Tuberculosis: vaccines in the pipeline

Immunological Interactions between Intestinal Helminth Infections and Tuberculosis

Helminth infections are among the neglected tropical diseases affecting billions of people globally, predominantly in developing countries. Helminths’ effects are augmented by coincident tuberculosis disease, which infects a third of the world’s population. The role of helminth infections on the pathogenesis and pathology of active tuberculosis (T.B.) remains controversial. Parasite-induced suppression of the efficacy of Bacille Calmette-Guerin (BCG) has been widely reported in helminth-endemic areas worldwide. T.B. immune response is predominantly proinflammatory T-helper type 1 (Th1)-dependent. On the other hand, helminth infections induce an opposing anti-inflammatory Th2 and Th3 immune-regulatory response. This review summarizes the literature focusing on host immune response profiles during single-helminth, T.B. and dual infections. It also aims to necessitate investigations into the complexity of immunity in helminth/T.B. coinfected patients since the research data are limited and contradictory. Helminths overlap geographically with T.B., particularly in Sub-Saharan Africa. Each disease elicits a response which may skew the immune responses. However, these effects are helminth species-dependent, where some parasites have no impact on the immune responses to concurrent T.B. The implications for the complex immunological interactions that occur during coinfection are highlighted to inform government treatment policies and encourage the development of high-efficacy T.B. vaccines in areas where helminths are prevalent.

Aerosol immunization by alginate coated mycobacterium (BCG/MIP) particles provide enhanced immune response and protective efficacy than aerosol of plain mycobacterium against M.tb. H37Rv infection in mice

Background

With the aim of preparing a more effective, safe and economical vaccine for tuberculosis, inhalable live mycobacterium formulations were evaluated.

Methods

Alginate particles in the size range of 2–4 μm were prepared by encapsulating live Bacille Calmette–Guérin (BCG) and “Mycobacterium indicus pranii” (MIP). These particles were characterized for their size, stability and release profile. Mice were immunized with liquid aerosol or dry powder aerosol (DPA) alginate encapsulated mycobacterium particles and their in-vitro recall response and infection with mycobacterium H37Rv were investigated.

Results

It was found that the DPA of alginate encapsulated mycobacterium particles invoked superior immune response and provided higher protection in mice than the liquid aerosol. The BCG encapsulated in alginate particles (BEAP) and MIP encapsulated in alginate particles (MEAP) were engulfed by bone marrow dendritic cells (BMDCs) and co-localized with lysosome. The MEAP/BEAP activated BMDCs exhibited higher chemotaxis movement and had enhanced ability of antigen presentation to T cells.

The in-vitro recall response of BEAP/MEAP immunized mice when compared in terms of proliferation index and Interferon gamma (IFN-gamma) released by splenocytes and mediastinal lymph node cells was found to be higher than mice immunized by liquid aerosol of BCG/MIP. Finally, different groups of immunized mice were infected with M. tb H37Rv and after 16 weeks the Colony forming units (CFUs) in lung and spleen estimated. The bacilli burden in the BEAP/MEAP immunized mice was significantly less than the respective liquid aerosol immunized mice and the histopathology of BEAP/MEAP immunized mice lungs showed very little damage.

Conclusions

These inhale-able vaccines formulation of alginate coated live mycobacterium are more immunogenic as compared to the aerosol of bacilli and they provide better protection in mice when infected with H37Rv.

Electronic supplementary material

The online version of this article (10.1186/s12879-019-4157-2) contains supplementary material, which is available to authorized users.

Mycobacterium indicus pranii as a booster vaccine enhances BCG induced immunity and confers higher protection in animal models of tuberculosis

BCG, the only approved vaccine protects against severe form of childhood tuberculosis but its protective efficacy wanes in adolescence. BCG has reduced the incidence of infant TB considerably in endemic areas; therefore prime-boost strategy is the most realistic measure for control of tuberculosis in near future. Mycobacterium indicus pranii (MIP) shares significant antigenic repertoire with Mtb and BCG and has been shown to impart significant protection in animal models of tuberculosis. In this study, MIP was given as a booster to BCG vaccine which enhanced the BCG mediated immune response, resulting in higher protection. MIP booster via aerosol route was found to be more effective in protection than subcutaneous route of booster immunization. Pro-inflammatory cytokines like IFN-γ, IL-12 and IL-17 were induced at higher level in infected lungs of 'BCG-MIP' group both at mRNA expression level and in secretory form when compared with 'only BCG' group. BCG-MIP groups had increased frequency of multifunctional T cells with high MFI for IFN-γ and TNF-α in Mtb infected mice. Our data demonstrate for the first time, potential application of MIP as a booster to BCG vaccine for efficient protection against tuberculosis. This could be very cost effective strategy for efficient control of tuberculosis.

Current perspective in tuberculosis vaccine development for high TB endemic regions

Tuberculosis (TB) continues to be a global epidemic, despite of the availability of Bacillus Calmette Guerin (BCG) vaccine for more than six decades. In an effort to eradicate TB, vaccinologist around the world have made considerable efforts to develop improved vaccine candidates, based on the understanding of BCG failure in developing world and immune response thought to be protective against TB. The present review represents a current perspective on TB vaccination research, including additional research strategies needed for increasing the efficacy of BCG, and for the development of new effective vaccines for high TB endemic regions.

A novel liposome adjuvant DPC mediates Mycobacterium tuberculosis subunit vaccine well to induce cell-mediated immunity and high protective efficacy in mice

Tuberculosis (TB) is a serious disease around the world, and protein based subunit vaccine is supposed to be a kind of promising novel vaccine against it. However, there is no effective adjuvant available in clinic to activate cell-mediated immune responses which is required for TB subunit vaccine. Therefore, it is imperative to develop new adjuvant. Here we reported an adjuvant composed of dimethyl dioctadecylammonium (DDA), Poly I:C and cholesterol (DPC for short). DDA can form a kind of cationic liposome with the ability to deliver and present antigen and can induce Th1 type cell-mediated immune response. Poly I:C, a ligand of TLR3 receptor, could attenuate the pathologic reaction induced by following Mycobacterium tuberculosis challenge. Cholesterol, which could enhance rigidity of lipid bilayer, is added to DDA and Poly I:C to improve the stability of the adjuvant. The particle size and Zeta-potential of DPC were analyzed in vitro. Furthermore, DPC was mixed with a TB fusion protein ESAT6-Ag85B-MPT64(190-198)-Mtb8.4-Rv2626c (LT70) to construct a subunit vaccine. The subunit vaccine-induced immune responses and protective efficacy against M. tuberculosis H37Rv infection in C57BL/6 mice were investigated. The results showed that the DPC adjuvant with particle size of 400 nm and zeta potential of 40 mV was in good stability. LT70 in the adjuvant of DPC generated strong antigen-specific humoral and cell-mediated immunity, and induced long-term higher protective efficacy against M. tuberculosis infection (5.41 ± 0.38log10CFU) than traditional vaccine Bacillus Calmette-Guerin (BCG) (6.01 ± 0.33log10CFU) and PBS control (6.53 ± 0.26log10CFU) at 30 weeks post-vaccination. In conclusion, DPC would be a promising vaccine adjuvant with the ability to stimulate Th1 type cell-mediated immunity, and could be used in TB subunit vaccine.

Prime-boost vaccination strategy with bacillus Calmette-Guérin (BCG) and liposomized alpha-crystalline protein 1 reinvigorates BCG potency

Bacillus Calmette-Guérin (BCG) remains the only available and most widely administered vaccine against Mycobacterium tuberculosis (Mtb), yet it fails to protect vaccinated individuals either from primary infection or reactivation of latent tuberculosis (TB). Despite BCG's variable efficacy against TB, the fact remains that BCG imparts protection in children against the disease, indicating that BCG possesses a wide protective antigenic repertoire. However, its failure to impart protection in adulthood can be linked to its failure to generate long-lived memory response and elicitation of an inadequate immune response against latency-associated antigens. Therefore, to improve the protective efficacy of BCG, a novel vaccination strategy is required. Consequently, in the present study, we have exploited the vaccination potential of liposomized α-crystalline 1 (Acr1L), a latency-associated antigen to induce enduring protective immunity against Mtb in BCG-primed animals. It is noteworthy that an increase in the multi-functional [interferon (IFN)-γ(hi) /tumour necrosis factor (TNF)-α(hi) ] CD4 and CD8 T cells were observed in BCG-primed and Acr1L-boosted (BCG-Acr1L) animals, compared to BCG alone. Further, substantial expansion of both central memory (CD44(hi) /CD62L(hi) ) and effector memory (CD44(hi) /CD62L(lo) ) populations of CD4 and CD8 T cells was noted. Importantly, BCG-Acr1L exhibited significantly better protection than BCG, as evidenced by a reduction in the bacterial burden and histopathological data of the lungs. In essence, BCG-Acr1L could be a potent future vaccination strategy to reinvigorate BCG potency.

An overview of tuberculosis plant-derived vaccines

Tuberculosis (TB) is a leading fatal infectious disease to which the current BCG vaccine has a questionable efficacy in adults. Thus, the development of improved vaccines against TB is needed. In addition, decreasing the cost of vaccine formulations is required for broader vaccination coverage through global vaccination programs. In this regard, the use of plants as biofactories and delivery vehicles of TB vaccines has been researched over the last decade. These studies are systematically analyzed in the present review and placed in perspective. It is considered that substantial preclinical trials are still required to address improvements in expression levels as well as immunological data. Approaches for testing additional antigenic configurations with higher yields and improved immunogenic properties are also discussed.

Global epidemiology of tuberculosis

Despite the availability of effective chemotherapy, tuberculosis (TB) killed 1.3 million people in 2012. Alongside HIV, it remains a top cause of death from an infectious disease. Global targets for reductions in the epidemiological burden of TB have been set for 2015 and 2050 within the context of the Millennium Development Goals (MDGs) and by the Stop TB Partnership. Achieving these targets is the focus of national and international efforts in TB control, and showing whether or not they are achieved is of major importance to guide future and sustainable investments. This article provides a short overview of sources of data to estimate TB disease burden; presents estimates of TB incidence, prevalence, and mortality in 2012 and an assessment of progress toward the 2015 targets for reductions in these indicators based on trends since 1990 and projections up to 2015; analyzes trends in TB notifications and in the implementation of the Stop TB Strategy; and considers prospects for elimination of TB after 2015.

BCG Δzmp1 vaccine induces enhanced antigen specific immune responses in cattle

Mycobacterium bovis (M. bovis) causes major economy and public health problem in numerous countries. In Great Britain, despite the use of a test-and-slaughter strategy, the incidence of bovine tuberculosis (bTB) in cattle has steadily risen in recent years. One strategy being considered to reduce the burden of bTB in cattle is the development of an efficient vaccine. The only current potentially available vaccine against tuberculosis, live attenuated M. bovis bacille Calmette-Guérin (BCG), has demonstrated variable efficacy in both humans and cattle and the development of improved vaccination strategies for cattle is a research priority. In this study we assessed the immunogenicity in cattle of two recombinant BCG strains, namely BCG Pasteur Δzmp1::aph and BCG Danish Δzmp1. By applying a recently defined predictive immune-correlate of protection (T cell memory responses measured by cultured ELISPOT), we have compared these two recombinant BCG with wild-type BCG Danish SSI. Our results demonstrated that both strains induced superior T cell memory responses compared to wild-type BCG. These data provide support for the prioritisation of testing BCG Danish Δzmp1 in vaccination/M. bovis challenge studies to determine its protective efficacy.

Enhanced protection against pulmonary mycobacterial challenge by chitosan-formulated polyepitope gene vaccine is associated with increased pulmonary secretory IgA and gamma-interferon(+) T cell responses

Induction of local (pulmonary) immunity plays a critical role in preventing dissemination of Mycobacterium tuberculosis (M. tb) during the early infection stage. To induce specific mucosal immunity, chitosan, a natural cationic polysaccharide, was employed as a mucosal gene carrier and complexed with pHSP65pep, our previously constructed multi-epitope gene vaccine, which induces splenic gamma-interferon (IFN-γ)(+) T helper cell 1 responses. The resultant chitosan-pHSP65pep was administered intranasally to BALB/c mice with four doses of 50 μg DNA followed by mycobacterial challenge 4 weeks after the final immunization. It was found that the chitosan formulation significantly induced production of secretory immunoglobulin A (P < 0.05) as determined by measuring its concentrations in lung lavage fluid and enhanced pulmonary CD4(+) and CD8(+) IFN-γ(+) T cell responses (P < 0.001) compared with naked gene vaccine. Improved protection against Mycobacterium bovis bacillus Calmette-Guérin (BCG) challenge was consistently achieved by the chitosan-DNA formulation both as the vaccine alone or in a BCG prime-vaccine boost immunization scenario. Our study shows that mucosal delivery of gene vaccine in a chitosan formulation remarkably enhances specific SIgA concentrations and mucosal IFN-γ(+) T cell response, which correlated positively with immunological protection.

Evaluation of the overall IFN-γ and IL-17 pro-inflammatory responses after DNA therapy of tuberculosis

Despite the enormous efforts displayed globally in the fight against tuberculosis, the disease incidence has modified slightly, which has led to a renewed interest in immunotherapy. In general, successful immunotherapeutic candidates against tuberculosis are agents that can trigger strong, specific pro-inflammatory responses, especially of the T-helper (Th) 1 pattern. However, how these pro-inflammatory agents effectively kill the bacteria without eliciting immunopathology is not well understood. We reasoned that, in addition to the specific immune response elicited by immunotherapy, the evaluation of the overall pro-inflammatory responses should provide additional and valuable information that will be useful in avoiding immunopathology. We evaluated the overall IFN-γ and IL-17 pro-inflammatory responses among CD4(+), CD8(+) and γδ T cells in the lungs of mice that were infected with M. tuberculosis and treated with a DNA vaccine in an immunotherapeutic regimen. Our results demonstrate that mice that effectively combat the pathogen develop a strong, specific Th1 immune response against the therapeutic antigen and have reduced lung inflammation, present in parallel a fine-tuning in the total IFN-γ- and IL-17-mediated immunity in the lungs. This modulation of the total immune response involves reducing the Th17 cell population, augmenting CD8(+) T cells that produce IFN-γ and increasing the total γδ T cell frequency. These results stress the importance of a broad evaluation of not only the specific immune response at the time to evaluate new immune interventional strategies against tuberculosis but also non-conventional T cells, such as γδ T lymphocytes.

Sequence and immunogenicity of a clinically approved novel measles virus vaccine vector

The measles virus vaccine (MVbv) is a clinically certified and well-tolerated vaccine strain that has been given both parenterally and mucosally. It has been extensively used in children and has proven to be safe and effective in eliciting protective immunity. This specific strain was therefore chosen to generate a measles viral vector. The genome of the commercial MVbv vaccine strain was isolated, sequenced and a plasmid, p(+)MVb, enabling transcription of the viral antigenome and rescue of MVb, was constructed. Phylogenic and phenotypic analysis revealed that MVbv and the rescued MVb constitute another evolutionary branch within the hitherto classified measles vaccines. Plasmid p(+)MVb was modified by insertion of artificial MV-type transcription units (ATUs) for the generation of recombinant viruses (rMVb) expressing additional proteins. Replication characteristics and immunogenicity of rMVb vectors were similar to the parental MVbv and to other vaccine strains. The expression of the additional proteins was stable over 10 serial virus transfers, which corresponds to an amplification greater than 10 ( 20) . The excellent safety record and its efficient application as aerosol may add to the usefulness of the derived vectors.

Bovine tuberculosis vaccine research: historical perspectives and recent advances

The emergence of wildlife reservoirs of Mycobacterium bovis infection in cattle as well as increased inter-regional trade with associated spread of M. bovis has led to renewed interest in the use of vaccines for the control of bovine tuberculosis (TB). Field efficacy trials performed in the early 20th century demonstrated the partial effectiveness of bacilli Calmette-Guerin (BCG) for the control of bovine TB. Recent experimental trials with cattle have demonstrated that: (1) subunit vaccines may boost immunity elicited by BCG in cattle, (2) T cell central memory immune responses evoked by protective vaccines correlate with protection upon subsequent M. bovis challenge, (3) BCG is particularly protective when administered to neonates, and (4) differentiation of infected from vaccinated animals (DIVA) is feasible in cattle using in vitro or in vivo methods. In regards to wildlife reservoirs, the efficacy of BCG delivered orally has been demonstrated for brushtail possums (in field trials) as well as Eurasian badgers, wild boar, and white-tailed deer (each in experimental challenge studies). Vaccine delivery to wildlife reservoirs will primarily be oral, although a parenteral route is being deployed for badgers in England. Vaccine efficacy trials, both experimental challenge and field studies, with cattle and their wildlife reservoirs represent a primary example of the one health approach, with outcomes relevant for both veterinary and medical applications.

Cellular immune responses in mice induced by M. tuberculosis PE35-DNA vaccine construct

The PE35 (Rv3872) gene of Mycobacterium tuberculosis is present in the region of difference (RD) one that is deleted in all vaccine strains of Mycobacterium bovis bacillus Calmette Guerin. The aim of this study was to clone PE35 DNA into a DNA vaccine plasmid with CMV promoter and interleukin-2 secretory signal and evaluate the recombinant plasmid for induction of antigen-specific cellular responses in mice. DNA corresponding to PE35 was PCR amplified from the genomic DNA of M. tuberculosis H(37) Rv, cloned into pGEMT-Easy vector and sub-cloned into the DNA vaccine vector pUMVC6. BALB/c mice were immunized with recombinant pUMVC6/PE35 and spleen cells were tested for T-helper (Th)1-type (antigen-induced proliferation and secretion of IFN-γ) and Th2-type (IL-5), and anti-inflammatory (IL-10) cytokine responses to pure recombinant PE35 protein and its synthetic peptides. Mice immunized with the recombinant plasmid DNA (pUMVC6/PE35) showed positive Th1-type cellular responses to pure PE35, but not to an irrelevant antigen, i.e. PPE68 (Rv3873). However, the vaccine construct did not induce antigen-specific Th2-type (IL-5) or anti-inflammatory (IL-10) reactivity to PE35. Testing with synthetic peptides showed that Th1-type cells recognizing various epitopes of PE35 were induced in mice immunized with pUMVC6/PE35 DNA. These results suggest that pUMVC6/PE35 may be useful as a safer vaccine candidate against TB.

Mycobacterium indicus pranii as stand-alone or adjunct immunotherapeutic in treatment of experimental animal tuberculosis

BACKGROUND & OBJECTIVES

Mycobacterium w (M.w) is a saprophytic cultivable mycobacterium and shares several antigens with M. tuberculosis. It has shown good immunomodulation in leprosy patients. Hence in the present study, the efficacy of M.w immunotherapy, alone or in combination with multi drug chemotherapeutic regimens was investigated against drug sensitive M. tuberculosis H37Rv and three clinical isolates with variable degree of drug resistance in mice.

METHODS

BALB/c mice were infected with M. tuberculosis H37Rv (susceptible to all first and second line drugs) and three clinical isolates taken from the epository of the Institute. The dose of 200 bacilli was used for infection via respiratory route in an aerosol chamber. Chemotherapy (5 days/wk) was given one month after infection and the vaccinated group was given a dose of 1x107 bacilli by subcutaneous route. Bacterial load was measured at 4 and 6 wk after initiation of chemotherapy.

RESULTS

M.w when given along with chemotherapy (4 and 6 wk) led to a greater reduction in the bacterial load in lungs and other organs of TB infected animals compared to. However, the reduction was significantly (P<0.05) more in terms of colony forming units (cfu) in both organs (lungs and spleen).

CONCLUSION

M.w (as immunomodulator) has beneficial therapeutic effect as an adjunct to chemotherapy.

A booster vaccine expressing a latency-associated antigen augments BCG induced immunity and confers enhanced protection against tuberculosis

BACKGROUND

In spite of a consistent protection against tuberculosis (TB) in children, Mycobacterium bovis Bacille Calmette-Guerin (BCG) fails to provide adequate protection against the disease in adults as well as against reactivation of latent infections or exogenous reinfections. It has been speculated that failure to generate adequate memory T cell response, elicitation of inadequate immune response against latency-associated antigens and inability to impart long-term immunity against M. tuberculosis infections are some of the key factors responsible for the limited efficiency of BCG in controlling TB.

METHODS/PRINCIPAL FINDINGS

In this study, we evaluated the ability of a DNA vaccine expressing α-crystallin--a key latency antigen of M. tuberculosis to boost the BCG induced immunity. 'BCG prime-DNA boost' regimen (B/D) confers robust protection in guinea pigs along with a reduced pathology in comparison to BCG vaccination (1.37 log(10) and 1.96 log(10) fewer bacilli in lungs and spleen, respectively; p<0.01). In addition, B/D regimen also confers enhanced protection in mice. Further, we show that B/D immunization in mice results in a heightened frequency of PPD and antigen specific multi-functional CD4 T cells (3(+)) simultaneously producing interferon (IFN)γ, tumor necrosis factor (TNF)α and interleukin (IL)2.

CONCLUSIONS/SIGNIFICANCE

These results clearly indicate the superiority of α-crystallin based B/D regimen over BCG. Our study, also demonstrates that protection against TB is predictable by an increased frequency of 3(+) Th1 cells with superior effector functions. We anticipate that this study would significantly contribute towards the development of superior booster vaccines for BCG vaccinated individuals. In addition, this regimen can also be expected to reduce the risk of developing active TB due to reactivation of latent infection.

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.

Tuberculosis immunity: opportunities from studies with cattle

Mycobacterium tuberculosis and M. bovis share >99% genetic identity and induce similar host responses and disease profiles upon infection. There is a rich history of codiscovery in the development of control measures applicable to both human and bovine tuberculosis (TB) including skin-testing procedures, M. bovis BCG vaccination, and interferon-γ release assays. The calf TB infection model offers several opportunities to further our understanding of TB immunopathogenesis. Recent observations include correlation of central memory immune responses with TB vaccine efficacy, association of SIRPα⁺ cells in ESAT-6:CFP10-elicited multinucleate giant cell formation, early γδ T cell responses to TB, antimycobacterial activity of memory CD4⁺ T cells via granulysin production, association of specific antibody with antigen burden, and suppression of innate immune gene expression in infected animals. Partnerships teaming researchers with veterinary and medical perspectives will continue to provide mutual benefit to TB research in man and animals.

Recombinant Mycobacterium smegmatis expressing an ESAT6-CFP10 fusion protein induces anti-mycobacterial immune responses and protects against Mycobacterium tuberculosis challenge in mice

The currently used vaccine against tuberculosis, Bacille Calmette-Guérin (BCG), has variable efficacy, so new vaccine development is crucial. In this study, we evaluated a recombinant vaccine prepared from non-pathogenic Mycobacterium smegmatis (rMS) that expresses a fusion of early secreted antigenic target 6-kDa antigen (ESAT6) and culture filtrate protein 10 (CFP10). C57BL/6 mice were immunized with the rMS expressing the ESAT6-CFP10 fusion protein (rM.S-e6c10) or with BCG. The mice in the rM.S-e6c10 group had a significantly higher titre of anti-ESAT6-CFP10 antibodies than did animals in the BCG or saline groups. Spleen cells from rM.S-e6c10-immunized mice exhibited a cytotoxic response to ESAT6 and CFP10-expressed target cells, but spleen cells from animals in the other groups did not. Levels of IFN-γ and IL-2 production by purified T cells from spleens were significantly higher in rM.S-e6c10 group than in BCG group. Finally, after M. tuberculosis (MTB)-challenged mice, dramatic reduction in the numbers of MTB colony-forming units (CFUs) in the lungs was observed for the mice immunized with the rMS. The protective efficacy of rM.S-e6c10 and BCG vaccination was similar based on measures of MTB burden and lung pathology. Our data indicate that the recombinant M. smegmatis vaccine expressing the ESAT6-CFP10 fusion protein has potential in clinic application.

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.

Airway luminal T cells: a newcomer on the stage of TB vaccination strategies

Protection against pulmonary tuberculosis (TB) by vaccination is often ascribed to the presence of TB-reactive T cells in the lung before infection. Challenging this view, new studies analyzing vaccine-induced T cells in various tissue compartments after parenteral immunization suggest a poor correlation between the presence of anti-TB T cells in the lung interstitium and spleen before Mycobacterium tuberculosis exposure and protection. In contrast, respiratory mucosal immunization leads to distribution of T cells not only in the lung interstitium and spleen, but also in the airway lumen, and the presence of these cells correlates well with protection. Furthermore, airway luminal recruitment of parenteral vaccine-induced T cells in peripheral tissues prior to M. tuberculosis challenge restores protection. We propose that understanding the biology of airway luminal T cells holds important implications for developing effective TB vaccination strategies.

BCG vaccination in the cotton rat (Sigmodon hispidus) infected by the pulmonary route with virulent Mycobacterium tuberculosis

To evaluate the usefulness of the American cotton rat (Sigmodon hispidus) in the evaluation of vaccine-induced resistance, we infected BCG-vaccinated and non-vaccinated cotton rats with Mycobacterium tuberculosis (H37Rv) via the respiratory route. Lung histopathology of these animals showed loose, disorganized granulomas which were non-necrotic up to 8 weeks post-infection. Moreover, we were not able to detect a DTH response after intradermal injection with PPD antigen. Prior BCG vaccination significantly reduced lung and spleen bacterial loads by 1-1.5log CFU and upregulated PPD-induced proliferation and production of IFNgamma in lymphocyte cultures. We conclude that pulmonary infection of the cotton rat with Mtb more closely resembles the phenotype seen in mice rather than guinea pigs.

Expression and immunogenicity of the mycobacterial Ag85B/ESAT-6 antigens produced in transgenic plants by elastin-like peptide fusion strategy

This study explored a novel system combining plant-based production and the elastin-like peptide (ELP) fusion strategy to produce vaccinal antigens against tuberculosis. Transgenic tobacco plants expressing the mycobacterial antigens Ag85B and ESAT-6 fused to ELP (TBAg-ELP) were generated. Purified TBAg-ELP was obtained by the highly efficient, cost-effective, inverse transition cycling (ICT) method and tested in mice. Furthermore, safety and immunogenicity of the crude tobacco leaf extracts were assessed in piglets. Antibodies recognizing mycobacterial antigens were produced in mice and piglets. A T-cell immune response able to recognize the native mycobacterial antigens was detected in mice. These findings showed that the native Ag85B and ESAT-6 mycobacterial B- and T-cell epitopes were conserved in the plant-expressed TBAg-ELP. This study presents the first results of an efficient plant-expression system, relying on the elastin-like peptide fusion strategy, to produce a safe and immunogenic mycobacterial Ag85B-ESAT-6 fusion protein as a potential vaccine candidate against tuberculosis.

Effect of serial subculturing on the genetic composition and cytotoxic activity of Mycobacterium tuberculosis

Continuous subculture has been observed to produce changes in the virulence of micro-organisms, e.g. rabies virus, poliovirus and Mycobacterium bovis BCG. The latter has been used as a vaccine for tuberculosis for the last 100 years; however, in some instances its efficacy has been observed to be very low. In order to determine whether similar changes can be produced in Mycobacterium tuberculosis, we selected four isolates, M. tuberculosis H37Rv, a Beijing strain (DR-689), and two more isolates with deletion of the phospholipase C locus (plcA-plcB-plcC ), and subjected them to serial culturing on Middlebrook 7H9 medium, with or without ox bile. After 100 passages, we performed RFLP-IS6110 analysis to determine whether genomic changes were produced. We also checked their genomic composition by microarray analysis. Changes in virulence were studied by measuring the cytotoxic effect of parental and subcultured isolates on a THP-1 macrophage monolayer. The most visible change was the change of position of an IS6110 band of approximately 1400 bp to approximately 1600 bp in the Beijing isolate subcultured in the ox bile medium. Analysis by microarray and PCR confirmation did not reveal any genomic changes. Cytotoxic activity was decreased in the isolates at levels close to that of BCG, and more consistently in those subcultured in the presence of ox bile.

Lactoferrin modulation of BCG-infected dendritic cell functions

Lactoferrin, an 80-kDa iron-binding protein with immune modulating properties, is a unique adjuvant component able to enhance efficacy of the existing Mycobacterium bovis Bacillus Calmette Guerin (BCG) vaccine to protect against murine model of tuberculosis. Although identified as having effects on macrophage presentation events, lactoferrin's capability to modulate dendritic cells (DCs) function when loaded with BCG antigens has not been previously recognized. In this study, the potential of lactoferrin to modulate surface expression of MHC II, CD80, CD86 and CD40 from bone marrow-derived dendritic cells (BMDCs) was examined. Generally, lactoferrin decreased pro-inflammatory cytokines [tumor necrosis factor (TNF)-alpha, IL-6 and IL-12p40] and chemokines [macrophage inflammatory protein (MIP)-1alpha and MIP-2] and increased regulatory cytokine, transforming growth factor-beta1 and a T-cell chemotatic factor, monocyte chemotactic protein-1, from uninfected or BCG-infected BMDCs. Culturing BCG-infected BMDCs with lactoferrin also enhanced their ability to respond to IFN-gamma activation through up-regulation of maturation markers: MHC I, MHC II and the ratio of CD86:CD80 surface expression. Furthermore, lactoferrin-exposed BCG-infected DCs increased stimulation of BCG-specific CD3(+)CD4(+) splenocytes, as defined by increasing IFN-gamma production. Finally, BCG-/lactoferrin-vaccinated mice possessed an increased pool of BCG antigen-specific IFN-gamma producing CD3(+)CD4(+)CD62L(-) splenocytes. These studies suggest a mechanism in which lactoferrin may exert adjuvant activity by enhancing DC function to promote generation of antigen-specific T cells.

Adjuvants induce distinct immunological phenotypes in a bovine tuberculosis vaccine model

Tuberculosis (TB) remains one of the most important infectious diseases of humans and animals. Mycobacterium bovis BCG, the only currently available TB vaccine, demonstrates variable levels of efficacy; therefore, a replacement or supplement to BCG is required. Protein subunit vaccines have shown promise but require the use of adjuvants to enhance their immunogenicity. Using the protective mycobacterial antigen Rv3019c, we have evaluated the induction of relevant immune responses by adjuvant formulations directly in the target species for bovine TB vaccines and compared these to responses induced by BCG. We demonstrate that two classes of adjuvant induce distinct immune phenotypes in cattle, a fact not previously reported for mice. A water/oil emulsion induced both an effector cell and a central memory response. A cationic-liposome adjuvant induced a central memory response alone, similar to that induced by BCG. This suggests that water/oil emulsions may be the most promising formulations. These results demonstrate the importance of testing adjuvant formulations directly in the target species and the necessity of measuring different types of immune response when evaluating immune responses.

Intranasal mucosal boosting with an adenovirus-vectored vaccine markedly enhances the protection of BCG-primed guinea pigs against pulmonary tuberculosis

Background

Recombinant adenovirus-vectored (Ad) tuberculosis (TB) vaccine platform has demonstrated great potential to be used either as a stand-alone or a boost vaccine in murine models. However, Ad TB vaccine remains to be evaluated in a more relevant and sensitive guinea pig model of pulmonary TB. Many vaccine candidates shown to be effective in murine models have subsequently failed to pass the test in guinea pig models.

Methods and Findings

Specific pathogen-free guinea pigs were immunized with BCG, AdAg85A intranasally (i.n), AdAg85A intramuscularly (i.m), BCG boosted with AdAg85A i.n, BCG boosted with AdAg85A i.m, or treated only with saline. The animals were then infected by a low-dose aerosol of M. tuberculosis (M.tb). At the specified times, the animals were sacrificed and the levels of infection in the lung and spleen were assessed. In separate studies, the long-term disease outcome of infected animals was monitored until the termination of this study. Immunization with Ad vaccine alone had minimal beneficial effects. Immunization with BCG alone and BCG prime-Ad vaccine boost regimens significantly reduced the level of M.tb infection in the tissues to a similar extent. However, while BCG alone prolonged the survival of infected guinea pigs, the majority of BCG-immunized animals succumbed by 53 weeks post-M.tb challenge. In contrast, intranasal or intramuscular Ad vaccine boosting of BCG-primed animals markedly improved the survival rate with 60% of BCG/Ad i.n- and 40% of BCG/Ad i.m-immunized guinea pigs still surviving by 74 weeks post-aerosol challenge.

Conclusions

Boosting, particularly via the intranasal mucosal route, with AdAg85A vaccine is able to significantly enhance the long-term survival of BCG-primed guinea pigs following pulmonary M.tb challenge. Our results thus support further evaluation of this viral-vectored TB vaccine in clinical trials.

Interaction of Mycobacterium tuberculosis with the host: consequences for vaccine development

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), remains a major worldwide health problem that causes more than 2 million deaths annually. In addition, an estimated 2 billion people are latently infected with M. tuberculosis. The bacterium is one of the oldest human pathogens and has evolved complex strategies for survival. Therefore, to be successful in the high endemic regions, any future TB vaccine strategy will have to be tailored in accordance with the resulting complexity of the TB infection and anti-mycobacterial immune response. In this review, we will discuss what is presently known about the interaction of M. tuberculosis with the immune system, and how this knowledge is used in new and more advanced vaccine strategies.

Enhanced and enduring protection against tuberculosis by recombinant BCG-Ag85C and its association with modulation of cytokine profile in lung

Background

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.

Methods/Principal Findings

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.

Conclusions/Significance

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.