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

Mycobacterium tuberculosis antigen 85B modifies BCG-induced antituberculosis immunity and favors pathogen survival

Tuberculosis is one of the deadliest infectious diseases worldwide. Mycobacterium tuberculosis has developed strategies not only to evade host immunity but also to manipulate it for its survival. We investigated whether Mycobacterium tuberculosis exploited the immunogenicity of Ag85B, one of its major secretory proteins, to redirect host antituberculosis immunity to its advantage. We found that administration of Ag85B protein to mice vaccinated with Bacillus Calmette-Guérin impaired the protection elicited by vaccination, causing a more severe infection when mice were challenged with Mycobacterium tuberculosis. Ag85B administration reduced Bacillus Calmette-Guérin-induced CD4 T-cell activation and IFN-γ, CCL-4, and IL-22 production in response to Mycobacterium tuberculosis-infected cells. On the other hand, it promoted robust Ag85B-responsive IFN-γ-producing CD4 T cells, expansion of a subset of IFN-γ/IL-10-producing CD4+FOXP3+Treg cells, differential activation of IL-17/IL-22 responses, and activation of regulatory and exhaustion pathways, including programmed death ligand 1 expression on macrophages. All this resulted in impaired intracellular Mycobacterium tuberculosis growth control by systemic immunity, both before and after the Mycobacterium tuberculosis challenge. Interestingly, Mycobacterium tuberculosis infection itself generated Ag85B-reactive inflammatory immune cells incapable of clearing Mycobacterium tuberculosis in both unvaccinated and Bacillus Calmette-Guérin-vaccinated mice. Our data suggest that Mycobacterium tuberculosis can exploit the strong immunogenicity of Ag85B to promote its own survival and spread. Since Ag85B is normally secreted by replicating bacteria and is commonly found in the lungs of the Mycobacterium tuberculosis-infected host, our findings may advance the understanding on the mechanisms of Mycobacterium tuberculosis pathogenesis and immune evasion.

Pathogenic Effects of M. tuberculosis-Specific Proteins ESAT-6 and CFP-10 in Macrophage Culture and in 3D-Granulemogenesis Model In Vitro

We studied the effects of M. tuberculosis secretory proteins ESAT-6 and CFP-10 on the properties of vaccinal mycobacteria BCG not producing these proteins. Phagocytosis of M. bovis by macrophages, proliferation of mycobacteria in macrophages, apoptosis and necrosis of macrophages, and the production of reactive oxygen and nitrogen species were studied. It was shown that both ESAT-6 and CFP-10 significantly increased the number of phagocytized mycobacteria by increasing the number of phagocytic-active macrophages and augment the intracellular proliferation of the pathogen. At the same time, macrophages preincubated with ESAT-6 and CFP-10 reduce the production of reactive oxygen and nitrogen species and are more susceptible to apoptosis and necrosis in the presence of mycobacteria. In summary, these proteins suppress macrophage-mediated mechanisms of anti-tuberculosis resistance and impart pronounced pathogenic properties to non-pathogenic mycobacteria that do not secrete ESAT-6 and CFP-10.

Tuberculosis vaccination needs to avoid 'decoy' immune reactions

Current search for a new effective vaccine against tuberculosis involves selected antigens, vectors and adjuvants. These are being evaluated usually by their booster inoculation following priming with Bacillus Calmette-Guerin. The purpose of this article is to point out, that despite being attenuated of virulence, priming with BCG may still involve immune mechanisms, which are not favourable for protection against active disease. It is postulated, that the responsible 'decoy' constituents selected during the evolution of pathogenic tubercle bacilli may be involved in the evasion from bactericidal host resistance and stimulate immune responses of a cytokine phenotype, which lead to the transition from latent closed granulomas to reactivation with infectious lung cavities. The decoy mechanisms appear as favourable for most infected subjects but leading in a minority of cases to pathology which can effectively transmit the infection. It is proposed that construction and development of new vaccine candidates could benefit from avoiding decoy-type immune mechanisms.

Proof of concept in utilizing in-trans surface display system of Lactobacillus plantarum as mucosal tuberculosis vaccine via oral administration in mice

Background

Tuberculosis is one of the most common and deadliest infectious diseases worldwide affecting almost a third of the world’s population. Although this disease is being prevented and controlled by the Bacille Calmette Guérin (BCG) vaccine, the protective efficacy is highly variable and substandard (0–80%) in adults. Therefore, novel and effective tuberculosis vaccine that can overcome the limitations from BCG vaccine need to be developed.

Results

A novel approach of utilizing an in-trans protein surface display system of Lactobacillus plantarum carrying and displaying combination of Mycobacterium tuberculosis subunit epitope antigens (Ag85B, CFP-10, ESAT-6, Rv0475 and Rv2031c) fused with LysM anchor motif designated as ACERL was constructed, cloned and expressed in Esherichia coli Rossetta expression host. Subsequently the binding capability of ACERL to the cell wall of L. plantarum was examined via the immunofluorescence microscopy and whole cell ELISA where successful attachment and consistent stability of cell wall binding up to 4 days was determined. The immunization of the developed vaccine of L. plantarum surface displaying ACERL (Lp ACERL) via the oral route was studied in mice for its immunogenicity effects. Lp ACERL immunization was able to invoke significant immune responses that favor the Th1 type cytokine response of IFN-γ, IL-12 and IL-2 as indicated by the outcome from the cytokine profiling of spleen, lung, gastrointestinal tract (GIT), and the re-stimulation of the splenocytes from the immunized mice. Co-administration of an adjuvant consisting of Lactococcus lactis secreting mouse IL-12 (LcIL-12) with Lp ACERL was also investigated. It was shown that the addition of LcIL-12 was able to further generate significant Th1 type cytokines immune responses, similar or better than that of Lp ACERL alone which can be observed from the cytokine profiling of the immunized mice’s spleen, lung and GIT.

Conclusions

This study represents a proof of concept in the development of L. plantarum as a carrier for a non-genetically modified organism (GMO) tuberculosis vaccine, which may be the strategy in the future for tuberculosis vaccine development.

Electronic supplementary material

The online version of this article (10.1186/s12896-018-0461-y) contains supplementary material, which is available to authorized users.

Dynamic balance of pro- and anti-inflammatory signals controls disease and limits pathology

Immune responses to pathogens are complex and not well understood in many diseases, and this is especially true for infections by persistent pathogens. One mechanism that allows for long-term control of infection while also preventing an over-zealous inflammatory response from causing extensive tissue damage is for the immune system to balance pro- and anti-inflammatory cells and signals. This balance is dynamic and the immune system responds to cues from both host and pathogen, maintaining a steady state across multiple scales through continuous feedback. Identifying the signals, cells, cytokines, and other immune response factors that mediate this balance over time has been difficult using traditional research strategies. Computational modeling studies based on data from traditional systems can identify how this balance contributes to immunity. Here we provide evidence from both experimental and mathematical/computational studies to support the concept of a dynamic balance operating during persistent and other infection scenarios. We focus mainly on tuberculosis, currently the leading cause of death due to infectious disease in the world, and also provide evidence for other infections. A better understanding of the dynamically balanced immune response can help shape treatment strategies that utilize both drugs and host-directed therapies.

Addressing diversity in tuberculosis using multidimensional approaches

Tuberculosis is a complex disease, which can affect many organs other than the lungs. Initial infection may be cleared without inducing immunological memory, or progress directly to primary disease. Alternatively, the infection may be controlled as latent TB infection, that may progress to active tuberculosis at a later stage. There is now a greater understanding that these infection states are part of a continuum, and studies using PET/CT imaging have shown that individual lung granulomas may respond to infection independently, in an un-synchronized manner. In addition, the Mycobacterium tuberculosis organisms themselves can exist in different states: as nonculturable forms, as 'persisters', as rapidly growing bacteria and a biofilm-forming cording phenotype. The 'omics' approaches of transcriptomics, metabolomics and proteomics can help reveal the mechanisms underlying these different infection states in the host, and identify biosignatures with diagnostic potential, that can predict the development of disease, in 'progressors' as early as 12-18 months before it can be detected clinically, or that can monitor the success of anti-TB therapy. Further insights can be obtained from studies of BCG vaccination and new TB vaccines. For example, epigenetic changes associated with trained immunity and a stronger immune responses following BCG vaccination can be identified. These omics approaches may be particularly valuable when linked to studies of mycobacterial growth inhibition, as a direct read-out of the ability to control mycobacterial growth. The second generation of omics studies is identifying much smaller signatures based on as few as 3 or 4 genes. Thus, narrowing down omics-derived biosignatures to a manageable set of markers now opens the way to field-friendly point of care assays.

Next-Generation Vaccines Based on Bacille Calmette-Guérin

Tuberculosis (TB), caused by the intracellular bacterium Mycobacterium tuberculosis (Mtb), remains a major health threat. A live, attenuated mycobacterium known as Bacille Calmette-Guérin (BCG), derived from the causative agent of cattle TB, Mycobacterium bovis, has been in clinical use as a vaccine for 90 years. The current incidence of TB demonstrates that BCG fails to protect sufficiently against pulmonary TB, the major disease manifestation and source of dissemination. The protective efficacy of BCG is on average 50% but varies substantially with geographical location and is poorer in those with previous exposure to mycobacteria. BCG can also cause adverse reactions in immunocompromised individuals. However, BCG has contributed to reduced infant TB mortality by protecting against extrapulmonary TB. In addition, BCG has been associated with reduced general childhood mortality by stimulating immune responses. In order to improve the efficacy of BCG, two major strategies have been employed. The first involves the development of recombinant live mycobacterial vaccines with improved efficacy and safety. The second strategy is to boost BCG with subunit vaccines containing Mtb antigens. This article reviews recombinant BCG strains that have been tested against TB in animal models. This includes BCG strains that have been engineered to induce increased immune responses by the insertion of genes for Mtb antigens, mammalian cytokines, or host resistance factors, the insertion of bacterial toxin-derived adjuvants, and the manipulation of bacterial genes in order to increase antigen presentation and immune activation. Subunit vaccines for boosting BCG are also briefly discussed.

Potential of Cationic Liposomes as Adjuvants/Delivery Systems for Tuberculosis Subunit Vaccines

The weakness of the BCG vaccine and its highly variable protective efficacy in controlling tuberculosis (TB) in different age groups as well as in different geographic areas has led to intense efforts towards the development and design of novel vaccines. Currently, there are several strategies to develop novel TB vaccines. Each strategy has its advantages and disadvantages. However, the most important of these strategies is the development of subunit vaccines. In recent years, the use of cationic liposome-based vaccines has been considered due to their capacity to elicit strong humoral and cellular immune responses against TB infections. In this review, we aim to evaluate the potential for cationic liposomes to be used as adjuvants/delivery systems for eliciting immune responses against TB subunit vaccines. The present review shows that cationic liposomes have extensive applications either as adjuvants or delivery systems, to promote immune responses against Mycobacterium tuberculosis (Mtb) subunit vaccines. To overcome several limitations of these particles, they were used in combination with other immunostimulatory factors such as TDB, MPL, TDM, and Poly I:C. Cationic liposomes can provide long-term storage of subunit TB vaccines at the injection site, confer strong electrostatic interactions with APCs, potentiate both humoral and cellular (CD4 and CD8) immune responses, and induce a strong memory response by the immune system. Therefore, cationic liposomes can increase the potential of different TB subunit vaccines by serving as adjuvants/delivery systems. These properties suggest the use of cationic liposomes to produce an efficient vaccine against TB infections.

Recombinant BCG vaccines: molecular features and their influence in the expression of foreign genes

Recombinant Mycobacterium bovis BCG vaccines (rBCG) were first developed in the 1990s as a means of expressing antigens from multiple pathogens. This review examines the key structural factors of recombinant M. bovis that influence the expression of the heterologous antigens and the generation of genetic and functional stability in rBCG, which are crucial for inducing strong and lasting immune responses. The fundamental aim of this paper is to provide an overview of factors that affect the expression of recombinant proteins in BCG and the generation of the immune response against the target antigens, including mycobacterial promoters, location of foreign antigens, and stability of the vectors. The reporter systems that have been employed for evaluation of these molecular features in BCG are also reviewed here.

Role of Interferons in the Development of Diagnostics, Vaccines, and Therapy for Tuberculosis

Tuberculosis (TB) is an airborne infection caused by Mycobacterium tuberculosis (Mtb). About one-third of the world's population is latently infected with TB and 5–15% of them will develop active TB in their lifetime. It is estimated that each case of active TB may cause 10–20 new infections. Host immune response to Mtb is influenced by interferon- (IFN-) signaling pathways, particularly by type I and type II interferons (IFNs). The latter that consists of IFN-γ has been associated with the promotion of Th1 immune response which is associated with protection against TB. Although this aspect remains controversial at present due to the lack of established correlates of protection, currently, there are different prophylactic, diagnostic, and immunotherapeutic approaches in which IFNs play an important role. This review summarizes the main aspects related with the biology of IFNs, mainly associated with TB, as well as presents the main applications of these cytokines related to prophylaxis, diagnosis, and immunotherapy of TB.

Recombinant BCG Expressing LTAK63 Adjuvant induces Superior Protection against Mycobacterium tuberculosis

In order to develop an improved BCG vaccine against tuberculosis we have taken advantage of the adjuvant properties of a non-toxic derivative of Escherichia coli heat labile enterotoxin (LT), LTAK63. We have constructed rBCG strains expressing LTAK63 at different expression levels. Mice immunized with BCG expressing low levels of LTAK63 (rBCG-LTAK63_lo) showed higher Th1 cytokines and IL-17 in the lungs, and when challenged intratracheally with Mycobacterium tuberculosis displayed a 2.0–3.0 log reduction in CFU as compared to wild type BCG. Histopathological analysis of lung tissues from protected mice revealed a reduced inflammatory response. Immunization with rBCG-LTAK63_lo also protected against a 100-fold higher challenge dose. Mice immunized with rBCG-LTAK63_lo produced an increase in TGF-β as compared with BCG after challenge, with a corresponding reduction in Th1 and Th17 cytokines, as determined by Real Time RT-PCR. Furthermore, rBCG-LTAK63_lo also displays protection against challenge with a highly virulent Beijing isolate. Our findings suggest that BCG with low-level expression of the LTAK63 adjuvant induces a stronger immune response in the lungs conferring higher levels of protection, and a novel mechanism subsequently triggers a regulatory immune response, which then limits the pathology. The rBCG-LTAK63_lo strain can be the basis of an improved vaccine against tuberculosis.

Boosting BCG-primed responses with a subunit Apa vaccine during the waning phase improves immunity and imparts protection against Mycobacterium tuberculosis

Heterologous prime-boosting has emerged as a powerful vaccination approach against tuberculosis. However, optimal timing to boost BCG-immunity using subunit vaccines remains unclear in clinical trials. Here, we followed the adhesin Apa-specific T-cell responses in BCG-primed mice and investigated its BCG-booster potential. The Apa-specific T-cell response peaked 32-52 weeks after parenteral or mucosal BCG-priming but waned significantly by 78 weeks. A subunit-Apa-boost during the contraction-phase of BCG-response had a greater effect on the magnitude and functional quality of specific cellular and humoral responses compared to a boost at the peak of BCG-response. The cellular response increased following mucosal BCG-prime-Apa-subunit-boost strategy compared to Apa-subunit-prime-BCG-boost approach. However, parenteral BCG-prime-Apa-subunit-boost by a homologous route was the most effective strategy in-terms of enhancing specific T-cell responses during waning in the lung and spleen. Two Apa-boosters markedly improved waning BCG-immunity and significantly reduced Mycobacterium tuberculosis burdens post-challenge. Our results highlight the challenges of optimization of prime-boost regimens in mice where BCG drives persistent immune-activation and suggest that boosting with a heterologous vaccine may be ideal once the specific persisting effector responses are contracted. Our results have important implications for design of prime-boost regimens against tuberculosis in humans.

Manipulation of BCG vaccine: a double-edged sword

Mycobacterium bovis Bacillus Calmette-Guérin (BCG), an attenuated vaccine derived from M. bovis, is the only licensed vaccine against tuberculosis (TB). Despite its protection against TB in children, the protective efficacy in pulmonary TB is variable in adolescents and adults. In spite of the current knowledge of molecular biology, immunology and cell biology, infectious diseases such as TB and HIV/AIDS are still challenges for the scientific community. Genetic manipulation facilitates the construction of recombinant BCG (rBCG) vaccine that can be used as a highly immunogenic vaccine against TB with an improved safety profile, but, still, the manipulation of BCG vaccine to improve efficacy should be carefully considered, as it can bring in both favourable and unfavourable effects. The purpose of this review is not to comprehensively review the interaction between microorganisms and host cells in order to use rBCG expressing M. tuberculosis (Mtb) immunodominant antigens that are available in the public domain, but, rather, to also discuss the limitations of rBCG vaccine, expressing heterologous antigens, during manipulation that pave the way for a promising new vaccine approach.

B Cells and Programmed Death-Ligand 2 Signaling Are Required for Maximal Interferon-γ Recall Response by Splenic CD4⁺ Memory T Cells of Mice Vaccinated with Mycobacterium tuberculosis Ag85B

CD4+ T cells producing interferon-γ are crucial for protection against Mycobacterium tuberculosis infection and are the cornerstone of tuberculosis vaccination and immunological diagnostic assays. Since emerging evidence indicates that B cells can modulate T cell responses to M. tuberculosis infection, we investigated the contribution of B cells in regulating interferon-γ recall response by memory Thelper1 cells specific for Ag85B, a leading candidate for tuberculosis sub-unit vaccines. We found that B cells were able to maximize the reactivation of CD4+ memory T cells and the interferon-γ response against ex vivo antigen recall in spleens of mice vaccinated with Ag85B. B cell-mediated increase of interferon-γ response was particular evident for high interferon-γ producer CD4+ memory T cells, likely because those T cells were required for triggering and amplification of B cell activation. A positive-feedback loop of mutual activation between B cells, not necessarily antigen-experienced but with integral phosphatidylinositol-3 kinase (PI3K) pathway and a peculiar interferon-γ-producing CD4highT cell subset was established. Programed death-ligand 2 (PD-L2), expressed both on B and the highly activated CD4high T cells, contributed to the increase of interferon-γ recall response through a PD1-independent pathway. In B cell-deficient mice, interferon-γ production and activation of Ag85B-specific CD4+ T cells were blunted against ex vivo antigen recall but these responses could be restored by adding B cells. On the other hand, B cells appeared to down-regulate interleukin-22 recall response. Our data point out that nature of antigen presenting cells determines quality and size of T cell cytokine recall responses. Thus, antigen presenting cells, including B cells, deserve to be considered for a better prediction of cytokine responses by peripheral memory T cells specific for M. tuberculosis antigens. We also invite to consider B cells, PD-L2 and PI3K as potential targets for therapeutic modulation of T cell cytokine responses for tuberculosis control.

Prospects in Mycobacterium bovis Bacille Calmette et Guérin (BCG) vaccine diversity and delivery: why does BCG fail to protect against tuberculosis?

Mycobacterium tuberculosis (M.tb) infection leads to active tuberculosis (TB), a disease that kills one human every 18s. Current therapies available to combat TB include chemotherapy and the preventative vaccine Mycobacterium bovis Bacille Calmette et Guérin (BCG). Increased reporting of drug resistant M.tb strains worldwide indicates that drug development cannot be the primary mechanism for eradication. BCG vaccination has been used globally for protection against childhood and disseminated TB, however, its efficacy at protecting against pulmonary TB in adult and aging populations is highly variable. In this regard, the immune response generated by BCG vaccination is incapable of sterilizing the lung post M.tb infection as indicated by the large proportion of individuals with latent TB infection that have received BCG. Although many new TB vaccine candidates have entered the development pipeline, only a few have moved to human clinical trials; where they showed no efficacy and/or were withdrawn due to safety regulations. These trials highlight our limited understanding of protective immunity against the development of active TB. Here, we discuss current vaccination strategies and their impact on the generation and sustainability of protective immunity against TB.

Association of quantitative interferon-γ responses with the progression of naturally acquired Mycobacterium bovis infection in wild European badgers (Meles meles)

Bovine tuberculosis is one of the biggest challenges facing cattle farming in Great Britain. European badgers (Meles meles) are a reservoir host for the causal agent, Mycobacterium bovis. There have been significant recent advances in diagnostic testing for tuberculosis in humans, cattle and badgers, with the development of species-specific assays for interferon-γ (IFN-γ), an important cytokine in tuberculous infections. Using data collected from longitudinal studies of naturally infected wild badgers, we report that the magnitude of the IFN-γ response to M. bovis antigens at the disclosing test event was positively correlated with subsequent progression of disease to a seropositive or excreting state. In addition, we show that the magnitude of the IFN-γ response, despite fluctuation, declined with time after the disclosing event for all badgers, but remained significantly higher in those animals with evidence of disease progression. We discuss how our findings may be related to the immunopathogenesis of natural M. bovis infection in badgers.

Oral bacillus Calmette-Guérin vaccine against tuberculosis: why not?

The bacillus Calmette-Guérin (BCG) vaccine is the only licensed vaccine for human use against tuberculosis (TB). Although controversy exists about its efficacy, the BCG vaccine is able to protect newborns and children against disseminated forms of TB, but fails to protect adults against active forms of TB. In the last few years, interest in the mucosal delivery route for the vaccine has been increasing owing to its increased capacity to induce protective immune responses both in the mucosal and the systemic immune compartments. Here, we show the importance of this route of vaccination in newly developed vaccines, especially for vaccines against TB.

Comparison of BCG prime-DNA booster and rBCG regimens for protection against tuberculosis

Developing an effective adult prophylaxis vaccine is a high priority in the global control of tuberculosis (TB), because TB remains an important public health problem and the current widely used BCG vaccine provides effective protection only for children but variable protection against adult TB. BCG priming-heterologous vaccines booster and recombinant BCG technologies have been thought as two important regimens for inducing effective protection against adult TB. Obviously, defining the protective efficacy of the two regimens would benefit more rational design of the future adult TB vaccines. In this study, a recombinant BCG strain (rBCG::685A) expressing the fusion protein of ESAT-6 and Ag85A (r685A) of Mycobacterium tuberculosis was constructed successfully and the secretion of r685A protein from rBCG strain was confirmed by western blotting with anti-ESAT-6 and anti-Ag85A polyclonal antibodies, respectively. The immune responses and protective effects in rBCG::685A vaccinated C57BL/6 mice were compared with that of our previous reported BCG prime-pcD685A booster regimen. Boosting BCG with pcD685A DNA elicited higher level of r685A protein specific IFN-γ secreted by splenocytes and a more significant increase of both TNF-α and iNOS responses in the lung, thus providing better control of bacterial growth in both lung and spleen of immunized mice challenged with virulent M. tuberculosis, compared with mice vaccinated with rBCG::685A or BCG alone. Our results have implications for development of more effective adult TB vaccines for improved control of TB.

A novel recombinant DNA vaccine encoding Mycobacterium tuberculosis ESAT-6 and FL protects against Mycobacterium tuberculosis challenge in mice

Mycobacterium tuberculosis 6-kDa early secretory antigenic target (ESAT-6) is a dominant target antigen for cell-mediated immunity in the early phase of tuberculosis. The fms-like tyrosine kinase 3 ligand (FL) that induces potent immune response has been used as an adjuvant in vaccine development. In this study, a new recombinant plasmid (pIRES-epitope-peptides-FL) encoding three T cell epitopes of ESAT-6 and FL was constructed, and the immunogenicity of the DNA vaccine was assessed in C57BL/6 mice immunized with the plasmid DNA vaccine. Additionally, a strategy of intramuscular injection with the DNA vaccine (prime) and intranasal administration of the epitope peptides (boost) was employed to induce higher immune reaction of the mice. The results showed that mice vaccinated with the recombinant plasmid DNA vaccine and boosted with the peptides not only increased the levels of Th1 cytokines (IFN-γ and IL-12), the number of IFN-γ⁺ T cells and activities of cytotoxic T lymphocytes as well as IgG, but also enhanced protection against Mycobacterium tuberculosis challenge. In conclusion, these data indicate that the novel recombinant pIRES-epitope-peptides-FL plasmid is a useful DNA vaccine for preventing Mycobacterium tuberculosis infection.

Environmental effects on protection against Mycobacterium tuberculosis after immunization with Ad85A

Previously we have shown that intradermal (i.d.) immunization with a recombinant adenovirus expressing antigen 85A (Ad85A) induced a strong splenic CD8T cell response in BALB/c mice but a weak lung immune response and did not protect mice against challenge with Mycobacterium tuberculosis (Mtb). After moving to a new animal house, the same i.d. immunization induced a strong lung immune response and the mice were protected against Mtb challenge. Increased numbers of antigen 85A-specific CD8 cells were present in lung tissue but were not recoverable by bronchoalveolar lavage (BAL). Mycobacterial growth was inhibited 21 days after Mtb challenge. In contrast, the effects of intranasal (i.n.) immunization did not change between the animal houses; 85A-specific T cells were recovered by BAL and were able to inhibit Mtb growth early after challenge. The effect of alterations to the environment was investigated by administering BCG or Mycobacterium abscessus in the drinking water, which induced protection against Mtb challenge, while Mycobacterium smegmatis did not. However, when Ad85A was given i.d. at the same time as BCG or M. abscessus, but not M. smegmatis, the protection induced by Ad85A was abolished. Treatment of mice with a CD25 antibody during the challenge period, abolished the suppressive effect of oral mycobacterial administration, suggesting that regulatory T cells (T regs) were involved. These results showed that exposure to environmental microorganisms can alter the protective immune response to a parenterally administered subunit vaccine, a result with important implications for the use of such vaccines in humans.

Lymph node targeting of BCG vaccines amplifies CD4 and CD8 T-cell responses and protection against Mycobacterium tuberculosis

Vaccination with Mycobacterium bovis BCG provides limited protection against pulmonary tuberculosis and a risk of dissemination in immune-compromised vaccinees. For the development of new TB vaccines that stimulate strong T-cell responses a variety of strategies is being followed, especially recombinant BCG and attenuated M. tuberculosis. The objective of the current study was to test potential benefits of vaccination through direct lymph-node targeting of wildtype BCG; the recommended route of vaccination with BCG is intradermal. C57BL/6 mice were immunised with BCG by intradermal, subcutaneous or intralymphatic injections. Cellular immune responses and protection against M. tuberculosis were determined. Intralymphatic vaccination was 100-1000 times more effective in stimulating BCG-specific immune responses than intradermal or subcutaneous immunisation. Intralymphatic administration stimulated high frequencies of mycobacterium-specific lymphocytes with strong proliferating capacity and production of TNF-α, IL-2, IL-17 and, especially, IFN-γ secretion by. CD4 and CD8 T cells. Most importantly, intralymphatic vaccination with 2×10(3)CFU BCG induced sustained protection against M. tuberculosis in intratracheally challenged C57BL/6 mice, whereas subcutaneous vaccination with 2×10(5)CFU BCG conferred only a transient protection. Hence, direct administration of M. bovis BCG to lymph nodes demonstrates that efficient targeting to lymph nodes may help to overcome the efficacy problems of vaccination with BCG.

Vaccination with a BCG strain overexpressing Ag85B protects cattle against Mycobacterium bovis challenge

Mycobacterium bovis is the causative agent of tuberculosis in cattle but also infects other animals, including humans. Previous studies in cattle have demonstrated that the protection induced by BCG is not complete. In order to improve the protection efficacy of BCG, in this study we overexpressed Ag85B in a BCG Pasteur strain, by using an expression system based on the use of an auxotrophic strain for the leucine amino acid, and complementation with leuD. We found that vaccination of cattle with BCG overexpressing Ag85B induced higher production of IL-17 and IL-4 mRNA upon purified protein derivative (PPDB) stimulation of peripheral blood mononuclear cells (PBMCs) than vaccination with BCG. Moreover, the IL-17 mRNA expression after vaccination negatively correlated with disease severity resulting from a subsequent challenge with M. bovis, suggesting that this cytokine is a potential biomarker of cattle protection against bovine tuberculosis. Importantly, vaccination with the recombinant BCG vaccine protected cattle better than the wild-type BCG Pasteur.

Roles and underlying mechanisms of ESAT-6 in the context of Mycobacterium tuberculosis-host interaction from a systems biology perspective

The 6kDa early secreted antigenic target (ESAT-6), an important and intensively studied virulence factor of Mycobacterium tuberculosis, acts alone or in combination with CFP-10 to influence the outcome of the host-pathogen interaction. Secreted ESAT-6 can disturb the activation of macrophages, induce apoptosis and subvert host immunity. ESAT-6 mediated autophagosome formation and TLR signaling deviation lead to abnormal activation of NF-κB and subsequent erroneous expression of NF-κB-dependent genes. The C-terminal amino acid residues 90-95 in ESAT-6 are essential for the interaction with host. In-depth appreciation of the multiple roles of ESAT-6 upon host can inform improvements for novel vaccines and diagnostic tools for tuberculosis.

Preclinical evidence for implementing a prime-boost vaccine strategy for tuberculosis

In this review, published peer-reviewed preclinical studies using prime-boost tuberculosis (TB) vaccine regimens in animal challenge models for tuberculosis have been evaluated. These studies have been divided into groups that describe prime-boost vaccine combinations that performed better than, equivalent to, or worse than the currently used BCG vaccine. Review of the data has revealed interesting findings, including that more than half of the published studies using BCG as a prime combined with a novel boost vaccine give better efficacy than BCG alone and that the greatest reduction in Mycobacterium tuberculosis (M.tb.) colonization of animal tissues is provided by viral vectored vaccines delivered intranasally. Careful evaluation of these data should assist in defining the value of prime-boost regimens for advancement into human TB vaccine trials and stimulate the development of criteria for choosing which vaccine candidates should be studied further.

Live attenuated Salmonella vaccines displaying regulated delayed lysis and delayed antigen synthesis to confer protection against Mycobacterium tuberculosis

Live recombinant attenuated Salmonella vaccine (RASV) strains have great potential to induce protective immunity against Mycobacterium tuberculosis by delivering M. tuberculosis antigens. Recently, we reported that, in orally immunized mice, RASV strains delivering the M. tuberculosis early secreted antigenic target 6-kDa (ESAT-6) protein and culture filtrate protein 10 (CFP-10) antigens via the Salmonella type III secretion system (SopE amino-terminal region residues 1 to 80 with two copies of ESAT-6 and one copy of CFP-10 [SopE(Nt80)-E2C]) afforded protection against aerosol challenge with M. tuberculosis. Here, we constructed and evaluated an improved Salmonella vaccine against M. tuberculosis. We constructed translational fusions for the synthesis of two copies of ESAT-6 plus CFP-10 fused to the OmpC signal sequence (OmpC(SS)-E2C) and amino acids 44 to 338 of antigen 85A (Ag85A(294)) flanked by the signal sequence (SS) and C-terminal peptide (CT) of β-lactamase (Bla(SS)-Ag85A(294)-Bla(CT)) to enable delivery via the Salmonella type II secretion system. The genes expressing these proteins were cloned as an operon transcribed from P(trc) into isogenic Asd(+)/MurA(+) pYA3681 lysis vector derivatives with different replication origins (pBR, p15A, pSC101), resulting in pYA4890, pYA4891, and pYA4892 for SopE(Nt80)-E2C/Ag85A(294) synthesis and pYA4893 and pYA4894 for OmpC(SS)-E2C/Ag85A(294) synthesis. Mice orally immunized with the RASV χ11021 strain engineered to display regulated delayed lysis and regulated delayed antigen synthesis in vivo and harboring pYA4891, pYA4893, or pYA4894 elicited significantly greater humoral and cellular immune responses, and the RASV χ11021 strain afforded a greater degree of protection against M. tuberculosis aerosol challenge in mice than RASVs harboring any other Asd(+)/MurA(+) lysis plasmid and immunization with M. bovis BCG, demonstrating that RASV strains displaying regulated delayed lysis with delayed antigen synthesis resulted in highly immunogenic delivery vectors for oral vaccination against M. tuberculosis infection.

Immunogenicity and protective efficacy of a fusion protein vaccine consisting of antigen Ag85B and HspX against Mycobacterium tuberculosis infection in mice

Subunit vaccines have the potential advantage to boost Mycobacterium bovis Bacillus Calmette-Guérin (BCG)-primed immunity in adults. However, most candidates are antigens highly expressed in replicating bacilli but not in dormant or persisting bacilli, which exist during Mycobacterium tuberculosis infection. We constructed M. tuberculosis fusion protein Ag85B-Mpt64(190-198) -HspX (AMH) and Ag85B-Mpt64(190-198) -Mtb8.4 (AMM), which consist of Ag85B, the 190-198 peptide of Mpt64, HspX (Rv2031c) and Mtb8.4 (Rv1174c), respectively. AMH and/or AMM were mixed with adjuvants composed of dimethyl-dioctyldecyl ammonium bromide and BCG polysaccharide nucleic acid (DDA-BCG PSN) to construct subunit vaccines. Mice were immunized thrice with Ag85B, AMH and AMM vaccines and the immunogenicity of the fusion protein vaccines was determined. Then, mice were primed with BCG and boosted twice with Ag85B, AMH, AMM and AMM + AMH vaccines, respectively, followed by challenging with M. tuberculosis virulent strain H37Rv, and the immune responses and protective effects were measured. It was found that mice immunized with AMH vaccine generated high levels of antigen-specific cell-mediated responses. Compared with the group injected only with BCG, the mice boosted with AMM, AMH and AMM + AMH produced higher levels of Ag85B-specific IgG1 and IgG2a and IFN-γ-secreting T cells upon Ag85B and Mycobacterium tuberculosis purified protein derivative (PPD) stimulation. It is interesting that only mice boosted with AMM + AMH had significantly lower bacterial count in the lungs than those receiving BCG, whereas mice boosted with AMH or AMM did not. The results suggest that AMH consisting of HspX, the antigen highly expressed in dormant bacilli, could be combined with antigens from replicating bacilli to enhance BCG primed immunity so as to provide better protection against both growing and non-growing bacteria that occur during the infection process.

[From genetics to genomics in the rational design of new Mycobacterium tuberculosis vaccines]

Tuberculosis (TB) is an infectious disease affecting people from all ages all over the world. It is estimated that one third of the world population lives infected with the causal agent: Mycobacterium tuberculosis. Despite availability and systematic administration of BCG vaccine in endemic areas, TB transmission remains elusive to control, partly because BGC efficacy has been shown to have wide variability (0-80%). Such variability in protection is attributed to factors including: the BCG strain used for immunization, pre-existing exposure to environmental saprophytic Mycobacterium species, and host genetic factors. In this context, efforts regarding to re-engineering BCG vaccines with the ability to prevent latent TB reactivation, providing long lasting protection, and devoid from collateral effects in immunosuppressed people are urgent. In this work we review the actual molecular «gene-by-gene» strategies aimed at generating BCG alternatives, and discuss the urgent necessity of high throughput technology methods for a rational design for a new TB vaccine.

Recombinant HBHA boosting effect on BCG-induced immunity against Mycobacterium tuberculosis infection

Heterologous prime-boost regimens are effective strategies to promote long-term memory and strong cellular Th1 responses to Mycobacterium tuberculosis, when BCG is used in the priming step. Subcutaneous or intranasal boosting of BCG-vaccinated newborn mice with native heparin-binding haemagglutinin (nHBHA) significantly enhances protection against M. tuberculosis. However, nHBHA is characterized by a complex methylation pattern in its C-terminal domain, which is important for protective immunogenicity in primary vaccination. In this study we addressed the question whether boosting with recombinant, non-methylated HBHA (rHBHA) produced in Escherichia coli may enhance protection of BCG-primed newborn mice. We found that while subcutaneous rHBHA boosting enhanced protection of BCG-primed mice against intranasal M. tuberculosis infection both in spleen and lungs, enhanced protection against aerosol infection was only seen in the spleen (0.72 logs; P < 0.05) but not in the lungs. Thus, in BCG-primed mice the methylation of the C-terminal domain of HBHA is dispensable for the induction of enhanced protection in the lungs against intranasal but not aerosol infection, whereas it enhances protection in the spleen in both challenge models. This report thus provides evidence that rHBHA may be considered as a booster vaccine against disseminated tuberculosis.

Proteomic profile of culture filtrate from the Brazilian vaccine strain Mycobacterium bovis BCG Moreau compared to M. bovis BCG Pasteur

Background

Bacille Calmette-Guerin (BCG) is currently the only available vaccine against tuberculosis (TB) and comprises a heterogeneous family of sub-strains with genotypic and phenotypic differences. The World Health Organization (WHO) affirms that the characterization of BCG sub-strains, both on genomic and proteomic levels, is crucial for a better comprehension of the vaccine. In addition, these studies can contribute in the development of a more efficient vaccine against TB. Here, we combine two-dimensional electrophoresis (2DE) and mass spectrometry to analyse the proteomic profile of culture filtrate proteins (CFPs) from M. bovis BCG Moreau, the Brazilian vaccine strain, comparing it to that of BCG Pasteur. CFPs are considered of great importance given their dominant immunogenicity and role in pathogenesis, being available for interaction with host cells since early infection.

Results

The 2DE proteomic map of M. bovis BCG Moreau CFPs in the pH range 3 - 8 allowed the identification of 158 spots corresponding to 101 different proteins, identified by MS/MS. Comparison to BCG Pasteur highlights the great similarity between these BCG strains. However, quantitative analysis shows a higher expression of immunogenic proteins such as Rv1860 (BCG1896, Apa), Rv1926c (BCG1965c, Mpb63) and Rv1886c (BCG1923c, Ag85B) in BCG Moreau when compared to BCG Pasteur, while some heat shock proteins, such as Rv0440 (BCG0479, GroEL2) and Rv0350 (BCG0389, DnaK), show the opposite pattern.

Conclusions

Here we report the detailed 2DE profile of CFPs from M. bovis BCG Moreau and its comparison to BCG Pasteur, identifying differences that may provide relevant information on vaccine efficacy. These findings contribute to the detailed characterization of the Brazilian vaccine strain against TB, revealing aspects that may lead to a better understanding of the factors leading to BCG's variable protective efficacy against TB.

Oral delivery of BCG Moreau Rio de Janeiro gives equivalent protection against tuberculosis but with reduced pathology compared to parenteral BCG Danish vaccination

There is a need for an improved vaccine to better control human tuberculosis (TB), as the only currently available TB vaccine, bacillus Calmette-Guerin (BCG) delivered parenterally, offers variable levels of efficacy. Therefore, recombinant strains expressing additional antigens are being developed alongside alternative routes to parenteral delivery. There is strong evidence that BCG Moreau (RdJ) is a safe and effective vaccine in humans when given by the oral route. This study compared the efficacy of a single oral dose of wild type BCG Moreau Rio de Janeiro (RdJ), or a recombinant RdJ strain expressing Ag85B-ESAT6 fusion protein, formulated with and without lipid to enhance oral delivery, with subcutaneous BCG Danish 1331 and saline control groups in a guinea pig aerosol infection model of pulmonary tuberculosis. Protection was measured as survival at 30 weeks post-challenge and reduced bacterial load and histopathology in lungs and spleen. Results showed that a single oral dose of BCG Moreau (RdJ) or recombinant BCG Moreau (RdJ)-Ag85B-ESAT6, formulated with or without lipid, gave protection equivalent to subcutaneously delivered BCG Danish in the 30 weeks post-challenge survival study. The orally delivered vaccines gave reduced pathology scores in the lungs (three of the four formulations) and spleens (all four formulations) compared to subcutaneously delivered BCG Danish. The oral wild type BCG Moreau (RdJ) in lipid and the unformulated oral wild type BCG Moreau (RdJ) vaccine also gave statistically lower bacterial loads in the lungs and spleens, respectively, compared to subcutaneously delivered BCG Danish. This study provides further evidence to show that lipid formulation does not impair vaccine efficacy and may enhance the delivery and stability of oral vaccines intended for use in countries with poor health infrastructure. Oral delivery also avoids needles (and associated cross-infection risks) and immunisation without the need for specially trained medical professional staff.

Time dependent expression of cytokines in Mycobacterium bovis infected cattle lymph nodes

Advancements in the current diagnostic and vaccination protocols employed against bovine tuberculosis rely heavily upon a sound knowledge of the bovine immunological response. Central to this is the importance of timing in the cellular immune profile and how this dynamic process evolves post-Mycobacterium bovis challenge. In the present study, we quantitatively analysed mRNA expression of interferon gamma (IFN-γ), tumour necrosis factor alpha (TNF-α) and interleukins (IL) 4 and 10 within select thoracic lymph nodes of cattle infected with M. bovis for 5, 12 and 19 weeks as compared to non-infected bovine tissues. The M. bovis infected lymph nodes displayed significantly higher expression levels of IFN-γ and TNF-α as compared to the non-infected lymph node tissues. This, in conjunction with undetectable levels of IL4, suggests a pro-inflammatory cytokine response. However a significant increase was also detected in IL10 mRNA which is consistent with a described aspect of T(H)1 type T cells in Leishmania infection, a 'self-limiting' process in which cells produced both IFN-γ and IL10 with the aim of controlling the heightened immunopathological responses. This was further reflected when comparing the cytokine profiles of the individual lymph node types, as those displaying a higher IFN-γ/IL10 ratio also had a greater level of gross pathology. This data highlights the important role of IL10 in the bovine response to M. bovis infection and supports its involvement as an immunological marker of disease progression.

Induction of neutralizing antibody responses to anthrax protective antigen by using influenza virus vectors: implications for disparate immune system priming pathways

Viral vectors based on influenza virus, rabies virus (RV), and vaccinia virus (VV) were used to express large polypeptide segments derived from the Bacillus anthracis protective antigen (PA). For the infectious influenza virus vector and recombinant VV constructs, the receptor binding domain (RBD or domain 4) or the lethal and edema factor binding domain (LEF or domain 1') were engineered into functional chimeric hemagglutinin (HA) glycoproteins. In the case of the RV vector, the viral glycoprotein (G) was used as a carrier for RBD in an inactivated form of the vector. These constructs were examined by using multiple homologous and heterologous prime/boost immunization regimens in order to optimize the induction of alpha-PA antibody responses. Several immunization combinations were shown to induce high titers of antibody recognizing the anthrax RBD and LEF domains, as well as the full-length PA protein in mice. The heterologous prime/boost immunization regimens that involved an initial intranasal administration of a live influenza virus vector, followed by an intramuscular boost with either the killed RV vector or the VV vector, were particularly effective, inducing antigen-specific antibodies at levels severalfold higher than homologous or alternative heterologous protocols. Furthermore, sera from several groups of the immunized mice demonstrated neutralization activity in an in vitro anthrax toxin neutralization assay. In some cases, such toxin-neutralizing activity was notably high, indicating that the mechanisms by which immunity is primed by live influenza virus vectors may have beneficial properties.

Adjuvants in tuberculosis vaccine development

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

Transient facial nerve paralysis (Bell's palsy) following intranasal delivery of a genetically detoxified mutant of Escherichia coli heat labile toxin

Background

An association was previously established between facial nerve paralysis (Bell's palsy) and intranasal administration of an inactivated influenza virosome vaccine containing an enzymatically active Escherichia coli Heat Labile Toxin (LT) adjuvant. The individual component(s) responsible for paralysis were not identified, and the vaccine was withdrawn.

Methodology/Principal Findings

Subjects participating in two contemporaneous non-randomized Phase 1 clinical trials of nasal subunit vaccines against Human Immunodeficiency Virus and tuberculosis, both of which employed an enzymatically inactive non-toxic mutant LT adjuvant (LTK63), underwent active follow-up for adverse events using diary-cards and clinical examination. Two healthy subjects experienced transient peripheral facial nerve palsies 44 and 60 days after passive nasal instillation of LTK63, possibly a result of retrograde axonal transport after neuronal ganglioside binding or an inflammatory immune response, but without exaggerated immune responses to LTK63.

Conclusions/Significance

While the unique anatomical predisposition of the facial nerve to compression suggests nasal delivery of neuronal-binding LT–derived adjuvants is inadvisable, their continued investigation as topical or mucosal adjuvants and antigens appears warranted on the basis of longstanding safety via oral, percutaneous, and other mucosal routes.

Frequencies of region of difference 1 antigen-specific but not purified protein derivative-specific gamma interferon-secreting T cells correlate with the presence of tuberculosis disease but do not distinguish recent from remote latent infections

The majority of individuals infected with Mycobacterium tuberculosis achieve lifelong immune containment of the bacillus. What constitutes this effective host immune response is poorly understood. We compared the frequencies of gamma interferon (IFN-gamma)-secreting T cells specific for five region of difference 1 (RD1)-encoded antigens and one DosR-encoded antigen in 205 individuals either with active disease (n = 167), whose immune responses had failed to contain the bacillus, or with remotely acquired latent infection (n = 38), who had successfully achieved immune control, and a further 149 individuals with recently acquired asymptomatic infection. When subjects with an IFN-gamma enzyme-linked immunospot (ELISpot) assay response to one or more RD1-encoded antigens were analyzed, T cells from subjects with active disease recognized more pools of peptides from these antigens than T cells from subjects with nonrecent latent infection (P = 0.002). The T-cell frequencies for peptide pools were greater for subjects with active infection than for subjects with nonrecent latent infection for summed RD1 peptide pools (P <or= 0.006) and culture filtrate protein 10 (CFP-10) antigen (P = 0.029). Individuals with recently acquired (<6 months) versus remotely acquired (>6 months) latent infection did not differ in numbers of peptide pools recognized, proportions recognizing any individual antigen or peptide pool, or antigen-specific T-cell frequencies (P >or= 0.11). The hierarchy of immunodominance for different antigens was purified protein derivative (PPD) > CFP-10 > early secretory antigenic target 6 > Rv3879c > Rv3878 > Rv3873 > Acr1, and the hierarchies were very similar for active and remotely acquired latent infections. Responses to the DosR antigen alpha-crystallin were not associated with latency (P = 0.373). In contrast to the RD1-specific responses, the responses to PPD were not associated with clinical status (P > 0.17) but were strongly associated with positive tuberculin skin test results (>or=15-mm induration; P <or= 0.01). Our results suggest that RD1-specific IFN-gamma-secreting T-cell frequencies correlate with the presence of disease rather than with protective immunity in M. tuberculosis-infected individuals and do not distinguish recently acquired asymptomatic infection from remotely acquired latent infection.

Mycobacterium tuberculosis culture filtrate proteins plus CpG Oligodeoxynucleotides confer protection to Mycobacterium bovis BCG-primed mice by inhibiting interleukin-4 secretion

Culture filtrate proteins (CFP) are potential targets for tuberculosis vaccine development. We previously showed that despite the high level of gamma interferon (IFN-gamma) production elicited by homologous immunization with CFP plus CpG oligodeoxynucleotides (CFP/CpG), we did not observe protection when these mice were challenged with Mycobacterium tuberculosis. In order to use the IFN-gamma-inducing ability of CFP antigens, in this study we evaluated a prime-boost heterologous immunization based on CFP/CpG to boost Mycobacterium bovis BCG vaccination in order to find an immunization schedule that could induce protection. Heterologous BCG-CFP/CpG immunization provided significant protection against experimental tuberculosis, and this protection was sustained during the late phase of infection and was even better than that conferred by a single BCG immunization. The protection was associated with high levels of antigen-specific IFN-gamma and interleukin-17 (IL-17) and low IL-4 production. The deleterious role of IL-4 was confirmed when IL-4 knockout mice vaccinated with CFP/CpG showed consistent protection similar to that elicited by BCG-CFP/CpG heterologous immunization. These findings show that a single dose of CFP/CpG can represent a new strategy to boost the protection conferred by BCG vaccination. Moreover, different immunological parameters, such as IFN-gamma and IL-17 and tightly regulated IL-4 secretion, seem to contribute to the efficacy of this tuberculosis vaccine.

Recombinant Mycobacterium bovis BCG

The Bacillus Calmette-Guerin (BCG) is an attenuated strain of Mycobacterium bovis that has been broadly used as a vaccine against human tuberculosis. This live bacterial vaccine is able to establish a persistent infection and induces both cellular and humoral immune responses. The development of mycobacterial genetic systems to express foreign antigens and the adjuvanticity of BCG are the basis of the potential use of this attenuated mycobacterium as a recombinant vaccine. Over the years, a range of strategies has been developed to allow controlled and stable expression of viral, bacterial and parasite antigens in BCG. Herein, we review the strategies developed to express heterologous antigens in BCG and the immune response elicited by recombinant BCG constructs. In addition, the use of recombinant BCG as an immunomodulator and future perspectives of BCG as a recombinant vaccine vector are discussed.