Selective delipidation of Mycobacterium bovis BCG enables direct pulmonary vaccination and enhances protection against Mycobacterium tuberculosis

BCG's role in strengthening immune responses: Implications for tuberculosis and comorbid diseases

The BCG vaccine represents a significant milestone in the prevention of tuberculosis (TB), particularly in children. Researchers have been developing recombinant BCG (rBCG) variants that can trigger lasting memory responses, thereby enhancing protection against TB in adults. The breakdown of immune surveillance is a key link between TB and other communicable and non-communicable diseases. Notably, TB is more prevalent among people with comorbidities such as HIV, diabetes, cancer, influenza, COVID-19, and autoimmune disorders. rBCG formulations have the potential to address both TB and HIV co-pandemics. TB increases the risk of lung cancer and immunosuppression caused by cancer can reactivate latent TB infections. Moreover, BCG's efficacy extends to bladder cancer treatment and blood glucose regulation in patients with diabetes and TB. Additionally, BCG provides cross-protection against unrelated pathogens, emphasizing the importance of BCG-induced trained immunity in COVID-19 and other respiratory diseases. Furthermore, BCG reduced the severity of pulmonary TB-induced influenza virus infections. Recent studies have proposed innovations in BCG delivery, revaccination, and attenuation techniques. Disease-centered research has highlighted the immunomodulatory effects of BCG on TB, HIV, cancer, diabetes, COVID-19, and autoimmune diseases. The complex relationship between TB and comorbidities requires a nuanced re-evaluation to understand the shared attributes regulated by BCG. This review assessed the interconnected relationships influenced by BCG administration in TB and related disorders, recommending the expanded use of rBCG in healthcare. Collaboration among vaccine research stakeholders is vital to enhance BCG's efficacy against global health challenges.

The frequency of CD38+ alveolar macrophages correlates with early control of M. tuberculosis in the murine lung

Tuberculosis, caused by Mycobacterium tuberculosis, remains an enduring global health challenge due to the limited efficacy of existing treatments. Although much research has focused on immune failure, the role of host macrophage biology in controlling the disease remains underappreciated. Here we show, through multi-modal single-cell RNA sequencing in a murine model, that different alveolar macrophage subsets play distinct roles in either advancing or controlling the disease. Initially, alveolar macrophages that are negative for the CD38 marker are the main infected population. As the infection progresses, CD38+ monocyte-derived and tissue-resident alveolar macrophages emerge as significant controllers of bacterial growth. These macrophages display a unique chromatin organization pre-infection, indicative of epigenetic priming for pro-inflammatory responses. Moreover, intranasal BCG immunization increases the numbers of CD38+ macrophages, enhancing their capability to restrict Mycobacterium tuberculosis growth. Our findings highlight the dynamic roles of alveolar macrophages in tuberculosis and open pathways for improved vaccines and therapies.

CD38+ Alveolar macrophages mediate early control of M. tuberculosis proliferation in the lung

Tuberculosis, caused by M.tuberculosis (Mtb), remains an enduring global health challenge, especially given the limited efficacy of current therapeutic interventions. Much of existing research has focused on immune failure as a driver of tuberculosis. However, the crucial role of host macrophage biology in controlling the disease remains underappreciated. While we have gained deeper insights into how alveolar macrophages (AMs) interact with Mtb, the precise AM subsets that mediate protection and potentially prevent tuberculosis progression have yet to be identified. In this study, we employed multi-modal scRNA-seq analyses to evaluate the functional roles of diverse macrophage subpopulations across different infection timepoints, allowing us to delineate the dynamic landscape of controller and permissive AM populations during the course of infection. Our analyses at specific time-intervals post-Mtb challenge revealed macrophage populations transitioning between distinct anti- and pro-inflammatory states. Notably, early in Mtb infection, CD38- AMs showed a muted response. As infection progressed, we observed a phenotypic shift in AMs, with CD38+ monocyte-derived AMs (moAMs) and a subset of tissue-resident AMs (TR-AMs) emerging as significant controllers of bacterial growth. Furthermore, scATAC-seq analysis of naïve lungs demonstrated that CD38+ TR-AMs possessed a distinct chromatin signature prior to infection, indicative of epigenetic priming and predisposition to a pro-inflammatory response. BCG intranasal immunization increased the numbers of CD38+ macrophages, substantially enhancing their capability to restrict Mtb growth. Collectively, our findings emphasize the pivotal, dynamic roles of different macrophage subsets in TB infection and reveal rational pathways for the development of improved vaccines and immunotherapeutic strategies.

A modified BCG with depletion of enzymes associated with peptidoglycan amidation induces enhanced protection against tuberculosis in mice

Mechanisms by which Mycobacterium tuberculosis (Mtb) evades pathogen recognition receptor activation during infection may offer insights for the development of improved tuberculosis (TB) vaccines. Whilst Mtb elicits NOD-2 activation through host recognition of its peptidoglycan-derived muramyl dipeptide (MDP), it masks the endogenous NOD-1 ligand through amidation of glutamate at the second position in peptidoglycan side-chains. As the current BCG vaccine is derived from pathogenic mycobacteria, a similar situation prevails. To alleviate this masking ability and to potentially improve efficacy of the BCG vaccine, we used CRISPRi to inhibit expression of the essential enzyme pair, MurT-GatD, implicated in amidation of peptidoglycan side-chains. We demonstrate that depletion of these enzymes results in reduced growth, cell wall defects, increased susceptibility to antibiotics, altered spatial localization of new peptidoglycan and increased NOD-1 expression in macrophages. In cell culture experiments, training of a human monocyte cell line with this recombinant BCG yielded improved control of Mtb growth. In the murine model of TB infection, we demonstrate that depletion of MurT-GatD in BCG, which is expected to unmask the D-glutamate diaminopimelate (iE-DAP) NOD-1 ligand, yields superior prevention of TB disease compared to the standard BCG vaccine. In vitro and in vivo experiments in this study demonstrate the feasibility of gene regulation platforms such as CRISPRi to alter antigen presentation in BCG in a bespoke manner that tunes immunity towards more effective protection against TB disease.

BCG-booster vaccination with HSP90-ESAT-6-HspX-RipA multivalent subunit vaccine confers durable protection against hypervirulent Mtb in mice

The quest for effective and enhanced multiantigenic tuberculosis (TB) subunit vaccine necessitates the induction of a protective pathogen-specific immune response while circumventing detrimental inflammation within the lung milieu. In line with this goal, we engineered a modified iteration of the quadrivalent vaccine, namely HSP90-ESAT-6-HspX-RipA (HEHR), which was coupled with the TLR4 adjuvant, CIA09A. The ensuing formulation was subjected to comprehensive assessment to gauge its protective efficacy against the hypervirulent Mycobacterium tuberculosis (Mtb) Haarlem clinical strain M2, following a BCG-prime boost regimen. Regardless of vaccination route, both intramuscular and subcutaneous administration with the HEHR vaccine exhibited remarkable protective efficacy in significantly reducing the Mtb bacterial burden and pulmonary inflammation. This underscores its notably superior protective potential compared to the BCG vaccine alone or a former prototype, the HSP90-E6 subunit vaccine. In addition, this superior protective efficacy was confirmed when testing a tag-free version of the HEHR vaccine. Furthermore, the protective immune determinant, represented by durable antigen-specific CD4+IFN-γ+IL-17A+ T-cells expressing a CXCR3+KLRG1- cell surface phenotype in the lung, was robustly induced in HEHR-boosted mice at 12 weeks post-challenge. Collectively, our data suggest that the BCG-prime HEHR boost vaccine regimen conferred improved and long-term protection against hypervirulent Mtb strain with robust antigen-specific Th1/Th17 responses.

Lung IL-17A-Producing CD4+ T Cells Correlate with Protection after Intrapulmonary Vaccination with Differentially Adjuvanted Tuberculosis Vaccines

Tuberculosis (TB), caused by Mycobacterium tuberculosis, results in approximately 1.6 million deaths annually. BCG is the only TB vaccine currently in use and offers only variable protection; however, the development of more effective vaccines is hindered by a lack of defined correlates of protection (CoP) against M. tuberculosis. Pulmonary vaccine delivery is a promising strategy since it may promote lung-resident immune memory that can respond rapidly to respiratory infection. In this study, CysVac2, a subunit protein previously shown to be protective against M. tuberculosis in mouse models, was combined with either Advax® adjuvant or a mixture of alum plus MPLA and administered intratracheally into mice. Peripheral immune responses were tracked longitudinally, and lung-local immune responses were measured after challenge. Both readouts were then correlated with protection after M. tuberculosis infection. Although considered essential for the control of mycobacteria, induction of IFN-γ-expressing CD4+ T cells in the blood or lungs did not correlate with protection. Instead, CD4+ T cells in the lungs expressing IL-17A correlated with reduced bacterial burden. This study identified pulmonary IL-17A-expressing CD4+ T cells as a CoP against M. tuberculosis and suggests that mucosal immune profiles should be explored for novel CoP.

Characterization of the Efficacy of a Split Swine Influenza A Virus Nasal Vaccine Formulated with a Nanoparticle/STING Agonist Combination Adjuvant in Conventional Pigs

Swine influenza A viruses (SwIAVs) are pathogens of both veterinary and medical significance. Intranasal (IN) vaccination has the potential to reduce flu infection. We investigated the efficacy of split SwIAV H1N2 antigens adsorbed with a plant origin nanoparticle adjuvant [Nano11-SwIAV] or in combination with a STING agonist ADU-S100 [NanoS100-SwIAV]. Conventional pigs were vaccinated via IN and challenged with a heterologous SwIAV H1N1-OH7 or 2009 H1N1 pandemic virus. Immunologically, in NanoS100-SwIAV vaccinates, we observed enhanced frequencies of activated monocytes in the blood of the pandemic virus challenged animals and in tracheobronchial lymph nodes (TBLN) of H1N1-OH7 challenged animals. In both groups of the virus challenged pigs, increased frequencies of IL-17A+ and CD49d+IL-17A+ cytotoxic lymphocytes were observed in Nano11-SwIAV vaccinates in the draining TBLN. Enhanced frequency of CD49d+IFNγ+ CTLs in the TBLN and blood of both the Nano11-based SwIAV vaccinates was observed. Animals vaccinated with both Nano11-based vaccines had upregulated cross-reactive secretory IgA in the lungs and serum IgG against heterologous and heterosubtypic viruses. However, in NanoS100-SwIAV vaccinates, a slight early reduction in the H1N1 pandemic virus and a late reduction in the SwIAV H1N1-OH7 load in the nasal passages were detected. Hence, despite vast genetic differences between the vaccine and both the challenge viruses, IN vaccination with NanoS100-SwIAV induced antigen-specific moderate levels of cross-protective immune responses.

A modified BCG with depletion of enzymes associated with peptidoglycan amidation induces enhanced protection against tuberculosis in mice

Mechanisms by which Mycobacterium tuberculosis (Mtb) evades pathogen recognition receptor activation during infection may offer insights for the development of improved tuberculosis (TB) vaccines. Whilst Mtb elicits NOD-2 activation through host recognition of its peptidoglycan-derived muramyl dipeptide (MDP), it masks the endogenous NOD-1 ligand through amidation of glutamate at the second position in peptidoglycan sidechains. As the current BCG vaccine is derived from pathogenic mycobacteria, a similar situation prevails. To alleviate this masking ability and to potentially improve efficacy of the BCG vaccine, we used CRISPRi to inhibit expression of the essential enzyme pair, MurT-GatD, implicated in amidation of peptidoglycan sidechains. We demonstrate that depletion of these enzymes results in reduced growth, cell wall defects, increased susceptibility to antibiotics and altered spatial localization of new peptidoglycan. In cell culture experiments, training of monocytes with this recombinant BCG yielded improved control of Mtb growth. In the murine model of TB infection, we demonstrate that depletion of MurT-GatD in BCG, resulting in unmasking of the D-glutamate diaminopimelate (iE-DAP) NOD-1 ligand, yields superior prevention of TB disease compared to the standard BCG vaccine. This work demonstrates the feasibility of gene regulation platforms such as CRISPRi to alter antigen presentation in BCG in a bespoke manner that tunes immunity towards more effective protection against TB disease.

Selective delipidation of Mycobacterium bovis BCG retains antitumor efficacy against non-muscle invasive bladder cancer

PURPOSE

Repeated instillations of bacillus Calmette et Guérin (BCG) are the gold standard immunotherapeutic treatment for reducing recurrence for patients with high-grade papillary non-muscle invasive bladder cancer (NMIBC) and for eradicating bladder carcinoma-in situ. Unfortunately, some patients are unable to tolerate BCG due to treatment-associated toxicity and bladder removal is sometimes performed for BCG-intolerance. Prior studies suggest that selectively delipidated BCG (dBCG) improves tolerability of intrapulmonary delivery reducing tissue damage and increasing efficacy in preventing Mycobacterium tuberculosis infection in mice. To address the lack of treatment options for NMIBC with BCG-intolerance, we examined if selective delipidation would compromise BCG's antitumor efficacy and at the same time increase tolerability to the treatment.

MATERIALS AND METHODS

Murine syngeneic MB49 bladder cancer models and in vitro human innate effector cell cytotoxicity assays were used to evaluate efficacy and immune impact of selective delipidation in Tokyo and TICE BCG strains.

RESULTS

Both dBCG-Tokyo and dBCG-TICE effectively treated subcutaneous MB49 tumors in mice and enhanced tumor-infiltrating CD8+ T and natural killer cells, similar to conventional BCG. However, when compared to conventional BCG, only dBCG-Tokyo retained a significant effect on intratumoral tumor-specific CD8+ and γδ T cells by increasing their frequencies in tumor tissue and their production of antitumoral function-related cytokines, i.e., IFN-γ and granzyme B. Further, dBCG-Tokyo but not dBCG-TICE enhanced the function and cytotoxicity of innate effector cells against human bladder cancer T24 in vitro.

CONCLUSIONS

These data support clinical investigation of dBCG-Tokyo as a treatment for patients with BCG-intolerant NMIBC.

A split influenza vaccine formulated with a combination adjuvant composed of alpha-D-glucan nanoparticles and a STING agonist elicits cross-protective immunity in pigs

BACKGROUND

Swine influenza A viruses (SwIAVs) pose an economic and pandemic threat, and development of novel effective vaccines is of critical significance. We evaluated the performance of split swine influenza A virus (SwIAV) H1N2 antigens with a plant-derived nanoparticle adjuvant alone (Nano-11) [Nano11-SwIAV] or in combination with the synthetic stimulator of interferon genes (STING) agonist ADU-S100 (NanoS100-SwIAV). Specific pathogen free (SPF) pigs were vaccinated twice via intramuscular (IM) or intradermal (ID) routes and challenged with a virulent heterologous SwIAV H1N1-OH7 virus.

RESULTS

Animals vaccinated IM or ID with NanoS100-SwIAV had significantly increased cross-reactive IgG and IgA titers in serum, nasal secretion and bronchoalveolar lavage fluid at day post challenge 6 (DPC6). Furthermore, NanoS100-SwIAV ID vaccinates, even at half the vaccine dose compared to their IM vaccinated counterparts, had significantly increased frequencies of CXCL10⁺ myeloid cells in the tracheobronchial lymph nodes (TBLN), and IFNγ⁺ effector memory T-helper/memory cells, IL-17A⁺ total T-helper/memory cells, central and effector memory T-helper/memory cells, IL-17A⁺ total cytotoxic T-lymphocytes (CTLs), and early effector CTLs in blood compared with the Nano11-SwIAV group demonstrating a potential dose-sparing effect and induction of a strong IL-17A⁺ T-helper/memory (Th17) response in the periphery. However, the frequencies of IFNγ⁺ late effector CTLs and effector memory T-helper/memory cells, IL-17A⁺ total CTLs, late effector CTLs, and CXCL10⁺ myeloid cells in blood, as well as lung CXCL10⁺ plasmacytoid dendritic cells were increased in NanoS100-SwIAV IM vaccinated pigs. Increased expression of IL-4 and IL-6 mRNA was observed in TBLN of Nano-11 based IM vaccinates following challenge. Furthermore, the challenge virus load in the lungs and nasal passage was undetectable in NanoS100-SwIAV IM vaccinates by DPC6 along with reduced macroscopic lung lesions and significantly higher virus neutralization titers in lungs at DPC6. However, NanoS100-SwIAV ID vaccinates exhibited significant reduction of challenge virus titers in nasal passages and a remarkable reduction of challenge virus in lungs.

CONCLUSIONS

Despite vast genetic difference (77% HA gene identity) between the H1N2 and H1N1 SwIAV, the NanoS100 adjuvanted vaccine elicited cross protective cell mediated immune responses, suggesting the potential role of this combination adjuvant in inducing cross-protective immunity in pigs.

A century of BCG vaccination: Immune mechanisms, animal models, non-traditional routes and implications for COVID-19

Bacillus Calmette-Guerin (BCG) has been used as a vaccine against tuberculosis since 1921 and remains the only currently approved vaccine for this infection. The recent discovery that BCG protects against initial infection, and not just against progression from latent to active disease, has significant implications for ongoing research into the immune mechanisms that are relevant to generate a solid host defense against Mycobacterium tuberculosis (Mtb). In this review, we first explore the different components of immunity that are augmented after BCG vaccination. Next, we summarize current efforts to improve the efficacy of BCG through the development of recombinant strains, heterologous prime-boost approaches and the deployment of non-traditional routes. These efforts have included the development of new recombinant BCG strains, and various strategies for expression of important antigens such as those deleted during the M. bovis attenuation process or antigens that are present only in Mtb. BCG is typically administered via the intradermal route, raising questions about whether this could account for its apparent failure to generate long-lasting immunological memory in the lungs and the inconsistent level of protection against pulmonary tuberculosis in adults. Recent years have seen a resurgence of interest in the mucosal and intravenous delivery routes as they have been shown to induce a better immune response both in the systemic and mucosal compartments. Finally, we discuss the potential benefits of the ability of BCG to confer trained immunity in a non-specific manner by broadly stimulating a host immunity resulting in a generalized survival benefit in neonates and the elderly, while potentially offering benefits for the control of new and emerging infectious diseases such as COVID-19. Given that BCG will likely continue to be widely used well into the future, it remains of critical importance to better understand the immune responses driven by it and how to leverage these for the design of improved vaccination strategies against tuberculosis.

Human Pulmonary Tuberculosis: Understanding the Immune Response in the Bronchoalveolar System

Mycobacterium tuberculosis, the causal agent of one of the most devastating infectious diseases worldwide, can evade or modulate the host immune response and remain dormant for many years. In this review, we focus on identifying the local immune response induced in vivo by M. tuberculosis in the lungs of patients with active tuberculosis by analyzing data from untouched cells from bronchoalveolar lavage fluid (BALF) or exhaled breath condensate (EBC) samples. The most abundant resident cells in patients with active tuberculosis are macrophages and lymphocytes, which facilitate the recruitment of neutrophils. The cellular response is characterized by an inflammatory state and oxidative stress produced mainly by macrophages and T lymphocytes. In the alveolar microenvironment, the levels of cytokines such as interleukins (IL), chemokines, and matrix metalloproteinases (MMP) are increased compared with healthy patients. The production of cytokines such as interferon (IFN)-γ and IL-17 and specific immunoglobulin (Ig) A and G against M. tuberculosis indicate that the adaptive immune response is induced despite the presence of a chronic infection. The role of epithelial cells, the processing and presentation of antigens by macrophages and dendritic cells, as well as the role of tissue-resident memory T cells (Trm) for in situ vaccination remains to be understood.

Intranasal bovine β-defensin-5 enhances antituberculosis immunity in a mouse model by a novel protein-based respiratory mucosal vaccine

Respiratory mucosal immunization is an effective immunization strategy against tuberculosis (TB), and effective mucosal vaccines require adjuvants that can promote protective immunity without deleterious inflammation. Mucosal BCG (Bacille Calmette-Guerin) is effective, but it causes a severe inflammatory response in the lung. A novel less cytotoxic mucosal vaccine AH-PB containing Mycobacterium tuberculosis (Mtb) cell surface antigens Ag85A and HspX (AH), as well as polyinosinic-polycytidylic acid (Poly IC) and bovine neutrophil β-defensin-5 (B5) adjuvants were prepared, with the overarching goal of protecting against TB. Then, the immunogenicity and protective efficacy of these vaccines via the intranasal route were evaluated in a mouse model. Results showed that intranasal AH-PB promoted tissue-resident memory T cells (T_RMs) development in the lung, induced antigen-specific antibody response in airway, provided protection against Mycobacterium bovis (M. bovis), conferred better protection than parenteral BCG in the later stage of infection, and boosted the protective immunity generated by BCG in mice. Moreover, both B5 and Poly IC were indispensable for the protection generated by AH-PB. Furthermore, intranasal immunization with AH-B5 fusion vaccines also provided similar protection against M. bovis compared to AH-PB. Collectively, B5-based TB vaccine via the intranasal route is a promising immunization strategy against bovine TB, and this kind of immunization strategy may be applied to human TB vaccine development. These findings highlight the potential importance of B5 as a mucosal adjuvant used in TB vaccines or other respiratory disease vaccines.

IL-10 Receptor Blockade Delivered Simultaneously with Bacillus Calmette-Guérin Vaccination Sustains Long-Term Protection against Mycobacterium tuberculosis Infection in Mice

Mycobacterium bovis bacillus Calmette-Guérin (BCG) immunization still remains the best vaccination strategy available to control the development of active tuberculosis. Protection afforded by BCG vaccination gradually wanes over time and although booster strategies have promise, they remain under development. An alternative approach is to improve BCG efficacy through host-directed therapy. Building upon prior knowledge that blockade of IL-10R1 during early Mycobacterium tuberculosis infection improves and extends control of M. tuberculosis infection in mice, we employed a combined anti-IL-10R1/BCG vaccine strategy. An s.c. single vaccination of BCG/anti-IL10-R1 increased the numbers of CD4+ and CD8+ central memory T cells and reduced Th1 and Th17 cytokine levels in the lung for up to 7 wk postvaccination. Subsequent M. tuberculosis challenge in mice showed both an early (4 wk) and sustained long-term (47 wk) control of infection, which was associated with increased survival. In contrast, protection of BCG/saline-vaccinated mice waned 8 wk after M. tuberculosis infection. Our findings demonstrate that a single and simultaneous vaccination with BCG/anti-IL10-R1 sustains long-term protection, identifying a promising approach to enhance and extend the current BCG-mediated protection against TB.

BCG vaccination strategies against tuberculosis: updates and perspectives

Bacillus Calmette-Guérin (BCG) is the only licensed vaccine against tuberculosis (TB). However, BCG has variable efficacy and cannot completely prevent TB infection and transmission. Therefore, the worldwide prevalence of TB calls for urgent development of a more effective TB vaccine. In the absence of other approved vaccines, it is also necessary to improve the efficacy of BCG itself. Intravenous (IV) BCG administration and BCG revaccination strategies have recently shown promising results for clinical usage. Therefore, it is necessary for us to revisit the BCG vaccination strategies and summarize the current research updates related to BCG vaccination. This literature review provides an updated overview and perspectives of the immunization strategies against TB using BCG, which may inspire the following research on TB vaccine development.

Interleukin-23 instructs protective multifunctional CD4 T cell responses after immunization with the Mycobacterium tuberculosis subunit vaccine H1 DDA/TDB independently of interleukin-17A

Interleukin (IL)-17A-producing T helper (Th)17 cells are increasingly being acknowledged to be associated with protective immunity to Mycobacterium tuberculosis (Mtb). Subunit vaccines potently promote protective immune responses against Mtb infection that correlate with an expansion of IL-23-dependent Th17 cells. Previous studies revealed that after vaccination, IL-23 is required for protection against challenge with Mtb but the underlying IL-23-dependent-and possibly IL-17A-mediated-mechanisms remain elusive. Therefore, we here analyzed the early outcome of Mtb infection in C57BL/6, IL-23p19-deficient (-/-), and IL-17A-/- mice after vaccination with the subunit vaccine H1-DDA/TDB to investigate the role of the IL-23-Th17 immune axis for the instruction of vaccine-induced protection. While in IL-23p19-/- mice the protective effect was reduced, protection after vaccination was maintained in IL-17A-/- animals for the course of infection of 6 weeks, indicating that after vaccination with H1-DDA/TDB early protection against Mtb is-although dependent on IL-23-not mediated by IL-17A. In contrast, IL-17A deficiency appears to have an impact on maintaining long-term protection. In fact, IL-23 instructed the vaccine-induced memory immunity in the lung, in particular the sustained expansion of tumor necrosis factor (TNF)+IL-2+ multifunctional T cells, independently of IL-17A. Altogether, a targeted induction of IL-23 during vaccination against Mtb might improve the magnitude and quality of vaccine-induced memory immune responses. KEY MESSAGES: After subunit Mtb vaccination with H1-DDA/TDB, IL-23 but not IL-17A contributes to vaccine-induced early protection against infection with Mtb. IL-17F does not compensate for IL-17A deficiency in terms of H1-DDA/TDB-induced protection against Mtb infection. IL 23 promotes the H1-DDA/TDB-induced accumulation of effector memory T cells independently of IL 17A. IL-23 arbitrates the induction of H1-specific IFN-γ-TNF+IL-2+ double-positive multifunctional CD4 T cells after subunit Mtb vaccination in an IL-17A-independent manner.

New Developments and Insights in the Improvement of Mycobacterium tuberculosis Vaccines and Diagnostics Within the End TB Strategy

PURPOSE OF REVIEW

The alignment of sustainable development goals (SDGs) with the End Tuberculosis (TB) strategy provides an integrated roadmap to implement key approaches towards TB elimination. This review summarizes current social challenges for TB control, and yet, recent developments in TB diagnosis and vaccines in the context of the End TB strategy and SDGs to transform global health.

RECENT FINDINGS

Advances in non-sputum based TB biomarkers and whole genome sequencing technologies could revolutionize TB diagnostics. Moreover, synergistic novel technologies such as mRNA vaccination, nanovaccines and promising TB vaccine models are key promising developments for TB prevention and control.

SUMMARY

The End TB strategy depends on novel developments in point-of-care TB diagnostics and effective vaccines. However, despite outstanding technological developments in these fields, TB elimination will be unlikely achieved if TB social determinants are not fully addressed. Indeed, the End TB strategy and SDGs emphasize the importance of implementing sustainable universal health coverage and social protection.

Protective efficacy of an attenuated Mtb ΔLprG vaccine in mice

Bacille Calmette-Guerin (BCG), an attenuated whole cell vaccine based on Mycobacterium bovis, is the only licensed vaccine against Mycobacterium tuberculosis (Mtb), but its efficacy is suboptimal and it fails to protect against pulmonary tuberculosis. We previously reported that Mtb lacking the virulence genes lprG and rv1410c (ΔLprG) was highly attenuated in immune deficient mice. In this study, we show that attenuated ΔLprG Mtb protects C57BL/6J, Balb/cJ, and C3HeB/FeJ mice against Mtb challenge and is as attenuated as BCG in SCID mice. In C3HeB/FeJ mice, ΔLprG vaccination resulted in innate peripheral cytokine production and induced high polyclonal PPD-specific cytokine-secreting CD4⁺ T lymphocytes in peripheral blood. The ΔLprG vaccine afforded protective efficacy in the lungs of C3H/FeJ mice following both H37Rv and Erdman aerosolized Mtb challenges. Vaccine efficacy correlated with antigen-specific PD-1-negative CD4⁺ T lymphocytes as well as with serum IL-17 levels after vaccination. We hypothesize that induction of Th17 cells in lung is critical for vaccine protection, and we show a serum cytokine biomarker for IL-17 shortly after vaccination may predict protective efficacy.

Many successful vaccines are based on attenuated human pathogens. The only licensed tuberculosis vaccine, BCG, is based on an attenuated version of live whole cell Mycobacterium bovis, the causative agent of tuberculosis (TB) in cattle. Advantages to using attenuated pathogens as vaccines include a broad antigen composition including proteins, lipids, carbohydrates and other molecules that can induce durable immune responses sometimes lasting decades. Here we test an attenuated Mycobacterium tuberculosis (Mtb), the causative agent of human TB, that lacks a key virulence factor as an alternative whole cell vaccine in mice. Attenuated Mtb lacking a key virulence protein, LprG, is immunogenic and protects mice against Mtb challenge. The LprG whole cell vaccine is protective in mice that develop lung pathology more similar to what is described in human TB and the LprG vaccine induces a key cytokine, IL-17, thought to be important for vaccine protection, in the peripheral blood early after vaccination. Together these data support the continued development of attenuated TB as a potential vaccine candidate. Furthermore our data suggests that serum IL-17 should be explored as a potential biomarker for vaccine efficacy in preclinical animal models.

Spreading of a mycobacterial cell-surface lipid into host epithelial membranes promotes infectivity

Several virulence lipids populate the outer cell wall of pathogenic mycobacteria. Phthiocerol dimycocerosate (PDIM), one of the most abundant outer membrane lipids, plays important roles in both defending against host antimicrobial programs and in evading these programs altogether. Immediately following infection, mycobacteria rely on PDIM to evade Myd88-dependent recruitment of microbicidal monocytes which can clear infection. To circumvent the limitations in using genetics to understand virulence lipids, we developed a chemical approach to track PDIM during Mycobacterium marinum infection of zebrafish. We found that PDIM's methyl-branched lipid tails enabled it to spread into host epithelial membranes to prevent immune activation. Additionally, PDIM’s affinity for cholesterol promoted this phenotype; treatment of zebrafish with statins, cholesterol synthesis inhibitors, decreased spreading and provided protection from infection. This work establishes that interactions between host and pathogen lipids influence mycobacterial infectivity and suggests the use of statins as tuberculosis preventive therapy by inhibiting PDIM spread.

Mucosal delivery of a multistage subunit vaccine promotes development of lung-resident memory T cells and affords interleukin-17-dependent protection against pulmonary tuberculosis

The development of effective vaccines against bacterial lung infections requires the induction of protective, pathogen-specific immune responses without deleterious inflammation within the pulmonary environment. Here, we made use of a polysaccharide-adjuvanted vaccine approach to elicit resident pulmonary T cells to protect against aerosol Mycobacterium tuberculosis infection. Intratracheal administration of the multistage fusion protein CysVac2 and the delta-inulin adjuvant Advax™ (formulated with a TLR9 agonist) provided superior protection against aerosol M. tuberculosis infection in mice, compared to parenteral delivery. Surprisingly, removal of the TLR9 agonist did not impact vaccine protection despite a reduction in cytokine-secreting T cell subsets, particularly CD4+IFN-γ+IL-2+TNF+ multifunctional T cells. CysVac2/Advax-mediated protection was associated with the induction of lung-resident, antigen-specific memory CD4+ T cells that expressed IL-17 and RORγT, the master transcriptional regulator of Th17 differentiation. IL-17 was identified as a key mediator of vaccine efficacy, with blocking of IL-17 during M. tuberculosis challenge reducing phagocyte influx, suppressing priming of pathogen-specific CD4+ T cells in local lymph nodes and ablating vaccine-induced protection. These findings suggest that tuberculosis vaccines such as CysVac2/Advax that are capable of eliciting Th17 lung-resident memory T cells are promising candidates for progression to human trials.

Lessons from Bacillus Calmette-Guérin: Harnessing Trained Immunity for Vaccine Development

Vaccine design traditionally focuses on inducing adaptive immune responses against a sole target pathogen. Considering that many microbes evade innate immune mechanisms to initiate infection, and in light of the discovery of epigenetically mediated innate immune training, the paradigm of vaccine design has the potential to change. The Bacillus Calmette-Guérin (BCG) vaccine induces some level of protection against Mycobacterium tuberculosis (Mtb) while stimulating trained immunity that correlates with lower mortality and increased protection against unrelated pathogens. This review will explore BCG-induced trained immunity, including the required pathways to establish this phenotype. Additionally, potential methods to improve or expand BCG trained immunity effects through alternative vaccine delivery and formulation methods will be discussed. Finally, advances in new anti-Mtb vaccines, other antimicrobial uses for BCG, and “innate memory-based vaccines” will be examined.

Pneumonia caused by Mycobacterium tuberculosis

Tuberculosis (TB) is one of the top ten leading causes of death worldwide. The causative agent of TB is Mycobacterium tuberculosis. Acute tuberculous pneumonia (TP) is an acute form of pulmonary TB. However, acute TP and non-tuberculous community-acquired pneumonia can be easily confused, resulting in deterioration of TP due to delayed treatment. Therefore, rapid and accurate diagnosis of acute TP is crucial in order to stop the transmission of TB. Moreover, development of new diagnostic tools (technologies and approaches), and flexible application of different therapy schemes will help to reduce the incidence of TP and promote the goal of ending the TB epidemic.

Live attenuated TB vaccines representing the three modern Mycobacterium tuberculosis lineages reveal that the Euro-American genetic background confers optimal vaccine potential

Background

Human tuberculosis (TB) is caused by a plethora of Mycobacterium tuberculosis complex (MTBC) strains belonging to seven phylogenetic branches. Lineages 2, 3 and 4 are considered “modern” branches of the MTBC responsible for the majority of worldwide TB. Since the current BCG vaccine confers variable protection against pulmonary TB, new candidates are investigated. MTBVAC is the unique live attenuated vaccine based on M. tuberculosis in human clinical trials.

Methods

MTBVAC was originally constructed by unmarked phoP and fadD26 deletions in a clinical isolate belonging to L4. Here we construct new vaccines based on isogenic gene deletions in clinical isolates of the L2 and L3 modern lineages. These three vaccine candidates were characterized at molecular level and also in animal experiments of protection and safety.

Findings

Safety studies in immunocompromised mice showed that MTBVAC-L2 was less attenuated than BCG Pasteur, while the original MTBVAC was found even more attenuated than BCG and MTBVAC-L3 showed an intermediate phenotype. The three MTBVAC candidates showed similar or superior protection compared to BCG in immunocompetent mice vaccinated with each MTBVAC candidate and challenged with three representative strains of the modern lineages.

Interpretation

MTBVAC vaccines, based on double phoP and fadD26 deletions, protect against TB independently of the phylogenetic linage used as template strain for their construction. Nevertheless, lineage L4 confers the best safety profile.

Funding

European Commission (TBVAC2020, H2020-PHC-643381), Spanish Ministry of Science (RTI2018-097625-B-I00), Instituto de Salud Carlos III (PI18/0336), Gobierno de Aragón/Fondo Social Europeo and the French National Research Council (ANR-10-LABX-62-IBEID, ANR-16-CE35-0009, ANR-16-CE15-0003).

Mucosal delivery of tuberculosis vaccines: a review of current approaches and challenges

Introduction: Tuberculosis (TB) remains a major health threat and it is now clear that the current vaccine, BCG, is unable to arrest the global TB epidemic. A new vaccine is needed to either replace or boost BCG so that a better level of protection could be achieved. The route of entry of Mycobacterium tuberculosis, the causative organism, is via inhalation making TB primarily a respiratory disease. There is therefore good reason to hypothesize that a mucosally delivered vaccine against TB could be more effective than one delivered via the systemic route.

Areas covered: This review summarizes the progress that has been made in the area of TB mucosal vaccines in the last few years. It highlights some of the strengths and shortcomings of the published evidence and aims to discuss immunological and practical considerations in the development of mucosal vaccines.

Expert opinion: There is a growing body of evidence that the mucosal approach to vaccination against TB is feasible and should be pursued. However, further key studies are necessary to both improve our understanding of the protective immune mechanisms operating in the mucosa and the technical aspects of aerosolized delivery, before such a vaccine could become a feasible, deployable strategy.

Underestimated Manipulative Roles of Mycobacterium tuberculosis Cell Envelope Glycolipids During Infection

The Mycobacterium tuberculosis cell envelope has been evolving over time to make the bacterium transmissible and adaptable to the human host. In this context, the M. tuberculosis cell envelope contains a peripheral barrier full of lipids, some of them unique, which confer M. tuberculosis with a unique shield against the different host environments that the bacterium will encounter at the different stages of infection. This lipid barrier is mainly composed of glycolipids that can be characterized by three different subsets: trehalose-containing, mannose-containing, and 6-deoxy-pyranose-containing glycolipids. In this review, we explore the roles of these cell envelope glycolipids in M. tuberculosis virulence and pathogenesis, drug resistance, and further, how these glycolipids may dictate the M. tuberculosis cell envelope evolution from ancient to modern strains. Finally, we address how these M. tuberculosis cell envelope glycolipids are impacted by the host lung alveolar environment, their role in vaccination and masking host immunity, and subsequently the impact of these glycolipids in shaping how M. tuberculosis interacts with host cells, manipulating their immune response to favor the establishment of an infection.

The Lung Mucosa Environment in the Elderly Increases Host Susceptibility to Mycobacterium tuberculosis Infection

As we age, there is an increased risk for the development of tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) infection. Few studies consider that age-associated changes in the alveolar lining fluid (ALF) may increase susceptibility by altering soluble mediators of innate immunity. We assessed the impact of adult or elderly human ALF during Mtb infection in vitro and in vivo. We identified amplification of pro-oxidative and proinflammatory pathways in elderly ALF and decreased binding capability of surfactant-associated surfactant protein A (SP-A) and surfactant protein D (SP-D) to Mtb. Human macrophages infected with elderly ALF-exposed Mtb had reduced control and fewer phagosome-lysosome fusion events, which was reversed when elderly ALF was replenished with functional SP-A/SP-D. In vivo, exposure to elderly ALF exacerbated Mtb infection in young mice. Our studies demonstrate how the pulmonary environment changes as we age and suggest that Mtb may benefit from declining host defenses in the lung mucosa of the elderly.