Boosting with a DNA vaccine expressing ESAT-6 (DNAE6) obliterates the protection imparted by recombinant BCG (rBCGE6) against aerosol Mycobacterium tuberculosis infection in guinea pigs

Immunological Characterization of Proteins Expressed by Genes Located in Mycobacterium tuberculosis-Specific Genomic Regions Encoding the ESAT6-like Proteins

The 6 kDa early secreted antigen target (ESAT6) is a low molecular weight and highly immunogenic protein of Mycobacterium tuberculosis with relevance in the diagnosis of tuberculosis and subunit vaccine development. The gene encoding the ESAT6 protein is located in the M. tuberculosis-specific genomic region known as the region of difference (RD)1. There are 11 M. tuberculosis-specific RDs absent in all of the vaccine strains of BCG, and three of them (RD1, RD7, and RD9) encode immunodominant proteins. Each of these RDs has genes for a pair of ESAT6-like proteins. The immunological characterizations of all the possible proteins encoded by genes in RD1, RD7 and RD9 have shown that, besides ESAT-6 like proteins, several other proteins are major antigens useful for the development of subunit vaccines to substitute or supplement BCG. Furthermore, some of these proteins may replace the purified protein derivative of M. tuberculosis in the specific diagnosis of tuberculosis by using interferon-gamma release assays and/or tuberculin-type skin tests. At least three subunit vaccine candidates containing ESAT6-like proteins as antigen components of multimeric proteins have shown efficacy in phase 1 and phase II clinical trials in humans.

Tuberculosis vaccine candidates based on mycobacterial cell envelope components

Even after decades searching for a new and more effective vaccine against tuberculosis, the scientific community is still pursuing this goal due to the complexity of its causative agent, Mycobacterium tuberculosis (Mtb). Mtb is a microorganism with a robust variety of survival mechanisms that allow it to remain in the host for years. The structure and nature of the Mtb envelope play a leading role in its resistance and survival. Mtb has a perfect machinery that allows it to modulate the immune response in its favor and to adapt to the host's environmental conditions in order to remain alive until the moment to reactivate its normal growing state. Mtb cell envelope protein, carbohydrate and lipid components have been the subject of interest for developing new vaccines because most of them are responsible for the pathogenicity and virulence of the bacteria. Many indirect evidences, mainly derived from the use of monoclonal antibodies, support the potential protective role of Mtb envelope components. Subunit and DNA vaccines, lipid extracts, liposomes and membrane vesicle formulations are some examples of technologies used, with encouraging results, to evaluate the potential of these antigens in the protective response against Mtb.

Guinea pig models for translation of the developmental origins of health and disease hypothesis into the clinic

Over 30 years ago Professor David Barker first proposed the theory that events in early life could explain an individual's risk of non-communicable disease in later life: the developmental origins of health and disease (DOHaD) hypothesis. During the 1990s the validity of the DOHaD hypothesis was extensively tested in a number of human populations and the mechanisms underpinning it characterised in a range of experimental animal models. Over the past decade, researchers have sought to use this mechanistic understanding of DOHaD to develop therapeutic interventions during pregnancy and early life to improve adult health. A variety of animal models have been used to develop and evaluate interventions, each with strengths and limitations. It is becoming apparent that effective translational research requires that the animal paradigm selected mirrors the tempo of human fetal growth and development as closely as possible so that the effect of a perinatal insult and/or therapeutic intervention can be fully assessed. The guinea pig is one such animal model that over the past two decades has demonstrated itself to be a very useful platform for these important reproductive studies. This review highlights similarities in the in utero development between humans and guinea pigs, the strengths and limitations of the guinea pig as an experimental model of DOHaD and the guinea pig's potential to enhance clinical therapeutic innovation to improve human health.

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.

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.

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

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

Lactococcus lactis carrying a DNA vaccine coding for the ESAT-6 antigen increases IL-17 cytokine secretion and boosts the BCG vaccine immune response

AIMS

A regimen utilizing Bacille Calmette-Guerin (BCG) and another vaccine system as a booster may represent a promising strategy for the development of an efficient tuberculosis vaccine for adults. In a previous work, we confirmed the ability of Lactococcus lactis fibronectin-binding protein A (FnBPA+) (pValac:ESAT-6), a live mucosal DNA vaccine, to produce a specific immune response in mice after oral immunization. In this study, we examined the immunogenicity of this strain as a booster for the BCG vaccine in mice.

METHODS AND RESULTS

After immunization, cytokine and immunoglobulin profiles were measured. The BCG prime L. lactis FnBPA+ (pValac:ESAT-6) boost group was the most responsive group, with a significant increase in splenic pro-inflammatory cytokines IL-17, IFN-γ, IL-6 and TNF-α compared with the negative control.

CONCLUSIONS

Based on the results obtained here, we demonstrated that L. lactis FnBPA+ (pValac:ESAT-6) was able to increase the BCG vaccine general immune response.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work is of great scientific and social importance because it represents the first step towards the development of a booster to the BCG vaccine using L. lactis as a DNA delivery system.

Immunogenicity and protective efficacy of recombinant Bacille Calmette-Guerin strains expressing mycobacterium antigens Ag85A, CFP10, ESAT-6, GM-CSF and IL-12p70

OBJECTIVE

This study aimed to evaluate the immunogenicity and protective efficacy of recombinant bacille calmette-guerin (rBCG) strains expressing Ag85A (A), CFP10 (C), ESAT6 (E), IL-12p70 (I), and fusion protein GM-CSF (G).

METHOD

rBCGs were established by integrating of A, C, E, I, G, AE, CE, IE, GC, GE and GCE into Mycobacterium bovis BCG-1173 and BCG-SH. The macro-effects of rBCGs on mice were evaluated by phenotype and weight. The immunogenicity of rBCGs was analyzed by lgG, lgG1 and lgG2a antibody titers, and IFN-γ and IL-4 contents through Enzyme-linked immunosorbent assay (ELISA). Meanwhile, the proportions of CD4⁺ and CD8⁺ T splenic lymphocytes were determined using flow cytometry. The protective efficacy of rBCGs was evaluated by bacterial load in spleen and lung tissues from immunized mice.

RESULTS

rBCGs exhibited no obvious side effects on mice. The antibody titers of lgG, lgG1 and lgG2a, proportion of CD4⁺ and CD8⁺ T cells, and concentrations of IFN-γ were found to be significantly higher in multiple-gene rBCGs than that in single-gene rBCGs (P < 0.05). Bacterial load in both spleen and lung tissues from mice infected with M. tuberculosis H37Rv were significantly reduced by rBCGs. A significantly lower bacterial load was revealed in rBCG-1173:A compared with multiple-gene rBCGs (P < 0.05).

CONCLUSION

Immunogenicity was better on multiple-gene rBCGs than on single-gene rBCGs, while excellent protective efficacy was exhibited on rBCG-1173:A and BCG-1173.

A comparative approach to strategies for cloning, expression, and purification of Mycobacterium tuberculosis mycolyl transferase 85B and evaluation of immune responses in BALB/c mice

Protein antigens have drawn a lot of attention from investigators working on tuberculosis vaccines. These proteins can be used to improve the immunogenicity of the new generation BCG vaccines or even replace them completely. Recombinant technology is used to insure the production of pure mycobacterial antigens in high quantities. Mycolyl transferase 85B (Ag85B) is a potent, mycobacterial antigen that significantly stimulates immune responses. Since Ag85B is an apolar protein, production of the water-soluble antigen is of interest. In this work, we report a systematic optimization strategy concerning cloning systems and purification methods, aiming at increasing the yield of recombinant Ag85B. Our optimized method resulted in a yield of 8 mg of recombinant Ag85B from 1 liter of induced culture (400 μg/ml) by using pET32a(+), Escherichia coli Rosseta-gami™(DE3) pLysS and a Ni-NTA agarose-based procedure and on-column re-solubilization. The purified recombinant Ag85B showed strong immunostimulating properties by inducing high levels of TNF-α, IFN-γ, IL-12, and IgG2a in immunized mice, therefore it can effectively be applied in TB vaccine researches.

Recombinant BCG: Innovations on an Old Vaccine. Scope of BCG Strains and Strategies to Improve Long-Lasting Memory

Bacille Calmette-Guérin (BCG), an attenuated vaccine derived from Mycobacterium bovis, is the current vaccine of choice against tuberculosis (TB). Despite its protection against active TB in children, BCG has failed to protect adults against TB infection and active disease development, especially in developing countries where the disease is endemic. Currently, there is a significant effort toward the development of a new TB vaccine. This review article aims to address publications on recombinant BCG (rBCG) published in the last 5 years, to highlight the strategies used to develop rBCG, with a focus on the criteria used to improve immunological memory and protection compared with BCG. The literature review was done in April 2013, using the key words TB, rBCG vaccine, and memory. This review discusses the BCG strains and strategies currently used for the modification of BCG, including: overexpression of Mycobacterium tuberculosis (Mtb) immunodominant antigens already present in BCG; gene insertion of immunodominant antigens from Mtb absent in the BCG vaccine; combination of introduction and overexpression of genes that are lost during the attenuation process of BCG; BCG modifications for the induction of CD8+ T-cell immune responses and cytokines expressing rBCG. Among the vaccines discussed, VPM1002, also called rBCGΔureC:hly, is currently in human clinical trials. Much progress has been made in the effort to improve BCG, with some promising candidates, but considerable work is still required to address functional long-lasting memory.

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.

Immunogenicity and protective efficacy of a novel recombinant BCG strain overexpressing antigens Ag85A and Ag85B

Recombinant Bacillus Calmette-Guérin (rBCG) strain is the promising vaccine candidate for tuberculosis (TB) prevention, which aims at providing more enduring and enhanced protection than the parental BCG vaccine. In this study, three rBCG strains overexpressing immunodominant antigens Ag85B (rBCG::85B), Ag85A (rBCG::85A), or both (rBCG::AB) of Mycobacterium tuberculosis were constructed, respectively. rBCG strains showed higher level of overexpression of Ag85A and/or Ag85B proteins than BCG containing empty vector pMV261(rBCG::261), which had low levels of endogenous expression of both proteins as expected. rBCG::AB strain could provide the strongest short-term and long-term protection in the lung against intravenous infection with virulent M. tuberculosis than rBCG::261 control and other two rBCG strains overexpressing single antigen. The stronger and longer-lasting protection provided by rBCG::AB than rBCG::261 was correlated with systemic in vitro antigen-specific IFN-γ responses. Therefore, our results indicate that rBCG::AB could be a very promising TB vaccine candidate and should be further evaluated for the preclinical test.

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.

Immunogenicity and protective efficacy against murine tuberculosis of a prime-boost regimen with BCG and a DNA vaccine expressing ESAT-6 and Ag85A fusion protein

Heterologous prime-boost regimens utilizing BCG as a prime vaccine probably represent the best hope for the development of novel tuberculosis (TB) vaccines. In this study, we examined the immunogenicity and protective efficacy of DNA vaccine (pcD685A) expressing the fusion protein of Ag85A and ESAT-6 (r685A) and its booster effects in BCG-immunized mice. The recombinant r685A fusion protein stimulated higher level of antigen-specific IFN-γ release in tuberculin skin test- (TST-) positive healthy household contacts of active pulmonary TB patients than that in TST-negative population. Vaccination of C57BL/6 mice with pcD685A resulted in significant protection against challenge with virulent Mycobacterium tuberculosis H37Rv when compared with the control group. Most importantly, pcD685A could act as a BCG booster and amplify Th1-type cell-mediated immunity in the lung of BCG-vaccinated mice as shown the increased expression of IFN-γ. The most significant reduction in bacterial load of both spleen and lung was obtained in mice vaccinated with BCG prime and pcD685A DNA booster when compared with BCG or pcD685A alone. Thus, our study indicates that pcD685A may be an efficient booster vaccine against TB with a strong ability to enhance prior BCG immunity.