What Have We Learnt about BCG Vaccination in the Last 20 Years?

COVID-19 vaccine development: What lessons can we learn from TB?

At the time of writing, the SARS-CoV-2 virus has infected more than 49 million people causing more than 1.2 million deaths worldwide since its emergence from Wuhan, China in December 2019. Vaccine development against SARS-CoV-2 has drawn the global attention in order to stop the spread of the virus, with more than 10 vaccines being tested in phase III clinical trials, as of November 2020. However, critical to vaccine development is consideration of the immunological response elicited as well as biological features of the vaccine and both need to be evaluated thoroughly. Tuberculosis is also a major infectious respiratory disease of worldwide prevalence and the vaccine development for tuberculosis has been ongoing for decades. In this review, we highlight some of the common features, challenges and complications in tuberculosis vaccine development, which may also be relevant for, and inform, COVID-19 vaccine development.

Overcoming immune dysfunction in the elderly: trained immunity as a novel approach

People with advanced age have a higher susceptibility to infections and exhibit increased mortality and morbidity as the ability of the immune system to combat infections decreases with age. While innate immune cells display functional defects such as decreased phagocytosis, chemotaxis and cytokine production, adaptive immune cells exhibit reduced receptor diversity, defective antibody production and a sharp decline in naive cell populations. Successful responses to vaccination in the elderly are critical to prevent common infections such as influenza and pneumonia, but vaccine efficacy decreases in older individuals compared with young adults. Trained immunity is a newly emerging concept that showed that innate immune cells possess non-specific immunological memory established through epigenetic and metabolic reprogramming upon encountering certain pathogenic stimuli. Clinical studies suggest that trained immunity can be utilized to enhance immune responses against infections and improve the efficiency of vaccinations in adults; however, how trained immunity responses are shaped with advanced age is still an open question. In this review, we provide an overview of the age-related changes in the immune system with a focus on innate immunity, discuss current vaccination strategies for the elderly, present the concept of trained immunity and propose it as a novel approach to enhance responses against infections and vaccinations in the elderly population.

Non-Tuberculous Mycobacteria Interference with BCG-Current Controversies and Future Directions

The global tuberculosis (TB) epidemic caused by the bacterial pathogen Mycobacterium tuberculosis (M.tb) continues unabated. The Mycobacterium bovis bacillus Calmette–Guérin (BCG) vaccination is widely utilized worldwide to protect against infection with M.tb. BCG vaccine protection against TB has had widely varying results for reasons that are not well understood. BCG vaccine interference by non-tuberculosis (NTM) mycobacterial species has been implicated as the potential cause of reduced BCG vaccine efficacy against M.tb. Ongoing efforts to develop new vaccines for TB requires a thorough understanding of the effect of NTM exposure on BCG vaccine efficacy, which may ultimately be a critical determinant of success. We reviewed the conflicting reports on whether NTM interferes with the BCG vaccine, potential explanations to help resolve the controversy, and strategies for developing better animal models. Further studies are needed to longitudinally track the effects of NTM exposure on BCG vaccine-induced host-protective anti-TB immunity.

Tuberculosis vaccination needs to avoid 'decoy' immune reactions

Current search for a new effective vaccine against tuberculosis involves selected antigens, vectors and adjuvants. These are being evaluated usually by their booster inoculation following priming with Bacillus Calmette-Guerin. The purpose of this article is to point out, that despite being attenuated of virulence, priming with BCG may still involve immune mechanisms, which are not favourable for protection against active disease. It is postulated, that the responsible 'decoy' constituents selected during the evolution of pathogenic tubercle bacilli may be involved in the evasion from bactericidal host resistance and stimulate immune responses of a cytokine phenotype, which lead to the transition from latent closed granulomas to reactivation with infectious lung cavities. The decoy mechanisms appear as favourable for most infected subjects but leading in a minority of cases to pathology which can effectively transmit the infection. It is proposed that construction and development of new vaccine candidates could benefit from avoiding decoy-type immune mechanisms.

GPCRs as an emerging host-directed therapeutic target against mycobacterial infection: From notion to reality

Mycobacterium tuberculosis (M. tb) is one of the successful pathogens and claim millions of deaths across the globe. The emergence of drug resistance in M. tb has created new hurdles in the tuberculosis elimination programme worldwide. Hence, there is an unmet medical need for alternative therapy, which could be achieved by targeting the host's critical signalling pathways that are compromised during M. tb infection. In this review, we have summarized some of the findings involving the modulation of host GPCRs in the regulation of the mycobacterial infection. Understanding the role of these GPCRs not only unravels signalling pathways during infection but also provides clues for targeting critical signalling intermediates for the development of GPCR-based host-directive therapy.

Protection against SARS-CoV-2 by BCG vaccination is not supported by epidemiological analyses

The Bacillus Calmette–Guerin (BCG) vaccine provides protection against tuberculosis (TB), and is thought to provide protection against non-TB infectious diseases. BCG vaccination has recently been proposed as a strategy to prevent infection with SARS-CoV-2 (CoV-2) to combat the COVID-19 outbreak, supported by its potential to boost innate immunity and initial epidemiological analyses which observed reduced severity of COVID-19 in countries with universal BCG vaccination policies. Seventeen clinical trials are currently registered to inform on the benefits of BCG vaccinations upon exposure to CoV-2. Numerous epidemiological analyses showed a correlation between incidence of COVID-19 and BCG vaccination policies. These studies were not systematically corrected for confounding variables. We observed that after correction for confounding variables, most notably testing rates, there was no association between BCG vaccination policy and COVD-19 spread rate or percent mortality. Moreover, we found variables describing co-morbidities, including cardiovascular death rate and smoking prevalence, were significantly associated COVID-19 spread rate and percent mortality, respectively. While reporting biases may confound our observations, our epidemiological findings do not provide evidence to correlate overall BCG vaccination policy with the spread of CoV-2 and its associated mortality.

The role of immunoinformatics in the development of T-cell peptide-based vaccines against Mycobacterium tuberculosis

INTRODUCTION

Tuberculosis (TB) is a major health problem worldwide. The BCG, the only authorized vaccine to fight TB, shows a variable protection in the adult population highlighting the need of a new vaccine. Immunoinformatics offers a variety of tools that can predict immunogenic T-cell peptides of Mycobacterium tuberculosis (Mtb) that can be used to create a new vaccine. Immunoinformatics has made possible the identification of immunogenic T-cell peptides of Mtb that have been tested in vitro showing a potential for using these molecules as part of a new TB vaccine.

AREAS COVERED

This review summarizes the most common immunoinformatics tools to identify immunogenic T-cell peptides and presents a compilation about research studies that have identified T-cell peptides of Mtb by using immunoinformatics. Also, it is provided a summary of the TB vaccines undergoing clinical trials.

EXPERT OPINION

In the next few years, the field of peptide-based vaccines will keep growing along with the development of more efficient and sophisticated immunoinformatic tools to identify immunogenic peptides with a greater accuracy.

The Systematic Review and Meta-Analysis on the Immunogenicity and Safety of the Tuberculosis Subunit Vaccines M72/AS01E and MVA85A

Background: Tuberculosis (TB) is a severe infectious disease with devastating effects on global public health. No TB vaccine has yet been approved for use on latent TB infections and healthy adults. In this study, we performed a systematic review and meta-analysis to evaluate the immunogenicity and safety of the M72/AS01_E and MVA85A subunit vaccines. The M72/AS01_E is a novel peptide-based vaccine currently in progress, which may increase the protection level against TB infection. The MVA85A was a viral vector-based TB subunit vaccine being used in the clinical trials. The vaccines mentioned above have been studied in various phase I/II clinical trials. Immunogenicity and safety is the first consideration for TB vaccine development.

Methods: The PubMed, Embase, and Cochrane Library databases were searched for published studies (until October 2019) to find out information on the M72/AS01_E and MVA85A candidate vaccines. The meta-analysis was conducted by applying the standard methods and processes established by the Cochrane Collaboration.

Results: Five eligible randomized clinical trials (RCTs) were selected for the meta-analysis of M72/AS01E candidate vaccines. The analysis revealed that the M72/AS01E subunit vaccine had an abundance of polyfunctional M72-specific CD4+ T cells [standardized mean difference (SMD) = 2.37] in the vaccine group versus the control group, the highest seropositivity rate [relative risk (RR) = 5.09]. The M72/AS01E vaccinated group were found to be at high risk of local injection site redness (RR = 2.64), headache (RR = 1.59), malaise (RR = 3.55), myalgia (RR = 2.27), fatigue (RR = 2.16), pain (RR = 3.99), swelling (RR = 5.09), and fever (RR = 2.04) compared to the control groups. The incidences of common adverse events of M72/AS01E were local injection site redness, headache, malaise, myalgia, fatigue, pain, swelling, fever, etc. Six eligible RCTs were selected for the meta-analysis on MVA85A candidate vaccines. The analysis revealed that the subunit vaccine MVA85A had a higher abundance of overall pooled proportion polyfunctional MVA85A-specific CD4+ T cells SMD = 2.41 in the vaccine group vs. the control group, with the highest seropositivity rate [estimation rate (ER) = 0.55]. The MVA85A vaccinated group were found to be at high risk of local injection site redness (ER = 0.55), headache (ER = 0.40), malaise (ER = 0.29), pain (ER = 0.54), myalgia (ER = 0.31), and fever (ER = 0.20). The incidences of common adverse events of MVA85A were local injection site redness, headache, malaise, pain, myalgia, fever, etc.

Conclusion: The M72/AS01_E and MVA85A vaccines against TB are safe and had immunogenicity in diverse clinical trials. The M72/AS01_E and MVA85A vaccines are associated with a mild adverse reaction. The meta-analysis on immunogenicity and safety of M72/AS01_E and MVA85A vaccines provides useful information for the evaluation of available subunit vaccines in the clinic.

An Overview of the Development of New Vaccines for Tuberculosis

Currently, there is only one licensed vaccine against tuberculosis (TB), the Bacillus Calmette–Guérin (BCG). Despite its protective efficacy against TB in children, BCG has failed to protect adults against pulmonary TB, lacks therapeutic value, and causes complications in immunocompromised individuals. Furthermore, it compromises the use of antigens present in the purified protein derivate of Mycobacterium tuberculosis in the diagnosis of TB. Many approaches, e.g., whole-cell organisms, subunit, and recombinant vaccines are currently being explored for safer and more efficacious TB vaccines than BCG. These approaches have been successful in developing a large number of vaccine candidates included in the TB vaccine pipeline and are at different stages of clinical trials in humans. This paper discusses current vaccination strategies, provides directions for the possible routes towards the development of new TB vaccines and highlights recent findings. The efforts for improved TB vaccines may lead to new licensed vaccines capable of replacing/supplementing BCG and conferring therapeutic value in patients with active/latent TB.

Optimisation of Mycobacterium bovis BCG Fermentation and Storage Survival

Mycobacterium bovis Bacillus Calmette–Guérin (M. bovis BCG) was generated over a century ago for protection against Mycobacterium tuberculosis (Mtb) and is one the oldest vaccines still in use. The BCG vaccine is currently produced using a pellicle growth method, which is a complex and lengthy process that has been challenging to standardise. Fermentation for BCG vaccine production would reduce the complexity associated with pellicle growth and increase batch to batch reproducibility. This more standardised growth lends itself to quantification of the total number of bacilli in the BCG vaccine by alternative approaches, such as flow cytometry, which can also provide information about the metabolic status of the bacterial population. The aim of the work reported here was to determine which batch fermentation conditions and storage conditions give the most favourable outcomes in terms of the yield and stability of live M. bovis BCG Danish bacilli. We compared different media and assessed growth over time in culture, using total viable counts, total bacterial counts, and turbidity throughout culture. We applied fluorescent viability dyes and flow cytometry to measure real-time within-culture viability. Culture samples were stored in different cryoprotectants at different temperatures to assess the effect of these combined conditions on bacterial titres. Roisin’s minimal medium and Middlebrook 7H9 medium gave comparable, high titres in fermenters. Flow cytometry proved to be a useful tool for enumeration of total bacterial counts and in the assessment of within-culture cell viability and cell death. Of the cryoprotectants evaluated, 5% (v/v) DMSO showed the most significant positive effect on survival and reduced the negative effects of low temperature storage on M. bovis BCG Danish viability. In conclusion, we have shown a reproducible, more standardised approach for the production, evaluation, and storage of high titre, viable, BCG vaccine.

BCG as a game-changer to prevent the infection and severity of COVID-19 pandemic?

The impact of COVID-19 is changing with country wise and depend on universal immunization policies. COVID-19 badly affects countries that did not have universal immunization policies or having them only for the selective population of countries (highly prominent population) like Italy, USA, UK, Netherland, etc. Universal immunization of BCG can provide great protection against the COVID-19 infection because the BCG vaccine gives broad protection against respiratory infections. BCG vaccine induces expressions of the gene that are involved in the antiviral innate immune response against viral infections with long-term maintenance of BCG vaccine-induced cellular immunity. COVID-19 cases are reported very much less in the countries with universal BCG vaccination policies such as India, Afghanistan, Nepal, Bhutan, Bangladesh, Israel, Japan, etc. as compared to without BCG implemented countries such as the USA, Italy, Spain, Canada, UK, etc. BCG vaccine provides protection for 50–60 years of immunization, so the elderly population needs to be revaccinated with BCG. Several countries started clinical trials of the BCG vaccine for health care workers and elderly people. BCG can be uses as a prophylactic treatment until the availability of the COVID-19 vaccine.

An Army Marches on Its Stomach: Metabolic Intermediates as Antimicrobial Mediators in Mycobacterium tuberculosis Infection

The cells of the immune system are reliant on their metabolic state to launch effective responses to combat mycobacterial infections. The bioenergetic profile of the cell determines the molecular fuels and metabolites available to the host, as well as to the bacterial invader. How cells utilize the nutrients in their microenvironment—including glucose, lipids and amino acids—to sustain their functions and produce antimicrobial metabolites, and how mycobacteria exploit this to evade the immune system is of great interest. Changes in flux through metabolic pathways alters the intermediate metabolites present. These intermediates are beginning to be recognized as key modulators of immune signaling as well as direct antimicrobial effectors, and their impact on tuberculosis infection is becoming apparent. A better understanding of how metabolism impacts immunity to Mycobacterium tuberculosis and how it is regulated and thus can be manipulated will open the potential for novel therapeutic interventions and vaccination strategies.

Integrating fish models in tuberculosis vaccine development

Tuberculosis is a chronic infection by Mycobacterium tuberculosis that results in over 1.5 million deaths worldwide each year. Currently, there is only one vaccine against tuberculosis, the Bacillus Calmette–Guérin (BCG) vaccine. Despite widespread vaccination programmes, over 10 million new M. tuberculosis infections are diagnosed yearly, with almost half a million cases caused by antibiotic-resistant strains. Novel vaccination strategies concentrate mainly on replacing BCG or boosting its efficacy and depend on animal models that accurately recapitulate the human disease. However, efforts to produce new vaccines against an M. tuberculosis infection have encountered several challenges, including the complexity of M. tuberculosis pathogenesis and limited knowledge of the protective immune responses. The preclinical evaluation of novel tuberculosis vaccine candidates is also hampered by the lack of an appropriate animal model that could accurately predict the protective effect of vaccines in humans. Here, we review the role of zebrafish (Danio rerio) and other fish models in the development of novel vaccines against tuberculosis and discuss how these models complement the more traditional mammalian models of tuberculosis.

Summary: In this Review, we discuss how zebrafish (Danio rerio) and other fish models can complement the more traditional mammalian models in the development of novel vaccines against tuberculosis.

What lies beneath the airway mucosal barrier? Throwing the spotlight on antigen-presenting cell function in the lower respiratory tract

The global prevalence of respiratory infectious and inflammatory diseases remains a major public health concern. Prevention and management strategies have not kept pace with the increasing incidence of these diseases. The airway mucosa is the most common portal of entry for infectious and inflammatory agents. Therefore, significant benefits would be derived from a detailed understanding of how immune responses regulate the filigree of the airways. Here, the role of different antigen‐presenting cells (APC) in the lower airways and the mechanisms used by pathogens to modulate APC function during infectious disease is reviewed. Features of APC that are unique to the airways and the influence they have on uptake and presentation of antigen to T cells directly in the airways are discussed. Current information on the crucial role that airway APC play in regulating respiratory infection is summarised. We examine the clinical implications of APC dysregulation in the airways on asthma and tuberculosis, two chronic diseases that are the major cause of illness and death in the developed and developing world. A brief overview of emerging therapies that specifically target APC function in the airways is provided.

Significantly Improved COVID-19 Outcomes in Countries with Higher BCG Vaccination Coverage: A Multivariable Analysis

The COVID-19 pandemic that started in China has spread within 3 months to the entire globe. We tested the hypothesis that the vaccination against tuberculosis by Bacille Calmette–Guérin vaccine (BCG) correlates with a better outcome for COVID-19 patients. Our analysis covers 55 countries complying with predetermined thresholds on the population size and number of deaths per million (DPM). We found a strong negative correlation between the years of BCG administration and the DPM along with the progress of the pandemic, corroborated by permutation tests. The results from multivariable regression tests with 23 economic, demographic, health-related, and pandemic restriction-related quantitative properties, substantiate the dominant contribution of BCG years to the COVID-19 outcomes. The analysis of countries according to an age-group partition reveals that the strongest correlation is attributed to the coverage in BCG vaccination of the young population (0–24 years). Furthermore, a strong correlation and statistical significance are associated with the degree of BCG coverage for the most recent 15 years, but no association was observed in these years for other broadly used vaccination protocols for measles and rubella. We propose that BCG immunization coverage, especially among the most recently vaccinated population, contribute to attenuation of the spread and severity of the COVID-19 pandemic.

Role of neutrophils in tuberculosis: A bird's eye view

Neutrophils are innate immune cells implicated in the process of killing Mycobacterium tuberculosis early during infection. Once the mycobacteria enter the human system, neutrophils sense and engulf them. By secreting bactericidal enzymes and α-defensins like human neutrophil peptides loaded in their granule armory, neutrophils kill the pathogen. Peripheral blood neutrophils secrete a wide range of cytokines like IL-8, IL-1-β and IFN-γ in response to mycobacterial infection. Thus they signal and activate distant immune cells thereby informing them of prevailing infection. The activated monocytes, dendritic cells and T cells further continue the immune response. As a final call, neutrophils release neutrophil extracellular traps in circulation which can trap mycobacteria in patients with active pulmonary tuberculosis. Extensive neutrophilic response is associated with inflammation, pulmonary destruction, and pathology. For example, inappropriate phagocytosis of mycobacteria-infected neutrophils can damage host cells due to necrosis of neutrophils, leading to chronic inflammation and tissue damage. This dual nature of neutrophils makes them double-edged swords during tuberculosis, and hence data available on neutrophil functions against mycobacterium are controversial and non-uniform. This article reviews the role of neutrophils in tuberculosis infection and highlights research gaps that need to be addressed. We focus on our understanding of new research ideologies targeting neutrophils (a) in the early stages of infection for boosting specific immune functions or (b) in the later stages of infection to prevent inflammatory conditions mediated by activated neutrophils. This would plausibly lead to the development of better tuberculosis vaccines and therapeutics in the future.

Tuberculosis vaccine: A journey from BCG to present

Tuberculosis (TB) is the leading cause of death worldwide due to an infectious disease, causing around 1.6 million deaths each year. This situation has become more complicated by the emergence of drug-resistant Mycobacterium tuberculosis (M.tb) and HIV-TB co-infection, which has significantly worsened TB prognosis and treatment. Despite years of intensive research, Bacille Calmette-Guerin (BCG) remains the only licensed vaccine and has variable efficacy. It provides protection against childhood TB but is not effective in adult pulmonary TB. As a result of intense research in understanding TB vaccinology, there are many new vaccine candidates in clinical development and many more in pre-clinical trials which aim either to replace or boost BCG vaccine. This review discusses the history of BCG vaccine development and summarizes limitations of the current vaccine strategy and recent advances in improving BCG immunization along with other new vaccines in clinical trials which are promising candidates for the future tuberculosis vaccinology program.

The Diversity Outbred Mouse Population Is an Improved Animal Model of Vaccination against Tuberculosis That Reflects Heterogeneity of Protection

We vaccinated the Diversity Outbred (DO) population of mice with BCG, the only vaccine currently used to protect against tuberculosis, and then challenged them with M. tuberculosis by aerosol. We found that the BCG-vaccinated DO mouse population exhibited a wide range of outcomes, in which outcomes in individual mice ranged from minimal respiratory or systemic disease to fulminant disease and death. The breadth of these outcomes appears similar to the range seen in people, indicating that DO mice may serve as an improved small-animal model to study tuberculosis infection and immunity. Moreover, sophisticated tools are available for the use of these mice to map genes contributing to control of vaccination. Thus, the present studies provided an important new tool in the fight against tuberculosis.

Many studies of Mycobacterium tuberculosis infection and immunity have used mouse models. However, outcomes of vaccination and challenge with M. tuberculosis in inbred mouse strains do not reflect the full range of outcomes seen in people. Previous studies indicated that the novel Diversity Outbred (DO) mouse population exhibited a spectrum of outcomes after primary aerosol infection with M. tuberculosis. Here, we demonstrate the value of this novel mouse population for studies of vaccination against M. tuberculosis aerosol challenge. Using the only currently licensed tuberculosis vaccine, we found that the DO population readily controlled systemic Mycobacterium bovis BCG bacterial burdens and that BCG vaccination significantly improved survival across the DO population upon challenge with M. tuberculosis. Many individual DO mice that were vaccinated with BCG and then challenged with M. tuberculosis exhibited low bacterial burdens, low or even no systemic dissemination, little weight loss, and only minor lung pathology. In contrast, some BCG-vaccinated DO mice progressed quickly to fulminant disease upon M. tuberculosis challenge. Across the population, most of these disease parameters were at most modestly correlated with each other and were often discordant. This result suggests the need for a multiparameter metric to better characterize “disease” and “protection,” with closer similarity to the complex case definitions used in people. Taken together, these results demonstrate that DO mice provide a novel small-animal model of vaccination against tuberculosis that better reflects the wide spectrum of outcomes seen in people.

IMPORTANCE We vaccinated the Diversity Outbred (DO) population of mice with BCG, the only vaccine currently used to protect against tuberculosis, and then challenged them with M. tuberculosis by aerosol. We found that the BCG-vaccinated DO mouse population exhibited a wide range of outcomes, in which outcomes in individual mice ranged from minimal respiratory or systemic disease to fulminant disease and death. The breadth of these outcomes appears similar to the range seen in people, indicating that DO mice may serve as an improved small-animal model to study tuberculosis infection and immunity. Moreover, sophisticated tools are available for the use of these mice to map genes contributing to control of vaccination. Thus, the present studies provided an important new tool in the fight against tuberculosis.

BCG and BCGΔBCG1419c protect type 2 diabetic mice against tuberculosis via different participation of T and B lymphocytes, dendritic cells and pro-inflammatory cytokines

Comorbidity between Tuberculosis (TB) and type 2 diabetes (T2D) is one of the greatest contributors to the spread of Mycobacterium tuberculosis (M. tuberculosis) in low- and middle-income countries. T2D compromises key steps of immune responses against M. tuberculosis and it might affect the protection afforded by vaccine candidates against TB. We compared the protection and immune response afforded by the BCGΔBCG1419c vaccine candidate versus that of wild-type BCG in mice with T2D. Vaccination with both BCGΔBCG1419c, BCG or infection with M. tuberculosis reduced weight loss, hyperglycemia, and insulin resistance during T2D progression, suggesting that metabolic changes affecting these parameters were affected by mycobacteria. For control of acute TB, and compared with non-vaccinated controls, BCG showed a dominant T CD4⁺ response whereas BCGΔBCG1419c showed a dominant T CD8⁺/B lymphocyte response. Moreover, BCG maintained an increased response in lung cells via IFN-γ, TNF-α, and IL-4, while BCGΔBCG1419c increased IFN-γ but reduced IL-4 production. As for chronic TB, and compared with non-vaccinated controls, both BCG strains had a predominant presence of T CD4⁺ lymphocytes. In counterpart, BCGΔBCG1419c led to increased presence of dendritic cells and an increased production of IL-1 β. Overall, while BCG effectively reduced pneumonia in acute infection, it failed to reduce it in chronic infection, whereas we hypothesize that increased production of IL-1 β induced by BCGΔBCG1419c contributed to reduced pneumonia and alveolitis in chronic TB. Our results show that BCG and BCGΔBCG1419c protect T2D mice against TB via different participation of T and B lymphocytes, dendritic cells, and pro-inflammatory cytokines.

BCG as a Case Study for Precision Vaccine Development: Lessons From Vaccine Heterogeneity, Trained Immunity, and Immune Ontogeny

Vaccines have been traditionally developed with the presumption that they exert identical immunogenicity regardless of target population and that they provide protection solely against their target pathogen. However, it is increasingly appreciated that vaccines can have off-target effects and that vaccine immunogenicity can vary substantially with demographic factors such as age and sex. Bacille Calmette-Guérin (BCG), the live attenuated Mycobacterium bovis vaccine against tuberculosis (TB), represents a key example of these concepts. BCG vaccines are manufactured under different conditions across the globe generating divergent formulations. Epidemiologic studies have linked early life immunization with certain BCG formulations to an unanticipated reduction (∼50%) in all-cause mortality, especially in low birthweight males, greatly exceeding that attributable to TB prevention. This mortality benefit has been related to prevention of sepsis and respiratory infections suggesting that BCG induces "heterologous" protection against unrelated pathogens. Proposed mechanisms for heterologous protection include vaccine-induced immunometabolic shifts, epigenetic reprogramming of innate cell populations, and modulation of hematopoietic stem cell progenitors resulting in altered responses to subsequent stimuli, a phenomenon termed "trained immunity." In addition to genetic differences, licensed BCG formulations differ markedly in content of viable mycobacteria key for innate immune activation, potentially contributing to differences in the ability of these diverse formulations to induce TB-specific and heterologous protection. BCG immunomodulatory properties have also sparked interest in its potential use to prevent or alleviate autoimmune and inflammatory diseases, including type 1 diabetes mellitus and multiple sclerosis. BCG can also serve as a model: nanoparticle vaccine formulations incorporating Toll-like receptor 8 agonists can mimic some of BCG's innate immune activation, suggesting that aspects of BCG's effects can be induced with non-replicating stimuli. Overall, BCG represents a paradigm for precision vaccinology, lessons from which will help inform next generation vaccines.

Innate immune memory of tissue-resident macrophages and trained innate immunity: Re-vamping vaccine concept and strategies

In the past few years, our understanding of immunological memory has evolved remarkably due to a growing body of new knowledge in innate immune memory and immunity. Immunological memory now encompasses both innate and adaptive immune memory. The hypo-reactive and hyper-reactive types of innate immune memory lead to a suppressed and enhanced innate immune protective outcome, respectively. The latter is also named trained innate immunity (TII). The emerging information on innate immune memory has not only shed new light on the mechanisms of host defense but is also revolutionizing our long-held view of vaccination and vaccine strategies. Our current review will examine recent progress and knowledge gaps in innate immune memory with a focus on tissue-resident Mϕs, particularly lung Mϕs, and their relationship to local antimicrobial innate immunity. We will also discuss the impact of innate immune memory and TII on our understanding of vaccine concept and strategies and the significance of respiratory mucosal route of vaccination against respiratory pathogens.

Cording Mycobacterium tuberculosis Bacilli Have a Key Role in the Progression towards Active Tuberculosis, Which is Stopped by Previous Immune Response

Cording was the first virulence factor identified in Mycobacterium tuberculosis (Mtb). We aimed to ascertain its role in the induction of active tuberculosis (TB) in the mouse strain C3HeB/FeJ by testing the immunopathogenic capacity of the H37Rv strain. We have obtained two batches of the same strain by stopping their growth in Proskauer Beck liquid medium once the mid-log phase was reached, in the noncording Mtb (NCMtb) batch, and two days later in the cording Mtb (CMtb) batch, when cording could be detected by microscopic analysis. Mice were challenged with each batch intravenously and followed-up for 24 days. CMtb caused a significant increase in the bacillary load at an early stage post-challenge (day 17), when a granulomatous response started, generating exudative lesions characterized by neutrophilic infiltration, which promoted extracellular bacillary growth together with cording formation, as shown for the first time in vivo. In contrast, NCMtb experienced slight or no bacillary growth and lesions could barely be detected. Previous Bacillus Calmette-Guérin (BCG) vaccination or low dose aerosol (LDA) Mtb infection were able to delay the progression towards active TB after CMtb challenge. While BCG vaccination also reduced bacillary load when NCMtb was challenged, LDA did not, and its proliferative lesions experienced neutrophil infiltration. Analysis of lung cytokine and chemokine profiles points to their capacity to block the production of CXCL-1 and further amplification of IL-1β, IL-17 and neutrophilic extracellular trap formation, all of which are essential for TB progression. These data highlight the key role of cording formation in the induction of active TB.

The effect of adjuvants and delivery systems on Th1, Th2, Th17 and Treg cytokine responses in mice immunized with Mycobacterium tuberculosis-specific proteins

Tuberculosis (TB) is a major health problem of global concern. The control of this disease requires appropriate preventive measures, including vaccines. In TB, T helper (Th)1 cytokines provide protection whereas Th2 and T regulatory (Treg) cytokines contribute to the pathogenesis and Th17 cytokines play a role in both protection and pathogenesis. Previous studies with Mycobacterium tuberculosis-specific proteins have identified seven low molecular weight proteins, PE35, ESXA, ESXB, Rv2346c, Rv2347c, Rv3619c, and Rv3620c, as immunodominant antigens inducing Th1-cell responses in humans following natural infection with M. tuberculosis. The aim of this study was to characterize the cytokine responses induced in mice immunized with these proteins, using various adjuvants and delivery systems, i.e. chemical adjuvants (Alum and IFA), non-pathogenic mycobacteria (M. smegmatis and M. vaccae) and a DNA vaccine plasmid (pUMVC6). The immune responses were monitored by quantifying the marker cytokines secreted by Th1 (IFN-ɣ), Th2 (IL-5), Treg (IL-10), and Th17 (IL-17A) cells. DNA corresponding to pe35, esxa, esxb, rv2346c, rv2347c, rv3619c, and rv3620c genes were cloned into the expression vectors pGES-TH-1, pDE22 and pUMVC6 for expression in Escherichia coli, mycobacteria and eukaryotic cells, respectively. Mice were immunized with the recombinants using different adjuvants and delivery systems, and spleen cells were stimulated in vitro with peptides of immunizing proteins to investigate antigen-specific secretion of Th1 (IFN-ɣ), Th2 (IL-5), Treg (IL-10), and Th17 (IL-17A) cytokines. The results showed that spleen cells, from mice immunized with all antigens, secreted the protective Th1 cytokine IFN-ɣ, except ESXB, with one or more adjuvants and delivery systems. However, only Rv3619c consistently induced Th1-biased responses, without the secretion of significant concentrations of Th2, Th17 and Treg cytokines, with all adjuvants and delivery systems. Rv3619c also induced antigen-specific IgG antibodies in immunized mice.

ATP-binding cassette (ABC) import systems of Mycobacterium tuberculosis: target for drug and vaccine development

Nutrient procurement specifically from nutrient-limiting environment is essential for pathogenic bacteria to survive and/or persist within the host. Long-term survival or persistent infection is one of the main reasons for the overuse of antibiotics, and contributes to the development and spread of antibiotic resistance. Mycobacterium tuberculosis is known for long-term survival within the host, and develops multidrug resistance. Before and during infection, the pathogen encounters various harsh environmental conditions. To cope up with such nutrient-limiting conditions, it is crucial to uptake essential nutrients such as ions, sugars, amino acids, peptides, and metals, necessary for numerous vital biological activities. Among the various types of transporters, ATP-binding cassette (ABC) importers are essentially unique to bacteria, accessible as drug targets without penetrating the cytoplasmic membrane, and offer an ATP-dependent gateway into the cell by mimicking substrates of the importer and designing inhibitors against substrate-binding proteins, ABC importers endeavour for the development of successful drug candidates and antibiotics. Alternatively, the production of antibodies against substrate-binding proteins could lead to vaccine development. In this review, we will emphasize the role of M. tuberculosis ABC importers for survival and virulence within the host. Furthermore, we will elucidate their unique characteristics to discover emerging therapies to combat tuberculosis.

relA is Achilles' heel for mycobacterial pathogens as demonstrated with deletion mutants in Mycobacterium avium subsp. paratuberculosis and mycobacterium bovis bacillus Calmette-Guérin (BCG)

Studies with Mycobacterium avium subsp. paratuberculosis (Map) in cattle revealed deletion of relA, a global regulator gene, abrogated ability of the mutant to establish a persistent infection, attributed to development of an immune response that cleared infection. Analysis of the recall response demonstrated presence of CD8 cytotoxic T cells that kill intracellular bacteria. Replication of the primary response demonstrated the CTL response could be elicited with the ΔMap/relA mutant or the target of the immune response, a 35 kD membrane protein. Follow up comparative studies with Mycobacterium bovis bacillus Calmette-Guérin (BCG) and a BCG relA (ΔBCG/relA) deletion mutant revealed deletion of relA enhanced the CTL response compared to BCG. Analysis of the cytokine profile of cells proliferating in response to stimulation with BCG or BCG/relA showed increased expression of IFN-γ, TNF-α, and IL-17 by cells stimulated with ΔBCG/relA in comparison with BCG. The proliferative and CTL responses were markedly reduced in response to stimulation with heat killed BCG or ΔBCG/relA. Intracellular bacterial killing was mediated through the perforin, granzyme B (GnzB), and the granulysin pathway. The data indicate relA is the Achilles' heel for pathogenic mycobacteria and deletion may be key to improving efficacy of attenuated vaccines for mycobacterial pathogens.

Expression of ESAT-6 antigen from Mycobacterium tuberculosis in broccoli: An edible plant

Tuberculosis (TB) is one of the major infectious diseases caused by Mycobacterium tuberculosis. The development of an effective and economical vaccine for controlling TB is essential especially for developing countries. Edible plants can serve as biofactories to produce vaccine antigens. In this study, 6 kDa early secretory antigenic target (ESAT-6) of M. tuberculosis was expressed in Brassica oleracea var. italica via Agrobacterium-mediated transformation to facilitate oral delivery of antigen. ESAT-6 gene was cloned using Gateway® cloning strategy. Transformation and presence of transgene was confirmed through PCR. Expression level of transgene was calculated via quantitative real-time PCR (qRT-PCR) and the maximum integrated transgene number was two. Maximum amount of total soluble fraction of ESAT-6 was evaluated by immunoblotting, estimated to accumulate up to 0.5% of total soluble protein. The recombinant ESAT-6 protein was further purified and detected using silver staining and Western blotting. ESAT-6 protein induced humoral immune response in mice immunized orally and subcutaneously. The expression of M. tuberculosis antigen in edible plants could aid in the development of cost-effective and oral delivery of an antigen-based subunit vaccine against TB. To the best our knowledge, it is the first report of expression of a vaccine antigen in broccoli.

BCG revaccination boosts adaptive polyfunctional Th1/Th17 and innate effectors in IGRA+ and IGRA- Indian adults

BACKGROUNDBacille Calmette-Guérin (BCG) vaccine is protective against Tuberculosis (TB) in children, but its efficacy wanes with age. Consequently, determining if BCG revaccination augments anti-TB immunity in young adults in TB endemic regions is vital.METHODSTwo hundred healthy adults, BCG vaccinated at birth, were tested for their IFN-γ release assay (IGRA) status. Of these, 28 IGRA+ and 30 IGRA- were BCG revaccinated, and 24 IGRA+ and 23 IGRA- subjects served as unvaccinated controls. T and innate cell responses to mycobacterial antigens were analyzed by 14-color flow cytometry over 34 weeks.RESULTSIFN-γ and/or IL-2 Ag85A- and BCG-specific CD4+ and CD8+ T cell responses were boosted by revacciantion at 4 and 34 weeks, respectively, and were > 2-fold higher in IGRA+ compared with IGRA- vaccinees. Polyfunctional Ag85A, BCG, and mycobacterium tuberculosis (Mtb) latency Ag-specific (LTAg-specific) CD4+ T cells expressing up to 8 cytokines were also significantly enhanced in both IGRA+ and IGRA- vaccinees relative to unvaccinated controls, most markedly in IGRA+ vaccinees. A focused analysis of Th17 responses revealed expansion of Ag85A-, BCG-, and LTAg-specific total IL-17A+,IL-17F+,IL-22+, and IL-10+ CD4+ T cell effectors in both IGRA+ and IGRA- subjects. Also, innate IFN-γ+ NK/γδ/NKT cell responses were higher in both IGRA+ and IGRA- vaccinees compared with controls. This is the first evidence to our knowledge that BCG revaccination significantly boosts antimycobacterial Th1/Th17 responses in IGRA+ and IGRA- subjects.CONCLUSIONThese data show that BCG revaccination is immunogenic in IGRA- and IGRA+ subjects, implying that Mtb preinfection in IGRA+ subjects does not impact immunogenicity. This has implications for public health and vaccine development strategies.FUNDINGThis work was funded principally by DBT-NIH (BT/MB/Indo-US/HIPC/2013).

BCG-Induced Cross-Protection and Development of Trained Immunity: Implication for Vaccine Design

The Bacillus Calmette-Guérin (BCG) is a live attenuated tuberculosis vaccine that has the ability to induce non-specific cross-protection against pathogens that might be unrelated to the target disease. Vaccination with BCG reduces mortality in newborns and induces an improved innate immune response against microorganisms other than Mycobacterium tuberculosis, such as Candida albicans and Staphylococcus aureus. Innate immune cells, including monocytes and natural killer (NK) cells, contribute to this non-specific immune protection in a way that is independent of memory T or B cells. This phenomenon associated with a memory-like response in innate immune cells is known as "trained immunity." Epigenetic reprogramming through histone modification in the regulatory elements of particular genes has been reported as one of the mechanisms associated with the induction of trained immunity in both, humans and mice. Indeed, it has been shown that BCG vaccination induces changes in the methylation pattern of histones associated with specific genes in circulating monocytes leading to a "trained" state. Importantly, these modifications can lead to the expression and/or repression of genes that are related to increased protection against secondary infections after vaccination, with improved pathogen recognition and faster inflammatory responses. In this review, we discuss BCG-induced cross-protection and acquisition of trained immunity and potential heterologous effects of recombinant BCG vaccines.

Chloroplast-based inducible expression of ESAT-6 antigen for development of a plant-based vaccine against tuberculosis

Mycobacterium tuberculosis causes tuberculosis in humans. The major disease burden of tuberculosis lies in developing countries. Lack of an effective vaccine for adults is one of the major hurdles for controlling this deadly disease. In the present study, 6 kDa early secretory antigenic target (ESAT-6) of M. tuberculosis was inducibly expressed in chloroplasts of Nicotiana tabacum. The expression of ESAT-6 in chloroplasts was controlled by T7 promoter that was activated by nuclear-generated signal peptide. Tobacco plants, containing nuclear component, were transformed via biolistic bombardment with pEXP-T7-ESAT-6 obtained by Gateway® cloning. Transformation and homoplasmic status of transplastomic plants was confirmed by polymerase chain reaction and Southern blotting. Plants were induced for protein expression by spraying with 5% ethanol for 1 day, 3 days, 7 days and 10 days. ESAT-6 protein was detected by immunoblot analysis and maximum protein was obtained for 10 days induced plants that was estimated to accumulate up to 1.2% of total soluble fraction of protein. Transplastomic plants showed completely normal morphology. Transplastomic and untransformed plants became slightly chlorotic upon prolonged exposure to ethanol until 10 days. Taken together, this data could help in the development of an antigen-based subunit vaccine against tuberculosis.

Immunogenicity and Safety of the M72/AS01E Candidate Vaccine Against Tuberculosis: A Meta-Analysis

Background: Currently, there is no tuberculosis (TB) vaccine recommended for use in latent TB infections and healthy adults. M72/AS01_E is a new peptide vaccine currently under development, which may improve protection against TB disease. This vaccine has been investigated in several phase I/II clinical trials. We conducted a meta-analysis to clarify the immunogenicity and safety of the M72/AS01_E peptide vaccine.

Methods: We searched the PubMed, Embase, and Cochrane Library databases for published studies (until December 2018) investigating this candidate vaccine. A meta-analysis was performed using the standard methods and procedures established by the Cochrane Collaboration.

Results: Seven eligible studies—involving 4,590 participants—were selected. The analysis revealed a vaccine efficacy was 57.0%, significantly higher abundance of polyfunctional M72-specific CD4⁺ T cells [standardized mean difference (SMD) = 2.58] in the vaccine group vs. the control group, the highest seropositivity rate [relative risk (RR) = 74.87] at 1 month after the second dose of vaccination (Day 60), and sustained elevated anti-M72 IgG geometric mean concentration at study end (Day 210) (SWD = 4.94). Compared with the control, participants who received vaccination were at increased risk of local injection site redness [relative risk (RR) = 5.99], local swelling (RR = 7.57), malaise (RR = 3.01), and fatigue (RR = 3.17). However, they were not at increased risk of headache (RR = 1.57), myalgia (RR = 0.97), and pain (RR = 3.02).

Conclusion: The M72/AS01_E vaccine against TB is safe and effective. Although the vaccine is associated with a mild adverse reaction, it is promising for the prevention of TB in healthy adults.

Phylogenomic and epidemiological insights into two clinical Mycobacterium bovis BCG strains circulating in South Africa

BACKGROUND

Mycobacterium bovis BCG is a live, attenuated tuberculosis vaccine. While the vaccine protects infants from tuberculosis, complications including disseminated infections have been reported following vaccination. Genetically diverse BCG sub-strains now exist following continuous passaging of the original Pasteur strain for vaccine manufacture. This genetic diversity reportedly influences the severity of disseminated BCG infections and the efficacy of BCG immunization.

METHODS

M. bovis BCG was isolated from infants suspected of being infected with tuberculosis. The whole genome of the clinical isolates and BCG Moscow were sequenced using Illumina Miseq and the sequences were analysed using CLC Genomics Workbench 7.0, PhyResSE v1.0, and Parsnp.

RESULTS AND CONCLUSIONS

Genetic variations between the clinical strains and the reference BCG Copenhagen were identified. The clinical strains shared only one mutation in a secretion protein. Mutations were identified in various antibiotic resistance genes in the BCG isolates, which suggests their potential as multidrug-resistant (MDR) phenotypes. Phylogenetic analysis showed that the two isolates were distantly related, and the M1_S48 clinical isolate was closely related to M. bovis BCG Moscow. The phylogenomics results imply that two different BCG strains may be circulating in South Africa. However, it is difficult to associate the BCG vaccine strain administered and the BCG strain supplied with specific adverse events, as BCGiosis is under-reported. This study presents background genomic information for future surveillance and tracking of the distribution of BCGiosis-associated mycobacteria. It is also the first to report on the genomes of clinical BCG strains in Africa.

Proteomic Analysis of Antigen 60 Complex of M. bovis Bacillus Calmette-Guérin Reveals Presence of Extracellular Vesicle Proteins and Predicted Functional Interactions

Tuberculosis (TB) is ranked among the top 10 causes of death worldwide. New biomarker-based serodiagnostics and vaccines are unmet needs stalling disease control. Antigen 60 (A60) is a thermostable mycobacterial complex typically purified from Bacillus Calmette-Guérin (BCG) vaccine. A60 was historically evaluated for TB serodiagnostic and vaccine potential with variable findings. Despite containing immunogenic proteins, A60 has yet to be proteomically characterized. Here, commercial A60 was (1) trypsin-digested in-solution, analyzed by LC-MS/MS, searched against M. tuberculosis H37Rv and M. bovis BCG Uniprot databases; (2) analyzed using STRING to predict protein-protein interactions; and (3) probed with anti-TB monoclonal antibodies and patient immunoglobulin G (IgG) on Western blot to evaluate antigenicity. We detected 778 proteins in two A60 samples (440 proteins shared), including DnaK, LprG, LpqH, and GroEL1/2, reportedly present in mycobacterial extracellular vesicles (EV). Of these, 107 were also reported in EVs of M. tuberculosis, and 27 key proteins had significant protein-protein interaction, with clustering for chaperonins, ribosomal proteins, and proteins for ligand transport (LpqH and LprG). On Western blot, 7/8 TB and 1/8 non-TB sera samples had reactivity against 37-50 kDa proteins, while LpqH, GroEL2, and PstS1 were strongly detected. In conclusion, A60 comprises numerous proteins, including EV proteins, with predicted biological interactions, which may have implications on biomarker and vaccine development.

Mycobacterium tuberculosis Metabolism

Mycobacterium tuberculosis is the cause of tuberculosis (TB), a disease which continues to overwhelm health systems in endemic regions despite the existence of effective combination chemotherapy and the widespread use of a neonatal anti-TB vaccine. For a professional pathogen, M. tuberculosis retains a surprisingly large proportion of the metabolic repertoire found in nonpathogenic mycobacteria with very different lifestyles. Moreover, evidence that additional functions were acquired during the early evolution of the M. tuberculosis complex suggests the organism has adapted (and augmented) the metabolic pathways of its environmental ancestor to persistence and propagation within its obligate human host. A better understanding of M. tuberculosis pathogenicity, however, requires the elucidation of metabolic functions under disease-relevant conditions, a challenge complicated by limited knowledge of the microenvironments occupied and nutrients accessed by bacilli during host infection, as well as the reliance in experimental mycobacteriology on a restricted number of experimental models with variable relevance to clinical disease. Here, we consider M. tuberculosis metabolism within the framework of an intimate host-pathogen coevolution. Focusing on recent advances in our understanding of mycobacterial metabolic function, we highlight unusual adaptations or departures from the better-characterized model intracellular pathogens. We also discuss the impact of these mycobacterial "innovations" on the susceptibility of M. tuberculosis to existing and experimental anti-TB drugs, as well as strategies for targeting metabolic pathways. Finally, we offer some perspectives on the key gaps in the current knowledge of fundamental mycobacterial metabolism and the lessons which might be learned from other systems.

The Humoral Immune Response to BCG Vaccination

Bacillus Calmette Guérin (BCG) is the only currently available vaccine against tuberculosis (TB), but it confers incomplete and variable protection against pulmonary TB in humans and bovine TB (bTB) in cattle. Insights into the immune response induced by BCG offer an underexploited opportunity to gain knowledge that may inform the design of a more efficacious vaccine, which is urgently needed to control these major global epidemics. Humoral immunity in TB and bTB has been neglected, but recent studies supporting a role for antibodies in protection against TB has driven a growing interest in determining their relevance to vaccine development. In this manuscript we review what is known about the humoral immune response to BCG vaccination and re-vaccination across species, including evidence for the induction of specific B cells and antibodies; and how these may relate to protection from TB or bTB. We discuss potential explanations for often conflicting findings and consider how factors such as BCG strain, manufacturing methodology and route of administration influence the humoral response. As novel vaccination strategies include BCG prime-boost regimens, the literature regarding off-target immunomodulatory effects of BCG vaccination on non-specific humoral immunity is also reviewed. Overall, reported outcomes to date are inconsistent, but indicate that humoral responses are heterogeneous and may play different roles in different species, populations, or individual hosts. Further study is warranted to determine whether a new TB vaccine could benefit from the targeting of humoral as well as cell-mediated immunity.

TIPICO IX: report of the 9th interactive infectious disease workshop on infectious diseases and vaccines

The Ninth Interactive Infectious Disease workshop TIPICO was held on November 22–23, 2018, in Santiago de Compostela, Spain. This 2-day academic experience addressed current and topical issues in the field of infectious diseases and vaccination. Summary findings of the meeting include: cervical cancer elimination will be possible in the future, thanks to the implementation of global vaccination action plans in combination with appropriate screening interventions. The introduction of appropriate immunization programs is key to maintain the success of current effective vaccines such as those against meningococcal disease or rotavirus infection. Additionally, reduced dose schedules might improve the efficiency of some vaccines (i.e., PCV13). New vaccines to improve current preventive alternatives are under development (e.g., against tuberculosis or influenza virus), while others to protect against infectious diseases with no current available vaccines (e.g., enterovirus, parechovirus and flaviviruses) need to be developed. Vaccinomics will be fundamental in this process, while infectomics will allow the application of precision medicine. Further research is also required to understand the impact of heterologous vaccine effects. Finally, vaccination requires education at all levels (individuals, community, healthcare professionals) to ensure its success by helping to overcome major barriers such as vaccine hesitancy and false contraindications.

Transposon libraries identify novel Mycobacterium bovis BCG genes involved in the dynamic interactions required for BCG to persist during in vivo passage in cattle

BACKGROUND

BCG is the most widely used vaccine of all time and remains the only licensed vaccine for use against tuberculosis in humans. BCG also protects other species such as cattle against tuberculosis, but due to its incompatibility with current tuberculin testing regimens remains unlicensed. BCG's efficacy relates to its ability to persist in the host for weeks, months or even years after vaccination. It is unclear to what degree this ability to resist the host's immune system is maintained by a dynamic interaction between the vaccine strain and its host as is the case for pathogenic mycobacteria.

RESULTS

To investigate this question, we constructed transposon mutant libraries in both BCG Pasteur and BCG Danish strains and inoculated them into bovine lymph nodes. Cattle are well suited to such an assay, as they are naturally susceptible to tuberculosis and are one of the few animal species for which a BCG vaccination program has been proposed. After three weeks, the BCG were recovered and the input and output libraries compared to identify mutants with in vivo fitness defects. Less than 10% of the mutated genes were identified as affecting in vivo fitness, they included genes encoding known mycobacterial virulence functions such as mycobactin synthesis, sugar transport, reductive sulphate assimilation, PDIM synthesis and cholesterol metabolism. Many other attenuating genes had not previously been recognised as having a virulence phenotype. To test these genes, we generated and characterised three knockout mutants that were predicted by transposon mutagenesis to be attenuating in vivo: pyruvate carboxylase, a hypothetical protein (BCG_1063), and a putative cyclopropane-fatty-acyl-phospholipid synthase. The knockout strains survived as well as wild type during in vitro culture and in bovine macrophages, yet demonstrated marked attenuation during passage in bovine lymph nodes confirming that they were indeed involved in persistence of BCG in the host.

CONCLUSION

These data show that BCG is far from passive during its interaction with the host, rather it continues to employ its remaining virulence factors, to interact with the host's innate immune system to allow it to persist, a property that is important for its protective efficacy.

Cell Differentiation Degree as a Factor Determining the Role for Different T-Helper Populations in Tuberculosis Protection

Efficient tuberculosis (TB) control depends on early TB prediction and prevention. Solution to these tasks requires knowledge of TB protection correlates (TB CoPs), i.e., laboratory markers that are mechanistically involved in the protection and which allow to determine how well an individual is protected against TB or how efficient the candidate TB vaccine is. The search for TB CoPs has been largely focused on different T-helper populations, however, the data are controversial, and no reliable CoPs are still known. Here we discuss the role of different T-helper populations in TB protection focusing predominantly on Th17, “non-classical” Th1 (Th1^*) and “classical” Th1 (cTh1) populations. We analyze how these populations differ besides their effector activity and suggest the hypothesis that: (i) links the protective potential of Th17, Th1^*, and cTh1 to their differentiation degree and plasticity; (ii) implies different roles of these populations in response to vaccination, latent TB infection (LTBI), and active TB. One of the clinically relevant outcomes of this hypothesis is that over-stimulating T cells during vaccination and biasing T cell response toward the preferential generation of Th1 are not beneficial. The review sheds new light on the problem of TB CoPs and will help develop better strategies for TB control.

Nanomedicines for the Delivery of Biologics

A special symposium of the Academy of Pharmaceutical Sciences Nanomedicines Focus Group reviewed the current status of the use of nanomedicines for the delivery of biologics drugs. This meeting was particularly timely with the recent approval of the first siRNA-containing product Onpattro™ (patisiran), which is formulated as a lipid nanoparticle for intravenous infusion, and the increasing interest in the use of nanomedicines for the oral delivery of biologics. The challenges in delivering such molecules were discussed with specific emphasis on the delivery both across and into cells. The latest developments in Molecular Envelope Technology® (Nanomerics Ltd, London, UK), liposomal drug delivery (both from an academic and industrial perspective), opportunities offered by the endocytic pathway, delivery using genetically engineered viral vectors (PsiOxus Technologies Ltd, Abingdon, UK), Transint™ technology (Applied Molecular Transport Inc., South San Francisco, CA, USA), which has the potential to deliver a wide range of macromolecules, and AstraZeneca's initiatives in mRNA delivery were covered with a focus on their uses in difficult to treat diseases, including cancers. Preclinical data were presented for each of the technologies and where sufficiently advanced, plans for clinical studies as well as early clinical data. The meeting covered the work in progress in this exciting area and highlighted some key technologies to look out for in the future.

Specific Binding Peptides from Rv3632: A Strategy for Blocking Mycobacterium tuberculosis Entry to Target Cells?

Tuberculosis is an infectious disease caused by Mycobacterium tuberculosis (Mtb, i.e., the aetiological agent); the WHO has established this disease as high priority due to its ensuing mortality. Mtb uses a range of mechanisms for preventing its elimination by an infected host; new, viable alternatives for blocking the host-pathogen interaction are thus sought constantly. This article updates our laboratory's systematic search for antigens using bioinformatics tools to clarify the Mtb H37Rv Rv3632 protein's topology and location. This article reports a C-terminal region consisting of peptides 39255 and 39256 (81Thr-Arg114) having high specific binding regarding two infection-related cell lines (A549 and U937); they inhibited mycobacterial entry to U937 cells in a concentration-dependent manner. Rv3632 forms part of the mycobacterial cell envelope, formed by six linear synthetic peptides. Circular dichroism enabled determining the protein's secondary structure. It was also found that peptide 39254 (61Gly-Thr83) was a HABP for alveolar epithelial cells and inhibited mycobacteria entry to these cells regardless of concentration. Sera from active or latent tuberculosis patients did not recognise HABPs 39254 and 39256. These sequences represent a promising approach aiming at their ongoing modification and for including them when designing a multi-epitope, anti-tuberculosis vaccine.

BCG Vaccination Prevents Reactivation of Latent Lymphatic Murine Tuberculosis Independently of CD4+ T Cells

Tuberculosis (TB) is a major global public health problem causing significant mortality and morbidity. In addition to ~10.4 million cases of active TB annually, it is estimated that about two billion people are latently infected with Mycobacterium tuberculosis (Mtb), the causative agent of TB. Reactivation of latent Mtb infection is the leading cause of death in patients with immunodeficiency virus (HIV) infection. The low efficiency of the only licensed anti-TB vaccine, Bacille Calmette–Guérin (BCG) to reduce pulmonary TB in adults contributes to this problem. Here we investigated if vaccination with conventional BCG or the genetically modified experimental BCGΔBCG1419c strain can prevent reactivation of latent lymphatic TB in a mouse model of induced reactivation, following the depletion of CD4⁺ T cells, as it occurs in HIV⁺ individuals. Vaccination with conventional BCG or BCGΔBCG1419c prevented reactivation of Mtb from the infected lymph node and the systemic spread of Mtb to spleen and lung. Prevention of reactivation was independent of vaccination route and was accompanied by reduced levels of circulating inflammatory cytokines and the absence of lung pathology. Our results demonstrate that vaccine-induced CD4⁺ T cells are not essential to prevent reactivation of latent lymphatic murine TB, and highlight the need to better understand how non-CD4⁺ immune cell populations participate in protective immune responses to control latent TB.

Immunization of Vγ2Vδ2 T cells programs sustained effector memory responses that control tuberculosis in nonhuman primates

Despite the urgent need for a better tuberculosis (TB) vaccine, relevant protective mechanisms remain unknown. We previously defined protective phosphoantigen (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP)–specific Vγ2Vδ2 T cells as a unique subset in primates, and, here, we immunized them selectively for protection against TB. A single respiratory vaccination of macaques with attenuated HMBPP-producing Listeria monocytogenes (Lm ΔactA prfA*), but not an HMBPP-lacking ΔgcpE Listeria strain, expanded Vγ2Vδ2 T cells, elicited Th1-like Vγ2Vδ2 T cell responses, and reduced TB infection/pathology after moderate-dose TB challenge. Such protection correlated with rapid memory-like, Th1-like Vγ2Vδ2 T cell responses, the presence of tissue-resident Vγ2Vδ2 T effectors coproducing IFN-γ/perforin and inhibiting intracellular Mycobacterium tuberculosis growth, and enhanced CD4⁺/CD8⁺ T cell responses. These findings establish a concept incorporating immunization of human Vγ2Vδ2 T cells for TB vaccine development.

Tuberculosis (TB) remains a leading killer among infectious diseases, and a better TB vaccine is urgently needed. The critical components and mechanisms of vaccine-induced protection against Mycobacterium tuberculosis (Mtb) remain incompletely defined. Our previous studies demonstrate that Vγ2Vδ2 T cells specific for (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP) phosphoantigen are unique in primates as multifunctional effectors of immune protection against TB infection. Here, we selectively immunized Vγ2Vδ2 T cells and assessed the effect on infection in a rhesus TB model. A single respiratory vaccination of macaques with an HMBPP-producing attenuated Listeria monocytogenes (Lm ΔactA prfA*) caused prolonged expansion of HMBPP-specific Vγ2Vδ2 T cells in circulating and pulmonary compartments. This did not occur in animals similarly immunized with an Lm ΔgcpE strain, which did not produce HMBPP. Lm ΔactA prfA* vaccination elicited increases in Th1-like Vγ2Vδ2 T cells in the airway, and induced containment of TB infection after pulmonary challenge. The selective immunization of Vγ2Vδ2 T cells reduced lung pathology and mycobacterial dissemination to extrapulmonary organs. Vaccine effects coincided with the fast-acting memory-like response of Th1-like Vγ2Vδ2 T cells and tissue-resident Vγ2Vδ2 effector T cells that produced both IFN-γ and perforin and inhibited intracellular Mtb growth. Furthermore, selective immunization of Vγ2Vδ2 T cells enabled CD4⁺ and CD8⁺ T cells to mount earlier pulmonary Th1 responses to TB challenge. Our findings show that selective immunization of Vγ2Vδ2 T cells can elicit fast-acting and durable memory-like responses that amplify responses of other T cell subsets, and provide an approach to creating more effective TB vaccines.

Safety and Immunogenicity of Early Bacillus Calmette-Guérin Vaccination in Infants Who Are Preterm and/or Have Low Birth Weights: A Systematic Review and Meta-analysis

IMPORTANCE

Bacillus Calmette-Guérin (BCG) vaccination is commonly delayed in infants who are preterm and have low birth weights (LBW) despite the association of early vaccination with better vaccination coverage and potentially nonspecific benefits for survival.

OBJECTIVE

To determine the safety, immunogenicity, and protective efficacy against tuberculosis (TB) of BCG vaccination given at or before 7 days after birth vs vaccination more than 7 days after birth among infants who are preterm and/or had LBW.

DATA SOURCES

Searches of Medline, Embase, and Global Health databases were conducted from inception until August 8, 2017.

STUDY SELECTION

Clinical trials, cohort studies, and case-control studies that included infants who were preterm and/or had LBW and reported safety, mortality, immunogenicity, proxies of vaccine take, and/or efficacy against TB.

DATA EXTRACTION AND SYNTHESIS

Two authors independently extracted data and assessed the quality of the studies. Data extracted included demographics, covariates, sources of bias, and effect estimates. Meta-analysis was performed using a random-effects model.

MAIN OUTCOMES AND MEASURES

Safety, mortality, immunogenicity, or other proxies of vaccine take, such as tuberculin skin test (TST) conversion and efficacy against tuberculosis.

RESULTS

Forty studies were included in a qualitative synthesis; infants who were preterm (born at 26-37 weeks' gestational age) and/or had LBW (0.69-2.5 kg at birth) were included. The BCG vaccine was administered at or before 7 days to 10 568 clinically stable infants who were preterm and/or had LBW; vaccination was administered to 4310 infants at varying times between 8 days and 12 months after birth. Twenty-one studies reporting safety found no cases of BCG-associated death or systemic disease in 8243 infants. Four studies reported no increase in all-cause mortality for infants who had LBW and who received early BCG vaccination compared with infants who had LBW with later vaccination or BCG-vaccinated infants of normal birth weight. Four studies reported lymphadenitis incidence; combined, these reported 0% to 2.9% incidence of vaccination within 7 days and 0% to 4.2% of vaccination after 7 days. Meta-analysis of 7 studies revealed no differences between early and delayed BCG vaccination for scar formation (n = 515; relative risk [RR], 1.01 [95% CI, 0.95-1.07]) or TST conversion (n = 397; RR, 0.97 [95% CI, 0.84-1.13]). Published data were insufficient to assess immunogenicity or protective efficacy against TB disease.

CONCLUSIONS AND RELEVANCE

Early BCG vaccination in healthy infants who are preterm and/or had LBW has a similar safety profile, reactogenicity, and TST conversion rate as delayed vaccination. Based on current evidence, early BCG vaccination in stable infants who are preterm and/or have LBW to optimize uptake is warranted.

How Far Are we Away From an Improved Vaccine For Tuberculosis? Current Efforts and Future Prospects

Tuberculosis still is a major public health problem worldwide, and vaccines may play a major role in its eradication. However, despite 20 years of intensive research, we still do not have a better vaccine than the Bacille Calmette-Guérin vaccine, which has been used since 1921 but exhibits only limited efficacy in the field. This effort has not, however, been entirely in vain as our understanding of TB vaccinology has been substantially expanded and there are currently 17 vaccine candidates in clinical development and several more in preclinical trials. This manuscript reviews the most important recent advances, concerns raised and future prospects in the TB vaccinology field.

The Wonder Years: What Can Primary School Children Teach Us About Immunity to Mycobacterium tuberculosis?

In high burden settings, the risk of infection with Mycobacterium tuberculosis increases throughout childhood due to cumulative exposure. However, the risk of progressing from tuberculosis (TB) infection to disease varies by age. Young children (<5 years) have high risk of disease progression following infection. The risk falls in primary school children (5 to <10 years), but rises again during puberty. TB disease phenotype also varies by age: generally, young children have intrathoracic lymph node disease or disseminated disease, while adolescents (10 to <20 years) have adult-type pulmonary disease. TB risk also exhibits a gender difference: compared to adolescent boys, adolescent girls have an earlier rise in disease progression risk and higher TB incidence until early adulthood. Understanding why primary school children, during what we term the "Wonder Years," have low TB risk has implications for vaccine development, therapeutic interventions, and diagnostics. To understand why this group is at low risk, we need a better comprehension of why younger children and adolescents have higher risks, and why risk varies by gender. Immunological response to M. tuberculosis is central to these issues. Host response at key stages in the immunopathological interaction with M. tuberculosis influences risk and disease phenotype. Cell numbers and function change dramatically with age and sexual maturation. Young children have poorly functioning innate cells and a Th2 skew. During the "Wonder Years," there is a lymphocyte predominance and a Th1 skew. During puberty, neutrophils become more central to host response, and CD4+ T cells increase in number. Sex hormones (dehydroepiandrosterone, adiponectin, leptin, oestradiol, progesterone, and testosterone) profoundly affect immunity. Compared to girls, boys have a stronger Th1 profile and increased numbers of CD8+ T cells and NK cells. Girls are more Th2-skewed and elicit more enhanced inflammatory responses. Non-immunological factors (including exposure intensity, behavior, and co-infections) may impact disease. However, given the consistent patterns seen across time and geography, these factors likely are less central. Strategies to protect children and adolescents from TB may need to differ by age and sex. Further work is required to better understand the contribution of age and sex to M. tuberculosis immunity.