Bacillus Calmette-Guérin (BCG) Revaccination of Adults with Latent Mycobacterium tuberculosis Infection Induces Long-Lived BCG-Reactive NK Cell Responses

Loss of circulating CD8α+ NK cells during human Mycobacterium tuberculosis infection

Natural Killer (NK) cells can recognize and kill Mtb-infected cells in vitro, however their role after natural human exposure has not been well-studied. To identify Mtb-responsive NK cell populations, we analyzed the peripheral blood of healthy household contacts of active Tuberculosis (TB) cases and source community donors in an endemic region of Port-au-Prince, Haiti by flow cytometry. We observed higher CD8α expression on NK cells in putative resistors (IGRA- contacts) with a progressive loss of these circulating cells during household-associated latent infection and disease. In vitro assays and CITE-seq analysis of CD8α+ NK cells demonstrated enhanced maturity, cytotoxic gene expression, and response to cytokine stimulation relative to CD8α- NK cells. CD8α+ NK cells also displayed dynamic surface expression dependent on MHC I in contrast to conventional CD8+ T cells. Together, these results support a specialized role for CD8α+ NK cell populations during Mtb infection correlating with disease resistance.

BCG activation of trained immunity is associated with induction of cross reactive COVID-19 antibodies in a BCG vaccinated population

BACKGROUND

Pakistan is endemic to a diverse set of parasitic, mycobacterial and viral diseases. The recognition of BCG Trained Immunity (TI) led us to postulate that the continued presence of BCG-TI may play a protective role, previously reported for both infectious and noninfectious conditions. Most of the previous studies have addressed the issue of BCG-TI in the paediatric populations. This study addressed the key issue of maintenance of BCG-TI in a wider age range (adolescent and adults) to identify the strength and quality of the immune responses.

OBJECTIVE

To assess the BCG-induced recall responses in healthy individuals by cytokines secreted from the TI network and its potential role in providing cross-protection against COVID-19 and other viral infections.

STUDY DESIGN

In this cross-sectional study, healthy young adults and adolescents (n = 20) were recruited from 16-40 years of age, with no prior history of TB treatment, autoimmune, or chronic inflammatory condition.

METHODS

BCG-induced cytokine responses were assessed using prototypic markers for cells of the TI network [macrophages [M1 (TNFα, IFNγ), M2 (IL10)], NK (IL2), Gamma delta (γδ) T (IL17, IL4)] and SARS CoV2 IgG antibodies against RBD using short-term (12 hrs.) cultures assay.

RESULTS

Significant differences were observed in the magnitude of recall responses to BCG with macrophage cytokines showing the highest mean levels of TNFα (9148 pg/ml) followed by IL10 (488 pg/ml) and IFNγ (355 pg/ml). The ratio of unstimulated vs.BCG-stimulated cytokines was 132 fold higher for TNFα, 40 fold fo r IL10, and 27 fold for IFNγ. Furthermore, SARS-CoV-2 antibodies were also detected in unstimulated plasma which showed cross reactivity with BCG.

CONCLUSION

The presence of cross reactive antibodies to SARS-CoV-2 and the relative ratio of pro- and anti-inflammatory cytokines secreted by activated TI cellular network may play a pivotal role in protection in the early stages of infection as observed during the COVID-19 pandemic in the younger age groups resulting in lower morbidity and mortality.

Expansion of memory Vδ2 T cells following SARS-CoV-2 vaccination revealed by temporal single-cell transcriptomics

γδ T cells provide rapid cellular immunity against pathogens. Here, we conducted matched single-cell RNA-sequencing and γδ-TCR-sequencing to delineate the molecular changes in γδ T cells during a longitudinal study following mRNA SARS-CoV-2 vaccination. While the first dose of vaccine primes Vδ2 T cells, it is the second administration that significantly boosts their immune response. Specifically, the second vaccination uncovers memory features of Vδ2 T cells, shaped by the induction of AP-1 family transcription factors and characterized by a convergent central memory signature, clonal expansion, and an enhanced effector potential. This temporally distinct effector response of Vδ2 T cells was also confirmed in vitro upon stimulation with SARS-CoV-2 spike-peptides. Indeed, the second challenge triggers a significantly higher production of IFNγ by Vδ2 T cells. Collectively, our findings suggest that mRNA SARS-CoV-2 vaccination might benefit from the establishment of long-lasting central memory Vδ2 T cells to confer protection against SARS-CoV-2 infection.

BCG vaccination induces innate immune memory in γδ T cells in humans

Bacillus Calmette-Guérin vaccine is well known for inducing trained immunity in myeloid and natural killer cells, which can explain its cross-protective effect against heterologous infections. Although displaying functional characteristics of both adaptive and innate immunity, γδ T-cell memory has been only addressed in a pathogen-specific context. In this study, we aimed to determine whether human γδ T cells can mount trained immunity and therefore contribute to the cross-protective effect of the Bacillus Calmette-Guérin vaccine. We investigated in vivo induction of innate memory in γδ T cells by Bacillus Calmette-Guérin vaccination in healthy human volunteers by combining single-cell RNA sequencing technology with immune functional assays. The total number of γδ T cells and membrane markers of activation was not influenced by Bacillus Calmette-Guérin vaccination. In contrast, Bacillus Calmette-Guérin changed γδ T cells' transcriptional programs and increased their responsiveness to heterologous bacterial and fungal stimuli, including lipopolysaccharide and Candida albicans, as simultaneously characterized by higher tumor necrosis factor and interferon γ production, weeks after vaccination. Human γδ T cells in adults display the potential to develop a trained immunity phenotype after Bacillus Calmette-Guérin vaccination.

Antigen-specific memory NK cell responses against HIV and influenza use the NKG2/HLA-E axis

Multiple studies have broadened the roles of natural killer (NK) cells functioning as purely innate lymphocytes by demonstrating that they are capable of putative antigen-specific immunological memory against multiple infectious agents including HIV-1 and influenza. However, the mechanisms underlying antigen specificity remain unknown. Here, we demonstrate that antigen-specific human NK cell memory develops upon exposure to both HIV and influenza, unified by a conserved and epitope-specific targetable mechanism largely dependent on the activating CD94/NKG2C receptor and its ligand HLA-E. We validated the permanent acquisition of antigen specificity by individual memory NK cells by single-cell cloning. We identified elevated expression of KLRG1, α4β7, and NKG2C as biomarkers of antigen-specific NK cell memory through complex immunophenotyping. Last, we uncovered individual HLA-E-restricted peptides that may constitute the dominant NK cell response in HIV-1- and influenza-infected persons in vivo. Our findings clarify the mechanisms contributing to antigen-specific memory NK cell responses and suggest that they could be potentially targeted therapeutically for vaccines or other therapeutic interventions.

Natural killer cell responses during SARS-CoV-2 infection and vaccination in people living with HIV-1

Natural killer (NK) cell subsets with adaptive properties are emerging as regulators of vaccine-induced T and B cell responses and are specialized towards antibody-dependent functions contributing to SARS-CoV-2 control. Although HIV-1 infection is known to affect the NK cell pool, the additional impact of SARS-CoV-2 infection and/or vaccination on NK cell responses in people living with HIV (PLWH) has remained unexplored. Our data show that SARS-CoV-2 infection skews NK cells towards a more differentiated/adaptive CD57+FcεRIγ- phenotype in PLWH. A similar subset was induced following vaccination in SARS-CoV-2 naïve PLWH in addition to a CD56bright population with cytotoxic potential. Antibody-dependent NK cell function showed robust and durable responses to Spike up to 148 days post-infection, with responses enriched in adaptive NK cells. NK cell responses were further boosted by the first vaccine dose in SARS-CoV-2 exposed individuals and peaked after the second dose in SARS-CoV-2 naïve PLWH. The presence of adaptive NK cells associated with the magnitude of cellular and humoral responses. These data suggest that features of adaptive NK cells can be effectively engaged to complement and boost vaccine-induced adaptive immunity in potentially more vulnerable groups such as PLWH.

Early innate cell interactions with Mycobacterium tuberculosis in protection and pathology of tuberculosis

Tuberculosis (TB) remains a significant global health challenge, claiming the lives of up to 1.5 million individuals annually. TB is caused by the human pathogen Mycobacterium tuberculosis (Mtb), which primarily infects innate immune cells in the lungs. These immune cells play a critical role in the host defense against Mtb infection, influencing the inflammatory environment in the lungs, and facilitating the development of adaptive immunity. However, Mtb exploits and manipulates innate immune cells, using them as favorable niche for replication. Unfortunately, our understanding of the early interactions between Mtb and innate effector cells remains limited. This review underscores the interactions between Mtb and various innate immune cells, such as macrophages, dendritic cells, granulocytes, NK cells, innate lymphocytes-iNKT and ILCs. In addition, the contribution of alveolar epithelial cell and endothelial cells that constitutes the mucosal barrier in TB immunity will be discussed. Gaining insights into the early cellular basis of immune reactions to Mtb infection is crucial for our understanding of Mtb resistance and disease tolerance mechanisms. We argue that a better understanding of the early host-pathogen interactions could inform on future vaccination approaches and devise intervention strategies.

BCG revaccination in adults enhances pro-inflammatory markers of trained immunity along with anti-inflammatory pathways

This study characterized mechanisms of Bacille Calmette-Guérin (BCG) revaccination-induced trained immunity (TI) in India. Adults, BCG vaccinated at birth, were sampled longitudinally before and after a second BCG dose. BCG revaccination significantly elevated tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, and IL-6 in HLA-DR+CD16-CD14hi monocytes, demonstrating induction of TI. Mycobacteria-specific CD4+ T cell interferon (IFN) γ, IL-2, and TNF-α were significantly higher in re-vaccinees and correlated positively with HLA-DR+CD16-CD14hi TI responses. This, however, did not translate into increased mycobacterial growth control, measured by mycobacterial growth inhibition assay (MGIA). Post revaccination, elevated secreted TNF-α, IL-1β, and IL-6 to "heterologous" fungal, bacterial, and enhanced CXCL-10 and IFNα to viral stimuli were also observed concomitant with increased anti-inflammatory cytokine, IL-1RA. RNA sequencing after revaccination highlighted a BCG and LPS induced signature which included upregulated IL17 and TNF pathway genes and downregulated key inflammatory genes: CXCL11, CCL24, HLADRA, CTSS, CTSC. Our data highlight a balanced immune response comprising pro- and anti-inflammatory mediators to be a feature of BCG revaccination-induced immunity.

Intravenous administration of BCG in mice promotes natural killer and T cell-mediated antitumor immunity in the lung

Intravesical administration of Bacillus Calmette-Guérin (BCG) was one of the first FDA-approved immunotherapies and remains a standard treatment for bladder cancer. Previous studies have demonstrated that intravenous (IV) administration of BCG is well-tolerated and effective in preventing tuberculosis infection in animals. Here, we examine IV BCG in several preclinical lung tumor models. Our findings demonstrate that BCG inoculation reduced tumor growth and prolonged mouse survival in models of lung melanoma metastasis and orthotopic lung adenocarcinoma. Moreover, IV BCG treatment was well-tolerated with no apparent signs of acute toxicity. Mechanistically, IV BCG induced tumor-specific CD8+ T cell responses, which were dependent on type 1 conventional dendritic cells, as well as NK cell-mediated immunity. Lastly, we also show that IV BCG has an additive effect on anti-PD-L1 checkpoint inhibitor treatment in mouse lung tumors that are otherwise resistant to anti-PD-L1 as monotherapy. Overall, our study demonstrates the potential of systemic IV BCG administration in the treatment of lung tumors, highlighting its ability to enhance immune responses and augment immune checkpoint blockade efficacy.

Innate (learned) memory

With the growing body of evidence, it is now clear that not only adaptive immune cells but also innate immune cells can mount a more rapid and potent nonspecific immune response to subsequent exposures. This process is known as trained immunity or innate (learned) immune memory. This review discusses the different immune and nonimmune cell types of the central and peripheral immune systems that can develop trained immunity. This review highlights the intracellular signaling and metabolic and epigenetic mechanisms underlying the formation of innate immune memory. Finally, this review explores the health implications together with the potential therapeutic interventions harnessing trained immunity.

Comparative immune responses to Mycobacterium tuberculosis in people with latent infection or sterilizing protection

There is great need for vaccines against tuberculosis (TB) more efficacious than the licensed BCG. Our goal was to identify new vaccine benchmarks by identifying immune responses that distinguish individuals able to eradicate the infection (TB-resisters) from individuals with latent infection (LTBI-participants). TB-resisters had higher frequencies of circulating CD8+ glucose monomycolate (GMM)+ Granzyme-B+ T cells than LTBI-participants and higher proportions of polyfunctional conventional and nonconventional T cells expressing Granzyme-B and/or PD-1 after ex vivo M. tuberculosis stimulation of blood mononuclear cells. LTBI-participants had higher expression of activation markers and cytokines, including IL10, and IFNγ. An exploratory analysis of BCG-recipients with minimal exposure to TB showed absence of CD8+GMM+Granzyme-B+ T cells, lower or equal proportions of Granzyme-B+PD-1+ polyfunctional T cells than TB-resisters and higher or equal than LTBI-participants. In conclusion, high Granzyme-B+PD-1+ T cell responses to M. tuberculosis and, possibly, of CD8+GMM+Granzyme-B+ T cells may be desirable for new TB vaccines.

Blood transcriptional correlates of BCG-induced protection against tuberculosis in rhesus macaques

Blood-based correlates of vaccine-induced protection against tuberculosis (TB) are urgently needed. Here, we analyze the blood transcriptome of rhesus macaques immunized with varying doses of intravenous (i.v.) BCG followed by Mycobacterium tuberculosis (Mtb) challenge. We use high-dose i.v. BCG recipients for "discovery" and validate our findings in low-dose recipients and in an independent cohort of macaques receiving BCG via different routes. We identify seven vaccine-induced gene modules, including an innate module (module 1) enriched for type 1 interferon and RIG-I-like receptor signaling pathways. Module 1 on day 2 post-vaccination highly correlates with lung antigen-responsive CD4 T cells at week 8 and with Mtb and granuloma burden following challenge. Parsimonious signatures within module 1 at day 2 post-vaccination predict protection following challenge with area under the receiver operating characteristic curve (AUROC) ≥0.91. Together, these results indicate that the early innate transcriptional response to i.v. BCG in peripheral blood may provide a robust correlate of protection against TB.

Airway T cells are a correlate of i.v. Bacille Calmette-Guerin-mediated protection against tuberculosis in rhesus macaques

Bacille Calmette-Guerin (BCG), the only approved Mycobacterium tuberculosis (Mtb) vaccine, provides limited durable protection when administered intradermally. However, recent work revealed that intravenous (i.v.) BCG administration yielded greater protection in macaques. Here, we perform a dose-ranging study of i.v. BCG vaccination in macaques to generate a range of immune responses and define correlates of protection. Seventeen of 34 macaques had no detectable infection after Mtb challenge. Multivariate analysis incorporating longitudinal cellular and humoral immune parameters uncovered an extensive and highly coordinated immune response from the bronchoalveolar lavage (BAL). A minimal signature predicting protection contained four BAL immune features, of which three remained significant after dose correction: frequency of CD4 T cells producing TNF with interferon γ (IFNγ), frequency of those producing TNF with IL-17, and the number of NK cells. Blood immune features were less predictive of protection. We conclude that CD4 T cell immunity and NK cells in the airway correlate with protection following i.v. BCG.

Newborn bacille Calmette-Guérin vaccination induces robust infant interferon-γ-expressing natural killer cell responses to mycobacteria

OBJECTIVES

The bacille Calmette-Guérin (BCG) vaccine is usually administered at birth to protect against severe forms of tuberculosis in children. BCG also confers some protection against other infections, possibly mediated by innate immune training. We investigated whether newborn BCG vaccination modulates myeloid and natural killer (NK) cell responses to mycobacteria.

METHODS

BCG vaccination was either administered at birth or delayed to 6 or 10 weeks of age in 130 South African infants. Whole blood was stimulated with BCG and clusters of differentiation (CD)4⁺ T, myeloid, and NK cell responses were measured by flow cytometry; the levels of secreted cytokines were measured by a multiplex bead array.

RESULTS

Newborn BCG vaccination was associated with significantly higher frequencies of BCG-reactive, cytokine-expressing CD4⁺ T cells, and interferon (IFN)-γ-expressing NK cells than in unvaccinated infants but no differences in cytokine-expressing CD33⁺ myeloid cells were observed. The induction of BCG-reactive IFN-γ-expressing NK cells was not associated with the markers of NK cell maturation, differentiation, or cytokine receptor expression. BCG-reactive NK cell responses correlated directly with the levels of secreted interleukin (IL)-2 and IFN-γ and the innate pro-inflammatory cytokines IL-6, IL-1β, and tumor necrosis factor (TNF) in BCG-vaccinated infants only.

CONCLUSION

We showed that BCG-reactive IFN-γ-expressing NK cells are strongly induced by BCG vaccination in infants and are likely amplified through bystander cytokines.

Research progress on specific and non-specific immune effects of BCG and the possibility of BCG protection against COVID-19

Bacille Calmette-Guérin (BCG) is the only approved vaccine for tuberculosis (TB) prevention worldwide. BCG has an excellent protective effect on miliary tuberculosis and tuberculous meningitis in children or infants. Interestingly, a growing number of studies have shown that BCG vaccination can induce nonspecific and specific immunity to fight against other respiratory disease pathogens, including SARS-CoV-2. The continuous emergence of variants of SARS-CoV-2 makes the protective efficiency of COVID-19-specific vaccines an unprecedented challenge. Therefore, it has been hypothesized that BCG-induced trained immunity might protect against COVID-19 infection. This study comprehensively described BCG-induced nonspecific and specific immunity and the mechanism of trained immunity. In addition, this study also reviewed the research on BCG revaccination to prevent TB, the impact of BCG on other non-tuberculous diseases, and the clinical trials of BCG to prevent COVID-19 infection. These data will provide new evidence to confirm the hypotheses mentioned above.

Bacillus Calmette-Guérin-induced interleukin-10 inhibits S100A8/A9 production and hinders development of T helper type 1 memory in mice

Tuberculosis caused by Mycobacterium tuberculosis (M.tb) is one of the main causes of human death in the world. Bacillus Calmette-Guérin (BCG) provides limited protection in adolescents and adults. To explore the factors reducing efficacy of BCG vaccine, we assess the impacts of interleukin (IL)-10 and alarmins S100A8/A9 on T-cell memory. We found that BCG-induced IL-10 inhibited production of S100A8/A9 in human peripheral blood mononuclear cells (PBMCs) and murine splenocytes. S100A9 deficiency inhibited IFN-γ production by CD4⁺ T cells in the early phase of BCG immunization and hindered the development of effector memory T helper type 1 (Th1) cells, while IL-10 deficiency promoted Th1 memory and blocking IL-10 signaling enhanced Th1 protective recall response against M.tb. IL-10 inhibited the binding of transcription factor CCAAT enhancer binding protein beta to S100a8/a9 promoter leading to S100A8/A9 reduction. S100A8/A9 heterodimer enhanced the IFN-γ production via receptor for advanced glycation end products signaling in CD4⁺ T cells. Our results demonstrate a hurdle to development of Th1 memory after BCG immunization and clarify the mechanism of the regulation of Th1 memory by IL-10 and S100A8/A9.

The impact of BCG dose and revaccination on trained immunity

The innate immune system can display heterologous memory-like responses termed trained immunity after stimulation by certain vaccinations or infections. In this randomized, placebo-controlled trial, we investigated the modulation of Bacille Calmette-Guérin (BCG)-induced trained immunity by BCG revaccination or high-dose BCG administration, in comparison to a standard dose. We show that monocytes from all groups of BCG-vaccinated individuals exerted increased TNFα production after ex-vivo stimulation with various unrelated pathogens. Similarly, we observed increased amounts of T-cell-derived IFNγ after M. tuberculosis exposure, regardless of the BCG intervention. NK cell cytokine production, especially after heterologous stimulation with the fungal pathogen Candida albicans, was predominantly boosted after high dose BCG administration. Cytokine production capacity before vaccination was inversely correlated with trained immunity. While the induction of a trained immunity profile is largely dose- or frequency independent, baseline cytokine production capacity is associated with the magnitude of the innate immune memory response after BCG vaccination.

BCG-activation of leukocytes is sufficient for the generation of donor-independent innate anti-tumor NK and γδ T-cells that can be further expanded in vitro

Bacillus Calmette-Guérin (BCG), the nonpathogenic Mycobacterium bovis strain used as tuberculosis vaccine, has been successfully used as treatment for non-muscle invasive bladder cancer for decades, and suggested to potentiate cellular and humoral immune responses. However, the exact mechanism of action is not fully understood. We previously described that BCG mainly activated anti-tumor cytotoxic NK cells with upregulation of CD56 and a CD16⁺ phenotype. Now, we show that stimulation of human peripheral blood mononuclear cells with iBCG, a preparation based on BCG-Moreau, expands oligoclonal γδ T-cells, with a cytotoxic phenotype, together with anti-tumor CD56^high CD16⁺ NK cells. We have used scRNA-seq, flow cytometry, and functional assays to characterize these BCG-activated γδ T-cells in detail. They had a high IFNγ secretion signature with expression of CD27⁺ and formed conjugates with bladder cancer cells. BCG-activated γδ T-cells proliferated strongly in response to minimal doses of cytokines and had anti-tumor functions, although not fully based on degranulation. BCG was sufficient to stimulate proliferation of γδ T-cells when cultured with other PBMC; however, BCG alone did not stimulate expansion of purified γδ T-cells. The characterization of these non-donor restricted lymphocyte populations, which can be expanded in vitro, could provide a new approach to prepare cell-based immunotherapy tools.

Immunologic Role of Innate Lymphoid Cells against Mycobacterial tuberculosis Infection

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. tb), is one of the leading causes of mortality due to respiratory tract infections worldwide. Infection by M. tb involves activation of a type I immune response characteristic of T helper type 1 (Th1) lymphocytes, natural killer (NK) cells, Interleukin-12 (IL-12), and interferon (IFN)-γ, all of which stimulate the activation of macrophages and robust phagocytosis in order to prevent further infectious manifestations and systemic dissemination. Recent discoveries about innate lymphoid cells (ILCs) have provided further insight about how these cells participate within the protective immune response against M. tb infection and help boost the type I immune response. In order to clearly understand the mechanisms of M. tb infection and advance the efficacy of future treatment and prevention, we must first look at the individual functions each type of immune cell plays within this process, specifically ILCs. By review of the recent literature and current evidence, our group aims to summarize the characterization of the three major groups of ILCs, including NK cells, and analyze the role that each group of ILCs play in the infectious process against M. tb in order to provide a more comprehensive understanding of the host immune response. Equally, previous studies have also highlighted the effects of how administration of the Bacille Calmette–Guérin (BCG) vaccine influences the cells and cytokines of the immune response against M. tb. Our group also aims to highlight the effects that BCG vaccine has on ILCs and how these effects provide added protection against M. tb.

Characterization of Mycobacterium tuberculosis-Specific Th22 Cells and the Effect of Tuberculosis Disease and HIV Coinfection

The development of a highly effective tuberculosis (TB) vaccine is likely dependent on our understanding of what constitutes a protective immune response to TB. Accumulating evidence suggests that CD4+ T cells producing IL-22, a distinct subset termed "Th22" cells, may contribute to protective immunity to TB. Thus, we characterized Mycobacterium tuberculosis-specific Th22 (and Th1 and Th17) cells in 72 people with latent TB infection or TB disease, with and without HIV-1 infection. We investigated the functional properties (IFN-γ, IL-22, and IL-17 production), memory differentiation (CD45RA, CD27, and CCR7), and activation profile (HLA-DR) of M. tuberculosis-specific CD4+ T cells. In HIV-uninfected individuals with latent TB infection, we detected abundant circulating IFN-γ-producing CD4+ T cells (median, 0.93%) and IL-22-producing CD4+ T cells (median, 0.46%) in response to M. tuberculosis The frequency of IL-17-producing CD4+ T cells was much lower, at a median of 0.06%. Consistent with previous studies, IL-22 was produced by a distinct subset of CD4+ T cells and not coexpressed with IL-17. M. tuberculosis-specific IL-22 responses were markedly reduced (median, 0.08%) in individuals with TB disease and HIV coinfection compared with IFN-γ responses. M. tuberculosis-specific Th22 cells exhibited a distinct memory and activation phenotype compared with Th1 and Th17 cells. Furthermore, M. tuberculosis-specific IL-22 was produced by conventional CD4+ T cells that required TCR engagement. In conclusion, we confirm that Th22 cells are a component of the human immune response to TB. Depletion of M. tuberculosis-specific Th22 cells during HIV coinfection may contribute to increased risk of TB disease.

Therapeutic Vaccines for Tuberculosis: An Overview

Tuberculosis (TB), caused by Mycobacterium tuberculosis is the world’s deadliest bacterial infection, resulting in more than 1.4 million deaths annually. The emergence of drug-resistance to first-line antibiotic therapy poses a threat to successful treatment, and novel therapeutic options are required, particularly for drug-resistant tuberculosis. One modality emerging for TB treatment is therapeutic vaccination. As opposed to preventative vaccination – the aim of which is to prevent getting infected by M. tuberculosis or developing active tuberculosis, the purpose of therapeutic vaccination is as adjunctive treatment of TB or to prevent relapse following cure. Several candidate therapeutic vaccines, using killed whole-cell or live attenuated mycobacteria, mycobacterial fragments and viral vectored vaccines are in current clinical trials. Other modes of passive immunization, including monoclonal antibodies directed against M. tuberculosis antigens are in various pre-clinical stages of development. Here, we will discuss these various therapeutics and their proposed mechanisms of action. Although the full clinical utility of therapeutic vaccination for the treatment of tuberculosis is yet to be established, they hold potential as useful adjunct therapies.

Durable Expansion of TCR-δ Meta-Clonotypes After BCG Revaccination in Humans

Mycobacterium bovis bacille Calmette-Guérin (BCG) has been used for 100 years and prevents disseminated tuberculosis and death in young children. However, it shows only partial efficacy against pulmonary tuberculosis (TB) in adults, so new vaccines are urgently needed. The protective efficacy of BCG depends on T cells, which are typically activated by pathogen-derived protein antigens that bind to highly polymorphic major histocompatibility complex (MHC) molecules. Some T cells recognize non-protein antigens via antigen presenting systems that are independent of genetic background, leading to their designation as donor-unrestricted T (DURT) cells. Whether live whole cell vaccines, like BCG, can induce durable expansions of DURT cells in humans is not known. We used combinatorial tetramer staining, multi-parameter flow cytometry, and immunosequencing to comprehensively characterize the effect of BCG on activation and expansion of DURT cell subsets. We examined peripheral blood mononuclear cells (PBMC) derived from a Phase I study of South African adults in which samples were archived at baseline, 3 weeks, and 52 weeks post-BCG revaccination. We did not observe a change in the frequency of total mucosal-associated invariant T (MAIT) cells, invariant natural killer T (iNKT) cells, germline encoded mycolyl-reactive (GEM) T cells, or γδ T cells at 52 weeks post-BCG. However, immunosequencing revealed a set of TCR-δ clonotypes that were expanded at 52 weeks post-BCG revaccination. These expanded clones expressed the Vδ2 gene segment and could be further defined on the basis of biochemical similarity into several 'meta-clonotypes' that likely recognize similar epitopes. Our data reveal that BCG vaccination leads to durable expansion of DURT cell clonotypes despite a limited effect on total circulating frequencies in the blood and have implications for defining the immunogenicity of candidate whole cell TB vaccines.

It Takes a Village: The Multifaceted Immune Response to Mycobacterium tuberculosis Infection and Vaccine-Induced Immunity

Despite co-evolving with humans for centuries and being intensely studied for decades, the immune correlates of protection against Mycobacterium tuberculosis (Mtb) have yet to be fully defined. This lapse in understanding is a major lag in the pipeline for evaluating and advancing efficacious vaccine candidates. While CD4+ T helper 1 (TH1) pro-inflammatory responses have a significant role in controlling Mtb infection, the historically narrow focus on this cell population may have eclipsed the characterization of other requisite arms of the immune system. Over the last decade, the tuberculosis (TB) research community has intentionally and intensely increased the breadth of investigation of other immune players. Here, we review mechanistic preclinical studies as well as clinical anecdotes that suggest the degree to which different cell types, such as NK cells, CD8+ T cells, γ δ T cells, and B cells, influence infection or disease prevention. Additionally, we categorically outline the observed role each major cell type plays in vaccine-induced immunity, including Mycobacterium bovis bacillus Calmette-Guérin (BCG). Novel vaccine candidates advancing through either the preclinical or clinical pipeline leverage different platforms (e.g., protein + adjuvant, vector-based, nucleic acid-based) to purposefully elicit complex immune responses, and we review those design rationales and results to date. The better we as a community understand the essential composition, magnitude, timing, and trafficking of immune responses against Mtb, the closer we are to reducing the severe disease burden and toll on human health inflicted by TB globally.

Single-cell RNA sequencing reveals induction of distinct trained immunity programs in human monocytes

Trained immunity refers to the long-lasting memory traits of innate immunity. Recent studies have shown that trained immunity is orchestrated by sustained changes in epigenetic marks and metabolic pathways, leading to an altered transcriptional response towards a second challenge. However, the potential heterogeneity of trained immunity induction in innate immune cells has not been explored. In this study, we demonstrate cellular transcriptional programs to four different inducers of trained immunity in monocyte populations at single-cell resolution. Specifically, we identified three monocyte subpopulations upon the induction of trained immunity, and replicated these findings in an in vivo study. In addition, we found gene signatures consistent with these functional programs in ulcerative colitis, sepsis and COVID-19 patients, suggesting the impact of trained immunity programs in immune-mediated diseases.

Effects of BCG vaccination on donor unrestricted T cells in two prospective cohort studies

BACKGROUND

Non-protein antigen classes can be presented to T cells by near-monomorphic antigen-presenting molecules such as CD1, MR1, and butyrophilin 3A1. Such T cells, referred to as donor unrestricted T (DURT) cells, typically express stereotypic T cell receptors. The near-unrestricted nature of DURT cell antigen recognition is of particular interest for vaccine development, and we sought to define the roles of DURT cells, including MR1-restricted MAIT cells, CD1b-restricted glucose monomycolate (GMM)-specific T cells, CD1d-restricted NKT cells, and γδ T cells, in vaccination against Mycobacterium tuberculosis.

METHODS

We compared and characterized DURT cells following primary bacille Calmette-Guerin (BCG) vaccination in a cohort of vaccinated and unvaccinated infants, as well as before and after BCG-revaccination in adults.

FINDINGS

BCG (re)vaccination did not modulate peripheral blood frequencies, T cell activation or memory profiles of MAIT cells, CD1b-restricted GMM-specific and germline-encoded mycolyl-reactive (GEM) cells or CD1d-restricted NKT cells. By contrast, primary BCG vaccination was associated with increased frequencies of γδ T cells as well as a novel subset of CD26⁺CD161⁺TRAV1-2^- IFN-γ-expressing CD4⁺ T cells in infants.

INTERPRETATION

Our findings, that most DURT cell populations were not modulated by BCG, do not preclude a role of BCG in modulating other qualitative aspects of DURT cells. More studies are required to understand the full potential of DURT cells in new TB vaccine strategies.

FUNDING

Aeras, the National Institutes of Health, and the Bill and Melinda Gates Foundation.

Harnessing Mycobacterium bovis BCG Trained Immunity to Control Human and Bovine Babesiosis

Babesiosis is a disease caused by tickborne hemoprotozoan apicomplexan parasites of the genus Babesia that negatively impacts public health and food security worldwide. Development of effective and sustainable vaccines against babesiosis is currently hindered in part by the absence of definitive host correlates of protection. Despite that, studies in Babesia microti and Babesia bovis, major causative agents of human and bovine babesiosis, respectively, suggest that early activation of innate immune responses is crucial for vertebrates to survive acute infection. Trained immunity (TI) is defined as the development of memory in vertebrate innate immune cells, allowing more efficient responses to subsequent specific and non-specific challenges. Considering that Mycobacterium bovis bacillus Calmette-Guerin (BCG), a widely used anti-tuberculosis attenuated vaccine, induces strong TI pro-inflammatory responses, we hypothesize that BCG TI may protect vertebrates against acute babesiosis. This premise is supported by early investigations demonstrating that BCG inoculation protects mice against experimental B. microti infection and recent observations that BCG vaccination decreases the severity of malaria in children infected with Plasmodium falciparum, a Babesia-related parasite. We also discuss the potential use of TI in conjunction with recombinant BCG vaccines expressing Babesia immunogens. In conclusion, by concentrating on human and bovine babesiosis, herein we intend to raise awareness of BCG TI as a strategy to efficiently control Babesia infection.

BCG vaccination strategies against tuberculosis: updates and perspectives

Bacillus Calmette-Guérin (BCG) is the only licensed vaccine against tuberculosis (TB). However, BCG has variable efficacy and cannot completely prevent TB infection and transmission. Therefore, the worldwide prevalence of TB calls for urgent development of a more effective TB vaccine. In the absence of other approved vaccines, it is also necessary to improve the efficacy of BCG itself. Intravenous (IV) BCG administration and BCG revaccination strategies have recently shown promising results for clinical usage. Therefore, it is necessary for us to revisit the BCG vaccination strategies and summarize the current research updates related to BCG vaccination. This literature review provides an updated overview and perspectives of the immunization strategies against TB using BCG, which may inspire the following research on TB vaccine development.

BCG re-vaccination in Malawi: 30-year follow-up of a large, randomised, double-blind, placebo-controlled trial

BACKGROUND

A large, double-blind, randomised, placebo-controlled trial of repeat BCG found 49% efficacy against leprosy but no protection against tuberculosis after 6-9 years' follow-up in 1995. We report here additional follow-up, which resulted in greatly increased tuberculosis case numbers, and allowed subgroup analysis.

METHODS

Nearly 47 000 individuals of all ages living in northern Malawi with a BCG vaccine scar were randomly assigned (1:1) between 1986 and 1989 to receive a second BCG or placebo. The investigators and project staff remained masked to all interventions. Enhanced passive surveillance ensured ascertainment of tuberculosis and leprosy to the end of 2018. Tuberculosis case definitions included rigorous microbiological or histological confirmation. Prespecified subgroup analyses were by tuberculosis type, age at vaccination, time since vaccination, previous tuberculin reactivity, HIV status and Mycobacterium tuberculosis lineage. The original trial is registered with ISRCTN registry, ISRCTN11311670.

FINDINGS

In follow-up until Dec 31, 2018, 824 participants had developed tuberculosis, including 786 with pulmonary disease, of whom 383 (63%) of 607 with known HIV status were HIV positive. There was no effect of a second BCG overall (odds ratio [OR] 0·92; 95% CI 0·80-1·05), or for pulmonary (0·93; 0·81-1·07), or lymph node tuberculosis (0·60; 0·31-1·17). The OR was lower for those with known HIV-negative tuberculosis (0·77; 0·59-1·00), for those vaccinated as children (aged <5 years, 0·74; 0·41-1·35; aged 5-14 years, 0·77; 0·60-0·99), and for cases arising at least 20 years after vaccination (0·79; 0·63-1·01). There were no differences by tuberculin status at vaccination, or lineage. There was no evidence of protection against leprosy beyond 10 years after vaccination (although there have been only nine diagnostically certain cases since 1995).

INTERPRETATION

There was no evidence that repeat BCG vaccination provides appreciable protection against overall tuberculosis in this rural African population with a high prevalence of HIV. Subgroup effects should not be overinterpreted given the multiple analyses done. However, the evidence for modest protection against HIV-negative tuberculosis, and for a delayed benefit in those vaccinated as children, is consistent with other observations in the literature.

FUNDING

LEPRA, Wellcome Trust, Bill & Melinda Gates Foundation.

Mycobacterium tuberculosis-Specific T Cell Functional, Memory, and Activation Profiles in QuantiFERON-Reverters Are Consistent With Controlled Infection

Reversion of immune sensitization tests for Mycobacterium tuberculosis (M.tb) infection, such as interferon-gamma release assays or tuberculin skin test, has been reported in multiple studies. We hypothesized that QuantiFERON-TB Gold (QFT) reversion is associated with a decline of M.tb-specific functional T cell responses, and a distinct pattern of T cell and innate responses compared to persistent QFT+ and QFT- individuals. We compared groups of healthy adolescents (n=~30 each), defined by four, 6-monthly QFT tests: reverters (QFT+/+/-/-), non-converters (QFT-/-/-/-) and persistent positives (QFT+/+/+/+). We stimulated peripheral blood mononuclear cells with M.tb antigens (M.tb lysate; CFP-10/ESAT-6 and EspC/EspF/Rv2348 peptide pools) and measured M.tb-specific adaptive T cell memory, activation, and functional profiles; as well as functional innate (monocytes, natural killer cells), donor-unrestricted T cells (DURT: γδ T cells, mucosal-associated invariant T and natural killer T-like cells) and B cells by flow cytometry. Projection to latent space discriminant analysis was applied to determine features that best distinguished between QFT reverters, non-converters and persistent positives. No longitudinal changes in immune responses to M.tb were observed upon QFT reversion. M.tb-specific Th1 responses detected in reverters were of intermediate magnitude, higher than responses in QFT non-converters and lower than responses in persistent positives. About one third of reverters had a robust response to CFP-10/ESAT-6. Among those with measurable responses, lower proportions of T_SCM (CD45RA+CCR7+CD27+) and early differentiated (CD45RA-) IFN-γ-TNF+IL-2- M.tb lysate-specific CD4+ cells were observed in reverters compared with non-converters. Conversely, higher proportions of early differentiated and lower proportions of effector (CD45RA-CCR7-) CFP10/ESAT6-specific Th1 cells were observed in reverters compared to persistent-positives. No differences in M.tb-specific innate, DURT or B cell functional responses were observed between the groups. Statistical modelling misclassified the majority of reverters as non-converters more frequently than they were correctly classified as reverters or misclassified as persistent positives. These findings suggest that QFT reversion occurs in a heterogeneous group of individuals with low M.tb-specific T cell responses. In some individuals QFT reversion may result from assay variability, while in others the magnitude and differentiation status of M.tb-specific Th1 cells are consistent with well-controlled M.tb infection.

Bacillus Calmette-Guerin (BCG) vaccination to treat endometriosis

Bacille Calmette-Guérin (BCG), a vaccine intended to protect against tuberculosis disease, can elicit protection against heterologous infections, and even specific types of cancer. In this mini-review, we will address the possible use of BCG as a therapeutic for endometriosis, a syndrome of chronic pelvic pain due to ectopic growth of endometrial-type tissue outside of the uterine lining. These implanted tissues cycle synchronously with menses in pre-menopausal women, generating cellular debris inciting chronic inflammation and tissue scarring leading to pelvic pain and infertility. Further, these lesions may evolve into ovarian clear cell carcinoma. We hypothesize that implantation, survival and transformation of these implants is enabled by a form of immune suppression within the peritoneum, which may be overcome by BCG vaccination.

High Prevalence of Active Tuberculosis in Adults and Children with Idiopathic Inflammatory Myositis as Compared with Systemic Lupus Erythematosus in a Tuberculosis Endemic Country: Retrospective Data Review from a Tertiary Care Centre in India

AIM

Infections are the leading cause of morbidity and mortality in idiopathic inflammatory myositis (IIM) with India being endemic for Tuberculosis (TB). We compared and contrasted the prevalence, clinical profile and outcomes of active TB in IIM with systemic lupus erythematosus (SLE).

METHODS

Medical records were reviewed for adults and children with IIM (Bohan and Peter criteria) and SLE (ACR criteria) at a tertiary care hospital in India from January 2015 to October 2017. Follow-up was recorded until February 2020 for all those who had developed active TB.

RESULTS

Of 167 (132 adults and 35 juvenile) IIM and 280 (131 adults and 149 juvenile) SLE, active TB occurred in 24 (14.4%) IIM (22 (16.7% of 132) adults; 2 (5.71% of 35) juvenile) and 18 (6.4%) SLE [(8 (6.1% of 131) adults; 10 (6.7% of 149) juvenile, p-value < 0.01]. Patients with IIM had higher odds of developing TB as compared with SLE [OR 2.24 (CI 1.5-5.5), p=0.007]. The risk of developing active TB was 68-fold and 30.4-fold higher in patients with IIM and SLE, respectively, as compared with the general population. Extrapulmonary forms were more common (14/24). Nearly half developed TB during active IIM, at a glucocorticoid dose of 0.25 (0-1.5) mg/kg/day. Over a follow-up duration of 27 months (8-184), all were cured of TB, though prolonged course of anti-tuberculous treatment was required in 25%, and five IIM relapsed during treatment.

CONCLUSION

Patients with IIM have increased risk of active TB, with common extrapulmonary forms, slow response, and relapses during treatment.

Phenotypic and Functional Characteristics of a Novel Influenza Virus Hemagglutinin-Specific Memory NK Cell

Immune memory represents the most efficient defense against invasion and transmission of infectious pathogens. In contrast to memory T and B cells, the roles of innate immunity in recall responses remain inconclusive. In this study, we identified a novel mouse spleen NK cell subset expressing NKp46 and NKG2A induced by intranasal influenza virus infection. These memory NK cells specifically recognize N-linked glycosylation sites on influenza hemagglutinin (HA) protein. Different from memory-like NK cells reported previously, these NKp46⁺ NKG2A⁺ memory NK cells exhibited HA-specific silence of cytotoxicity but increase of gamma interferon (IFN-γ) response against influenza virus-infected cells, which could be reversed by pifithrin-μ, a p53-heat shock protein 70 (HSP70) signaling inhibitor. During recall responses, splenic NKp46⁺ NKG2A⁺ NK cells were recruited to infected lung and modulated viral clearance of virus and CD8⁺ T cell distribution, resulting in improved clinical outcomes. This long-lived NK memory bridges innate and adaptive immune memory response and promotes the homeostasis of local environment during recall response.IMPORTANCE In this study, we demonstrate a novel hemagglutinin (HA)-specific NKp46⁺ NKG2A⁺ NK cell subset induced by influenza A virus infection. These memory NK cells show virus-specific decreased cytotoxicity and increased gamma interferon (IFN-γ) on reencountering the same influenza virus antigen. In addition, they modulate host recall responses and CD8 T cell distribution, thus bridging the innate immune and adaptive immune responses during influenza virus infection.

A century of BCG: Impact on tuberculosis control and beyond

BCG turns 100 this year and while it might not be the perfect vaccine, it has certainly contributed significantly towards eradication and prevention of spread of tuberculosis (TB). The search for newer and better vaccines for TB is an ongoing endeavor and latest results from trials of candidate TB vaccines such as M72AS01 look promising. However, recent encouraging data from BCG revaccination trials in adults combined with studies on mucosal and intravenous routes of BCG vaccination in non-human primate models have renewed interest in BCG for TB prevention. In addition, several well-demonstrated non-specific effects of BCG, for example, prevention of viral and respiratory infections, give BCG an added advantage. Also, BCG vaccination is currently being widely tested in human clinical trials to determine whether it protects against SARS-CoV-2 infection and/or death with detailed analyses and outcomes from several ongoing trials across the world awaited. Through this review, we attempt to bring together information on various aspects of the BCG-induced immune response, its efficacy in TB control, comparison with other candidate TB vaccines and strategies to improve its efficiency including revaccination and alternate routes of administration. Finally, we discuss the future relevance of BCG use especially in light of its several heterologous benefits.

HLA-DR-Positive NK Cells Expand in Response to Mycobacterium Tuberculosis Antigens and Mediate Mycobacteria-Induced T Cell Activation

NK cells play an important role in the control of tuberculosis infection: they are not only able to kill the infected cells, but also control the activity of macrophages and development of the adaptive immune response. Still, there is little information on the role of specific NK cell subsets in this network. In this study, we focused on the mycobacteria-driven responses of the NK cells expressing HLA-DR – a type of MHC class II. We have revealed that this subset is increased in the peripheral blood of patients with primary diagnosed tuberculosis, and expands in response to in vitro stimulation with ultrasonically destroyed Mycobacterium tuberculosis cells (sonicate). The expanded HLA-DR⁺ NK cells had less differentiated phenotype, higher proliferative activity and increased expression of NKp30 and NKp46 receptors. HLA-DR⁺CD56^dim NK cells showed higher IFNγ production and degranulation level than the respective HLA-DR⁻ NK cells in response to both 24 h and 7 day stimulation with sonicate, while HLA-DR⁺CD56^bright NK cells mostly demonstarted similar high responsiveness to the same stimulating conditions as their HLA-DR⁻CD56^bright counterparts. After preliminary incubation with destroyed mycobacteria, cytokine-activated HLA-DR-expressing NK cells were able to mediate mycobacteria-induced and HLA-DR-dependent cytokine production in autologous CD4⁺ T cells. Thus, functionally active HLA-DR⁺ cells seem to be one of the NK cell subsets providing an important link to the adaptive immunity.

Natural Killer Cells: From Innate to Adaptive Features

Natural killer (NK) cells are innate lymphocytes that provide critical host defense against pathogens and cancer. Originally heralded for their early and rapid effector activity, NK cells have been recognized over the last decade for their ability to undergo adaptive immune processes, including antigen-driven clonal expansion and generation of long-lived memory. This review presents an overview of how NK cells lithely partake in both innate and adaptive responses and how this versatility is manifest in human NK cell-mediated immunity.

The immune landscape in tuberculosis reveals populations linked to disease and latency

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) latently infects approximately one-fourth of the world's population. The immune mechanisms that govern progression from latent (LTBI) to active pulmonary TB (PTB) remain poorly defined. Experimentally Mtb-infected non-human primates (NHP) mirror the disease observed in humans and recapitulate both PTB and LTBI. We characterized the lung immune landscape in NHPs with LTBI and PTB using high-throughput technologies. Three defining features of PTB in macaque lungs include the influx of plasmacytoid dendritic cells (pDCs), an Interferon (IFN)-responsive macrophage population, and activated T cell responses. In contrast, a CD27+ Natural killer (NK) cell subset accumulated in the lungs of LTBI macaques. This NK cell population was also detected in the circulation of LTBI individuals. This comprehensive analysis of the lung immune landscape will improve the understanding of TB immunopathogenesis, providing potential targets for therapies and vaccines for TB control.

The role of donor-unrestricted T-cells, innate lymphoid cells, and NK cells in anti-mycobacterial immunity

Vaccination strategies against mycobacteria, focusing mostly on classical T‐ and B‐cells, have shown limited success, encouraging the addition of alternative targets. Classically restricted T‐cells recognize antigens presented via highly polymorphic HLA class Ia and class II molecules, while donor‐unrestricted T‐cells (DURTs), with few exceptions, recognize ligands via genetically conserved antigen presentation molecules. Consequently, DURTs can respond to the same ligands across diverse human populations. DURTs can be activated either through cognate TCR ligation or via bystander cytokine signaling. TCR‐driven antigen‐specific activation of DURTs occurs upon antigen presentation via non‐polymorphic molecules such as HLA‐E, CD1, MR1, and butyrophilin, leading to the activation of HLA‐E–restricted T‐cells, CD1‐restricted T‐cells, mucosal‐associated invariant T‐cells (MAITs), and TCRγδ T‐cells, respectively. NK cells and innate lymphoid cells (ILCs), which lack rearranged TCRs, are activated through other receptor‐triggering pathways, or can be engaged through bystander cytokines, produced, for example, by activated antigen‐specific T‐cells or phagocytes. NK cells can also develop trained immune memory and thus could represent cells of interest to mobilize by novel vaccines. In this review, we summarize the latest findings regarding the contributions of DURTs, NK cells, and ILCs in anti–M tuberculosis, M leprae, and non‐tuberculous mycobacterial immunity and explore possible ways in which they could be harnessed through vaccines and immunotherapies to improve protection against Mtb.

Ebola virus glycoprotein stimulates IL-18-dependent natural killer cell responses

BACKGROUND

NK cells are activated by innate cytokines and viral ligands to kill virus-infected cells. These functions are enhanced during secondary immune responses and after vaccination by synergy with effector T cells and virus-specific antibodies. In human Ebola virus infection, clinical outcome is strongly associated with the initial innate cytokine response, but the role of NK cells has not been thoroughly examined.

METHODS

The novel 2-dose heterologous Adenovirus type 26.ZEBOV (Ad26.ZEBOV) and modified vaccinia Ankara-BN-Filo (MVA-BN-Filo) vaccine regimen is safe and provides specific immunity against Ebola glycoprotein, and is currently in phase 2 and 3 studies. Here, we analyzed NK cell phenotype and function in response to Ad26.ZEBOV, MVA-BN-Filo vaccination regimen and in response to in vitro Ebola glycoprotein stimulation of PBMCs isolated before and after vaccination.

RESULTS

We show enhanced NK cell proliferation and activation after vaccination compared with baseline. Ebola glycoprotein–induced activation of NK cells was dependent on accessory cells and TLR-4–dependent innate cytokine secretion (predominantly from CD14⁺ monocytes) and enriched within less differentiated NK cell subsets. Optimal NK cell responses were dependent on IL-18 and IL-12, whereas IFN-γ secretion was restricted by high concentrations of IL-10.

CONCLUSION

This study demonstrates the induction of NK cell effector functions early after Ad26.ZEBOV, MVA-BN-Filo vaccination and provides a mechanism for the activation and regulation of NK cells by Ebola glycoprotein.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02313077.

FUNDING

United Kingdom Medical Research Council Studentship in Vaccine Research, Innovative Medicines Initiative 2 Joint Undertaking, EBOVAC (grant 115861) and Crucell Holland (now Janssen Vaccines and Prevention B.V.), European Union’s Horizon 2020 research and innovation programme and European Federation of Pharmaceutical Industries and Associations (EFPIA).

Durable natural killer cell responses after heterologous two-dose Ebola vaccination

Natural killer (NK) cells are implicated among immune effectors after vaccination against viral pathogens, including Ebola virus. The two-dose heterologous Ebola virus vaccine regimen, adenovirus type 26.ZEBOV followed by modified vaccinia Ankara-BN-Filo (EBOVAC2 consortium, EU Innovative Medicines Initiative), induces NK cell activation and anti-Ebola glycoprotein (GP) antibody-dependent NK cell activation post-dose 1, which is further elevated post-dose 2. Here, in a multicentre, phase 2 clinical trial (EBL2001), we demonstrate durable ex vivo NK cell activation 180 days after dose 2, with responses enriched in CD56^bright NK cells. In vitro antibody-dependent responses to immobilised Ebola GP increased after dose 1, and remained elevated compared to pre-vaccination levels in serum collected 180 days later. Peak NK cell responses were observed post-dose 2 and NK cell IFN-γ responses remained significantly elevated at 180 days post-dose 2. Individual variation in NK cell responses were influenced by both anti-Ebola GP antibody concentrations and intrinsic interindividual differences in NK cell functional capacity. In summary, this study demonstrates durable NK cell responses after Ad26.ZEBOV, MVA-BN-Filo Ebola virus vaccination and could inform the immunological evaluation of future iterations of the vaccine regimen and vaccination schedules.

COVID-19 Infection and Previous BCG Vaccination Coverage in the Ecuadorian Population

The Bacillus Calmette–Guérin (BCG) is a well-known vaccine with almost a century of use, with the apparent capability to improve cytokine production and epigenetics changes that could develop a better response to pathogens. It has been postulated that BCG protection against SARS-CoV-2 has a potential role in the pandemic, through the presence of homologous amino acid sequences. To identify a possible link between BCG vaccination coverage and COVID-19 cases, we used official epidemic data and Ecuadorian Ministry of Health and Pan American Health Organization vaccination information. BCG information before 1979 was available only at a national level. Therefore, projections based on the last 20 years were performed, to compare by specific geographic units. We used a Mann–Kendall test to identify BCG coverage variations, and mapping was conducted with a free geographic information system (QGIS). Nine provinces where BCG vaccine coverage was lower than 74.25% show a significant statistical association (χ² Pearson’s = 4.800, df = 1, p = 0.028), with a higher prevalence of cases for people aged 50 to 64 years than in younger people aged 20 to 49 years. Despite the availability of BCG vaccination data and the mathematical models needed to compare these data with COVID-19 cases, our results show that, in geographic areas where BCG coverage was low, 50% presented a high prevalence of COVID-19 cases that were young; thus, low-coverage years were more affected.

Is mapping the BCG vaccine-induced immune responses the key to improving the efficacy against tuberculosis?

In recent years, the century-old Mycobacterium bovis Bacillus Calmette-Guérin (BCG) vaccine against tuberculosis (TB) has been re-evaluated for its capacity to stem the global tide of TB. There is increasing evidence that the efficacy of BCG can be improved by the modified administration methods and schedules. Here, we first discuss recent approaches of vaccine administration, revaccination or boosting that have been used to try to improve the efficacy of BCG against TB. We then dive deeper into studies investigating the immune correlates of protection and describe studies that have investigated BCG-specific T-cell responses and the influence of environmental exposures. These studies all highlight that there is still a lot to learn about the immune response induced by BCG, both in terms of phenotype and specificity, which has been surprisingly understudied. We argue that several critical gaps in knowledge exist and must be addressed by future research to rationally improve the efficacy of BCG, including comprehensive, proteome-wide understanding of the epitopes derived from BCG recognized by BCG-vaccinated individuals, the phenotype of responding antigen-specific T cells and how previous exposure to environmental mycobacteria affect these parameters and thus influence vaccine efficacy. The development of modern techniques allows us to answer some of these questions to better understand how BCG works in terms of both protection against TB and the immune response that it triggers.

A Bovine Enteric Mycobacterium Infection Model to Analyze Parenteral Vaccine-Induced Mucosal Immunity and Accelerate Vaccine Discovery

Mycobacterial diseases of cattle are responsible for considerable production losses worldwide. In addition to their importance in animals, these infections offer a nuanced approach to understanding persistent mycobacterial infection in native host species. Mycobacteriumavium ssp. paratuberculosis (MAP) is an enteric pathogen that establishes a persistent, asymptomatic infection in the small intestine. Difficulty in reproducing infection in surrogate animal models and limited understanding of mucosal immune responses that control enteric infection in the natural host have been major barriers to MAP vaccine development. We previously developed a reproducible challenge model to establish a consistent MAP infection using surgically isolated intestinal segments prepared in neonatal calves. In the current study, we evaluated whether intestinal segments could be used to screen parenteral vaccines that alter mucosal immune responses to MAP infection. Using Silirum^® – a commercial MAP bacterin – we demonstrate that intestinal segments provide a platform for assessing vaccine efficacy within a relatively rapid period of 28 days post-infection. Significant differences between vaccinates and non-vaccinates could be detected using quantitative metrics including bacterial burden in intestinal tissue, MAP shedding into the intestinal lumen, and vaccine-induced mucosal immune responses. Comparing vaccine-induced responses in mucosal leukocytes isolated from the site of enteric infection versus blood leukocytes revealed substantial inconsistences between these immune compartments. Moreover, parenteral vaccination with Silirum did not induce equal levels of protection throughout the small intestine. Significant control of MAP infection was observed in the continuous but not the discrete Peyer’s patches. Analysis of these regional mucosal immune responses revealed novel correlates of immune protection associated with reduced infection that included an increased frequency of CD335⁺ innate lymphoid cells, and increased expression of IL21 and IL27. Thus, intestinal segments provide a novel model to accelerate vaccine screening and discovery by testing vaccines directly in the natural host and provides a unique opportunity to interrogate mucosal immune responses to mycobacterial infections.

Deciphering the Immunological Phenomenon of Adaptive Natural Killer (NK) Cells and Cytomegalovirus (CMV)

Natural killer (NK) cells play a significant and vital role in the first line of defense against infection through their ability to target cells without prior sensitization. They also contribute significantly to the activation and recruitment of both innate and adaptive immune cells through the production of a range of cytokines and chemokines. In the context of cytomegalovirus (CMV) infection, NK cells and CMV have co-evolved side by side to employ several mechanisms to evade one another. However, during this co-evolution the discovery of a subset of long-lived NK cells with enhanced effector potential, increased antibody-dependent responses and the potential to mediate immune memory has revolutionized the field of NK cell biology. The ability of a virus to imprint on the NK cell receptor repertoire resulting in the expansion of diverse, highly functional NK cells to this day remains a significant immunological phenomenon that only occurs in the context of CMV. Here we review our current understanding of the development of these NK cells, commonly referred to as adaptive NK cells and their current role in transplantation, infection, vaccination and cancer immunotherapy to decipher the complex role of CMV in dictating NK cell functional fate.

Vaccine strategies for the Mtb/HIV copandemic

One-third of world’s population is predicted to be infected with tuberculosis (TB). The resurgence of this deadly disease has been inflamed by comorbidity with human immunodeficiency virus (HIV). The risk of TB in people living with HIV (PLWH) is 15–22 times higher than people without HIV. Development of a single vaccine to combat both diseases is an ardent but tenable ambition. Studies have focused on the induction of specific humoral and cellular immune responses against HIV-1 following recombinant BCG (rBCG) expressing HIV-1 antigens. Recent advances in the TB vaccines led to the development of promising candidates such as MTBVAC, the BCG revaccination approach, H4:IC31, H56:IC31, M72/AS01 and more recently, intravenous (IV) BCG. Modification of these vaccine candidates against TB/HIV coinfection could reveal key correlates of protection in a representative animal model. This review discusses the (i) potential TB vaccine candidates that can be exploited for use as a dual vaccine against TB/HIV copandemic (ii) progress made in the realm of TB/HIV dual vaccine candidates in small animal model, NHP model, and human clinical trials (iii) the failures and promising targets for a successful vaccine strategy while delineating the correlates of vaccine-induced protection.

Multidimensional analyses reveal modulation of adaptive and innate immune subsets by tuberculosis vaccines

We characterize the breadth, function and phenotype of innate and adaptive cellular responses in a prevention of Mycobacterium tuberculosis infection trial. Responses are measured by whole blood intracellular cytokine staining at baseline and 70 days after vaccination with H4:IC31 (subunit vaccine containing Ag85B and TB10.4), Bacille Calmette-Guerin (BCG, a live attenuated vaccine) or placebo (n = ~30 per group). H4:IC31 vaccination induces Ag85B and TB10.4-specific CD4 T cells, and an unexpected NKTlike subset, that expresses IFN-γ, TNF and/or IL-2. BCG revaccination increases frequencies of CD4 T cell subsets that either express Th1 cytokines or IL-22, and modestly increases IFNγ-producing NK cells. In vitro BCG re-stimulation also triggers responses by donor-unrestricted T cells, which may contribute to host responses against mycobacteria. BCG, which demonstrated efficacy against sustained Mycobacterium tuberculosis infection, modulates multiple immune cell subsets, in particular conventional Th1 and Th22 cells, which should be investigated in discovery studies of correlates of protection.

Fetal public Vγ9Vδ2 T cells expand and gain potent cytotoxic functions early after birth

Vγ9Vδ2 T cells are a major human blood γδ T cell population that respond in a T cell receptor (TCR)-dependent manner to phosphoantigens which are generated by a variety of microorganisms. It is not clear how Vγ9Vδ2 T cells react toward the sudden microbial exposure early after birth. We found that human Vγ9Vδ2 T cells with a public/shared fetal-derived TCR repertoire expanded within 10 wk postpartum. Such an expansion was not observed in non-Vγ9Vδ2 γδ T cells, which possessed a private TCR repertoire. Furthermore, only the Vγ9Vδ2 T cells differentiated into potent cytotoxic effector cells by 10 wk of age, despite their fetal origin. Both the expansion of public fetal Vγ9Vδ2 T cells and their functional differentiation were not affected by newborn vaccination with the phosphoantigen-containing bacillus Calmette-Guérin (BCG) vaccine. These findings suggest a strong and early priming of the public fetal-derived Vγ9Vδ2 T cells promptly after birth, likely upon environmental phosphoantigen exposure.

Chronic Immune Activation in TB/HIV Co-infection

HIV co-infection is the most critical risk factor for the reactivation of latent tuberculosis (TB) infection (LTBI). While CD4+ T cell depletion has been considered the major cause of HIV-induced reactivation of LTBI, recent work in macaques co-infected with Mycobacterium tuberculosis (Mtb)/simian immunodeficiency virus (SIV) suggests that cytopathic effects of SIV resulting in chronic immune activation and dysregulation of T cell homeostasis correlate with reactivation of LTBI. This review builds on compelling data that the reactivation of LTBI during HIV co-infection is likely to be driven by the events of HIV replication and therefore highlights the need to have optimum translational interventions directed at reactivation due to co-infection.

Key recent advances in TB vaccine development and understanding of protective immune responses against Mycobacterium tuberculosis

Tuberculosis is the leading infectious disease killer globally due to a single pathogen. Despite wide deployment of standard drug regimens, modern diagnostics and a vaccine (bacille Calmette Guerin, BCG), the global tuberculosis epidemic is inadequately controlled. Novel, effective vaccine(s) are a crucial element of the World Health Organization End TB Strategy. TB vaccine research and development has recently been catalysed by several factors, including a revised strategy focused first on preventing pulmonary TB in adolescents and adults who are the main source of transmission, and encouraging evaluations of novel efficacy endpoints. Renewed enthusiasm for TB vaccine research has also been stimulated by recent preclinical and clinical advancements. These include new insights into underlying protective immune responses, including potential roles for 'trained' innate immunity and Th1/Th17 CD4+ (and CD8+) T cells. The field has been further reinvigorated by two positive proof of concept efficacy trials: one evaluating a potential new use of BCG in preventing high risk populations from sustained Mycobacterium tuberculosis infection and the second evaluating a novel, adjuvanted, recombinant protein vaccine candidate (M72/AS01E) for prevention of disease in adults already infected. Fourteen additional candidates are currently in various phases of clinical evaluation and multiple approaches to next generation vaccines are in discovery and preclinical development. The two positive efficacy trials and recent studies in nonhuman primates have enabled the first opportunities to discover candidate vaccine-induced correlates of protection, an effort being undertaken by a broad research consortium.

Effects of Pregnancy and Isoniazid Preventive Therapy on M. tuberculosis Interferon Gamma Response Assays in Women with HIV

BACKGROUND

Pregnancy is accompanied by immune suppression. We hypothesized that M. tuberculosis-specific inflammatory responses used to identify latent tuberculosis infection (LTBI) lose positivity during pregnancy. We also hypothesized that isoniazid preventive therapy (IPT) may revert LTBI diagnoses because of its sterilizing activity.

METHODS

944 women with HIV participating in a randomized, double-blind, placebo-controlled study comparing 28 weeks of IPT antepartum versus postpartum, were tested by QuantiFERON-gold-in-tube (QGIT) antepartum and by QGIT and tuberculin skin test (TST) at delivery and postpartum. Serial QGIT positivity was assessed by logistic regression using generalized estimating equations.

RESULTS

From entry to delivery, 68 (24%) of 284 QGIT-positive women (24%) reverted to QGIT-negative or indeterminate. Of these, 42 (62%) recovered QGIT positivity postpartum. The loss of QGIT positivity during pregnancy was explained by decreased IFNγ production in response to TB antigen and/or mitogen. At delivery, QGIT identified 205 and TST 113 women with LTBI. Corresponding numbers postpartum were 229 and 122 women. QGIT and TST kappa agreement coefficients were 0.4 and 0.5, respectively. Among QGIT-positive women antepartum or at delivery, 34 (12%) reverted to QGIT-negative after IPT. There were no differences between women who initiated IPT antepartum or postpartum.

CONCLUSIONS

Decreased IFNγ responses in pregnancy reduced QGIT positivity, suggesting that this test cannot reliably rule out LTBI during pregnancy. TST was less affected by pregnancy, but had lower positivity compared to QGIT at all time points. IPT was associated with loss of QGIT positivity, the potential clinical consequences of which need to be investigated.