A Case for Antibodies as Mechanistic Correlates of Immunity in Tuberculosis

B cell heterogeneity in human tuberculosis highlights compartment-specific phenotype and functional roles

B cells are important in tuberculosis (TB) immunity, but their role in the human lung is understudied. Here, we characterize B cells from lung tissue and matched blood of patients with TB and found they are decreased in the blood and increased in the lungs, consistent with recruitment to infected tissue, where they are located in granuloma associated lymphoid tissue. Flow cytometry and transcriptomics identify multiple B cell populations in the lung, including those associated with tissue resident memory, germinal centers, antibody secretion, proinflammatory atypical B cells, and regulatory B cells, some of which are expanded in TB disease. Additionally, TB lungs contain high levels of Mtb-reactive antibodies, specifically IgM, which promotes Mtb phagocytosis. Overall, these data reveal the presence of functionally diverse B cell subsets in the lungs of patients with TB and suggest several potential localized roles that may represent a target for interventions to promote immunity or mitigate immunopathology.

Borrelia-specific antibody profiles and complement deposition in joint fluid distinguish antibiotic-refractory from -responsive Lyme arthritis

Lyme arthritis, caused by the spirochete Borrelia burgdorferi, is the most common feature of late disseminated Lyme disease in the United States. While most Lyme arthritis resolves with antibiotics, termed "antibiotic-responsive", some individuals develop progressive synovitis despite antibiotic therapy, called "antibiotic-refractory" Lyme arthritis (LA). The primary drivers behind antibiotic-refractory arthritis remain incompletely understood. We performed a matched, cross-compartmental comparison of antibody profiles from blood and joint fluid of individuals with antibiotic-responsive (n = 11) or antibiotic-refractory LA (n = 31). While serum antibody profiles poorly discriminated responsive from refractory patients, a discrete profile of B.burgdorferi-specific antibodies in joint fluid discriminated antibiotic-responsive from refractory LA. Cross-compartmental comparison of antibody glycosylation, IgA1, and antibody-dependent complement deposition (ADCD) revealed more poorly coordinated humoral responses and increased ADCD in refractory disease. These data reveal B.burgdorferi-specific serological markers that may support early stratification and clinical management, and point to antibody-dependent complement activation as a key mechanism underlying persistent disease.

Development and application of the direct mycobacterial growth inhibition assay: a systematic review

Introduction

First described by Wallis et al. in 2001 for the assessment of TB drugs, the direct mycobacterial growth inhibition assay (MGIA) offers a tractable ex vivo tool measuring the combined influences of host immunity, strain virulence and intervention effects. Over the past 13 years, we have led efforts to adapt the direct MGIA for the assessment of TB vaccines including optimisation, harmonisation and validation of BCG vaccine-induced responses as a benchmark, as well as assay transfer to institutes worldwide.

Methods

We have performed a systematic review on the primary published literature describing the development and applications of the direct MGIA from 2001 to June 2023 in accordance with the PRISMA reporting guidelines.

Results

We describe 63 studies in which the direct MGIA has been applied across species for the evaluation of TB drugs and novel TB vaccine candidates, the study of clinical cohorts including those with comorbidities, and to further understanding of potential immune correlates of protection from TB. We provide a comprehensive update on progress of the assay since its conception and critically evaluate current findings and evidence supporting its utility, highlighting priorities for future directions.

Discussion

While further standardisation and validation work is required, significant advancements have been made in the past two decades. The direct MGIA provides a potentially valuable tool for the early evaluation of TB drug and vaccine candidates, clinical cohorts, and immune mechanisms of mycobacterial control.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42023423491.

Selection of vaccine-candidate peptides from Mycobacterium avium subsp. paratuberculosis by in silico prediction, in vitro T-cell line proliferation, and in vivo immunogenicity

Mycobacterium avium subspecies paratuberculosis (MAP) is a global concern in modern livestock production worldwide. The available vaccines against paratuberculosis do not offer optimal protection and interfere with the diagnosis of bovine tuberculosis. The aim of this study was to identify immunogenic MAP-specific peptides that do not interfere with the diagnosis of bovine tuberculosis. Initially, 119 peptides were selected by either (1) identifying unique MAP peptides that were predicted to bind to bovine major histocompatibility complex class II (MHC-predicted peptides) or (2) selecting hydrophobic peptides unique to MAP within proteins previously shown to be immunogenic (hydrophobic peptides). Subsequent testing of peptide-specific CD4+ T-cell lines from MAP-infected, adult goats vaccinated with peptides in cationic liposome adjuvant pointed to 23 peptides as being most immunogenic. These peptides were included in a second vaccine trial where three groups of eight healthy goat kids were vaccinated with 14 MHC-predicted peptides, nine hydrophobic peptides, or no peptides in o/w emulsion adjuvant. The majority of the MHC-predicted (93%) and hydrophobic peptides (67%) induced interferon-gamma (IFN-γ) responses in at least one animal. Similarly, 86% of the MHC-predicted and 89% of the hydrophobic peptides induced antibody responses in at least one goat. The immunization of eight healthy heifers with all 119 peptides formulated in emulsion adjuvant identified more peptides as immunogenic, as peptide specific IFN-γ and antibody responses in at least one heifer was found toward 84% and 24% of the peptides, respectively. No peptide-induced reactivity was found with commercial ELISAs for detecting antibodies against Mycobacterium bovis or MAP or when performing tuberculin skin testing for bovine tuberculosis. The vaccinated animals experienced adverse reactions at the injection site; thus, it is recommend that future studies make improvements to the vaccine formulation. In conclusion, immunogenic MAP-specific peptides that appeared promising for use in a vaccine against paratuberculosis without interfering with surveillance and trade tests for bovine tuberculosis were identified by in silico analysis and ex vivo generation of CD4+ T-cell lines and validated by the immunization of goats and cattle. Future studies should test different peptide combinations in challenge trials to determine their protective effect and identify the most MHC-promiscuous vaccine candidates.

Vaccine development against tuberculosis before and after Covid-19

Coronavirus disease (Covid-19) has not only shaped awareness of the impact of infectious diseases on global health. It has also provided instructive lessons for better prevention strategies against new and current infectious diseases of major importance. Tuberculosis (TB) is a major current health threat caused by Mycobacterium tuberculosis (Mtb) which has claimed more lives than any other pathogen over the last few centuries. Hence, better intervention measures, notably novel vaccines, are urgently needed to accomplish the goal of the World Health Organization to end TB by 2030. This article describes how the research and development of TB vaccines can benefit from recent developments in the Covid-19 vaccine pipeline from research to clinical development and outlines how the field of TB research can pursue its own approaches. It begins with a brief discussion of major vaccine platforms in general terms followed by a short description of the most widely applied Covid-19 vaccines. Next, different vaccination regimes and particular hurdles for TB vaccine research and development are described. This specifically considers the complex immune mechanisms underlying protection and pathology in TB which involve innate as well as acquired immune mechanisms and strongly depend on fine tuning the response. A brief description of the TB vaccine candidates that have entered clinical trials follows. Finally, it discusses how experiences from Covid-19 vaccine research, development, and rollout can and have been applied to the TB vaccine pipeline, emphasizing similarities and dissimilarities.

Features and protective efficacy of human mAbs targeting Mycobacterium tuberculosis arabinomannan

A better understanding of the epitopes most relevant for antibody-mediated protection against tuberculosis (TB) remains a major knowledge gap. We have shown that human polyclonal IgG against the Mycobacterium tuberculosis (M. tuberculosis) surface glycan arabinomannan (AM) and related lipoarabinomannan (LAM) is protective against TB. To investigate the impact of AM epitope recognition and Fcγ receptor (FcγR) binding on antibody functions against M. tuberculosis, we isolated a high-affinity human monoclonal antibody (mAb; P1AM25) against AM and showed its binding to oligosaccharide (OS) motifs we previously found to be associated with in vitro functions of human polyclonal anti-AM IgG. Human IgG1 P1AM25, but not 2 other high-affinity human IgG1 anti-AM mAbs reactive with different AM OS motifs, enhanced M. tuberculosis phagocytosis by macrophages and reduced intracellular growth in an FcγR-dependent manner. P1AM25 in murine IgG2a, but neither murine IgG1 nor a non-FcγR-binding IgG, given intraperitoneally prior to and after aerosolized M. tuberculosis infection, was protective in C57BL/6 mice. Moreover, we demonstrated the protective efficacy of human IgG1 P1AM25 in passive transfer with M. tuberculosis-infected FcγR-humanized mice. These data enhance our knowledge of the important interplay between both antibody epitope specificity and Fc effector functions in the defense against M. tuberculosis and could inform development of vaccines against TB.

Monoclonal antibodies to lipoarabinomannan/arabinomannan - characteristics and implications for tuberculosis research and diagnostics

Antibodies to the mycobacterial surface lipoglycan lipoarabinomannan (LAM) and its related capsular polysaccharide arabinomannan (AM) are increasingly important for investigations focused on both understanding mechanisms of protection against Mycobacterium tuberculosis (Mtb) and developing next-generation point-of-care tuberculosis (TB) diagnostics. We provide here an overview of the growing pipeline of monoclonal antibodies (mAbs) to LAM/AM. Old and new methodologies for their generation are reviewed and we outline and discuss their glycan epitope specificity and other features with implications for the TB field.

Hybrid Immunity Shifts the Fc-Effector Quality of SARS-CoV-2 mRNA Vaccine-Induced Immunity

Despite the robust immunogenicity of SARS-CoV-2 mRNA vaccines, emerging data have revealed enhanced neutralizing antibody and T cell cross-reactivity among individuals that previously experienced COVID-19, pointing to a hybrid immune advantage with infection-associated immune priming. Beyond neutralizing antibodies and T cell immunity, mounting data point to a potential role for additional antibody effector functions, including opsinophagocytic activity, in the resolution of symptomatic COVID-19. Whether hybrid immunity modifies the Fc-effector profile of the mRNA vaccine-induced immune response remains incompletely understood. Thus, here we profiled the SARS-CoV-2 specific humoral immune response in a group of individuals with and without prior COVID-19. As expected, hybrid Spike-specific antibody titers were enhanced following the primary dose of the mRNA vaccine but were similar to those achieved by naive vaccinees after the second mRNA vaccine dose. Conversely, Spike-specific vaccine-induced Fc-receptor binding antibody levels were higher after the primary immunization in individuals with prior COVID-19 and remained higher following the second dose compared to those in naive individuals, suggestive of a selective improvement in the quality, rather than the quantity, of the hybrid humoral immune response. Thus, while the magnitude of antibody titers alone may suggest that any two antigen exposures-either hybrid immunity or two doses of vaccine alone-represent a comparable prime/boost immunologic education, we find that hybrid immunity offers a qualitatively improved antibody response able to better leverage Fc-effector functions against conserved regions of the virus. IMPORTANCE Recent data indicates improved immunity to SARS-CoV-2 in individuals who experience a combination of two mRNA vaccine doses and infection, "hybrid immunity," compared to individuals who receive vaccination or experience infection alone. While previous infection accelerates the vaccine-induced immune response following the first dose of mRNA vaccination, subsequent doses demonstrate negligible increases in antibody titers or T cell immunity. Here, using systems serology, we observed a unique antibody profile induced by hybrid immunity, marked by the unique induction of robust Fc-recruiting antibodies directed at the conserved region of the viral Spike antigen, the S2-domain, induced at lower levels in individuals who only received mRNA vaccination. Thus, hybrid immunity clearly redirects vaccine-induced immunodominance, resulting in the induction of a robust functional humoral immune response to the most highly conserved region of the SARS-CoV-2 Spike antigen, which may be key to protection against existing and emerging variants of concern. Thus, next-generation vaccines able to mimic hybrid immunity and drive a balanced response to conserved regions of the Spike antigen may confer enhanced protection against disease.

Changing paradigms in the treatment of tuberculosis

Tuberculosis, caused by Mycobacterium tuberculosis, is a disease long dealt with, but still remains the second leading cause of death world-wide. The current anti-tubercular chemotherapy primarily targets the microbial pathogenesis, which however, is failing due to the development of drug resistance. Moreover, with fewer new drugs reaching the market, there is a need to focus on alternate treatment approaches that could be used as stand-alone or adjunct therapy and the existing drugs, referred to as Track II chemotherapy. This article is an attempt to review the changing global patterns of tuberculosis and its treatment. Further, newer drug delivery approaches like multi-particulate drug carriers which increase the therapeutic efficacy and bring down the systemic toxicity associated with drugs have also been discussed. There is also a need to use interventions which can be used as Track II therapy. Host-directed therapeutics (HDT) is an emerging area concept in which host cell functions and hence the response to pathogens can be modulated, which can help manage TB. HDT decreases damage induced due to inflammation and necrosis in the lungs and other parts of the body due to the disease. Various immuno-modulatory pathways have been discussed in this review which could be explored further to treat TB. An in-depth understanding of multi-particulate drug carriers and HDT could help in dealing with tuberculosis; however, there is still a long way to go.

Selective transfer of maternal antibodies in preterm and fullterm children

Preterm newborns are more likely to suffer from infectious diseases at birth compared to children delivered at term. Whether this is due to compromised cellular, humoral, or organ-specific development remains unclear. To begin to define whether maternal-fetal antibody transfer profiles differ across preterm (PT) and fullterm (FT) infants, the overall quantity and functional quality of an array of 24 vaccine-, endemic pathogen-, and common antigen-specific antibodies were assessed across a cohort of 11 PT and 12 term-delivered maternal:infant pairs from birth through week 12. While total IgG levels to influenza, pneumo, measles, rubella, EBV, and RSV were higher in FT newborns, selective Fc-receptor binding antibodies was noted in PT newborns. In fact, near equivalent antibody-effector functions were observed across PT and FT infants, despite significant quantitative differences in transferred antibody levels. Moreover, temporal transfer analysis revealed the selective early transfer of FcRn, FcγR2, and FcγR3 binding antibodies, pointing to differential placental sieving mechanisms across gestation. These data point to selectivity in placental transfer at distinct gestational ages, to ensure that children are endowed with the most robust humoral immunity even if born preterm.

A century of BCG vaccination: Immune mechanisms, animal models, non-traditional routes and implications for COVID-19

Bacillus Calmette-Guerin (BCG) has been used as a vaccine against tuberculosis since 1921 and remains the only currently approved vaccine for this infection. The recent discovery that BCG protects against initial infection, and not just against progression from latent to active disease, has significant implications for ongoing research into the immune mechanisms that are relevant to generate a solid host defense against Mycobacterium tuberculosis (Mtb). In this review, we first explore the different components of immunity that are augmented after BCG vaccination. Next, we summarize current efforts to improve the efficacy of BCG through the development of recombinant strains, heterologous prime-boost approaches and the deployment of non-traditional routes. These efforts have included the development of new recombinant BCG strains, and various strategies for expression of important antigens such as those deleted during the M. bovis attenuation process or antigens that are present only in Mtb. BCG is typically administered via the intradermal route, raising questions about whether this could account for its apparent failure to generate long-lasting immunological memory in the lungs and the inconsistent level of protection against pulmonary tuberculosis in adults. Recent years have seen a resurgence of interest in the mucosal and intravenous delivery routes as they have been shown to induce a better immune response both in the systemic and mucosal compartments. Finally, we discuss the potential benefits of the ability of BCG to confer trained immunity in a non-specific manner by broadly stimulating a host immunity resulting in a generalized survival benefit in neonates and the elderly, while potentially offering benefits for the control of new and emerging infectious diseases such as COVID-19. Given that BCG will likely continue to be widely used well into the future, it remains of critical importance to better understand the immune responses driven by it and how to leverage these for the design of improved vaccination strategies against tuberculosis.

ST6Gal1 in plasma is dispensable for IgG sialylation

The glycosylation of IgG has attracted increased attention due to the impact of N-glycan modifications at N297 on IgG function, acting primarily through modulation of Fc domain conformation and Fcγ receptor binding affinities and signaling. However, the mechanisms regulating IgG glycosylation and especially α2,6-sialylation of its N-glycan remain poorly understood. We observed previously that IgG is normally sialylated in mice with B cells lacking the sialyltransferase ST6Gal1. This supported the hypothesis that IgG may be sialylated outside of B cells, perhaps through the action of hepatocyte-released plasma ST6Gal1. Here we demonstrate that this model is incorrect. Animals lacking hepatocyte expressed ST6Gal1 retain normal IgG α2,6-sialylation, despite the lack of detectable ST6Gal1 in plasma. Moreover, we confirmed that B cells were not a redundant source of IgG sialylation. Thus, while α2,6-sialylation is lacking in IgG from mice with germline ablation of ST6Gal1, IgG α2,6-sialylation is normal in mice lacking ST6Gal1 in either hepatocytes or B cells. These results indicate that IgG α2,6-sialylation arises after release from a B cell, but is not dependent on plasma-localized ST6Gal1 activity.

The role of antibodies in tuberculosis diagnosis, prophylaxis and therapy: a review from the ESGMYC study group

Tuberculosis (TB) is still responsible for the deaths of >1 million people yearly worldwide, and therefore its correct diagnosis is one of the key components of any TB eradication programme. However, current TB diagnostic tests have many limitations, and improved diagnostic accuracy is urgently needed. To improve the diagnostic performance of traditional serology, a combination of different Mycobacterium tuberculosis (MTB) antigens and different antibody isotypes has been suggested, with some showing promising performance for the diagnosis of active TB. Given the incomplete protection conferred by bacille Calmette-Guérin (BCG) vaccination against adult pulmonary TB, efforts to discover novel TB vaccines are ongoing. Efficacy studies from advanced TB vaccines designed to stimulate cell-mediated immunity failed to show protection, suggesting that they may not be sufficient and warranting the need for other types of immunity. The role of antibodies as tools for TB therapy, TB diagnosis and TB vaccine design is discussed. Finally, we propose that the inclusion of antibody-based TB vaccines in current clinical trials may be advisable to improve protection.

The COVID-19/Tuberculosis Syndemic and Potential Antibody Therapy for TB Based on the Lessons Learnt From the Pandemic

2020 will be marked in history for the dreadful implications of the COVID-19 pandemic that shook the world globally. The pandemic has reshaped the normality of life and affected mankind in the aspects of mental and physical health, financial, economy, growth, and development. The focus shift to COVID-19 has indirectly impacted an existing air-borne disease, Tuberculosis. In addition to the decrease in TB diagnosis, the emergence of the TB/COVID-19 syndemic and its serious implications (possible reactivation of latent TB post-COVID-19, aggravation of an existing active TB condition, or escalation of the severity of a COVID-19 during TB-COVID-19 coinfection), serve as primary reasons to equally prioritize TB. On a different note, the valuable lessons learnt for the COVID-19 pandemic provide useful knowledge for enhancing TB diagnostics and therapeutics. In this review, the crucial need to focus on TB amid the COVID-19 pandemic has been discussed. Besides, a general comparison between COVID-19 and TB in the aspects of pathogenesis, diagnostics, symptoms, and treatment options with importance given to antibody therapy were presented. Lastly, the lessons learnt from the COVID-19 pandemic and how it is applicable to enhance the antibody-based immunotherapy for TB have been presented.

A Mycobacterium tuberculosis Specific IgG3 Signature of Recurrent Tuberculosis

South Africa has the highest prevalence of HIV and tuberculosis (TB) co-infection globally. Recurrent TB, caused by relapse or reinfection, makes up the majority of TB cases in South Africa, and HIV infected individuals have a greater likelihood of developing recurrent TB. Given that TB remains a leading cause of death for HIV infected individuals, and correlates of TB recurrence protection/risk have yet to be defined, here we sought to understand the antibody associated mechanisms of recurrent TB by investigating the humoral response in a longitudinal cohort of HIV co-infected individuals previously treated for TB with and without recurrent disease during follow-up, in order to identify antibody correlates of protection between individuals who do not have recurrent TB and individuals who do. We used a high-throughput, “systems serology” approach to profile biophysical and functional characteristics of antibodies targeting antigens from Mycobacterium tuberculosis (Mtb). Differences in antibody profiles were noted between individuals with and without recurrent TB, albeit these differences were largely observed close to the time of re-diagnosis. Individuals with recurrent TB had decreased Mtb-antigen specific IgG3 titers, but not other IgG subclasses or IgA, compared to control individuals. These data point to a potential role for Mtb-specific IgG3 responses as biomarkers or direct mediators of protective immunity against Mtb recurrence.

The knowns and unknowns of latent Mycobacterium tuberculosis infection

Humans have been infected with Mycobacterium tuberculosis (Mtb) for thousands of years. While tuberculosis (TB), one of the deadliest infectious diseases, is caused by uncontrolled Mtb infection, over 90% of presumed infected individuals remain asymptomatic and contain Mtb in a latent TB infection (LTBI) without ever developing disease, and some may clear the infection. A small number of heavily Mtb-exposed individuals appear to resist developing traditional LTBI. Because Mtb has mechanisms for intracellular survival and immune evasion, successful control involves all of the arms of the immune system. Here, we focus on immune responses to Mtb in humans and nonhuman primates and discuss new concepts and outline major knowledge gaps in our understanding of LTBI, ranging from the earliest events of exposure and infection to success or failure of Mtb control.

BCG-induced protection against Mycobacterium tuberculosis infection: Evidence, mechanisms, and implications for next-generation vaccines

The tuberculosis (TB) vaccine Bacillus Calmette-Guérin (BCG) was introduced 100 years ago, but as it provides insufficient protection against TB disease, especially in adults, new vaccines are being developed and evaluated. The discovery that BCG protects humans from becoming infected with Mycobacterium tuberculosis (Mtb) and not just from progressing to TB disease provides justification for considering Mtb infection as an endpoint in vaccine trials. Such trials would require fewer participants than those with disease as an endpoint. In this review, we first define Mtb infection and disease phenotypes that can be used for mechanistic studies and/or endpoints for vaccine trials. Secondly, we review the evidence for BCG-induced protection against Mtb infection from observational and BCG re-vaccination studies, and discuss limitations and variation of this protection. Thirdly, we review possible underlying mechanisms for BCG efficacy against Mtb infection, including alternative T cell responses, antibody-mediated protection, and innate immune mechanisms, with a specific focus on BCG-induced trained immunity, which involves epigenetic and metabolic reprogramming of innate immune cells. Finally, we discuss the implications for further studies of BCG efficacy against Mtb infection, including for mechanistic research, and their relevance to the design and evaluation of new TB vaccines.

Tuberculosis endotypes to guide stratified host-directed therapy

There is hope that host-directed therapy (HDT) for Tuberculosis (TB) can either shorten treatment duration, help cure drug resistant disease or limit the immunopathology. Many candidate HDT drugs have been proposed, however solid evidence only exists for a few select patient groups. The clinical presentation of TB is variable, with differences in severity, tissue pathology, and bacillary burden. TB clinical phenotypes likely determine the potential benefit of HDT. Underlying TB clinical phenotypes, there are TB "endotypes," defined as distinct molecular profiles, with specific metabolic, epigenetic, transcriptional, and immune phenotypes. TB endotypes can be characterized by either immunodeficiency or pathologic excessive inflammation. Additional factors, like comorbidities (HIV, diabetes, helminth infection), structural lung disease or Mycobacterial virulence also drive TB endotypes. Precise disease phenotyping, combined with in-depth immunologic and molecular profiling and multimodal omics integration, can identify TB endotypes, guide endotype-specific HDT, and improve TB outcomes, similar to advances in cancer medicine.

B-Cells and Antibodies as Contributors to Effector Immune Responses in Tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is still a major threat to mankind, urgently requiring improved vaccination and therapeutic strategies to reduce TB-disease burden. Most present vaccination strategies mainly aim to induce cell-mediated immunity (CMI), yet a series of independent studies has shown that B-cells and antibodies (Abs) may contribute significantly to reduce the mycobacterial burden. Although early studies using B-cell knock out animals did not support a major role for B-cells, more recent studies have provided new evidence that B-cells and Abs can contribute significantly to host defense against Mtb. B-cells and Abs exist in many different functional subsets, each equipped with unique functional properties. In this review, we will summarize current evidence on the contribution of B-cells and Abs to immunity toward Mtb, their potential utility as biomarkers, and their functional contribution to Mtb control.

Human antibodies targeting a Mycobacterium transporter protein mediate protection against tuberculosis

Mycobacterium tuberculosis (Mtb) exposure drives antibody responses, but whether patients with active tuberculosis elicit protective antibodies, and against which antigens, is still unclear. Here we generate monoclonal antibodies from memory B cells of one patient to investigate the B cell responses during active infection. The antibodies, members of four distinct B cell clones, are directed against the Mtb phosphate transporter subunit PstS1. Antibodies p4-36 and p4-163 reduce Mycobacterium bovis-BCG and Mtb levels in an ex vivo human whole blood growth inhibition assay in an FcR-dependent manner; meanwhile, germline versions of p4-36 and p4-163 do not bind Mtb. Crystal structures of p4-36 and p4-170, complexed to PstS1, are determined at 2.1 Å and 2.4 Å resolution, respectively, to reveal two distinctive PstS1 epitopes. Lastly, a prophylactic p4-36 and p4-163 treatment in Mtb-infected Balb/c mice reduces bacterial lung burden by 50%. Our study shows that inhibitory anti-PstS1 B cell responses arise during active tuberculosis.

Pulmonary MTBVAC vaccination induces immune signatures previously correlated with prevention of tuberculosis infection

To fight tuberculosis, better vaccination strategies are needed. Live attenuated Mycobacterium tuberculosis-derived vaccine, MTBVAC, is a promising candidate in the pipeline, proven to be safe and immunogenic in humans so far. Independent studies have shown that pulmonary mucosal delivery of Bacillus Calmette-Guérin (BCG), the only tuberculosis (TB) vaccine available today, confers superior protection over standard intradermal immunization. Here we demonstrate that mucosal MTBVAC is well tolerated, eliciting polyfunctional T helper type 17 cells, interleukin-10, and immunoglobulins in the airway and yielding a broader antigenic profile than BCG in rhesus macaques. Beyond our previous work, we show that local immunoglobulins, induced by MTBVAC and BCG, bind to M. tuberculosis and enhance pathogen uptake. Furthermore, after pulmonary vaccination, but not M. tuberculosis infection, local T cells expressed high levels of mucosal homing and tissue residency markers. Our data show that pulmonary MTBVAC administration has the potential to enhance its efficacy and justifies further exploration of mucosal vaccination strategies in preclinical efficacy studies.

Compromised Humoral Functional Evolution Tracks with SARS-CoV-2 Mortality

The urgent need for an effective SARS-CoV-2 vaccine has forced development to progress in the absence of well-defined correlates of immunity. While neutralization has been linked to protection against other pathogens, whether neutralization alone will be sufficient to drive protection against SARS-CoV-2 in the broader population remains unclear. Therefore, to fully define protective humoral immunity, we dissected the early evolution of the humoral response in 193 hospitalized individuals ranging from moderate to severe. Although robust IgM and IgA responses evolved in both survivors and non-survivors with severe disease, non-survivors showed attenuated IgG responses, accompanied by compromised Fcɣ receptor binding and Fc effector activity, pointing to deficient humoral development rather than disease-enhancing humoral immunity. In contrast, individuals with moderate disease exhibited delayed responses that ultimately matured. These data highlight distinct humoral trajectories associated with resolution of SARS-CoV-2 infection and the need for early functional humoral immunity.

Is interleukin-2 an optimal marker for diagnosing tuberculosis infection? A systematic review and meta-analysis

BACKGROUND

Latent tuberculosis infection (LTBI) is a huge reservoir for the deadlier TB disease. Accurate identification of LTBI is a key strategy to eliminate TB. Therefore, a systematic review and meta-analysis approach was used to assess diagnostic potential of IL-2 for LTBI.

METHODS

PubMed, Web of Science, the Cochrane Library and Embase were searched. The pooled sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), area under the summary receiver operating characteristic curve (AUROC) and hierarchical summary receiver operating characteristic curve (HSROC) were estimated by bivariate and HSROC models.

RESULTS

Twenty-seven studies including 1404 participants and 1986 samples met the inclusion criteria. The pooled sensitivity, specificity, PLR, NLR, DOR and AUROC of IL-2 were separately as 87%, 98%, 34.78, 0.14, 256.41 and 0.98, indicating a very powerful differentiating ability of IL-2 for LTBI from non-TB controls. For differentiating ATB from LTBI, the pooled sensitivity, specificity, PLR, NLR, DOR and AUROC of IL-2 were 83%, 76%, 3.41, 0.22, 15.47 and 0.87, respectively, suggesting a good differentiating ability of IL-2.

CONCLUSIONS

These findings showed that IL-2 is a powerful marker for differentiating LTBI from non-TB controls and a good marker for differentiating ATB from LTBI individuals.

Inducible nitric oxide synthase blockade with aminoguanidine, protects mice infected with Nocardia brasiliensis from actinomycetoma development

Mycetoma is a chronic infectious disease that can be caused by fungi or bacteria, Madurella mycetomatis and Nocardia brasiliensis are frequent etiologic agents of this disease. Mycetoma produced by bacteria is known as actinomycetoma. In mycetoma produced by fungi (eumycetoma) and actinomycetoma, diagnosis of the disease is based on clinical findings: severe inflammation, with deformities of affected tissues, abscesses, fistulae, sinuses and discharge of purulent material that contains micro colonies of the etiologic agent. Microscopic examination of infected tissue is similar regardless of the offending microbe; hallmark of infected tissue is severe inflammation with abundant neutrophils around micro colonies and granuloma formation with macrophages, lymphocytes, dendritic and foamy cells. Even though medical treatment is available for mycetoma patients, amputation, or surgical intervention is frequently needed. The pathogenesis of actinomycetoma is little known, most information was obtained from experimental animal models infected with bacteria. In other experimental mice infections with different microbes, it was demonstrated that nitric oxide is responsible for the intracellular killing of Mycobacterium tuberculosis by activated macrophages. Nitric oxide is a free radical with potent stimulatory and suppressive effects in innate and adaptive immunity. The unstable nitric oxide molecule is produced by action of nitric oxide synthases on L-arginine. There are three nitric oxide synthases expressed in different cells and tissues, two are constitutively expressed one in neurons, and the other in endothelial cells and one that is inducible in macrophages. Aminoguanidine is a competitive inhibitor of inducible nitric oxide synthase. Its administration in experimental animals may favor or harm them. We used aminoguanidine in mice infected with Nocardia brasiliensis, and demonstrated that all treated animals were protected from actinomycetoma development. Anti N. brasiliensis antibodies and T cell proliferation were not affected, but inflammation was reduced.

mSphere of Influence: Learning from Nature-Antibody Profiles Important for Protection of Young Infants

Esther Ndungo works in the field of maternal-infant immunity against enteric pathogens. In this mSphere of Influence article, she reflects on how the paper “Fc glycan-mediated regulation of placental antibody transfer” by Jennewein et al. (M. F. Jennewein, I. Goldfarb, S. Dolatshahi, C. Cosgrove, et al., Cell 178:202–215.e14, 2019, https://doi.org/10.1016/j.cell.2019.05.044) impressed upon her the value of thinking “outside the box” and looking to nature to guide her research.

Esther Ndungo works in the field of maternal-infant immunity against enteric pathogens. In this mSphere of Influence article, she reflects on how the paper “Fc glycan-mediated regulation of placental antibody transfer” by Jennewein et al. (M. F. Jennewein, I. Goldfarb, S. Dolatshahi, C. Cosgrove, et al., Cell 178:202–215.e14, 2019, https://doi.org/10.1016/j.cell.2019.05.044) impressed upon her the value of thinking “outside the box” and looking to nature to guide her research.

Antibodies targeting Mycobacterium tuberculosis peptides inhibit mycobacterial entry to infection target cells

The humoral immunity regarding tuberculosis can contribute towards controlling the mycobacteria and the disease. Antigens mediating such type of immunity should thus be evaluated for formulating anti-tuberculosis vaccines. The antigen recognition of seven peptides derived from proteins on Mtb H37Rv envelope and a further seven peptides modified from them was evaluated in sera taken from people suffering Mtb infection and others free from it. Peptide sequences' ability to inhibit Mtb entry to human macrophages was determined in vitro and, after isolating peptide-specific IgG antibodies, it was ascertained which ones were exercising such inhibitory function. Aotus were inoculated with the modified peptides for evaluating the activity of the antibodies so produced. Human QTF+ and QTF- sera recognised some of the peptides and inhibited Mtb entry. The same effect was seen with peptide-specific IgG regarding all the native sequences and modified ones. Sera taken from inoculated Aotus was also able to reduce the pathogen's entry. The data showed that some peptides evaluated in this study could induce antibodies able to inhibit the pathogen's entry to human macrophages, i.e. they could represent candidates for part of an anti-tuberculosis vaccine. The methodology used here complements the evaluation of promising antigens for designing effective vaccines.

Challenges of Immune Response Diversity in the Human Population Concerning New Tuberculosis Diagnostics, Therapies, and Vaccines

Universal approaches to the prevention and treatment of human diseases fail to take into account profound immune diversity resulting from genetic variations across populations. Personalized or precision medicine takes into account individual lifestyle, environment, and biology (genetics and immune status) and is being adopted in several disease intervention strategies such as cancer and heart disease. However, its application in infectious diseases, particularly global diseases such as tuberculosis (TB), is far more complex and in a state of infancy. Here, we discuss the impact of human genetic variations on immune responses and how they relate to failures seen in current TB diagnostic, therapy, and vaccine approaches across populations. We offer our perspective on the challenges and potential for more refined approaches going forward.

Effects of anticoagulants and Ficoll on human serum antibody reactivities and functions against Mycobacterium tuberculosis

The ability to utilize leftover samples containing anticoagulants or Ficoll would provide substantial opportunities for future antibody and biomarker studies. Some anticoagulants might influence antibody reactivity against pathogens, but comprehensive studies investigating effects in the context of TB are lacking. We enrolled 24 individuals with and without history of M. tuberculosis and/or HIV-infection and investigated TB antibody reactivities, function, and other host protein biomarkers in simultaneously obtained serum and plasma from serum separation, EDTA, heparin, acid citrate dextrose (ACD), or mononuclear cell preparation (CPT™) tubes which contain heparin and Ficoll. Antibody isotype reactivities to two mycobacterial antigens, as well as phagocytosis of M. tuberculosis, correlated strongly and significantly between serum and plasma, irrespective of type of anticoagulant or Ficoll present (r ≥ 0.85, p < 0.0001). However, the presence of ACD resulted in slightly lower values than those obtained with serum in both indirect (antibody reactivities to mycobacterial antigens) and Sandwich ELISAs (soluble CD14 measurements). Our data demonstrate that leftover plasma, regardless of containing anticoagulants or Ficoll, can be used in TB antibody or other host protein biomarker studies but suggest the value of a correction factor when using ACD plasma interchangeably with serum in antibody binding studies.

Whole genome profiling refines a panel of correlates to predict vaccine efficacy against Mycobacterium tuberculosis

New vaccines are needed to combat the public health threat posed by M. tuberculosis (M. tb), but no correlates have been defined to aid vaccine development. Using mouse models, we previously developed an in vitro system that measures the ability of M. tb-immune lymphocytes to control bacterial replication during co-culture with M. tb-infected macrophages. We demonstrated that the degree of in vitro growth control by lymphocytes from mice given vaccines of varying efficacy reflected the relative degree of in vivo protection against lethal challenge. Further, using targeted analyses of gene expression in lymphocytes recovered from co-cultures, we found mediators whose relative expression also correlated with in vitro and in vivo outcomes. Here we advanced those findings by employing genome-wide expression analyses. We first screened splenocytes recovered from co-cultures by microarray, revealing additional genes whose expression correlated with protection. After applying pathway analyses to down-select gene candidates, we used both splenocytes and peripheral blood lymphocytes to validate microarray findings by qRT-PCR. We then subjected data from top candidates to rigorous statistical analyses. Resulting correlate candidates, including CXCL9, IFN-γ, and CCL5, significantly predicted protection with high specificity. These findings therefore refine and extend a panel of relevant immune correlates to advance vaccine development.

The intracellular pathogen concept

The intracellular pathogen concept classifies pathogenic microbes on the basis of their site of replication and dependence on host cells. This concept played a fundamental role in establishing the field of cellular microbiology, founded in part by Dr. Pascale Cossart, whose seminal contributions are honored in this issue of Molecular Microbiology. The recognition that microbes can access and replicate in privileged compartments within host cells has led to many new and fruitful lines of investigation into the biology of the cell and mechanisms of cell-mediated immunity. However, like any scientific concept, the intracellular pathogen concept can become a dogma that constrains thinking and oversimplifies complex and dynamic host-pathogen interactions. Growing evidence has blurred the distinction between "intracellular" and "extracellular" pathogens and demonstrated that many pathogens can exist both within and outside of cells. Although the intracellular pathogen concept remains useful, it should not be viewed as a rigid classification of pathogenic microbes, which exhibit remarkable variation and complexity in their behavior in the host.

Role of the Microbiota in the Modulation of Vaccine Immune Responses

The human immune system and the microbiota co-evolve, and their balanced relationship is based on crosstalk between the two systems through the course of life. This tight association and the overall composition and richness of the microbiota play an important role in the modulation of host immunity and may impact the immune response to vaccination. The availability of innovative technologies, such as next-generation sequencing (NGS) and correlated bioinformatics tools, allows a deeper investigation of the crosstalk between the microbiota and human immune responses. This review discusses the current knowledge on the influence of the microbiota on the immune response to vaccination and novel tools to deeply analyze the impact of the microbiome on vaccine responses.

Tools for Assessing the Protective Efficacy of TB Vaccines in Humans: in vitro Mycobacterial Growth Inhibition Predicts Outcome of in vivo Mycobacterial Infection

Tuberculosis (TB) remains a leading global cause of morbidity and mortality and an effective new vaccine is urgently needed. A major barrier to the rational development of novel TB vaccines is the lack of a validated immune correlate or biomarker of protection. Mycobacterial Growth Inhibition Assays (MGIAs) provide an unbiased measure of ability to control mycobacterial growth in vitro, and may represent a functional correlate of protection. However, the biological relevance of any potential correlate can only be assessed by determining the association with in vivo protection from either a controlled mycobacterial infection or natural development of TB disease. Our data demonstrate that the direct MGIA using peripheral blood mononuclear cells (PBMC) is measuring a biologically relevant response that correlates with protection from in vivo human BCG infection across two independent cohorts. This is the first report of an MGIA correlating with in vivo protection in the species-of-interest, humans, and furthermore on a per-individual as well as per-group basis. Control of mycobacterial growth in the MGIA is associated with a range of immune parameters measured post-BCG infection in vivo including the IFN-γ ELISpot response, frequency of PPD-specific IFN-γ or TNF-α producing CD4+ T cells and frequency of specific sub-populations of polyfunctional CD4+ T cells. Distinct transcriptomic profiles are associated with good vs. poor mycobacterial control in the MGIA, with good controllers showing enrichment for gene sets associated with antigen processing/presentation and the IL-23 pathway, and poor controllers showing enrichment for hypoxia-related pathways. This study represents an important step toward biologically validating the direct PBMC MGIA for use in TB vaccine development and furthermore demonstrates the utility of this assay in determining relevant immune mechanisms and pathways of protection.