Epitope-specific CD4+, but not CD8+, T-cell responses induced by recombinant influenza A viruses protect against Mycobacterium tuberculosis infection

Tuberculosis vaccine developments and efficient delivery systems: A comprehensive appraisal

Despite the widespread use of the Bacillus Calmette-Guérin (BCG) vaccine, Mycobacterium tuberculosis (MTB) continues to be a global burden. Vaccination has been proposed to prevent and treat tuberculosis (TB) infection, and several of them are in different phases of clinical trials. Though vaccine production is in progress but requires more attention. There are several TB vaccines in the trial phase, most of which are based on a combination of proteins/adjuvants or recombinant viral vectors used for selected MTB antigens. In this review, we attempted to discuss different types of TB vaccines based on the vaccine composition, the immune responses generated, and their clinical trial phases. Furthermore, we have briefly overviewed the effective delivery systems used for the TB vaccine and their effectiveness in different vaccines.

Recent advance in the development of tuberculosis vaccines in clinical trials and virus-like particle-based vaccine candidates

Tuberculosis (TB) remains a serious public health threat around the world. An effective vaccine is urgently required for cost-effective, long-term control of TB. However, the only licensed vaccine Bacillus Calmette-Guerin (BCG) is limited to prevent TB for its highly variable efficacy. Substantial progress has been made in research and development (R&D) of TB vaccines in the past decades, and a dozen vaccine candidates, including live attenuated mycobacterial vaccines, killed mycobacterial vaccines, adjuvanted subunit vaccines, viral vector vaccines, and messenger RNA (mRNA) vaccines were developed in clinical trials to date. Nevertheless, many challenges to the successful authorization for the use and deployment of an effective tuberculosis vaccine remain. Therefore, it is still necessary and urgent to continue exploring new vaccine construction approaches. Virus-like particles (VLPs) present excellent prospects in the field of vaccine development because of their helpful immunological features such as being safe templates without containing viral nucleic acid, repetitive surface geometry, conformational epitopes similar to natural viruses, and enhancing both innate and adaptive immune responses. The marketization process of VLP vaccines has never stopped despite VLP vaccines face several shortcomings such as their complex and slow development process and high production cost, and several VLP-based vaccines, including vaccines against Human papillomavirus (HPV), Hepatitis B Virus (HBV) and malaria, are successfully licensed for use at the market. In this review, we provide an update on the current progress regarding the development of TB vaccines in clinical trials and seek to give an overview of VLP-based TB vaccine candidates.

CXCR3 Provides a Competitive Advantage for Retention of Mycobacterium tuberculosis-Specific Tissue-Resident Memory T Cells Following a Mucosal Tuberculosis Vaccine

Mycobacterium tuberculosis is a major human pathogen, and new vaccines are needed to prevent transmission. Mucosal vaccination may confer protection against M. tuberculosis by stimulating tissue-resident memory (TRM) CD4+ T cells in the lungs. The chemokine receptor CXCR3 promotes lung recruitment of T cells, but its role in TRM development is unknown. This study demonstrates the recombinant influenza A virus vaccine PR8.p25, expressing the immunodominant M. tuberculosis T cell epitope p25, induces CXCR3 expression on p25-specific CD4+ T cells in the lungs so that the majority of vaccine-induced CD4+ TRM expresses CXCR3 at 6 weeks. However, CXCR3-/- mice developed equivalent antigen-specific CD4+ T cell responses to wild-type (WT) mice following PR8.p25, and surprisingly retained more p25-specific CD4+ TRM in the lungs than WT mice at 6 weeks. The adoptive transfer of CXCR3-/- and WT P25 T cells into WT mice revealed that the initial recruitment of vaccine-induced CD4+ T cells into the lungs was independent of CXCR3, but by 6 weeks, CXCR3-deficient P25 T cells, and especially CXCR3-/- TRM, were significantly reduced compared to CXCR3-sufficient P25 T cells. Therefore, although CXCR3 was not essential for CD4+ TRM recruitment or retention, it provided a competitive advantage for the induction of M. tuberculosis-specific CD4+ TRM in the lungs following pulmonary immunization.

IgGκ Signal Peptide Enhances the Efficacy of an Influenza Vector Vaccine against Respiratory Syncytial Virus Infection in Mice

Intranasal vaccination using influenza vectors is a promising approach to developing vaccines against respiratory pathogens due to the activation of the mucosa-associated immune response. However, there is no clear evidence of a vector design that could be considered preferable. To find the optimal structure of an influenza vector with a modified NS genomic segment, we constructed four vector expressing identical transgene sequences inherited from the F protein of the respiratory syncytial virus (RSV). Two vectors were designed aiming at transgene accumulation in the cytosol. Another two were supplemented with an IgGκ signal peptide prior to the transgene for its extracellular delivery. Surprisingly, adding the IgGκ substantially enhanced the T-cell immune response to the CD8 epitope of the transgene. Moreover, this strategy allowed us to obtain a better protection of mice from the RSV challenge after a single intranasal immunization. Protection was achieved without antibodies, mediated by a balanced T-cell immune response including the formation of the RSV specific effector CD8+ IFNγ+/IL10+-producing cells and the accumulation of Treg cells preventing immunopathology in the lungs of infected mice. In addition to the presented method for optimizing the influenza vector, our results highlight the possibility of achieving protection against RSV through a respiratory-associated T-cell immune response alone.

Towards the development of subunit vaccines against tuberculosis: The key role of adjuvant

According to the World Health Organization (WHO), tuberculosis (TB) is the leading cause of death triggered by a single infectious agent, worldwide. Bacillus Calmette-Guerin (BCG) is the only currently licensed anti-TB vaccine. However, other strategies, including modification of recombinant BCG vaccine, attenuated Mycobacterium tuberculosis (Mtb) mutant constructs, DNA and protein subunit vaccines, are under extensive investigation. As whole pathogen vaccines can trigger serious adverse reactions, most current strategies are focused on the development of safe anti-TB subunit vaccines; this is especially important given the rising TB infection rate in immunocompromised HIV patients. The whole Mtb genome has been mapped and major antigens have been identified; however, optimal vaccine delivery mode is still to be established. Isolated protein antigens are typically poorly immunogenic so adjuvants are required to induce strong and long-lasting immune responses. This article aims to review the developmental status of anti-TB subunit vaccine adjuvants.

Boosting BCG with recombinant influenza A virus tuberculosis vaccines increases pulmonary T cell responses but not protection against Mycobacterium tuberculosis infection

The current Mycobacterium bovis BCG vaccine provides inconsistent protection against pulmonary infection with Mycobacterium tuberculosis. Immunity induced by subcutaneous immunization with BCG wanes and does not promote early recruitment of T cell to the lungs after M. tuberculosis infection. Delivery of Tuberculosis (TB) vaccines to the lungs may increase and prolong immunity at the primary site of M. tuberculosis infection. Pulmonary immunization with recombinant influenza A viruses (rIAVs) expressing an immune-dominant M. tuberculosis CD4⁺ T cell epitope (PR8-p25 and X31-p25) stimulates protective immunity against lung TB infection. Here, we investigated the potential use of rIAVs to improve the efficacy of BCG using simultaneous immunization (SIM) and prime-boost strategies. SIM with parenteral BCG and intranasal PR8-p25 resulted in equivalent protection to BCG alone against early, acute and chronic M. tuberculosis infection. Boosting BCG with rIAVs increased the frequency of IFN-γ-secreting specific T cells (p<0.001) and polyfunctional CD4⁺ T cells (p<0.05) in the lungs compared to the BCG alone, however, this did not result in a significant increase in protection against M. tuberculosis compared to BCG alone. Therefore, sequential pulmonary immunization with these rIAVs after BCG increased M. tuberculosis-specific memory T cell responses in the lung, but not protection against M. tuberculosis infection.

Immunological Assessment of Lung Responses to Inhalational Lipoprotein Vaccines Against Bacterial Pathogens

Lipopeptides or lipoproteins show potential as safe and effective subunit vaccines for protection against bacterial pathogens. Provided suitable adjuvants are selected, such as the TLR2-stimulating molecules Pam₂Cys and Pam₃Cys, these may be formulated as inhalational vaccines to optimize localized pulmonary immune responses. Here, we present methods to assess antigen-specific memory lymphocyte responses to novel vaccines, with a focus on immune responses in the lung tissue and bronchoalveolar space. We describe detection of T-cell responses via leukocyte restimulation, followed by intracellular cytokine staining and flow cytometry, enzyme-linked immunosorbent spot assay (ELISpot), and sustained leukocyte restimulation for detection of antigen-specific memory responses. We also detail assessment of antibody responses to vaccine antigens, via enzyme-linked immunosorbent assay (ELISA)-based detection. These methods are suitable for testing a wide range of pulmonary vaccines.

A recombinant bovine adenoviral mucosal vaccine expressing mycobacterial antigen-85B generates robust protection against tuberculosis in mice

Although the BCG vaccine offers partial protection, tuberculosis remains a leading cause of infectious disease death, killing ∼1.5 million people annually. We developed mucosal vaccines expressing the autophagy-inducing peptide C5 and mycobacterial Ag85B-p25 epitope using replication-defective human adenovirus (HAdv85C5) and bovine adenovirus (BAdv85C5) vectors. BAdv85C5-infected dendritic cells (DCs) expressed a robust transcriptome of genes regulating antigen processing compared to HAdv85C5-infected DCs. BAdv85C5-infected DCs showed enhanced galectin-3/8 and autophagy-dependent in vitro Ag85B-p25 epitope presentation to CD4 T cells. BCG-vaccinated mice were intranasally boosted using HAdv85C5 or BAdv85C5 followed by infection using aerosolized Mycobacterium tuberculosis (Mtb). BAdv85C5 protected mice against tuberculosis both as a booster after BCG vaccine (>1.4-log10 reduction in Mtb lung burden) and as a single intranasal dose (>0.5-log10 reduction). Protection was associated with robust CD4 and CD8 effector (TEM), central memory (TCM), and CD103+/CD69+ lung-resident memory (TRM) T cell expansion, revealing BAdv85C5 as a promising mucosal vaccine for tuberculosis.

Assessment of CD27 expression on T-cells as a diagnostic and therapeutic tool for patients with smear-negative pulmonary tuberculosis

Background

There is a global focus on illness diagnosis in smear-negative and latent tuberculosis infectious populations (SN-TB and LTBI). CD27 has been suggested to play a direct role in active TB. Little is known about smear-negative individuals. Here, we tried to investigate whether it has a role in smear-negative populations. The expression of CD27 and MTB-specific CD27 in CD4⁺ T cells (“CD27⁻CD4⁺” and “CD27⁻IFN-γ⁺CD4⁺”) was evaluated in MTB-unexposed controls (HC), TB contacts (TB-C) and SN-TB individuals by flow cytometry. The sensitivity, specificity and AUC (area under curve) of “CD27⁻IFN-γ⁺CD4⁺” cells to distinguish SN-TBs from HCs and TB-Cs were determined by receiver operating characteristic (ROC) curve analysis. The clinical index was selected from the clinical laboratory and evaluated for correlation with “CD27⁻IFN-γ⁺CD4⁺” cells by Spearman statistical analysis.

Results

We observed that the percentages of “CD27⁻IFN-γ⁺CD4⁺” cells were significantly increased in the SN-TB group compared with the HC and TB-C groups (AUC was 0.88, sensitivity was 82.14%, specificity was 80.00%, and P < 0.0001). The percentage of “CD27⁻IFN-γ⁺CD4⁺” cells was negatively correlated with WBC (white blood cell count) (r = − 0.3019, P = 0.0182) and positively correlated with IgE (immunoglobulin E) (r = 0.2805, P = 0.0362). Furthermore, “CD27⁻IFN-γ⁺CD4⁺” cells were significantly decreased, especially in the > 50 years group, after clinical treatment.

Conclusion

The present results demonstrated that the percentage of “CD27⁻IFN-γ⁺CD4⁺” cells might be a conceivable molecular indicator in the diagnosis of SN-TB and was influenced by its outcome of therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12865-021-00430-y.

Mucosal Influenza Vector Vaccine Carrying TB10.4 and HspX Antigens Provides Protection against Mycobacterium tuberculosis in Mice and Guinea Pigs

New strategies providing protection against tuberculosis (TB) are still pending. The airborne nature of Mycobacterium tuberculosis (M.tb) infection assumes that the mucosal delivery of the TB vaccine could be a more promising strategy than the systemic route of immunization. We developed a mucosal TB vaccine candidate based on recombinant attenuated influenza vector (Flu/THSP) co-expressing truncated NS1 protein NS1(1–124) and a full-length TB10.4 and HspX proteins of M.tb within an NS1 protein open reading frame. The Flu/THSP vector was safe and stimulated a systemic TB-specific CD4+ and CD8+ T-cell immune response after intranasal immunization in mice. Double intranasal immunization with the Flu/THSP vector induced protection against two virulent M.tb strains equal to the effect of BCG subcutaneous injection in mice. In a guinea pig TB model, one intranasal immunization with Flu/THSP improved protection against M.tb when tested as a vaccine candidate for boosting BCG-primed immunity. Importantly, enhanced protection provided by a heterologous BCG-prime → Flu/THSP vector boost immunization scheme was associated with a significantly reduced lung and spleen bacterial burden (mean decrease of 0.77 lg CFU and 0.72 lg CFU, respectively) and improved lung pathology 8.5 weeks post-infection with virulent M.tb strain H37Rv.

Advax adjuvant formulations promote protective immunity against aerosol Mycobacterium tuberculosis in the absence of deleterious inflammation and reactogenicity

The development of safe and effective adjuvants is a critical goal of vaccine development programs. In this report, we defined the immunostimulatory profile and protective effect against aerosol Mycobacterium tuberculosis infection of vaccine formulations incorporating the semi-crystalline adjuvant δ-inulin (Advax). Advax formulated with CpG oligonucleotide and the QS-21 saponin (Advax^CpQS) was the most effective combination, demonstrated by the capacity of CysVac2/Advax^CpQS to significantly reduce the bacterial burden in the lungs of M. tuberculosis-infected mice. CysVac2/Advax^CpQS protection was associated with rapid influx of neutrophils, macrophages and monocytes to the site of vaccination and the induction of antigen-specific IFN-γ⁺/IL-2⁺/TNF⁺ polyfunctional CD4⁺ T cells in the lung. When compared to the highly potent adjuvant combination of monophosphoryl lipid A and dimethyldioctadecylammonium bromide (MPL/DDA), Advax^CpQS imparted a similar level of protective efficacy yet without the profound stimulation of inflammatory cytokines and vaccination site ulceration observed with MPL/DDA. Addition of DDA to CysVac2/Advax^CpQS further improved the protective effect of the vaccine, which correlated with increased polyfunctional CD4⁺ T cells in the lung but with no increase in vaccine reactogenicity. The data demonstrate that Advax formulations can decouple protective tuberculosis immunity from reactogenicity, making them ideal candidates for human application.

The generation of T-cell memory to protect against tuberculosis

Tuberculosis (TB) kills more individuals each year than any other single pathogen and a more effective vaccine is critical for the global control of the disease. Although there has been recent progress in the clinical testing of candidates, no new vaccine has been licensed for use and correlates of protective immunity in humans have not been defined. Prior Mycobacterium tuberculosis infection does not appear to confer long-term protective immunity in humans; thus mimicking the natural immune response to infection may not be a suitable approach to develop improved TB vaccines. Data from animal testing are used to progress vaccines through the "vaccine pipeline", but studies in animals have not been able to predict efficacy in humans. Furthermore, although the generation of conventional CD4⁺ T-cell responses are considered necessary to control infection with M. tuberculosis, these do not necessarily correlate with protection induced by candidate vaccines and other immune components may play a role, including donor unrestricted T cells, tissue-resident memory T cells and anti-M. tuberculosis antibodies. This review will summarize the current understanding of the protective immune responses following M. tuberculosis infection or vaccination, with a particular focus on vaccines that have recently entered clinical trials.

CXCR6-Deficiency Improves the Control of Pulmonary Mycobacterium tuberculosis and Influenza Infection Independent of T-Lymphocyte Recruitment to the Lungs

T-lymphocytes are critical for protection against respiratory infections, such as Mycobacterium tuberculosis and influenza virus, with chemokine receptors playing an important role in directing these cells to the lungs. CXCR6 is expressed by activated T-lymphocytes and its ligand, CXCL16, is constitutively expressed by the bronchial epithelia, suggesting a role in T-lymphocyte recruitment and retention. However, it is unknown whether CXCR6 is required in responses to pulmonary infection, particularly on CD4⁺ T-lymphocytes. Analysis of CXCR6-reporter mice revealed that in naïve mice, lung leukocyte expression of CXCR6 was largely restricted to a small population of T-lymphocytes, but this population was highly upregulated after either infection. Nevertheless, pulmonary infection of CXCR6-deficient mice with M. tuberculosis or recombinant influenza A virus expressing P25 peptide (rIAV-P25), an I-A^b-restricted epitope from the immunodominant mycobacterial antigen, Ag85B, demonstrated that the receptor was redundant for recruitment of T-lymphocytes to the lungs. Interestingly, CXCR6-deficiency resulted in reduced bacterial burden in the lungs 6 weeks after M. tuberculosis infection, and reduced weight loss after rIAV-P25 infection compared to wild type controls. This was paradoxically associated with a decrease in Th1-cytokine responses in the lung parenchyma. Adoptive transfer of P25-specific CXCR6-deficient T-lymphocytes into WT mice revealed that this functional change in Th1-cytokine production was not due to a T-lymphocyte intrinsic mechanism. Moreover, there was no reduction in the number or function of CD4⁺ and CD8⁺ tissue resident memory cells in the lungs of CXCR6-deficient mice. Although CXCR6 was not required for T-lymphocyte recruitment or retention in the lungs, CXCR6 influenced the kinetics of the inflammatory response so that deficiency led to increased host control of M. tuberculosis and influenza virus.

Deciphering protective immunity against tuberculosis: implications for vaccine development

INTRODUCTION

The development of more effective tuberculosis (TB) vaccines is essential for the global control of TB. Recently, there have been major advances in the field, but an important hindrance remains the lack of correlates of protection against TB. This requires each vaccine candidate to undergo clinical efficacy trials based on data from animal protection studies, but the results from animal models do not necessarily predict efficacy in humans.

AREAS COVERED

In this review we summarize our current knowledge of immune mechanisms that may contribute to protective immunity against TB following vaccination and relate these to protective efficacy in animal models and recent clinical trials. Although some initial trials did not reproduce protection against TB in humans, recent trials have demonstrated promising efficacy for three vaccine approaches.

EXPERT OPINION

Although CD4⁺ T lymphocytes are essential for protection against TB, there is no clear correlation between conventional CD4⁺ or CD8⁺ T cell responses and protective efficacy of TB vaccines. Recent attention has focused on other immune responses, including donor unrestricted T cells, B lymphocytes, and antibodies. Prospective studies on samples from vaccinated individuals protected in recent trials will allow evaluation of these alternative immune mechanisms as potential correlates of protection.

Pulmonary immunization with a recombinant influenza A virus vaccine induces lung-resident CD4+ memory T cells that are associated with protection against tuberculosis

The lung is the primary site of infection with the major human pathogen, Mycobacterium tuberculosis. Effective vaccines against M. tuberculosis must stimulate memory T cells to provide early protection in the lung. Recently, tissue-resident memory T cells (T_RM) were found to be phenotypically and transcriptional distinct from circulating memory T cells. Here, we identified M. tuberculosis-specific CD4⁺ T cells induced by recombinant influenza A viruses (rIAV) vaccines expressing M. tuberculosis peptides that persisted in the lung parenchyma with the phenotypic and transcriptional characteristics of T_RMs. To determine if these rIAV-induced CD4⁺ T_RM were protective independent of circulating memory T cells, mice previously immunized with the rIAV vaccine were treated with the sphingosine-1-phosphate receptor modulator, FTY720, prior to and during the first 17 days of M. tuberculosis challenge. This markedly reduced circulating T cells, but had no effect on the frequency of M. tuberculosis-specific CD4⁺ T_RMs in the lung parenchyma or their cytokine response to infection. Importantly, mice immunized with the rIAV vaccine were protected against M. tuberculosis infection even when circulating T cells were profoundly depleted by the treatment. Therefore, pulmonary immunization with the rIAV vaccine stimulates lung-resident CD4⁺ memory T cells that are associated with early protection against tuberculosis infection.

Protective efficacy of recombinant BCG over-expressing protective, stage-specific antigens of Mycobacterium tuberculosis

Tuberculosis (TB) remains a major cause of mortality and morbidity worldwide, yet current control strategies, including the existing BCG vaccine, have had little impact on disease control. CysVac2, a fusion protein comprising stage-specific Mycobacterium tuberculosis antigens, provided superior protective efficacy against chronic M. tuberculosis infection in mice, compared to BCG. To determine if the delivery of CysVac2 in the context of BCG could improve BCG-induced immunity and protection, we generated a recombinant strain of BCG overexpressing CysVac2 (rBCG:CysVac2). Expression of CysVac2 in BCG was facilitated by the M. tuberculosis hspX promoter, which is highly induced inside phagocytic cells and induces strong cellular immune responses to antigens expressed under its regulation. Intradermal vaccination with rBCG:CysVac2 resulted in increased monocyte/macrophage recruitment and enhanced antigen-specific CD4⁺ T cell priming compared to parental BCG, indicating CysVac2 overexpression had a marked effect on rBCG induced-immunity. Further, rBCG:CysVac2 was a more potent inducer of antigen-specific multifunctional CD4⁺ T cells (CD4⁺IFN-γ⁺TNF⁺IL-2⁺) than BCG after vaccination of mice. This improved immunogenicity however did not influence protective efficacy, with both BCG and rBCG:CysVac2 affording comparable level of protection aerosol infection with M. tuberculosis. Boosting either BCG or rBCG:CysVac2 with the CysVac2 fusion protein resulted in a similar improvement in protective efficacy. These results demonstrate that the expression of protective antigens in BCG can augment antigen-specific immunity after vaccination but does not alter protection against infection, further highlighting the challenge of developing effective vaccines to control TB.

Influenza interaction with cocirculating pathogens and its impact on surveillance, pathogenesis, and epidemic profile: A key role for mathematical modelling

Evidence is mounting that influenza virus interacts with other pathogens colonising or infecting the human respiratory tract. Taking into account interactions with other pathogens may be critical to determining the real influenza burden and the full impact of public health policies targeting influenza. This is particularly true for mathematical modelling studies, which have become critical in public health decision-making. Yet models usually focus on influenza virus acquisition and infection alone, thereby making broad oversimplifications of pathogen ecology. Herein, we report evidence of influenza virus interactions with bacteria and viruses and systematically review the modelling studies that have incorporated interactions. Despite the many studies examining possible associations between influenza and Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, Neisseria meningitidis, respiratory syncytial virus (RSV), human rhinoviruses, human parainfluenza viruses, etc., very few mathematical models have integrated other pathogens alongside influenza. The notable exception is the pneumococcus-influenza interaction, for which several recent modelling studies demonstrate the power of dynamic modelling as an approach to test biological hypotheses on interaction mechanisms and estimate the strength of those interactions. We explore how different interference mechanisms may lead to unexpected incidence trends and possible misinterpretation, and we illustrate the impact of interactions on public health surveillance using simple transmission models. We demonstrate that the development of multipathogen models is essential to assessing the true public health burden of influenza and that it is needed to help improve planning and evaluation of control measures. Finally, we identify the public health, surveillance, modelling, and biological challenges and propose avenues of research for the coming years.

SAFETY AND IMMUNOGENICITY OF COLD-ADAPTED RECOMBINANT INFLUENZA VECTOR EXPRESSING ESAT-6 AND AG85А ANTIGENS OF M. TUBERCULOSIS

Recombinant viral vectors represent one of the most promising platforms for creating a new generation of vaccines against tuberculosis. We constructed a vaccine candidate based on a cold-adapted influenza vector with a truncated NS1 protein containing an insert of tuberculosis ESAT-6 and Ag85A antigens. The recombinant virus possessed a cold-adapted and temperature-sensitive phenotype and was attenuated for mice when administered intranasally. Immunofluorescent staining and Western blot showed the expression of ESAT-6 protein in MDCK cells infected by recombinant virus. After intranasal administration to mice, the recombinant virus stimulated a specific anti-tuberculosis CD4 + Th1-type response with the formation of polyfunctional antigen-specific T cells.

Delta inulin-based adjuvants promote the generation of polyfunctional CD4+ T cell responses and protection against Mycobacterium tuberculosis infection

There is an urgent need for the rational design of safe and effective vaccines to protect against chronic bacterial pathogens such as Mycobacterium tuberculosis. Advax™ is a novel adjuvant based on delta inulin microparticles that enhances immunity with a minimal inflammatory profile and has entered human trials to protect against viral pathogens. In this report we determined if Advax displays broad applicability against important human pathogens by assessing protective immunity against infection with M. tuberculosis. The fusion protein CysVac2, comprising the M. tuberculosis antigens Ag85B (Rv1886c) and CysD (Rv1285) formulated with Advax provided significant protection in the lungs of M. tuberculosis-infected mice. Protection was associated with the generation of CysVac2-specific multifunctional CD4+ T cells (IFN-γ+TNF+IL-2+). Addition to Advax of the TLR9 agonist, CpG oligonucleotide (AdvaxCpG), improved both the immunogenicity and protective efficacy of CysVac2. Immunisation with CysVac2/AdvaxCpG resulted in heightened release of the chemoattractants, CXCL1, CCL3, and TNF, and rapid influx of monocytes and neutrophils to the site of vaccination, with pronounced early priming of CysVac2-specific CD4+ T cells. As delta inulin adjuvants have shown an excellent safety and tolerability profile in humans, CysVac2/AdvaxCpG is a strong candidate for further preclinical evaluation for progression to human trials.

Mycobacterium tuberculosis components expressed during chronic infection of the lung contribute to long-term control of pulmonary tuberculosis in mice

Tuberculosis (TB) remains a major cause of mortality and morbidity worldwide, yet current control strategies, including the existing BCG vaccine, have had little impact on disease control. The tubercle bacillus modifies protein expression to adapt to chronic infection of the host, and this can potentially be exploited to develop novel therapeutics. We identified the gene encoding the first step of the Mycobacterium tuberculosis sulphur assimilation pathway, cysD, as highly induced during chronic infection in the mouse lung, suggesting therapies based on CysD could be used to target infection. Vaccination with the composite vaccine CysVac2, a fusion of CysD and the immunogenic Ag85B of M. tuberculosis, resulted in the generation of multifunctional CD4+ T cells (interferon (IFN)-γ+TNF+IL-2+IL-17+) in the lung both pre- and post-aerosol challenge with M. tuberculosis. CysVac2 conferred significant protection against pulmonary M. tuberculosis challenge and was particularly effective at controlling late-stage infection, a property not shared by BCG. CysVac2 delivered as a booster following BCG vaccination afforded greater protection against M. tuberculosis challenge than BCG alone. The antigenic components of CysVac2 were conserved amongst M. tuberculosis strains, and protective efficacy afforded by CysVac2 was observed across varying murine MHC haplotypes. Strikingly, administration of CysVac2 to mice previously infected with M. tuberculosis reduced bacterial load and immunopathology in the lung compared with BCG-vaccinated mice. These results indicate that CysVac2 warrants further investigation to assess its potential to control pulmonary TB in humans.

Novel approaches to preclinical research and TB vaccine development

The 4th Global Forum on TB Vaccines, convened in Shanghai, China, from 21 - 24 April 2015, brought together a wide and diverse community involved in tuberculosis vaccine research and development to discuss the current status of, and future directions for this critical effort. This paper summarizes the sessions on Low-Dose NHP Challenge Models, Novel Approaches to Animal Models for TB Vaccine R&D, Novel Antigen Delivery Strategies, and Next Generation TB Vaccines and Vaccine Concepts. Summaries of all sessions from the 4th Global Forum are compiled in a special supplement of Tuberculosis. [August 2016, Vol 99, Supp S1, S1-S30].

TB vaccines; promoting rapid and durable protection in the lung

TB vaccine discovery has focused on IFN-γ both for the selection of antigens and vaccine delivery strategies. Recent breakthroughs in our understanding of the requirements for immunological memory and the expression of immunity to TB in the lung now provide a framework for reconsidering that strategy. We will discuss the status of the TB vaccine field, recent insights into the role of central memory cells and the potential of tissue-resident memory cells in vaccine promoted protection against TB.