Recent Developments in Mycobacteria-Based Live Attenuated Vaccine Candidates for Tuberculosis

A Modular Self-Assembling and Self-Adjuvanting Multiepitope Peptide Nanoparticle Vaccine Platform to Improve the Efficacy and Immunogenicity of BCG

After more than a century since its initial development, Bacille Calmette-Guérin (BCG) remains the only licensed vaccine against tuberculosis (TB). Subunit boosters are considered a viable strategy to enhance BCG efficacy, which often wanes in adolescence. While many studies on booster subunit vaccines have concentrated on recombinant proteins, here we developed a novel modular peptide-based subunit vaccine platform that is flexible, cold-chain independent and customizable to diverse circumstances and populations. Each individual peptide building block consists of a linear arrangement comprising a 15-leucine self-assembly inducer moiety, a Mycobacterium tuberculosis (Mtb) target epitope and an human leukocyte antigen E (HLA-E) binding moiety, with each moiety separated by a triple lysine spacer. The building blocks, in any combination, are able to form a multiepitope nanoparticle. Six Mtb epitopes were selected to produce the self-assembling and self-adjuvating peptide-based TB nano-vaccine candidate PNx6. In vivo vaccination-challenge experiments demonstrated that subcutaneous boost of parenteral BCG immunization with PNx6 significantly enhanced its immunogenicity and improved its protective efficacy in a murine model of TB by more than 5-fold. This study presents evidence that purely amphiphilic peptides self-assemble into self-adjuvating nanoparticles with appropriate size and morphology for TB vaccination with great potential for a multitude of other diseases.

CD8 + T cells mediate vaccination-induced lymphatic containment of latent Mycobacterium tuberculosis infection following immunosuppression, while B cells are dispensable

It is estimated that two billion people are latently infected with Mycobacterium tuberculosis ( Mtb ), the causative agent of tuberculosis (TB). Latent Mtb infection (LTBI) can occur in multiple organs, including the lymphatics. The risk of LTBI reactivation increases in immunocompromised conditions, such as coinfection with human immunodeficiency virus (HIV), and during treatment of autoimmune diseases and organ transplantation. The immunological correlates of protection against TB, including against reactivation of LTBI, remain largely elusive. Here, we used a mouse model of latent lymphatic Mtb infection to dissect the immunological mechanisms underlying LTBI containment versus reactivation. We show that immunosuppression-mediated reactivation of lymphatic LTBI and the subsequent spread to non-lymphatic organs can be prevented by vaccination with multiple recombinant BCG (rBCG) strains despite the deficiency of CD4 + T cells. Using spatial transcriptomics, multi-parameter imaging, network analysis and bioinformatic integration of histopathological images, we reveal that immunosuppression is associated with a distinct repositioning of non-CD4 immune cells at the edge of TB lesions within the infection-draining cervical lymph nodes. While B cells increased in numbers, they are dispensable for the containment of LTBI. Lymphatic Mtb infection in different immune cell-deficient mouse strains, antibody-mediated cell depletion and adoptive transfer experiments into highly susceptible mice unequivocally show that vaccination-mediated prevention of LTBI reactivation is critically dependent on CD8 + T cells. These findings have profound implications for our understanding of immunity to TB and the management of LTBI.

Tuberculosis vaccines and therapeutic drug: challenges and future directions

Tuberculosis (TB) remains a prominent global health challenge, with the World Health Organization documenting over 1 million annual fatalities. Despite the deployment of the Bacille Calmette-Guérin (BCG) vaccine and available therapeutic agents, the escalation of drug-resistant Mycobacterium tuberculosis strains underscores the pressing need for more efficacious vaccines and treatments. This review meticulously maps out the contemporary landscape of TB vaccine development, with a focus on antigen identification, clinical trial progress, and the obstacles and future trajectories in vaccine research. We spotlight innovative approaches, such as multi-antigen vaccines and mRNA technology platforms. Furthermore, the review delves into current TB therapeutics, particularly for multidrug-resistant tuberculosis (MDR-TB), exploring promising agents like bedaquiline (BDQ) and delamanid (DLM), as well as the potential of host-directed therapies. The hurdles in TB vaccine and therapeutic development encompass overcoming antigen diversity, enhancing vaccine effectiveness across diverse populations, and advancing novel vaccine platforms. Future initiatives emphasize combinatorial strategies, the development of anti-TB compounds targeting novel pathways, and personalized medicine for TB treatment and prevention. Despite notable advances, persistent challenges such as diagnostic failures and protracted treatment regimens continue to impede progress. This work aims to steer future research endeavors toward groundbreaking TB vaccines and therapeutic agents, providing crucial insights for enhancing TB prevention and treatment strategies.

Mycobacterium bovis mutant in the virulence factors PhoP, ESAT-6 and CFP-10 persisted in mouse organs after a year post-vaccination

A vaccine for bovine tuberculosis is urgently needed. The BCG vaccine (the Bacille Calmette-Guérin), currently the only licensed vaccine for tuberculosis in humans, offers variable protection in cattle. However, BCG is a highly safe vaccine, and any alternative vaccine must not only offer greater protection than BCG but also match and improve its safety profile. Mice are the most widely used animal models in tuberculosis research, particularly for pre-clinical vaccine evaluation. In these animal models, the key indicator of infection or vaccine efficacy is the mycobacteria load in the lungs. In this study, we evaluated the long-term protection conferred by vaccinating BALB/c mice with a Mycobacterium bovis triple mutant lacking the virulence genes phoP, esxA, and esxB. Our findings showed that the triple mutant protected the lungs of mice against M. bovis challenge for up to one-year post-vaccination. However, the bacterial load in the spleens predominantly comprised the vaccine strain, and the lungs also contained some of these bacteria. These results suggest that the vaccine strain persisted in the mouse organs for at least one year, which raised concerns about its potential safety for animal vaccination.

A multistage Sendai virus vaccine incorporating latency-associated antigens induces protection against acute and latent tuberculosis

One-quarter of the world's population is infected with Mycobacterium tuberculosis (Mtb). After initial exposure, more immune-competent persons develop asymptomatic latent tuberculosis infection (LTBI) but not active diseases, creates an extensive reservoir at risk of developing active tuberculosis. Previously, we constructed a novel recombinant Sendai virus (SeV)-vectored vaccine encoding two dominant antigens of Mtb, which elicited immune protection against acute Mtb infection. In this study, nine Mtb latency-associated antigens were screened as potential supplementary vaccine candidate antigens, and three antigens (Rv2029c, Rv2028c, and Rv3126c) were selected based on their immune-therapeutic effect in mice, and their elevated immune responses in LTBI human populations. Then, a recombinant SeV-vectored vaccine, termed SeV986A, that expresses three latency-associated antigens and Ag85A was constructed. In murine models, the doses, titers, and inoculation sites of SeV986A were optimized, and its immunogenicity in BCG-primed and BCG-naive mice were determined. Enhanced immune protection against the Mtb challenge was shown in both acute-infection and latent-infection murine models. The expression levels of several T-cell exhaustion markers were significantly lower in the SeV986A-vaccinated group, suggesting that the expression of latency-associated antigens inhibited the T-cell exhaustion process in LTBI infection. Hence, the multistage quarter-antigenic SeV986A vaccine holds considerable promise as a novel post-exposure prophylaxis vaccine against tuberculosis.

Immune correlates of protection as a game changer in tuberculosis vaccine development

The absence of validated correlates of protection (CoPs) hampers the rational design and clinical development of new tuberculosis vaccines. In this review, we provide an overview of the potential CoPs in tuberculosis vaccine research. Major hindrances and potential opportunities are then discussed. Based on recent progress, it is reasonable to anticipate that success in the ongoing efforts to identify CoPs would be a game-changer in tuberculosis vaccine development.

Prevalence and epidemic pattern of ecdemic multidrug-resistant tuberculosis during 2012-2022 in Hangzhou, China: implication for public health strategies

BACKGROUND

To assess the prevalence and epidemic pattern of multidrug-resistant tuberculosis in Hangzhou City, Zhejiang Province, China during 2012-2022.

METHODS

All the tuberculosis cases undergoing drug susceptibility testing during 2012-2022 were included in this study. De-identified information was extracted from the electronic database Tuberculosis Information Management System for analysis of drug resistance prevalence in Hangzhou and ecdemic multidrug-resistant tuberculosis which originated from other regions. Chi-square tests were used to compare drug resistance rates between different groups, while Chi-square tests for trend were used to evaluate the change of drug resistance rates over the years of 2012-2022. The sources and destinations of ecdemic multidrug-resistant tuberculosis were illustrated using a Sankey diagram.

RESULTS

Of 21,127 cases included in this study, 1119 (5.3%) were multidrug-resistant tuberculosis. A significant decline in multidrug-resistant tuberculosis rates was observed during 2012-2022. There was a significant difference in multidrug-resistant tuberculosis rates among immigrant population and local residents in Hangzhou City. Of 1119 multidrug-resistant tuberculosis cases, 515(46%) were ecdemic multidrug-resistant tuberculosis cases, of which 277(53.8%) were from other parts of Zhejiang Province and 238(46.2%) were from other provinces in China. Anhui, Jiangxi and Sichuan were among top three provinces which were the source of ecdemic multidrug-resistant tuberculosis cases. Three districts including Xiaoshan, Shangcheng and Linping districts had the most cases in Hangzhou. The proportion of ecdemic multidrug-resistant tuberculosis cases in Binjiang, Xiaoshan, Qiantang and Linping districtalso exceeded 30% of total cases.

CONCLUSIONS

Multidrug-resistant tuberculosis prevalence has been declining in Hangzhou. Migrant population contributed to a significant potion of cases in Hangzhou. Interventions should be tailed to local and migrant residents.

Enhanced Glycosylation Caused by Overexpression of Rv1002c in a Recombinant BCG Promotes Immune Response and Protects against Mycobacterium tuberculosis Infection

Tuberculosis (TB) is a major global health threat despite its virtual elimination in developed countries. Issues such as drug accessibility, emergence of multidrug-resistant strains, and limitations of the current BCG vaccine highlight the urgent need for more effective TB control measures. This study constructed BCG strains overexpressing Rv1002c and found that the rBCG-Rv1002c strain secreted more glycosylated proteins, significantly enhancing macrophage activation and immune protection against Mycobacterium tuberculosis (M. tb). These results indicate that Rv1002c overexpression promotes elevated levels of O-glycosylation in BCG bacteriophages, enhancing their phagocytic and antigenic presentation functions. Moreover, rBCG-Rv1002c significantly upregulated immune regulatory molecules on the macrophage surface, activated the NF-κB pathway, and facilitated the release of large amounts of NO and H2O2, thereby enhancing bacterial control. In mice, rBCG-Rv1002c immunization induced greater innate and adaptive immune responses, including increased production of multifunctional and long-term memory T cells. Furthermore, rBCG-Rv1002c-immunized mice exhibited reduced lung bacterial load and histological damage upon M. tb infection. This result shows that it has the potential to be an excellent candidate for a preventive vaccine against TB.

Comparison of the transcriptome, lipidome, and c-di-GMP production between BCGΔBCG1419c and BCG, with Mincle- and Myd88-dependent induction of proinflammatory cytokines in murine macrophages

We have previously reported the transcriptomic and lipidomic profile of the first-generation, hygromycin-resistant (HygR) version of the BCGΔBCG1419c vaccine candidate, under biofilm conditions. We recently constructed and characterized the efficacy, safety, whole genome sequence, and proteomic profile of a second-generation version of BCGΔBCG1419c, a strain lacking the BCG1419c gene and devoid of antibiotic markers. Here, we compared the antibiotic-less BCGΔBCG1419c with BCG. We assessed their colonial and ultrastructural morphology, biofilm, c-di-GMP production in vitro, as well as their transcriptomic and lipidomic profiles, including their capacity to activate macrophages via Mincle and Myd88. Our results show that BCGΔBCG1419c colonial and ultrastructural morphology, c-di-GMP, and biofilm production differed from parental BCG, whereas we found no significant changes in its lipidomic profile either in biofilm or planktonic growth conditions. Transcriptomic profiling suggests changes in BCGΔBCG1419c cell wall and showed reduced transcription of some members of the DosR, MtrA, and ArgR regulons. Finally, induction of TNF-α, IL-6 or G-CSF by bone-marrow derived macrophages infected with either BCGΔBCG1419c or BCG required Mincle and Myd88. Our results confirm that some differences already found to occur in HygR BCGΔBCG1419c compared with BCG are maintained in the antibiotic-less version of this vaccine candidate except changes in production of PDIM. Comparison with previous characterizations conducted by OMICs show that some differences observed in BCGΔBCG1419c compared with BCG are maintained whereas others are dependent on the growth condition employed to culture them.

The Immunogenicity and Safety of Mycobacterium tuberculosis-mosR-Based Double Deletion Strain in Mice

Mycobacterium tuberculosis (M. tuberculosis) remains a significant global health threat, accounting for ~1.7 million deaths annually. The efficacy of the current vaccine, M. bovis BCG, ranges from 0 to 80% in children and does not prevent adulthood tuberculosis. We explored the immune profile and safety of a live-attenuated M. tuberculosis construct with double deletions of the mosR and echA7 genes, where previously, single mutations were protective against an M. tuberculosis aerosol challenge. Over 32 weeks post-vaccination (WPV), immunized mice with M. tuberculosisΔmosRΔechA7 (double mutant) were sacrificed to evaluate the vaccine persistence, histopathology, and immune responses. Interestingly, despite similar tissue colonization between the vaccine double mutant and wild-type M. tuberculosis, the vaccine construct showed a greater reaction to the ESAT-6, TB.10, and Ag85B antigens with peptide stimulation. Additionally, there was a greater number of antigen-specific CD4 T cells in the vaccine group, accompanied by significant polyfunctional T-cell responses not observed in the other groups. Histologically, mild but widely distributed inflammatory responses were recorded in the livers and lungs of the immunized animals at early timepoints, which turned into organized inflammatory foci via 32WPV, a pathology not observed in BCG-immunized mice. A lower double-mutant dose resulted in significantly less tissue colonization and less tissue inflammation. Overall, the double-mutant vaccine elicited robust immune responses dominated by antigen-specific CD4 T cells, but also triggered tissue damage and vaccine persistence. The findings highlight key features associated with the immunogenicity and safety of the examined vaccine construct that can benefit the future evaluation of other live vaccines.

Vaccines against Tuberculosis: Where Are We Now?

Tuberculosis (TB) is among the top 10 leading causes of death in low-income countries. Statistically, TB kills more than 30,000 people each week and leads to more deaths than any other infectious disease, such as acquired immunodeficiency syndrome (AIDS) and malaria. TB treatment is largely dependent on BCG vaccination and impacted by the inefficacy of drugs, absence of advanced vaccines, misdiagnosis improper treatment, and social stigma. The BCG vaccine provides partial effectiveness in demographically distinct populations and the prevalence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB incidences demands the design of novel TB vaccines. Various strategies have been employed to design vaccines against TB, such as: (a) The protein subunit vaccine; (b) The viral vector vaccine; (c) The inactivation of whole-cell vaccine, using related mycobacteria, (d) Recombinant BCG (rBCG) expressing Mycobacterium tuberculosis (M.tb) protein or some non-essential gene deleted BCG. There are, approximately, 19 vaccine candidates in different phases of clinical trials. In this article, we review the development of TB vaccines, their status and potential in the treatment of TB. Heterologous immune responses generated by advanced vaccines will contribute to long-lasting immunity and might protect us from both drug-sensitive and drug-resistant TB. Therefore, advanced vaccine candidates need to be identified and developed to boost the human immune system against TB.

Machine Learning Prediction of Mycobacterial Cell Wall Permeability of Drugs and Drug-like Compounds

The cell wall of Mycobacterium tuberculosis and related organisms has a very complex and unusual organization that makes it much less permeable to nutrients and antibiotics, leading to the low activity of many potential antimycobacterial drugs against whole-cell mycobacteria compared to their isolated molecular biotargets. The ability to predict and optimize the cell wall permeability could greatly enhance the development of novel antitubercular agents. Using an extensive structure-permeability dataset for organic compounds derived from published experimental big data (5371 compounds including 2671 penetrating and 2700 non-penetrating compounds), we have created a predictive classification model based on fragmental descriptors and an artificial neural network of a novel architecture that provides better accuracy (cross-validated balanced accuracy 0.768, sensitivity 0.768, specificity 0.769, area under ROC curve 0.911) and applicability domain compared with the previously published results.

Palmitic acid-modified GnRH-Th epitope peptide immunocastration vaccine (W/O/W adjuvant) can effectively ensure the castration and reduce the smelly smell in boars

Introduction

Recent studies have demonstrated the effectiveness of Gonadotropin-releasing hormone (GnRH) in inhibiting testicular growth and development in male animals to achieve castration while improving the meat quality of various livestock species, including cattle, sheep, goats, and pigs.

Methods

In this research, a GnRH-Th vaccine was synthesized using the Fmoc solid-phase synthesis technique, and the T helper (Th) antigen was modified with palmitic acid to improve its efficacy. The vaccine was then coated with a water-in-oil-in-water adjuvant to improve stability and safety. After passing safety and stability tests, the vaccine was administered to 13-week-old boars.

Results

The results showed that it was stable, safe, and effective for up to 15 months. Moreover, the vaccine did not negatively affect the growth rate and body weight of the pigs. The palmitic acid-modified "GnRH-Th epitope peptide immunocastration vaccine (Water-in-Oil-in-Water (W/O/W)) effectively reduced the testosterone concentration and achieved castration. The concentration of androstenone and skatole hormones significantly decreased, leading to improved meat quality in the boars. The boars were then slaughtered at 33 weeks of age, and the results showed that the meat quality of the vaccinated boars was superior to that of the non-vaccinated control group (p < 0.05).

Discussion

This study demonstrated that GnRH can safely and effectively achieve immune castration in boars after coupling T cell epitopes, palmitic acid modification and W-O-W coating. Provide a better method for the further development of GnRH and the realization of animal welfare.

Evaluation of Mycobacterium avium subsp. paratuberculosis isocitrate lyase (IcL) and ABC transporter (BacA) knockout mutants as vaccine candidates

There has been little success in controlling Johne's disease, caused by Mycobacterium avium subsp. paratuberculosis, due to suboptimal diagnostics and the ineffectiveness of available vaccines. By knocking out BacA and IcL, genes required for MAP survival in dairy calves, two live-attenuated vaccine candidates were created. This study evaluated the host-specific attenuation of MAP IcL and BacA mutants in mouse and calf models, as well as the elicited immune responses. Deletion mutants were generated in MAP strain A1-157 through specialized transduction and found viable in vitro. First, the mutants' attenuation and elicited cytokine secretion were assessed in a mouse model, 3 weeks after intraperitoneal inoculation with MAP strains. Later, vaccine strains were assessed in a natural host infection model where calves received 10⁹CFU oral dose of MAP wild-type or mutant strains at 2 weeks old. Transcription levels of cytokines in PBMCs were evaluated at 12-, 14-, and 16-weeks post-inoculation (WPI) and MAP colonization in tissue was assessed at 4.5 months after inoculation. Whereas both vaccine candidates colonized mouse tissues similarly to wild-type strain, both failed to persist in calf tissues. In either mouse or calf models, gene deletion did not reduce immunogenicity. Instead, inoculation with ΔBacA induced a greater upregulation of proinflammatory cytokines than ΔIcL and wild-type in both models and a greater expansion of cytotoxic and memory T-cells than uninfected control in calves. ΔBacA and wild-type strains significantly increased secretion of IP-10, MIG, TNFα, and RANTES in mice serum compared to uninfected control. This agreed with upregulation of IL-12, IL-17, and TNFα in calves inoculated with ΔBacA at all time points. The ΔBacA also gave rise to greater populations of CD4+CD45RO+, and CD8+ cells than uninfected control calves at 16 WPI. Low survival rate of MAP in macrophages co-incubated with PBMCs isolated from the ΔBacA group indicated that these cell populations are capable of killing MAP. Overall, the immune response elicited by ΔBacA is stronger compared to ΔIcL and it is maintained over two different models and over time in calves. Further investigation is warranted to evaluate the BacA mutant's protection against MAP infection as a live attenuated vaccine candidate.