Mapping of TH1 helper T-cell epitopes on major secreted mycobacterial antigen 85A in mice infected with live Mycobacterium bovis BCG

CD4+ T-Cell Epitope Prediction by Combined Analysis of Antigen Conformational Flexibility and Peptide-MHCII Binding Affinity

Antigen processing in the class II MHC pathway depends on conventional proteolytic enzymes, potentially acting on antigens in native-like conformational states. CD4+ epitope dominance arises from a competition among antigen folding, proteolysis, and MHCII binding. Protease-sensitive sites, linear antibody epitopes, and CD4+ T-cell epitopes were mapped in plague vaccine candidate F1-V to evaluate the various contributions to CD4+ epitope dominance. Using X-ray crystal structures, antigen processing likelihood (APL) predicts CD4+ epitopes with significant accuracy for F1-V without considering peptide-MHCII binding affinity. We also show that APL achieves excellent performance over two benchmark antigen sets. The profiles of conformational flexibility derived from the X-ray crystal structures of the F1-V proteins, Caf1 and LcrV, were similar to the biochemical profiles of linear antibody epitope reactivity and protease sensitivity, suggesting that the role of structure in proteolysis was captured by the analysis of the crystal structures. The patterns of CD4+ T-cell epitope dominance in C57BL/6, CBA, and BALB/c mice were compared to epitope predictions based on APL, MHCII binding, or both. For a sample of 13 diverse antigens, the accuracy of epitope prediction by the combination of APL and I-A^b-MHCII-peptide affinity reached 36%. When MHCII allele specificity was also diverse, such as in human immunity, prediction of dominant epitopes by APL alone reached 42% when using a stringent scoring threshold. Because dominant CD4+ epitopes tend to occur in conformationally stable antigen domains, crystal structures typically are available for analysis by APL, and thus, the requirement for a crystal structure is not a severe limitation.

Mycobacterial Lipoprotein Z Triggers Efficient Innate and Adaptive Immunity for Protection Against Mycobacterium tuberculosis Infection

Mycobacterial lipoproteins are considered to be involved in both virulence and immunoregulatory processes during Mycobacterium tuberculosis (M.tb) infection. In our previous investigations on the immunoreactivity of more than 30 M.tb proteins in active TB patients, we identified mycobacterial lipoprotein Z (LppZ) as one of the most immune dominant antigens. How LppZ triggers immune responses is still unclear. In this study, we analyzed LppZ-mediated innate and adaptive immunity using a murine air pouch model and an M.tb infection model, respectively. We found that LppZ could not only recruit inflammatory cells but also induce the production of proinflammatory cytokines inside the pouches. LppZ could also induce strong Th1 responses following immunization and confer protection against challenge with M.tb virulent strain H37Rv at a similar level to BCG vaccination but with less pathological damage in the lungs. Furthermore, we revealed the presence of LppZ-specific functional CD4⁺ T cells in the lungs of the challenged mice that were capable of secreting double or triple cytokines, including IFN-γ, IL-2, and TNF-α. Our study thus demonstrates that LppZ is of strong immunogenicity during M.tb infection in both humans and mice and has the ability to trigger effective innate and cellular immunity. Considering the limitations of candidate antigens in the pipeline of TB vaccine development, LppZ-mediated immune protection against M.tb challenge in the mouse model implies its potential application in vaccine development.

Microphysiologic Human Tissue Constructs Reproduce Autologous Age-Specific BCG and HBV Primary Immunization in vitro

Current vaccine development disregards human immune ontogeny, relying on animal models to select vaccine candidates targeting human infants, who are at greatest risk of infection worldwide, and receive the largest number of vaccines. To help accelerate and de-risk development of early-life effective immunization, we engineered a human age-specific microphysiologic vascular-interstitial interphase, suitable for pre-clinical modeling of distinct age-targeted immunity in vitro. Our Tissue Constructs (TCs) enable autonomous extravasation of monocytes that undergo rapid self-directed differentiation into migratory Dendritic Cells (DCs) in response to adjuvants and licensed vaccines such as Bacille Calmette-Guérin (BCG) or Hepatitis B virus Vaccine (HBV). TCs contain a confluent human endothelium grown atop a tri-dimensional human extracellular matrix substrate, employ human age-specific monocytes and autologous non heat-treated plasma, and avoid the use of xenogenic materials and exogenous cytokines. Vaccine-pulsed TCs autonomously generated DCs that induced single-antigen recall responses from autologous naïve and memory CD4+ T lymphocytes, matching study participant immune-status, including BCG responses paralleling donor PPD status, BCG-induced adenosine deaminase (ADA) activity paralleling infant cohorts in vivo, and multi-dose HBV antigen-specific responses as demonstrated by lymphoproliferation and TCR sequencing. Overall, our microphysiologic culture method reproduced age- and antigen-specific recall responses to BCG and HBV immunization, closely resembling those observed after a birth immunization of human cohorts in vivo, offering for the first time a new approach to early pre-clinical selection of effective age-targeted vaccine candidates.

Rational design, preparation and characterization of recombinant Ag85B variants and their glycoconjugates with T-cell antigenic activity against Mycobacterium tuberculosis

Tuberculosis is the deadliest infectious disease in the world. The variable efficacy of the current treatments highlights the need for more effective agents against this disease. In the past few years, we focused on the investigation of antigenic glycoconjugates starting from recombinant Ag85B (rAg85B), a potent protein antigen from Mycobacterium tuberculosis. In this paper, structural modifications were rationally designed in order to obtain a rAg85B variant protein able to maintain its immunogenicity after glycosylation. Lysine residues involved in the main T-epitope sequences (namely, K30 and K282) have been substituted with arginine to prevent their glycosylation by a lysine-specific reactive linker. The effectiveness of the mutation strategy and the detailed structure of resulting neo-glycoconjugates have been studied by intact mass spectrometry, followed by peptide and glycopeptide mapping. The effect of K30R and K282R mutations on the T-cell activity of rAg85B has also been investigated with a preliminary immunological evaluation performed by enzyme-linked immunospotting on the different variant proteins and their glycosylation products. After glycosylation, the two variant proteins with an arginine in position 30 completely retain the original T-cell activity, thus representing adequate antigenic carriers for the development of efficient glycoconjugate vaccines against tuberculosis.

Cyclipostins and cyclophostin analogs inhibit the antigen 85C from Mycobacterium tuberculosis both in vitro and in vivo

An increasing prevalence of cases of drug-resistant tuberculosis requires the development of more efficacious chemotherapies. We previously reported the discovery of a new class of cyclipostins and cyclophostin (CyC) analogs exhibiting potent activity against Mycobacterium tuberculosis both in vitro and in infected macrophages. Competitive labeling/enrichment assays combined with MS have identified several serine or cysteine enzymes in lipid and cell wall metabolism as putative targets of these CyC compounds. These targets included members of the antigen 85 (Ag85) complex (i.e. Ag85A, Ag85B, and Ag85C), responsible for biosynthesis of trehalose dimycolate and mycolylation of arabinogalactan. Herein, we used biochemical and structural approaches to validate the Ag85 complex as a pharmacological target of the CyC analogs. We found that CyC_7β, CyC_8β, and CyC₁₇ bind covalently to the catalytic Ser¹²⁴ residue in Ag85C; inhibit mycolyltransferase activity (i.e. the transfer of a fatty acid molecule onto trehalose); and reduce triacylglycerol synthase activity, a property previously attributed to Ag85A. Supporting these results, an X-ray structure of Ag85C in complex with CyC_8β disclosed that this inhibitor occupies Ag85C's substrate-binding pocket. Importantly, metabolic labeling of M. tuberculosis cultures revealed that the CyC compounds impair both trehalose dimycolate synthesis and mycolylation of arabinogalactan. Overall, our study provides compelling evidence that CyC analogs can inhibit the activity of the Ag85 complex in vitro and in mycobacteria, opening the door to a new strategy for inhibiting Ag85. The high-resolution crystal structure obtained will further guide the rational optimization of new CyC scaffolds with greater specificity and potency against M. tuberculosis.

Efficacy Testing of H56 cDNA Tattoo Immunization against Tuberculosis in a Mouse Model

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a global threat. The only approved vaccine against TB, Mycobacterium bovis bacillus Calmette–Guérin (BCG), provides insufficient protection and, being a live vaccine, can cause disseminated disease in immunocompromised individuals. Previously, we found that intradermal cDNA tattoo immunization with cDNA of tetanus toxoid fragment C domain 1 fused to cDNA of the fusion protein H56, comprising the Mtb antigens Ag85B, ESAT-6, and Rv2660c, induced antigen-specific CD8⁺ T cell responses in vivo. As cDNA tattoo immunization would be safer than a live vaccine in immunocompromised patients, we tested the protective efficacy of intradermal tattoo immunization against TB with H56 cDNA, as well as with H56_E, a construct optimized for epitope processing in a mouse model. As Mtb antigens can be used in combination with BCG to boost immune responses, we also tested the protective efficacy of heterologous prime-boost, using dermal tattoo immunization with H56_E cDNA to boost BCG immunization in mice. Dermal H56 and H56_E cDNA immunization induced H56-specific CD4⁺ and CD8⁺ T cell responses and Ag85B-specific IgG antibodies, but did not reduce bacterial loads, although immunization with H56_E ameliorated lung pathology. Both subcutaneous and intradermal immunization with BCG resulted in broad cellular immune responses, with increased frequencies of CD4⁺ T effector memory cells, T follicular helper cells, and germinal center B cells, and resulted in reduced bacterial loads and lung pathology. Heterologous vaccination with BCG/H56_E cDNA induced increased H56-specific CD4⁺ and CD8⁺ T cell cytokine responses compared to vaccination with BCG alone, and lung pathology was significantly decreased in BCG/H56_E cDNA immunized mice compared to unvaccinated controls. However, bacterial loads were not decreased after heterologous vaccination compared to BCG alone. CD4⁺ T cells responding to Ag85B- and ESAT-6-derived epitopes were predominantly IFN-γ⁺TNF-α⁺ and TNF-α⁺IL-2⁺, respectively. In conclusion, despite inducing appreciable immune responses to Ag85B and ESAT-6, intradermal H56 cDNA tattoo immunization did not substantially enhance the protective effect of BCG under the conditions tested.

Recombinant Invasive Lactococcus lactis Carrying a DNA Vaccine Coding the Ag85A Antigen Increases INF-γ, IL-6, and TNF-α Cytokines after Intranasal Immunization

Tuberculosis (TB) remains a major threat throughout the world and in 2015 it caused the death of 1.4 million people. The Bacillus Calmette-Guérin is the only existing vaccine against this ancient disease; however, it does not provide complete protection in adults. New vaccines against TB are eminently a global priority. The use of bacteria as vehicles for delivery of vaccine plasmids is a promising vaccination strategy. In this study, we evaluated the use of, an engineered invasive Lactococcus lactis (expressing Fibronectin-Binding Protein A from Staphylococcus aureus) for the delivery of DNA plasmid to host cells, especially to the mucosal site as a new DNA vaccine against tuberculosis. One of the major antigens documented that offers protective responses against Mycobacterium tuberculosis is the Ag85A. L. lactis FnBPA⁺ (pValac:Ag85A) which was obtained and used for intranasal immunization of C57BL/6 mice and the immune response profile was evaluated. In this study we observed that this strain was able to produce significant increases in the amount of pro-inflammatory cytokines (IFN-γ, TNF-α, and IL-6) in the stimulated spleen cell supernatants, showing a systemic T helper 1 (Th1) cell response. Antibody production (IgG and sIgA anti-Ag85A) was also significantly increased in bronchoalveolar lavage, as well as in the serum of mice. In summary, these findings open new perspectives in the area of mucosal DNA vaccine, against specific pathogens using a Lactic Acid Bacteria such as L. lactis.

Strategies to enhance immunogenicity of cDNA vaccine encoded antigens by modulation of antigen processing

Most vaccines are based on protective humoral responses while for intracellular pathogens CD8(+) T cells are regularly needed to provide protection. However, poor processing efficiency of antigens is often a limiting factor in CD8(+) T cell priming, hampering vaccine efficacy. The multistage cDNA vaccine H56, encoding three secreted Mycobacterium tuberculosis antigens, was used to test a complete strategy to enhance vaccine' immunogenicity. Potential CD8(+) T cell epitopes in H56 were predicted using the NetMHC3.4/ANN program. Mice were immunized with H56 cDNA using dermal DNA tattoo immunization and epitope candidates were tested for recognition by responding CD8(+) T cells in ex vivo assays. Seven novel CD8(+) T cell epitopes were identified. H56 immunogenicity could be substantially enhanced by two strategies: (i) fusion of the H56 sequence to cDNA of proteins that modify intracellular antigen processing or provide CD4(+) T cell help, (ii) by substitution of the epitope's hydrophobic C-terminal flanking residues for polar glutamic acid, which facilitated their proteasome-mediated generation. We conclude that this whole strategy of in silico prediction of potential CD8(+) T cell epitopes in novel antigens, followed by fusion to sequences with immunogenicity-enhancing properties or modification of epitope flanking sequences to improve proteasome-mediated processing, may be exploited to design novel vaccines against emerging or 'hard to treat' intracellular pathogens.

CD4+ T-cell epitope prediction using antigen processing constraints

T-cell CD4+ epitopes are important targets of immunity against infectious diseases and cancer. State-of-the-art methods for MHC class II epitope prediction rely on supervised learning methods in which an implicit or explicit model of sequence specificity is constructed using a training set of peptides with experimentally tested MHC class II binding affinity. In this paper we present a novel method for CD4+ T-cell eptitope prediction based on modeling antigen-processing constraints. Previous work indicates that dominant CD4+ T-cell epitopes tend to occur adjacent to sites of initial proteolytic cleavage. Given an antigen with known three-dimensional structure, our algorithm first aggregates four types of conformational stability data in order to construct a profile of stability that allows us to identify regions of the protein that are most accessible to proteolysis. Using this profile, we then construct a profile of epitope likelihood based on the pattern of transitions from unstable to stable regions. We validate our method using 35 datasets of experimentally measured CD4+ T cell responses of mice bearing I-Ab or HLA-DR4 alleles as well as of human subjects. Overall, our results show that antigen processing constraints provide a significant source of predictive power. For epitope prediction in single-allele systems, our approach can be combined with sequence-based methods, or used in instances where little or no training data is available. In multiple-allele systems, sequence-based methods can only be used if the allele distribution of a population is known. In contrast, our approach does not make use of MHC binding prediction, and is thus agnostic to MHC class II genotypes.

Increased B and T Cell Responses in M. bovis Bacille Calmette-Guérin Vaccinated Pigs Co-Immunized with Plasmid DNA Encoding a Prototype Tuberculosis Antigen

The only tuberculosis vaccine currently available, bacille Calmette-Guérin (BCG) is a poor inducer of CD8(+) T cells, which are particularly important for the control of latent tuberculosis and protection against reactivation. As the induction of strong CD8(+) T cell responses is a hallmark of DNA vaccines, a combination of BCG with plasmid DNA encoding a prototype TB antigen (Ag85A) was tested. As an alternative animal model, pigs were primed with BCG mixed with empty vector or codon-optimized pAg85A by the intradermal route and boosted with plasmid delivered by intramuscular electroporation. Control pigs received unformulated BCG. The BCG-pAg85A combination stimulated robust and sustained Ag85A specific antibody, lymphoproliferative, IL-6, IL-10 and IFN-γ responses. IgG1/IgG2 antibody isotype ratio reflected the Th1 helper type biased response. T lymphocyte responses against purified protein derivative of tuberculin (PPD) were induced in all (BCG) vaccinated animals, but responses were much stronger in BCG-pAg85A vaccinated pigs. Finally, Ag85A-specific IFN-γ producing CD8(+) T cells were detected by intracellular cytokine staining and a synthetic peptide, spanning Ag85A131-150 and encompassing two regions with strong predicted SLA-1*0401/SLA-1*0801 binding affinity, was promiscuously recognized by 6/6 animals vaccinated with the BCG-pAg85A combination. Our study provides a proof of concept in a large mammalian species, for a new Th1 and CD8(+) targeting tuberculosis vaccine, based on BCG-plasmid DNA co-administration.

Novel human recombinant antibodies against Mycobacterium tuberculosis antigen 85B

Background

Tuberculosis is the leading cause of death due to bacterial infections worldwide, mainly caused by Mycobacterium tuberculosis. The antigen 85 complex comprises a set of major secreted proteins of M. tuberculosis, which are potential biomarkers for diagnostic.

Results

In this work, the first human single chain fragment variable (scFv) antibodies specific for the tuberculosis biomarker 85 B were selected by phage display from naïve antibody gene libraries (HAL7/8). Produced as scFv-Fc in mammalian cells, these antibodies were further characterized and analysed for specificity and applicability in different tuberculosis antigen detection assays. Sandwich detection of recombinant 85 B was successful in enzyme linked immunosorbent assay (ELISA), lateral flow immunoassay and immunoblot. Whereas detection of M. tuberculosis cell extracts and culture filtrates was only possible in direct ELISA and immunoblot assays. It was found that the conformation of 85 B, depending on sample treatment, influenced antigen detection.

Conclusions

Recombinant antibodies, selected by phage display, may be applicable for 85 B detection in various assays. These antibodies are candidates for the development of future point of care tuberculosis diagnostic kits. Using 85 B as a biomarker, the antigen conformation influenced by sample treatment is important.

The Immunodominant T-Cell Epitopes of the Mycolyl-Transferases of the Antigen 85 Complex of M. tuberculosis

The Ag85 complex is a 30–32 kDa family of three proteins (Ag85A, Ag85B, and Ag85C), which all three possess enzymatic mycolyl-transferase activity involved in the coupling of mycolic acids to the arabinogalactan of the cell wall and in the biogenesis of cord factor. By virtue of their strong potential to induce Th1-type immune responses, important for the control of intracellular infections, members of the Ag85 family rank among the most promising TB vaccine candidate antigens. Ag85A and Ag85B, initially purified from Mycobacterium bovis bacillus Calmette–Guérin (BCG)/Mycobacterium tuberculosis culture filtrate respectively, induce strong T-cell proliferation and IFN-γ production in most healthy individuals latently infected with M. tuberculosis and in BCG-vaccinated mice and humans but not in tuberculosis patients. Members of the Ag85 complex are highly conserved in other mycobacterial species. Mice and humans infected with Mycobacterium ulcerans or cattle infected with M. bovis or Mycobacterium avium subsp. paratuberculosis also show strong T-cell responses to this protein family. Using synthetic overlapping peptides, bio-informatic prediction programs and tetramer-binding studies, a number of immunodominant CD4⁺ and CD8⁺ T-cell epitopes have been identified in experimental animal models as well as in humans, using proliferation and Th1 cytokine secretion as main read-outs. The results from these studies are summarized in this review.

Analysis of the vaccine potential of plasmid DNA encoding nine mycolactone polyketide synthase domains in Mycobacterium ulcerans infected mice

There is no effective vaccine against Buruli ulcer. In experimental footpad infection of C57BL/6 mice with M. ulcerans, a prime-boost vaccination protocol using plasmid DNA encoding mycolyltransferase Ag85A of M. ulcerans and a homologous protein boost has shown significant, albeit transient protection, comparable to the one induced by M. bovis BCG. The mycolactone toxin is an obvious candidate for a vaccine, but by virtue of its chemical structure, this toxin is not immunogenic in itself. However, antibodies against some of the polyketide synthase domains involved in mycolactone synthesis, were found in Buruli ulcer patients and healthy controls from the same endemic region, suggesting that these domains are indeed immunogenic. Here we have analyzed the vaccine potential of nine polyketide synthase domains using a DNA prime/protein boost strategy. C57BL/6 mice were vaccinated against the following domains: acyl carrier protein 1, 2, and 3, acyltransferase (acetate) 1 and 2, acyltransferase (propionate), enoylreductase, ketoreductase A, and ketosynthase load module. As positive controls, mice were vaccinated with DNA encoding Ag85A or with M. bovis BCG. Strongest antigen specific antibodies could be detected in response to acyltransferase (propionate) and enoylreductase. Antigen-specific Th1 type cytokine responses (IL-2 or IFN-γ) were induced by vaccination against all antigens, and were strongest against acyltransferase (propionate). Finally, vaccination against acyltransferase (propionate) and enoylreductase conferred some protection against challenge with virulent M. ulcerans 1615. However, protection was weaker than the one conferred by vaccination with Ag85A or M. bovis BCG. Combinations of these polyketide synthase domains with the vaccine targeting Ag85A, of which the latter is involved in the integrity of the cell wall of the pathogen, and/or with live attenuated M. bovis BCG or mycolactone negative M. ulcerans may eventually lead to the development of an efficacious BU vaccine.

Identification of T cell epitopes of Mycobacterium tuberculosis with biolistic DNA vaccination

Tuberculosis (TB) has been listed as one of the most prevalent and serious infectious diseases worldwide. The etiological pathogen of TB is Mycobacterium tuberculosis (Mtb), a facultative intracellular bacterium. Mycobacterium bovis bacillus Calmette-Guérin (BCG) is the only approved vaccine against TB to date. BCG has been widely used, but the efficacy is questionable, especially in adult pulmonary TB. Therefore, more effective, safe and reliable TB vaccines have been urgently needed. T cell-mediated cellular immune response is a key immune response for effective protective immunity against TB. DNA vaccines using Mtb antigens have been studied as promising future TB vaccines. Most TB DNA vaccine studies so far reported used intramuscular or intradermal injection with needles, as these methods tend to induce a type 1 helper T lymphocyte (Th1)-type immune response that is critical for the protective immunity. We have been using DNA vaccines with gene gun bombardment for T cell epitope identification of various Mtb antigens. We show here our strategy to identify precise Mtb T cell epitopes using DNA vaccines with gene gun bombardment.

Intravital imaging reveals limited antigen presentation and T cell effector function in mycobacterial granulomas

Cell-mediated adaptive immunity is critical for host defense, but little is known about T cell behavior during delivery of effector function. Here we investigate relationships among antigen presentation, T cell motility, and local production of effector cytokines by CD4+ T cells within hepatic granulomas triggered by Bacille Calmette-Guérin or Mycobacterium tuberculosis. At steady-state, only small fractions of mycobacteria-specific T cells showed antigen-induced migration arrest within granulomas, resulting in low-level, polarized secretion of cytokines. However, exogenous antigen elicited rapid arrest and robust cytokine production by the vast majority of effector T cells. These findings suggest that limited antigen presentation and/or recognition within granulomas evoke a muted T cell response drawing on only a fraction of the host's potential effector capacity. Our results provide new insights into the regulation of host-protective functions, especially how antigen availability influences T cell dynamics and, in turn, effector T cell function during chronic infection.

Pathological role of interleukin 17 in mice subjected to repeated BCG vaccination after infection with Mycobacterium tuberculosis

Infection usually leads to the development of acquired immune responses associated with clearance or control of the infecting organism. However, if not adequately regulated, immune-mediated pathology can result. Tuberculosis is a worldwide threat, and development of an effective vaccine requires that the protective immune response to Mycobacterium tuberculosis (Mtb) be dissected from the pathological immune response. This distinction is particularly important if new vaccines are to be delivered to Mtb-exposed individuals, as repeated antigenic exposure can lead to pathological complications. Using a model wherein mice are vaccinated with bacille Calmette-Guérin after Mtb infection, we show that repeated vaccination results in increased IL-17, tumor necrosis factor, IL-6, and MIP-2 expression, influx of granulocytes/neutrophils, and lung tissue damage. This pathological response is abrogated in mice deficient in the gene encoding IL-23p19 or in the presence of IL-17–blocking antibody. This finding that repeated exposure to mycobacterial antigen promotes enhanced IL-17–dependent pathological consequences has important implications for the design of effective vaccines against Mtb.

Immunization of mice with a recombinant adenovirus vaccine inhibits the early growth of Mycobacterium tuberculosis after infection

Background

In pulmonary Mycobacterium tuberculosis (Mtb) infection, immune responses are delayed compared to other respiratory infections, so that antigen-specific cells are not detected in the lungs earlier than day 14. Even after parenteral immunization with Bacille Calmette Guerin (BCG) or a subunit vaccine, the immune response after Mtb challenge is only slightly accelerated and the kinetics of pulmonary Mtb growth do not differ between naïve and immunized animals up to day 14.

Methods and Findings

Mice were immunized intranasally with a recombinant adenovirus expressing mycobacterial antigen 85A (Ad85A), challenged by aerosol with Mtb and the kinetics of Mtb growth in the lungs measured. Intranasal immunization with Ad85A inhibits Mtb growth in the early phase of infection, up to day 8. Protection is sustained for at least 7 months and correlates with the presence of antigen-specific activated effector CD8 T cells in the lungs. Antigen 85A-specific T cells respond to antigen presenting cells from the lungs of mice immunized with Ad85A 23 weeks previously, demonstrating the persistence of antigen in the lungs.

Conclusions/Significance

Intranasal immunization with Ad85A can inhibit early growth of Mtb because it establishes a lung antigen depot and maintains an activated lung-resident lymphocyte population. We propose that an optimal immunization strategy for tuberculosis should aim to induce both lung and systemic immunity, targeting the early and late phases of Mtb growth.

Prime-Boost Immunization of Codon Optimized HIV-1 CRF01_AE Gag in BCG with Recombinant Vaccinia Virus Elicits MHC Class I and II Immune Responses in Mice

The HIV-1 CRF01_AE gag gene was modified by codon restriction for Mycobacterium spp. and transformed into BCG; and it was designated as rBCG/codon optimized gagE. This produced 11 fold higher HIV-1 gag protein expression than the recombinant native gene rBCG/HIV-1gagE. In mice, CTL activity could be induced either by a single immunization of the codon optimized construct or by using it as a priming antigen in the prime-boost modality with recombinant Vaccinia virus expressing native HIV-1 gag. Specific secreted cytokine responses were also investigated. Only when rBCG gag was codon optimized did the prime-boost immunization produce significantly enhanced IFN-γ and IL-2 secretion indicating recognition via CD4+ and CD8+ T cells, and these responses seemed to be codon optimized immunogen dose-responsive. On contrary, the prime-boost vaccination using an equal amount of native rBCG/HIV-1gagE instead, or a single rBCG/codon optimized gagE immunization, had no similar effect on the cytokine secretion. These findings suggest that the use of recombinant codon BCG construct with recombinant Vaccinia virus encoding CRF01_AE gag as the prime-boost HIV vaccine candidate, will induce CD4+ Th1 and CD8+ T cell cytokine secretions in addition to enhancing CD8+ CTL response.

Resistance to mycobacterial infection: a pattern of early immune responses leads to a better control of pulmonary infection in C57BL/6 compared with BALB/c mice

In this study, we have compared the immunological responses associated with early pulmonary mycobacterial infection in two mouse strains, BALB/c and C57BL/6 known to exhibit distinct differences in susceptibility to infection with several pathogens. We infected mice via the intranasal route. We have demonstrated that BALB/c was less able to control mycobacterial growth in the lungs during the early phase of pulmonary infection. Our results showed that during the early phase (day 3 to week 1), BALB/c mice exhibited a delay in the production of TNF and IFN-gamma in the lungs compared to C57BL/6 mice. Levels of IL-12 and soluble TNF receptors (sTNFR) were comparable between the mouse strains. The cellular subset distribution in these mice before and after infection showed a higher increase in CD11b+ cells in the lungs of C57BL/6, compared to BALB/c as early as day 3 postinfection. At early time points, higher levels of monocyte chemoattractant protein (MCP)-1 and macrophage inflammatory protein 1 (MIP)-alpha were detected in C57BL/6 than BALB/c mice. In vitro, BCG-infected bone marrow derived macrophages (BMM) from both mouse strains displayed similar capacities to either phagocytose bacteria or produce soluble mediators such as TNF, IL-12 and nitric oxide (NO). Although IFN-gamma stimulation of infected BMM in both mouse strains resulted in the induction of antimycobacterial activity, BALB/c mice had a reduced capacity to kill ingested bacteria. The above observations indicate that the chain of early, possibly innate immunological events occurring during pulmonary mycobacterial infection may directly impact on increased susceptibility or resistance to infection.

Cutinase-like proteins of Mycobacterium tuberculosis: characterization of their variable enzymatic functions and active site identification

Discovery and characterization of novel secreted enzymes of Mycobacterium tuberculosis are important for understanding the pathogenesis of one of the most important human bacterial pathogens. The proteome of M. tuberculosis contains over 400 potentially secreted proteins, the majority of which are uncharacterized. A family of seven cutinase-like proteins (CULPs) was identified by bioinformatic analysis, expressed and purified from Escherichia coli, and characterized in terms of their enzymatic activities. These studies revealed a functional diversity of enzyme classes based on differential preferences for substrate chain length. One member, Culp1, exhibited strong esterase activity, 40-fold higher than that of Culp6, which had strong activity as a lipase. Another, Culp4, performed moderately as an esterase and weakly as a lipase. Culp6 lipase activity was optimal above pH 7.0, and fully maintained to pH 8.5. None of the CULP members exhibited cutinase activity. Site-directed mutagenesis of each residue of the putative catalytic triad in Culp6 confirmed that each was essential for activity toward all fatty acid chain lengths of nitrophenyl esters and lipolytic function. Culp1 and Culp2 were present only in culture supernatants of M. tuberculosis, while Culp6, which is putatively essential for mycobacterial growth, was retained in the cell wall, suggesting the proteins play distinct roles in mycobacterial biology.

Immunogenicity and protective efficacy of prime-boost regimens with recombinant (delta)ureC hly+ Mycobacterium bovis BCG and modified vaccinia virus ankara expressing M. tuberculosis antigen 85A against murine tuberculosis

In the light of the recent emergence of multidrug-resistant and extensively drug-resistant strains of Mycobacterium tuberculosis, the epidemic of tuberculosis (TB) in populations coinfected with human immunodeficiency virus, and the failure of Mycobacterium bovis bacillus Calmette-Guerin (BCG) to protect against disease, new vaccines against TB are urgently needed. Two promising new vaccine candidates are the recombinant DeltaureC hly(+) BCG (recBCG), which has been developed to replace the current BCG vaccine strain, and modified vaccinia virus Ankara (MVA) expressing M. tuberculosis antigen 85A (MVA85A), which is a leading candidate vaccine designed to boost the protective efficacy of BCG. In the present study, we examined the effect of MVA85A boosting on the protection afforded at 12 weeks postchallenge by BCG and recBCG by using bacterial CFU as an efficacy readout. recBCG-immunized mice were significantly better protected against aerosol challenge with M. tuberculosis than mice immunized with the parental strain of BCG. Intradermal boosting with MVA85A did not reduce the bacterial burden any further. In order to identify a marker for the development of a protective immune response against M. tuberculosis challenge, we analyzed splenocytes after priming or prime-boosting by using intracytoplasmic cytokine staining and assays for cytokine secretion. Boosting with MVA85A, but not priming with BCG or recBCG, greatly increased the antigen 85A-specific T-cell response, suggesting that the mechanism of protection may differ from that against BCG or recBCG. We show that the numbers of systemic multifunctional cytokine-producing cells did not correlate with protection against aerosol challenge in BALB/c mice. This emphasizes the need for new biomarkers for the evaluation of TB vaccine efficacy.

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.

Genetic toggling of alkaline phosphatase folding reveals signal peptides for all major modes of transport across the inner membrane of bacteria

Prediction of export pathway specificity in prokaryotes is a challenging endeavor due to the similar overall architecture of N-terminal signal peptides for the Sec-, SRP- (signal recognition particle), and Tat (twin arginine translocation)-dependent pathways. Thus, we sought to create a facile experimental strategy for unbiased discovery of pathway specificity conferred by N-terminal signals. Using a limited collection of Escherichia coli strains that allow protein oxidation in the cytoplasm or, conversely, disable protein oxidation in the periplasm, we were able to discriminate the specific mode of export for PhoA (alkaline phosphatase) fusions to signal peptides for all of the major modes of transport across the inner membrane (Sec, SRP, or Tat). Based on these findings, we developed a mini-Tn5 phoA approach to isolate pathway-specific export signals from libraries of random fusions between exported proteins and the phoA gene. Interestingly, we observed that reduced PhoA was exported in a Tat-independent manner when targeted for Tat export in the absence of the essential translocon component TatC. This suggests that initial docking to TatC serves as a key specificity determinant for Tat-specific routing of PhoA, and in its absence, substrates can be rerouted to the Sec pathway, provided they remain compatible with the Sec export mechanism. Finally, the utility of our approach was demonstrated by experimental verification that four secreted proteins from Mycobacterium tuberculosis carrying putative Tat signals are bona fide Tat substrates and thus represent potential Tat-dependent virulence factors in this important human pathogen.

Effect of attenuation of Treg during BCG immunization on anti-mycobacterial Th1 responses and protection against Mycobacterium tuberculosis

BACKGROUND

The functional equilibrium between natural regulatory T cells (Treg) and effector T cells can affect the issue of numerous infections. In unvaccinated mice, the influence of Treg in the control of primary infection with mycobacteria remains controversial.

METHODOLOGY

Here, we evaluated the role of Treg during prophylactic vaccination with Mycobacterium bovis BCG (Bacillus Calmette-Guérin) on the induction of T cell responses and on the protective effect against subsequent M. tuberculosis challenge in mice.

PRINCIPAL FINDINGS

We demonstrated that, subsequent to BCG injection, Treg were recruited to the draining lymph nodes and negatively control anti-mycobacterial CD4(+)--but not CD8(+)--T-cell responses. Treatment of BCG-immunized mice with an anti-CD25 mAb (PC61) induced an increase IFN-gamma response against both subdominant and immunodominant regions of the protective immunogen TB10.4. In Treg-attenuated, BCG-immunized mice, which were then infected with M. tuberculosis, the lung mycobacterial load was significantly, albeit moderately, reduced compared to the control mice.

CONCLUSIONS

Our results provide the first demonstration that attenuation of Treg subset concomitant to BCG vaccination has a positive, yet limited, impact on the protective capacity of this vaccine against infection with M. tuberculosis. Thus, for rational design of improved BCG, it should be considered that, although the action of Treg does not represent the major cause of the limited efficiency of BCG, the impact of this cell population on the subsequent control of M. tuberculosis growth is significant and measurable.

Improved protective efficacy of a species-specific DNA vaccine encoding mycolyl-transferase Ag85A from Mycobacterium ulcerans by homologous protein boosting

Vaccination with plasmid DNA encoding Ag85A from M. bovis BCG can partially protect C57BL/6 mice against a subsequent footpad challenge with M. ulcerans. Unfortunately, this cross-reactive protection is insufficient to completely control the infection. Although genes encoding Ag85A from M. bovis BCG (identical to genes from M. tuberculosis) and from M. ulcerans are highly conserved, minor sequence differences exist, and use of the specific gene of M. ulcerans could possibly result in a more potent vaccine. Here we report on a comparison of immunogenicity and protective efficacy in C57BL/6 mice of Ag85A from M. tuberculosis and M. ulcerans, administered as a plasmid DNA vaccine, as a recombinant protein vaccine in adjuvant or as a combined DNA prime-protein boost vaccine. All three vaccination formulations induced cross-reactive humoral and cell-mediated immune responses, although species-specific Th1 type T cell epitopes could be identified in both the NH₂-terminal region and the COOH-terminal region of the antigens. This partial species-specificity was reflected in a higher—albeit not sustained—protective efficacy of the M. ulcerans than of the M. tuberculosis vaccine, particularly when administered using the DNA prime-protein boost protocol.

Buruli ulcer (BU) is an infectious disease characterized by deep, ulcerating skin lesions, particularly on arms and legs, that are provoked by a toxin. BU is caused by a microbe belonging to the same family that also causes tuberculosis and leprosy. The disease is emerging as a serious health problem, especially in West Africa. Vaccines are considered to be the most cost-effective strategy to control and eventually eradicate an infectious disease. For the moment, however, there is no good vaccine against BU, and it is still not fully understood which immune defence mechanisms are needed to control the infection. The identification of microbial components that are involved in the immune control is an essential step in the development of an effective vaccine. In this paper, we describe the identification of one of these microbial components, i.e., antigen 85A, a protein involved in the integrity of the cell wall of the microbe. Our findings obtained in a mouse model now need to be extended to other experimental animals and later to humans. Combination with a vaccine targeting the toxin may be a way to strengthen the effectiveness of the vaccine.

Inhibition of phagosome maturation by mycobacteria does not interfere with presentation of mycobacterial antigens by MHC molecules

Pathogenic mycobacteria escape host innate immune responses by surviving within phagosomes of host macrophages and blocking their delivery to lysosomes. Avoiding lysosomal delivery may also be involved in the capacity of living mycobacteria to modulate MHC class I- or II-dependent T cell responses, which may contribute to their pathogenicity in vivo. In this study, we show that the presentation of mycobacterial Ags is independent of the site of intracellular residence inside professional APCs. Infection of mouse macrophages or dendritic cells in vitro with mycobacterial mutants that are unable to escape lysosomal transfer resulted in an identical efficiency of Ag presentation compared with wild-type mycobacteria. Moreover, in vivo, such mutants induced CD4(+) Th1 or CD8(+) CTL responses in mice against various mycobacterial Ags that were comparable to those induced by their wild-type counterparts. These results suggest that the limiting factor for the generation of an adaptive immune response against mycobacteria is not the degree of lysosomal delivery. These findings are important in the rational design of improved vaccines to combat mycobacterial diseases.

Variation in the Immuno-pathological Responses of Lambs after Experimental Infection with Different Strains of Mycobacterium avium subsp. paratuberculosis

Ruminant infection by Mycobacterium avium subsp. paratuberculosis (MAP) causes a granulomatous inflammatory response in the intestine and associated lymph nodes. Differences either in the affected organs or in the inflammatory infiltrate were observed between species and individuals. Such differences are usually attributed to variations in host immune responses or to inconsistent effects among different MAP strains. To evaluate if different MAP strains induce different immuno-pathological responses in lambs, 28 one-month-old individuals were divided into six groups and inoculated with different MAP strains. Groups 1 and 2 were inoculated with two bovine strains isolated in Argentina that showed different genetic patterns after BstEII-IS900-RFLP (hereafter strains E and A respectively). Group 3 was inoculated with a bovine strain isolated in Spain obtained after a previous step of culture (patterns C1). Group 4 was inoculated with a homogenate of intestinal mucosa of a clinical case affected by the same bovine strain as that of group 3. Group 5 was inoculated with an ovine strain that was directly purified from the intestinal mucosa of a clinical case, and group 6 was kept as control (i.e. no inoculation). Peripheral immune responses were assessed until 150 days post-infection (dpi), when lambs were humanely killed. Pathological studies were performed in tissues from the intestine and lymph nodes. Lesion types and inflammatory infiltrates were examined as indicators of pathogenicity. All the lambs infected with bovine MAP strains showed a common lesion pattern regardless of the strain type. Such pattern was characterized by focal lesions mainly in the mesenteric lymph nodes, the presence of fibrous tissue, and, occasionally, necrosis in the granulomas as well as the presence of numerous giant cells. Differences in lesion severity were observed among groups: lambs from groups 1 and 2 had the highest number of granulomas and the largest lymph node area affected. Lesions in animals from group 5 (infected with an ovine strain) were more severe and occurred mostly in the intestinal lymphoid tissue; necrosis, fibrosis or giant cells were never detected in this group. These results indicate that the MAP strain type induces different pathological responses in lambs.

Mucosal prime-boost vaccination for tuberculosis based on TLR triggering OprI lipoprotein from Pseudomonas aeruginosa fused to mycolyl-transferase Ag85A

Toll-like receptor (TLR) triggering is an important step in the induction of T helper (Th) type 1 T cells which are key players in protection against the intracellular pathogen Mycobacterium (M.) tuberculosis. Here we report on the construction of a fusion protein consisting of a tuberculosis vaccine candidate mycolyl-transferase antigen 85A (Ag85A, Rv3804c) coupled to the outer membrane lipoprotein I (OprI) from Pseudomonas (P.) aeruginosa, a documented TLR2/TLR4 trigger. Subcutaneous boosting with this fusion protein in the absence of adjuvant increased significantly the Ag85A-specific humoral but not cellular immune responses of Ag85A-DNA vaccinated mice. Intranasal priming of C57BL/6 mice with live, attenuated Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccine, followed by intranasal boosting with OprI-Ag85A increased systemic and local antigen-specific interferon (IFN)-gamma and interleukin (IL)-2 responses in spleen, draining cervical and mediastinal lymph nodes and particularly in lung tissue, as compared to responses in mice only vaccinated with BCG vaccine. Despite enhanced immune responses, boosting with OprI-Ag85A did not increase protective efficacy against M. tuberculosis of either plasmid DNA or BCG vaccine in this experimental setting.

Cutting edge: IFN-gamma regulates the induction and expansion of IL-17-producing CD4 T cells during mycobacterial infection

T cell responses are important to the control of infection but are deleterious if not regulated. IFN-gamma-deficient mice infected with mycobacteria exhibit enhanced accumulation of activated effector T cells and neutrophils within granulomatous lesions. These cells do not control bacterial growth and compromise the integrity of the infected tissue. We show that IFN-gamma-deficient mice have increased numbers of IL-17-producing T cells following infection with Mycobacterium bovis bacille Calmette Guérin. Furthermore, exogenous IFN-gamma increases IL-12 and decreases IL-23 production by bacille Calmette Guérin-infected bone marrow-derived dendritic cells and reduces the frequency of IL-17-producing T cells induced by these bone marrow-derived dendritic cells. These data support the hypothesis that, during mycobacterial infection, both IFN-gamma- and IL-17-producing T cells are induced, but that IFN-gamma serves to limit the IL-17-producing T cell population. This counterregulation pathway may be an important factor in limiting mycobacterially associated immune-mediated pathology.

Immunogenicity and protective efficacy of tuberculosis DNA vaccines combining mycolyl-transferase Ag85A and phosphate transport receptor PstS-3

DNA vaccines encoding the 32,000 MW mycolyl-transferase Ag85A and the 40,000 MW phosphate-binding protein PstS-3 can elicit protective immune responses against experimental infection with Mycobacterium tuberculosis in C57BL/6 mice. Here we have analysed the vaccine potential of a combination of both antigens using plasmid vectors expressing either a fusion protein of both antigens or the separate proteins driven by two independent promoters (in pBudCE4.1 vector). Comparable levels of Ag85A specific T helper 1 (Th1) type immune responses could be induced by the two combination vaccines and the single vaccine encoding the mycolyl-transferase, whereas induction of PstS-3 specific Th1-mediated responses was impaired in both combination vaccines. In contrast, magnitude of CD8+ mediated responses against the PstS-3 protein was comparable following combination or single DNA vaccination. Antigenic competition was also observed at the antibody level; PstS-3 specific levels being lower in mice vaccinated with the fusion vector and Ag85A specific levels being lower in mice vaccinated with the combination pBudCE4.1 vector (as compared to levels obtained following single plasmid immunization). Protection against M. tuberculosis was only modestly improved in mice vaccinated with the DNA combinations. It is possible that prior activation of Ag85A specific CD4+ T cells directed against this common mycobacterial antigen leads to cross-competition for major histocompatibility complex class II-restricted peptide complexes of the Pst-3 antigen. This may have implications for future combination vaccines using Ag85.

High frequency of CD4+ T cells specific for the TB10.4 protein correlates with protection against Mycobacterium tuberculosis infection

TB10.4 is a newly identified antigen of Mycobacterium tuberculosis recognized by human and murine T cells upon mycobacterial infection. Here, we show that immunization with Mycobacterium bovis BCG induces a strong, genetically controlled, Th1 immune response against TB10.4 in mice. BALB/c and C57BL/6 strains behave as high and low responders to TB10.4 protein, respectively. The TB10.4:74-88 peptide was identified as an immunodominant CD4+ T-cell epitope for H-2d mice. Since recent results, as well as the present study, have raised interest in TB10.4 as a subunit vaccine, we analyzed immune responses induced by this antigen delivered by a new vector, the adenylate cyclase (CyaA) of Bordetella pertussis. CyaA is able to target dendritic cells and to deliver CD4+ or CD8+ T-cell epitopes to the major histocompatibility complex class II/I molecule presentation pathways, triggering specific Th1 or cytotoxic T-lymphocyte (CTL) responses. Several CyaA harboring either the entire TB10.4 protein or various subfragments containing the TB10.4:20-28 CTL epitope were shown to induce TB10.4-specific Th1 CD4+ and CD8+ T-cell responses. However, none of the recombinant CyaA, injected in the absence of adjuvant, was able to induce protection against M. tuberculosis infection. In contrast, TB10.4 protein administered with a cocktail of strong adjuvants that triggered a strong Th1 CD4+ T-cell response induced significant protection against M. tuberculosis challenge. These results confirm the potential value of the TB10.4 protein as a candidate vaccine and show that the presence of high frequencies of CD4+ T cells specific to this strong immunogen correlates with protection against M. tuberculosis infection.

An increase in antimycobacterial Th1-cell responses by prime-boost protocols of immunization does not enhance protection against tuberculosis

Bordetella pertussis adenylate cyclase (CyaA) toxoid is a powerful nonreplicative immunization vector targeting dendritic cells, which has already been used successfully in prophylactic and therapeutic vaccination in various preclinical animal models. Here, we investigated the potential of CyaA, harboring strong mycobacterial immunogens, i.e., the immunodominant regions of antigen 85A or the complete sequence of the 6-kDa early secreted antigenic target (ESAT-6) protein, to induce antimycobacterial immunity. By generating T-cell hybridomas or by using T cells from mice infected with mycobacteria, we first demonstrated that the in vitro delivery of 85A or ESAT-6 to antigen-presenting cells by CyaA leads to processing and presentation, by major histocompatibility complex class II molecules, of the same epitopes as those displayed upon mycobacterial infection. Importantly, compared to the recombinant protein alone, the presentation of ESAT-6 in vitro was 100 times more efficient upon its delivery to antigen-presenting cells in fusion to CyaA. Immunization with CyaA-85A or CyaA-ESAT-6 in the absence of any adjuvant induced strong antigen-specific lymphoproliferative, interleukin-2 (IL-2) and gamma interferon (IFN-gamma) cytokine responses, in the absence of any IL-4 or IL-5 production. When used as boosters after priming with a BCG expressing ESAT-6, the CyaA-85A and CyaA-ESAT-6 proteins were able to strikingly increase the sensitivity and intensity of proliferative and Th1-polarized responses and notably the frequency of antigen-specific IFN-gamma-producing CD4+ T cells. However, immunization with these CyaA constructs as subunit vaccines alone or as boosters did not allow induction or improvement of protection against Mycobacterium tuberculosis infection. These results question the broadly admitted correlation between the frequency of IFN-gamma-producing CD4+ T cells and the level of protection against tuberculosis.

Members of the 30- to 32-kilodalton mycolyl transferase family (Ag85) from culture filtrate of Mycobacterium avium subsp. paratuberculosis are immunodominant Th1-type antigens recognized early upon infection in mice and cattle

The characterization of protective antigens is essential for the development of an effective, subunit-based vaccine against paratuberculosis. Surface-exposed and secreted antigens, present abundantly in mycobacterial culture filtrate (CF), are among the well-known protective antigens of Mycobacterium tuberculosis and Mycobacterium bovis. Culture filtrate, prepared from Mycobacterium avium subsp. paratuberculosis ATCC 19698 grown as a surface pellicle on synthetic Sauton medium, was strongly and early recognized in experimentally infected B6 bg/bg beige mice and cattle, as indicated by elevated spleen cell gamma interferon (IFN-gamma) secretion and lymphoproliferative responses of peripheral blood mononuclear cells, respectively. Strong proliferative and ex vivo IFN-gamma responses against antigen 85 (Ag85) complex (a major protein component from M. bovis BCG culture filtrate) could be detected in cattle as early as 10 weeks after oral M. avium subsp. paratuberculosis infection. Synthetic peptides from the Ag85A and Ag85B components of this complex were strongly recognized, whereas T-cell responses were weaker against peptides from the Ag85C protein. A promiscuous T-cell epitope spanning amino acids 145 to 162 of Ag85B (identical sequence in M. bovis and M. avium subsp. paratuberculosis) was identified in experimentally infected cattle. Finally, young calves, born from cows with confirmed paratuberculosis, demonstrated proliferative responses to purified, recombinant Ag85A and Ag85B from M. avium subsp. paratuberculosis. These results indicate that the M. avium subsp. paratuberculosis Ag85 homologues are immunodominant T-cell antigens that are recognized early in experimental and natural infection of cattle.

Improved Humoral Immunity Against Tuberculosis ESAT-6 Antigen by Chimeric DNA Prime and Protein Boost Strategy

Ag85A and ESAT-6 proteins of Mycobacterium tuberculosis (M.TB) are important protective antigens. The 32-kDa Ag85A is a strong immunogen in both small and large animals. However, the 6-kDa ESAT-6 has relatively low inherent immunogenicity, especially in large animals. To improve the immunogenicity of ESAT-6 in animals, we made chimeric DNA vaccines, HG856K and HG856A, by inserting the esat-6 gene into the Kpn I or Acc I endonuclease restriction site of the ag85a gene, respectively. BALB/c mice were injected intramuscularly three times with the 10-microg singular DNA vaccine (HG85 encoding for Ag85A or HG6 encoding for ESAT-6) or chimeric DNA vaccine (HG856K or HG856A) followed by electroporation (EP). Ten days after the last DNA vaccination, mice received a booster immunization intraperitoneally with 50-microg pure recombinant protein Ag85A or ESAT-6 without adjuvant. Additional groups of mice immunized with chimeric DNA vaccines were boosted with two mixed proteins (Ag85A/ESAT-6) at the same time. The results showed that the immunogenicity of M.TB ESAT-6 antigen was not improved by priming with the HG6 DNA vaccine. However, the humoral immunity against the ESAT-6 antigen was significantly increased in the mice primed with chimeric DNA vaccines, HG856K or HG856A, followed by boosting with ESAT-6 or ESAT-6/Ag85A mixed proteins.

Protective immunity against Mycobacterium bovis induced by vaccination with Rv3109c--a member of the esat-6 gene family

In a number of clinical studies the current TB vaccine, Mycobacterium bovis bacille Calmette-Guerin (BCG), has provided little or no protection against pulmonary tuberculosis in cattle and man. A new generation of vaccines is therefore required to replace or supplement BCG. Safety concerns surrounding a number of strategies make protein subunits an attractive approach. Moreover, novel prime-boost strategies based on primary immunisations with BCG are not only showing promise but also present a clear strategy for testing new TB vaccines in clinical studies. We report the evaluation of six protein vaccine candidates for their ability to induce protective immunity in a murine virulent M. bovis challenge model. One protein (Rv3019c) induced reproducibly significant protection in the spleen and lungs approaching that induced by BCG. Detailed analysis of antigen-specific T cell responses revealed that despite robust responses in the spleen and lungs of vaccinated mice, there was no correlation between these responses and the protective efficacy of the vaccine. Significantly, Rv3019c also stimulated IFN-gamma responses in PBMC from BCG vaccinated cattle, indicating its potential for use in a heterologous prime-boost strategy in conjunction with BCG in the target species.

Immunogenicity of mycobacterial PPE44 (Rv2770c) in Mycobacterium bovis BCG-infected mice

The Pro-Pro-Glu (PPE) protein family of Mycobacterium tuberculosis includes 69 glycine-rich proteins with a conserved N-terminal domain. Their role in tuberculosis is unknown, but it has been speculated that they may have an important immunological significance. In this investigation, the immunogenicity of the ppe44 (Rv2770c) gene product in BALB/c mice infected subcutaneously or intravenously with Mycobacterium bovis bacille Calmette-Guerin (BCG) was evaluated. Mice infected subcutaneously developed high titres of anti-PPE44 IgG1 antibodies, while PPE44-specific IgG2a antibodies were absent at all times tested. PPE44-primed cells from draining lymph nodes and spleen produced low levels of IFN-gamma, and a moderate degree of delayed-type hypersensitivity was observed following PPE44 intracutaneous challenge. In mice infected intravenously, the anti-PPE44 IgG1 antibody response was markedly higher compared with the subcutaneous infection; anti-PPE44 IgG2a antibodies at titres approximately 0.5-2.0 log(10) lower than IgG1 were detected. Interferon (IFN)-gamma production in PPE44-stimulated spleen-cell cultures was transient. These results indicate that PPE44 represents a novel mycobacterial antigen expressed during subcutaneous and intravenous infection by M. bovis BCG in BALB/c mice. Both infection models seem to polarize the immune response to PPE44 towards a Th2 phenotype, as testified by the IgG1 isotype being predominant over IgG2a and by the low IFN-gamma and delayed-type hypersensitivity responses.

Influence of ESAT-6 Secretion System 1 (RD1) ofMycobacterium tuberculosison the Interaction between Mycobacteria and the Host Immune System

The chromosomal locus encoding the early secreted antigenic target, 6 kDa (ESAT-6) secretion system 1 of Mycobacterium tuberculosis, also referred to as "region of difference 1 (RD1)," is absent from Mycobacterium bovis bacillus Calmette-Guerin (BCG). In this study, using low-dose aerosol infection in mice, we demonstrate that BCG complemented with RD1 (BCG::RD1) displays markedly increased virulence which albeit does not attain that of M. tuberculosis H37Rv. Nevertheless, phenotypic and functional analyses of immune cells at the site of infection show that the capacity of BCG::RD1 to initiate recruitment/activation of immune cells is comparable to that of fully virulent H37Rv. Indeed, in contrast to the parental BCG, BCG::RD1 mimics H37Rv and induces substantial influx of activated (CD44highCD45RB(-)CD62L(-)) or effector (CD45RB(-)CD27(-)) T cells and of activated CD11c(+)CD11bhigh cells to the lungs of aerosol-infected mice. For the first time, using in vivo analysis of transcriptome of inflammatory cytokines and chemokines of lung interstitial CD11c+ cells, we show that in a low-dose aerosol infection model, BCG::RD1 triggered an activation/inflammation program comparable to that induced by H37Rv while parental BCG, due to its overattenuation, did not initiate the activation program in lung interstitial CD11c+ cells. Thus, products encoded by the ESAT-6 secretion system 1 of M. tuberculosis profoundly modify the interaction between mycobacteria and the host innate and adaptive immune system. These modifications can explain the previously described improved protective capacity of BCG::RD1 vaccine candidate against M. tuberculosis challenge.

Cell-mediated immune responses in children towards secreted proteins of Mycobacterium bovis BCG

BACKGROUND

There is a need to develop an improved anti-TB vaccine for adequate control and elimination of tuberculosis, to control the spread of MDR-TB and TB/HIV co-infection. Studies in children have indicated that BCG vaccination has certain beneficial effects, especially against miliary TB and TB meningitis, but needs to be improved for protection against pulmonary tuberculosis.

OBJECTIVE

The aim of the present study was to identify the immunogenic proteins in the culture filtrate (CF) of Mycobacterium bovis BCG by studying the effector mechanism of protection in children, which may help in the formulation of an effective vaccine against tuberculosis.

MATERIALS AND METHODS

Lymphoproliferative responses (LTT) and the levels of IL-2 and IFN-gamma (Th1 cytokines) released into the culture supernatants were estimated (by ELISA) in short-term cultures of PBMC of BCG vaccinated (n=25) and unvaccinated (n=15) children and children with tuberculosis (n=15) against 10 different fractions of CF (mol.wt > or = 90-<14 kDa).

RESULTS

The mean stimulation indices (SI) in LTT against all the (10) fractions in vaccinated children were high when compared to the unvaccinated and diseased groups; however, of the 10 fractions, F3, F4, F6, F8 and F9 elicited significantly higher SIs than the other fractions (p<0.05). In the vaccinated children, the SI (5.58+/-1.57), levels of IL-2 (381.66+/-16.40 pg/ml) and IFN-gamma (732+/-62.36 pg/ml) in the cultures stimulated by fraction 8 (34-30k Da) were significantly higher (p<0.001), than responses to the other fractions and also to those of other groups of children.

CONCLUSION

Thus, the peptides within the cluster 34-30 kDa appear to be promising vaccine candidates by virtue of their immunodominant nature specifically priming Th1 cells in normal, BCG-vaccinated children.

Induction of in vivo functional Db-restricted cytolytic T cell activity against a putative phosphate transport receptor of Mycobacterium tuberculosis

Using plasmid vaccination with DNA encoding the putative phosphate transport receptor PstS-3 from Mycobacterium tuberculosis and 36 overlapping 20-mer peptides spanning the entire PstS-3 sequence, we determined the immunodominant Th1-type CD4(+) T cell epitopes in C57BL/10 mice, as measured by spleen cell IL-2 and IFN-gamma production. Furthermore, a potent IFN-gamma-inducing, D(b)-restricted CD8(+) epitope was identified using MHC class I mutant B6.C-H-2(bm13) mice and intracellular IFN-gamma and whole blood CD8(+) T cell tetramer staining. Using adoptive transfer of CFSE-labeled, peptide-pulsed syngeneic spleen cells from naive animals into DNA vaccinated or M. tuberculosis-infected recipients, we demonstrated a functional in vivo CTL activity against this D(b)-restricted PstS-3 epitope. IFN-gamma ELISPOT responses to this epitope were also detected in tuberculosis-infected mice. The CD4(+) and CD8(+) T cell epitopes defined for PstS-3 were completely specific and not recognized in mice vaccinated with either PstS-1 or PstS-2 DNA. The H-2 haplotype exerted a strong influence on immune reactivity to the PstS-3 Ag, and mice of the H-2(b, p, and f) haplotype produced significant Ab and Th1-type cytokine levels, whereas mice of H-2(d, k, r, s, and q) haplotype were completely unreactive. Low responsiveness against PstS-3 in MHC class II mutant B6.C-H-2(bm12) mice could be overcome by DNA vaccination. IFN-gamma-producing CD8(+) T cells could also be detected against the D(b)-restricted epitope in H-2(p) haplotype mice. These results highlight the potential of DNA vaccination for the induction and characterization of CD4(+) and particularly CD8(+) T cell responses against mycobacterial Ags.

Identification of murine H2-Dd- and H2-Ab-restricted T-cell epitopes on a novel protective antigen, MPT51, of Mycobacterium tuberculosis

Both CD4(+) type 1 helper T (Th1) cells and CD8(+) cytotoxic T lymphocytes (CTL) play pivotal roles in protection against Mycobacterium tuberculosis infection. Here, we identified Th1 and CTL epitopes on a novel protective antigen, MPT51, in BALB/c and C57BL/6 mice. Mice were immunized with plasmid DNA encoding MPT51 by using a gene gun, and gamma interferon (IFN-gamma) production from the immune spleen cells was analyzed in response to a synthetic overlapping peptide library covering the mature MPT51 sequence. In BALB/c mice, only one peptide, p21-40, appeared to stimulate the immune splenocytes to produce IFN-gamma. Flow cytometric analysis with intracellular IFN-gamma and the T-cell phenotype revealed that the p21-40 peptide contains an immunodominant CD8(+) T-cell epitope. Further analysis with a computer-assisted algorithm permitted identification of a T-cell epitope, p24-32. In addition, a major histocompatibility complex class I stabilization assay with TAP2-deficient RMA-S cells transfected with K(d), D(d), or L(d) indicated that the epitope is presented by D(d). Finally, we proved that the p24-32/D(d) complex is recognized by IFN-gamma-producing CTL. In C57BL/6 mice, we observed H2-A(b)-restricted dominant and subdominant Th1 epitopes by using T-cell subset depletion analysis and three-color flow cytometry. The data obtained are useful for analyzing the role of MPT51-specific T cells in protective immunity and for designing a vaccine against M. tuberculosis infection.

Bacillus Calmette-Guérin-induced interleukin-12 did not additionally improve clinical and immunologic parameters in asthmatic children treated with sublingual immunotherapy

OBJECTIVE

To evaluate the effect of bacillus Calmette-Guérin (BCG) as an adjuvant to specific sublingual immunotherapy (SLIT) on the cytokine profile of peripheral blood mononuclear cells (PBMCs) and clinical outcome.

METHODS

Thirty-two children with asthma and rhinitis allergic to house dust mite (HDM) with negative purified protein derivative (PPD) skin test response were enrolled. After a run-in period of 8 weeks, patients were randomized to receive either SLIT only (n=16) or one dose of BCG immunization before initiation of SLIT (n=16) with a standardized Dermatophagoides pteronyssinus (D. pteronyssinus)+D. farinea 50/50 extract. PPD-negative asthmatics (n=5) allergic to HDM receiving inhaled therapy only were included for comparison of cytokine levels in PBMC cultures. Efficacy was assessed both at the end of run-in and 6 months of treatment periods with criteria including symptom, medication and quality-of-life (QoL) scores, IgE levels, lung function, provocation concentration (PC20), eosinophil count and skin prick tests. IL-4, IL-5, IL-10, IL-12, IL-13 and IFN-gamma levels were determined in antigen specifically and polyclonally stimulated PBMC cultures.

RESULTS

Both treatment groups showed significant improvement at the end of 6 months for asthma and rhinitis scores and QoL, number of asthma attacks, amount of beta2-agonists, inhaled and intranasal steroids, blood eosinophil counts and PC20. Interestingly, phytohaemagglutinin (PHA)-stimulated IL-12 and D. pteronyssinus-stimulated IFN-gamma in PBMC were significantly higher in the treatment groups than controls. In addition, IL-12 levels in response to D. pteronyssinus and PHA stimulation were significantly higher in the SLIT+BCG group than the SLIT alone group and controls.

CONCLUSION

The present study demonstrates that successful SLIT is parallel to increased IFN-gamma production by PBMC. Although simultaneous BCG vaccination enhanced IL-12 production, it did not additionally improve the clinical outcome.

A recombinant vaccine expressing a mammalian Mycobacterium sp. antigen is immunostimulatory but not protective in striped bass

A recombinant vaccine was constructed for piscine mycobacteriosis utilizing a Brucella abortus strain RB51 vector expressing a mammalian Mycobacterium sp. 85A antigen. Juvenile striped bass were inoculated with the resulting construct at doses equivalent to 10(6), 10(7), 10(8), 10(9), and 10(10) colony-forming units/fish. Blood and tissue samples from these fish demonstrated significant specific humoral and cell-mediated immune responses towards the 85A antigen in a dose-dependent manner. However, survival studies determined that inoculated fish failed to demonstrate cross-protective responses after live Mycobacterium marinum challenge 70 days post-inoculation.

The immunogenic peptide for Th1 development

Th1 cells play a critical role in the induction of cell-mediated immune responses and eradication of intracellular pathogen. The dose and route of immunization of antigen are also determining factors. It remains unclear what types of immunogenic peptide can induce the Th1 development and how it acts to regulate the immune system. Ag85B (also known as alpha antigen or MPT59) has been shown to be the most potent antigen species yet purified in humans and in mice. Strong Th1 responses have been elicited in vitro from PPD(+) asymptomatic individuals and Ag85B-primed cells of C57BL/6 (I-A(b)) mice. Peptide-25 (aa240-254) of Ag85B is a major Th1 cell epitope in I-A(b) mice. Active immunization of C57BL/6 mice with Peptide-25 can induce the development of CDT4(+) TCRVbeta11(+) and CDT4(+) TCRVbeta11(-)Th1 cells that produce IFN-gamma- and TNF-alpha, and protects against subsequent infection with live Mycobacterium tuberculosis H37Rv IFN-gamma. Peptide-25 has a potent adjuvant activity in both humoral and cell-mediated immune responses that is mediated by Th1 cells. We would propose to designate Peptide-25 as "Th1-inducing peptide".

Recombinant BCG exporting ESAT-6 confers enhanced protection against tuberculosis

The live tuberculosis vaccines Mycobacterium bovis BCG (bacille Calmette-Guérin) and Mycobacterium microti both lack the potent, secreted T-cell antigens ESAT-6 (6-kDa early secretory antigenic target) and CFP-10 (10-kDa culture filtrate protein). This is a result of independent deletions in the region of deletion-1 (RD1) locus, which is intact in virulent members of the Mycobacterium tuberculosis complex. To increase their immunogenicity and protective capacity, we complemented both vaccines with different constructs containing the esxA and esxB genes, which encode ESAT-6 and CFP-10 respectively, as well as a variable number of flanking genes. Only reintroduction of the complete locus, comprising at least 11 genes, led to full secretion of the antigens and resulted in specific ESAT-6-dependent immune responses; this suggests that the flanking genes encode a secretory apparatus. Mice and guinea pigs vaccinated with the recombinant strain BCG::RD1-2F9 were better protected against challenge with M. tuberculosis, showing less severe pathology and reduced dissemination of the pathogen, as compared with control animals immunized with BCG alone.

Mapping of murine Th1 helper T-Cell epitopes of mycolyl transferases Ag85A, Ag85B, and Ag85C from Mycobacterium tuberculosis

BALB/c (H-2(d)) and C57BL/6 (H-2(b)) mice were infected intravenously with Mycobacterium tuberculosis H37Rv or vaccinated intramuscularly with plasmid DNA encoding each of the three mycolyl transferases Ag85A, Ag85B, and Ag85C from M. tuberculosis. Th1-type spleen cell cytokine secretion of interleukin-2 (IL-2) and gamma interferon (IFN-gamma) was analyzed in response to purified Ag85 components and synthetic overlapping peptides covering the three mature sequences. Tuberculosis-infected C57BL/6 mice reacted strongly to some peptides from Ag85A and Ag85B but not from Ag85C, whereas tuberculosis-infected BALB/c mice reacted only to peptides from Ag85A. In contrast, spleen cells from both mouse strains produced elevated levels of IL-2 and IFN-gamma following vaccination with Ag85A, Ag85B, and Ag85C DNA in response to peptides of the three Ag85 proteins, and the epitope repertoire was broader than in infected mice. Despite pronounced sequence homology, a number of immunodominant regions contained component specific epitopes. Thus, BALB/c mice vaccinated with all three Ag85 genes reacted against the same amino acid region, 101 to 120, that was also immunodominant for Ag85A in M. bovis BCG-vaccinated and tuberculosis-infected H-2(d) haplotype mice, but responses were completely component specific. In C57BL/6 mice, a cross-reactive T-cell response was detected against two carboxy-terminal peptides spanning amino acids 241 to 260 and 261 to 280 of Ag85A and Ag85B. These regions were not recognized at all in C57BL/6 mice vaccinated with Ag85C DNA. Our results underline the need for comparative analysis of all three Ag85 components in future vaccination studies.

Temperature-induced changes in the cell-wall components of Mycobacterium thermoresistibile

The mycobacterial cell wall consists of a core composed of peptidoglycan linked to the heteropolysaccharide arabinogalactan, which in turn is attached to mycolic acids. A variety of free lipids complements the mycolyl residues, whereas phosphatidylinositol mannosides (PIMs), lipoarabinomannan and proteins are interspersed in this framework. As a consequence, the cell envelope is extremely rich in lipids and early work has shown that the lipid content may vary with environmental conditions. To extend these studies, the influence of growth temperature on cell envelope components in Mycobacterium thermoresistibile, a temperature-resistant mycobacterial species, was investigated. Mycolic acid synthesis was reduced at 55 degrees C compared to 37 degrees C and the production of fatty acids, presumably precursors of mycolic acids, was increased. Since fatty acids are elongated by the type II fatty acid synthase complex and consequently by a mycobacterial beta-ketoacyl acyl carrier protein synthase (KasA), leading to mycolic acids, the expression level of KasA was analysed by Western blotting. KasA expression was significantly decreased at 55 degrees C over 37 degrees C. Important changes in the mycolic acid composition were observed and characterized by reduced levels of cyclopropanation and the concomitant accumulation of the cis-olefin derivatives. In addition, striking differences involved in complex lipid composition, including acylated trehaloses and trehalose dimycolate (TDM) were also observed. At 55 degrees C, M. thermoresistibile produced less TDM than at 37 degrees C, which could be explained by the down-regulation of antigen 85 (Ag85) expression as shown by Western blotting. The Ag85 complex represents a family of proteins known to catalyse the transfer of mycolates to trehalose, thereby generating TDM. Furthermore, at 55 degrees C the level of phosphatidyl-inositol hexamannoside (PIM(6)) synthesis, but not that of other PIM species, was dramatically reduced. This observation could be correlated to a decrease of mannosyltransferase activity associated with membranes prepared from cells grown at 55 degrees C as compared to 37 degrees C. Altogether, this study suggests that mycobacteria are capable of inducing important cell-wall changes in response to temperature variations, which may represent a strategy developed by the bacteria to adapt to environmental changes.

The M. tuberculosis antigen 85 complex and mycolyltransferase activity

AIMS

The antigen 85 complex (Ag85) from Mycobacterium tuberculosis consists of three abundantly secreted proteins (FbpA, FbpB and FbpC2) which play a key role in the pathogenesis of tuberculosis and also exhibit cell wall mycolyltransferase activity. A related protein with similarity to the Ag85 complex was recently annotated in the M. tuberculosis genome as FbpC1. An investigation was carried out to determine whether FbpC1 may also possess mycolyltransferase activity, a characteristic feature of the Ag85 complex.

METHODS AND RESULTS

Heterologous expression of FbpA, FbpC1 and FbpC2 was performed in Escherichia coli. Recombinant proteins were purified under non-denaturating conditions and used in an in vitro mycolyltransferase assay.

CONCLUSIONS

In contrast to FbpA and FbpC2, recombinant FbpC1 did not possess in vitro mycolyltransferase activity and was not recognized by two monoclonal antibodies to the native Ag85.

SIGNIFICANCE AND IMPACT OF THE STUDY

Mycolyltransferase activity is restricted to FbpA, FbpbB and FbpC2 only; the actual function of FbpC1 remains to be established.