Recombinant BCG Overexpressing phoP-phoR Confers Enhanced Protection against Tuberculosis

Recombinant BCG vaccine expressing multistage antigens of Mycobacterium tuberculosis provides long-term immunity against tuberculosis in BALB/c mice

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) persistently kills nearly 1.5 million lives per year in the world, whereas the only licensed TB vaccine BCG exhibits unsatisfactory efficacy in adults. Taking BCG as a vehicle to express Mtb antigens is a promising way to enhance its efficacy against Mtb infection. In this study, the immune efficacy of recombination BCG (rBCG-ECD003) expressing specific antigens ESAT-6, CFP-10, and nDnaK was evaluated at different time points after immunizing BALB/c mice. The results revealed that rBCG-ECD003 induced multiple Th1 cytokine secretion including IFN-γ, TNF-α, IL-2, and IL-12 when compared to the parental BCG. Under the action of PPD or ECD003, rBCG-ECD003 immunization resulted in a significant increase in the proportion of IL-2+ and IFN-γ+IL-2+ CD4+T cells. Importantly, rBCG-ECD003 induced a stronger long-term humoral immune response without compromising the safety of the parental BCG vaccine. By means of the protective efficacy assay in vitro, rBCG-ECD003 showed a greater capacity to inhibit Mtb growth in the long term. Collectively, these features of rBCG-ECD003 indicate long-term protection and the promising effect of controlling Mtb infection.

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

Vaccination is an excellent approach to stimulating the host immune response and reducing human morbidity and mortality against microbial infections, such as tuberculosis (TB). Bacillus Calmette-Guerin (BCG) is the most widely administered vaccine in the world and the only vaccine approved by the World Health Organization (WHO) to protect against TB. Although BCG confers "protective" immunity in children against the progression of Mycobacterium tuberculosis (Mtb) infection into active TB, this vaccine is ineffective in protecting adults with active TB manifestations, such as multiple-, extensive-, and total-drug-resistant (MDR/XDR/TDR) cases and the co-existence of TB with immune-compromising health conditions, such as HIV infection or diabetes. Moreover, BCG can cause disease in individuals with HIV infection or other immune compromises. Due to these limitations of BCG, novel strategies are urgently needed to improve global TB control measures. Since live vaccines elicit a broader immune response and do not require an adjuvant, developing recombinant BCG (rBCG) vaccine candidates have received significant attention as a potential replacement for the currently approved BCG vaccine for TB prevention. In this report, we aim to present the latest findings and outstanding questions that we consider worth investigating regarding novel mycobacteria-based live attenuated TB vaccine candidates. We also specifically discuss the important features of two key animal models, mice and rabbits, that are relevant to TB vaccine testing. Our review emphasizes that the development of vaccines that block the reactivation of latent Mtb infection (LTBI) into active TB would have a significant impact in reducing the spread and transmission of Mtb. The results and ideas discussed here are only based on reports from the last five years to keep the focus on recent developments.

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.

Recent developments in systems biology and genetic engineering toward design of vaccines for TB

Tuberculosis (TB) is one of the most prevalent diseases worldwide. The currently available Bacillus Calmette-Guérin vaccine is not sufficient in protecting against pulmonary TB. Although many vaccines have been evaluated in clinical trials, but none of them yet has proven to be more successful. Thus, new strategies are urgently needed to design more effective TB vaccines. The emergence of new technologies will undoubtedly accelerate the process of vaccine development. This review summarizes the potential and validated applications of emerging technologies, including: systems biology (genomics, proteomics, and transcriptomics), genetic engineering, and other computational tools to discover and develop novel vaccines against TB. It also discussed that the significant implementation of these approaches will play crucial roles in the development of novel vaccines to cure and control TB.

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

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

After 100 Years of BCG Immunization against Tuberculosis, What Is New and Still Outstanding for This Vaccine?

In 2021, most of the world was reasonably still concerned about the COVID-19 pandemic, how cases were up and down in different countries, how the vaccination campaigns were ongoing, and most people were familiar with the speed with which vaccines against SARS-Co-V2 were developed, analyzed, and started to be applied in an attempt to curb the pandemic. Because of this, it may have somehow passed relatively inadvertently for people outside of the field that the vaccine used to control tuberculosis (TB), Mycobacterium bovis Bacille Calmette-Guérin (BCG), was first applied to humans a century ago. Over these years, BCG has been the vaccine applied to most human beings in the world, despite its known lack of efficacy to fully prevent respiratory TB. Several strategies have been employed in the last 20 years to produce a novel vaccine that would replace, or boost, immunity and protection elicited by BCG. In this work, to avoid potential redundancies with recently published reviews, I only aim to present my current thoughts about some of the latest findings and outstanding questions that I consider worth investigating to help develop a replacement or modified BCG in order to successfully fight TB, based on BCG itself.

Thirty years of recombinant BCG: new trends for a centenary vaccine

Introduction: Global perception of the potential for Bacille Calmette-Guérin (BCG), and consequently recombinant BCG (rBCG), in a variety of prophylactic and therapeutic applications has been increasing. A century of information on BCG, and three decades of experience with rBCG, has generated solid knowledge in this field.Area covered: Here, we review the current state of knowledge of BCG and rBCG development. Molecular tools have facilitated the expression of a variety of molecules in BCG, with the aim of improving its efficacy as a tuberculosis vaccine, generating polyvalent vaccines against other pathogens, including viruses, bacteria, and parasites, and developing immunotherapy approaches against noninvasive bladder cancer. BCG's recently appraised heterologous effects and prospects for expanding its application to other diseases are also addressed.Expert opinion: There are high expectations for new tuberculosis vaccines currently undergoing advanced clinical trials, which could change the prospects of the field. Systems biology could reveal effective biomarkers of protection, which would greatly support vaccine development. The development of appropriate large-scale production processes would further support implementation of new vaccines and rBCG products. The next few years should consolidate the broader applications of BCG and produce insights into improvements using the recombinant BCG technology.

Mast cells modulate early responses to Mycobacterium bovis Bacillus Calmette-Guerin by phagocytosis and formation of extracellular traps

The early interactions between the vaccine Mycobacterium bovis Bacillus Calmette Guerin (BCG) and host peripheral innate immune cells like Mast cells (MCs) may pave the way for generating appropriate protective innate and adaptive immune responses. Mice on administration of BCG by intratracheal instillation showed a massive increase in MC numbers in the infected lung. In vitro co-culture of BCG and rodent Rat Basophilic Leukaemia (RBL-2H3) MCs led to significant killing of BCG. RBL-2H3 MCs were able to phagocytose BCG, take up BCG-derived antigens by macropinocytosis, generate Reactive Oxygen Species (ROS) and degranulate. Further, a few MCs died and released MC extracellular traps (MCETs) having DNA, histones and tryptase to trap BCG. This study highlights the multi-pronged effector responses of MCs on encountering BCG. These responses or their evasion may lead to success or failure of BCG vaccine to provide long term immunity to infections.

Early innate and adaptive immune perturbations determine long-term severity of chronic virus and Mycobacterium tuberculosis coinfection

Chronic viral infections increase severity of Mycobacterium tuberculosis (Mtb) coinfection. Here, we examined how chronic viral infections alter the pulmonary microenvironment to foster coinfection and worsen disease severity. We developed a coordinated system of chronic virus and Mtb infection that induced central clinical manifestations of coinfection, including increased Mtb burden, extra-pulmonary dissemination, and heightened mortality. These disease states were not due to chronic virus-induced immunosuppression or exhaustion; rather, increased amounts of the cytokine TNFα initially arrested pulmonary Mtb growth, impeding dendritic cell mediated antigen transportation to the lymph node and subverting immune-surveillance, allowing bacterial sanctuary. The cryptic Mtb replication delayed CD4 T cell priming, redirecting T helper (Th) 1 toward Th17 differentiation and increasing pulmonary neutrophilia, which diminished long-term survival. Temporally restoring CD4 T cell induction overcame these diverse disease sequelae to enhance Mtb control. Thus, Mtb co-opts TNFα from the chronic inflammatory environment to subvert immune-surveillance, avert early immune function, and foster long-term coinfection.

Vaccines Against Tuberculosis: Problems and Prospects (Review)

Despite the efforts of the global medical and scientific community, tuberculosis remains the leading cause of death from infectious diseases. The expectation of success associated with the development of new anti-TB drugs was not justified, and the attention of researchers was largely drawn to the creation of new mycobacterial strains for vaccination against tuberculosis. The proposed review contains current information on the existing vaccine strains and the development of new, genetically engineered strains for the prevention of tuberculosis and the prevention and treatment of other diseases. The review includes relevant information on the correlation between BCG vaccination and the frequency and severity of COVID-19 infection.

Preclinical Progress of Subunit and Live Attenuated Mycobacterium tuberculosis Vaccines: A Review following the First in Human Efficacy Trial

Tuberculosis (TB) is the global leading cause of death from an infectious agent with approximately 10 million new cases of TB and 1.45 million deaths in 2018. Bacille Calmette-Guérin (BCG) remains the only approved vaccine for Mycobacterium tuberculosis (M. tb, causative agent of TB), however clinical studies have shown BCG has variable effectiveness ranging from 0–80% in adults. With 1.7 billion people latently infected, it is becoming clear that vaccine regimens aimed at both post-exposure and pre-exposure to M. tb will be crucial to end the TB epidemic. The two main strategies to improve or replace BCG are subunit and live attenuated vaccines. However, following the failure of the MVA85A phase IIb trial in 2013, more varied and innovative approaches are being developed. These include recombinant BCG strains, genetically attenuated M. tb and naturally attenuated mycobacteria strains, novel methods of immunogenic antigen discovery including for hypervirulent M. tb strains, improved antigen recognition and delivery strategies, and broader selection of viral vectors. This article reviews preclinical vaccine work in the last 5 years with focus on those tested against M. tb challenge in relevant animal models.

Cloning, Expression and Purification of Espc, Espb and Espc/Espb Proteins of Mycobacterium tuberculosis ESX-1 Secretion System

BACKGROUND

It is estimated that one third of the world's population is infected with Mycobacterium tuberculosis (Mtb), the causative agent of Tuberculosis (TB). The BCG vaccine is widely used to fight against TB; however, many question its ability to provide complete protection from Mtb. Recently, the "Region of Difference 1" (RD1) set of genes were shown to be involved in the pathogenesis of Mtb. Downstream of RD1 transcription region, two proteins are encoded, known as EspB and EspC, which were found to contribute to Mtb virulence.In this study these two proteins are targeted as potential vaccine candidates against TB.

METHODS

The EspB and EspC Mtb genes were codon-optimized for expression and synthesis in Escherichia coli (E. coli). The amplicons were cloned into a pET21a expression vector and transformed into E. coli BL21(DE3). The expression and purity of the expressed proteins (i.e. rEspC, rEspB and rEspC/EspB) were confirmed by SDS-PAGE and Western blotting. Moreover, BALB/c mice were immunized against Mtb using the recombinant proteins. Finally, the mice sera were analyzed via Western blotting.

RESULTS

EspC, EspB, and EspC/EspB fusion genes were cloned and expressed in E. coli. Both SDS-PAGE and Western blots confirmed the presence and successful purification of the desired proteins. Moreover, antisera produced against the purified recombinant proteins reacted with Mtb proteins.

CONCLUSION

rEspC, rEspB, and rEspC/EspB could be expressed and purified using an E. coli expression system. The recombinant proteins induced the production of antibodies in BALB/c mice that reacted with Mtb proteins.

Mycobacterial virulence: impact on immunogenicity and vaccine research

The borderline between virulence and efficacy in live attenuated vaccine strains is often blurred and this is also the case for the Bacillus Calmette–Guérin (BCG), the only currently licensed anti-tuberculosis vaccine used on a large, global scale, which was obtained almost 100 years ago. While BCG is more than 99% identical at the genome level to Mycobacterium tuberculosis, the causative pathogen of human tuberculosis, some important differences in virulence factors cause naturally irreversible attenuation and safety of this vaccine in the immunocompetent host. Some of these virulence factors are involved in persistence capacities of the vaccine strains and also represent strong immunogens, responsible for inducing different host signaling pathways, which have to be taken into consideration for the development of revised and new vaccine strains. Here we discuss a number of selected mycobacterial features in relation to their biological functions and potential impact on virulence and vaccine efficacy.

Vaccination of guinea pigs with BCGΔBCG1419c transiently reduces hematogenous spread of M. tuberculosis to the spleen

The guinea pig has proven to be a reliable model for testing vaccine candidates against tuberculosis (TB) because of its capacity to produce human-like disease associated to primary TB, thus providing a more stringent test of the ability of a vaccine to prevent disease and deaths. Here, the BCGΔBCG1419c vaccine candidate, which previously has been shown to provide protection in mice, was tested in a guinea pig model. We found that this vaccine candidate was as effective as parental BCG in reducing M. tuberculosis H37Rv replication in lungs, and significantly reducing hematogenous spread to spleen at 60 days post-infection in comparison with BCG. Moreover, lung histopathological examination revealed comparable protection between the parental and mutant BCG strains, with some differences in prevention of primary lesions or necrosis at a single time point post-infection in a strain-dependent manner. Our results show that the BCGΔBCG1419c vaccine candidate is as effective as BCG in reducing M. tuberculosis H37Rv replication in lungs and reducing lung pathology, as well as significantly improving control of its dissemination to spleens up to 60 days post-infection.