol Mtb challenge as parenterally immunized animals. After Mtb challenge, anti-ESAT-6 IFN-gamma responses sharply increased in non-vaccinated mice as a hallmark of infection. Parenterally immunized mice that controlled Mtb infection, displayed anti-ESAT-6 IFN-gamma responses as high as non-immunized infected mice, compromising the possible use of ESAT-6 as a diagnostic tool. Interestingly, in mucosally immunized mice that were equally protected, post-challenge ESAT-6-specific IFN-gamma T-cell response remained low.

Evaluation of immune responses and protective efficacy in a goat model following immunization with a coctail of recombinant antigens and a polyprotein of Mycobacterium avium subsp. paratuberculosis

The protective efficacy of four recombinant antigens (85A, 85B, superoxide dismutase [SOD], and a fusion polypeptide [Map74F]) of Mycobacterium avium subsp. paratuberculosis (MAP) along with the adjuvant dimethydioctadecyl ammonium bromide (DDA) was assessed in a goat challenge model. Animals were immunized with the four antigens with adjuvant DDA (Group I, eight goat kids) or without the adjuvant (Group II, eight goat kids) or adjuvant only (Group III, nine goat kids). Animals were boostered 3 weeks after the primary vaccination and challenged 3 weeks after the booster. Significant antigen-specific lymphoproliferation was observed in the immunized animals 3 weeks after the booster immunization. This response increased further at 4 weeks after the booster. Similarly, antigen-specific IFN-gamma responses increased in the immunized animals 3 weeks after the booster. The response was significantly higher for 85A and Map74F at 10 weeks after primary vaccination (APV) in Group I animals compared to the other two groups. CD4+ T-cell populations were higher in the vaccinated animals from 6 to 10 weeks APV than those of the control animals. A significant increase in recombinant antigen-specific IFN-gamma gene expression was detected in the vaccinated animals. At necropsy (38 weeks APV), our multicomponent subunit vaccine imparted a significant protection in terms of reduction of MAP burden in target organs as compared to sham-immunized goats. This study indicates that our multicomponent subunit vaccine induced a good Th1 response and conferred protection against MAP infection in a goat challenge model.

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.

Intratracheal administration of third-generation lentivirus vector encoding MPT51 from Mycobacterium tuberculosis induces specific CD8+ T-cell responses in the lung

The present study evaluates the potential of improved third-generation lentivirus vector with respect to their use as an in vivo-administered T-cell vaccine against tuberculosis. Intratracheal administration of the lentivirus vector encoding MPT51 of Mycobacterium tuberculosis could induce MPT51-specific CD8+ T cells in the mediastinal lymph nodes 2 weeks after the administration. The vaccination could generate MPT51-specific memory CD8+ T cells in the lung, but not in the lymph nodes. Further, a single intratracheal immunization of MPT51 lentiviral vaccine decreased significantly the number of virulent M. tuberculosis in the lung after intratracheal challenge of the bacillus. These findings suggest that intratracheal immunization of the third-generation lentiviral vaccines is a promising vaccination strategy against pulmonary tuberculosis.

Oral vaccination of mice with lipid-encapsulated Mycobacterium bovis BCG: anatomical sites of bacterial replication and immune activity

Lipid microencapsulation of Mycobacterium bovis bacille Calmette-Guérin (BCG) produces an oral delivery vaccine that can establish systemic cell-mediated immune reactivity and protection against aerosol mycobacterial challenge in mice. Here, we describe the lymphatic and mucosal sites of bacterial replication, and location of Mycobacterium-specific IFN-gamma-secreting cell populations, following oral vaccination of BALB/c mice. Eight weeks following a single oral dose of lipid-encapsulated BCG, viable BCG organisms were recovered from the mesenteric lymph nodes (MLN) of 11/12 mice investigated (93%). Live bacteria were also occasionally recovered from the cervical lymph nodes (17%) and Peyer's patches (8%), but not from homogenates of the lungs or spleen. Strong Mycobacterium-specific IFN-gamma production was recorded among isolated splenocytes, but not among populations of mononuclear cells derived from the MLN or lungs. Oral vaccination of mice with lipid-encapsulated BCG thus appears to promote a state of systemic immunological reactivity more akin to that observed following parenteral rather than conventional oral vaccination, despite the fact that replicating bacilli are restricted to lymphatic tissues of the alimentary tract. Possible patterns of lymphocyte sensitization and trafficking are discussed.

Mucosal immunization with recombinant heparin-binding haemagglutinin adhesin suppresses extrapulmonary dissemination of Mycobacterium bovis bacillus Calmette-Guérin (BCG) in infected mice

It is generally accepted that cellular immunity plays a critical role in the protection against Mycobacterium tuberculosis, an intracellular pathogen. Recently, however, an increasing number of reports indicate the important contribution of humoral immunity against mycobacterial infection. Since M. tuberculosis establishes its primary lesion in the lung, induction of humoral immunity in the airway tract by mucosal immunization regime could provide protective immunity against tuberculosis. In this study, mycobacterial heparin-binding haemagglutinin adhesin (HBHA) was used as an immunization antigen because HBHA is an essential virulence factor required for the infection of lung epithelial cells and extrapulmonary dissemination of mycobacteria. The effects of intranasal immunization with a yeast-expressed recombinant (r) HBHA co-administered with a mucosal adjuvant cholera toxin (CT) on the induction of humoral and cellular immunity were examined, and its protective efficacy against pulmonary challenge infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG) was evaluated. HBHA-specific antibodies were induced in serum and airway tract of immunized mice, which specifically recognized native HBHA expressed on M. bovis BCG. Th1-type immunity against mycobacterial antigens was also enhanced in the lung of immunized mice after pulmonary BCG infection. Furthermore, the immunization suppressed bacterial load in the spleen after pulmonary BCG infection. These results indicate that systemic and local humoral immunity induced by the HBHA-based mucosal vaccine impairs extrapulmonary dissemination, thus providing immune protection against mycobacterial infection.

Should a new tuberculosis vaccine be administered intranasally?

Most of the world's population is vaccinated with the only available vaccine against tuberculosis (TB), the Bacillus Calmette-Guérin (BCG) vaccine that was developed almost a century ago. Despite the wide coverage of the BCG vaccine, there are great variations in protective efficacy among different study populations. BCG vaccination protects against childhood forms of TB, but this immunity wanes with age, resulting in none, or insufficient, protection against adult pulmonary TB (PTB). PTB is the major disease manifestation of TB in adults and it causes death at the most productive age, further adding to poverty in already impoverished countries. Therefore, new more effective vaccines and novel immunisation strategies are urgently needed. The most common route of TB is by inhalation of tubercle bacilli leading to the establishment of a primary infection in the lung. Immunising through the nasal mucosal surface should therefore have advantage over other routes, as such vaccine administration elicits protective immune responses also in the lung, i.e. at the site of primary infection. Several new TB-vaccine candidates have been evaluated for their protective efficacy in animal models using the mucosal route of immunisation. In formulating such vaccines, the adjuvants and delivery systems are crucially important.

Tuberculosis subunit vaccine development: Impact of physicochemical properties of mycobacterial test antigens

Tuberculosis caused by Mycobacterium tuberculosis continues to be one of the major public health problems in the world. The eventual control of this disease will require the development of a safe and effective vaccine. One of the approaches receiving a great deal of attention recently is subunit vaccination. An efficacious antituberculous subunit vaccine requires the identification and isolation of key components of the pathogen that are capable of inducing a protective immune response. Clues to identify promising subunit vaccine candidates may be found in their physicochemical and immunobiological properties. In this article, we review the evidence that the physicochemical properties of mycobacterial components can greatly impact the induction of either protective or deleterious immune response and consequently influence the potential utility as an antituberculous subunit vaccine.

Mucosal administration of Ag85B-ESAT-6 protects against infection with Mycobacterium tuberculosis and boosts prior bacillus Calmette-Guerin immunity

We have examined the intranasal administration of a vaccine against Mycobacterium tuberculosis (M.tb) consisting of the mucosal adjuvant LTK63 and the Ag Ag85B-ESAT-6. Vaccination with LTK63/Ag85B-ESAT-6 gave a strong and sustained Th1 response mediated by IFN-gamma-secreting CD4 cells, which led to long-lasting protection against tuberculosis, equivalent to that observed with bacillus Calmette-Guérin (BCG) or Ag85B-ESAT-6 in dimethyldioctadecylammonium bromide/monophosphoryl lipid A. Because a crucial element of novel vaccine strategies is the ability to boost BCG-derived immunity, we also tested whether LTK63/Ag85B-ESAT-6 could act as a BCG booster vaccine in BCG-vaccinated mice. We found that vaccinating with LTK63/Ag85B-ESAT-6 strongly boosted prior BCG-stimulated immunity. Compared with BCG-vaccinated nonboosted mice, we observed that infection with M.tb led to a significant increase in anti-M.tb-specific CD4 T cells in the lungs of LTK63/Ag85B-ESAT-6-boosted animals. This correlated with a significant increase in the protection against M.tb in LTK63/Ag85B-ESAT-6-boosted mice, compared with BCG-vaccinated animals. Thus, LTK63/Ag85B-ESAT-6 represents an efficient preventive vaccine against tuberculosis with a strong ability to boost prior BCG immunity.

Mutant Escherichia coli enterotoxin as a mucosal adjuvant induces specific Th1 responses of CD4+ and CD8+ T cells to nasal killed-bacillus calmette–guerin in mice

On single nasal immunization of mice with killed-bacillus calmette-guerin (BCG) plus a mutant Escherichia coli enterotoxin, delayed-type hypersensitivity was induced and BCG-infection decreased. Spleen cells, particularly CD4+ T cells among them produced IL-2, IFNgamma and TNFalpha in response to the killed-BCG or purified protein derivatives. CD8+ T cells including cytotoxic T lymphocytes produced IFNgamma and TNFalpha. However, both types of T cells reacted a little to Ag85B. The mutant induces cellular immunity to nasal killed-BCG vaccine and decreases BCG-infection. CD4+ and CD8+ T cells produce cytokines effective for tuberculosis. Although killed-BCG loses some antigens like Ag85B, nasal killed-BCG plus the mutant is useful for tuberculosis.

Polymeric IgR knockout mice are more susceptible to mycobacterial infections in the respiratory tract than wild-type mice

It is generally accepted that cellular, and not humoral immunity, plays the crucial role in defense against intracellular bacteria. However, accumulating data indicate the importance of humoral immunity for the defense against a number of intracellular bacteria, including mycobacteria. We have investigated the role of secretory IgA, the main isotype found in mucosal tissues, in protection against mycobacterial infection, using polymeric IgR (pIgR)-deficient mice. Characterization of the humoral response induced after intra-nasal immunizations with the mycobacterial antigen PstS-1 revealed a loss of antigen-specific IgA response in saliva from the knockout mice. IgA level in the bronchoalveolar lavage of knockout mice was similar to wild-type level, although the IgA antibodies must have reached the lumen by other means than pIgR-mediated transport. Infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG) demonstrated that the immunized pIgR-/- mice were more susceptible to BCG infection than immunized wild-type mice, based on higher bacterial loads in the lungs. This was accompanied by a reduced production of both IFN-gamma and tumor necrosis factor-alpha (TNF-alpha) in the lungs. Additionally, the pIgR-/- mice displayed reduced natural resistance to mycobacterial infection proved by significantly higher bacterial growth in their lungs compared with wild-type mice after infection with virulent Mycobacterium tuberculosis. The knockout mice appeared to have a delayed mycobacteria-induced immune response with reduced expression of protective mediators, such as IFN-gamma, TNF-alpha, inducible nitric oxide synthase and regulated upon activation normal T cell sequence, during early infection. Collectively, our results show that actively secreted IgA plays a role in protection against mycobacterial infections in the respiratory tract, by blocking entrance of bacilli into the lungs, in addition to modulation of the mycobacteria-induced pro-inflammatory response.

Immune systems in developed and developing countries; implications for the design of vaccines that will work where BCG does not

New vaccine candidates for tuberculosis are beginning to enter clinical trials. In this review we discuss issues surrounding the design of these candidates, and the way they were screened in animal models. First, screening vaccines for their ability to attenuate inevitably fatal tuberculosis in immunologically naïve mice might be leading to the selection of inappropriate candidates. We need to screen vaccines for their ability to stop the development of progressive disease, since this is what they must achieve in man. A solution to this problem is proposed. Secondly, we point out that some mouse models of tuberculosis in laboratories in developing countries, where exposure to environmental mycobacteria is large, mimic neglected aspects of human disease more closely than do low-dose infections in hyper-susceptible immunologically naïve mice in the USA or Europe. We need to think more about geographical differences in immunological experience, and these mouse models can help us. Thirdly, we conclude that in developing countries where BCG fails this is not because there is too little Th1 response, but rather because the Th1 response is rendered ineffective and immunopathological by other subversive mechanisms, including IL-4 responses and inappropriate regulatory T cell function. Therefore, we suggest that vaccines that will work in those countries might need to have immunoregulatory properties that can switch off pre-existing subversive mechanisms, and block their development in the future. The development of such vaccines, that might work where BCG does not, will require a greater understanding of the roles of the many types of regulatory T cell in tuberculosis.

Histopathogenesis of experimental Mycobacterium bovis infection in mice

In-bred strains of mice are commonly used to model pathogenic infections due to their cost and utility. In order to understand better the nature of experimental tuberculosis in mice, we infected BALB/c mice with a virulent field isolate of Mycobacterium bovis. Mice were sacrificed at intervals in order to visualise the pathological lesions in major internal organs. Pathological lesions in tissues increased in number and severity over time and replicated many of the salient features observed in badgers and cattle infected with M. bovis. These similarities are discussed. Examination of pathological lesions at terminal stages of infection enabled us to suggest the lethal effects of M. bovis mediated through the host response. We conclude that the mouse is a relevant surrogate species in which to study the virulence of M. bovis, as well as the influence of vaccination on its pathogenicity.

Oral delivery of lipid-encapsulated Mycobacterium bovis BCG extends survival of the bacillus in vivo and induces a long-term protective immune response against tuberculosis

The success of oral-route vaccination using Mycobacterium bovis bacille Calmette-Guérin (BCG) relies on delivery of live, actively metabolising bacilli to confer protection. Here, we describe that lipid-microencapsulation can extend the in vivo survival of bacilli when fed to mice, and can induce a long-lasting protective immune response. Feeding mice with lipid-encapsulated BCG (L-BCG) resulted in greater recovery of viable BCG bacilli from the mesenteric lymph nodes (MLN) compared to mice fed non-encapsulated BCG. A time-course study indicated persistence of viable BCG bacilli in MLN up to 30 weeks post-vaccination, similar to the duration of viable BCG recovery from the spleen following subcutaneous vaccination. The persistence of viable bacilli in the MLN of L-BCG mice invoked long-lasting systemic cell-mediated immune reactivity, with responses similar to those observed in subcutaneously-vaccinated mice. Further, L-BCG-vaccinated mice showed a high degree of protection against aerogenic challenge with virulent M. bovis at 30 weeks post-vaccination, with significant reductions in lung and spleen pathogen burdens. This study identifies that lipid-encapsulation of live BCG bacilli can facilitate increased in vivo survival and immunogenicity of the vaccine in orally-vaccinated mice, and highlights protection via this route for up to 7 months post-immunisation.

Multicomponent antituberculous subunit vaccine based on immunodominant antigens of Mycobacterium tuberculosis

The low molecular mass polypeptides of secretory proteome of Mycobacterium tuberculosis are dominant targets for recognition by lymphocytes of human models of immunity to tuberculosis. In the present study, we evaluated the inherent immunogenicity of 102 individual polypeptides purified from low molecular mass region below 40kDa in mouse model of immunization. The aim of this study was to identify molecules relevant for development of subunit vaccine against tuberculosis based on high degree of immunogenecity. Here, we demonstrate that experimental multicomponent subunit vaccine (MSV) consisting of five immunodominant polypeptides with high immunogenicity (CFP-25, CFP-20.5, Ag85B, Ag85A and CPF-32) induced both cellular and humoral immune responses characterized by Th1 and Th2 cytokine induction and imparted significant protection when administered with DDA-MPL adjuvants in C57BL/6J mice. The degree of protection imparted by experimental MSV on the basis of decrease in CFU's from target organs (lungs and spleen) was comparable to BCG and total mycobacterial culture filtrate proteins (CFPs) based vaccines. These results, therefore, suggest the potential of multicomponent subunit vaccination against tuberculosis based on strongly immunogenic proteins of M. tuberculosis.

Recent developments in tuberculosis vaccines

PURPOSE OF REVIEW

The aim is to review findings related to the use of Bacille Calmette-Guerin (BCG) vaccine, focusing on its limitations and benefits in controlling tuberculosis (TB). Some new TB vaccines, which have entered or are expected to enter clinical trials, are highlighted.

RECENT FINDINGS

BCG is currently the only available vaccine against TB, and is widely administered within the World Health Organization Expanded Programme for Immunization. Several trials have shown that the protective efficacy of BCG varies between different populations. Recently, a 60-year follow-up study of American Indians reported the long-term efficacy of BCG to be 52%. The reasons for the low efficacy of the BCG vaccine may be generic differences in the BCG strains, differences in immunological properties of study populations or exposure to environmental factors such as mycobacteria. The low efficacy of the BCG vaccine has encouraged the search for a new vaccine. Among new vaccine candidates are live attenuated Mycobacterium tuberculosis vaccines, recombinant BCG, DNA vaccines, subunit vaccines and fusion proteins with novel adjuvants and delivery systems.

SUMMARY

Today, most of the world's population is vaccinated with BCG. It is generally accepted that BCG protects against childhood TB but this immunity wanes with age, resulting in no or insufficient protection against TB. Using modern techniques, several research groups have developed more than 200 new vaccine candidates. Some of these vaccines are now in clinical trials. The clinical evaluation of these new vaccines should be designed to cover a heterogeneous population with great variation in immune responses.

Role of IgA in the defense against respiratory infections IgA deficient mice exhibited increased susceptibility to intranasal infection with Mycobacterium bovis BCG

IgA is the predominant Ig isotype in mucosal tissue and is believed to be involved in defense against viral and bacterial infections at these sites. Here, we examined the role of IgA in the protection against intranasal (i.n.) infection with Mycobacterium bovis Bacillus Calmette-Guerin (BCG). IgA deficient (IgA-/-) mice and wild type non-targeted littermate (IgA+/+) mice were immunized by i.n. route with the mycobacterium surface antigen PstS-1 formulated with cholera toxin (CT). Our data showed that IgA-/- mice were more susceptible to BCG infection compared to IgA+/+ mice, as revealed by the higher bacterial loads in the lungs and bronchoalveolar lavage (BAL). Analysis of the Ig levels and the antibody responses to PstS-1 showed that IgA-/- mice had no detectable IgA either in the saliva or in the BAL. However, these mice displayed higher levels of total and specific IgM than IgA+/+ mice in both mucosal fluids. More importantly, analysis of the cytokine responses revealed a reduction in the IFN-gamma and TNF-alpha production in the lungs of IgA-/- compared to IgA+/+ mice. Altogether, our results suggest that IgA may play a role in protection against mycobacterial infections in the respiratory tract by blocking the pathogen entrance and/or by modulating the pro-inflammatory responses.

Protein expression by a Beijing strain differs from that of another clinical isolate and Mycobacterium tuberculosis H37Rv

The Beijing strain family has often been associated with tuberculosis (TB) outbreaks and drug resistance worldwide. In this study the authors have compared the protein expression and antigen recognition profiles of a local Beijing strain with a less prevalent clinical isolate belonging to the family 23 strain lineage, and the laboratory strain Mycobacterium tuberculosis H37Rv. Using two-dimensional electrophoresis, liquid chromatography tandem mass spectrometry and Western blot analysis several proteins were identified as quantitatively increased or decreased in both clinical strains compared to H37Rv. Remarkably, the Beijing strain showed increased expression of alpha-crystallin and decreased expression of Hsp65, PstS1, and the 47 kDa protein compared to the other clinical strain and H37Rv. One- and two-dimensional Western blot analysis of antigens expressed by the three strains, using plasma from TB patients, confirmed differential antigen expression by strains and patient-to-patient variation in humoral immunity. These observed protein differences could aid the elucidation of mechanisms underlying the success of the Beijing strain family, measured by global dissemination, compared to other M. tuberculosis strains.

Intranasal bacille Calmette-Guerin (BCG) vaccine dosage needs balancing between protection and lung pathology

Intranasal vaccination may offer practical benefits and better protection against respiratory infections, including tuberculosis. In this paper, we investigated the persistence of the Mycobacterium bovis-strain bacille Calmette-Guerin (BCG) Pasteur, lung granuloma formation and protection against pathogenic tuberculous challenge in mice. A pronounced BCG dose-dependent granulomatous infiltration of the lungs was observed following intranasal, but not after subcutaneous, vaccination. Corresponding doses of BCG, over a 100-fold range, imparted similar protection against H37Rv challenge when comparing the intranasal and subcutaneous vaccination routes. Interestingly, a BCG dose-dependent reduction of the H37Rv challenge infection was observed in the lungs, but not in the spleens, following both intranasal and subcutaneous vaccination. In the light of the observed concurrence between the extent of granuloma formation and the level of protection of the lungs, we conclude that intranasal vaccination leading to best protective efficacy needs to be balanced with an acceptable safety margin avoiding undue pathology in the lungs.

Comparative evaluation of intranasal and subcutaneous route of immunization for development of mucosal vaccine against experimental tuberculosis

Activation of mucosal immunity in the respiratory tract is crucial for protection against respiratory infections. Whether the intranasal route of vaccination imparts better protection against pulmonary tuberculosis than that of subcutaneous vaccination remains a debatable issue. In this study, we have investigated the effect of the routes of immunization on the induction of immunoprotection against experimental tuberculosis employing mycobacterial culture filtrate proteins complexed with dimethyldioctadecylammonium bromide. Vaccination via intranasal and subcutaneous routes triggered immune activation in the spleen and cervical lymph node, while the former route of vaccination lead to higher antigen-specific lymphocyte proliferation, interferon-gamma, interleukin-12 and interleukin-4 responses in cervical lymph node and induction of antigen-specific IgA responses at mucosal level of the respiratory tract. Mice vaccinated via the intranasal route were found to be better protected against experimental tuberculosis particularly in lung compared to subcutaneous-immunized mice. These results emphasize the importance of the intranasal route vaccination in tuberculosis.

Single mucosal, but not parenteral, immunization with recombinant adenoviral-based vaccine provides potent protection from pulmonary tuberculosis

Bacillus Calmette-Guerin (BCG) vaccine has failed to control the global tuberculosis (TB) epidemic, and there is a lack of safe and effective mucosal vaccines capable of potent protection against pulmonary TB. A recombinant replication-deficient adenoviral-based vaccine expressing an immunogenic Mycobacterium tuberculosis Ag Ag85A (AdAg85A) was engineered and evaluated for its potential to be used as a respiratory mucosal TB vaccine in a murine model of pulmonary TB. A single intranasal, but not i.m., immunization with AdAg85A provided potent protection against airway Mycobacterium tuberculosis challenge at an improved level over that by cutaneous BCG vaccination. Systemic priming with an Ag85A DNA vaccine and mucosal boosting with AdAg85A conferred a further enhanced immune protection which was remarkably better than BCG vaccination. Such superior protection triggered by AdAg85 mucosal immunization was correlated with much greater retention of Ag-specific T cells, particularly CD4 T cells, in the lung and was shown to be mediated by both CD4 and CD8 T cells. Thus, adenoviral TB vaccine represents a promising novel vaccine platform capable of potent mucosal immune protection against TB. Our study also lends strong evidence that respiratory mucosal vaccination is critically advantageous over systemic routes of vaccination against TB.

Mucosal immunization against respiratory bacterial pathogens

Bacterial respiratory diseases remain a major cause of morbidity and mortality throughout the world. The young and the elderly are particularly susceptible to the pathogens that cause these diseases. Therapeutic approaches remain dependent upon antibiotics contributing to the persistent increases in antibiotic resistance. The main causes of respiratory disease discussed in this review are Mycobacterium tuberculosis, Corynebacterium diphtheriae, Bordatella pertussis, Streptococcus pneumoniae, non-typeable Haemophilus influenzae, Moraxella catarrhalis and Pseudomonas aeruginosa. All these organisms initiate disease at the mucosal surface of the respiratory tract and thus the efficacy of the host's response to infection needs to be optimal at this site. Vaccines available for diseases caused by many of these pathogens have limitations in accessibility or efficacy, highlighting the need for improvements in approaches and products. The most significant challenges in both therapy and prevention of disease induced by bacteria in the respiratory tract remain the development of non-injectable vaccines and delivery systems/immunization regimens that improve mucosal immunity.

Passive protection with immunoglobulin A antibodies against tuberculous early infection of the lungs

We report on a new approach toward protection against tuberculosis, based on passive inoculation with immunoglobulin A (IgA) antibodies. In a mouse model of tuberculous lung infection, intranasal inoculations of mice with an IgA monoclonal antibody (mAb) against the alpha-crystallin antigen of Mycobacterium tuberculosis reduced up to 10-fold the lung bacterial counts at nine days after either aerosol- or intranasal challenge. This effect involved synergism between mAb inoculations shortly before and 3 days after infection. Monomeric IgA reduced the colony-forming unit counts to the same extent as the polymeric IgA, suggesting antibody targeting to Fcalpha, rather than poly-immunoglobulin receptors on infected lung macrophages. The protective effect was of short duration, presumably due to the rapid degradation of the intranasally applied IgA. Our results provide evidence of an alternative approach which could be further developed toward immunoprophylaxis against tuberculosis in immunocompromised subjects.

Immunization with heat-killed Mycobacterium bovis bacille Calmette–Guerin (BCG) in Eurocine™ L3 adjuvant protects against tuberculosis

The current live attenuated vaccine against tuberculosis, BCG, poses a risk of disseminated infections in immunocompromised subjects. Therefore, in this study we compared the protective effect of a heat-killed bacille Calmette-Guerin (H-kBCG) vaccine given in a new adjuvant (Eurocine L3) with the protection provided by the conventional live attenuated BCG vaccine in mice (C57BL/6 and BALB/c) challenged with virulent Mycobacterium tuberculosis (strain Harlingen). The H-kBCG vaccine alone, in accordance with earlier studies, did not give any or only gave slight protection compared to sham-vaccinated controls. However, the same vaccine given with Eurocine L3 adjuvant, either formulated as a suspension or as an emulsion, afforded significant levels of protection. This protection was at least as good as that of the control live attenuated BCG vaccine. The Eurocine L3 adjuvant is approved for human use as a nasal vaccine adjuvant and a successful phase I trial with nasal immunization with diphtheria vaccine has recently been performed in Sweden. Here we show that, in mice, intranasal priming with H-kBCG in Eurocine L3 adjuvant followed by intranasal booster resulted in the same level of protection as subcutaneous priming followed by intranasal booster. All H-kBCG formulations in the Eurocine L3 adjuvant elicited mycobacterial antigen-specific serum IgG and IFN gamma responses. In general, among the different vaccine formulation(s) in the Eurocine L3 adjuvant those that produced a relatively high Th2 response, as measured by IgG1/IgG2a ratio and IFN gamma production in vitro, were the most protective. In conclusion, H-kBCG in Eurocine L3 adjuvant could represent a safe and a more stable alternative to the conventional live BCG vaccine.

Single intranasal mucosal Mycobacterium bovis BCG vaccination confers improved protection compared to subcutaneous vaccination against pulmonary tuberculosis

Whether the intranasal (i.n.) route of Mycobacterium bovis BCG vaccination provides better protection against pulmonary tuberculosis than subcutaneous (s.c.) vaccination remains an incompletely solved issue. In the present study, we compared both immune responses and protection elicited by single BCG vaccinations via the i.n. or s.c. route in BALB/c mice. While both i.n. and s.c. vaccination triggered comparable levels of primary immune activation in the spleen and draining lymph nodes, i.n. vaccination led to a greater antigen-specific gamma interferon recall response in splenocytes than s.c. vaccination upon secondary respiratory mycobacterial challenge, accompanied by an increased frequency of antigen-specific lymphocytes. There was also a quicker cellular response in the lungs of i.n. vaccinated mice upon mycobacterial challenge. Mice vaccinated i.n. were found to be much better protected, particularly in the lung, than s.c. vaccinated counterparts against pulmonary tuberculosis at both 3 and 6 months postvaccination. These results suggest that the i.n. route of vaccination improves the protective effect of the current BCG vaccine.

Design and evaluation of an aerosol infection chamber for small animals

In this report, we describe the design of an aerosol exposure chamber to reproducibly produce uniformly distributed clouds of droplet nuclei. The device can deliver desired number of bacilli (20-2000) in lungs of mice. All safety measures to handle infectious bacteria have been incorporated in the design and it is controlled remotely by a personal computer. It is an indispensable device to study the protective efficacy of vaccine candidates against Mycobacterium tuberculosis infection. This device would also be useful to study immunization and drug delivery by nasal route in experimental animals.

Novel vaccination strategies based on recombinant Mycobacterium bovis BCG

In this manuscript, we will review the utilization of Mycobacterium bovis Bacille Calmette-Guerin (BCG) as a vaccine against tuberculosis (TB) and as a carrier system for heterologous antigens. BCG is one of the most widely used vaccines. Novel techniques in genome manipulation allow the construction of virulence-attenuated recombinant (r)-BCG strains that can be employed as homologous vaccines, or as heterologous antigen delivery systems, for priming pathogen-specific immunity against infectious diseases, including TB. Several approaches are available for heterologous antigen expression and compartmentalization in BCG and recent findings show the potential to modulate and direct the immune responses induced by r-BCG strains as desired. Recent achievements in complete genome analysis of various target pathogens, combined with a better understanding of protective pathogen-specific immune responses, form the basis for the rational design of a new generation of recombinant mycobacterial vaccines against a multitude of infectious diseases.

B- and T-cell responses to the mycobacterium surface antigen PstS-1 in the respiratory tract and adjacent tissues. Role of adjuvants and routes of immunization

Induction of mucosal immunity in the respiratory tract is crucial for protection against respiratory infections. Here, we have investigated the effects of the routes of immunization as well as of three different adjuvants on the induction of mucosal immune responses. Mice were immunized using intranasal (i.n.) or intraperitoneal (i.p.) routes with the mycobacterium PstS-1 antigen. Cholera toxin (CT), detoxified pertussis toxin (detPT) and RU 41.740 from Klebsiella pneumoniae were compared as mucosal adjuvants. Our data showed that i.n. route of immunization induced the most favorable stimulation of mucosal antigen-specific IgA responses supported by mixed Th cells producing IL-4, IL-5, IFN-gamma. In contrast, i.p. immunizations elicited only enhancement of systemic responses, predominantly of the Th2 type. Furthermore, the use of CT as mucosal adjuvant resulted in the stimulation of a mixed Th cell response whereas detPT evoked mainly Th2 type of responses. Likewise CT, the RU 41.740 adjuvant elicited a mixed Th cell response, albeit supported by much lower numbers of CD4(+) T-cells. Thus, i.n. route of immunization favors the induction of mucosal and systemic immune responses, while the Th cell development at mucosal inductive site is influenced by the adjuvant used for immunizations.