Maintenance and recall of memory T cell populations against tuberculosis: Implications for vaccine design

Advancement in diagnostic approaches for latent tuberculosis: distinguishing recent from remote infections

Tuberculosis (TB) remains as a significant global health threat to date, with latent TB infection (LTBI) serving as a major reservoir for future active disease cases. A practical approach to an effective control and eradication of TB hence, requires an explicit identification of infected patient whom are at high risk of progressing from latent to active TB, particularly in those recently infected individuals. Current diagnostic tools however, including Tuberculin Skin Test and Interferon-Gamma Release Assays, are still lacking for their ability to critically distinguish between recent and remote infections, leading to insufficiency in optimizing targeted preventive treatment strategies. This review examines the limitations of current diagnostic tools and explores novel biomarkers to enhance distinction within the infection timeline in LTBI diagnostics. Advancement in immune profiling, dormancy antigen, along with molecular and transcriptomic approaches holds great promise to develop a diagnostic tools with better accuracy to differentiate recent from remote infections, thereby optimizing targeted interventions to improve TB control strategies. These underscores the need for further research into these emerging diagnostic tools to facilitate an effective public health strategies and contribute to the united efforts in End TB Strategy.

Memory Cells in Infection and Autoimmunity: Mechanisms, Functions, and Therapeutic Implications

Memory cells are central to the adaptive immune system's ability to remember and respond effectively to previously encountered pathogens. While memory cells provide robust protection against infections, they can also contribute to autoimmunity when regulation fails. Here, we review the roles of memory T and B cells in infection and autoimmunity, focusing on their differentiation, activation, effector functions, and underlying regulatory mechanisms. We elaborate on the precise mechanisms by which memory cells contribute to autoimmune diseases, highlighting insights from current research on how pathogenic memory responses are formed and sustained in autoimmunity. Finally, we explore potential therapeutic strategies aimed at modulating memory cells to prevent or treat autoimmune disorders, including B cell-depleting therapies (e.g., Rituximab), T cell-targeting agents (e.g., Abatacept), and cytokine inhibitors (e.g., IL-17 or IL-23 blockers) that are currently used in diseases such as rheumatoid arthritis, multiple sclerosis, and psoriasis.

One Health Approach to the Computational Design of a Lipoprotein-Based Multi-Epitope Vaccine Against Human and Livestock Tuberculosis

Tuberculosis (TB) remains a major cause of ill health and one of the leading causes of death worldwide, with about 1.25 million deaths estimated in 2023. Control measures have focused principally on early diagnosis, the treatment of active TB, and vaccination. However, the widespread emergence of anti-tuberculosis drug resistance remains the major public health threat to progress made in global TB care and control. Moreover, the Bacillus Calmette-Guérin (BCG) vaccine, the only licensed vaccine against TB in children, has been in use for over a century, and there have been considerable debates concerning its effectiveness in TB control. A multi-epitope vaccine against TB would be an invaluable tool to attain the Global Plan to End TB 2023-2030 target. A rational approach that combines several B-cell and T-cell epitopes from key lipoproteins was adopted to design a novel multi-epitope vaccine candidate. In addition, interactions with TLR4 were implemented to assess its ability to elicit an innate immune response. The conservation of the selected proteins suggests the possibility of cross-protection in line with the One Health approach to disease control. The vaccine candidate was predicted to be both antigenic and immunogenic, and immune simulation analyses demonstrated its ability to elicit both humoral and cellular immune responses. Protein-protein docking and normal-mode analyses of the vaccine candidate with TLR4 predicted efficient binding and stable interaction. This study provides a promising One Health approach for the design of multi-epitope vaccines against human and livestock tuberculosis. Overall, the designed vaccine candidate demonstrated immunogenicity and safety features that warrant further experimental validation in vitro and in vivo.

The Plasma Membrane P-Type ATPase CtpA Is Required for Mycobacterium tuberculosis Virulence in Copper-Activated Macrophages in a Mouse Model of Progressive Tuberculosis

Background/Objective: Finding new targets to attenuate Mycobacterium tuberculosis (Mtb) is key in the development of new TB vaccines. In this context, plasma membrane P-type ATPases are relevant for mycobacterial homeostasis and virulence. In this work, we investigate the role of the copper-transporting P-type ATPase CtpA in Mtb virulence. Methods: The impact of CtpA deletion on Mtb's capacity to overcome redox stress and proliferate in mouse alveolar macrophages (MH-S) was evaluated, as well as its effect on Mtb immunogenicity. Moreover, the influence of CtpA on the pathogenicity of Mtb in a mouse (BALB/c) model of progressive TB was examined. Results: We found that MH-S cells infected with wild-type (MtbH37Rv) or the mutant strain (MtbH37RvΔctpA) showed no difference in Mtb bacterial load. However, the same macrophages under copper activation (50 µM CuSO4) showed impaired replication of the mutant strain. Furthermore, the mutant MtbΔctpA strain showed an inability to control reactive oxygen species (ROS) induced by PMA addition during MH-S infection. These results, together with the high expression of the Nox2 mRNA observed in MH-S cells infected with the Mtb∆ctpA strain at 3 and 6 days post-infection, suggest a potential role for CtpA in overcoming redox stress under infection conditions. In addition, MtbΔctpA-infected BALB/c mice survived longer with significantly lower lung bacterial loads and tissue damage in their lungs than MtbH37Rv-infected mice. Conclusions: This suggests that CtpA is involved in Mtb virulence and that it may be a target for attenuation.

BAFF and APRIL immunotherapy following Bacille Calmette-Guérin vaccination enhances protection against pulmonary tuberculosis in mice

Introduction

Bacille Calmette-Guérin (BCG), the only tuberculosis vaccine currently in clinical use, provides inadequate long-term protection. Administered at birth, BCG induces broad immune responses against a large number of antigens shared with Mycobacterium tuberculosis (Mtb), but protection wanes over time. We have previously shown that unconventional B cell subsets play a role in tuberculosis control.

Methods

High-dimensional flow cytometry and multiplex cytokine analysis were employed to investigate the effects of immunotherapy on BCG-vaccinated mice in an Mtb challenge model.

Results

In this study, we investigate the potential of recombinant cytokines targeting B cells - B-cell activating factor (BAFF) and A proliferation-inducing ligand (APRIL) - to modulate BCG immunity and improve protection in mice. Both cytokines play overlapping roles in B cell development and peripheral survival. Following subcutaneous BCG vaccination, immunotherapy with BAFF or APRIL resulted in an increased frequency of unconventional B cells potentially transitioning into antibody-producing plasma cells. Concurrently, we observed an increased frequency of central memory T cells, a subset critical for protective immunity. Changes in cellular immune responses were accompanied by reduced pro-inflammatory cytokine profiles and a contraction of the leukocyte population in lungs. Importantly, mice receiving BCG vaccination followed by BAFF or APRIL immunotherapy exhibited superior long-term protection against pulmonary tuberculosis relative to controls that received only BCG.

Conclusion

In summary, our findings demonstrate that combining BCG vaccination with B cell targeted immunomodulatory therapies can improve long-term protection against pulmonary tuberculosis, highlighting the continued relevance and underutilized potential of BCG as a vaccine platform.

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

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

Alterations in purine and pyrimidine metabolism associated with latent tuberculosis infection: insights from gut microbiome and metabolomics analyses

Individuals with latent tuberculosis infection (LTBI) account for almost 30% of the population worldwide and have the potential to develop active tuberculosis (ATB). Despite this, the current understanding of the pathogenesis of LTBI is limited. The gut microbiome can be altered in tuberculosis patients, and an understanding of the changes associated with the progression from good health to LTBI to ATB can provide novel perspectives for understanding the pathogenesis of LTBI by identifying microbial and molecular biomarkers associated therewith. In this study, fecal samples from healthy controls (HC), individuals with LTBI and ATB patients were collected for gut microbiome and metabolomics analyses. Compared to HC and LTBI subjects, participants with ATB showed a significant decrease in gut bacterial α-diversity. Additionally, there were significant differences in gut microbial communities and metabolism among the HC, LTBI, and ATB groups. PICRUSt2 analysis revealed that microbiota metabolic pathways involving the degradation of purine and pyrimidine metabolites were upregulated in LTBI and ATB individuals relative to HCs. Metabolomic profiling similarly revealed that purine and pyrimidine metabolite levels were decreased in LTBI and ATB samples relative to those from HCs. Further correlation analyses revealed that the levels of purine and pyrimidine metabolites were negatively correlated with those of gut microbial genera represented by Ruminococcus_gnavus_group (R. gnavus), and the levels of R. gnavus were also positively correlated with adenosine nucleotide degradation II, which is a purine degradation pathway. Moreover, a combined signature including hypoxanthine and xanthine was found to effectively distinguish between LTBI and HC samples (area under the curve [AUC] of training set = 0.796; AUC of testing set = 0.924). Therefore, through gut microbiome and metabolomic analyses, these findings provide valuable clues regarding how alterations in gut purine and pyrimidine metabolism are linked to the pathogenesis of LTBI.IMPORTANCEThis study provides valuable insight into alterations in the gut microbiome and metabolomic profiles in a cohort of adults with LTBI and ATB. Perturbed gut purine and pyrimidine metabolism in LTBI was associated with the compositional alterations of gut microbiota, which may be an impetus for developing novel diagnostic strategies and interventions targeting LTBI.

Impaired Mycobacterium tuberculosis-specific T-cell memory phenotypes and functional profiles among adults with type 2 diabetes mellitus in Uganda

Background

Efforts to eradicate tuberculosis (TB) are threatened by diabetes mellitus (DM), which confers a 3-fold increase in the risk of TB disease. The changes in the memory phenotypes and functional profiles of Mycobacterium tuberculosis (Mtb)-specific T cells in latent TB infection (LTBI)-DM participants remain poorly characterised. We, therefore, assessed the effect of DM on T-cell phenotype and function in LTBI and DM clinical groups.

Methods

We compared the memory phenotypes and function profiles of Mtb-specific CD4+ and CD8+ T cells among participants with LTBI-DM (n=21), LTBI-only (n=17) and DM-only (n=16). Peripheral blood mononuclear cells (PBMCs) were stimulated with early secretory antigenic 6 kDa (ESAT-6) and culture filtrate protein 10 (CFP-10) peptide pools or phytohemagglutinin (PHA). The memory phenotypes (CCR7/CD45RA), and functional profiles (HLA-DR, PD-1, CD107a, IFN-γ, IL-2, TNF, IL-13, IL-17A) of Mtb-specific CD4+ and CD8+ T cells were characterised by flow cytometry.

Results

Naïve CD4+ T cells were significantly decreased in the LTBI-DM compared to the LTBI-only participants [0.47 (0.34-0.69) vs 0.91 (0.59-1.05); (p<0.001)]. Similarly, CD8+ HLA-DR expression was significantly decreased in LTBI-DM compared to LTBI-only participants [0.26 (0.19-0.33) vs 0.52 (0.40-0.64); (p<0.0001)], whereas CD4+ and CD8+ PD-1 expression was significantly upregulated in the LTBI-DM compared to the LTBI-only participants [0.61 (0.53-0.77) vs 0.19 (0.10-0.28); (p<0.0001) and 0.41 (0.37-0.56) vs 0.29 (0.17-0.42); (p=0.007)] respectively. CD4+ and CD8+ IFN-γ production was significantly decreased in the LTBI-DM compared to the LTBI-only participants [0.28 (0.19-0.38) vs 0.39 (0.25-0.53); (p=0.030) and 0.36 (0.27-0.49) vs 0.55 (0.41-0.88); (p=0.016)] respectively. CD4+ TNF and CD8+ IL-17A production were significantly decreased in participants with LTBI-DM compared to those with LTBI-only [0.38 (0.33-0.50) vs 0.62 (0.46-0.87); (p=0.004) and 0.29 (0.16-0.42) vs 0.47 (0.29-0.52); (0.017)] respectively. LTBI-DM participants had significantly lower dual-functional (IFN-γ+IL-2+ and IL-2+TNF+) and mono-functional (IFN-γ+ and TNF+) CD4+ responses than LTBI-only participants. LTBI-DM participants had significantly decreased dual-functional (IFN-γ+IL-2+, IFN-γ+ TNF+ and IL-2+TNF+) and mono-functional (IFN-γ+, IL-2+ and TNF+) central and effector memory CD4+ responses compared to LTBI-only participants.

Conclusion

Type 2 DM impairs the memory phenotypes and functional profiles of Mtb-specific CD4+ and CD8+ T cells, potentially indicating underlying immunopathology towards increased active TB disease risk.

The significance of stem cell-like memory T cells in viral and bacterial vaccines: A mini review

Vaccination has become a widely used method to induce immune protection against microbial pathogens, including viral and bacterial microorganisms. Both humoral and cellular immunity serve a critical role in neutralizing and eliminating these pathogens. An effective vaccine should be able to induce a long-lasting immune memory response. Recent investigations on different subsets of T cells have identified a new subset of T cells using multi-parameter flow cytometry, which possess stem cell-like properties and the ability to mount a rapid immune response upon re-exposure to antigens known as stem cell-like memory T cells (TSCM). One of the major challenges with current vaccines is their limited ability to maintain long-term memory in the adaptive immune system. Recent evidence suggests that a specific subgroup of memory T cells has the unique ability to retain their longevity for up to 25 years, as observed in the case of the yellow fever vaccine. Therefore, in this study, we tried to explore and discuss the potential role of this new T cell memory subset in the development of viral and bacterial vaccines.

Immunological characteristics of a recombinant alphaherpesvirus with an envelope-embedded Cap protein of circovirus

Introduction

Variant pseudorabies virus (PRV) is a newly emerged zoonotic pathogen that can cause human blindness. PRV can take advantage of its large genome and multiple non-essential genes to construct recombinant attenuated vaccines carrying foreign genes. However, a major problem is that the foreign genes in recombinant PRV are only integrated into the genome for independent expression, rather than assembled on the surface of virion.

Methods

We reported a recombinant PRV with deleted gE/TK genes and an inserted porcine circovirus virus 2 (PCV2) Cap gene into the extracellular domain of the PRV gE gene using the Cre-loxP recombinant system combined with the CRISPR-Cas9 gene editing system. This recombinant PRV (PRV-Cap), with the envelope-embedded Cap protein, exhibits a similar replication ability to its parental virus.

Results

An immunogenicity assay revealed that PRV-Cap immunized mice have 100% resistance to lethal PRV and PCV2 attacks. Neutralization antibody and ELISPOT detections indicated that PRV-Cap can enhance neutralizing antibodies to PRV and produce IFN-γ secreting T cells specific for both PRV and PCV2. Immunological mechanistic investigation revealed that initial immunization with PRV-Cap stimulates significantly early activation and expansion of CD69+ T cells, promoting the activation of CD4 Tfh cell dependent germinal B cells and producing effectively specific effector memory T and B cells. Booster immunization with PRV-Cap recalled the activation of PRV-specific IFN-γ+IL-2+CD4+ T cells and IFN-γ+TNF-α+CD8+ T cells, as well as PCV2-specific IFN-γ+TNF-α+CD8+ T cells.

Conclusion

Collectively, our data suggested an immunological mechanism in that the recombinant PRV with envelope-assembled PCV2 Cap protein can serve as an excellent vaccine candidate for combined immunity against PRV and PCV2, and provided a cost-effective method for the production of PRV- PCV2 vaccine.

Tuberculosis Vaccines and T Cell Immune Memory

Tuberculosis (TB) remains a major infectious disease partly due to the lack of an effective vaccine. Therefore, developing new and more effective TB vaccines is crucial for controlling TB. Mycobacterium tuberculosis (M. tuberculosis) usually parasitizes in macrophages; therefore, cell-mediated immunity plays an important role. The maintenance of memory T cells following M. tuberculosis infection or vaccination is a hallmark of immune protection. This review analyzes the development of memory T cells during M. tuberculosis infection and vaccine immunization, especially on immune memory induced by BCG and subunit vaccines. Furthermore, the factors affecting the development of memory T cells are discussed in detail. The understanding of the development of memory T cells should contribute to designing more effective TB vaccines and optimizing vaccination strategies.

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.

Immunogenicity and protective efficacy of RipA, a peptidoglycan hydrolase, against Mycobacterium tuberculosis Beijing outbreak strains

Given that individuals with latent tuberculosis (TB) infection represent the major reservoir of TB infection, latency-associated antigens may be promising options for development of improved multi-antigenic TB subunit vaccine. Thus, we selected RipA, a peptidoglycan hydrolase required for efficient cell division of Mycobacterium tuberculosis (Mtb), as vaccine candidate. We found that RipA elicited activation of dendritic cells (DCs) by induction of phenotypic maturation, increased production of inflammatory cytokines, and prompt stimulation of MAPK and NF-κB signaling pathways. In addition, RipA-treated DCs promoted Th1-polarzied immune responses of naïve CD4+ T cells with increased proliferation and activated T cells from Mtb-infected mice, which conferred enhanced control of mycobacterial growth inside macrophages. Moreover, mice immunized with RipA formulated in GLA-SE adjuvant displayed remarkable generation of Ag-specific polyfunctional CD4+ T cells in both lung and spleen. Following an either conventional or ultra-low dose aerosol challenges with 2 Mtb Beijing clinical strains, RipA/GLA-SE-immunization was not inferior to BCG by mediating protection as single Ag. Collectively, our findings highlighted that RipA could be a novel candidate as a component of multi-antigenic TB subunit vaccines.