Protective immunity to tuberculosis with Ag85B-ESAT-6 in a synthetic cationic adjuvant system IC31

[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.

Tuberculosis vaccines in clinical trials

Effective prophylactic and/or therapeutic vaccination is a key strategy for controlling the global TB epidemic. The partial effectiveness of the existing TB vaccine, bacille Calmette-Guérin (BCG), suggests effective vaccination is possible and highlights the need for an improved vaccination strategy. Clinical trials are evaluating both modifications to the existing BCG immunization methods and also novel TB vaccines, designed to replace or boost BCG. Candidate vaccines in clinical development include live mycobacterial vaccines designed to replace BCG, subunit vaccines designed to boost BCG and therapeutic vaccines designed as an adjunct to chemotherapy. There is a great need for validated animal models, identification of immunological biomarkers of protection and field sites with the capacity for large-scale efficacy testing in order to develop and license a novel TB vaccine or regimen.

Immunological biomarkers of tuberculosis

Currently there are no sufficiently validated biomarkers to aid the evaluation of new tuberculosis vaccine candidates, the improvement of tuberculosis diagnostics or the development of more effective and shorter treatment regimens. To date, the detection of Mycobacterium tuberculosis or its products has not been able to adequately address these needs. Understanding the interplay between the host immune system and M. tuberculosis may provide a platform for the identification of suitable biomarkers, through both unbiased and targeted hypothesis-driven approaches. Here, we review immunological markers, their relation to M. tuberculosis infection stages and their potential use in the fight against tuberculosis.

The two component adjuvant IC31® potentiates the protective immunity induced by a dengue 2 recombinant fusion protein in mice

Here we evaluated the suitability of the synthetic adjuvant IC31® to potentiate the protective capacity of PD5 protein (domain III of the envelope protein of dengue 2 virus fused to the carrier protein P64k). Unlike Alum, PD5 mixed with IC31® induced complete protection against virus challenge in mice and increased IFN-γ secretion after in vitro re-stimulation. The induced antibody response was highly specific to the homologous serotype and showed both IgG1 and IgG2a subtypes. IC31® is a promising adjuvant for PD5 recombinant protein based vaccination against dengue. Future work should address the suitability of PD5/IC31® formulations in non-human primate models.

Ag85B-ESAT-6 adjuvanted with IC31® promotes strong and long-lived Mycobacterium tuberculosis specific T cell responses in volunteers with previous BCG vaccination or tuberculosis infection

New TB vaccines are urgently needed because of the apparent lack of effect of the BCG vaccine on rates of adult contagious pulmonary tuberculosis and the risk of disseminated BCG disease in immunocompromised individuals. Since BCG appears to protect children, the primary target for vaccine development is a booster vaccine for adults but such vaccines ideally need to be able to efficiently prime mycobacterially naïve individuals as well as boost individuals previously vaccinated with BCG and those latently infected with TB. Protective immunity against Mycobacterium tuberculosis depends mainly on the generation of a Th1-type cellular immune response characterized by interferon-gamma (IFN-γ) production. In the present study, we monitored safety and IFN-γ responses in healthy BCG-vaccinated and prior or latently TB-infected individuals receiving a novel vaccine composed of the fusion protein Ag85B-ESAT-6 combined with the adjuvant IC31(®), administered at 0 and 2 months. Vaccination caused few local or systemic adverse effects besides transient soreness at the injection site, but it elicited strong antigen-specific T cell responses against Ag85B-ESAT-6 and both the Ag85B and ESAT-6 components, that could be augmented by second vaccination. The strong responses persisted through 32 weeks of follow-up, indicating the induction of a persistent memory response in the vaccine recipients.

Tuberculosis vaccines: present and future

There has never been a greater need for a new protective tuberculosis vaccine. Bacille Calmette-Guerin remains the cornerstone of any vaccine strategy, but improving its immunogenicity and efficacy has now become an urgent global health priority. This review discusses the main vaccines currently in clinical development and other novel vaccine strategies in the pipeline. It addresses the key questions in vaccine design, including antigen selection, route of vaccine delivery and immune correlates of vaccine-induced protection. There is an opportunity to identify such correlates from ongoing and future Phase II/III trials and, as these emerge, they can be used to validate the most relevant and predictive animal models with which to develop the next generation of new vaccines.

New adjuvants for human vaccines

Despite their obvious benefits, decades of research and hundreds of pre-clinical candidates, only a handful of adjuvants are approved for prophylactic vaccination of humans. The slow pace of development is due to a number of knowledge gaps, the most important of which is the complexity involved in designing adjuvants that are both potent and well tolerated. Recent advances in our understanding of innate immunity have led to the identification of immune pathways and adjuvant formulations more suitable for clinical advancement. One area of particular interest is the discovery of agonists that target the toll-like receptors. This review highlights recent progress of clinically approved vaccine adjuvants and identifies potential novel adjuvants that can broaden the development of new vaccines against infectious diseases.

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.

Chlamydia muridarum T-cell antigens formulated with the adjuvant DDA/TDB induce immunity against infection that correlates with a high frequency of gamma interferon (IFN-gamma)/tumor necrosis factor alpha and IFN-gamma/interleukin-17 double-positive CD4+ T cells

Major impediments to developing a Chlamydia vaccine lie in identifying immunologically relevant T-cell antigens and delivery in a manner to stimulate protective immunity. Using an immunoproteomic approach, we previously identified three immunodominant Chlamydia T-cell antigens (PmpG-1, PmpE/F-2, and RplF). Because RplF has high homology to a human ortholog, it may not be suitable for human vaccine development. Therefore, in this study, we evaluated protection against Chlamydia infection in the genital tract in C57BL/6 mice immunized with Chlamydia-specific membrane proteins PmpG-1, PmpE/F-2, and major outer membrane protein (MOMP; as a reference) or a combination of them formulated with one of three adjuvants, CpG oligodeoxynucleotide (CpG-ODN), AbISCO-100 (AbISCO), or DDA/TDB (dimethyldioctadecylammonium bromide/D-(+)-trehalose 6,6'-dibehenate). The results show that immunization with the CpG-ODN formulation failed to provide protection against Chlamydia infection; the AbISCO formulation conferred moderate protection, and the DDA/TDB formulation showed the highest degree of protective efficacy. The combination of PmpG-1, PmpE/F-2, and MOMP proteins formulated with DDA/TDB exhibited the greatest degree of protection among all vaccine groups studied. Moreover, this vaccine combination also engendered significant protection in BALB/c mice, which have a different major histocompatibility complex (MHC) background. We measured cell-mediated immune cytokine responses in mice immunized with PmpG-1 mixed with each of the three adjuvants. The results demonstrate that mice immunized with the DDA/TDB formulation induced the strongest gamma interferon (IFN-gamma) and interleukin-17 (IL-17) responses, characterized by the highest frequency of IFN-gamma/tumor necrosis factor alpha (TNF-alpha) and IFN-gamma/IL-17 double-positive CD4(+) T cells. In conclusion, a Chlamydia vaccine based on the recombinant proteins PmpG-1, PmpE/F-2, and MOMP delivered in a DDA/TDB adjuvant conferred protection against infection that correlated with IFN-gamma/TNF-alpha and IFN-gamma/IL-17 double-positive CD4(+) T cells.

Ag85B-ESAT-6 adjuvanted with IC31 promotes strong and long-lived Mycobacterium tuberculosis specific T cell responses in naïve human volunteers

Though widely used, the BCG vaccine has had little apparent effect on rates of adult pulmonary tuberculosis. Moreover, the risk of disseminated BCG disease in immunocompromised individuals means that improved TB vaccines ideally need to be able to efficiently prime mycobacterially-naïve individuals as well as boost individuals previously vaccinated with BCG. Protective immunity against Mycobacterium tuberculosis is thought to depend on the generation of a Th1-type cellular immune response characterized by interferon-gamma (IFN-gamma) production. In the present study, we monitored safety and IFN-gamma responses in healthy TB-naïve humans receiving an entirely novel vaccine, composed of the fusion protein Ag85B-ESAT-6, administered at 0 and 2 months either as recombinant protein alone or combined with two concentrations of the novel adjuvant IC31. Vaccination did not cause local or systemic adverse effects besides transient soreness at the injection site, but it elicited strong antigen-specific T cell responses against H1 and both the Ag85B and the ESAT-6 components. These strong responses persisted through 2.5 years of follow-up, indicating the induction of a substantial memory response in the vaccine recipients.

The development and preliminary evaluation of a new Mycobacterium tuberculosis vaccine comprising Ag85b, HspX and CFP-10:ESAT-6 fusion protein with CpG DNA and aluminum hydroxide adjuvants

Ag85b and HspX of Mycobacterium tuberculosis (Mtb) (H37Rv) were expressed and purified in this study. These two proteins were combined with another fusion protein CFP-10:ESAT-6 (C/E) (Ag), then mixed with the adjuvants CpG DNA and aluminum hydroxide and used to vaccinate mice and guinea pigs challenged with Mtb (H37Rv). The number of spleen lymphocytes secreting Ag85b, HspX and C/E-specific interferon-gamma were significantly higher in the Ag+Al+CpG group than in the Ag and CpG groups. The combination of Ag, Al and CpG induced the highest concentrations of anti-Ag85b, anti-HspX and anti-C/E immunoglobulin G in mouse serum. Mouse peritoneal macrophages from the Ag+Al+CpG group secreted significantly higher levels of interleukin-12 compared with macrophages from the other groups. The total mean liver, lung and spleen lesion scores and bacterial loads in the spleen in guinea pigs vaccinated with Ag+Al+CpG were lower than those of the other groups, but no significant difference was found. These results show that the mixture of Ag85b, HspX and C/E with a combination of CpG and aluminum adjuvants can induce both humoral and cellular immune responses in mice, whereas it plays only a small role in the control of disease progression in guinea pigs challenged with Mtb.

Immunoprophylaxis of tuberculosis: an update of emerging trends

Developing effective prophylactics to combat tuberculosis is currently in an exploratory stage. The HIV pandemic and emergence of multi- and extensively drug-resistant strains of Mycobacterium tuberculosis indicate that the current preventive measures against this ever-evolving pathogen are inadequate. The currently available vaccine BCG in its present form affords variable protection which usually wanes with aging. Various reasons have been cited to explain the discrepancies in the efficacy of BCG, including generic differences in the different BCG vaccine strains used in immunization program throughout the world. The low efficacy of BCG vaccine has promoted the search for novel vaccines for tuberculosis. The search strategies aim at completely replacing the existing vaccine and/or augmenting/improving the current BCG vaccine. Among new vaccine candidates are live attenuated M. tuberculosis vaccines, recombinant BCG, DNA vaccines, subunit vaccine, and fusion protein-based vaccines. More than 200 new vaccine candidates have been developed as a result of research work over the past few years. To date, at least eight vaccine candidates are undergoing clinical evaluation, with a few of them successfully qualifying in the first phase of clinical testing. These recent advances present an optimistic insight whereby a new tuberculosis vaccine might be expected to be available for public use in the next few years.

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.

Evaluation of new vaccines for tuberculosis in the guinea pig model

The guinea pig is a very useful animal model for evaluating new tuberculosis candidate vaccines. In addition to established methods for bacterial load determinations, new technologies are emerging that allow us to specifically evaluate effects of vaccines on the pathology of the disease process and the expression by the host of cell mediated immunity. Limitations to the model include housing and related costs, which often contribute to issue with study design and adequate statistical power, and the use of laboratory strains of Mycobacterium tuberculosis which lack the high virulence and immune evasion properties of newly emerging clinical isolates.

Evasion and subversion of antigen presentation by Mycobacterium tuberculosis

Mycobacterium tuberculosis is one of the most successful of human pathogens and has acquired the ability to establish latent or progressive infection and persist even in the presence of a fully functioning immune system. The ability of M. tuberculosis to avoid immune-mediated clearance is likely to reflect a highly evolved and coordinated program of immune evasion strategies, including some that interfere with antigen presentation to prevent or alter the quality of T-cell responses. Here, we review an extensive array of published studies supporting the view that antigen presentation pathways are targeted at many points by pathogenic mycobacteria. These studies show the multiple potential mechanisms by which M. tuberculosis may actively inhibit, subvert or otherwise modulate antigen presentation by major histocompatibility complex class I, class II and CD1 molecules. Unraveling the mechanisms by which M. tuberculosis evades or modulates antigen presentation is of critical importance for the development of more effective new vaccines based on live attenuated mycobacterial strains.

Protection and polyfunctional T cells induced by Ag85B-TB10.4/IC31 against Mycobacterium tuberculosis is highly dependent on the antigen dose

BACKGROUND

Previously we have shown that Ag85B-TB10.4 is a highly efficient vaccine against tuberculosis when delivered in a Th1 inducing adjuvant based on cationic liposomes. Another Th1 inducing adjuvant, which has shown a very promising profile in both preclinical and clinical trials, is IC31. In this study, we examined the potential of Ag85B-TB10.4 delivered in the adjuvant IC31 for the ability to induce protection against infection with Mycobacterium tuberculosis. In addition, we examined if the antigen dose could influence the phenotype of the induced T cells.

METHODS AND FINDINGS

We found that vaccination with the combination of Ag85B-TB10.4 and IC31 resulted in high numbers of polyfunctional CD4 T cells co-expressing IL-2, IFN-gamma and TNF-alpha. This correlated with protection against subsequent challenge with M.tb in the mouse TB model. Importantly, our results also showed that both the vaccine induced T cell response, and the protective efficacy, was highly dependent on the antigen dose. Thus, whereas antigen doses of 5 and 15 microg did not induce significant protection against M.tb, reducing the dose to 0.5 microg selectively increased the number of polyfunctional T cells and induced a strong protection against infection with M.tb. The influence of antigen dose was also observed in the guinea pig model of aerosol infection with M.tb. In this model a 2.5 fold increase in the antigen dose reduced the protection against infection with M.tb to the level observed in non-vaccinated animals.

CONCLUSIONS/SIGNIFICANCE

Small changes in the antigen dose can greatly influence the induction of specific T cell subpopulations and the dose is therefore a crucial factor when testing new vaccines. However, the adjuvant IC31 can, with the optimal dose of Ag85B-TB10.4, induce strong protection against Mycobacterium tuberculosis. This vaccine has now entered clinical trials.

A liposome-based mycobacterial vaccine induces potent adult and neonatal multifunctional T cells through the exquisite targeting of dendritic cells

BACKGROUND

In the search for more potent and safer tuberculosis vaccines, CAF01 was identified as a remarkable formulation. Based on cationic liposomes and including a synthetic mycobacterial glycolipid as TLR-independent immunomodulator, it induces strong and protective T helper-1 and T helper-17 adult murine responses to Ag85B-ESAT-6, a major mycobacterial fusion protein. Here, we assessed whether these properties extend to early life and how CAF01 mediates its adjuvant properties in vivo.

METHODS/FINDINGS

Following adult or neonatal murine immunization, Ag85B-ESAT-6/CAF01 similarly reduced the post-challenge bacterial growth of M. bovis BCG, whereas no protection was observed using Alum as control. This protection was mediated by the induction of similarly strong Th1 and Th17 responses in both age groups. Multifunctional Th1 cells were already elicited after a single vaccine dose and persisted at high levels for at least 6 months even after neonatal priming. Unexpectedly, this potent adjuvanticity was not mediated by a massive targeting/activation of dendritic cells: in contrast, very few DCs in the draining lymph nodes were bearing the labeled antigen/adjuvant. The increased expression of the CD40 and CD86 activation markers was restricted to the minute portion of adjuvant-bearing DCs. However, vaccine-associated activated DCs were recovered several days after immunization.

CONCLUSION

The potent adult and neonatal adjuvanticity of CAF01 is associated in vivo with an exquisite but prolonged DC uptake and activation, fulfilling the preclinical requirements for novel tuberculosis vaccines to be used in early life.

Heterologous prime-boost vaccinations for poverty-related diseases: advantages and future prospects

Classical vaccination approaches, based on a single vaccine administered in a homologous prime-boost schedule and optimized to induce primarily neutralizing antibodies, are unlikely to be sufficiently efficacious to prevent TB, malaria or HIV infections. Novel vaccines, capable of inducing a more powerful immune response, in particular T-cell immunity, are desperately needed. Combining different vaccine modalities that are able to complement each other and induce broad and sustainable immunity is a promising approach. This review provides an overview of heterologous prime-boost vaccination modalities currently in development for the 'big three' poverty-related diseases and emphasizes the need for innovative vaccination approaches.

IC31, a two-component novel adjuvant mixed with a conjugate vaccine enhances protective immunity against pneumococcal disease in neonatal mice

IC31 is a novel adjuvant which combines the immunostimulatory effects of an 11-mer antibacterial peptide (KLKL(5)KLK) and a synthetic oligodeoxynucleotide (ODN1a) which is a Toll-like receptor 9 agonist without containing cytosine phosphate guanine (CpG) motifs. The effects of IC31 on neonatal immune response to vaccination have not been reported. Neonatal mice were immunized once or twice with a Streptococcus pneumoniae serotype 1 polysaccharide conjugate containing Tetanus Toxoid (Pnc1-TT) carrier protein, with or without IC31 or CpG-ODN. IC31 significantly enhanced IgG1, IgG2a and IgG2b antibodies (Ab) to the serotype 1 polysaccharide. One dose of Pnc1-TT and low dose IC31 elicited high Ab levels that protected the neonatal mice completely from bacteraemia and significantly reduced lung infection following i.n. challenge with serotype 1 pneumococcal strain. One-sixth of an adult murine dose of IC31 was sufficient and optimal for induction of protective immunity in neonatal mice. Two doses of Pnc1-TT with or without adjuvants protected the neonatal mice completely, but more rapid Ab response was observed when IC31 was given with the Pnc1-TT. IC31 is a promising new adjuvant for neonatal vaccinations, rapidly enhancing protective humoral responses when combined with Pnc1-TT.

CpG oligonucleotide, host defense peptide and polyphosphazene act synergistically, inducing long-lasting, balanced immune responses in cattle

Vaccines consisting of subunit or protein antigens are less immunogenic than traditional vaccines, and therefore require formulation with an adjuvant. Conventional adjuvants, however, often cause undesirable injection site reactions and Th2-biased immune responses. Therefore, novel vaccine adjuvants which can safely enhance and selectively bias the resulting immune response are required. Here the adjuvant combination of CpG ODN, indolicidin and polyphosphazene (CpG+indol+PP) was evaluated for its ability to enhance and modulate the immune response when formulated with the antigen hen egg lysozyme (HEL). Cattle immunized with HEL co-adjuvanted with CpG+indol+PP developed higher antigen-specific humoral responses, and long-lasting cell-mediated immune responses, as evidenced by elevated levels of IFN-gamma secretion by re-stimulated PBMCs, that were superior even to EMULSIGEN((R)), an oil-in-water based adjuvant that was used as positive control. Physical characterization of the vaccines indicated that formulation of HEL with CpG+indol+PP resulted in the formation of antigen-adjuvant complexes, which may have contributed to their enhanced immunogenicity. Furthermore, the addition of polyphosphazene to CpG ODN and indolicidin dose-dependently enhanced the secretion of the cytokines IFN-alpha, TNF-alpha and IFN-gammain vitro, indicating that polyphosphazene can also synergize with CpG ODN and indolicidin to stimulate innate immune responses.

Adjuvanticity of a synthetic cord factor analogue for subunit Mycobacterium tuberculosis vaccination requires FcRgamma-Syk-Card9-dependent innate immune activation

Novel vaccination strategies against Mycobacterium tuberculosis (MTB) are urgently needed. The use of recombinant MTB antigens as subunit vaccines is a promising approach, but requires adjuvants that activate antigen-presenting cells (APCs) for elicitation of protective immunity. The mycobacterial cord factor Trehalose-6,6-dimycolate (TDM) and its synthetic analogue Trehalose-6,6-dibehenate (TDB) are effective adjuvants in combination with MTB subunit vaccine candidates in mice. However, it is unknown which signaling pathways they engage in APCs and how these pathways are coupled to the adaptive immune response. Here, we demonstrate that these glycolipids activate macrophages and dendritic cells (DCs) via Syk-Card9-Bcl10-Malt1 signaling to induce a specific innate activation program distinct from the response to Toll-like receptor (TLR) ligands. APC activation by TDB and TDM was independent of the C-type lectin receptor Dectin-1, but required the immunoreceptor tyrosine-based activation motif-bearing adaptor protein Fc receptor gamma chain (FcRgamma). In vivo, TDB and TDM adjuvant activity induced robust combined T helper (Th)-1 and Th-17 T cell responses to a MTB subunit vaccine and partial protection against MTB challenge in a Card9-dependent manner. These data provide a molecular basis for the immunostimulatory activity of TDB and TDM and identify the Syk-Card9 pathway as a rational target for vaccine development against tuberculosis.

Adult-like anti-mycobacterial T cell and in vivo dendritic cell responses following neonatal immunization with Ag85B-ESAT-6 in the IC31 adjuvant

Background

With the exception of some live vaccines, e.g. BCG, subunit vaccines formulated with “classical” adjuvants do not induce similar responses in neonates as in adults. The usual neonatal profile is characterized by lower levels of TH1-associated biomarkers. This has hampered the development of new neonatal vaccines for diseases that require early protection. Tuberculosis is one of the major targets for neonatal immunization. In this study, we assessed the immunogenicity of a novel candidate vaccine comprising a mycobacterial fusion protein, Ag85B-ESAT-6, in a neonatal murine immunization model.

Methods/Findings

The Ag85B-ESAT-6 fusion protein was formulated either with a classical alum based adjuvant or with the novel IC31® adjuvant. Following neonatal or adult immunization, 3 parameters were studied in vivo: (1) CD4⁺ T cell responses, (2) vaccine targeting/activation of dendritic cells (DC) and (3) protection in a surrogate mycobacterial challenge model. Conversely to Alum, IC31® induced in both age groups strong Th1 and Th17 responses, characterized by multifunctional T cells expressing IL-2 and TNF-α with or without IFN-γ. In the draining lymph nodes, a similarly small number of DC contained the adjuvant and/or the antigen following neonatal or adult immunization. Expression of CD40, CD80, CD86 and IL-12p40 production was focused on the minute adjuvant-bearing DC population. Again, DC targeting/activation was similar in adults and neonates. These DC/T cell responses resulted in an equivalent reduction of bacterial growth following infection with M. bovis BCG, whereas no protection was observed when Alum was used as adjuvant.

Conclusion

Neonatal immunization with the IC31®- adjuvanted Ag85B-ESAT-6 subunit vaccine elicited adult-like multifunctional protective anti-mycobacterial T cell responses through the induction of an adult pattern of in vivo DC activation.

Cationic liposomes formulated with synthetic mycobacterial cordfactor (CAF01): a versatile adjuvant for vaccines with different immunological requirements

BACKGROUND

It is now emerging that for vaccines against a range of diseases including influenza, malaria and HIV, the induction of a humoral response is insufficient and a substantial complementary cell-mediated immune response is necessary for adequate protection. Furthermore, for some diseases such as tuberculosis, a cellular response seems to be the sole effector mechanism required for protection. The development of new adjuvants capable of inducing highly complex immune responses with strong antigen-specific T-cell responses in addition to antibodies is therefore urgently needed.

METHODS AND FINDINGS

Herein, we describe a cationic adjuvant formulation (CAF01) consisting of DDA as a delivery vehicle and synthetic mycobacterial cordfactor as immunomodulator. CAF01 primes strong and complex immune responses and using ovalbumin as a model vaccine antigen in mice, antigen specific cell-mediated- and humoral responses were obtained at a level clearly above a range of currently used adjuvants (Aluminium, monophosphoryl lipid A, CFA/IFA, Montanide). This response occurs through Toll-like receptor 2, 3, 4 and 7-independent pathways whereas the response is partly reduced in MyD88-deficient mice. In three animal models of diseases with markedly different immunological requirement; Mycobacterium tuberculosis (cell-mediated), Chlamydia trachomatis (cell-mediated/humoral) and malaria (humoral) immunization with CAF01-based vaccines elicited significant protective immunity against challenge.

CONCLUSION

CAF01 is potentially a suitable adjuvant for a wide range of diseases including targets requiring both CMI and humoral immune responses for protection.

Paediatric tuberculosis

Tuberculosis continues to cause an unacceptably high toll of disease and death among children worldwide, particularly in the wake of the HIV epidemic. Increased international travel and immigration have led to a rise in childhood tuberculosis rates even in traditionally low burden, industrialised settings, and threaten to promote the emergence and spread of multidrug-resistant strains. Whereas intense scientific and clinical research efforts into novel diagnostic, therapeutic, and preventive interventions have focused on tuberculosis in adults, childhood tuberculosis has been relatively neglected. However, children are particularly vulnerable to severe disease and death following infection, and those with latent infection become the reservoir for future transmission following disease reactivation in adulthood, fuelling future epidemics. Further research into the epidemiology, immune mechanisms, diagnosis, treatment, and prevention of childhood tuberculosis is urgently needed. Advances in our understanding of tuberculosis in children would provide insights and opportunities to enhance efforts to control this disease.

Protective anti-mycobacterial T cell responses through exquisite in vivo activation of vaccine-targeted dendritic cells

Vaccine efficacy largely depends upon DC targeting and activation. The most potent TLR soluble ligands induce diffuse DC activation, which may be associated with marked pro-inflammatory responses and possibly adverse effects. This raises the concern that effective vaccine adjuvants may similarly rely on widespread DC activation. Using a promising candidate vaccine against tuberculosis (fusion protein of Ag85B and 6-kDa early secretory antigenic target (ESAT-6)) formulated in the potent IC31 adjuvant, DC targeting and activation was studied in vivo, following the fate of antigen and adjuvant in the draining lymph nodes, to define the magnitude of DC targeting/activation required in vivo to induce protective vaccine responses. Unexpectedly, protective IFN-gamma-mediated Ag85B-ESAT-6/IC31 responses were associated to the activation of a minute population (less than 0.3%) of CD11c(+) lymph node DC, without detectable systemic pro-inflammatory responses. This activated peripheral tissue-derived DC population, characterized by enhanced CD80, CD86, CD40 and IL-12p40 expression, was only identified when focusing on adjuvant- or antigen-labeled CD11c(+) DC, which were found to support T cell proliferation. Immunization with aluminum hydroxide adjuvant (Alum) resulted in a similar proportion of antigen-associated DC but without detectable enhancement of CD80, CD86, CD40 or IL-12p40 expression. Thus, potent protective IFN-gamma-producing responses may be elicited by the exquisite activation of a minute number of in vivo targeted DC.

Confronting the scientific obstacles to global control of tuberculosis

Tuberculosis (TB) is a major threat to global health, recently exacerbated by the emergence of highly drug-resistant forms of the disease-causing pathogen and synergy with HIV/AIDS. In 2006, the Stop TB Partnership published "The global plan to stop TB: 2006--2015," which set out a vision of halving the prevalence of and mortality caused by the disease by 2015, followed by eliminating the disease as a public health problem by 2050. This vision depends on the development of improved diagnostics, simpler treatment, and more effective vaccination. Recently, active translational research pipelines directed toward each of these goals have been established, but improved understanding of the fundamental biology of this complex disease will prove to be the key to radical advances in TB control.

Adjuvant modulation of the cytokine balance in Mycobacterium tuberculosis subunit vaccines; immunity, pathology and protection

It is known that protection against tuberculosis is mediated primarily by T helper type 1 (Th1) cells but the influence of the Th1/Th2 balance of a vaccination response on the subsequent protection and pathology during infection has not been studied in detail. We designed a panel of Ag85B-ESAT-6 subunit vaccines based on adjuvants with different Th1/Th2-promoting activities and studied cellular responses, bacterial replication and pathology in the lungs of mice infected with Mycobacterium tuberculosis. All vaccines induced cell-mediated and humoral responses but with markedly different interferon-gamma : interleukin-5 (IFN-gamma : IL-5) and immunoglobulin G1 (IgG1) : IgG2 ratios. The vaccines promoted different levels of control of bacterial replication with the most efficient protection being exerted by cationic liposomes containing monophosphoryl lipid A and low to completely absent immunity with conventional aluminium. The level of protection correlated with the amount of IFN-gamma produced in response to the vaccine whereas there was no inverse correlation with the level of IL-5. Characterizing a protective response was an accelerated recruitment of IL-17 and IFN-gamma-producing lymphocytes resulting in the early formation of granulomas containing clustered inducible nitric oxide synthase-activated macrophages. In comparison, non-protected mice exhibited a different inflammatory infiltrate rich in neutrophil granulocytes. This study indicates that the adjuvant component of a tuberculosis vaccine may be crucial in determining the kinetics by which effective granulomas, pivotal in controlling bacterial growth, are formed.

TLR9-mediated recognition of DNA

The mammalian immune system senses pathogens through pattern recognition receptors (PRRs) and responds with activation. The Toll-like receptor (TLR) family that consists of 13 receptors plays a critical role in this process. TLRmediated signaling activates immune cells and leads to an innate immune response with subsequent initiation of an adaptive immune response. Toll-like receptor 9 (TLR9) recognizes deoxyribonucleic acid (DNA) leading to cellular activation and cytokine production influencing the immune response against viruses and bacteria. The stimulation of TLR9 will be exploited for adjuvant therapy and treatment of cancer or allergy. In this review we will discuss TLR9 ligands, TLR9 expression, signaling, and the therapeutic potential of TLR9 ligands in treatment of infectious or allergic diseases and cancer.

Tuberculosis subunit vaccines: from basic science to clinical testing

More than 80 years after the introduction of Bacillus Calmette-GuErin, the first tuberculosis vaccine, new vaccines for tuberculosis are finally in clinical trials. The selection of antigens on which new subunit vaccines are based represent the first fulfillment of the promise of proteomics and genomics, and the delivery systems for these antigens are likewise the first fruits of the improved understanding of how the host immune system recognizes pathogens. However, clinical trials are still at Phase I and there remain formidable obstacles to the registration of the first new TB vaccines. Here the authors review the vaccines in clinical trials and discuss the different approaches they take to stimulating immunity to Mycobacterium tuberculosis infection, focusing on recombinant subunit vaccines. The challenges that confront these approaches and how they are being addressed are then discussed.

Cloning and expression of protective antigens of Mycobacterium tuberculosis Ag85B and ESAT-6 in Francisella tularensis 15/10

The possibility of expression of genes encoding mycobacterial antigens in Francisella tularensis 15/10 vaccine strain cells has been shown for the first time. To obtain stable and effective expression of mycobacterial antigens in the F. tularensis cells, the plasmid vector pPMC1 and hybrid genes consisting of the leader part FL of the F. tularensis membrane protein FopA and structural moieties of the mature protein Ag85B or the fused protein Ag85B-ESAT-6 were constructed. Recombinant strains F. tularensis RVp17 and RVp18 expressing protective mycobacterial antigens in the fused proteins FL-Ag85B and FL-Ag85B-ESAT-6, respectively, were obtained. Expression of the protective mycobacterial antigens in F. tularensis was analyzed using specific antisera to the recombinant proteins Ag85-(His)6 and ESAT-6-(His)6 isolated from Escherichia coli producer strains created on the basis of the pET23b(+) and pET24b(+) vectors. The expression of heterologous protective antigens in F. tularensis 15/10 is promising for creation of live recombinant anti-tuberculosis vaccines on the basis of the tularemia vaccine strain.

Childhood tuberculosis: old and new vaccines

The world is witnessing an escalation of the tuberculosis (TB) epidemic, particularly in sub-Saharan Africa and South-East Asia. The problem has been compounded by the evolution of the human immunodeficiency virus pandemic, the increase in multidrug-resistant TB and the emergence of extensively drug-resistant TB. This has led to renewed interest in vaccines aimed at preventing tuberculosis. The current Bacille Calmette-Guérin (BCG) vaccine prevents the invasive complications of childhood tuberculosis, such as meningitis and miliary disease, but provides variable protection against adult pulmonary disease. This review discusses the history of the BCG vaccine, the reasons for its variable efficacy, protective immunity and TB, and the evolution of and obstacles to development of new candidate vaccines. Several new TB vaccines have demonstrated promising results in animal models; a number have gone into phase I clinical trials in humans, and it is anticipated that phase III trials will commence by 2009. Licensing of an effective new TB vaccine by 2015 is thus a possibility.

Tuberculosis subunit vaccine development: Impact of physicochemical properties of mycobacterial test antigens

Tuberculosis caused by Mycobacterium tuberculosis continues to be one of the major public health problems in the world. The eventual control of this disease will require the development of a safe and effective vaccine. One of the approaches receiving a great deal of attention recently is subunit vaccination. An efficacious antituberculous subunit vaccine requires the identification and isolation of key components of the pathogen that are capable of inducing a protective immune response. Clues to identify promising subunit vaccine candidates may be found in their physicochemical and immunobiological properties. In this article, we review the evidence that the physicochemical properties of mycobacterial components can greatly impact the induction of either protective or deleterious immune response and consequently influence the potential utility as an antituberculous subunit vaccine.

Tuberculosis subunit vaccine design: the conflict of antigenicity and immunogenicity

The attempts to find an effective antituberculous subunit vaccine are based on the assumption that it must drive a Th1 response. In the absence of effective correlates of protection, a vast array of mycobacterial components are being evaluated worldwide either on the basis of their ability to be recognized by T lymphocytes in in vitro assays during early stage of animal or human infection (antigenicity) or their capacity to induce T cell response following immunization in animal models (immunogenicity). The putative vaccine candidates selected using either of these strategies are then subjected to challenge studies in different animal models to evaluate the protective efficacy. Here we review the outcome of this current scheme of selection of vaccine candidates using an 'antigenicity' or 'immunogenicity' criterion on the actual protective efficacy observed in experimental animal models. The possible implications for the success of some of the leading vaccine candidates in clinical trials will also be discussed.

Vaccine strategies against latent tuberculosis infection

The leading tuberculosis (TB) vaccines currently in clinical trials are all designed as prophylactic vaccines. Although these vaccines are highly active, they will most probably not result in sterilizing immunity and, therefore, will not solve the global problem of latent TB. An attractive strategy is to target the remaining dormant bacteria with vaccines based upon antigens induced as the bacteria change from active multiplication to non-replicating dormancy (latency antigens) or during reactivation as dormant bacteria resume active metabolism (resuscitation antigens). These late-stage antigens might have potential as post-exposure vaccines or could form the basis for a multi-stage vaccine strategy, in which they are combined with prophylactic vaccines based on early antigens from replicating bacteria.