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 ΔureC 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.
The tuberculosis vaccine Mycobacterium bovis bacille Calmette-Guérin (BCG) was equipped with the membrane-perforating listeriolysin (Hly) of Listeria monocytogenes, which was shown to improve protection against Mycobacterium tuberculosis. Following aerosol challenge, the Hly-secreting recombinant BCG (hly+ rBCG) vaccine was shown to protect significantly better against aerosol infection with M. tuberculosis than did the parental BCG strain. The isogenic, urease C–deficient hly+ rBCG (ΔureC hly+ rBCG) vaccine, providing an intraphagosomal pH closer to the acidic pH optimum for Hly activity, exhibited still higher vaccine efficacy than parental BCG. ΔureC hly+ rBCG also induced profound protection against a member of the M. tuberculosis Beijing/W genotype family while parental BCG failed to do so consistently. Hly not only promoted antigen translocation into the cytoplasm but also apoptosis of infected macrophages. We concluded that superior vaccine efficacy of ΔureC hly+ rBCG as compared with parental BCG is primarily based on improved cross-priming, which causes enhanced T cell–mediated immunity.
The long-term control of tuberculosis (TB) will require the development of more effective anti-TB vaccines, as the only licensed vaccine, Mycobacterium bovis bacille Calmette-Guérin (BCG), has limited protective efficacy against infectious pulmonary TB. Subunit vaccines have an improved safety profile over live, attenuated vaccines, such as BCG, and may be used in immuno-compromised individuals. MPT83 (Rv2873) is a secreted mycobacterial lipoprotein expressed on the surface of Mycobacterium tuberculosis. In this study, we examined whether recombinant MPT83 is recognized during human and murine M. tuberculosis infection. We assessed the immunogenicity and protective efficacy of MPT83 as a protein vaccine, with monophosphyl lipid A (MPLA) in dimethyl-dioctadecyl ammonium bromide (DDA) as adjuvant, or as a DNA vaccine in C57BL/6 mice and mapped the T cell epitopes with peptide scanning. We demonstrated that rMPT83 was recognised by strong proliferative and Interferon (IFN)-γ-secreting T cell responses in peripheral blood mononuclear cells (PBMC) from patients with active TB, but not from healthy, tuberculin skin test-negative control subjects. MPT83 also stimulated strong IFN-γ T cell responses during experimental murine M. tuberculosis infection. Immunization with either rMPT83 in MPLA/DDA or DNA-MPT83 stimulated antigen-specific T cell responses, and we identified MPT83127–135 (PTNAAFDKL) as the dominant H-2b-restricted CD8+ T cell epitope within MPT83. Further, immunization of C57BL/6 mice with rMPT83/MPLA/DDA or DNA-MPT83 stimulated significant levels of protection in the lungs and spleens against aerosol challenge with M. tuberculosis. Interestingly, immunization with rMPT83 in MPLA/DDA primed for stronger IFN-γ T cell responses to the whole protein following challenge, while DNA-MPT83 primed for stronger CD8+ T cell responses to MPT83127–135. Therefore MPT83 is a protective T cell antigen commonly recognized during human M. tuberculosis infection and should be considered for inclusion in future TB subunit vaccines.
This study was performed to examine the adaptive immune response generated by three Mycobacterium bovis bacillus Calmette-Guérin (BCG) substrains to determine if the number of genomic regions of deletion played a significant role in determining the magnitude of the immune response or affected their ability to reduce the bacterial burden following low-dose aerosol challenge with a virulent M. tuberculosis strain. BCG Connaught, Pasteur, and Sweden were chosen as representative substrains, as they possessed many, intermediate, and few regions of deletion, respectively, as a result of changes in the genome in various regions. Mice were vaccinated subcutaneously and were then examined at 14, 21, and 42 days postvaccination. BCG was observed in the spleen, lung, and lymph nodes. BCG Connaught induced a greater pulmonary T-cell response than the other two substrains at day 14 postvaccination, although by 42 days postvaccination activated T-cell levels dropped to the levels observed in control mice for all three substrains. Among the three substrains, BCG Connaught induced significantly greater levels of interleukin-12 in bone marrow-derived macrophage cultures. Mice challenged at days 14, 21, and 42 postvaccination displayed an equal capacity to reduce the bacterial burden in the lungs and spleen. The data provide evidence that although the BCG substrains generated qualitatively and quantitatively different immune responses, they induced similar reductions in the bacterial burden against challenge with a virulent M. tuberculosis strain in the mouse model of tuberculosis. The data raise questions about the assessment of vaccine immune responses and the relationship to a vaccine's ability to reduce the bacterial burden.
Continuous high global tuberculosis (TB) mortality rates and variable vaccine efficacy of Mycobacterium bovis Bacille Calmette-Guérin (BCG) motivate the search for better vaccine regimes. Relevant models are required to downselect the most promising vaccines entering clinical efficacy testing and to identify correlates of protection.
Methods and Findings
Here, we evaluated immunogenicity and protection against Mycobacterium tuberculosis in rhesus monkeys with two novel strategies: BCG boosted by modified vaccinia virus Ankara expressing antigen 85A (MVA.85A), and attenuated M. tuberculosis with a disrupted phoP gene (SO2) as a single-dose vaccine. Both strategies were well tolerated, and immunogenic as evidenced by induction of specific IFNγ responses. Antigen 85A-specific IFNγ secretion was specifically increased by MVA.85A boosting. Importantly, both MVA.85A and SO2 treatment significantly reduced pathology and chest X-ray scores upon infectious challenge with M. tuberculosis Erdman strain. MVA.85A and SO2 treatment also showed reduced average lung bacterial counts (1.0 and 1.2 log respectively, compared with 0.4 log for BCG) and significant protective effect by reduction in C-reactive protein levels, body weight loss, and decrease of erythrocyte-associated hematologic parameters (MCV, MCH, Hb, Ht) as markers of inflammatory infection, all relative to non-vaccinated controls. Lymphocyte stimulation revealed Ag85A-induced IFNγ levels post-infection as the strongest immunocorrelate for protection (spearman's rho: −0.60).
Both the BCG/MVA.85A prime-boost regime and the novel live attenuated, phoP deficient TB vaccine candidate SO2 showed significant protective efficacy by various parameters in rhesus macaques. Considering the phylogenetic relationship between macaque and man and the similarity in manifestations of TB disease, these data support further development of these primary and combination TB vaccine candidates.
Mycobacterium bovis Bacille Calmette Guérin (BCG) was first administered to humans in 1921 and has subsequently been delivered to an estimated 3 billion individuals, with a low incidence of serious complications. The vaccine is immunogenic and is stable and cheap to produce. Additionally, the vaccine can be engineered to express foreign molecules in a functional form, and this has driven the development of BCG as a recombinant vector to protect against infectious diseases and malignancies such as cancer. However, it is now clear that the existing BCG vaccine has proved insufficient to control the spread of tuberculosis, and a major focus of tuberculosis vaccine development programs is the construction and testing of modified forms of BCG. This review summarizes the strategies employed to develop recombinant forms of BCG and describes the potential of these vaccines to stimulate protective immunity and protect against Mycobacterium tuberculosis infection.
recombinant BCG; tuberculosis; vaccine; protective immunity; cytokines
Tuberculosis (TB) disease caused by Mycobacterium tuberculosis (M. tb) remains one of the leading infectious causes of death and disease throughout the world. The only licensed vaccine, Mycobacterium bovis bacille Calmette–Guérin (BCG) confers highly variable protection against pulmonary disease. An effective vaccination regimen would be the most efficient way to control the epidemic. However, BCG does confer consistent and reliable protection against disseminated disease in childhood, and most TB vaccine strategies being developed incorporate BCG to retain this protection. Cellular immunity is necessary for protection against TB and all the new vaccines in development are focused on inducing a strong and durable cellular immune response. There are two main strategies being pursued in TB vaccine development. The first is to replace BCG with an improved whole organism mycobacterial priming vaccine, which is either a recombinant BCG or an attenuated strain of M. tb. The second is to develop a subunit boosting vaccine, which is designed to be administered after BCG vaccination, and to enhance the protective efficacy of BCG. This article reviews the leading candidate vaccines in development and considers the current challenges in the field with regard to efficacy testing.
tuberculosis; vaccine; bacille Calmette–Guérin; clinical trials; efficacy; immune correlates
Tuberculosis remains one of the most significant diseases of humans and animals. The only currently available vaccine against this disease is a live, attenuated vaccine, bacillus Calmette-Guérin (BCG), which was originally derived from Mycobacterium bovis and despite its variable efficacy is the most widely administered vaccine in the world. With the advent of the human immunodeficiency virus-AIDS pandemic concern has been raised over the safety of BCG. Moreover, since BCG sensitizes vaccinated individuals to the tuberculin test, vaccination with BCG prevents diagnosis of infection in vaccinated individuals. Recently, auxotrophic strains of BCG have been generated by insertional mutagenesis which have been shown to be safer than the parent BCG strain following administration to mice with severe combined immunodeficiency disease. These strains have also been shown to give comparable protection against intravenous and intratracheal challenge of BALB/c mice with M. tuberculosis relative to conventional BCG. Here we report that one of these mutants, a leucine auxotroph of BCG, conferred significant protection of the lungs and spleens of guinea pigs infected with M. bovis and protection of the spleens of guinea pigs infected with M. tuberculosis in the absence of a cutaneous hypersensitivity reaction to tuberculin. Therefore, protective immunity to tuberculosis may, at least in part, be achieved without sensitization to the tuberculin skin test. These results indicate that it may be possible to develop a new generation of vaccines based on BCG that are protective, are safe for use in the immunocompromised, and do not preclude the use of the tuberculin skin test in both humans and animals.
A lipid-based formulation has been developed for oral delivery of Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccine. The formulated M. bovis BCG was fed to BALB/c mice to test for immune responses and protection against M. bovis infection. The immune responses included antigen-specific cytokine responses, spleen cell proliferation, and lymphocyte-mediated macrophage inhibition of M. bovis. Oral delivery of formulated M. bovis BCG to mice induced strong splenic gamma interferon levels and macrophage inhibition of virulent M. bovis compared with results with nonformulated M. bovis BCG. Formulated oral M. bovis BCG significantly reduced the bacterial burden in the spleen and lungs of mice following aerosol challenge with virulent M. bovis. Our data suggest that oral delivery of formulated M. bovis BCG is an effective means of inducing protective immune responses against tuberculosis. Lipid-based, orally delivered mycobacterial vaccines may be a safe and practical method of controlling tuberculosis in humans and animals.
The variable efficacy (0–80%) of Mycobacterium bovis Bacille Calmette Guréin (BCG) vaccine against adult tuberculosis (TB) necessitates development of alternative vaccine candidates. Development of recombinant BCG (rBCG) over-expressing promising immunodominant antigens of M. tuberculosis represents one of the potential approaches for the development of vaccines against TB.
A recombinant strain of BCG - rBCG85C, over expressing the antigen 85C, a secretory immuno-dominant protein of M. tuberculosis, was evaluated for its protective efficacy in guinea pigs against M. tuberculosis challenge by aerosol route. Immunization with rBCG85C resulted in a substantial reduction in the lung (1.87 log10, p<0.01) and spleen (2.36 log10, p<0.001) bacillary load with a commensurate reduction in pathological damage, when compared to the animals immunized with the parent BCG strain at 10 weeks post-infection. rBCG85C continued to provide superior protection over BCG even when post-challenge period was prolonged to 16 weeks. The cytokine profile of pulmonary granulomas revealed that the superior protection imparted by rBCG85C was associated with the reduced levels of pro-inflammatory cytokines - interleukin (IL)-12, interferon (IFN)-γ, tumor necrosis factor (TNF)-α, moderate levels of anti-inflammatory cytokine - transforming growth factor (TGF)-β along with up-regulation of inducible nitric oxide synthase (iNOS). In addition, the rBCG85C vaccine induced modulation of the cytokine levels was found to be associated with reduced fibrosis and antigen load accompanied by the restoration of normal lung architecture.
These results clearly indicate the superiority of rBCG85C over BCG as a promising prophylactic vaccine against TB. The enduring protection observed in this study gives enough reason to postulate that if an open-ended study is carried out with low dose of infection, rBCG85C vaccine in all likelihood would show enhanced survival of guinea pigs.
M. bovis Bacille Calmette-Guérin (BCG), currently the only available vaccine against tuberculosis (TB), fails to adequately protect individuals from active and latent TB infection. New vaccines are desperately needed to decrease the worldwide burden of TB.
Methods and Findings
We created a recombinant strain of BCG that overproduces an L,D-transpeptidase in order to alter the bacterial peptidoglycan layer and consequently increase the ability of this immunogen to protect against virulent M. tuberculosis (Mtb). We demonstrate that this novel recombinant BCG protects mice against virulent Mtb at least as well as control BCG, as measured by its ability to reduce bacterial burden in lungs and spleen, reduce lung histopathology, and prolong survival. A nutrient starved recombinant BCG preparation, while offering comparable protection, elicited a response characterized by elevated levels of select Th1 cytokines.
Recombinant BCG overexpressing a L,D-transpeptidase that is nutrient starved elicits a stronger Th1 type response and is at least as protective as parent BCG. Results from this study suggest that nutrient starvation treatment of live BCG vaccines should be further investigated as a way to increase host induction of Th-1 related cytokines in the development of experimental anti-TB vaccines.
(See the editorial commentary by Dockrell, on pages 1029–31.)
Background. There is currently no safe human challenge model of Mycobacterium tuberculosis infection to enable proof-of-concept efficacy evaluation of candidate vaccines against tuberculosis. In vivo antimycobacterial immunity could be assessed using intradermal Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccination as a surrogate for M. tuberculosis infection.
Methods. Healthy BCG-naive and BCG-vaccinated volunteers were challenged with intradermal BCG. BCG load was quantified from skin biopsy specimens by polymerase chain reaction (PCR) and culture colony-forming units. Cellular infiltrate was isolated by suction blisters and examined by flow cytometry. Prechallenge immune readouts were correlated with BCG load after challenge.
Results. In BCG-naive volunteers, live BCG was detected at the challenge site for up to 4 weeks and peaked at 2 weeks. Infiltration of mainly CD15+ neutrophils was observed in blister fluid. In previously BCG-vaccinated individuals, PCR analysis of skin biopsy specimens reflected a degree of mycobacterial immunity. There was no significant correlation between BCG load after challenge and mycobacterial-specific memory T cells measured before challenge by cultured enzyme-linked immunospot assay.
Conclusions. This novel experimental human challenge model provides a platform for the identification of correlates of antimycobacterial immunity and will greatly facilitate the rational down-selection of candidate tuberculosis vaccines. Further evaluation of this model with BCG and new vaccine candidates is warranted.
Mycobacterium bovis bacillus Calmette-Guérin (BCG) is the only vaccine approved for prevention of tuberculosis. It has been postulated that serial passage of BCG over the years may have resulted in attenuation of its effectiveness. Because interleukin-12 (IL-12) and oligodeoxynucleotides (ODN) containing cytidine phosphate guanosine (CpG) motifs have been shown to enhance Th1 responses in vivo, they were chosen as adjuvants to increase the effectiveness of BCG vaccination. In this report, mice were vaccinated with BCG with or without IL-12 or CpG ODN and then challenged 6 weeks later via the aerosol route with the Erdman strain of M. tuberculosis. Mice vaccinated with BCG alone showed a 1- to 2-log reduction in bacterial load compared with control mice that did not receive any vaccination prior to M. tuberculosis challenge. Moreover, the bacterial loads of mice vaccinated with BCG plus IL-12 or CpG ODN were a further two- to fivefold lower than those of mice vaccinated with BCG alone. As an immune correlate, the antigen-specific production IFN-γ and mRNA expression in spleen cells prior to challenge were evaluated. Mice vaccinated with BCG plus IL-12 or CpG ODN showed enhanced production of IFN-γ compared with mice vaccinated with BCG alone. Finally, granulomas in BCG-vaccinated mice were smaller and more lymphocyte rich than those in unvaccinated mice; however, the addition of IL-12 or CpG ODN to BCG vaccination did not alter granuloma formation or result in added pulmonary damage. These observations support a role for immune adjuvants given with BCG vaccination to enhance its biologic efficacy.
Vaccination with Mycobacterium bovis bacille Calmette-Guérin (BCG) has variable efficacy in preventing tuberculosis. We hypothesized that some of this variation might be due to differences among BCG strains. To test this, neonates in Orizaba, Mexico, were vaccinated with one of three different BCG strains (BCG-Brazil [BBCG], BCG-Denmark [DBCG], or BCG-Japan [JBCG]). One year after vaccination, peripheral blood mononuclear cells (PBMC) were obtained and recall immune responses to culture filtrate proteins (CFP) of Mycobacterium tuberculosis were evaluated using quantitative real-time PCR. CFP-activated PBMC from BBCG- and DBCG-immunized children expressed high levels of cytokines characteristic of an adaptive immune response (gamma interferon, interleukin-2β [IL-12β], and IL-27), while those from children immunized with JBCG did not. In contrast, vaccination with JBCG resulted in significantly greater expression of cytokines characteristic of a proinflammatory immune response (IL-1α, IL-1β, IL-6, and IL-24) in PBMC activated with CFP compared to PBMC from children vaccinated with BBCG or DBCG. Thus, different strains of BCG can activate different immune pathways, which may affect long-term vaccine efficacy.
Vaccination of neonatal calves with Mycobacterium bovis bacillus Calmette-Guérin (BCG) induces a significant degree of protection against infection with virulent M. bovis, the causative agent of bovine tuberculosis (bTB). We compared two strains of BCG, Pasteur and Danish, in order to confirm that the current European human vaccine strain (BCG Danish) induced protective immunity in calves, and we assessed immune responses to determine correlates of protection that could assist future vaccine evaluation in cattle. Both vaccine strains induced antigen (purified protein derivate [PPD])-specific gamma interferon (IFN-γ) in whole-blood cultures. These responses were not significantly different for BCG Pasteur and BCG Danish and peaked at week 2 to 4 postvaccination. Vaccination with either BCG Danish or BCG Pasteur induced significant protection against bTB, with reductions in both lesion score and bacteriological burden evident in both groups of vaccinated calves compared with nonvaccinated control calves. Measurement of IFN-γ-expressing T lymphocytes postvaccination and postchallenge revealed both correlates and surrogates of protective efficacy. The frequency of central memory T lymphocytes present at 12 weeks postvaccination (at the time of M. bovis challenge) correlated significantly with protection. Conversely, the number of IFN-γ-expressing effector T cells present after M. bovis challenge was correlated with disease. These results demonstrate that vaccination of neonatal calves with either BCG Pasteur or BCG Danish induces protective immune responses against TB. In addition, we show that measurement of antigen-specific T lymphocyte populations may provide a reliable means for identifying protective vaccine candidates.
The present study examined the differential contribution of host genetic background and mycobacterial pathogen variability to biological and mechanistic phenotypes of infection. For this purpose, A/J and C57BL/6J mice were infected intravenously with a low dose of Mycobacterium tuberculosis H37Rv or the Russia, Japan, and Pasteur substrains of Mycobacterium bovis bacille Calmette-Guérin (BCG). The pulmonary bacterial counts (number of CFU) and transcript levels of select cytokines (e.g., Ifng, Il12b, and Il4) at 1, 3, and 6 weeks postinfection were measured as biological and mechanistic phenotypes, respectively. The individual and combined impact of the host and mycobacteria on these phenotypes was assessed using three-way analysis of variance (ANOVA), which partitions phenotypic variation into host, pathogen, time, and interaction effects. All phenotypes, except pulmonary Il4 transcript levels, displayed evidence for host-mycobacterium specificity by means of significant interaction terms. Pulmonary expression profiles of 34 chemokines and chemokine-related genes were compared across the hosts and mycobacteria. The differences in induction of these immune messenger genes between A/J and C57BL/6J mice were modest and generally failed to reach significance. In contrast, the mycobacteria induced significant variance in a subset of the immune messenger genes, which was more evident in A/J mice relative to that in C57BL/6J mice. Overall, the results demonstrated the importance of considering the joint effects of the mycobacterial and host genetic backgrounds on susceptibility to mycobacterial infections.
Pathogenic mycobacteria must acquire iron in the host in order to multiply and cause disease. To do so, they release abundant quantities of siderophores called exochelins, which have the capacity to scavenge iron from host iron-binding proteins and deliver it to the mycobacteria. In this study, we have characterized the exochelins of Mycobacterium bovis, the causative agent of bovine and occasionally of human tuberculosis, and the highly attenuated descendant of M. bovis, bacillus Calmette-Guérin (BCG), widely used as a vaccine against human tuberculosis. The M. bovis type strain, five substrains of M. bovis BCG (Copenhagen, Glaxo, Japanese, Pasteur, and Tice), and two strains of virulent Mycobacterium tuberculosis all produce the same set of exochelins, although the relative amounts of individual exochelins may differ. Among these mycobacteria, the total amount of exochelins produced is greatest in M. tuberculosis, intermediate in M. bovis, and smallest in M. bovis BCG.
Bacille Calmette Guérin substrain Moreau Rio de Janeiro is an attenuated strain of Mycobacterium bovis that has been used extensively as an oral tuberculosis vaccine. We assessed its potential as a challenge model to study clinical and immunological events following repeated mycobacterial gut infection. Seven individuals received three oral challenges with approximately 107 viable bacilli. Clinical symptoms, T-cell responses and gene expression patterns in peripheral blood were monitored. Clinical symptoms were relatively mild and declined following each oral challenge. Delayed T-cell responses were observed, and limited differential gene expression detected by microarrays. Oral challenge with BCG Moreau Rio de Janeiro vaccine was immunogenic in healthy volunteers, limiting its potential to explore clinical innate immune responses, but with low reactogenicity.
BCG; Oral challenge; Innate immunity
BCG vaccines are substrains of Mycobacterium bovis derived by attenuation in vitro. After the original attenuation (1908 to 1921), BCG strains were maintained by serial propagation in different BCG laboratories (1921 to 1961). As a result, various BCG substrains developed which are now known to differ in a number of genetic and phenotypic properties. However, to date, none of these differences has permitted a direct phenotype-genotype link. Since BCG strains differ in their abilities to synthesize methoxymycolic acids and since recent work has shown that the mma3 gene is responsible for O-methylation of hydroxymycolate precursors to form methoxymycolic acids, we analyzed methoxymycolate production and mma3 gene sequences for a genetically defined collection of BCG strains. We found that BCG strains obtained from the Pasteur Institute in 1927 and earlier produced methoxymycolates in vitro but that those obtained from the Pasteur Institute in 1931 and later all failed to synthesize methoxymycolates, and furthermore, the mma3 sequence of the latter strains differs from that of Mycobacterium tuberculosis H37Rv by a point mutation at bp 293. Site-specific introduction of this guanine-to-adenine mutation into wild-type mma3 (resulting in the replacement of glycine 98 with aspartic acid) eliminated the ability of this enzyme to produce O-methylated mycolic acids when the mutant was cloned in tandem with mma4 into Mycobacterium smegmatis. These findings indicate that a point mutation in mma3 occurred between 1927 and 1931, and that this mutant population became the dominant clone of BCG at the Pasteur Institute.
The immunogenic proteins MPB64 and MPB80 of Mycobacterium bovis BCG were purified to homogeneity and compared with MPB70. MPB70 and MPB80 showed a similar distribution in substrains of BCG, both being present in high concentrations in culture fluids of BCG substrain Tokyo, BCG Moreau, BCG Russia, and BCG Sweden and in only very small amounts in BCG Glaxo, BCG Tice, BCG Copenhagen, and BCG Pasteur. In various physicochemical properties MPB70 and MPB80 were closely similar, but MPB80 had a distinctly lower pI value. The N-terminal amino acid sequence was identical for the first 30 residues. In reactions with anti-MPB70 antibodies and delayed-type hypersensitivity skin reactions, MPB70 and MPB80 also had very similar properties. These results show that MPB70 and MPB80 are two closely similar forms of the same gene product, and postsynthetic changes probably explain the observed differences. By contrast, MPB64 had a higher molecular weight. The N-terminal amino acid sequence showed no homology with MPB70, and these two proteins showed no immunologic similarity. MPB64 and MPB70 showed only very restricted cross-reactivity with other species of mycobacteria but cross-reacted with Nocardia asteroides. The similar occurrence in eight different substrains of BCG indicated that the two proteins are influenced by similar control mechanisms, but in contrast to MPB70, MPB64 occurred in sufficient concentration in two strains of Mycobacterium tuberculosis to give a distinct spot in two-dimensional polyacrylamide gel electrophoresis of their culture fluids.
Previous work with small-animal laboratory models of tuberculosis has shown that vaccination strategies based on heterologous prime-boost protocols using Mycobacterium bovis bacillus Calmette-Guérin (BCG) to prime and modified vaccinia virus Ankara strain (MVA85A) or recombinant attenuated adenoviruses (Ad85A) expressing the mycobacterial antigen Ag85A to boost may increase the protective efficacy of BCG. Here we report the first efficacy data on using these vaccines in cattle, a natural target species of tuberculous infection. Protection was determined by measuring development of disease as an end point after M. bovis challenge. Either Ad85A or MVA85A boosting resulted in protection superior to that given by BCG alone: boosting BCG with MVA85A or Ad85A induced significant reduction in pathology in four/eight parameters assessed, while BCG vaccination alone did so in only one parameter studied. Protection was particularly evident in the lungs of vaccinated animals (median lung scores for naïve and BCG-, BCG/MVA85A-, and BCG/Ad85A-vaccinated animals were 10.5, 5, 2.5, and 0, respectively). The bacterial loads in lymph node tissues were also reduced after viral boosting of BCG-vaccinated calves compared to those in BCG-only-vaccinated animals. Analysis of vaccine-induced immunity identified memory responses measured by cultured enzyme-linked immunospot assay as well as in vitro interleukin-17 production as predictors of vaccination success, as both responses, measured before challenge, correlated positively with the degree of protection. Therefore, this study provides evidence of improved protection against tuberculosis by viral booster vaccination in a natural target species and has prioritized potential correlates of vaccine efficacy for further evaluation. These findings also have implications for human tuberculosis vaccine development.
Mycobacterium bovis BCG is the only available vaccine against tuberculosis. Reasons for why diverse BCG substrains induce different levels of protection in clinical trials remain unclear. The aim of this study was to compare the effectiveness of 10 BCG substrains in a mouse model of pulmonary tuberculosis. BALB/c mice were subcutaneously vaccinated and 2 months later were challenged with Mycobacterium tuberculosis H37Rv by intratracheal injection. Two and 4 months after challenge, delayed-type hypersensitivity (DTH) response, lung tissue affected by pneumonia, CFU, T-cell counts, and cytokine expression (interleukin-2 [IL-2], IL-4, IL-10, and gamma interferon) were determined. A differential protective effect of the diverse BCG substrains was found. BCG Phipps led to the largest and most persistent reduction of CFU counts and of the area of pneumonia at 2 and 4 months after challenge. This protection was accompanied by reduced IL-10-producing T cells. Contemporary BCG substrains induce a wide range of protection in this animal model. These data can help in the selection of the best vaccine for human immunization and for the development of novel recombinant BCG-based vaccine.
Mycobacterium bovis bacille Calmette-Guerin (BCG) provides only limited protection against pulmonary tuberculosis. We tested the hypothesis that BCG might have retained immunomodulatory properties from its pathogenic parent that limit its protective immunogenicity. Mutation of the molecules involved in immunomodulation might then improve its vaccine potential. We studied the vaccine potential of BCG mutants deficient in the secreted acid phosphatase, SapM, or in the capping of the immunomodulatory ManLAM cell wall component with α-1,2-oligomannoside. Both systemic and intratracheal challenge of mice with Mycobacterium tuberculosis following vaccination showed that the SapM mutant, compared to the parental BCG vaccine, provided better protection: it led to longer-term survival. Persistence of the SapM-mutated BCG in vivo resembled that of the parental BCG indicating that this mutation will likely not compromise the safety of the BCG vaccine. The SapM mutant BCG vaccine was more effective than the parental vaccine in inducing recruitment and activation of CD11c+MHC-IIintCD40int dendritic cells (DCs) to the draining lymph nodes. Thus, SapM acts by inhibiting recruitment of DCs and their activation at the site of vaccination.
Mycobacterium; SapM; tuberculosis; vaccine; BCG
The gene of the immunogenic protein MPT64 found in culture filtrates of Mycobacterium tuberculosis H37Rv was cloned and sequenced. A comparison showed mpt64 and the gene encoding MPB64 from Mycobacterium bovis BCG Tokyo to be identical except for one silent mutation. The regions encoding the promoter and the signal peptide were also well conserved for the two sequences. Southern blot experiments on genomic mycobacterial DNA showed the presence of mpt64 in the M. tuberculosis substrains H37Rv, H37Ra, and Erdman and in the M. bovis BCG substrains Tokyo, Moreau, and Russian, whereas the M. bovis BCG substrains Glaxo, Pasteur, Canadian, Tice, and Danish 1331 and Mycobacterium leprae lack the gene. Southern blot analyses revealed differences in the restriction enzyme patterns within the M. tuberculosis substrains as well as within the M. bovis BCG substrains, indicating either different chromosomal localization of mpt64 or that mutations have occurred at different locations on the chromosomes. N-terminal and C-terminal deletion mutants were constructed for the mapping of B-cell epitopes on MPT64 with five monoclonal antibodies, C24b1, C24b2, C24b3, L24b4, and L24b5. Western blot (immunoblot) analysis revealed that the murine antibodies bind to one linear and three conformational epitopes.
Effective prophylactic and/or therapeutic vaccination is a key strategy for controlling the global TB epidemic. The partial effectiveness of the existing TB vaccine, bacille Calmette–Guérin (BCG), suggests effective vaccination is possible and highlights the need for an improved vaccination strategy. Clinical trials are evaluating both modifications to the existing BCG immunization methods and also novel TB vaccines, designed to replace or boost BCG. Candidate vaccines in clinical development include live mycobacterial vaccines designed to replace BCG, subunit vaccines designed to boost BCG and therapeutic vaccines designed as an adjunct to chemotherapy. There is a great need for validated animal models, identification of immunological biomarkers of protection and field sites with the capacity for large-scale efficacy testing in order to develop and license a novel TB vaccine or regimen.
BCG; clinical trials; mycobacteria; prophylactic; subunit; therapeutic; tuberculosis; vaccine