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

Chemical and Biological Characterization of Mycobacterium Tuberculosis-Specific ESAT6-Like Proteins and their Potentials in the Prevention of Tuberculosis and Asthma

Early Secreted Antigenic Target 6 kDa (ESAT6) is a potent immunogenic protein secreted by the bacteria causing tuberculosis, i.e., Mycobacterium tuberculosis. Another highly immunogenic culture filtrate protein whose gene is linked to ESAT6/ESXA is known as CFP10/ESXB. Because of their high immunogenicity and specificity to M. tuberculosis, these proteins have been proposed as a vaccine to prevent tuberculosis and diagnose the active/latent disease. However, the same proteins cannot be used for prevention and diagnosis because immunized but healthy people will also show a positive response and be falsely reported as diseased. Therefore, in this review article, the search was made to identify if any other ESAT6-like proteins exist in the M. tuberculosis genome. The search identified 21 additional ESAT-like proteins, i.e., ESXC to ESXW. Immunological characterization has shown that some of them (especially ESXV) were able to induce immune responses in vitro with cells obtained from tuberculosis patients and healthy donors. When the protein ESXV was tested in different recombinant forms (expressed in Escherichia coli, mycobacterial vectors, and DNA plasmids) and injected in mice, immune responses were induced to multiple epitopes of the protein. Furthermore, immunization of mice with ESXV protected them from infection with M. tuberculosis. The same protein was also able to protect mice against the induction of asthma. These results suggest that ESXV has the potential to protect against two major diseases of the world, i.e., tuberculosis and asthma, and hence may be used as a common vaccine for both diseases.

Mycobacterium smegmatis, a Promising Vaccine Vector for Preventing TB and Other Diseases: Vaccinomics Insights and Applications

Mycobacterium smegmatis (M.sm) is frequently used as an alternative model organism in Mycobacterium tuberculosis (M.tb) studies. While containing high sequence homology with M.tb, it is considered non-pathogenic in humans. As such it has been used to study M.tb and other infections in vivo and more recently been explored for potential therapeutic applications. A body of previous research has highlighted the potential of using genetically modified M.sm displaying rapid growth and unique immunostimulatory characteristics as an effective vaccine vector. Novel systems biology techniques can further serve to optimize these delivery constructs. In this article, we review recent advancements in vaccinomics tools that support the efficacy of a M.sm-based vaccine vector. Moreover, the integration of systems biology and molecular omics techniques in these pioneering studies heralds a potential accelerated pipeline for the development of next-generation recombinant vaccines against rapidly developing diseases.

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.

High-yield production of major T-cell ESAT6-CFP10 fusion antigen of M. tuberculosis complex employing codon-optimized synthetic gene

Translation engineering and bioinformatics have accelerated the rate at which gene sequences can be improved to generate multi-epitope proteins. Strong antigenic proteins for tuberculosis diagnosis include individual ESAT6 and CFP10 proteins or derived peptides. Obtention of heterologous multi-component antigens in E. coli without forming inclusion bodies remain a biotechnological challenge. The gene sequence for ESAT6-CFP10 fusion antigen was optimized by codon bias adjust for high-level expression as a soluble protein. The obtained fusion protein of 23.7 kDa was observed by SDS-PAGE and Western blot analysis after Ni-affinity chromatography and the yield of expressed soluble protein reached a concentration of approximately 67 mg/L in shake flask culture after IPTG induction. Antigenicity was evaluated at 4 μg/mL in whole blood cultures from bovines, and protein stimuli were assessed using a specific in vitro IFN-γ release assay. The hybrid protein was able to stimulate T-cell specific responses of bovine TB suspects. The results indicate that improved E. coli codon usage is a good and cost-effective strategy to potentialize large scale production of multi-epitope proteins with sustained antigenic properties for diagnostic purposes.

Immunomodulatory Effects of Recombinant Mycobacterium smegmatis Expressing Antigen-85B Epitopes in Infected J774A.1 Murine Macrophages

Tuberculosis (TB) causes more than 1.5 million deaths each year, remaining a significant global health problem. Mycobacterium smegmatis (M. smegmatis) and Mycobacterium tuberculosis (M. tuberculosis) share features, which support the use of the former use in new generation TB vaccine development. In a previous study, the specific humoral and cellular immunogenicity of a recombinant M. smegmatis strain expressing epitopes from M. tuberculosis Ag85B protein (rMs064), was demonstrated in mice. In the current study, the immunomodulatory capacity of rMs064 was determined in a J774A.1 murine macrophage cell line. To determine the immunomodulatory effect of rMs064 in J774A.1 macrophages, the expression of inducible nitric oxide synthase (iNOS) and production of nitric oxide (NO) was evaluated. The expression of activation surface markers (MHC-II, CD40, CD80 and CD86) and the production of cytokines (IL-1β, TNF-α, IL-12p70 and IL-6) was also determined in rMs064 infected J774A.1 macrophages. Our findings showed the ability of rMs064 to induce substantial increases in macrophage activation markers expression; MHC class II and CD40, compared with M. smegmatis transformed with the empty vector (rMs012) and uninfected cells. rMs064 induced significant increases in IL-12p70 compared to uninfected cells. The expression of iNOS and CD86, and the production of IL-1β, and TNF-α were increased in rMs064 and rMs012, compared to uninfected cells. rMs064 demonstrated its immunomodulatory ability by stimulating the innate immune response, which supports its further evaluation as a TB vaccine candidate.

Immunodominant Mycobacterium tuberculosis Protein Rv1507A Elicits Th1 Response and Modulates Host Macrophage Effector Functions

Mycobacterium tuberculosis (M. tb) persists as latent infection in nearly a quarter of the global population and remains the leading cause of death among infectious diseases. While BCG is the only vaccine for TB, its inability to provide complete protection makes it imperative to engineer BCG such that it expresses immunodominant antigens that can enhance its protective potential. In-silico comparative genomic analysis of Mycobacterium species identified M. tb Rv1507A as a “signature protein” found exclusively in M. tb. In-vitro (cell lines) and in-vivo experiments carried out in mice, using purified recombinant Rv1507A revealed it to be a pro-inflammatory molecule, eliciting significantly high levels of IL-6, TNF-α, and IL-12. There was increased expression of activation markers CD69, CD80, CD86, antigen presentation molecules (MHC I/MHCII), and associated Th1 type of immune response. Rv1507A knocked-in M. smegmatis also induced significantly higher pro-inflammatory Th1 response and higher survivability under stress conditions, both in-vitro (macrophage RAW264.7 cells) and in-vivo (mice). Sera derived from human TB patients showed significantly enhanced B-cell response against M. tb Rv1507A. The ability of M. tb Rv1507A to induce immuno-modulatory effect, B cell response, and significant memory response, renders it a putative vaccine candidate that demands further exploration.

ESAT-6 regulates autophagous response through SOD-2 and as a result induces intracellular survival of Mycobacterium bovis BCG

Mycobacterium is known for subverting the host defense machinery, and one such mechanism is the inhibition of autophagy. Here, we have demonstrated that Mycobacterium tuberculosis (MTB) secretes a virulence factor; an early secretory antigenic target protein (ESAT-6) into the phagosome, which induces the expression and activity of mitochondrial superoxide dismutase (SOD-2) of macrophages. Using a series of experiments, and Mycobacterium bovis BCG as a model strain (where ESAT-6 protein is not expressed), we have delineated that the protein regulates SOD-2 of macrophages. The expression and augmentation of SOD-2 activity were confirmed by either incubating the macrophages with ESAT-6 protein, transfection of macrophage by esat6 gene using a eukaryotic promoter vector, or by infection with different mycobacterial strains. The induction of acidification of phagosomal compartment containing bacteria was observed in cells that express low levels of SOD-2. This was further confirmed by observing a significant decrease in the M. bovis BCG intracellular load in the sod-2 knocked-down macrophages.

The effect of adjuvants and delivery systems on Th1, Th2, Th17 and Treg cytokine responses in mice immunized with Mycobacterium tuberculosis-specific proteins

Tuberculosis (TB) is a major health problem of global concern. The control of this disease requires appropriate preventive measures, including vaccines. In TB, T helper (Th)1 cytokines provide protection whereas Th2 and T regulatory (Treg) cytokines contribute to the pathogenesis and Th17 cytokines play a role in both protection and pathogenesis. Previous studies with Mycobacterium tuberculosis-specific proteins have identified seven low molecular weight proteins, PE35, ESXA, ESXB, Rv2346c, Rv2347c, Rv3619c, and Rv3620c, as immunodominant antigens inducing Th1-cell responses in humans following natural infection with M. tuberculosis. The aim of this study was to characterize the cytokine responses induced in mice immunized with these proteins, using various adjuvants and delivery systems, i.e. chemical adjuvants (Alum and IFA), non-pathogenic mycobacteria (M. smegmatis and M. vaccae) and a DNA vaccine plasmid (pUMVC6). The immune responses were monitored by quantifying the marker cytokines secreted by Th1 (IFN-ɣ), Th2 (IL-5), Treg (IL-10), and Th17 (IL-17A) cells. DNA corresponding to pe35, esxa, esxb, rv2346c, rv2347c, rv3619c, and rv3620c genes were cloned into the expression vectors pGES-TH-1, pDE22 and pUMVC6 for expression in Escherichia coli, mycobacteria and eukaryotic cells, respectively. Mice were immunized with the recombinants using different adjuvants and delivery systems, and spleen cells were stimulated in vitro with peptides of immunizing proteins to investigate antigen-specific secretion of Th1 (IFN-ɣ), Th2 (IL-5), Treg (IL-10), and Th17 (IL-17A) cytokines. The results showed that spleen cells, from mice immunized with all antigens, secreted the protective Th1 cytokine IFN-ɣ, except ESXB, with one or more adjuvants and delivery systems. However, only Rv3619c consistently induced Th1-biased responses, without the secretion of significant concentrations of Th2, Th17 and Treg cytokines, with all adjuvants and delivery systems. Rv3619c also induced antigen-specific IgG antibodies in immunized mice.

Biological Characteristics of Severe Combined Immunodeficient Mice Produced by CRISPR/Cas9-Mediated Rag2 and IL2rg Mutation

Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas)9 is a novel and convenient gene editing system that can be used to construct genetically modified animals. Recombination activating gene 2 (Rag2) is a core component that is involved in the initiation of V(D)J recombination during T- and B-cells maturation. Separately, the interleukin-2 receptor gamma chain gene (IL2rg) encoded the protein-regulated activity of natural killer (NK) cells and shared common receptors of some cytokines. Rag2 and IL2rg mutations cause immune system disorders associated with T-, B-, and NK cell function and some cytokine activities. In the present study, 2 single-guide RNAs (sgRNAs) targeted on Rag2 and IL2rg genes were microinjected into the zygotes of BALB/c mice with Cas9 messenger RNA (mRNA) to create Rag2/IL2rg^-/- double knockout mice, and the biological characteristics of the mutated mice were subsequently analyzed. The results showed that CRISPR/Cas9-induced indel mutation displaced the frameshift of Rag2 and IL2rg genes, resulting in a decrease in the number of T-, B-, and NK cells and the destruction of immune-related tissues like the thymus and spleen. Mycobacterium tuberculosis 85B antigen could not induce cellular and humoral immune response in mice. However, this aberrant immune activity compromised the growth of several tumor heterogenous grafts in the mutated mice, including orthotopic and subcutaneous transplantation tumors. Thus, Rag2/IL2rg^-/- knockout mice possessed features of severe combined immunodeficiency (SCID), which is an ideal model for human xenograft.

Antitumor effect of recombinant Mycobacterium smegmatis expressing MAGEA3 and SSX2 fusion proteins

Mycobacterium smegmatis (M. smegmatis), which is a nonpathogenic and fast-growing mycobacterium, is a potential vaccine vector capable of expressing heterologous antigens. Spontaneous humoral and cellular immune responses have been demonstrated against cancer/testis antigens (CTA), including melanoma-associated antigen A (MAGEA) and SSX. In the present study, recombinant plasmids expressing MAGEA3 and SSX2 were constructed. The recombinant plasmids were transferred into M. smegmatis to generate the novel antitumor DNA vaccine. As MAGEA3 and SSX2 were in different ligation sequences, the two DNA vaccines were recombinant M. smegmatis MAGEA3-SSX2 (rM.S-MS) and recombinant M. smegmatis SSX2-MAGEA3 (rM.S-SM), respectively. The expression levels of Fusion proteins were assessed by western blotting. BALB/c mice were immunized with rM.S and western blot analysis was used to determine whether antibodies against MAGEA3 or SSX2 were produced in immunized mice. EC9706 cells were inoculated into BALB/c nude mice and the mice were maintained until an obvious visible tumor appeared on the back. Subsequently, the blood from the rM.S immunized BALB/c mice was injected into the BALB/c nude mice via the tail vein. In order to evaluate the antitumor effect of the vaccines, tumor volume and weight were measured 5 to 21 days after injection. Mice were euthanized on day 21 of tumor growth, and the tumor was dissected and weighed. The two fusion proteins were expressed in the rM.S and the specific fusion protein antibodies were expressed in the blood of immunized BALB/c mice. The tumor volumes and weight in the recombinant M. smegmatis MAGEA3 (rM.S-M) and recombinant M. smegmatis SSX2 (rM.S-S) groups were significantly reduced compared with the control group. Furthermore, the decrease in tumor volumes and weight in the rM.S-MS and rM.S-SM groups was more severe than in the rM.S-M or rM.S-S groups. There was no significant difference in the antitumor effect of the rM.S-MS and rM.S-SM groups. The present findings suggest that this rM.S may be a potential candidate therapeutic vaccine for the treatment of cancer.

The current status, challenges, and future developments of new tuberculosis vaccines

Mycobacterium tuberculosis complex causes tuberculosis (TB), one of the top 10 causes of death worldwide. TB results in more fatalities than multi-drug resistant (MDR) HIV strain related coinfection. Vaccines play a key role in the prevention and control of infectious diseases. Unfortunately, the only licensed preventive vaccine against TB, bacilli Calmette-Guérin (BCG), is ineffective for prevention of pulmonary TB in adults. Therefore, it is very important to develop novel vaccines for TB prevention and control. This literature review provides an overview of the innate and adaptive immune response during M. tuberculosis infection, and presents current developments and challenges to novel TB vaccines. A comprehensive understanding of vaccines in preclinical and clinical studies provides extensive insight for the development of safer and more efficient vaccines, and may inspire new ideas for TB prevention and treatment.

Fc-based delivery system enhances immunogenicity of a tuberculosis subunit vaccine candidate consisting of the ESAT-6:CFP-10 complex

Tuberculosis (TB) remains a major global health threat despite chemotherapy and Bacilli Calmette-Guérin (BCG) vaccination. Therefore, a safer and more effective vaccine against TB is urgently needed. This study evaluated the immunogenicity of a recombinant fusion protein consisting of early secreted antigenic target protein 6 kDa (ESAT-6), culture filtrate protein 10 kDa (CFP-10) and the Fc-domain of mouse IgG2a as a novel subunit vaccine. The recombinant expression vectors (pPICZαA-ESAT-6:CFP-10:Fcγ2a and pPICZαA-ESAT-6:CFP-10:His) were transferred into Pichia pastoris. After SDS-PAGE and immunoblotting, the immunogenicity of the recombinant proteins was evaluated in mice. When both recombinant proteins (ESAT-6:CFP-10:Fcγ2a and ESAT-6:CFP-10:His) were used for vaccination, Th1-type cellular responses were induced producing high levels of IFN-γ and IL-12. However, the Fc-tagged recombinant protein induced more effective Th1-type cellular responses with a small increase in IL-4 as compared to the BCG and ESAT-6:CFP-10:His groups. Moreover, mice primed with BCG and then supplemented with ESAT-6:CFP-10:Fcγ2a produced the highest levels of IFN-γ and IL-12 in immunized groups. The findings indicate that when Fcγ2a is fused to the ESAT-6:CFP-10 complex, as a delivery vehicle, there could be an increase in the immunogenicity of this type of subunit vaccine. Therefore, additional investigations are necessary for the development of appropriate Fc-based tuberculosis vaccines.

Recombinant Mycobacterium smegmatis with a pMyong2 vector expressing Human Immunodeficiency Virus Type I Gag can induce enhanced virus-specific immune responses

Recently, we have developed a novel Mycobacterium-Escherichia coli shuttle vector system using pMyong2, which can provide an enhanced expression of heterologous genes in recombinant Mycobacterium smegmatis (rSmeg). To investigate the usefulness of rSmeg using pMyong2 in vaccine application, we vaccinated M. smegmatis with pMyong2 system expressing Human Immunodeficiency Virus Type I (HIV-1) Gag p24 antigen (rSmeg-pMyong2-p24) into mice and examined its cellular and humoral immune responses against HIV gag protein. We found that rSmeg-pMyong2-p24 expressed higher levels of Gag protein in bacteria, macrophage cell line (J774A.1) and mouse bone marrow derived dendritic cells (BMDCs) compared to rSmeg strains using two other vector systems, pAL5000 derived vector (rSmeg-pAL-p24) and the integrative plasmid, pMV306 (rSmeg-pMV306-p24). Inoculation of mice with rSmeg-pMyong2-p24 elicited more effective immunity compared to the other two rSmeg strains, as evidenced by higher levels of HIV-1 Gag-specific CD4 and CD8 T lymphocyte proliferation, interferon gamma ELISPOT cell induction, and antibody production. Furthermore, rSmeg-pMyong2-p24 showed a higher level of cytotoxic T cell response against target cells expressing Gag p24 proteins. Our data suggest that Mycobacterium-Escherichia coli shuttle vector system with pMyong2 may provide an advantage in vaccine application of rSmeg over other vector systems.

Recombinant Bacillus subtilis spores for the delivery of Mycobacterium tuberculosis Ag85B-CFP10 secretory antigens

Tuberculosis continues to be a great cause of morbidity and mortality in different parts of the world. Unfortunately, the current BCG vaccine being administered is not fully protective against tuberculosis; therefore, there is a great need for alternate vaccines. With an aim to develop such vaccines, we have analyzed the utility of Bacillus subtilis spores for the expression of two major immunodominant antigens of Mycobacterium tuberculosis, Ag85B and CFP10. We created three recombinant B. subtilis strains to express a truncated fusion of Ag85B_191-325 and CFP10_1-70 antigens (T85BCFP), either on the spore coat (MTAG1 strain) or in the cytosol of B. subtilis (MTAG 2 and MTAG 3 strains). Examination of spores isolated from these strains revealed successful expression of T85BCFP antigens on the spore coat of MTAG1 as well as in the cytosol of vegetatively grown cells of MTAG2 and MTAG3, indicating that spores can indeed express M. tuberculosis antigens. In vitro antigen presentation assays with spore-infected mouse bone marrow derived macrophages (BMDM) showed that all three recombinant spores could deliver these antigens to antigen presenting cells (APCs). Mice immunized with recombinant spores displayed significantly higher levels of Ag85B specific IFN-γ producing cells in the spleen than in mice immunized with wild-type (non-recombinant) spores. In addition, these mice showed relatively higher levels of Ag85B specific IgG antibodies in the serum in comparison to mice immunized with non-recombinant spores, thus providing additional evidence that recombinant spores can deliver these antigens in vivo. These results suggest that B. subtilis spores are ideal vehicles for antigen delivery and have great potential in the development of primary and booster vaccines against tuberculosis.

Safety of Recombinant Fusion Protein ESAT6-CFP10 as a Skin Test Reagent for Tuberculosis Diagnosis: an Open-Label, Randomized, Single-Center Phase I Clinical Trial

This trial was conducted to explore the safety of recombinant fusion protein ESAT6-CFP10 as a skin test reagent for the diagnosis of Mycobacterium tuberculosis infection. Twenty-four healthy adult volunteers were recruited and randomized into four groups (groups A to D) to study four increasing doses of ESAT6-CFP10. All subjects in each dose group received an intradermal injection of reagent (0.1 ml) via the Mantoux technique. Then, the vital signs of all subjects were monitored, and skin reactions around injection sites and adverse events were recorded at different detection time points after the skin test. No serious adverse events were observed in this study. A total of 3 subjects had unexpected events. One subject in group A developed subcutaneous hemorrhage 24 h after the skin test, one subject in group B was found with red spots 15 min after the skin test, and another subject in group A showed abnormity during a chest X-ray after the skin test without affecting her health. One of three adverse events (red spots) was probably related to the recombinant ESAT6-CFP10 reagent. A single dose of 1, 5, 10, or 20 μg/ml of recombinant ESAT6-CFP10 as a skin test reagent for M. tuberculosis infection diagnosis is well tolerated and safe in China. (This study has been registered at ClinicalTrials.gov under registration no. NCT01999231.).

Autophagy-Related Proteins Target Ubiquitin-Free Mycobacterial Compartment to Promote Killing in Macrophages

Autophagy is a lysosomal degradative process that plays essential functions in innate immunity, particularly, in the clearance of intracellular bacteria such as Mycobacterium tuberculosis. The molecular mechanisms involved in autophagy activation and targeting of mycobacteria, in innate immune responses of macrophages, are only partially characterized. Autophagy targets pathogenic M. tuberculosis via a cytosolic DNA recognition- and an ubiquitin-dependent pathway. In this report, we show that non-pathogenic M. smegmatis induces a robust autophagic response in THP-1 macrophages with an up regulation of several autophagy-related genes. Autophagy activation relies in part on recognition of mycobacteria by Toll-like receptor 2 (TLR2). Notably, LC3 targeting of M. smegmatis does not rely on membrane damage, ubiquitination, or autophagy receptor recruitment. Lastly, M. smegmatis promotes recruitment of several autophagy proteins, which are required for mycobacterial killing. In conclusion, our study uncovered an alternative autophagic pathway triggered by mycobacteria which involves cell surface recognition but not bacterial ubiquitination.

The mc2-CMX vaccine induces an enhanced immune response against Mycobacterium tuberculosis compared to Bacillus Calmette-Guérin but with similar lung inflammatory effects

Although the attenuated Mycobacterium bovis Bacillus Calmette-Guérin (BCG) vaccine has been used since 1921, tuberculosis (TB) control still proceeds at a slow pace. The main reason is the variable efficacy of BCG protection against TB among adults, which ranges from 0-80%. Subsequently, the mc2-CMX vaccine was developed with promising results. Nonetheless, this recombinant vaccine needs to be compared to the standard BCG vaccine. The objective of this study was to evaluate the immune response induced by mc2-CMX and compare it to the response generated by BCG. BALB/c mice were immunised with both vaccines and challenged with Mycobacterium tuberculosis (Mtb). The immune and inflammatory responses were evaluated by ELISA, flow cytometry, and histopathology. Mice vaccinated with mc2-CMX and challenged with Mtb induced an increase in the IgG1 and IgG2 levels against CMX as well as recalled specific CD4+ T-cells that produced T-helper 1 cytokines in the lungs and spleen compared with BCG vaccinated and challenged mice. Both vaccines reduced the lung inflammatory pathology induced by the Mtb infection. The mc2-CMX vaccine induces a humoral and cellular response that is superior to BCG and is efficiently recalled after challenge with Mtb, although both vaccines induced similar inflammatory reductions.

Fused Mycobacterium tuberculosis multi-stage immunogens with an Fc-delivery system as a promising approach for the development of a tuberculosis vaccine

Tuberculosis (TB) remains a major health problem worldwide. Currently, the Bacilli Calmette-Guérin (BCG) is the only available licensed TB vaccine, which has low efficacy in protection against adult pulmonary TB. Therefore, the development of a safe and effective vaccine against TB needs global attention. In the present study, a novel multi-stage subunit vaccine candidate from culture filtrate protein-10 (CFP-10) and heat shock protein X (HspX) of Mycobacterium tuberculosis fused to the Fc domain of mouse IgG2a as a selective delivery system for antigen-presenting cells (APCs) was produced and its immunogenicity assessed. The optimized gene constructs were introduced into pPICZαA expression vectors, and the resultant plasmids (pPICZαA-CFP-10:Hspx:Fcγ2a and pPICZαA-CFP-10:Hspx:His) were transferred into Pichia pastoris by electroporation. The identification of both purified recombinant fusion proteins was evaluated by SDS-PAGE and immunoblotting. Then the immunogenicity of the recombinant proteins with and without BCG was evaluated in BALB/c mice by assessing the level of IFN-γ, IL-12, IL-4, IL-17 and TGF-β cytokines. Both multi-stage vaccines (CFP-10:HspX:Fcγ2a and CFP-10:HspX:His) induced Th1-type cellular responses by producing high level of IFN-γ (272 pg/mL, p<0.001) and IL-12 (191 pg/mL, p<0.001). However, the Fc-tagged recombinant protein induced more effective Th1-type cellular responses with a low level of IL-4 (10 pg/mL) compared to the CFP-10:HspX:His group. The production of IFN-γ to CFP-10:HspX:Fcγ2a was markedly consistent and showed an increasing trend for IL-12 compared with the BCG or CFP-10:HspX:His primed and boosted groups. Findings revealed that CFP-10:Hspx:Fcγ2a fusion protein can elicit strong Th1 antigen-specific immune responses in favor of protective immunity in mice and could provide new insight for introducing an effective multi-stage subunit vaccine against TB.

IL-17A Autoantibody Induced by Recombinant Mycobacterium smegmatis Expressing Ag85A-IL-17A Fusion Protein

Interleukin-17A is a newly described proinflammatory cytokine, which plays important roles in autoimmune diseases as well as asthma. In current work, we constructed a recombinant plasmid pMFA42S-Ag85a-IL-17a by inserting fusion gene Ag85a-IL-17a into shuttle vector pMFA42S, which was transformed to Mycobacterium smegmatis by electroporation to obtain recombinant M. smegmatis named rMS-Ag85a-IL-17a. The comparison of growth pattern between M. smegmatis and rMS-Ag85a-IL-17a suggested fusion gene had no significant influence on the growth of strains, and rMS-Ag85a-IL-17a expressed fusion protein Ag85A-IL-17A which had good immunogenicity revealed by Western blot. M. smegmatis and rMS-Ag85a-IL-17a were performed to intranasally immunize mice; then, antibody response in sera was detected by enzyme-linked immunosorbent assay. Our findings demonstrated that rMS-Ag85a-IL-17a could induce specific IL-17A autoantibody in mice, which laid the foundation for further study.

Prime-boost vaccination with Bacillus Calmette Guerin and a recombinant adenovirus co-expressing CFP10, ESAT6, Ag85A and Ag85B of Mycobacterium tuberculosis induces robust antigen-specific immune responses in mice

Tuberculosis (TB) remains to be a prevalent health issue worldwide. At present, Mycobacterium bovis Bacillus Calmette Guerin (BCG) is the singular anti-TB vaccine available for the prevention of disease in humans; however, this vaccine only provides limited protection against Mycobacterium tuberculosis (Mtb) infection. Therefore, the development of alternative vaccines and strategies for increasing the efficacy of vaccination against TB are urgently required. The present study aimed to evaluate the ability of a recombinant adenoviral vector (Ad5-CEAB) co-expressing 10-kDa culture filtrate protein, 6-kDa early-secreted antigenic target, antigen 85 (Ag85)A and Ag85B of Mtb to boost immune responses following primary vaccination with BCG in mice. The mice were first subcutaneously primed with BCG and boosted with two doses of Ad5-CEAB via an intranasal route. The immunological effects of Ad5-CEAB boosted mice primed with BCG were then evaluated using a series of immunological indexes. The results demonstrated that the prime-boost strategy induced a potent antigen-specific immune response, which was primarily characterized by an enhanced T cell response and increased production of cytokines, including interferon-γ, tumor necrosis factor-α and interleukin-2, in mice. In addition, this vaccination strategy was demonstrated to have an elevated humoral response with increased concentrations of antigen-specific bronchoalveolar lavage secretory immunoglobulin (Ig)A and serum IgG in mice compared with those primed with BCG alone. These data suggested that the regimen of subcutaneous BCG prime and mucosal Ad5-CEAB boost was a novel strategy for inducing a broad range of antigen-specific immune responses to Mtb antigens in vivo, which may provide a promising strategy for further development of adenoviral-based vaccine against Mtb infection.

Immunogenicity of a recombinant Mycobacterium smegmatis vaccine expressing the fusion protein CMX in cattle from Goiás State, Brazil

This study aimed to evaluate the immunogenicity of a recombinant Mycobacterium smegmatis vaccine expressing the CMX fusion protein composed of immunodominant epitopes Ag85C, MPT51 and HspX of Mycobacterium tuberculosis, which are important mycobacteria virulence factors. A group of Nelore heifers that were 10 to 12 months of age and negative for the tuberculin skin test (TST) were immunized with four doses of the recombinant vaccine mc(2)-CMX (M. smegmatis-Ag85C-MPT51-HspX) during a period of one year. Before each immunization, blood was collected to obtain sera for antibody analysis. Serological analysis demonstrated that mc(2)-CMX was able to induce a humoral response with increased levels of specific IgG antibodies against CMX, despite minimum antibody levels being detected for individual Ag85C, MPT51 or HspX recombinant antigens. However, there was no significant increase in specific CD4(+) IFN-γ-positive T cells. Lymphadenomegaly was observed in superficial cervical lymph nodes adjacent to the site of vaccination among mc(2)-CMX-vaccinated bovines, and the histopathological analysis demonstrated follicular hyperplasia without inflammatory infiltrate or granuloma formation. Animals remained negative for the TST until the end of the experiments, showing no cross-reactivity with the recombinant vaccine and tuberculin proteins. We discuss the potential of mc(2)-CMX to induce an immune response in cattle.

Prime-boost with Mycobacterium smegmatis recombinant vaccine improves protection in mice infected with Mycobacterium tuberculosis

The development of a new vaccine as a substitute for Bacillus Calmette-Guerin or to improve its efficacy is one of the many World Health Organization goals to control tuberculosis. Mycobacterial vectors have been used successfully in the development of vaccines against tuberculosis. To enhance the potential utility of Mycobacterium smegmatis as a vaccine, it was transformed with a recombinant plasmid containing the partial sequences of the genes Ag85c, MPT51, and HspX (CMX) from M. tuberculosis. The newly generated recombinant strain mc(2)-CMX was tested in a murine model of infection. The recombinant vaccine induced specific IgG1 or IgG2a responses to CMX. CD4(+) and CD8(+) T cells from the lungs and spleen responded ex vivo to CMX, producing IFN-γ, IL17, TNF-α, and IL2. The vaccine thus induced a significant immune response in mice. Mice vaccinated with mc(2)-CMX and challenged with M. tuberculosis showed better protection than mice immunized with wild-type M. smegmatis or BCG. To increase the safety and immunogenicity of the CMX antigens, we used a recombinant strain of M. smegmatis, IKE (immune killing evasion), to express CMX. The recombinant vaccine IKE-CMX induced a better protective response than mc(2)-CMX. The data presented here suggest that the expression of CMX antigens improves the immune response and the protection induced in mice when M. smegmatis is used as vaccine against tuberculosis.

Immunotherapeutic efficacy of recombinant Mycobacterium smegmatis expressing Ag85B-ESAT6 fusion protein against persistent tuberculosis infection in mice

The application of immunotherapy in combination with chemotherapy is considered an effective treatment strategy against persistent Mycobacterium tuberculosis (Mtb) infection. In this study, we constructed a novel recombinant Mycobacterium smegmatis (rMS) strain that expresses Ag85B and ESAT6 fusion protein (AE-rMS). Immunization of C57BL/6 mice with AE-rMS generated mainly Th1-type immune responses by strongly stimulating IFN-γ- and IL-2-producing splenocytes and increasing antigen-specific cytotoxic T lymphocyte (CTL) activity. To test the immunotherapeutic efficacy of AE-rMS, a persistent tuberculosis infection (PTBI) model was established via tail-vein injection of C57BL/6 mice with 1×10(4) colony forming units (CFU) of Mtb strain H37Rv in combination with concurrent chemotherapy drugs isoniazid (INH) and pyrazinamide (PZA). PTBI mice immunized with AE-rMS showed high levels of IFN-γ secreted by splenocytes and decreased bacteria loads in lung. Treatment with only the anti-tuberculosis (anti-TB) drugs RFP and INH (RI), decreased bacteria loads to low levels, with the Th1-type immune response further attenuated. Moreover, AE-rMS, when combined with RI treatment, further reduced the bacteria load as well as the pathological tissue damage in lung. Together, these results demonstrated the essential roles of AE-rMS-induced Th1-type responses, providing an effective treatment strategy by combining AE-rMS and RI for persistent TB.

Novel particulate vaccines utilizing polyester nanoparticles (bio-beads) for protection against Mycobacterium bovis infection - a review

Bovine tuberculosis (TB) continues to be a major health problem in cattle and development of a safe effective vaccine to control TB in cattle would be very useful. This paper reviews progress and provides new data in development of a TB bio-bead vaccine based on polyester nanoparticle inclusions which were produced by bioengineered bacteria. Polyhydroxybutyrate (PHB) biopolyester nanoparticles (bio-beads) have been produced which displayed mycobacterial antigens, Ag85A and ESAT-6, on the surface of the bio-beads for use as vaccines for the control of tuberculosis. Bio-beads were purified from the host production bacteria, Escherichia coli and the generally regarded as safe (GRAS) bacterium, Lactococcus lactis. Previous published studies showed that vaccination with Ag85A/ESAT-6 bio-beads induced antigen-specific IFN-γ, IL-17A, IL-6, TNF-α and IL-2 in splenocytes, but no significant increase in IL-4, IL-5 or IL-10. New results showed that antigen-specific IFN-γ release was induced by both CD4 and CD8 T cells in mice vaccinated with the Ag85A/ESAT-6 bio-beads. Mice vaccinated with Ag85A/ESAT-6 bio-beads alone or in combination with BCG had significantly lower bacterial counts from the lungs and spleen following aerosol challenge with Mycobacterium bovis compared to control groups. This unique approach to the design and production of bacterial-derived bio-beads displaying antigens enables a cost-effective way to express a diverse antigen repertoire for use as vaccines to combat TB or other diseases.

Recombinant Mycobacterium smegmatis expressing Hsp65-hIL-2 fusion protein and its influence on lymphocyte function in mice

OBJECTIVE

To construct a strain of recombinant Mycobacterium smegmatis expressing the heat shock protein 65 (Hsp65) and human interleukin 2 (IL-2) fusion protein (rMS-Hsp65/IL-2) and to explore the effect of this construct on lymphocyte function in mice.

METHODS

The fusion gene encoding Hsp65-hIL-2 was cloned into shuttle vector pSMT3. The recombinant plasmid pSMT3-Hsp65-hIL-2 was transferred to Mycobacterium smegmatis by electroporation. Positive clones were selected by hygromycin and identified by PCR. The expression of fusion protein Hsp65-hIL-2 was verified using indirect immunofluorescence staining. Mice were immunized for two times by subcutaneously injection with 1×10(6) CFU rMS-Hsp65/IL-2 at a three-week interval. Two weeks after the second immunization, mice were sacrificed and the serum samples were collected for determination of anti-Hsp65 specific IgG. Splenic lymphocytes were isolated and treated with the rMS-Hsp65/IL-2 to determine lymphocytic proliferation activity by MTT assay. IFN-γ- and IL-2 in the medium of the treated cells were also determined by ELISA.

RESULTS

Successful construction of rMS-Hsp65/IL-2 was verified by PCR and immunofluorescence staining. Compared to the splenic lymphocytes isolated from mice immunized with Bacille Calmette-Guerin or mice immunized with Mycobacterium smegmatis alone, the splenic lymphocytes isolated from mice immunized with rMS-Hsp65/IL-2 showed a marked increase in the proliferation of lymphocytes, together with an increased production of important cytokines such as IFN-γ-and IL-2.

CONCLUSIONS

rMS-Hsp65/IL-2 markedly enhances lymphocyte function. Therefore, the fusion protein generated by rMS-Hsp65/IL-2 may be of potential value in generating an effective vaccine against tuberculosis.

Protective and therapeutic efficacy of Mycobacterium smegmatis expressing HBHA-hIL12 fusion protein against Mycobacterium tuberculosis in mice

Tuberculosis (TB) remains a major worldwide health problem. The only vaccine against TB, Mycobacterium bovis Bacille Calmette-Guerin (BCG), has demonstrated relatively low efficacy and does not provide satisfactory protection against the disease. More efficient vaccines and improved therapies are urgently needed to decrease the worldwide spread and burden of TB, and use of a viable, metabolizing mycobacteria vaccine may be a promising strategy against the disease. Here, we constructed a recombinant Mycobacterium smegmatis (rMS) strain expressing a fusion protein of heparin-binding hemagglutinin (HBHA) and human interleukin 12 (hIL-12). Immune responses induced by the rMS in mice and protection against Mycobacterium tuberculosis (MTB) were investigated. Administration of this novel rMS enhanced Th1-type cellular responses (IFN-γ and IL-2) in mice and reduced bacterial burden in lungs as well as that achieved by BCG vaccination. Meanwhile, the bacteria load in M. tuberculosis infected mice treated with the rMS vaccine also was significantly reduced. In conclusion, the rMS strain expressing the HBHA and human IL-12 fusion protein enhanced immunogencity by improving the Th1-type response against TB, and the protective effect was equivalent to that of the conventional BCG vaccine in mice. Furthermore, it could decrease bacterial load and alleviate histopathological damage in lungs of M. tuberculosis infected mice.

Oral immunization with recombinant Mycobacterium smegmatis expressing the outer membrane protein 26-kilodalton antigen confers prophylactic protection against Helicobacter pylori infection

Helicobacter pylori infection is prevalent worldwide and results in chronic gastritis, which may lead to gastric mucosa-associated lymphoid tissue lymphoma and gastric cancer. We have previously reported that oral immunization with recombinant Mycobacterium smegmatis expressing the H. pylori outer membrane protein 26-kilodalton (Omp26) antigen affords therapeutic protection against H. pylori infection in mice. In the present study, we investigated the prophylactic effects of this vaccine candidate on H. pylori challenge in mice. We found that oral immunization with recombinant Mycobacterium Omp26 significantly reduced H. pylori colonization in the stomach compared to inoculation with wild-type M. smegmatis in control mice. Six of the recombinant Mycobacterium-immunized mice (60%) were completely protected from H. pylori infection. The severity of H. pylori-associated chronic gastritis assessed histologically was significantly milder in mice vaccinated with recombinant Mycobacterium than in control animals. Mice immunized with recombinant Mycobacterium showed enhanced antigen-specific lymphocyte proliferation and antibody responses. Moreover, immunization with recombinant Mycobacterium resulted in an increased expression of interleukin-2 and gamma interferon in the stomach and spleen, as determined by reverse transcription-PCR analysis. Our results collectively suggest that vaccination with recombinant Mycobacterium Omp26 confers prophylactic protection against H. pylori infection. The inhibition of H. pylori colonization is associated with the induction of antigen-specific humoral and cell-mediated immune responses.

Comparative evaluation of MPT83 (Rv2873) for T helper-1 cell reactivity and identification of HLA-promiscuous peptides in Mycobacterium bovis BCG-vaccinated healthy subjects

MPT83 (Rv2873), a surface lipoprotein excreted in the culture of Mycobacterium tuberculosis, is immunoreactive in antibody assays in humans and animals and provides protection as a combined DNA vaccine in mice and cattle. This study was undertaken to determine the reactivity of MPT83 in T helper 1 (Th1)-cell assays, i.e., antigen-induced proliferation and gamma interferon (IFN-γ) secretion, using peripheral blood mononuclear cells (PBMCs) obtained from Mycobacterium bovis bacillus Calmette-Guérin (BCG)-vaccinated and/or M. tuberculosis-infected healthy subjects. PBMCs were tested with complex mycobacterial antigens and pools of synthetic peptides corresponding to MPT63, MPT83, MPB70, LppX, PPE68, CFP10, and ESAT-6. The results showed that MPT83 is among the strongest Th1 cell antigens of M. tuberculosis, and it was recognized equally strongly by BCG-vaccinated and by BCG-vaccinated and M. tuberculosis-infected healthy subjects. Furthermore, HLA heterogeneity of the responding donors suggested that MPT83 was presented to Th1 cells by several HLA-DR molecules. The analysis of the mature MPT83 sequence (amino acids [aa] 1 to 220) and its 14 overlapping synthetic peptides for binding prediction to HLA class II molecules and actual recognition of the peptides by PBMCs from HLA-DR-typed subjects in antigen-induced proliferation and IFN-γ assays suggested that Th1 cell epitopes were scattered throughout the sequence of MPT83. In addition, the HLA-promiscuous nature of at least three peptides, i.e., P11 (aa 151 to 175), P12 (aa 166 to 190), and P14 (aa 196 to 220), was suggested by HLA-DR binding predictions and recognition by HLA-DR heterogeneous donors in Th1 cell assays. These results support the inclusion of MPT83 in an antigen cocktail to develop a new antituberculosis vaccine.

Effects of Mycobacterium tuberculosis ESAT-6/CFP-10 fusion protein on the autophagy function of mouse macrophages

Autophagy plays specific roles in host innate and adaptive immune responses to numerous intracellular pathogens, including Mycobacterium tuberculosis. The ESAT-6 and CFP-10 proteins are secreted by M. tuberculosis and play important roles in pathogenesis. We hypothesized that these two proteins may affect the autophagy function of host macrophages during infection with M. tuberculosis, thereby shaping the immune reaction toward the pathogen. Interestingly, we found that rapamycin-induced autophagy of macrophages infected with M. tuberculosis H37Rv enhanced localization of mycobacteria with autophagosomes and lysosomes. Ectopic expression of the ESAT-6/CFP-10 fusion in macrophages dramatically inhibited autophagosome formation, and M. tuberculosis survival inside infected macrophages was significantly affected as well. Further, M. tuberculosis viability was increased by the fusion protein. Expression levels of autophagy-related genes (ATG), especially atg8, also decreased (p<0.05). These results suggested that ESAT-6 and CFP-10 proteins play significant roles in autophagy formation in M. tuberculosis infection and that autophagosome formation is regulated through the expression of ATG.

A novel recombinant Mycobacterium bovis bacillus Calmette-Guerin strain expressing human granulocyte macrophage colony-stimulating factor and Mycobacterium tuberculosis early secretory antigenic target 6 complex augments Th1 immunity

Since Mycobacterium bovis bacillus Calmette-Guerin strain (BCG) fails to protect adults from pulmonary tuberculosis (TB), there is an urgent need for developing a new vaccine. In this study, we constructed a novel recombinant BCG strain (rBCG) expressing human granulocyte macrophage colony-stimulating factor (GM-CSF) and the 6 kDa early secretory antigenic target (ESAT6) of Mycobacterium tuberculosis, named rBCG:GE (expressing GMCSF-ESAT6 complex), and evaluated the immunogenicity of the construct in BALB/c mice. Our results indicated that the rBCG:GE was able to induce higher titer of antibody than the conventional BCG, the rBCG:G (expressing GM-CSF) and the rBCG:E (expressing ESAT6). Moreover, the rBCG:GE also elicited a longer-lasting and stronger Th1 cellular immune responses than the other groups, which was confirmed by the incremental proliferation of splenocytes, the increased percentages of CD4(+) and CD8(+) T cells of spleen, the elevated level of interferon-γ in splenocyte culture after tuberculin-purified protein derivative stimulation, and the increased concentration of GM-CSF in serum. The data presented here suggested the possibility that the recombinant BCG:GE might be a good vaccine candidate to TB.

Recombinant Mycobacterium smegmatis vaccine candidates

Mycobacterium smegmatis is a species of rapidly growing saprophytes with a number of properties that make it an effective vaccine vector. Recombinant M. smegmatis expressing protective antigens of different pathogens and molecules modulating the immune responses offers some potential for reduction of the burden of tuberculosis, HIV and hepatitis B infections. This paper discusses the molecular methods used to generate recombinant M. smegmatis and the results obtained with some of these recombinants.