Construction and evaluation of a multistage Mycobacterium tuberculosis subunit vaccine candidate Mtb10.4–HspX

Understanding the structural and functional implications of lysine succinylation in Mycobacterium tuberculosis heat shock protein 16.3

Heat shock protein 16.3 (Hsp16.3), a major immunodominant antigen of Mycobacterium tuberculosis, exhibits molecular chaperone function that is essential for pathogen's survival and slow growth inside hosts, as well as for enhancing the efficacy of Bacillus Calmette-Guérin (BCG) vaccine. Proteomic studies revealed that Hsp16.3 undergoes lysine succinylation in vivo at all lysine residues (K47, K64, K78, K85, K114, K119 and K132) except K136. However, the effects of succinylation on its structure and function remain unexplored. This study investigated the impact of succinylation, induced by physiological (succinyl-CoA) and/or non-physiological (succinic anhydride) donors, on the structure, stability and chaperone function of Hsp16.3. Succinylation of all eight lysine residues, affirmed via fluorescamine assay and mass spectrometry, led to structural (secondary and tertiary) alterations, as indicated by circular dichroism (CD), fluorescence and in-silico analyses. Succinylation induced oligomeric dissociation (dodecamer to dimer) and enhanced surface hydrophobicity of Hsp16.3. Moreover, succinylation reduced protein stability, making it more conformationally flexible and less compact, as revealed by urea-denaturation, chymotrypsin-digestion and computational studies. Despite this reduced stability, succinylated Hsp16.3 exhibited enhanced chaperone activity, offering improved protection to stressed-prone client proteins. These findings provide useful insights into this modification, offering potential therapeutic avenues for targeting Hsp16.3 in M. tuberculosis infection.

The adjuvant effect of manganese on tuberculosis subunit vaccine Bfrb-GrpE

Protein subunit vaccines, lacking pathogen-associated molecular patterns that trigger immune responses, rely on adjuvants to induce robust immune responses against the target pathogen. Thus, selection of adjuvants plays a crucial role in the design of protein subunit vaccines. Recently, there has been growing interest in utilizing cGAS-STING agonists as vaccine adjuvants. In this study, we investigated the adjuvant effect of manganese (Mn), a cGAS-STING agonist, on the tuberculosis subunit vaccine Bfrb-GrpE (BG) in a mouse model. Initially, mice were administered with BG-Mn(J), and its immunogenicity and protective efficacy were assessed six weeks after the final immunization. The results showed that Mn(J) enhanced both the cellular and humoral immune responses to the BG vaccine and conferred effective protection against M. tuberculosis H37Ra infection in mice, leading to a significant reduction of 2.0 ± 0.17 Log10 CFU in spleens and 1.3 ± 0.17 Log10 CFU in lungs compared to the PBS control group. Additionally, we assessed the BG-Mn(J) vaccine in a surrogate model of tuberculosis in rabbit skin model. The vaccination with BG-Mn(J) also provided effective protection in the rabbit model, as indicated by a decreased bacterial load at the infection site, minimal pathological damage, and accelerated healing. These findings suggest that Mn(J) holds promise as an adjuvant for tuberculosis vaccines, underscoring its potential to enhance vaccine efficacy and offer protection against tuberculosis infection.

The combination of Mycobacterium tuberculosis fusion proteins LT33 and LT28 induced strong protective immunity in mice

Effective subunit vaccines for tuberculosis (TB) must target antigenic components at various stages of infection. In this study, we constructed fusion proteins using secreted antigens from Mycobacterium tuberculosis (M. tuberculosis), specifically ESAT6, CFP10, MPT64, and Rv2645 from the proliferation stage, along with latency-associated antigens Rv1738 and Rv1978. The resulting fusion proteins, designated LT33 (ESAT6-CFP10-Rv1738) and LT28 (MPT6461-170-Rv19788-60-Rv264521-80), were combined with an adjuvant containing dimethyldioctadecylammonium bromide (DDA), polyriboinosinic polyribocytidylic acid (PolyI:C), and cholesterol to construct subunit vaccines. We evaluated the subunit vaccine effect in C57BL/6 mice and revealed that LT33 and LT28 exhibited strong immunogenicity and induced protective efficacy against aerosol challenge with M. tuberculosis H37Rv. Notably, the combination of LT33 and LT28 led to a significant reduction of 0.77 log10 colony-forming units (CFU) of H37Rv in the lungs compared to the adjuvant control group, highlighting their potential as promising candidates for subunit vaccine against M. tuberculosis infection.

DNA and RNA vaccines against tuberculosis: a scoping review of human and animal studies

Introduction

To comprehensively identify and provide an overview of in vivo or clinical studies of nucleic acids (NA)-based vaccines against TB we included human or animal studies of NA vaccines for the prevention or treatment of TB and excluded in vitro or in silico research, studies of microorganisms other than M. tuberculosis, reviews, letters, and low-yield reports.

Methods

We searched PubMed, Scopus, Embase, selected Web of Science and ProQuest databases, Google Scholar, eLIBRARY.RU, PROSPERO, OSF Registries, Cochrane CENTRAL, EU Clinical Trials Register, clinicaltrials.gov, and others through WHO International Clinical Trials Registry Platform Search Portal, AVMA and CABI databases, bioRxiv, medRxiv, and others through OSF Preprint Archive Search. We searched the same sources and Google for vaccine names (GX-70) and scanned reviews for references. Data on antigenic composition, delivery systems, adjuvants, and vaccine efficacy were charted and summarized descriptively.

Results

A total of 18,157 records were identified, of which 968 were assessed for eligibility. No clinical studies were identified. 365 reports of 345 animal studies were included in the review. 342 (99.1%) studies involved DNA vaccines, and the remaining three focused on mRNA vaccines. 285 (82.6%) studies used single-antigen vaccines, while 48 (13.9%) used multiple antigens or combinations with adjuvants. Only 12 (3.5%) studies involved multiepitope vaccines. The most frequently used antigens were immunodominant secretory antigens (Ag85A, Ag85B, ESAT6), heat shock proteins, and cell wall proteins. Most studies delivered naked plasmid DNA intramuscularly without additional adjuvants. Only 4 of 17 studies comparing NA vaccines to BCG after M. tuberculosis challenge demonstrated superior protection in terms of bacterial load reduction. Some vaccine variants showed better efficacy compared to BCG.

Systematic review registration

https://osf.io/, identifier F7P9G.

Promising Cytokine Adjuvants for Enhancing Tuberculosis Vaccine Immunity

Tuberculosis, caused by Mycobacterium tuberculosis (M. tuberculosis), remains a formidable global health challenge, affecting a substantial portion of the world's population. The current tuberculosis vaccine, bacille Calmette-Guérin (BCG), offers limited protection against pulmonary tuberculosis in adults, underscoring the critical need for innovative vaccination strategies. Cytokines are pivotal in modulating immune responses and have been explored as potential adjuvants to enhance vaccine efficacy. The strategic inclusion of cytokines as adjuvants in tuberculosis vaccines holds significant promise for augmenting vaccine-induced immune responses and strengthening protection against M. tuberculosis. This review delves into promising cytokines, such as Type I interferons (IFNs), Type II IFN, interleukins such as IL-2, IL-7, IL-15, IL-12, and IL-21, alongside the use of a granulocyte-macrophage colony-stimulating factor (GM-CSF) as an adjuvant, which has shown effectiveness in boosting immune responses and enhancing vaccine efficacy in tuberculosis models.

A novel multistage antigens ERA005f confer protection against Mycobacterium tuberculosis by driving Th-1 and Th-17 type T cell immune responses

Introduction

Tuberculosis (TB) is a major threat to human health. In 2021, TB was the second leading cause of death after COVID-19 among infectious diseases. The Bacillus Calmette-Guérin vaccine (BCG), the only licensed TB vaccine, is ineffective against adult TB. Therefore, there is an urgent need to develop new effective vaccines.

Methods

In this study, we developed a novel multistage subunit vaccine (ERA005f) comprising various proteins expressed in metabolic states, based on three immunodominant antigens (ESAT-6, Rv2628, and Ag85B). We utilized the E. coli prokaryotic expression system to express ERA005f and subsequently purified the protein using nickel affinity chromatography and anion exchange. Immunogenicity and protective efficacy of ERA005f and ERA005m were evaluated in BALB/c mice.

Results

ERA005f was consistently expressed as an inclusion body in a prokaryotic expression system, and a highly pure form of the protein was successfully obtained. Both ERA005f and ERA005m significantly improved IgG titers in the serum. In addition, mice immunized with ERA005f and ERA005m generated higher titers of antigen-specific IgG2a than the other groups. Elispot results showed that, compared with other groups, ERA005f increased the numbers of IFN-γ-secreting and IL-4-secreting T cells, especially the number of IFN-γ-secreting T cells. Meanwhile, ERA005f induced a higher number of IFN-γ+ T lymphocytes than ERA005m did. In addition, ERA005f improved the expression of cytokines, including IFN-γ, IL-12p70, TNF-α, IL-17, and GM-CSF and so on. Importantly, both ERA005f and ERA005m significantly inhibited the growth of Mtb.

Conclusion

The novel multistage antigen ERA005f elicited a strong antigen-specific humoral response and Th-1 and Th-17 cell-mediated immunity in mice. Meanwhile, it can effectively inhibit H37Rv growth in vitro, and represents a correlate of protection in vivo, indicating that ERA005f may exhibit excellent protective efficacy against Mycobacterium tuberculosis H37Rv infection. Our study suggests that ERA005f has the potential to be a promising multistage tuberculosis vaccine candidate.

Construction and evaluation of a novel multi-antigenic Mycobacterium tuberculosis subunit vaccine candidate BfrB-GrpE/DPC

Tuberculosis poses a significant threat to human health due to the lack of an effective vaccine. Although promising progress has been made in the development of tuberculosis vaccines, new vaccines that broaden the antigenic repertoire need to be developed to eradicate this illness. In this study, we used Mycobacterium tuberculosis ferritin BfrB and heat-shock protein GrpE to construct a novel multi-antigenic fusion protein, BfrB-GrpE (BG). BG protein was stably overexpressed in the soluble form in Escherichia coli at a high yield and purified via sequential salt fractionation and hydrophobic chromatography. Purified BG was emulsified in an adjuvant containing N, N'-dimethyl-N, N'-dioctadecylammonium bromide, polyinosinic-polycytidylic acid, and cholesterol (DPC) to construct the BG/DPC vaccine, which stimulated strong cellular and humoral immune responses in mice. Moreover, combination of BG with our previously developed vaccine, Mtb10.4-HspX (MH), containing antigens from both the proliferating and dormant stages, significantly reduced the bacterial counts in the lungs and spleens of M. tuberculosis-infected mice. Importantly, mice that received BG + MH/DPC after M. tuberculosis H37Rv infection survived slightly better (100% survival) than those that received the BCG vaccine (80% survival), although the difference was not statistically significant. Our findings can aid in the selection of antigens and optimization of vaccination regimens to improve the efficacy of tuberculosis vaccines.

Vaccination with mycobacterial lipid loaded nanoparticle leads to lipid antigen persistence and memory differentiation of antigen-specific T cells

Mycobacterium tuberculosis (Mtb) infection elicits both protein and lipid antigen-specific T cell responses. However, the incorporation of lipid antigens into subunit vaccine strategies and formulations has been underexplored, and the characteristics of vaccine-induced Mtb lipid-specific memory T cells have remained elusive. Mycolic acid (MA), a major lipid component of the Mtb cell wall, is presented by human CD1b molecules to unconventional T cell subsets. These MA-specific CD1b-restricted T cells have been detected in the blood and disease sites of Mtb-infected individuals, suggesting that MA is a promising lipid antigen for incorporation into multicomponent subunit vaccines. In this study, we utilized the enhanced stability of bicontinuous nanospheres (BCN) to efficiently encapsulate MA for in vivo delivery to MA-specific T cells, both alone and in combination with an immunodominant Mtb protein antigen (Ag85B). Pulmonary administration of MA-loaded BCN (MA-BCN) elicited MA-specific T cell responses in humanized CD1 transgenic mice. Simultaneous delivery of MA and Ag85B within BCN activated both MA- and Ag85B-specific T cells. Notably, pulmonary vaccination with MA-Ag85B-BCN resulted in the persistence of MA, but not Ag85B, within alveolar macrophages in the lung. Vaccination of MA-BCN through intravenous or subcutaneous route, or with attenuated Mtb likewise reproduced MA persistence. Moreover, MA-specific T cells in MA-BCN-vaccinated mice differentiated into a T follicular helper-like phenotype. Overall, the BCN platform allows for the dual encapsulation and in vivo activation of lipid and protein antigen-specific T cells and leads to persistent lipid depots that could offer long-lasting immune responses.

Key advances in vaccine development for tuberculosis-success and challenges

Breakthrough findings in the clinical and preclinical development of tuberculosis (TB) vaccines have galvanized the field and suggest, for the first time since the development of bacille Calmette-Guérin (BCG), that a novel and protective TB vaccine is on the horizon. Here we highlight the TB vaccines that are in the development pipeline and review the basis for optimism in both the clinical and preclinical space. We describe immune signatures that could act as immunological correlates of protection (CoP) to facilitate the development and comparison of vaccines. Finally, we discuss new animal models that are expected to more faithfully model the pathology and complex immune responses observed in human populations.

Bridging the gaps to overcome major hurdles in the development of next-generation tuberculosis vaccines

Although tuberculosis (TB) remains one of the leading causes of death from an infectious disease worldwide, the development of vaccines more effective than bacille Calmette-Guérin (BCG), the only licensed TB vaccine, has progressed slowly even in the context of the tremendous global impact of TB. Most vaccine candidates have been developed to strongly induce interferon-γ (IFN-γ)-producing T-helper type 1 (Th1) cell responses; however, accumulating evidence has suggested that other immune factors are required for optimal protection against Mycobacterium tuberculosis (Mtb) infection. In this review, we briefly describe the five hurdles that must be overcome to develop more effective TB vaccines, including those with various purposes and tested in recent promising clinical trials. In addition, we discuss the current knowledge gaps between preclinical experiments and clinical studies regarding peripheral versus tissue-specific immune responses, different underlying conditions of individuals, and newly emerging immune correlates of protection. Moreover, we propose how recently discovered TB risk or susceptibility factors can be better utilized as novel biomarkers for the evaluation of vaccine-induced protection to suggest more practical ways to develop advanced TB vaccines. Vaccines are the most effective tools for reducing mortality and morbidity from infectious diseases, and more advanced technologies and a greater understanding of host-pathogen interactions will provide feasibility and rationale for novel vaccine design and development.

Severe persistent mycobacteria antigen stimulation causes lymphopenia through impairing hematopoiesis

Miliary tubersculosis (TB), an acute systemic blood disseminated tuberculosis mainly caused by Mycobacterium tuberculosis (M. tuberculosis), can cause signs of lymphopenia in clinical patients. To investigate whether/how persistent mycobacteria antigen stimulation impairs hematopoiesis and the therapeutic effect of interleukin-7 (IL-7), a mouse model of Mycobacterium Bovis Bacillus Calmette-Guérin (BCG) intravenous infection with/without an additional stimulation with M. tuberculosis multi-antigen cocktail containing ESAT6-CFP10 (EC) and Mtb10.4-HspX (MH) was established. Consistent with what happened in miliary TB, high dose of BCG intravenous infection with/without additional antigen stimulation caused lymphopenia in peripheral blood. In which, the levels of cytokines IFN-γ and TNF-α in serum increased, and consequently the expression levels of transcription factors Batf2 and IRF8 involved in myeloid differentiation were up-regulated, while the expression levels of transcription factors GATA2 and NOTCH1 involved in lymphoid commitment were down-regulated, and the proliferating activity of bone marrow (BM) lineage^- c-Kit⁺ (LK) cells decreased. Furthermore, recombinant Adeno-Associated Virus 2-mediated IL-7 (rAAV2-IL-7) treatment could significantly promote the elevation of BM lymphoid progenitors. It suggests that persistent mycobacteria antigen stimulation impaired lymphopoiesis of BM hematopoiesis, which could be restored by complement of IL-7.

Fusion peptide constructs from antigens of M. tuberculosis producing high T-cell mediated immune response

Non availability of effective anti-TB vaccine impedes TB control which remains a crucial global health issue. A fusion molecule based on immunogenic antigens specific to different growth phases of Mycobacterium tuberculosis can enhance T-cell responses required for developing a potent vaccine. In this study, six antigens including EspC, TB10.4, HspX, PPE57, CFP21 and Rv1352 were selected for constructing EspC-TB10.4 (bifu25), TnCFP21-Rv1352 (bifu29), HspX-EspC-TB10.4 (trifu37), HspX-TnCFP21-Rv1352 (trifu44) and HspX-EspC-TB10.4-PPE57 (tetrafu56) fusion proteins. Th1-cell epitopes of EspC, PPE57 and Rv1352 antigens were predicted for the first time using different in silico tools. The fusion molecule tetrafu56, which consisted of antigens from both the replicating and the dormant stages of Mtb, induced a release of 397 pg/mL of IFN-γ from PBMCs of the active TB patients. This response was comparable to the response obtained with cocktail of the component antigens (396 pg/mL) as well as to the total of the responses obtained separately for each of its component antigens (388 pg/mL). However, PBMCs from healthy samples in response to tetrafu56 showed IFN-γ release of only 26.0 pg/mL Thus a previous exposure of PBMCs to Mtb antigens in TB plasma samples resulted in 15-fold increase in IFN-γ response to tetrafu56 as compared to the PBMCs from the healthy controls. Hence, most of the T-cell epitopes of the individual antigens seem to be available for T-cell interactions in the form of the fusion. Further investigation in animal models should substantiate the immune efficacy of the fusion molecule. Thus, the fusion tetrafu56 seems to be a potential candidate for developing an effective multistage vaccine against TB.

Emerging advances in identifying signal transmission molecules involved in the interaction between Mycobacterium tuberculosis and the host

Tuberculosis caused by Mycobacterium tuberculosis (MTB) is an ancient chronic infectious disease and is still the leading cause of death worldwide due to a single infectious disease. MTB can achieve immune escape by interacting with host cells through its special cell structure and secreting a variety of effector proteins. Innate immunity-related pattern recognition receptors (PPR receptors) play a key role in the regulation of signaling pathways.

In this review, we focus on the latest research progress on related signal transduction molecules in the interaction between MTB and the host. In addition, we provide new research ideas for the development of new anti-tuberculosis drug targets and lead compounds and provide an overview of information useful for approaching future tuberculosis host-oriented treatment research approaches and strategies, which has crucial scientific guiding significance and research value.

Evaluating the Performance of PPE44, HSPX, ESAT-6 and CFP-10 Factors in Tuberculosis Subunit Vaccines

Mycobacterium tuberculosis (M. tuberculosis) is an intracellular pathogen causing long-term infection in humans that mainly attacks macrophages and can escape from the immune system with the various mechanisms. The only FDA-approved vaccine against M. tuberculosis (MTB) is Mycobacterium bovis bacillus Calmette-Guérin (BCG). The protection of this vaccine typically lasts 10–15 years. Due to the increasing number of people becoming ill with MTB each year worldwide, the need to develop a new effective treatment against the disease has been increased. During the past two decades, the research budget for TB vaccine has quadrupled to over half a billion dollars. Most of these research projects were based on amplifying and stimulating the response of T-cells and developing the subunit vaccines. Additionally, these studies have demonstrated that secretory and immunogenic proteins of MTB play a key role in the pathogenesis of the bacteria. Therefore, these proteins were used to develop the new subunit vaccines. In this review, based on the use of these proteins in the successful new subunit vaccines, the PPE44, HSPX, CFP-10 and ESAT-6 antigens were selected and the role of these antigens in designing and developing new subunit vaccines against TB and for the prevention of TB were investigated.

Optimizing the Boosting Schedule of Subunit Vaccines Consisting of BCG and "Non-BCG" Antigens to Induce Long-Term Immune Memory

Boosting Bacillus Calmette-Guérin (BCG) with subunit vaccine is expected to induce long-term protection against tuberculosis (TB). However, it is urgently needed to optimize the boosting schedule of subunit vaccines, which consists of antigens from or not from BCG, to induce long-term immune memory. To address it two subunit vaccines, Mtb10.4-HspX (MH) consisting of BCG antigens and ESAT6-CFP10 (EC) consisting of antigens from the region of difference (RD) of Mycobacterium tuberculosis (M. tuberculosis), were applied to immunize BCG-primed C57BL/6 mice twice or thrice with different intervals, respectively. The long-term antigen-specific immune responses and protective efficacy against M. tuberculosis H37Ra were determined. The results showed that following BCG priming, MH boosting twice at 12-24 weeks or EC immunizations thrice at 12-16-24 weeks enhanced the number and function of long-lived memory T cells with improved protection against H37Ra, while MH boosting thrice at 12-16-24 weeks or twice at 8-14 weeks and EC immunizations twice at 12-24 weeks or thrice at 8-10-14 weeks didn't induce long-term immunity. It suggests that following BCG priming, both BCG antigens MH boosting twice and "non-BCG" antigens EC immunizations thrice at suitable intervals induce long-lived memory T cell-mediated immunity.

A century of attempts to develop an effective tuberculosis vaccine: Why they failed?

Tuberculosis (TB) remains a major global health problem despite widespread use of the Bacillus BCG vaccine. This situation is worsened by co-infection with HIV, and the development of multidrug-resistant Mycobacterium tuberculosis (Mtb) strains. Thus, novel vaccine candidates and improved vaccination strategies are urgently needed in order to reduce the incidence of TB and even to eradicate TB by 2050. Over the last few decades, 23 novel TB vaccines have entered into clinical trials, more than 13 new vaccines have reached various stages of preclinical development, and more than 50 potential candidates are in the discovery stage as next-generation vaccines. Nevertheless, why has a century of attempts to introduce an effective TB vaccine failed? Who should be blamed -scientists, human response, or Mtb strategies? Literature review reveals that the elimination of latent or active Mtb infections in a given population seems to be an epigenetic process. With a better understanding of the connections between bacterial infections and gene expression conditions in epigenetic events, opportunities arise in designing protective vaccines or therapeutic agents, particularly as epigenetic processes can be reversed. Therefore, this review provides a brief overview of different approaches towards novel vaccination strategies and the mechanisms underlying these approaches.

Chitosan nanoparticles containing fusion protein (Hspx–PPE44–EsxV) and resiquimod adjuvant (HPERC) as a novel booster vaccine for Mycobacterium tuberculosis

This study attempted to explore the immunogenicity of chitosan nanoparticles containing fusion protein (Hspx–PPE44–EsxV; HPE) and resiquimod adjuvant (HPERC) in BALB/c mice. HPE was initially expressed in E. coli BL21 cells. HPE and resiquimod adjuvant were then encapsulated in chitosan nanoparticles (HPERC). One group of mice were subcutaneously vaccinated on days 0, 14, and 28 with HPERC, and the other group was primed with bacilli Calmette-Guérin (BCG) on day 0 and then boosted with HPERC on days 14 and 28. Two weeks after the last injection, IFN-γ, IL-4, and IL-17 in spleen cell culture supernatants, and IgG2a and IgG1 titers in sera were measured. HPERC size was 130.84 ± 12.08 nm ( n = 5). Zeta potential of HPERC was 29 ± 4 mv. The highest IFN-γ concentration was detected in BCG-primed mice that were boosted with HPERC. In addition, IL-17 production was significantly increased in all groups compared with that of control, except in those that received nanoparticle (NP), adjuvant (ADJ), NP/ADJ, and fusion protein (Hspx–PPE44–EsxV) (HPE). Comparison of IFN-γ and IL-4 concentration determined that Th1 was activated in BCG-primed and HPERC-boosted group in comparison to the other groups. No significant difference in concentration of IL-4 was observed between groups receiving HPERC and BCG-primed and HPERC-boosted group in comparison to group BCG. Concentrations of IgG2a and IgG1 also increased compared to the control group and the rate of IgG2a was higher compared to IgG1. Chitosan containing HPERC vaccine could induce a high level of specific cytokines in mice. The group of mice which first received BCG and then HPERC as booster vaccine could produce significant amounts of IFN-γ, IL-17, and IgG2a.

Insights into the molecular determinants involved in Mycobacterium tuberculosis persistence and their therapeutic implications

The establishment of persistent infections and the reactivation of persistent bacteria to active bacilli are the two hurdles in effective tuberculosis treatment. Mycobacterium tuberculosis, an etiologic tuberculosis agent, adapts to numerous antibiotics and resists the host immune system causing a disease of public health concern. Extensive research has been employed to combat this disease due to its sheer ability to persist in the host system, undetected, waiting for the opportunity to declare itself. Persisters are a bacterial subpopulation that possesses transient tolerance to high doses of antibiotics. There are certain inherent mechanisms that facilitate the persister cell formation in Mycobacterium tuberculosis, some of those had been characterized in the past namely, stringent response, transcriptional regulators, energy production pathways, lipid metabolism, cell wall remodeling enzymes, phosphate metabolism, and proteasome protein degradation. This article reviews the recent advancements made in various in vitro persistence models that assist to unravel the mechanisms involved in the persister cell formation and to hunt for the possible preventive or treatment measures. To tackle the persister population the immunodominant proteins that express specifically at the latent phase of infection can be used for diagnosis to distinguish between the active and latent tuberculosis, as well as to select potential drug or vaccine candidates. In addition, we discuss the genes engaged in the persistence to get more insights into resuscitation and persister cell formation. The in-depth understanding of persistent cells of mycobacteria can certainly unravel novel ways to target the pathogen and tackle its persistence.

A new poly(I:C)-decorated PLGA-PEG nanoparticle promotes Mycobacterium tuberculosis fusion protein to induce comprehensive immune responses in mice intranasally

Protein-based subunit vaccine against tuberculosis (TB) is regarded as safer but with lower immunogenicity. To investigate effective adjuvant to improve the immunogenicity of TB subunit vaccine, we modified ploy(I:C) onto PLGA-PEG copolymer nanoparticle with polydopamine to produce a new nanoparticle adjuvant named "PLGA-PEG-poly(I:C)" (NP). M. tuberculosis fusion proteins Mtb10.4-HspX and ESAT-6-Rv2626c (M4) were encapsulated in the nanoparticles to produce the NP/M4 subunit vaccine. The PLGA-PEG/M4 nanoparticle was 200.21 ± 1.07 nm in diameter, and the polydispersity index (PDI) was 0.127 ± 0.02. Following modification with poly(I:C) by polydopamine, the NP/M4 was administered to C57BL/6 female mice intranasally and the immune responses were evaluated. The NP/M4 significantly induced antigen-specific CD4⁺ T cells proliferation, IL-2 and IFN-γ production. In addition, the NP/M4 could promote the production of antigen-specific IgG, IgG1, IgG2c in serum, and sIgA in lung washings. Overall, our results indicated that the NP would be a potential TB subunit vaccine adjuvant with the ability to induce strong Th1-type cell-mediated immunity and humoral immune responses.

Construction and immunogenicity of a T cell epitope-based subunit vaccine candidate against Mycobacterium tuberculosis

Despite antibiotic treatment and Bacille Calmette-Guérin (BCG) vaccination, Mycobacterium tuberculosis remains a major public health burden in most developing countries. Therefore, developing an improved vaccine is high priority. In this study, we cloned the genes of the immunodominant antigen of M. tuberculosis viz. its 38-kDa antigen (Pst homolog) (Rv0934, PstS1), and its T cell epitopes (amino acid [aa]169-405 and [aa]802-1119), which we termed PstS1p. Prokaryotic expression showed that the two recombinant proteins were mainly in the form of inclusion bodies. We also evaluated the immunity and immunogenicity of PstS1 and PstS1p. Both PstS1 and its T cell epitopes elicited significantly higher antigen-specific immunoglobulin G (IgG) antibodies in mouse serum, indicating that they enhanced antibody response. They also elicited the T helper 1 (Th1)-type response and promoted CD4⁺ T cell proliferation. Compared to PstS1, PstS1p promoted stronger cell-mediated immune response. These data indicate that PstS1p is highly immunogenic in mice, and may be a promising candidate vaccine for controlling tuberculosis.

Immunogenicity of HspX/EsxS fusion protein of Mycobacterium tuberculosis along with ISCOMATRIX and PLUSCOM nano-adjuvants after subcutaneous administration in animal model

BACKGROUND

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. tuberculosis), is one of the most common and dangerous infectious diseases in the world. Despite vaccination with BCG, it is still considered as a major health problem. Therefore, design and production of an effective novel vaccine against TB is necessary. Our aim was to evaluate immunogenicity of HspX/EsxS fusion protein of M. tuberculosis along with ISCOMATRIX, PLUSCOM nano-adjuvants and MPLA through the subcutaneous route in mice model.

METHODS

HspX/EsxS fused protein of M. tuberculosis was cloned, expressed and purified in the prokaryotic system. ISCOMATRIX and PLUSCOM nano-adjuvants were prepared by film hydration method. Subcutaneous immunization of BALB/c mice was performed by different formulations. IFN-γ, IL-4, IL-17 and TGF-β cytokines levels as well as serum IgG1, IgG2a.

RESULTS

Our results showed that subcutaneous administration of mice with HspX/EsxS along with three adjuvants, ISCOMATRIX, PLUSCOM and MPLA increased immunogenicity of multi-stage fusion protein of M. tuberculosis. Additionally, HspX/EsxS protein + ISCOMATRIX or + PLUSCOM nano-adjuvants induced stronger Th1, IgG2a and IgG1 immune responses compared to MPLA adjuvant. Totally, HspX/EsxS/ISCOMATRIX/MPLA, HspX/EsxS/PLUSCOM/MPLA and two BCG booster groups could significantly induce higher Th1 and IgG2a immune responses.

CONCLUSION

With regard to ability of ISCOMATRIX, PLUSCOM and MPLA adjuvants to increase immunogenicity of HspX/EsxS protein through induction of IFN-γ and IgG2a immune responses, it seems that these adjuvants and especially ISCOMATRIX and PLUSCOM, could also improve BCG efficacy as a BCG booster.

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.

Id3 and Bcl6 Promote the Development of Long-Term Immune Memory Induced by Tuberculosis Subunit Vaccine

Long-lived memory cell formation and maintenance are usually regulated by cytokines and transcriptional factors. Adjuvant effects of IL-7 have been studied in the vaccines of influenza and other pathogens. However, few studies investigated the adjuvant effects of cytokines and transcriptional factors in prolonging the immune memory induced by a tuberculosis (TB) subunit vaccine. To address this research gap, mice were treated with the Mycobacterium tuberculosis (M. tuberculosis) subunit vaccine Mtb10.4-HspX (MH) plus ESAT6-Ag85B-MPT64<190-198>-Mtb8.4-Rv2626c (LT70), together with adeno-associated virus-mediated IL-7 or lentivirus-mediated transcriptional factor Id3, Bcl6, Bach2, and Blimp1 at 0, 2, and 4 weeks, respectively. Immune responses induced by the vaccine were examined at 25 weeks after last immunization. The results showed that adeno-associated virus-mediated IL-7 allowed the TB subunit vaccine to induce the formation of long-lived memory T cells. Meanwhile, IL-7 increased the expression of Id3, Bcl6, and bach2-the three key transcription factors for the generation of long-lived memory T cells. The adjuvant effects of transcriptional factors, together with TB fusion protein MH/LT70 vaccination, showed that both Bcl6 and Id3 increased the production of antigen-specific antibodies and long-lived memory T cells, characterized by high proliferative potential of antigen-specific CD4+ and CD8+ T cells, and IFN-γ secretion in CD4+ and CD8+ T cells, respectively, after re-exposure to the same antigen. Overall, our study suggests that IL-7 and transcriptional factors Id3 and Bcl6 help the TB subunit vaccine to induce long-term immune memory, which contributes to providing immune protection against M. tuberculosis infection.

Fusion Cytokines IL-7-Linker-IL-15 Promote Mycobacterium Tuberculosis Subunit Vaccine to Induce Central Memory like T Cell-Mediated Immunity

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. tuberculosis), is among the most serious infectious diseases worldwide. Adjuvanted protein subunit vaccines have been demonstrated as a kind of promising novel vaccine. This study proposed to investigate whether cytokines interliukine-7 (IL-7) and interliukine-15 (IL-15) help TB subunit vaccines induce long-term cell-mediated immune responses, which are required for vaccination against TB. In this study, mice were immunized with the M. tuberculosis protein subunit vaccines combined with adnovirus-mediated cytokines IL-7, IL-15, IL-7-IL-15, and IL-7-Linker-IL-15 at 0, 2, and 4 weeks, respectively. Twenty weeks after the last immunization, the long-term immune responses, especially the central memory-like T cells (T_CM like cell)-mediated immune responses, were determined with the methods of cultured IFN-γ-ELISPOT, expanded secondary immune responses, cell proliferation, and protective efficacy against Mycobacterium bovis Bacilli Calmette-Guerin (BCG) challenge, etc. The results showed that the group of vaccine + rAd-IL-7-Linker-IL-15 induced a stronger long-term antigen-specific T_CM like cells-mediated immune responses and had higher protective efficacy against BCG challenge than the vaccine + rAd-vector control group, the vaccine + rAd-IL-7 and the vaccine + rAd-IL-15 groups. This study indicated that rAd-IL-7-Linker-IL-15 improved the TB subunit vaccine’s efficacy by augmenting T_CM like cells and provided long-term protective efficacy against Mycobacteria.

IL-2 Restores T-Cell Dysfunction Induced by Persistent Mycobacterium tuberculosis Antigen Stimulation

Tuberculosis (TB) is a chronic disease mainly caused by Mycobacterium tuberculosis. The function of T cells usually decreased and even exhausted in severe TB such as multiple drug resistant TB (MDR-TB), which might lead to the failure of treatment in return. The mechanism of T cell dysfunction in TB is still not clear. In this study we set up a mouse model of T cell dysfunction by persistent M. tuberculosis antigen stimulation and investigated the therapeutic role of interleukin 2 (IL-2) in it. C57BL/6 mice were primed with Mycobacterium bovis Bacillus Calmette-Guérin (BCG) and boosted repeatedly with a combination of M. tuberculosis fusion proteins Mtb10.4-HspX (MH) plus ESAT6-Ag85B-MPT64 _<190-198>-Mtb8.4-Rv2626c (LT70) or MH plus ESAT6 and CFP10 with adjuvant of N, N'-dimethyl-N, N'-dioctadecylammonium bromide (DDA) plus polyinosinic-polycytidylic acid (Poly I:C). Following persistent antigen stimulation, the mice were treated with IL-2 and the therapeutic effects were analyzed. The results showed that compared with the mice that received transient antigen stimulation (boost twice), persistent antigen stimulation (boost more than 10 times) resulted in decrease of antigen specific IFN-γ and IL-2 production, reduction of memory CD8⁺ T cells, over-expression of immune checkpoint programmed cell death protein 1 (PD-1), and impaired the protective immunity against bacterial challenge. Treating the T cell functionally exhausted mice with IL-2 restored antigen-specific T cell responses and protective efficacy. In conclusion, persistent stimulation with M. tuberculosis antigens induced T cell dysfunction, which could be restored by complement of IL-2.

Persistent stimulation with Mycobacterium tuberculosis antigen impairs the proliferation and transcriptional program of hematopoietic cells in bone marrow

Mycobacterium tuberculosis (M. tuberculosis) persistent infection might cause the dysfunction of hematopoiesis. To investigate whether M. tuberculosis persistent antigen stimulation impairs the proliferation and differentiation of hematopoietic stem and progenitor cells characterized as lineage^- c-Kit⁺ (LK cells), C57BL/6 mice were primed with Mycobacterium bovis Bacillus Calmette-Guérin (BCG) and boosted with a cocktail of M. tuberculosis antigens ESAT6, CFP10 and Mtb10.4-HspX (MH) along with adjuvant N, N'-dimethyl-N, N'-dioctadecylammonium bromide (DDA) plus polyinosinic-polycytidylic acid (Poly I:C) weekly for 12 or 22 weeks. The cytokine production by splenic T cells, proliferation of LK cells and transcriptional events during differentiation of bone marrow (BM) c-Kit⁺ cells were investigated. Meanwhile, the mice were treated with interleukin 2 (IL-2) and the therapeutic effects were analyzed. We found that antigen specific interferon-γ (IFN-γ) production by splenic CD4⁺ T cells increased following antigen stimulation for 12 weeks, but it declined after continuous stimulation for 22 weeks. The long-term exposure of mice to M. tuberculosis antigen compromised the proliferation of LK cells. Moreover, the expression of transcription factors in the c-Kit⁺ cells was adjusted, with up-regulation of IRF8 and Batf2 involved in myeloid differentiation and down-regulation of NOTCH1 and GATA2 participated in T-cell lineage commitment. The concentrations of IFN-γ in BM of the persistent antigen group were higher than that in sham control at the 12th week, while the concentrations of IL-2 in BM of the persistent antigen group were lower compared with the transient antigen stimulation control. Following IL-2 treatment, the concentrations of IL-2 in BM increased while IFN-γ got declined. IL-2 treatment could restore the expression levels of those transcription factors and the proliferating activity of LK cells impaired by persistent antigen stimulation. Our results indicate that M. tuberculosis antigen persistent stimulation decreases the proliferating activity of LK cells, promotes myelopoietic differentiation, and represses lymphopoietic differentiation as a consequence of elevated IFN-γ production. IL-2 supplementation contributes to maintaining the homeostasis of hemopoiesis.

Tuberculosis vaccine candidates based on mycobacterial cell envelope components

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

The DosR antigen Rv1737c from Mycobacterium tuberculosis confers inflammation regulation in tuberculosis infection

There is an urgent need to identify the potential risk factors for activating latent Mycobacterium tuberculosis infection. In this study, we evaluated the immune function of Rv1737c, which is a latency-associated antigen of dormancy survival regulator (DosR) of M. tuberculosis in a mouse model. Our data showed that mice pretreated with recombinant Rv1737c (rRv1737c) exhibited higher levels of antigen-specific antibodies (IgG, IgM and IgA) than sham-treated mice. Following Bacilli Calmette-Guerin (BCG) challenge, rRv1737c adjuvanted with cholera toxin subunit B (CTB) induced diffuse lung inflammation and fibrosis compared to the control mice. The inflammatory pathogenesis due to rRv1737c pre-exposure was associated with a switch in the macrophage phenotype from M1 to activated M2 and was characterized by IL-10 production. Intracellular cytokine analysis further showed that the rRv1737c-pretreated mice exhibited an increased frequency of Th2 cells in the lungs, lymph nodes and spleen after BCG challenge. Furthermore, IFN-γ expression increased in the lungs after rRv1737c pretreatment compared to that in the sham mice. Accordingly, lung cells from rRv1737c-immunized mice stimulated with killed BCG produced higher levels of multiple cytokines, such as IFN-γ, IL-10 and IL-6. The results confirmed that the pathological features of rRv1737c promoted inflammation. Overall, our findings provide direct evidence of the pro-inflammatory function of rRv1737c in a murine model of BCG infection, indicating that Rv1737c is a pathogenic antigen of M. tuberculosis and may be key to the recurrence of latent infection.

Ursolic acid and carvacrol may be potential inhibitors of dormancy protein small heat shock protein16.3 of Mycobacterium tuberculosis

Small heat shock protein16.3 (sHSP16.3) is a crucial protein for survival of Mycobacterium tuberculosis (MTB) in its host. Besides, this protein acts as a molecular chaperone during stress and is indispensable for MTB's growth, virulence and cell-wall thickening. sHSP16.3 is also a promising candidate for vaccine, serodiagnosis and drug design as well. In the present study, we have targeted sHSP16.3 with two phytochemicals, namely ursolic acid and carvacrol using in silico approach. Molecular docking analysis showed that both phytochemicals (ursolic acid and carvacrol) have docked with sHSP16.3 and shown tendency to inhibit the function of this vital protein of MTB. In addition, both compounds have exhibited strong compatibility with sHSP16.3 during whole 60 ns duration of molecular dynamics simulation. Further, the molecular mechanic/generalized Born/Poisson-Boltzmann surface area (MM/G/P/BSA) free energies were calculated which showed that both phytocompounds have stable and favourable binding energies causing strong binding with binding site of sHSP16.3. Taking together, the data of present study suggest that both phytocompounds may be potential inhibitor of sHSP16.3 of MTB and a best alternative to standard anti-tuberculosis drugs.

Prolonged intervals during Mycobacterium tuberculosis subunit vaccine boosting contributes to eliciting immunity mediated by central memory-like T cells

It is believed that central memory T cells (T_CM) provide long-term protection against tuberculosis (TB). However, the effects of TB subunit vaccine immunization schedule, especially the vaccination intervals, on T cell immune memory is still unclear. In this study, mice were immunized with fusion protein ESAT6-Ag85B-MPT64 (190-198)-Mtb8.4-Rv2626c (LT70) based subunit vaccine three times according to the following schedules: ① 0, 3rd and 6th week respectively (0-3-6w), ② 0, 4th and 12th week (0-4-12w), and ③ 0, 4th and 24th week (0-4-24w). We found that both schedules of 0-4-12w and 0-4-24w induced higher level of antigen specific IL-2, IFN-γ and TNF-α than 0-3-6w immunization. Among them, 0-4-12w induced the highest level of IL-2, which is a key cytokine mainly produced by T_CM. Moreover, by cultured IFN-γ ELISPOT and cell proliferation assay etc., we found that the vaccination schedule of 0-4-12w elicited higher numbers of T_CM like cells, stronger T_CM - mediated immune responses and higher protective efficacy against M. bovis BCG challenge than 0-3-6w did. It suggests that prolonging the vaccination interval of TB subunit vaccine to some extent contributes to inducing more abundant T_CM like cells and providing stronger immune protection against mycobacteria infection.

Insights into Macrophage Autophagy in Latent Tuberculosis Infection: Role of Heat Shock Protein 16.3

Tuberculosis (TB) is a major bacterial infectious disease worldwide that is predominantly caused by Mycobacterium tuberculosis (Mtb). The comorbidity of multiple drug-resistant TB strains with HIV and diabetes is widespread. In the presence of these diseases, host immunity is weakened, allowing the recovery of dormant bacilli and leading to recurrent TB infection. As an important component of the host innate and adaptive immune responses, macrophage autophagy plays a significant role in protecting the host against TB. However, dormant bacilli can escape from autophagosomes and/or suppress autophagy, thus surviving within the host for an extended period of time, although the underlying mechanism remains elusive. Heat shock protein 16.3 (Hsp16.3, HspX, Rv2031c, and Acr) is one of the immunodominant proteins expressed during latent TB infection (LTBI). It may help maintain the protein stability and long-term viability of Mtb by inhibiting macrophage autophagy, resulting in LBTI. In this review, we discuss how dormant bacilli escape from autophagosomes, and we focus on the role of Hsp16.3 in regulating macrophage autophagy in LTBI so as to provide a firm basis for further studies. Hsp16.3 may represent a potential biomarker of LTBI and novel pharmacological target for anti-tubercular drugs.

Potential of Cationic Liposomes as Adjuvants/Delivery Systems for Tuberculosis Subunit Vaccines

The weakness of the BCG vaccine and its highly variable protective efficacy in controlling tuberculosis (TB) in different age groups as well as in different geographic areas has led to intense efforts towards the development and design of novel vaccines. Currently, there are several strategies to develop novel TB vaccines. Each strategy has its advantages and disadvantages. However, the most important of these strategies is the development of subunit vaccines. In recent years, the use of cationic liposome-based vaccines has been considered due to their capacity to elicit strong humoral and cellular immune responses against TB infections. In this review, we aim to evaluate the potential for cationic liposomes to be used as adjuvants/delivery systems for eliciting immune responses against TB subunit vaccines. The present review shows that cationic liposomes have extensive applications either as adjuvants or delivery systems, to promote immune responses against Mycobacterium tuberculosis (Mtb) subunit vaccines. To overcome several limitations of these particles, they were used in combination with other immunostimulatory factors such as TDB, MPL, TDM, and Poly I:C. Cationic liposomes can provide long-term storage of subunit TB vaccines at the injection site, confer strong electrostatic interactions with APCs, potentiate both humoral and cellular (CD4 and CD8) immune responses, and induce a strong memory response by the immune system. Therefore, cationic liposomes can increase the potential of different TB subunit vaccines by serving as adjuvants/delivery systems. These properties suggest the use of cationic liposomes to produce an efficient vaccine against TB infections.

Immunogenicity and protective efficacy of multistage vaccine candidates (Mtb8.4-HspX and HspX-Mtb8.4) against Mycobacterium tuberculosis infection in mice

In this study, Mtb8.4 and HspX, which are expressed at proliferating and dormant stages of Mycobacterium tuberculosis (M. tuberculosis), respectively, were chosen to construct two fusion proteins, Mtb8.4-HspX (8.4H) and HspX-Mtb8.4 (H8.4), and we investigated whether the antigen dose and protein sequential order could impact the immunogenicity and protective efficacy of these fusion protein vaccines against M. tuberculosis. C57BL/6 mice were vaccinated with new constructions containing a fusion protein with adjuvant of N, N'-dimethyl-N, N'-dioctadecylammonium bromide (DDA) or a mixed adjuvant composed of DDA, polyribocytidylic acid and gelatin (DPG), and the antigen specific immune responses and protective efficacy against M. tuberculosis H37Rv were evaluated. The results showed that both antigens, Mtb8.4-HspX and HspX-Mtb8.4, could elicit strong human T cell responses. With the existing of DDA adjuvant, HspX-Mtb8.4 induced significantly higher secretion level of IFN-γ and TNF-α in spleen cells than Mtb8.4-HspX (p<0.05). In its protective efficacy study, the isolated bacterial Colony Form Unit (CFU) in H8.4-DPG group was significantly reduced compared to 8.4H-DPG group (p<0.05). Furthermore, with the stimulation of Mtb8.4 in vitro, the secretion of IFN-γ and TNF-α from mice immunized with 20μg of H8.4 exhibited relative higher level than the group immunized by 7μg of H8.4 (p<0.05), whereas, IL-2 secreting showed contrary result. The data suggest that the antigen sequential order and dose selection should be considered when a tuberculosis protein vaccine is to be constructed and its immune strategy is to be planned.

Potent Antigen-Adjuvant Delivery System by Conjugation of Mycobacterium tuberculosis Ag85B-HspX Fusion Protein with Arabinogalactan-Poly(I:C) Conjugate

Protein-based vaccine is promising to improve or replace Mycobacterium bovis BCG vaccine for its specificity, safety, and easy production. However, protein-based vaccine calls for potent adjuvants and improved delivery systems to protect against Mycobacterium tuberculosis. Poly(I:C) is one of the most potent pathogen-associated molecular patterns that signals primarily via TLR3. Arabinogalactan (AG) is a biocompatible polysaccharide that can increase splenocyte proliferation and stimulate macrophages. The AG-poly(I:C) conjugate (AG-P) showed an adjuvant potency through a synergistic interaction of AG and poly(I:C). Ag85B and HspX are two important virulent protein antigens of Mycobacterium tuberculosis and Ag85B-HspX fusion protein (AH) was prepared. An antigen-adjuvant delivery system (AH-AG-P) was developed by conjugation of AH with AG-P to ensure that both AH and AG-P reach the APCs simultaneously. AH-AG-P elicited high AH-specific IgG titers and stimulated lymphocyte proliferation. AH-AG-P provoked the secretion of Th1-type cytokines (TNF-α, IFN-γ, and IL-2) and Th2-type cytokines (IL-4 and IL-10). Pharmacokinetics revealed that conjugation with AG-P could prolong the serum exposure of AH to the immune system. Pharmacodynamics suggested that conjugation with AG-P led to a rapid and intense production of AH-specific IgG. Accordingly, conjugation with AG-P could promote a robust cellular and humoral immune response to AH. Thus, conjugation of AH with a potent adjuvant AG-P is an effective strategy to develop an efficacious protein-based vaccine against Mycobacterium tuberculosis.

A multistage mycobacterium tuberculosis subunit vaccine LT70 including latency antigen Rv2626c induces long-term protection against tuberculosis

To develop an effective subunit vaccine which could target tubercle bacilli with different metabolic states and provide effective protective immunity, we fused antigens ESAT6, Ag85B, peptide 190-198 of MPT64, and Mtb8.4 mainly expressed by proliferating bacteria and latency-associated antigen Rv2626c together to construct a multistage protein ESAT6-Ag85B-MPT64(190-198)-Mtb8.4-Rv2626c (LT70 for short) with the molecular weight of 70 kDa. The human T-cell responses to LT70 and other antigens were analyzed. The immune responses of LT70 in the adjuvant of DDA and Poly I:C and its protective efficacy against Mycobacterium tuberculosis (M. tuberculosis) infection in C57BL/6 mice were evaluated. The results showed that LT70 was stably produced in Escherichia coli and could be purified by successive salting-out and chromatography. LT70 could be strongly recognized by human T cells from TB patients and persons who are supposed latently infected with M. tuberculosis. The subunit vaccine LT70 generated strong antigen-specific humoral and cell-mediated immunity, and induced higher protective efficacy (5.41±0.37 Log10 CFU in lung) than traditional vaccine Bacillus Calmette-Guerin (6.01±0.33 Log10 CFU) and PBS control (6.53±0.26 Log10 CFU) at 30 weeks post vaccination (10 weeks post-challenge) against M. tuberculosis infection (p < 0.05). These findings suggested that LT70 would be a promising subunit vaccine candidate against M. tuberculosis infection.

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

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

B cells and antibodies in the defense against Mycobacterium tuberculosis infection

Better understanding of the immunological components and their interactions necessary to prevent or control Mycobacterium tuberculosis (Mtb) infection in humans is critical for tuberculosis (TB) vaccine development strategies. Although the contributory role of humoral immunity in the protection against Mtb infection and disease is less defined than the role of T cells, it has been well-established for many other intracellular pathogens. Here we update and discuss the increasing evidence and the mechanisms of B cells and antibodies in the defense against Mtb infection. We posit that B cells and antibodies have a variety of potential protective roles at each stage of Mtb infection and postulate that such roles should be considered in the development strategies for TB vaccines and other immune-based interventions.

Evaluation of Humoral Immunity to Mycobacterium tuberculosis-Specific Antigens for Correlation with Clinical Status and Effective Vaccine Development

Although tuberculosis remains a major global health problem, Bacille Calmette-Guérin (BCG) is the only available vaccine. However, BCG has limited applications, and a more effective vaccine is needed. Cellular mediated immunity (CMI) is thought to be the most important immune response for protection against Mycobacterium tuberculosis (Mtb). However, the recent failure of a clinical trial for a booster BCG vaccine and increasing evidence of antibody-mediated immunity prompted us to evaluate humoral immunity to Mtb-specific antigens. Using Enzyme-Linked ImmunoSpot and Enzyme-Linked ImmunoSorbent Assays, we observed less correlation of both CMI and IgG titers with patient clinical status, including serum concentration of C reactive protein. However, IgA titers against Mtb were significantly correlated with clinical status, suggesting that specific IgA antibodies protect against Mtb proliferation. In addition, in some cases, IgA antibody titers were significantly associated with the serum concentration of total albumin, which supports the idea that humoral immunity can be influenced by the nutritional status. Based on these observations, we propose that the induction of humoral immunity should be included as an option in TB vaccine development strategies.

Interleukin-28B Plays a Therapeutic Role on Mouse U14 Cervical Cancer Cells by Down-Regulating CD4+CD25+FoxP3+Regulatory T Cells In Vivo

AIM

To investigate the immunotherapeutic effectiveness of adenoviral vector expressing mouse interleukin (IL)-28B (Ad-mIL-28B) against cervical cancer and its mechanism.

METHOD

U14 cervical cancer cell-bearing mice were treated with Ad-mIL-28B. Meanwhile, whole cell vaccine was prepared by repeated freezing and thawing U14 cells. Then CD4⁺CD25⁺FoxP3⁺regulatory T (Treg) cells were evaluated by flow cytometry. Tumor volume and metastasis in BALB/c and C57BL/6j mice were detected.

RESULTS

Ad-mIL-28B treatment significantly decreased the number of CD4⁺CD25⁺FoxP3⁺Treg cells. Subsequently, there was a significant decrease in the size of tumor tissue and the numbers of heteromorphic tumor cells. The tumor metastasis in the lung and liver of the Ad-mIL-28B group also decreased. However, there was no therapeutic effect observed for whole cell vaccine on U14 tumor-bearing mice.

CONCLUSION

Interleukin-28B can inhibit the growth and metastasis of cervical cancer in U14 tumor-bearing mice by down-regulating Treg cells.

Multi-Stage Tuberculosis Subunit Vaccine Candidate LT69 Provides High Protection against Mycobacterium tuberculosis Infection in Mice

Effective tuberculosis (TB) vaccine should target tubercle bacilli with various metabolic states and confer long-term protective immunity. In this study, we constructed a novel multi-stage TB subunit vaccine based on fusion protein ESAT6-Ag85B-MPT64(190-198)-Mtb8.4-HspX (LT69 for short) which combined early expressed antigens and latency-associated antigen. The fusion protein was mixed with an adjuvant being composed of N, N’-dimethyl-N, N’-dioctadecylammonium bromide (DDA) and polyriboinosinic polyribocytidylic acid (PolyI:C) to construct subunit vaccine, whose immunogenicity and protective ability were evaluated in C57BL/6 mice. The results showed that LT69 had strong immunogenicity and high protective effect against Mycobacterium tuberculosis (M. tuberculosis) H37Rv aerosol challenge. Low-dose (2 μg) of LT69 generated long-term immune memory responses and provided effective protection, which was even higher than traditional vaccine BCG did at 30 weeks post the last vaccination. In conclusion, multistage subunit vaccine LT69 showed high and long-term protection against M. tuberculosis infection in mice, whose effect could be enhanced by using a relative low dosage of antigen.

Role of B cells and antibodies in acquired immunity against Mycobacterium tuberculosis

Accumulating evidence has documented a role for B cells and antibodies (Abs) in the immunity against Mycobacterium tuberculosis (Mtb). Passive transfer studies with monoclonal antibodies (mAbs) against mycobacterial antigens have shown protection against the tubercle bacillus. B cells and Abs are believed to contribute to an enhanced immune response against Mtb by modulating various immunological components in the infected host including the T-cell compartment. Nevertheless, the extent and contribution of B cells and Abs to protection against Mtb remains uncertain. In this article we summarize the most relevant findings supporting the role of B cells and Abs in the defense against Mtb and discuss the potential mechanisms of protection.

A novel antigen-carrier system: the Mycobacterium tuberculosis Acr protein carried by raw starch microparticles

Microparticles have been used as promising carriers for in vivo vaccine delivery. However, the processes for immobilizing peptides or proteins on microparticles usually require the use of undesirable compounds and complex protocols. In this work, we propose a new immobilization and delivery system with raw starch microparticles and a starch binding domain (SBD) tag fusion protein. The heat shock protein alpha crystallin from Mycobacterium tuberculosis was used as model. The immunogenicity of the system was investigated in BALB/c mice inoculated with purified Acr-SBDtag protein (pAcr-SBDtag) and starch immobilized Acr-SBDtag protein (μAcr-SBDtag) by oral and intranasal routes. We demonstrated mucosal immunization with the μAcr-SBDtag protein induced systemic antibodies that were predominantly immunoglobulin G2a (IgG2a). An analysis of the cytokines from spleen cells and lung homogenates revealed that loaded microparticles induced the secretion of interferon-γ (INF-γ), suggesting an adjuvant effect from the immobilization. The immune responses induced by immobilized protein were primarily affected by the route of administration. These results demonstrate that the system exhibits the necessary characteristics to improve antigen release and presentation to antigen presenting cells (APCs) in the mucosae. Because no extra adjuvants were used, we posit that the system may be suitable for delivery and presentation to the field of subunit vaccine development.

Microstructured liposome subunit vaccines reduce lung inflammation and bacterial load after Mycobacterium tuberculosis infection

BACKGROUND

Tuberculosis is a disease affecting millions of people throughout the world. One of the main problems in controlling the disease is the low efficacy of the Bacillus Calmette-Guérin (BCG) vaccine in protecting young adults. The development of new vaccines that induce a long-lasting immune response or that stimulate the immunity induced by BCG may improve the control of tuberculosis.

METHODS

The use of microstructured liposomes containing HspX, with or without MPL or CpG DNA adjuvants, as vaccines for tuberculosis was evaluated. The HspX-specific humoral and cellular immune responses to the different vaccine formulations were compared.

RESULTS

All vaccines containing liposome microparticles and HspX were immunogenic. Vaccines formulated with CpG DNA and HspX induced the strongest humoral and cellular immune responses, mainly by inducing interferon-γ and tumor necrosis factor-α expression by both CD4(+) and CD8(+) T cells. HspX and MPL mainly induced CD8(+) T-cell activation and specific humoral responses. When evaluated the protective efficacy of the formulations against Mycobacterium tuberculosis challenge, the microstructured liposome containing L-HspX and L-HspX-CPG DNA reduced both lung inflammatory lesions and the bacterial load.

CONCLUSION

We have thus demonstrated, for the first time, the use of microstructured liposomes as an adjuvant and delivery system for a vaccine formulation against tuberculosis.

HspX vaccination and role in virulence in the guinea pig model of tuberculosis

Mycobacterium tuberculosis (Mtb) currently infects billions of people; many of whom are latently infection and at risk for reactivation. Mycobacterium bovis Bacille Calmette-Guerin (BCG) while approved as a vaccine, is unable to prevent reactivation of latent tuberculosis infection (LTBI). Subunit vaccines boosting BCG or given alone are being tested for efficacy in LTBI models. Alpha-crystallin (Acr, HspX), is a latency associated protein and subunit vaccine candidate. In this report, three HspX formulas (native and two recombinant variants) were used as vaccines in the guinea pig model of tuberculosis; none were protective during challenge with WT Mtb. However, recombinant HspX was protective in animals challenged with a strain of Mtb lacking hspX (X4-19), indicating protection was driven by molecules co-purifying with HspX or an adjuvant effect of recombinant HspX in this system. Mtb X4-19 was significantly less virulent than WT Mtb. Quantitative PCR and whole genome sequencing identified several genes (Rv2030c-Rv2032, Rv1062, Rv1771, Rv1907, and Rv3479) with altered expression that may contribute to loss of virulence. Physiological differences required for the establishment of Mtb infection in different hosts may affect the potential of subunit vaccines to elicit protection, supporting the need for rigorous biochemical and modeling analyses when developing tuberculosis vaccines.

A novel vaccine p846 encoding Rv3615c, Mtb10.4, and Rv2660c elicits robust immune response and alleviates lung injury induced by Mycobacterium infection

Development of effective anti-tuberculosis (TB) vaccines is one of the important steps to improve control of TB. Cell-mediated immune response significantly affects the control of M. tuberculosis infection. Thus, vaccines able to elicit strong cellular immune response hold special advantages against TB. In this study, three well-defined mycobacterial antigens (Rv3615c, Mtb10.4 [Rv0228], and Rv2660c) were engineered as a novel triple-antigen fusion DNA vaccine p846. The p846 vaccine consists of a high density of CD4(+) and CD8(+) T-cell epitopes. Intramuscular immunization of p846 induced robust T cells mediated immune response comparable to that of bacillus Calmette-Guérin (BCG) vaccination but more effective than that of individual antigen vaccination. After mycobacterial challenge, p846 immunization decreased bacterial burden at least 15-fold compared with individual antigen-based vaccination. Notably, the lungs of mice immunized with p846 exhibited fewer inflammatory cell infiltrates and less damage than those of control group mice. Our data demonstrate that the potential of p846 vaccine to protect against TB and the feasibility of this design strategy for further TB vaccine development.