New Alternative Vaccine Component AgainstMycobacterium Tuberculosis- Heat Shock Protein 16.3 or its T-Cell Epitope

Lysine acetylation of Hsp16.3: Effect on its structure, chaperone function and influence towards the growth of Mycobacterium tuberculosis

Hsp16.3 plays a vital role in the slow growth of Mycobacterium tuberculosis via its chaperone function. Many secretory proteins, including Hsp16.3 undergo acetylation in vivo. Seven lysine (K) residues (K64, K78, K85, K114, K119, K132 and K136) in Hsp16.3 are acetylated inside pathogen. However, how lysine acetylation affects its structure, chaperone function and pathogen's growth is still elusive. We examined these aspects by executing in vitro chemical acetylation (acetic anhydride modification) and by utilizing a lysine acetylation mimic mutant (Hsp16.3-K64Q/K78Q/K85Q/K114Q/K119Q/K132Q/K136Q). Far- and near-UV CD measurements revealed that the chemically acetylated proteins(s) and acetylation mimic mutant has altered secondary and tertiary structure than unacetylated/wild-type protein. The chemical modification and acetylation mimic mutation also disrupted the oligomeric assembly, increased surface hydrophobicity and reduced stability of Hsp16.3, as revealed by GF-HPLC, 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid binding and urea denaturation experiments, respectively. These structural changes collectively led to an enhancement in chaperone function (aggregation and thermal inactivation prevention ability) of Hsp16.3. Moreover, when the H37Rv strain expressed the acetylation mimic mutant protein, its growth was slower in comparison to the strain expressing the wild-type/unacetylated Hsp16.3. Altogether, these findings indicated that lysine acetylation improves the chaperone function of Hsp16.3 which may influence pathogen's growth in host environment.

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.

Role of ATP-Small Heat Shock Protein Interaction in Human Diseases

Adenosine triphosphate (ATP) is an important fuel of life for humans and Mycobacterium species. Its potential role in modulating cellular functions and implications in systemic, pulmonary, and ocular diseases is well studied. Plasma ATP has been used as a diagnostic and prognostic biomarker owing to its close association with disease’s progression. Several stresses induce altered ATP generation, causing disorders and illnesses. Small heat shock proteins (sHSPs) are dynamic oligomers that are dominantly β-sheet in nature. Some important functions that they exhibit include preventing protein aggregation, enabling protein refolding, conferring thermotolerance to cells, and exhibiting anti-apoptotic functions. Expression and functions of sHSPs in humans are closely associated with several diseases like cataracts, cardiovascular diseases, renal diseases, cancer, etc. Additionally, there are some mycobacterial sHSPs like Mycobacterium leprae HSP18 and Mycobacterium tuberculosis HSP16.3, whose molecular chaperone functions are implicated in the growth and survival of pathogens in host species. As both ATP and sHSPs, remain closely associated with several human diseases and survival of bacterial pathogens in the host, therefore substantial research has been conducted to elucidate ATP-sHSP interaction. In this mini review, the impact of ATP on the structure and function of human and mycobacterial sHSPs is discussed. Additionally, how such interactions can influence the onset of several human diseases is also discussed.

Peptide-Based Vaccines for Tuberculosis

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis. As a result of the coronavirus disease 2019 (COVID-19) pandemic, the global TB mortality rate in 2020 is rising, making TB prevention and control more challenging. Vaccination has been considered the best approach to reduce the TB burden. Unfortunately, BCG, the only TB vaccine currently approved for use, offers some protection against childhood TB but is less effective in adults. Therefore, it is urgent to develop new TB vaccines that are more effective than BCG. Accumulating data indicated that peptides or epitopes play essential roles in bridging innate and adaptive immunity and triggering adaptive immunity. Furthermore, innovations in bioinformatics, immunoinformatics, synthetic technologies, new materials, and transgenic animal models have put wings on the research of peptide-based vaccines for TB. Hence, this review seeks to give an overview of current tools that can be used to design a peptide-based vaccine, the research status of peptide-based vaccines for TB, protein-based bacterial vaccine delivery systems, and animal models for the peptide-based vaccines. These explorations will provide approaches and strategies for developing safer and more effective peptide-based vaccines and contribute to achieving the WHO’s End TB Strategy.

Prediction and identification of CD4+ T cell epitope for the protective antigens of Mycobacterium tuberculosis

CD4+T cell epitopes plays a key role in anti-tuberculosis (TB) immunity, CD4+T cell epitopes suitable for the domestic population are lacking. Therefore, we predicted and identified novel CD4+T cell epitopes.The bioinformatics software, namely, DNAStar (DNASTAR of the United States), SYFPEITHI (INTERFACTORS INSTITUT Für ZELL Biologie of Germany), RANKPEP, and NetMHC IIpan (National Cancer Institute, United States of America), were used to comprehensively predict the CD4+T cell immune epitope of Mycobacterium TB, and the predicted epitope polypeptide was synthesized by the standard Fmoc scheme. The proliferation of PBMC and CD4+T cells stimulated by peptides was preliminarily detected by the CCK8 method. Then, the candidate polypeptides screened out by the CCK8 method were verified again by the BrdU assay, and flow cytometry was performed to analyze further the extent of their stimulation on the proliferation of CD4+T cells. The changes in the secreted cytokines IFN-γ, TNF-α, IL-2, and IL-10 before and after the candidate polypeptide stimulation of CD4+T lymphocytes were detected by ELISA. The preliminary humoral immunity test was conducted by indirect ELISA to evaluate the serological diagnostic value of the CD4+T cell epitope polypeptide.In this study, 5 novel candidate CD4+T cell epitope polypeptides with the amino acid sequences of LQGQWRGAAGTAAQA, PVTLAETGSTLLYPL, AAAWGGSGSEAYQGV, QFVYAGAMSGLLDPS, and KAALTRTASNMNAAA and others that have not been reported in the research were predicted. For convenience, the 5 candidates were successively named as P39, P50, P40, P185, and P62. P39, P62, and the mixed peptide P39+P62 could effectively induce the proliferation of CD4+T cells and increase the secretion of IFN-γ, TNF-α, and IL-2 from the CD4+T cells, while reducing the content of IL-10. The serological test showed that the sensitivity, specificity, and area under the receiver operating characteristic curve (AUC) of P39 were 75%, 67.71%, and 0.844, respectively. The sensitivity, specificity, and AUC of P62 were 91.66%, 46.87%, and 0.649, respectively. The sensitivity of the mixed peptide P39+P62 was 95.83%, the specificity was 97.91%, and the AUC was 0.793.The P39 and P62 polypeptides were predicted and identified as potential CD4+T cell immune epitope polypeptides of M. TB. The polypeptide had better diagnosis effect, which provided potential candidate epitope polypeptides for the development of TB-specific diagnosis reagents and novel TB epitope vaccines.

Serodiagnostic evaluation of fusion proteins from multiple antigens of Mycobacterium tuberculosis for active TB

Tuberculosis (TB) is a global health problem, being prevalent in the developing countries. A rapid, reliable and cost effective diagnostic method would help in controlling TB in the endemic populations. Development of suitable fusion molecules detecting multiple antibodies produced against Mycobacterium tuberculosis antigens would enhance sensitivity of serodiagnostic assays. In this study, EspC, CFP7 and PPE57 antigens of M. tuberculosis were selected for constructing fusion molecules after prediction of B-cell epitopes using in silico tools. Fusion proteins EspC-CFP7, HspX-EspC-CFP7 and HspX-EspC-CFP7-PPE57 were expressed in E.coli (BL21). The serodiagnostic potential of the individual antigens and their fusions was analyzed by screening 230 plasma samples of pulmonary TB patients. The single antigens HspX, EspC, CFP7, PPE57 showed sensitivities of 30%, 31%, 22% and 35%, respectively. The fusion protein EspC-CFP7 showed sensitivity of 43%. Linking of HspX antigen to the N-terminus of EspC-CFP7 fusion molecule increased sensitivity to 58%, while joining PPE57 antigen to the C-terminus of HspX-EspC-CFP7 increased sensitivity to 69%. The fusion protein HspX-EspC-CFP7-PPE57 seems to be a promising molecule for use in the development of fusions with higher sensitivity.

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.

Effects of Mycobacterium tuberculosis Mutant Strain Hsp16.3 Gene on Murine RAW 264.7 Macrophage Autophagy

Heat shock protein Hsp16.3 is closely related to latent Mycobacterium tuberculosis (MTB) infection and plays an important role in sustained survival when MTB is dormant. In this study, the Hsp16.3 gene mutant MTB H37Rv strain (Hsp16.3ΔMTB) was obtained through gene recombination and infected into murine RAW 264.7 macrophages. Western blotting and immunofluorescence showed increased expression of the autophagy-related protein LC3, and transmission electron microscopy showed significantly increased macrophage autophagosomes, suggesting that Hsp16.3ΔMTB facilitates murine macrophage autophagy. These findings have implications for preventing and controlling tuberculosis.

Screening putative antigens as stimulators in the Mycobacterium bovis interferon-gamma release assay for cattle

Bovine tuberculosis (BTB) represents not only a significant economic concern, but also an important public health problem. Currently, interferon-gamma (IFN-γ) release assays (IGRAs) are widely used as an adjunct to the tuberculin test (TST) for the diagnosis of BTB. A great number of international studies have demonstrated that the sensitivity of the IFN-γ assay, which uses purified protein derivatives (PPDs) as diagnostic reagents, is superior to that of the TST. However, there are concerns about its specificity, largely because of the cross reactivity of common antigens shared by pathogenic and non-pathogenic mycobacterial species. The use of pathogen-specific antigens theoretically offers the most effective way to improve the specificity of IGRAs. In this study, we evaluated the potential utility of 13 purified recombinant putative antigens, which are highly specific to the Mycobacterium tuberculosis complex, as diagnostic reagents in IGRAs. A CFP-10-ESAT-6 fusion protein (abbreviated CE) displayed the greatest potential, whereas four region of difference 2 (RD2) antigens, especially Rv1985c were identified as potential candidate antigens, and can be included in an IGRA cocktail, together with CE as stimulators in the IFN-γ release assay for the diagnosis of BTB.

Mycobacterium tuberculosis Secreted Proteins As Potential Biomarkers for the Diagnosis of Active Tuberculosis and Latent Tuberculosis Infection

Background

The detection of Mycobacterium tuberculosis (Mtb) specific human antibodies has been an important diagnostic aid in the diagnosis of tuberculosis (TB) cases with smear‐negative sputum samples, especially for the screening of high‐risk population. This study focused on the analysis and comparison of the four potential Mtb‐secreted proteins (ESAT6, CFP10, Ag85B, Hsp16.3) and the fusion protein Ag85B‐Hsp16.3 as new markers in the serodiagnosis between active TB and latent TB infection (LTBI).

Methods

These five recombinant proteins were produced and used in optimized ELISA to detect IgG serum antibodies against the four secreted proteins. The capacity of identifying infection was evaluated either in active TB patients or LTBI individuals, which was compared with the control groups consisting of hospitalized non‐TB individuals.

Results

The results showed that Ag85B‐Hsp16.3/ESAT6 and Hsp16.3/ESAT6 were the best‐associated antigens for serology diagnosis of the active TB and LTBI individuals because of their specificity, sensitivity, YI values, and positive rates, respectively. ELISA test demonstrated that 41.67% (25/60) of blood donors respond to Ag85B‐Hsp16.3/ESAT6. The consistency of this positive respond with clinical diagnosis almost reached 84% (21/25).

Conclusion

Thus, a combined test of multiple Mtb‐secreted proteins Ag85B, Hsp16.3, and ESAT6 may be the ascendant preliminary screening antigens for active TB or LTBI patients.

Tuberculosis vaccine research in China

It is now privately acknowledged that there may be little if any perceptible impact of the national Bacille Calmette-Guerin (BCG) vaccination program on disease prevalence, despite the extensive coverage of the newborn infant population and likely benefit in the early years of life. A better preventive vaccine than BCG is now being sought by Chinese researchers. Urgency has been added to the control problem by the emergence of multidrug-resistant tuberculosis (TB). Furthermore, expensive second-line drugs seem unlikely to be made available by the government to treat drug-resistant cases, so attention in addition has turned to the potential of immunotherapy as an adjunct to chemotherapy. Research trends are summarized here.

Monoclonal antibodies against a Mycobacterium tuberculosis Ag85B-Hsp16.3 fusion protein

The secreted Mycobacterium tuberculosis (MTB) proteins, Ag85B and Hsp16.3, have been the focus of intensive research in recent years. These proteins have high sensitivity in bacterium-negative tuberculosis (TB) patients, and are valuable for the rapid diagnosis of bacterium-negative TB. Fusion proteins including multiple antigens such as Ag85B and Hsp16.3 provide improved sensitivity and specificity for serological diagnosis of active TB compared with a single antigen. Many studies have shown that the production of MAbs recognizing a specific repertoire of M. tuberculosis antigens and the tests based on monoclonal antibodies have been found to be valuable in positive detection of TB, particularly for smear-positive pulmonary TB. A number of MAbs are currently used for serodiagnosis of TB. Therefore, an Ag85B-Hsp16.3 fusion protein was expressed and purified using an E. coli system in this study. Three Ag85B-Hsp16.3 fusion protein-specific MAbs were generated by routine murine hybridoma techniques. The titer, specificity, and relative affinity of all three MAbs were determined by ELISA and the serological responses were analyzed. The levels of antigens in a proportion of TB patients were shown to be significantly higher than those in healthy controls. The sensitivity and specificity of the currently available detection systems is likely to be improved by the employment of a combination of these MAbs with others that are already in use.

A review of murine models of latent tuberculosis infection

The mechanisms of latency and the causes of reactivation of Mycobacterium tuberculosis remain poorly understood; an important reason for this gap in knowledge is the absence of a standardized animal model of latent tuberculosis infection (LTBI). A complete LTBI model should incorporate 2 aspects of LTBI: a persistent infection model with a low bacterial load and a latent infection model that is modified from the Cornell model. Many parameters must be carefully considered to establish an LTBI model, including the inoculating dose, the route of infection, the time interval between infection and the initiation of antibiotic therapy, and the genetic background of the host animal. The responsiveness of this mouse model of LTBI can be assessed through the integrated use of indices, including Karnofsky performance status, bacterial load in spleen and lungs, induced levels of interferon-gamma and tumour necrosis factor-alpha, expression of interleukin (IL)-10 and IL-4 in tissues, specific antigen load in organs, time required for hormone-induced TB relapse, expression level of dormancy genes, and CD4 T-cell count.