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Review

A review of the BCG vaccine and other approaches toward tuberculosis eradication

, , , , & ORCID Icon
Pages 2454-2470 | Received 19 Nov 2020, Accepted 29 Jan 2021, Published online: 26 Mar 2021

ABSTRACT

Despite aggressive eradication efforts, Tuberculosis (TB) remains a global health burden, one that disproportionally affects poorer, less developed nations. The only vaccine approved for TB, the Bacillus of Calmette and Guérin (BCG) vaccine remains controversial because it’s stated efficacy has been cited as anywhere from 0 to 80%. Nevertheless, there have been exciting discoveries about the mechanism of action of the BCG vaccine that suggests it has a role in immunization schedules today. We review recent data suggesting the vaccine imparts protection against both tuberculosis and non-tuberculosis pathogens via a newly discovered immune system called trained immunity. BCG’s efficacy also appears to be tied to its affect on granulocytes at the epigenetic and hematopoietic stem cell levels, which we discuss in this article at length. We also write about how the different strains of the BCG vaccine elicit different immune responses, suggesting that certain BCG strains are more immunogenic than others. Finally, our review delves into how the current vaccine is being reformulated to be more efficacious, and track the development of the next generation vaccines against TB.

Introduction

Although nearly eradicated in developed countries, tuberculosis (TB), the disease caused by the bacteria Mycobacterium tuberculosis (M. tb), is estimated to have infected over a quarter of the world’s population and remains the global leading cause of death by a single pathogen.Citation1 Despite the existence of a standardized antibiotic regimen against TB, issues with access to medicine, the rise of Multidrug Resistance TB (MDR-TB) and Extreme Multidrug-resistant TB (XMDR-TB) continue to make TB a global public health burden.Citation1 In areas where TB burden is low, disease prevention is mainly controlled with proper hygiene and screening, vaccination being neither required nor recommended. It is only in areas with a high TB burden where the BCG vaccine is given regularly. The discrepancy in recommendations is due in part to large inconsistencies in the efficacy of the vaccine, which ranges from 0% to 80% effective in preventing for the prevention of TB.Citation2

This review paper gives a brief overview of the pathophysiology of TB and the historical background of the development of the BCG vaccine. We also discuss a possible mechanism of action of the vaccine, which involves its ability to attenuate a lesser-known immune system called trained immunity. The vaccine appears to also invoke epigenetic reprogramming in hematopoietic stem cells. Finally, we discuss the work being done to change the route of administration of the vaccine, and briefly introduce the numerous approaches toward either augmenting the efficacy of the current vaccine or develop a new vaccine to supersede BCG.

Pathophysiology of tuberculosis

TB is an airborne infection spread by aerosolized particles harboring tubercle bacilli, the etiological agent of the disease.Citation3 Tubercle bacilli most commonly infects the airways and lungs of exposed individuals.Citation3,Citation4 Following inoculation in the new host, tubercle bacilli are phagocytosed primarily by macrophages and dendritic cells which aggregate into structures called granulomas.Citation3 M. tb, the primary causative agent of TB disease, persists within immune cells by evading multiple cellular pathways and organelles, particularly with the endocytic and autophagic pathways. The ability to disrupt autophagy allows intracellular persistence of M. tb.Citation3 Patient immunocompetency is crucial to the development of TB disease as immunocompromised groups have more severe disease manifestations.Citation4

Current BCG immunization protocol

The BCG vaccine is the only vaccine currently recommended for the prevention of TB. Vaccination recommendations vary between countries, with endemicity of TB often being the basis for issuing recommendations.Citation5–7 Universal recommendation of the BCG vaccine is commonplace in most countries.Citation5,Citation6 These countries either recommend single dose administration, or utilize schedules encompassing multiple doses.Citation1,Citation5,Citation7 The World Health Organization (WHO) recommends vaccinating neonates residing in high-incidence TB and/or Leprosy settings with a single dose of the BCG vaccine at birth.Citation1 Furthermore, neonates residing in low-incidence settings and at high risk of contracting TB disease and/or Leprosy should also be considered for vaccination.Citation6 High-risk neonates, defined as those with close contact to currently or previously infected individuals. Repeat BCG vaccination is not currently recommended by the WHO as evidence arguing its efficacy is insufficient.Citation4 Despite its wide range of purported efficacy in preventing primary TB, with many studies predicting efficacy anywhere between 0 and 80%, the BCG vaccine continues to be a mandatory vaccine for much of the world.Citation4,Citation6 The vaccine’s strong safety profile, measured as one major side effect from vaccine administration per one million doses administered to immunocompetent individuals, may also be a reason for its continued use in TB endemic countries.Citation4

Vaccine efficacy may be dependent on vaccine strain

One hypothesis for the wide efficacy range is the genotypic differences within the BCG vaccine. The vaccine, was first produced by passing a pathogenic Mycobacterium bovis (M. bovis) strain over 230 times throughout a period of 10 years, which eventually led to its attenuation.Citation2 Once the vaccine’s efficacy was established, Calmette and Guerin distributed their strain globally in 1924 to regions that requested their newfound vaccine. Eventually, geographical isolation permitted independent mutations among samples, promoting genotypic variation between once identical strains.Citation8

More recent advancements in genomic sequencing laid light to these genotypic changes, termed regions of differentiation (RD). From these studies emerged at least 16 different RDs in the world’s supply of BCG vaccines.Citation8 Further studies into the strains found an additional 14 different sub-strains, each named after the region in which they were distributed to.Citation8 Six of the most researched sub-strains are BCG Tokyo (BCG Japan), BCG TICE, BCG Danish, BCG Pasteur, BCG China, and BCG Prague. BCG strain distribution tends to be regional, and international vaccine distribution is mainly controlled by UNICEF, who receives its BCG vaccine from four suppliers.Citation8 These four suppliers produce three vaccine strains: BCG Denmark, BCG Russia, and BCG Japan.Citation1,Citation8

Early research identifying variation in efficacy between individual strains is sparse, conflicting, and in many cases, poorly designed: either demographics were uncontrolled, studies were not randomized, nonpopular strains were used, or endpoints/immune markers were not equivalently analyzed.Citation9–11 Nevertheless there is some preliminary data that suggests different strains produce differing immunological responses.Citation8

A randomized trial in Australia on 288 infants assigned to one of three treatment groups (BCG Denmark, BCG Japan, BCG Russia) showed infants vaccinated with BCG Denmark and BCG Japan had a larger polyclonal CD4 T cell response accompanied by a greater increase in associated cytokines when compared to infants vaccinated with BCG Russia.Citation8 A more current study found some association between administration of BCG Beijing with higher levels of TB drug resistance later on in life.Citation11 A very interesting case out of Orizaba, Mexico the BCG strain given affects the immune response. Peripheral Blood Mononuclear Cells (PBMCs) were harvested from neonates who had received one of three different BCG strains, which were then infected in vitro by M. tb.Citation12 Subsequent analysis found different BCG strains elicited very different cytokine expression profiles.Citation12 Most importantly, they found that vaccination with BCG-Brazil or BCG-Denmark induced cytokines involved in the adaptive immune system, while BCG-Japan strain-induced proinflammatory response and memory formation.Citation12 The relationship between BCG strain and immune response was also seen in a study conducted in Nigeria and South Africa, where CD4 T cell responses following BCG vaccination were more robust and durable following inoculation with BCG-Denmark over BCG-Russia or BCG-Bulgaria.Citation13 Finally, variation in immune response between vaccine strains was also noted among murine model studies,Citation14 and dosage/route of administration also seems to affect the immune response.Citation15 Although vaccine efficacy cannot be extrapolated from these findings, it is safe to say that different strains induce different immunological response profiles. Further research into the immunological response to the BCG vaccine has led to another theory of how the BCG vaccine might protect against TB known as trained immunity.

BCG vaccine response may trigger “trained immunity” in the innate immune system

Human immunity is classically parsed into two distinct systems, the more nonspecific but broad spectrum coverage innate system and the highly specific and memory driven adaptive system, which is also termed cell-mediated immunity and humoral immunity.Citation16 Classical teachings in immunology suggests that innate immunity, though highly effective, produces no “memory” after an attack and instead relies on chemokine gradients and physiologic changes to clear infections.Citation16 Recent discoveries by Dr Netea Mihai suggest a memory component in the innate immune system, which she has coined “trained immunity”.Citation17 The immunological background of trained immunity is based on the resistance mechanisms of plants. First postulated by Kenneth Chester in 1933 and later coined “systemic acquired resistance” (SAR), plants inoculated with a specific pathogen gained immunity to a number of pathogens, including those which the plant was never exposed to.Citation17

While the exact mechanisms of trained immunity remain unknown, early data suggests that cross protection may trigger “heightened” alertness in the innate immune system .Citation18 Garly et. al discovered that children with a BCG scar and a positive tuberculin reaction residing in high mortality areas of Guinea Bissau had overall lower mortality than children with no history of receiving the BCG vaccine. No similar trend was observed in children who had received previous diphtheria or tetanus immunization.Citation18 Roth et. al discovered that children who received the BCG vaccine had lower mortality rates than their non-BCG vaccinated peers against malaria, further suggesting that BCG vaccination confers some form of protection against non-tuberculous diseases.Citation19 Conferred protection spans mycobacterial pathogens like M. leprae,Citation20 viruses, like Respiratory Syncytial Virus (RSV),Citation21 intestinal nematodes,Citation22 and yeast, like Candida.Citation18 Further in vitro studies revealed human adult monocytes receiving the BCG vaccine had increased IFN-y production two weeks and three months following S aureus and C albicans inoculation.Citation23 More importantly, these augmentations to the immune system were intact one year after initial vaccination.Citation23 A persistent increase in pro-inflammatory cytokine production post in vitro LPS-mediated challenge remained. Additionally, increased concentrations of pattern recognition receptors (PRRs), specifically Toll-Like Receptor 4 (TLR4), TLR2, and C type lectins on monocytes, were also observed.Citation23

This idea of using the BCG vaccine as a broad-spectrum immunization was first tested in the elderly. The ACTIVATE (a randomized clinical trial for enhanced trained immune responses through BCG vaccination to prevent infection of the elderly) trial concluded its phase 3 randomized control trial in Greece in 2019 after administering either the BCG vaccine or a placebo in 202 patients on the last day of hospitalization.Citation24 As this population is very susceptible to infection, efficacy of the vaccination was measured via time to first infection between those receiving BCG against placebo, and blood samples were drawn in 57 patients (31 placebo and 26 BCG vaccinated) to assess cytokine levels and PBMC activation. Overall, BCG vaccinated individuals had a significantly increased “time to first infection time “over the placebo cohort – 16 weeks vs 11 weeks .Citation24 In addition, analysis of the PBMCs showed enhanced cytokine response to potential pathogens, specifically IL-6 and TNF-alpha.

Finally, using the yellow fever vaccine (YFV) as a model for an in vivo viral infection, BCG vaccination was shown to provide cross immunization against non-tuberculosis infections.Citation25 YFV is a live-attenuated viral vaccine, and YFV viremia peaks on the fifth day following vaccination.Citation26 Analysis of YFV concentrations in subjects who were administered a BCG vaccine 1 month prior to a YFV vaccine found lower concentrations of YFV in samples, as well as a lower circulating concentration of proinflammatory cytokines.Citation25 Notably, ex vivo infection of PBMCs gathered from the YFV and BCG vaccinated subjected with C. albicans showed higher levels of IL-1b expression and subsequent lower YFV viremia concentrations. IL-1b has been shown to be an important marker of trained immunity activation,Citation27 suggesting that BCG vaccination offers some sort of cross immune protection against non-tuberculosis infections.Citation25

Activation of natural killer cells might influence immune response to BCG vaccine

Another emerging hypothesis on the mechanism of trained immunity focuses on the actions of Natural Killer (NK) cells.Citation28 As part of the innate immune system, these should not harbor memory. Recent studies, however, have shown that murine and human NK cells augment IFN-y release upon reinfection.Citation27,Citation29 NK cells promote phagolysosome fusion within antigen-presenting cells (APCs) infected by M. tb, thus increasing M. tb killing.Citation30 According to Dhiman et. al, this is accomplished by the release of IL-22, a cytokine also released by memory CD4 + T cells in response to infections.Citation30 IL-22 was thought to trigger the release of antimicrobial peptides via direct induction.Citation30,Citation31 Experiments performed by Dhiman showed that the release of IL-22 by CD4 T cells caused intracellular mycobacterial growth arrest, thus supporting previous predictions.Citation30

NK cells may also induce the production of proinflammatory cytokines in response to unrelated pathogens following periods of 2 weeks and 3-months post BCG vaccination.Citation29 In a series of animal and human trials, Kleinnijenhuis et. al demonstrated that proinflammatory markers such as IFN-y and IL1 in humans increased post BCG vaccinationCitation23,Citation27,Citation29,Citation32 following an in vitro challenge of blood samples against Candida albicans and Staphylococcus aureus.Citation29 A similar increase in proinflammatory markers was seen among mice vaccinated with BCG followed by infection with C. albicans.Citation29 The importance of the NK cell response in BCG vaccine-induced cross protection against unrelated pathogens was further studied in mice with severe immunodeficiency (SCID).Citation32 SCID mice vaccinated with BCG prior to challenge with lethal candida had a 100% survival rate compared to the 30% survival rate seen in control mice.Citation29 The importance of NK cells in BCG-induced immunity was discovered when the same test was administered among NOD/SCID/IL2Ry (NSG) mice.Citation29 These mice not only lacked the B and T cell activation seen in SCID mice, but also lacked functional NK cells.Citation23 Following intravenous candida infection, all normal mice vaccinated with BCG survived, but the survival rate for NSG mice fell to about 70% despite receiving the vaccine. This suggested that NK cells have a crucial role in cross protection, and that BCG vaccination was necessary to induce cross protection.Citation23

The BCG vaccine and its epigenetic effects

The upregulation of PRRs seen after BCG vaccination also seems to be mediated by epigenetics.Citation23 Expression of PRRs like TLR4 and MR on monocytes were elevated in BCG vaccinated subjects when compared to unvaccinated subjects,Citation23 remaining so even one year post-vaccination.Citation23 Therefore, investigations into how a more reactive immune response to M. tb infections is activated have led to findings that suggest epigenetic programming is involved.

When BCG was used as a replacement for mycobacterial infection in mice, researchers discovered an increase in IL-15 production from phagocytes infected with M. bovis, the mycobacterial strain of the BCG vaccine.Citation33 IL-15 has been shown to stimulate NK cell production of IFN-y.Citation33 Thus, its release in the face of mycobacterial challenge is of great interest. IL-15 production at the mRNA and protein levels was detected in mice following in vitro BCG inoculation,Citation33 noteworthy support of BCG’s ability to affect immunity at the epigenetic level. Furthermore, levels of IFN-y in serum were significantly higher in mice with upregulated Il-15 expression than at baseline.Citation33

Further research into the composition of BCG vaccinated vs. unvaccinated monocytes showed differences in key receptors.Citation32 Monocytes from humans who were vaccine-naïve showed significant increase in TLR4 expression following BCG vaccinatio .Citation32 Alongside CD14 and CD11b expression, TLR4 expression remained elevated 3 months post immunization.Citation32 This suggests that BCG vaccination caused some form of monocyte “training”, via one or several signaling pathways. Kleinnijenhuis, et al. inhibited receptors on monocytes exposed to BCG in vitro, specifically TLR2, TLR4, and NOD2.Citation32 Successful education was determined by proinflammatory cytokine expression levels following training and subsequent exposure to a non-mycobacterial challenge.Citation32 Of the three receptors, only monocytes from NOD2 deficient patients failed to mount a noticeable cytokine response to the challenge,Citation32 suggesting that monocyte education is an epigenetic process that is influenced by the NOD2 pathway.

These experiments strongly suggest BCG vaccination’s ability to incite epigenetic reprogramming of monocytes via changes in the expression of certain receptors.Citation27,Citation32,Citation33 A more recent paper suggests that epigenetic modification affects hematopoietic stem cell (HSC) differentiation in the bone marrow,Citation34 leading to the development of monocytes specifically programmed to recognize M. tb. Compared to B and T cells, monocytes and macrophages have very short lifespans,Citation34 therefore, hypotheses suggest that any memory component the vaccine imparts begins at the stem cell level.Citation32,Citation34 Kaufman et. al administered BCG-TICE via IV into mice and found the attenuated strain in bone marrowCitation34 where it remained detectable for up to 7 months post vaccination.Citation34 This persistence of the vaccine in close proximity to HSCs, supported the idea that BCG may cause HSC expansion. Indeed, after tracking bone marrow (BM) expansion via the HSC progenitor lineage LKS+ population in both BCG vaccinated and non-vaccinated mice, it was only seen in the vaccinated group.Citation34 Transcriptomic data from this experiment showed BCG immunized HSCs favored myeloid lineage lymphocyte proliferation, upregulation of IFN-dependent gene expression, and increased production of “trained” monocytes/macrophages which were more effective in producing antimycobacterial immunity via elevated expression of IFN-y, TNF-α, and IL-10.Citation34 These effects were established by the different histone modifications seen between BCG primed and non-primed monocytes,Citation34 specifically H3K27 acetylation and H3K4 trimethylation.Citation32,Citation34 These findings were noted prior to subsequent M. tb challenge, further suggesting that BCG’s efficacy as a vaccine might begin via epigenetic modifications. Notably, H3K27 acetylation was also found in PMBCs studied in the aforementioned ACTIVATE trial, though the authors conceded that their sample size was too small to draw a direct correlation between their findings and any further implication of epigenetic changes.Citation24

The aforementioned study on YFV viremia also showed epigenetic changes that attenuated specific proinflammatory pathways following vaccination.Citation25 Monocytes that had been primed with BCG had enhanced IL-8 and IL-1b expression following YFV introduction, both in cytokine and mRNA concentrations.Citation25 Interestingly, these expression levels remained low if the monocytes were also treated with a histone methyltransferase inhibitor, suggesting the expression is correlated to histone/epigenetic modifications.Citation25 The epigenetic changes evident in the murine model were later confirmed to occur in humans in vivo. After administering the BCG vaccine in 15 healthy but BCG naïve individuals, Cirovic, et. al analyzed blood count, PBMCs, immune activation markers, and bone marrow aspirates immediately following vaccination, then 14- and 90-days post vaccination.Citation35 While there were no changes in the number of mature myeloid or myeloid progenitor populations in either the peripheral blood or bone marrow, there was evidence of transcriptional and epigenetic changes as long as 90 days post vaccination.Citation35 Transcriptome analysis completed on the BM aspirates and PBMCs revealed increased upregulation of genes associated with myeloid and granulocyte activation pathways, with additional Gene Ontology Enrichment Analysis (GOEA) of the enriched pathways finding genes associated with neutrophil activation (such as those from the SERPINA family) and transcription factor (TF) activity being affected the most.Citation35 Furthermore, the transcriptomic changes in the epigenome of CD14+ macrophages in BCG vaccinated individuals were different compared to the nonvaccinated population.Citation35 These upregulated pathways were consistent with the same pathways found in HSCs, suggesting that the epigenetic changes caused by vaccination was imprinted into the progenitor cell line and passed into the succeeding individual cells.

Different routes of BCG vaccination

There has also been a considerable push to reformulate the current BCG vaccine, which is administered intradermally (ID), into an oral vaccine.Citation36 Oral administration is cheaper, requires limited medical skill to administer, easier to distribute, and is a familiar route to most people. Direct mucosal exposure to the vaccine is considered highly immunogenicCitation37 but formulating a vaccine into a form that can withstand the degrading properties of mucosa, especially the stomach, has limited its use.Citation36

One possible means around this problem is to coat the dry powder form of the vaccine in Eudragit copolymers.Citation38 Already used in enteric coating formulations of ibuprofen and other oral medications, this coating is acid-resistant and protects against early degradation of the drug.Citation38 From a materials science perspective, this study was a success in creating a modern day oral tablet form of this vaccine, but the authors found that the immense pressure needed to compact the BCG powder to a digestible size lead to decreased efficacy via death of the live attenuated bacteria that make the vaccine.Citation38 Future oral BCG vaccines therefore need to take into consideration not only the size of an oral tablet, but also the number of viable colonies that might exist per administration.

Oral administration of the vaccine is also being meticulously studied in animal sciences. European badgers (meles meles) are a major reservoir host for bovine tuberculosis, a TB-like illness that endangers cattle herds.Citation39 Today, bovine TB control is focused on vaccinating badgers with BCG via an intramuscular formulary (BadgerBCG),Citation40 as the culprit is a pathogenic strain of M. bovis.Citation39 As this effort is costly, dangerous, and not sustainable,Citation41 considerable effort has gone into formulating a sustainable oral form of the BCG vaccineCitation40 . BCG vaccine in the oral form is formulated with badger bait and left in the wild, with the idea that eventually, a large enough population will be inoculated to maintain herd immunity.Citation39 Notably, initiatives to mass inoculate wild badger populations have run into a myriad of problems, chief among them producing enough of the vaccine to be viable in an oral formulary.Citation41 While some of this quantity issue has been resolved with a new method of culturing the vaccine stain in bioreactors,Citation41 the more pressing problem arises in the fact that the oral form of BCG is most effective when taken up in the oral mucosa compared to the ileal mucosa.Citation41 From these animal studies, a viable human oral BCG vaccine could be created using a bioreactor to create enough viable colonies to survive a pill mold, then instructing recipients to allow the tablet to dissolve in their mouths to allow for oral mucosa uptake of the vaccine. However, such a method has yet to be tested, and more studies need to be done on both the production and administration side before moving forward. Fortunately, other routes of administration are currently being explored today with considerably more success.

An aerosolized formulation of the BCG vaccine is also being studied for as an improved delivery mechanism. Murine experiments have shown that aerosolized BCG elicits a stronger CD4 and CD8 T cell response to M. tb infection following vaccination, especially in lung vasculature.Citation37,Citation42 Mice were then challenged with M. bovis, and 8 weeks later were sacrificed, after which the amount of bacterial infection in various organs were quantified.Citation42 Notably, the M. bovis burden in the lungs was significantly reduced in mice who had received the aerosolized vaccine, while there was no reduction in bacterial burden in those that received the ID formulation.Citation42 Unfortunately, histological analysis of the lungs showed a stronger granulomatous inflammation reaction in mice who received BCG via aerosol versus the traditional route, suggesting there may have been more damage incurred in the lungs when BCG is aerosolized.Citation42 This result, if found to be true in subsequent experiments, would warrant further research into the safety of an aerosolized BCG vaccine.

Of all the available routes of administration, the intravenous (IV) route has elicited the strongest immune response.Citation43 When BCG was given IV compared to oral or ID administration into Macaques Monkeys, the IV formulation promoted a five-fold increase in total cells, especially T cells, in bronchoalveolar lavage (BAL) samples.Citation43 IV administration also elicited a 100-fold increase from the ID response in cytokine concentrations classically associated with TB infection (IFNγ, IL-2, TNF, and IL-17), and these levels remained elevated for longer than compared to ID administration.Citation43 Titer levels of M. tb specific IgG, IgA, and IgM also peaked higher and longer following IV administration compared to ID, suggesting that the immune response elicited may be more effective in combating TB.Citation43 While IV administration of BCG may seem attractive, its efficacy is limited to infrastructure issues, as it requires even more medical knowledge and healthcare professional experience than ID or oral administration. IV bags are more cumbersome to store and ship, and patients may be turned off by the idea of receiving a drip. Larger needles also mean higher risk of complications, so further work must be done to quantify how much more efficacious IV administration is over the current ID formulary before placing the necessary investments into IV vaccinations.

Finally, an even more novel approach to vaccine administration was tested in 2017, when the non-reconstituted vaccine was directly loaded into the hollow tips of a dissolvable microneedle array (MNA).Citation44 Tested on mice, the MNA was first pressed through the epidermis, where the sharp tips of the MNAs dissolved to release the vaccine into the epidermis and dermis.Citation44 Initial results showed limited site infection and evidence of cytokine production and T cell activation resembling post-BCG inoculation. This method has multiple advantages over the current route of administration. It does not require reconstitution, decreasing error, and need for skilled practitioners. It can be stored like dry powder, increasing shelf life .Citation44 More studies need to be done to test vaccine efficacy and affordability, but the technique is certainly promising.

The future of tuberculosis vaccination – development of a novel vaccine

Given the wide range of reported efficacy of the BCG vaccine, considerable research has also gone into developing the next generation of TB preventative vaccinations. Going beyond BCG reformulation, there appear to be three different approaches to vaccine development: development of an entirely new TB vaccine, creation of a novel recombinant vaccine derived from the existing BCG vaccine, and development of a booster vaccination to reinforce an existing BCG vaccination. The three approaches will now be discussed. A summary of the next generation vaccine candidates is listed in .

Table 1. Summary of current anti-TB vaccine candidates according to tuberculosis vaccine initiative

Method 1 – development of a new TB vaccine

The first approach involves the advent of a novel vaccine via the exploitation of various mycobacterial species, viral vectors, or the construction of fusion proteins ().

A novel TB vaccine based on a different mycobacterial species

Mycobacterium indicus pranii (M. pranii)Citation124 is a nonpathogenic atypical mycobacterium historically exploited for its efficacy against leprotic infections.Citation125 However, it shares highly antigenic forms of the Proline-Glutamate/Proline-Proline-Glutamate (PE/PPE) family of proteins with M. tb, thus suggesting efficacy in granting immunity against M. tb.Citation126 Animal models have demonstrated the safety and preventative effects of heat-killed M. pranii.Citation45,Citation127 In fact, dynamic Th1 responses with greater secretion of IL-12 and IFN-y cytokines in concomitance with the influx of CD4+ and CD8 + T cells in the lungs were observed in animals subcutaneously injected with heat-killed M. pranii.Citation45,Citation127 Furthermore, the apoptotic process and autophagy of infected macrophages was significantly accelerated; thereby, facilitating antigen presentation in the M. pranii -vaccinated group .Citation128 As a result, the M. pranii -vaccinated group portrayed markedly reduced lung pathology and bacterial burden as well as enhanced survivability.Citation45 Interestingly, M. pranii can be administered via the mucosal route, inducing more powerful Th1 immune responses, increased localization of CD4+ and CD8 + T cells in the lungs, activation and maturation of dendritic cells (DCs), and enhancing migration of bone marrow-derived dendritic cells (BMDCs) via upregulation of CCR7.Citation45,Citation129,Citation130 Further studies were conducted to explore M. pranii’s immunotherapeutic role, suggesting enhanced bacterial clearance and improved lung pathology among guinea pig modelsCitation131. Finally, Sharman et al demonstrated the efficacy of intra-dermal injections of M. pranii in conversion of sputum culture in patients with advanced pulmonary TB.Citation46

Another mycobacterium species that has been exploited for therapeutic purposes is Mycobacterium vaccae (M. vaccae).Citation47,Citation132 In numerous studies, M. vaccae has consistently demonstrated its efficacy against M. tb, possibly by inducing a Th1-biased response while suppressing Th2.Citation47,Citation48 In subsequent human trials, M. vaccae failed to provide protective benefits as a single dose regimen, Citation49,Citation50 but three and five-dose regimens of M. vaccae were well-tolerated with minimal adverse reactions and conferred protection against M. tb among healthyCitation51 and HIV-infected subjects.Citation52,Citation53 Notably, PPD skin test conversion and alteration of HIV viral load were not observed in either regimen.Citation51–53 M. vaccae vaccines are available in either injectable or oral form (). The injectable form was investigated as a single therapeutic vaccine agent with protective capacity against pulmonary TB in mice.Citation133 Nevertheless, it is frequently used in conjunction with immunotherapy in human trials, substantially enhancing TB immunotherapy with 68% clearance of sputum smear compared to 23.1% in placebo.Citation134 Therefore, M. vaccae is an anti-TB vaccine currently in phase III of clinical trials which has produced phenomenal results.

A novel TB vaccine based on insertion of an antigenic protein into a viral vector

Besides attenuating similar pathogens to elicit an immune response, considerable effort has been made to utilize a viral vector in a new vaccine. The rhesus macaque Cytomegalovirus/TB vaccine (RhMCV/Tb) contains vectors that express nine different M. tb proteinsCitation54 (). Among the nine proteins, antigen-85A (Ag85A) was the most immunogenic, capable of eliciting and maintaining high-frequency T cell responses, especially the effector memory phenotype CD8+ and CD4 + T cells.Citation54 Furthermore, the Ag85A-specific T cell response produced both TNF-α and IFN- γ cytokines, which led to a more robust and longer-lasting immune response compared to one generated by the traditional BCG vaccine.Citation54 The overall disease and bacterial burden were also significantly lower in the RhCMV/TB-vaccinated group when compared to the BCG-vaccinated and control group .Citation54 Intriguingly, the objective data also suggest that BCG-induced inflammation suppressed several protective genes, namely MMP8, CTSG, and CD52, and offset the protective innate immune responses induced by RhCMV/TB alone, thereby curtailing the immune response in RhCMV/TB regimen preceded by BCG vaccination .Citation54 Therefore, RhCMV/TB vaccination alone suffices in mounting a robust immune response and conferring immunity against M. tb.

Like the RhCMV/TB vaccine, ChadOx1/PPE15 is a vaccine comprised a chimpanzee adenovirus expressing a mycobacterial antigen-encoding vector.Citation55,Citation135,Citation136 Among the expressing antigens, PPE15 was most immunogenic, thus, its presence on ChadOx1 affords significant protective immunity which manifests in reduced M. tb bacterial load.Citation55 However, immunity granted by the ChadOx1/PPE15 vaccine depends on the administration route. Intranasal administration elicited differentiation of lung parenchymal naive CD4+ and CD8 + T cells into the protective CXCR3+ KLRG1- phenotype, while intramuscular administration induced the CX3CR1+ KLRG1+ phenotype, which is predominantly found in blood vessels and incapable of migrating to infected lung tissue.Citation55 Notably, administration of the ChadOx1/PPE15 vaccine to mice already primed with BCG vaccine elicited a greater immune response than in mice given only BCG, as measured by a larger concentration of CD4+ cells post vaccination.Citation55 Conversely, a prominent CD8 + T cell response was observed in ChadOx1/PPE15-vaccinated mice without prior BCG vaccination.Citation55 Nevertheless, both vaccination regimens were able to provide superior protection compared to their respective control group.

Finally, subunit vaccines represent the third class of vaccines that might supplement BCG vaccination (). This vaccination class isolates immunogenic antigens from bacteria, viruses, or fungi then fuses them to a nonimmunogenic adjuvant. In TB research, the most promising subunit vaccines include AEC/BC02, H1/IC31, M72/AS01E, and RUTI.

A novel TB vaccine based on construction of a fusion protein

A novel vaccine constructed via the fusion of M. tb-specific antigens Ag85B and ESAT-6/CFP-10 (AEC), and adjuvanted by BCG CpG and aluminum salt (BC02), the AEC/BC02 vaccine was first introduced and proven effective in reducing the bacterial load in guinea pigs by Chen et al..Citation56,Citation57 Additionally, Lu et al. uncovered the dose-dependent relationship between AEC/BC02 vaccination and the induction of a highly antigen-specific IFN-y response.Citation57 Interestingly, the AEC/BC02 vaccine was inferior to the BCG vaccine in terms of prevention; however, it substantially reduced bacterial burden and gross pathology in latent infectionCitation57 .

Another notable subunit vaccine is H1/IC31, comprised of fusion proteins ESAT6 and Ag85B, formulated in the IC31 adjuvant system which is composed of a leucine-rich peptide and oligodeoxynucleotide known as ODN1a ().Citation58 Studies revealed a two-dose regimen of H1/IC31 vaccine was safe in human adults irrespective of their BCG status, prior M. tb infection,Citation59,Citation60 or HIV status.Citation61 These findings are in concordance with the data from a recent phase II trial, in which a two-dose regimen of 15 µg H1-IC31 vaccine optimally evoked vaccine-specific durable polyfunctional CD4 + T cells in healthy M. tb-infected and M. tb-uninfected adolescents.Citation62

Similarly, M72/AS01E is a subunit vaccine comprised a fusion of mycobacterial antigens M. tb32A and M. tb39A, formulated with the AS01 adjuvant system ().Citation137 Many studies described the clinical safety profile of the vaccine and its long-lasting polyfunctional CD4 + T cells expressing IFN- γ, IL-2, and TNF-α among BCG-vaccinated infants,Citation63 as well as healthy HIV-infectedCitation64 and M. tb-infected adults.Citation65 M72/AS01E has been shown to render 54% protection against disease activation in M. tb-infected adults.Citation66 Furthermore, Kumarasamy et al. observed a greater vaccine-induced seroconversion rate with a steep increase of seroconversion upon administration of a second dose, thereby permitting optimal resistance against M. tb.Citation138

In contrast with the aforementioned subunit vaccines, which are preventative vaccines, RUTI has been studied for its therapeutic efficacy against TB. RUTI is a poly-antigenic liposomal vaccine comprised antigens corresponding to latency, expressed by M. tb under stressful conditions.Citation139 RUTI has been shown to reduce bacterial burden and macrophage infiltration in granulomas, promote strong IFN-y secretion during Th1 immune responses in murine models, and produce a balanced Th1/Th2 response in addition to M. tb antigen-specific IgG antibodies.Citation67–70 These preclinical trials suggest that RUTI can successfully induce a well-balanced immune response via promotion of protective cellular immune responses and prevention of excessive inflammation. In human trials, a double-blind, randomized, controlled phase I study has concluded the tolerability and immunogenicity of RUTI in healthy adults.Citation71 Similarly, a randomized, double-blind, phase II trial demonstrated the safety profile and conferred immunity among adults with latent TB treated with a 1-month isoniazid regimen.Citation72 Additionally, RUTI vaccine did not impair CD4+ counts and HIV viral loads, thus, the course of HIV progression in HIV-positive subjects remained unaltered.Citation72

Method 2 – development of a novel recombinant vaccine derived from an existing BCG strain

Growing evidence supports the efficacy of genetically modified parental BCG strains known as recombinant BCG vaccines. Currently, there are four recombinant BCG vaccines under investigation to replace the parental BCG strain ().

The first of these vaccines is BCG-Zmp1, a vaccine still in its preclinical phase.Citation73 The BCG-Zmp1 vaccine is an attenuated M. bovis BCG vaccine with a knock-out mutation of the zmp1 gene, which encodes for the zinc metalloprotease Zmp1.Citation73 Johansen et al. discovered that mice immunized with zmp1-deficient BCG strain could mount an intense immune response through the proliferation of antigen-specific T-cells and increased secretion of cytokines, particularly IFN- γ, when compared to mice vaccinated with wild-type BCG.Citation73 It is worth mentioning that enhancement in the BCG-Zmp1 vaccine’s immunogenicity did not come at the expense of diminished persistency or heightened pathology of M. bovis.Citation73 Likewise, a study conducted on guinea pig models ascertained the vaccine’s safety and efficacy compared to BCG-vaccinated and non-vaccinated control groups, as measured via bacterial load in the lungs and spleen.Citation74 Moreover, survival time was substantially extended among immunocompromised mice vaccinated with BCG-Zmp1 than with BCG alone.Citation74 Therefore, the BCG-Zmp1 vaccine confers superior protection against M. tb due to its high immunogenicity and improved safety profile when compared to traditional BCG vaccination in murine models.

The second vaccine candidate in preclinical trials is SapM:TnBCG, which contains a SapM gene deletion from the parental M. bovis BCG strain ().Citation140 SapM gene encodes secreted acid phosphatase, which primarily interrupts host macrophage maturation and lysosome-phagosome fusion, thus playing a critical role in M. tb’s pathogenesis.Citation75 Compared to parental BCG, mice vaccinated with SapM:TnBCG exhibit a more robust Th1 immune response with a decline in bacterial load and increase in long-term survival.Citation75 Interestingly, while autophagy, maturation, and lysosome-phagosome fusion were not significantly varied between the two strains, a greater degree of DC migration and activation in the lymph nodes was observed among SapM:TnBCG-vaccinated mice.Citation75

The third preclinical vaccine candidate is CysVac2, a recombinant BCG vaccine expressing a fusion protein containing the antigen Ag85B and CysD, a protein expressed during persistent infection with M. tb ().Citation76 CysVac2 vaccination in mice elicited a significant influx of innate immune cells, particularly neutrophils, macrophages, and DCs, at the injection site. Ag85B-specific CD4 + T cell numbers were increased in the draining lymph node and the spleen.Citation77 Furthermore, a greater number of IFN- γ secreting cells were seen in CysVac2 vaccinated mice when compared to BCG-vaccinated and unvaccinated control groups. Thus, CysVac2 vaccine conferred greater resistance against M. tb infection while significantly reducing pulmonary bacterial load.Citation77 Boosting previously BCG-vaccinated mice with CysVac2 revealed a steady reduction in bacterial load compared to both the unvaccinated group and BCG-group boosted only with an adjuvant.Citation77 This phenomenon is thought to be the result of increased CysD-specific CD4 + T cell numbers, which secrete IFN-y and TN-α in response to the expression of CysD during late-stage infection. The CysVac2-prime and boost regimen confer sustainable protective immunity both prior to and after M. tb exposure.Citation77

Lastly, VPM1002 is a recombinant BCG vaccine in which the listeriolysin O encoding gene (hly) of Listeria monocytogenes replaces the urease C gene in BCG ().Citation141 Hly gene expression in BCG facilitates cytosolic release of antigens and mycobacterial DNA along with consequent activation of autophagy, antigen presentation, immune system activation, and apoptosis.Citation142 The safety profile of VPM1002 was comparable to BCG in animal models including both SCID and healthy mice, guinea pigs, and newborn rabbits.Citation79 In fact, the VPM1002 strain is less virulent and never disseminates into the lungs in VPM1002-vaccinated mice.Citation81 Moreover, VPM1002 vaccination conferred remarkable protective efficacy with significant Th1 response and bacterial load reduction compared to the BCG control group.Citation80–83 In a phase I trial, both single-dose and three-dose regimens of VPM1002 were well-tolerated, stimulating marked quantities of polyfunctional T cells co-expressing TNF-α, IFN- γ, and IL-2 against M. tb.Citation141 Similarly, a phase II trial concluded the comparable safety and efficacy of VPM1002 to BCG in newborns.Citation84 Since VPM1002 is also effective in clearing M. tb among M. tb-exposed mice,Citation83 a phase III trial of post-exposure vaccination with VPM1002 is currently underway in India.

Method 3 – development of a BCG vaccine augmenting booster vaccine

The concept of BCG revaccination as a booster in BCG-primed populations has been investigated over the past decades with conflicting results. One study demonstrated that BCG revaccination increased the magnitude of the immune response with robust multifunctional BCG-specific CD4 + T cells; however, this did not alter the response rate of CD4 + T cells .Citation85 Likewise, Nemes et al. concluded that BCG revaccination confers 45.4% efficacy against M. tb infection.Citation86 Conversely, two large-scale randomized trials revealed no additional benefits of BCG revaccination against TB.Citation87,Citation88 These incongruent findings may be due to the geographical variation and mutation of BCG strains, leading to differential responses and efficacies. Nonetheless, priming with BCG produced mild to moderate injection site reactions which were temporary and resolved without any sequelae among adolescents with initial BCG-administration at birth.Citation85,Citation86 More recent attempts to boost initial vaccination have led to the development of novel booster vaccines derived from either a viral vector, fusion protein, or new bacterial species ().

Adenovirus type 5 (Ad5), owing to its inherent property of evoking a dynamic immune response, has been used as a vector to express mycobacterial antigen Ag85A in efforts to control M. tb infection. Compelling evidence has demonstrated superior effectiveness of the BCG-prime Ad5Ag85A-boost regimen against TB in mice,Citation89 cattle,Citation89 and goat compared to BCG alone.Citation90 Of note, animals who received the heterologous prime-boost regimen consistently showed attenuated bacterial burden as well as attenuated lung and lymph node lesions.Citation89,Citation90,Citation143 Furthermore, the frequency of Ag85A-specific CD4 + T cells was significantly increased, hence conferring a greater degree of protection against TB in the bovine model.Citation91 Interestingly, immune responses resulting from Ad5Ag85A vaccination are administration route-dependent (). In the murine model, the intramuscular route induced robust Ag85A-specific T-cell responses in the spleen and lung interstitial with little to no protection against pulmonary M. tb.Citation92 Conversely, the intranasal route elicited more significant T cell responses in the lungs, thereby promoting better protection following pulmonary challengeCitation92

Ad5-CEAB is another recombinant adenovirus vector expressing M. tb antigens (). In the BCG-prime Ad5-CEAB-boost regimen, the antigen-specific T cell responses in mice were significantly potentiated with an elevation of the anti-mycobacterial cytokines IFN-γ, TNF-α, and IL-2 when compared to BCG alone.Citation93 Hence, it may be promising in providing resistance against M. tb in BCG-vaccinated group.

Like the aforementioned vaccine, the Ad35-TBS vaccine (AERAS-402), which is a recombinant adenovirus 35 vector expressing a different set of M. tb antigens, elicited strong CD8+ and CD4 + T-cell responses in a dose-dependent manner among murine models.Citation94 Furthermore, intramuscular Ad35-TBS produced more efficient and robust T-cell responses than intranasal immunization ().Citation95 Nonetheless, both vaccination routes led to improvements in lung histology when compared to non-vaccinated mice.Citation95 Furthermore, Abel et al. revealed the promising results of AERAS-402 vaccination in QuantiFERON Gold (QFT) negative adults through induction of multifunctional CD4+ and CD8 + T cells.Citation144 Following BCG priming, the AERAS-402 vaccine greatly increased the number of multifunctional CD4 + T cells producing IFN- γ, TNF-α, and IL-2 along with the number of multifunctional CD8 + T cells producing IFN- γ, perforin, and CD107a.Citation95 Collectively, the immune profile generated by heterologous BCG-prime AREAS-402-boosting confers optimal immunity against TB in human adults when compared to AREAS-402 vaccinated adults alone.Citation95

GaMtbvac is a sophisticated vaccine comprised Ag85A and ESAT6-CFP10 fused with a dextran-binding domain fixated on dextran along with an adjuvant system containing a DEAE-dextran core and the TLR9 agonist, CpG oligodeoxynucleotides ().Citation96 GaMtbvac portrays powerful immunogenicity and can generate high antigen-specific antibody titers and IFN- γ. GaMtbvac -vaccinated mice were found to effectively control the disease with significantly lower bacterial loads in the lungs and spleen compared to non-vaccinated mice.Citation96 Furthermore, prime-boost regimens in the murine model were also investigated for their efficacy against TB. A homologous prime-boost regimen using GaMtbvac inadequately reduced bacterial burden in the lungs and spleen compared to BCG vaccination alone.Citation96 Conversely, heterologous BCG-prime GaMtbvac -boost, considerably enhanced antigen-specific responses while reducing bacterial burden when compared to homologous vaccination with GaMtbvac and BCG alone.Citation96 The safety and effectiveness of heterologous regimens were further assessed in BCG-vaccinated human adults.Citation97 Adverse effects associated with GaMtbvac were considered mild and transient, resolving spontaneously. GaMtbvac vaccine-induced Ag85A-specific T-cell responses resulted in the secretion of IL-2 and TNF-α soon after injection, whereas ESAT6-CFP10-specific T-cell responses occurred during later stages with hallmark TNF-α, IL-10, IL-17, and IL-9 elevation among BCG-vaccinated adults.Citation97 Of note, GaMtbvac also stimulates pronounced secretion of vaccine-specific IgG; its role against M. tb, however, is yet to be elucidated.Citation97

H4:IC31, also known as AERAS-404, is comprised of a TB10.4 and Ag85B fusion protein adjuvanted in a mixture of the leucin-rich peptide and oligodeoxynucleotide, ODN1a ().Citation98 HC:IC31 was proven safe and adequately protective against M. tb challenges with a significant reduction in bacterial burden among murine models.Citation98 Protection resulted from antigen-specific polyfunctional CD4 + T cells co-expressing IFN- γ, TNF-α, and IL-2.Citation98 Furthermore, H4:IC31 showed an acceptable safety profile in human adults with prior BCG vaccination.Citation145 Interestingly, the H4:IC31 vaccine induced the highest antigen-specific T cell response among the low-dose group when compared to the placebo and high-dose groups in mouseCitation145 and human models.Citation99 Thus, H4:IC31 shows promise as a BCG booster with superior efficacy at a low dose.Citation99,Citation100

H56:IC31 is a novel subunit vaccine composed of a Ag85B, ESAT-6, and Rv2660c fusion protein in an IC31 adjuvant system ().Citation101 Many studies reveal the immunogenicity and efficacy of this vaccine in reducing bacterial burden and lung pathology among BCG pre-vaccinated miceCitation101 and nonhuman primates.Citation102,Citation103 H56:IC31 has an acceptable safety profile and shows favorable differentiation of antigen-specific polyfunctional CD4 + T cells expressing IFN- γ, TNF-α, and IL-2.Citation104 Furthermore, H56:IC31 yielded greatest results at lower doses in BCG-vaccinated human adults.Citation104 Vaccination with H56:IC31 at low doses (either 5 µg:500 nmol or 15 µg:500 nmol), induced high frequency and durable antigen-specific polyfunctional CD4 + T cell responses, irrespective of infection status. Furthermore, the number of vaccinations was dependent on the patient’s QFT status. In QFT negative individuals, three doses of H56:IC31 conferred robust and durable polyfunctional CD4 + T cell, whereas no additional benefits were seen from the third immunization in QFT positive individuals.Citation105

ID93/GLA-SE is a subunit vaccine comprised a fusion of four mycobacterial antigens combined with glucopyranosyl lipid adjuvant, a TLR4 agonist, and emulsified in an oil-and-water solution ().Citation106 Previous studies had demonstrated the safety and efficacy of the vaccine in mice,Citation107,Citation109 and nonhuman primates.Citation106 Many studies describe the ability of ID93/GLA-SE to induce differentiation of CD4 + T cells into polyfunctional CD4 + T cells double expressing either CD154+ IFN- γ+ or CD154+ TNF-α+ cytokines in miceCitation109 and in TB naïve humans.Citation110 Therefore, ID93/GLA-SE alone can significantly reduce bacterial burden and increase survivability in miceCitation109 as well as significantly increase antibody responses which mediate NK cell degranulation/activation and THP1 monocyte mediated antibody-dependent phagocytosis in humans.Citation110 Furthermore, ID93/GLA-SE, when administered after BCG-priming, can enhance survival against TB in the guinea pig modelCitation106,Citation107 and against M. tb K, a hyper-virulent strain, in the mouse model.Citation108 Interestingly, the tuberculin skin test (TST), a delayed-type hypersensitivity (DTH) reaction in response to BCG vaccination and M. tb infection, had been uncompromised in ID93/GLA-SE-vaccinated animals. Therefore, in contrast to BCG vaccine, TST’s integrity in ID93/GLA-SE vaccinated specimens remained intact, thus preserving its utility in identifying potential exposure to M. tb.Citation111

DAR-901 is an inactivated whole-cell mycobacterial vaccine manufactured from the SRL172 strain whose use as a booster is under investigation.Citation112 DAR-901 is comparably safe and immunogenic, conferring superior protection against M. tb when compared to BCG alone in both murine modelsCitation112 and human adultsCitation113,Citation114 due to stimulation of IFN-y production (). Nonetheless, studies establishing the efficacy of the vaccine presented mixed results. DAR-901 induces a smaller magnitude polyfunctional CD4 + T cell response with no significant differences in T cell cytokine production when compared to the BCG booster vaccine. Furthermore, CD4 + T cells induced by the DAR-901 vaccine were short-lived and nonresponsive to mycobacterial antigens from M. tb lysate.Citation114 Conversely, von Reyn et al. demonstrated that 1 mg of DAR-901 could induce both cellular and humoral responses, accompanied by substantial IFN-γ production in the presence of M. tb lysate among healthy adults with prior BCG vaccination.Citation113 Furthermore, IFN-γ assay remained negative after 3 doses of DAR-901. Thus, the booster can be employed as a preventative vaccine without interrupting M. tb screeningCitation114 .

MTBVAC is a live-attenuated M. tb vaccine with genetic deletion of two major mycobacterial virulence factors:fadD26 and phoP.Citation146 MTBVAC was deemed safe when tested in immunocompromised mice and guinea pigs.Citation115 Congruently, Aguilo et al. observed that MTBVAC did not affect growth and development, thus suggesting its safety in newborn mice.Citation116 Furthermore, M. TBVAC had a similar safety profile to BCG when administered subcutaneously in adults and in infants.Citation117 Many studies among mice,Citation118 goats,Citation119 and nonhuman primatesCitation120 have investigated MTBVAC protectivity against M. tb as quantified by bacterial load, lung pathology, and survival rate. Overall, M. TBVAC confers superior protection in mouse models when compared to BCG vaccination.Citation116,Citation147 Furthermore, the first phase I trial in humans demonstrated excellent safety, similar immunogenicity, and a greater polyfunctional CD4 + T cell response when compared to BCG vaccination ().Citation121 Clark et al. demonstrated greater protection against M. tb among BCG-primed MTBVAC-boosted guinea pigs when compared to those vaccinated with BCG alone.Citation122 Surprisingly, heat-killed MTBVAC, when administered intranasally, could also induce profound humoral and cellular responses both systemically and locally in BCG-primed animals.Citation123 Altogether, evidence suggests that MTBVAC confers greater immunity than BCG when administered alone and even more so in the BCG- MTBVAC prime-boost regimen.

Conclusion

BCG vaccination remains crucial during childhood in much of the world. While its efficacy has been historically challenged, newer research conducted with stronger parameters and controls have shed light into how vaccine strain variations may affect efficacy and the immune system upon administration. As the mechanism of action of the BCG vaccine continues to be discovered, more attention to the strain of BCG vaccine used, as well as the epigenetic changes it may elicit, might allow us to better time and control vaccination-induced immune responses. Subsequent efforts toward full eradication have led to creative ways of reconstituting an old vaccine into a newer, more efficacious form, and the development of the next generation of vaccines and adjuncts. promises to be a growing area of research that might lead to a more effective and consistent vaccine.

Additional information

Funding

We appreciate the funding support from National Institutes of Health (NIH) award [RHL143545-01A1].

References

  • World Health, O., 2018. BCG vaccine: WHO position paper, February 2018 – Recommendations. Vaccine, 36(24), pp.3408–3410
  • Tran, V., Liu, J. and Behr, M., 2014. BCG Vaccines. Microbiology Spectrum, 2(1), pp.mgm2-0028–2013
  • Bussi, C. and Gutierrez, M., 2019. Mycobacterium tuberculosis infection of host cells in space and time. FEMS Microbiology Reviews, 43(4), pp.341–361
  • Lyon, S. and Rossman, M., 2017. Pulmonary Tuberculosis. Microbiology Spectrum, 5(1), pp.1–13
  • Horwitz, M., Harth, G., Dillon, B. and Masleša-Galić, S., 2009. Commonly administered BCG strains including an evolutionarily early strain and evolutionarily late strains of disparate genealogy induce comparable protective immunity against tuberculosis. Vaccine, 27(3), pp.441–445
  • Zwerling, A., Behr, M., Verma, A., Brewer, T., Menzies, D. and Pai, M., 2011. The BCG World Atlas: A Database of Global BCG Vaccination Policies and Practices. PLoS Medicine, 8(3), p.e1001012
  • Eshete, A., Shewasinad, S. and Hailemeskel, S., 2020. Immunization coverage and its determinant factors among children aged 12–23 months in Ethiopia: a systematic review, and Meta- analysis of cross-sectional studies. BMC Pediatrics, 20(1), p.283
  • Ritz, N., Hanekom, W., Robins-Browne, R., Britton, W. and Curtis, N., 2008. Influence of BCG vaccine strain on the immune response and protection against tuberculosis. FEMS Microbiology Reviews, 32(5), pp.821–841
  • Roy, A., Eisenhut, M., Harris, R., Rodrigues, L., Sridhar, S., Habermann, S., Snell, L., Mangtani, P., Adetifa, I., Lalvani, A. and Abubakar, I., 2014. Effect of BCG vaccination against Mycobacterium tuberculosis infection in children: systematic review and meta-analysis. BMJ, 349, p.g4643
  • Ekanem, A., Oloyede, I., Ekrikpo, U., Idung, A. and Edward, E.. Rate of BCG Immunization in HIV-Exposed Infants in a Selected Primary Health Centre in Southern Nigeria: Implications of No Vaccine Policy for HIV-Positive Infants. J of Tropical Pediatrics. 2020 Jun 27 [accessed 2020 Dec 1]:[7 p.] doi:10.1093/tropej/fmaa030
  • Kousha, A., Farajnia, S., Ansarin, K., Khalili, M., Shariat, M. and Sahebi, L., 2020. Does the BCG vaccine have different effects on strains of tuberculosis?. Clinical & Experimental Immunology, 203(2), pp.281–285
  • Wu, B., Huang, C., Garcia, L., de Leon, A., Osornio, J., Bobadilla-del-Valle, M., Ferreira, L., Canizales, S., Small, P., Kato-Maeda, M., Krensky, A. and Clayberger, C., 2007. Unique Gene Expression Profiles in Infants Vaccinated with Different Strains of Mycobacterium bovis Bacille Calmette-Guérin. Infection and Immunity, 75(7), pp.3658–3664
  • Kiravu, A., Osawe, S., Happel, A., Nundalall, T., Wendoh, J., Beer, S., Dontsa, N., Alinde, O., Mohammed, S., Datong, P., Cameron, D., Rosenthal, K., Abimiku, A., Jaspan, H. and Gray, C., 2019. Bacille Calmette-Guérin Vaccine Strain Modulates the Ontogeny of Both Mycobacterial-Specific and Heterologous T Cell Immunity to Vaccination in Infants. Frontiers in Immunology, 10, p.2307
  • Castillo-Rodal, A., Castañón-Arreola, M., Hernández-Pando, R., Calva, J., Sada-Díaz, E. and López-Vidal, Y., 2006. Mycobacterium bovis BCG Substrains Confer Different Levels of Protection against Mycobacterium tuberculosis Infection in a BALB/c Model of Progressive Pulmonary Tuberculosis. Infection and Immunity, 74(3), pp.1718–1724
  • Davids, V., Hanekom, W., Mansoor, N., Gamieldien, H., Gelderbloem, S., Hawkridge, A., Hussey, G., Hughes, E., Soler, J., Murray, R., Ress, S. and Kaplan, G., 2006. The Effect of Bacille Calmette‐Guérin Vaccine Strain and Route of Administration on Induced Immune Responses in Vaccinated Infants. The Journal of Infectious Diseases, 193(4), pp.531–536
  • Tanner, R., Villarreal-Ramos, B., Vordermeier, H. and McShane, H., 2019. The Humoral Immune Response to BCG Vaccination. Frontiers in Immunology, 10, p.1317
  • Netea, M., Quintin, J. and van der Meer, J., 2011. Trained Immunity: A Memory for Innate Host Defense. Cell Host & Microbe, 9(5), pp.355–361
  • Garly, M., Martins, C., Balé, C., Baldé, M., Hedegaard, K., Gustafson, P., Lisse, I., Whittle, H. and Aaby, P., 2003. BCG scar and positive tuberculin reaction associated with reduced child mortality in West Africa. Vaccine, 21(21–22), pp.2782–2790
  • Roth, A., Gustafson, P., Nhaga, A., Djana, Q., Poulsen, A., Garly, M., Jensen, H., Sodemann, M., Rodriques, A. and Aaby, P., 2005. BCG vaccination scar associated with better childhood survival in Guinea-Bissau. International Journal of Epidemiology, 34(3), pp.540–547
  • Setia, M., Steinmaus, C., Ho, C. and Rutherford, G., 2006. The role of BCG in prevention of leprosy: a meta-analysis. The Lancet Infectious Diseases, 6(3), pp.162–170
  • Stensballe, L., Nante, E., Jensen, I., Kofoed, P., Poulsen, A., Jensen, H., Newport, M., Marchant, A. and Aaby, P., 2005. Acute lower respiratory tract infections and respiratory syncytial virus in infants in Guinea-Bissau: a beneficial effect of BCG vaccination for girls. Vaccine, 23(10), pp.1251–1257
  • Elliott, A., Nakiyingi, J., Quigley, M., French, N., Gilks, C. and Whitworth, J., 1999. Inverse association between BCG immunisation and intestinal nematode infestation among HIV-1-positive individuals in Uganda. The Lancet, 354(9183), pp.1000–1001
  • Kleinnijenhuis, J., Quintin, J., Preijers, F., Benn, C., Joosten, L., Jacobs, C., van Loenhout, J., Xavier, R., Aaby, P., van der Meer, J., van Crevel, R. and Netea, M., 2013. Long-Lasting Effects of BCG Vaccination on Both Heterologous Th1/Th17 Responses and Innate Trained Immunity. Journal of Innate Immunity, 6(2), pp.152–158
  • Giamarellos-Bourboulis, E., Tsilika, M., Moorlag, S., Antonakos, N., Kotsaki, A., Domínguez-Andrés, J., Kyriazopoulou, E., Gkavogianni, T., Adami, M., Damoraki, G., Koufargyris, P., Karageorgos, A., Bolanou, A., Koenen, H., van Crevel, R., Droggiti, D., Renieris, G., Papadopoulos, A. and Netea, M., 2020. Activate: Randomized Clinical Trial of BCG Vaccination against Infection in the Elderly. Cell, 183(2), pp.315-323.e9
  • Arts, R., Moorlag, S., Novakovic, B., Li, Y., Wang, S., Oosting, M., Kumar, V., Xavier, R., Wijmenga, C., Joosten, L., Reusken, C., Benn, C., Aaby, P., Koopmans, M., Stunnenberg, H., van Crevel, R. and Netea, M., 2018. BCG Vaccination Protects against Experimental Viral Infection in Humans through the Induction of Cytokines Associated with Trained Immunity. Cell Host & Microbe, 23(1), pp.89-100.e5
  • Edupuganti, S., Eidex, R., Keyserling, H., Akondy, R., Lanciotti, R., Orenstein, W., Teuwen, D., Akondy, R., Orenstein, W., del Rio, C., Pan, Y., Querec, T., Lipman, H., Barrett, A., Ahmed, R., Teuwen, D., Cetron, M. and Mulligan, M., 2013. A Randomized, Double-Blind, Controlled Trial of the 17D Yellow Fever Virus Vaccine Given in Combination with Immune Globulin or Placebo: Comparative Viremia and Immunogenicity. The American Journal of Tropical Medicine and Hygiene, 88(1), pp.172–177
  • Portevin, D. and Young, D., 2013. Natural Killer Cell Cytokine Response to M. bovis BCG Is Associated with Inhibited Proliferation, Increased Apoptosis and Ultimate Depletion of NKp44+CD56bright Cells. PLoS ONE, 8(7), p.e68864
  • Wang, D., Gu, X., Liu, X., Wei, S., Wang, B. and Fang, M., 2018. NK cells inhibit anti-Mycobacterium bovis BCG T cell responses and aggravate pulmonary inflammation in a direct lung infection mouse model. Cellular Microbiology, 20(7), p.e12833
  • Kleinnijenhuis, J., Quintin, J., Preijers, F., Joosten, L., Jacobs, C., Xavier, R., van der Meer, J., van Crevel, R. and Netea, M., 2014. BCG-induced trained immunity in NK cells: Role for non-specific protection to infection. Clinical Immunology, 155(2), pp.213–219
  • Dhiman, R., Indramohan, M., Barnes, P., Nayak, R., Paidipally, P., Rao, L. and Vankayalapati, R., 2009. IL-22 Produced by Human NK Cells Inhibits Growth of Mycobacterium tuberculosis by Enhancing Phagolysosomal Fusion. The Journal of Immunology, 183(10), pp.6639–6645
  • Zheng, Y., Valdez, P., Danilenko, D., Hu, Y., Sa, S., Gong, Q., Abbas, A., Modrusan, Z., Ghilardi, N., de Sauvage, F. and Ouyang, W., 2008. Interleukin-22 mediates early host defense against attaching and effacing bacterial pathogens. Nature Medicine, 14(3), pp.282–289
  • Kleinnijenhuis, J., Quintin, J., Preijers, F., Joosten, L., Ifrim, D., Saeed, S., Jacobs, C., van Loenhout, J., de Jong, D., Stunnenberg, H., Xavier, R., van der Meer, J., van Crevel, R. and Netea, M., 2012. Bacille Calmette-Guerin induces NOD2-dependent nonspecific protection from reinfection via epigenetic reprogramming of monocytes. Proceedings of the National Academy of Sciences, 109(43), pp.17537–17542
  • Umemura, M., Nishimura, H., Hirose, K., Matsuguchi, T. and Yoshikai, Y., 2001. Overexpression of IL-15 In Vivo Enhances Protection AgainstMycobacterium bovisBacillus Calmette-Guérin Infection Via Augmentation of NK and T Cytotoxic 1 Responses. The Journal of Immunology, 167(2), pp.946–956
  • Kaufmann, E., Sanz, J., Dunn, J., Khan, N., Mendonça, L., Pacis, A., Tzelepis, F., Pernet, E., Dumaine, A., Grenier, J., Mailhot-Léonard, F., Ahmed, E., Belle, J., Besla, R., Mazer, B., King, I., Nijnik, A., Robbins, C., Barreiro, L. and Divangahi, M., 2018. BCG Educates Hematopoietic Stem Cells to Generate Protective Innate Immunity against Tuberculosis. Cell, 172(1–2), pp.176-190.e19
  • Cirovic, B., de Bree, L., Groh, L., Blok, B., Chan, J., van der Velden, W., Bremmers, M., van Crevel, R., Händler, K., Picelli, S., Schulte-Schrepping, J., Klee, K., Oosting, M., Koeken, V., van Ingen, J., Li, Y., Benn, C., Schultze, J., Joosten, L., Curtis, N., Netea, M. and Schlitzer, A., 2020. BCG Vaccination in Humans Elicits Trained Immunity via the Hematopoietic Progenitor Compartment. Cell Host & Microbe, 28(2), pp.322-334.e5
  • Luca, S., Mihaescu, T., 2013. History of BCG Vaccine. Maedica, 8, pp.53–58
  • Derrick, S., Kolibab, K., Yang, A. and Morris, S., 2014. Intranasal Administration of Mycobacterium bovis BCG Induces Superior Protection against Aerosol Infection with Mycobacterium tuberculosis in Mice. Clinical and Vaccine Immunology, 21(10), pp.1443–1451
  • Saleem, I., Coombes, A. and Chambers, M., 2019. In Vitro Evaluation of Eudragit Matrices for Oral Delivery of BCG Vaccine to Animals. Pharmaceutics, 11(6), p.270
  • Balseiro, A., Prieto, J., Álvarez, V., Lesellier, S., Davé, D., Salguero, F., Sevilla, I., Infantes-Lorenzo, J., Garrido, J., Adriaensen, H., Juste, R. and Barral, M., 2020. Protective Effect of Oral BCG and Inactivated Mycobacterium bovis Vaccines in European Badgers (Meles meles) Experimentally Infected With M. bovis. Frontiers in Veterinary Science, 7, p.41
  • Palphramand, K., Delahay, R., Robertson, A., Gowtage, S., Williams, G., McDonald, R., Chambers, M. and Carter, S., 2017. Field evaluation of candidate baits for oral delivery of BCG vaccine to European badgers, Meles meles. Vaccine, 35(34), pp.4402–4407
  • Lesellier, S., Birch, C., Davé, D., Dalley, D., Gowtage, S., Palmer, S., McKenna, C., Williams, G., Ashford, R., Weyer, U., Beatham, S., Coats, J., Nunez, A., Sanchez-Cordon, P., Spiropoulos, J., Powell, S., Sawyer, J., Pascoe, J., Hendon-Dunn, C., Bacon, J. and Chambers, M., 2020. Bioreactor-Grown Bacillus of Calmette and Guérin (BCG) Vaccine Protects Badgers against Virulent Mycobacterium bovis When Administered Orally: Identifying Limitations in Baited Vaccine Delivery. Pharmaceutics, 12(8), p.782
  • Kaveh, D., Garcia-Pelayo, M., Bull, N., Sanchez-Cordon, P., Spiropoulos, J. and Hogarth, P., 2020. Airway delivery of both a BCG prime and adenoviral boost drives CD4 and CD8 T cells into the lung tissue parenchyma. Scientific Reports, 10(1), p.18703
  • Darrah, P., Zeppa, J., Maiello, P., Hackney, J., Wadsworth, M., Hughes, T., Pokkali, S., Swanson, P., Grant, N., Rodgers, M., Kamath, M., Causgrove, C., Laddy, D., Bonavia, A., Casimiro, D., Lin, P., Klein, E., White, A., Scanga, C., Shalek, A., Roederer, M., Flynn, J. and Seder, R., 2020. Prevention of tuberculosis in macaques after intravenous BCG immunization. Nature, 577(7788), pp.95–102
  • Chen, F., Yan, Q., Yu, Y. and Wu, M., 2017. BCG vaccine powder-laden and dissolvable microneedle arrays for lesion-free vaccination. Journal of Controlled Release, 255, pp.36–44
  • Gupta, A., Ahmad, F., Ahmad, F., Gupta, U., Natarajan, M., Katoch, V. and Bhaskar, S., 2012. Protective efficacy of Mycobacterium indicus pranii against tuberculosis and underlying local lung immune responses in guinea pig model. Vaccine, 30(43), pp.6198–6209
  • Sharma, S., Katoch, K., Sarin, R., Balambal, R., Kumar Jain, N., Patel, N., Murthy, K., Singla, N., Saha, P., Khanna, A., Singh, U., Kumar, S., Sengupta, A., Banavaliker, J., Chauhan, D., Sachan, S., Wasim, M., Tripathi, S., Dutt, N., Jain, N., Joshi, N., Penmesta, S., Gaddam, S., Gupta, S., Khamar, B., Dey, B., Mitra, D., Arora, S., Bhaskar, S. and Rani, R., 2017. Efficacy and Safety of Mycobacterium indicus pranii as an adjunct therapy in Category II pulmonary tuberculosis in a randomized trial. Scientific Reports, 7(1), p.3354
  • Hernandez-Pando, R., Pavön, L., Arriaga, K., Orozco, H., Madrid-Marina, V. and Rook, G., 1997. Pathogenesis of tuberculosis in mice exposed to low and high doses of an environmental mycobacterial saprophyte before infection. Infection and immunity, 65(8), pp.3317–3327
  • Abou-Zeid, C., Gares, M., Inwald, J., Janssen, R., Zhang, Y., Young, D., Hetzel, C., Lamb, J., Baldwin, S., Orme, I., Yeremeev, V., Nikonenko, B. and Apt, A., 1997. Induction of a type 1 immune response to a recombinant antigen from Mycobacterium tuberculosis expressed in Mycobacterium vaccae. Infection and immunity, 65(5), pp.1856–1862
  • Immunotherapy with Mycobacterium vaccae in patients with newly diagnosed pulmonary tuberculosis: a randomised controlled trial. Durban Immunotherapy Trial Group. Lancet. 1999;354(9173):116–19.
  • Mayo, R. and Stanford, J., 2000. Double-blind placebo-controlled trial of Mycobacterium vaccae immunotherapy for tuberculosis in KwaZulu, South Africa, 1991–1997. Transactions of the Royal Society of Tropical Medicine and Hygiene, 94(5), pp.563–568
  • von Reyn, C., Arbeit, R., Yeaman, G., Waddell, R., Marsh, B., Morin, P., Modlin, J. and Remold, H., 1997. Immunization of Healthy Adult Subjects in the United States with Inactivated Mycobacterium vaccae Administered in a Three-Dose Series. Clinical Infectious Diseases, 24(5), pp.843–848
  • Marsh, B., Von Reyn, C., Arbeit, R. and Morin, P., 1997. Immunization of HIV-Infected Adults With a Three-Dose Series of Inactivated Mycobacterium vaccae. The American Journal of the Medical Sciences, 313(6), pp.377–383
  • von Reyn, C., Marsh, B., Waddell, R., Lein, A., Tvaroha, S., Morin, P. and Modlin, J., 1998. Cellular Immune Responses to Mycobacteria in Healthy and Human Immunodeficiency Virus–Positive Subjects in the United States After a Five‐Dose Schedule ofMycobacterium vaccaeVaccine. Clinical Infectious Diseases, 27(6), pp.1517–1520
  • Hansen, S., Zak, D., Xu, G., Ford, J., Marshall, E., Malouli, D., Gilbride, R., Hughes, C., Ventura, A., Ainslie, E., Randall, K., Selseth, A., Rundstrom, P., Herlache, L., Lewis, M., Park, H., Planer, S., Turner, J., Fischer, M., Armstrong, C., Zweig, R., Valvo, J., Braun, J., Shankar, S., Lu, L., Sylwester, A., Legasse, A., Messerle, M., Jarvis, M., Amon, L., Aderem, A., Alter, G., Laddy, D., Stone, M., Bonavia, A., Evans, T., Axthelm, M., Früh, K., Edlefsen, P. and Picker, L., 2018. Prevention of tuberculosis in rhesus macaques by a cytomegalovirus-based vaccine. Nature Medicine, 24(2), pp.130–143
  • Stylianou, E., Harrington-Kandt, R., Beglov, J., Bull, N., Pinpathomrat, N., Swarbrick, G., Lewinsohn, D., Lewinsohn, D. and McShane, H., 2018. Identification and Evaluation of Novel Protective Antigens for the Development of a Candidate Tuberculosis Subunit Vaccine. Infection and Immunity, 86(7), pp.e00014–18
  • Chen, L., Xu, M., Wang, Z., Chen, B., Du, W., Su, C., Shen, X., Zhao, A., Dong, N., Wang, Y. and Wang, G., 2010. The development and preliminary evaluation of a newMycobacterium tuberculosis vaccine comprising Ag85b, HspX and CFP-10:ESAT-6 fusion protein with CpG DNA and aluminum hydroxide adjuvants. FEMS Immunology & Medical Microbiology, 59(1), pp.42–52
  • Lu, J., Chen, B., Wang, G., Fu, L., Shen, X., Su, C., Du, W., Yang, L. and Xu, M., 2015. Recombinant tuberculosis vaccine AEC/BC02 induces antigen-specific cellular responses in mice and protects guinea pigs in a model of latent infection. Journal of Microbiology, Immunology and Infection, 48(6), pp.597–603
  • Agger, E., Rosenkrands, I., Olsen, A., Hatch, G., Williams, A., Kritsch, C., Lingnau, K., von Gabain, A., Andersen, C., Korsholm, K. and Andersen, P., 2006. Protective immunity to tuberculosis with Ag85B-ESAT-6 in a synthetic cationic adjuvant system IC31. Vaccine, 24(26), pp.5452–5460
  • van Dissel, J., Arend, S., Prins, C., Bang, P., Tingskov, P., Lingnau, K., Nouta, J., Klein, M., Rosenkrands, I., Ottenhoff, T., Kromann, I., Doherty, T. and Andersen, P., 2010. Ag85B–ESAT-6 adjuvanted with IC31® promotes strong and long-lived Mycobacterium tuberculosis specific T cell responses in naïve human volunteers. Vaccine, 28(20), pp.3571–3581
  • van Dissel, J., Soonawala, D., Joosten, S., Prins, C., Arend, S., Bang, P., Tingskov, P., Lingnau, K., Nouta, J., Hoff, S., Rosenkrands, I., Kromann, I., Ottenhoff, T., Doherty, T. and Andersen, P., 2011. Ag85B–ESAT-6 adjuvanted with IC31® promotes strong and long-lived Mycobacterium tuberculosis specific T cell responses in volunteers with previous BCG vaccination or tuberculosis infection. Vaccine, 29(11), pp.2100–2109
  • Reither, K., Katsoulis, L., Beattie, T., Gardiner, N., Lenz, N., Said, K., Mfinanga, E., Pohl, C., Fielding, K., Jeffery, H., Kagina, B., Hughes, E., Scriba, T., Hanekom, W., Hoff, S., Bang, P., Kromann, I., Daubenberger, C., Andersen, P. and Churchyard, G., 2014. Safety and Immunogenicity of H1/IC31®, an Adjuvanted TB Subunit Vaccine, in HIV-Infected Adults with CD4+ Lymphocyte Counts Greater than 350 cells/mm3: A Phase II, Multi-Centre, Double-Blind, Randomized, Placebo-Controlled Trial. PLoS ONE, 9(12), p.e114602
  • Mearns, H., Geldenhuys, H., Kagina, B., Musvosvi, M., Little, F., Ratangee, F., Mahomed, H., Hanekom, W., Hoff, S., Ruhwald, M., Kromann, I., Bang, P., Hatherill, M., Andersen, P., Scriba, T., Rozot, V., Abrahams, D., Mauff, K., Smit, E., Brown, Y., Hughes, E., Makgotlho, E., Keyser, A., Erasmus, M., Makhethe, L., Africa, H., Hopley, C. and Steyn, M., 2017. H1:IC31 vaccination is safe and induces long-lived TNF-α+IL-2+CD4 T cell responses in M. tuberculosis infected and uninfected adolescents: A randomized trial. Vaccine, 35(1), pp.132–141
  • Idoko, O., Owolabi, O., Owiafe, P., Moris, P., Odutola, A., Bollaerts, A., Ogundare, E., Jongert, E., Demoitié, M., Ofori-Anyinam, O. and Ota, M., 2014. Safety and immunogenicity of the M72/AS01 candidate tuberculosis vaccine when given as a booster to BCG in Gambian infants: An open-label randomized controlled trial. Tuberculosis, 94(6), pp.564–578
  • Kumarasamy, N., Poongulali, S., Bollaerts, A., Moris, P., Beulah, F., Ayuk, L., Demoitié, M., Jongert, E. and Ofori-Anyinam, O., 2016. A Randomized, Controlled Safety, and Immunogenicity Trial of the M72/AS01 Candidate Tuberculosis Vaccine in HIV-Positive Indian Adults. Medicine, 95(3), p.e2459
  • Gillard, P., Yang, P., Danilovits, M., Su, W., Cheng, S., Pehme, L., Bollaerts, A., Jongert, E., Moris, P., Ofori-Anyinam, O., Demoitié, M. and Castro, M., 2016. Safety and immunogenicity of the M72/AS01 E candidate tuberculosis vaccine in adults with tuberculosis: A phase II randomised study. Tuberculosis, 100, pp.118–127
  • Van Der Meeren, O., Hatherill, M., Nduba, V., Wilkinson, R., Muyoyeta, M., Van Brakel, E., Ayles, H., Henostroza, G., Thienemann, F., Scriba, T., Diacon, A., Blatner, G., Demoitié, M., Tameris, M., Malahleha, M., Innes, J., Hellström, E., Martinson, N., Singh, T., Akite, E., Khatoon Azam, A., Bollaerts, A., Ginsberg, A., Evans, T., Gillard, P. and Tait, D., 2018. Phase 2b Controlled Trial of M72/AS01EVaccine to Prevent Tuberculosis. New England Journal of Medicine, 379(17), pp.1621–1634
  • Guirado, E., Gil, O., Cáceres, N., Singh, M., Vilaplana, C. and Cardona, P., 2008. Induction of a Specific Strong Polyantigenic Cellular Immune Response after Short-Term Chemotherapy Controls Bacillary Reactivation in Murine and Guinea Pig Experimental Models of Tuberculosis. Clinical and Vaccine Immunology, 15(8), pp.1229–1237
  • Vilaplana, C., Gil, O., Cáceres, N., Pinto, S., Díaz, J. and Cardona, P., 2011. Prophylactic Effect of a Therapeutic Vaccine against TB Based on Fragments of Mycobacterium tuberculosis. PLoS ONE, 6(5), p.e20404
  • Prabowo, S., Painter, H., Zelmer, A., Smith, S., Seifert, K., Amat, M., Cardona, P. and Fletcher, H., 2019. RUTI Vaccination Enhances Inhibition of Mycobacterial Growth ex vivo and Induces a Shift of Monocyte Phenotype in Mice. Frontiers in Immunology, 10, p.894
  • Cardona, P., Amat, I., Gordillo, S., Arcos, V., Guirado, E., Díaz, J., Vilaplana, C., Tapia, G. and Ausina, V., 2005. Immunotherapy with fragmented Mycobacterium tuberculosis cells increases the effectiveness of chemotherapy against a chronical infection in a murine model of tuberculosis. Vaccine, 23(11), pp.1393–1398
  • Vilaplana, C., Montané, E., Pinto, S., Barriocanal, A., Domenech, G., Torres, F., Cardona, P. and Costa, J., 2010. Double-blind, randomized, placebo-controlled Phase I Clinical Trial of the therapeutical antituberculous vaccine RUTI®. Vaccine, 28(4), pp.1106–1116
  • Nell, A., D’lom, E., Bouic, P., Sabaté, M., Bosser, R., Picas, J., Amat, M., Churchyard, G. and Cardona, P., 2014. Safety, Tolerability, and Immunogenicity of the Novel Antituberculous Vaccine RUTI: Randomized, Placebo-Controlled Phase II Clinical Trial in Patients with Latent Tuberculosis Infection. PLoS ONE, 9(2), p.e89612
  • Johansen, P., Fettelschoss, A., Amstutz, B., Selchow, P., Waeckerle-Men, Y., Keller, P., Deretic, V., Held, L., Kündig, T., Böttger, E. and Sander, P., 2011. Relief from Zmp1-Mediated Arrest of Phagosome Maturation Is Associated with Facilitated Presentation and Enhanced Immunogenicity of Mycobacterial Antigens. Clinical and Vaccine Immunology, 18(6), pp.907–913
  • Sander, P., Clark, S., Petrera, A., Vilaplana, C., Meuli, M., Selchow, P., Zelmer, A., Mohanan, D., Andreu, N., Rayner, E., Dal Molin, M., Bancroft, G., Johansen, P., Cardona, P., Williams, A. and Böttger, E., 2015. Deletion of zmp1 improves Mycobacterium bovis BCG-mediated protection in a guinea pig model of tuberculosis. Vaccine, 33(11), pp.1353–1359
  • Vergne, I., Chua, J., Lee, H., Lucas, M., Belisle, J. and Deretic, V., 2005. Mechanism of phagolysosome biogenesis block by viable Mycobacterium tuberculosis. Proceedings of the National Academy of Sciences, 102(11), pp.4033–4038
  • Counoupas, C., Pinto, R., Nagalingam, G., Hill-Cawthorne, G., Feng, C., Britton, W. and Triccas, J., 2016. Mycobacterium tuberculosis components expressed during chronic infection of the lung contribute to long-term control of pulmonary tuberculosis in mice. npj Vaccines, 1(1), p.16012
  • Counoupas, C., Pinto, R., Nagalingam, G., Britton, W. and Triccas, J., 2018. Protective efficacy of recombinant BCG over-expressing protective, stage-specific antigens of Mycobacterium tuberculosis. Vaccine, 36(19), pp.2619–2629
  • Counoupas, C., Pinto, R., Nagalingam, G., Britton, W., Petrovsky, N. and Triccas, J., 2017. Delta inulin-based adjuvants promote the generation of polyfunctional CD4+ T cell responses and protection against Mycobacterium tuberculosis infection. Scientific Reports, 7(1), p.8582
  • Kaufmann, S., Cotton, M., Eisele, B., Gengenbacher, M., Grode, L., Hesseling, A. and Walzl, G., 2014. The BCG replacement vaccine VPM1002: from drawing board to clinical trial. Expert Review of Vaccines, 13(5), pp.619–630
  • Grode, L., Seiler, P., Baumann, S., Hess, J., Brinkmann, V., Eddine, A., Mann, P., Goosmann, C., Bandermann, S., Smith, D., Bancroft, G., Reyrat, J., Soolingen, D., Raupach, B. and Kaufmann, S., 2005. Increased vaccine efficacy against tuberculosis of recombinant Mycobacterium bovis bacille Calmette-Guerin mutants that secrete listeriolysin. Journal of Clinical Investigation, 115(9), pp.2472–2479
  • Vogelzang, A., Perdomo, C., Zedler, U., Kuhlmann, S., Hurwitz, R., Gengenbacher, M. and Kaufmann, S., 2014. Central Memory CD4+ T Cells Are Responsible for the Recombinant Bacillus Calmette-Guérin ΔureC::hly Vaccine's Superior Protection Against Tuberculosis. The Journal of Infectious Diseases, 210(12), pp.1928–1937
  • Desel, C., Dorhoi, A., Bandermann, S., Grode, L., Eisele, B. and Kaufmann, S., 2011. Recombinant BCG ΔureC hly+ Induces Superior Protection Over Parental BCG by Stimulating a Balanced Combination of Type 1 and Type 17 Cytokine Responses. The Journal of Infectious Diseases, 204(10), pp.1573–1584
  • Gengenbacher, M., Kaiser, P., Schuerer, S., Lazar, D. and Kaufmann, S., 2016. Post-exposure vaccination with the vaccine candidate Bacillus Calmette–Guérin ΔureC::hly induces superior protection in a mouse model of subclinical tuberculosis. Microbes and Infection, 18(5), pp.364–368
  • Loxton, A., Knaul, J., Grode, L., Gutschmidt, A., Meller, C., Eisele, B., Johnstone, H., van der Spuy, G., Maertzdorf, J., Kaufmann, S., Hesseling, A., Walzl, G. and Cotton, M., 2016. Safety and Immunogenicity of the Recombinant Mycobacterium bovis BCG Vaccine VPM1002 in HIV-Unexposed Newborn Infants in South Africa. Clinical and Vaccine Immunology, 24(2), pp.e00439–16
  • Bekker, L., Dintwe, O., Fiore-Gartland, A., Middelkoop, K., Hutter, J., Williams, A., Randhawa, A., Ruhwald, M., Kromann, I., Andersen, P., DiazGranados, C., Rutkowski, K., Tait, D., Miner, M., Andersen-Nissen, E., De Rosa, S., Seaton, K., Tomaras, G., McElrath, M., Ginsberg, A. and Kublin, J., 2020. A phase 1b randomized study of the safety and immunological responses to vaccination with H4:IC31, H56:IC31, and BCG revaccination in Mycobacterium tuberculosis-uninfected adolescents in Cape Town, South Africa. EClinicalMedicine, 21, p.100313
  • Nemes, E., Geldenhuys, H., Rozot, V., Rutkowski, K., Ratangee, F., Bilek, N., Mabwe, S., Makhethe, L., Erasmus, M., Toefy, A., Mulenga, H., Hanekom, W., Self, S., Bekker, L., Ryall, R., Gurunathan, S., DiazGranados, C., Andersen, P., Kromann, I., Evans, T., Ellis, R., Landry, B., Hokey, D., Hopkins, R., Ginsberg, A., Scriba, T. and Hatherill, M., 2018. Prevention of M. tuberculosis Infection with H4:IC31 Vaccine or BCG Revaccination. New England Journal of Medicine, 379(2), pp.138–149
  • Barreto, M., Pereira, S., Pilger, D., Cruz, A., Cunha, S., Sant’Anna, C., Ichihara, M., Genser, B. and Rodrigues, L., 2011. Evidence of an effect of BCG revaccination on incidence of tuberculosis in school-aged children in Brazil: Second report of the BCG-REVAC cluster-randomised trial. Vaccine, 29(31), pp.4875–4877
  • Rodrigues, L., Pereira, S., Cunha, S., Genser, B., Ichihara, M., de Brito, S., Hijjar, M., Cruz, A., Sant'Anna, C., Bierrenbach, A., Barreto, M. and Dourado, I., 2005. Effect of BCG revaccination on incidence of tuberculosis in school-aged children in Brazil: the BCG-REVAC cluster-randomised trial. The Lancet, 366(9493), pp.1290–1295
  • Vordermeier, H., Villarreal-Ramos, B., Cockle, P., McAulay, M., Rhodes, S., Thacker, T., Gilbert, S., McShane, H., Hill, A., Xing, Z. and Hewinson, R., 2009. Viral Booster Vaccines Improve Mycobacterium bovis BCG-Induced Protection against Bovine Tuberculosis. Infection and Immunity, 77(8), pp.3364–3373
  • Pérez de Val, B., Villarreal-Ramos, B., Nofrarías, M., López-Soria, S., Romera, N., Singh, M., Abad, F., Xing, Z., Vordermeier, H. and Domingo, M., 2012. Goats Primed with Mycobacterium bovis BCG and Boosted with a Recombinant Adenovirus Expressing Ag85A Show Enhanced Protection against Tuberculosis. Clinical and Vaccine Immunology, 19(9), pp.1339–1347
  • Metcalfe, H., Steinbach, S., Jones, G., Connelley, T., Morrison, W., Vordermeier, M. and Villarreal-Ramos, B., 2016. Protection associated with a TB vaccine is linked to increased frequency of Ag85A-specific CD4 + T cells but no increase in avidity for Ag85A. Vaccine, 34(38), pp.4520–4525
  • Wang, J., Thorson, L., Stokes, R., Santosuosso, M., Huygen, K., Zganiacz, A., Hitt, M. and Xing, Z., 2004. Single Mucosal, but Not Parenteral, Immunization with Recombinant Adenoviral-Based Vaccine Provides Potent Protection from Pulmonary Tuberculosis. The Journal of Immunology, 173(10), pp.6357–6365
  • Li, W., Li, M., Deng, G., Zhao, L., Liu, X. and Wang, Y., 2015. Prime-boost vaccination with Bacillus Calmette Guerin and a recombinant adenovirus co-expressing CFP10, ESAT6, Ag85A and Ag85B of Mycobacterium tuberculosis induces robust antigen-specific immune responses in mice. Molecular Medicine Reports, 12(2), pp.3073–3080
  • Radošević, K., Wieland, C., Rodriguez, A., Weverling, G., Mintardjo, R., Gillissen, G., Vogels, R., Skeiky, Y., Hone, D., Sadoff, J., van der Poll, T., Havenga, M. and Goudsmit, J., 2007. Protective Immune Responses to a Recombinant Adenovirus Type 35 Tuberculosis Vaccine in Two Mouse Strains: CD4 and CD8 T-Cell Epitope Mapping and Role of Gamma Interferon. Infection and Immunity, 75(8), pp.4105–4115
  • Hoft, D., Blazevic, A., Stanley, J., Landry, B., Sizemore, D., Kpamegan, E., Gearhart, J., Scott, A., Kik, S., Pau, M., Goudsmit, J., McClain, J. and Sadoff, J., 2012. A recombinant adenovirus expressing immunodominant TB antigens can significantly enhance BCG-induced human immunity. Vaccine, 30(12), pp.2098–2108
  • Tkachuk, A., Gushchin, V., Potapov, V., Demidenko, A., Lunin, V. and Gintsburg, A., 2017. Multi-subunit BCG booster vaccine GamTBvac: Assessment of immunogenicity and protective efficacy in murine and guinea pig TB models. PLOS ONE, 12(4), p.e0176784
  • Vasina, D., Kleymenov, D., Manuylov, V., Mazunina, E., Koptev, E., Tukhovskaya, E., Murashev, A., Gintsburg, A., Gushchin, V. and Tkachuk, A., 2019. First-In-Human Trials of GamTBvac, a Recombinant Subunit Tuberculosis Vaccine Candidate: Safety and Immunogenicity Assessment. Vaccines, 7(4), p.166
  • Aagaard, C., Hoang, T., Izzo, A., Billeskov, R., Troudt, J., Arnett, K., Keyser, A., Elvang, T., Andersen, P. and Dietrich, J., 2009. Protection and Polyfunctional T Cells Induced by Ag85B-TB10.4/IC31® against Mycobacterium tuberculosis Is Highly Dependent on the Antigen Dose. PLoS ONE, 4(6), p.e5930
  • Geldenhuys, H., Mearns, H., Miles, D., Tameris, M., Hokey, D., Shi, Z., Bennett, S., Andersen, P., Kromann, I., Hoff, S., Hanekom, W., Mahomed, H., Hatherill, M., Scriba, T., van Rooyen, M., Bruce McClain, J., Ryall, R. and de Bruyn, G., 2015. The tuberculosis vaccine H4:IC31 is safe and induces a persistent polyfunctional CD4 T cell response in South African adults: A randomized controlled trial. Vaccine, 33(30), pp.3592–3599
  • Norrby, M., Vesikari, T., Lindqvist, L., Maeurer, M., Ahmed, R., Mahdavifar, S., Bennett, S., McClain, J., Shepherd, B., Li, D., Hokey, D., Kromann, I., Hoff, S., Andersen, P., de Visser, A., Joosten, S., Ottenhoff, T., Andersson, J. and Brighenti, S., 2017. Safety and immunogenicity of the novel H4:IC31 tuberculosis vaccine candidate in BCG-vaccinated adults: Two phase I dose escalation trials. Vaccine, 35(12), pp.1652–1661
  • Aagaard, C., Hoang, T., Dietrich, J., Cardona, P., Izzo, A., Dolganov, G., Schoolnik, G., Cassidy, J., Billeskov, R. and Andersen, P., 2011. A multistage tuberculosis vaccine that confers efficient protection before and after exposure. Nature Medicine, 17(2), pp.189–194
  • Lin, P., Dietrich, J., Tan, E., Abalos, R., Burgos, J., Bigbee, C., Bigbee, M., Milk, L., Gideon, H., Rodgers, M., Cochran, C., Guinn, K., Sherman, D., Klein, E., Janssen, C., Flynn, J. and Andersen, P., 2012. The multistage vaccine H56 boosts the effects of BCG to protect cynomolgus macaques against active tuberculosis and reactivation of latent Mycobacterium tuberculosis infection. Journal of Clinical Investigation, 122(1), pp.303–314
  • Billeskov, R., Tan, E., Cang, M., Abalos, R., Burgos, J., Pedersen, B., Christensen, D., Agger, E. and Andersen, P., 2016. Testing the H56 Vaccine Delivered in 4 Different Adjuvants as a BCG-Booster in a Non-Human Primate Model of Tuberculosis. PLOS ONE, 11(8), p.e0161217
  • Luabeya, A., Kagina, B., Tameris, M., Geldenhuys, H., Hoff, S., Shi, Z., Kromann, I., Hatherill, M., Mahomed, H., Hanekom, W., Andersen, P., Scriba, T., Schoeman, E., Krohn, C., Day, C., Africa, H., Makhethe, L., Smit, E., Brown, Y., Suliman, S., Hughes, E., Bang, P., Snowden, M., McClain, B. and Hussey, G., 2015. First-in-human trial of the post-exposure tuberculosis vaccine H56:IC31 in Mycobacterium tuberculosis infected and non-infected healthy adults. Vaccine, 33(33), pp.4130–4140
  • Suliman, S., Luabeya, A., Geldenhuys, H., Tameris, M., Hoff, S., Shi, Z., Tait, D., Kromann, I., Ruhwald, M., Rutkowski, K., Shepherd, B., Hokey, D., Ginsberg, A., Hanekom, W., Andersen, P., Scriba, T., Hatherill, M., Oelofse, R., Stone, L., Swarts, A., Onrust, R., Jacobs, G., Coetzee, L., Khomba, G., Diamond, B., Companie, A., Veldsman, A., Mulenga, H., Cloete, Y., Steyn, M., Africa, H., Nkantsu, L., Smit, E., Botes, J., Bilek, N. and Mabwe, S., 2019. Dose Optimization of H56:IC31 Vaccine for Tuberculosis-Endemic Populations. A Double-Blind, Placebo-controlled, Dose-Selection Trial. American Journal of Respiratory and Critical Care Medicine, 199(2), pp.220–231
  • Bertholet, S., Ireton, G., Ordway, D., Windish, H., Pine, S., Kahn, M., Phan, T., Orme, I., Vedvick, T., Baldwin, S., Coler, R. and Reed, S., 2010. A Defined Tuberculosis Vaccine Candidate Boosts BCG and Protects Against Multidrug-Resistant Mycobacterium tuberculosis. Science Translational Medicine, 2(53), pp.53ra74
  • Baldwin, S., Bertholet, S., Reese, V., Ching, L., Reed, S. and Coler, R., 2012. The Importance of Adjuvant Formulation in the Development of a Tuberculosis Vaccine. The Journal of Immunology, 188(5), pp.2189–2197
  • Kwon, K., Lee, A., Larsen, S., Baldwin, S., Coler, R., Reed, S., Cho, S., Ha, S. and Shin, S., 2019. Long-term protective efficacy with a BCG-prime ID93/GLA-SE boost regimen against the hyper-virulent Mycobacterium tuberculosis strain K in a mouse model. Scientific Reports, 9(1), p.15560
  • Baldwin, S., Reese, V., Huang, P., Beebe, E., Podell, B., Reed, S. and Coler, R., 2015. Protection and Long-Lived Immunity Induced by the ID93/GLA-SE Vaccine Candidate against a Clinical Mycobacterium tuberculosis Isolate. Clinical and Vaccine Immunology, 23(2), pp.137–147
  • Coler, R., Day, T., Ellis, R., Piazza, F., Beckmann, A., Vergara, J., Rolf, T., Lu, L., Alter, G., Hokey, D., Jayashankar, L., Walker, R., Snowden, M., Evans, T., Ginsberg, A. and Reed, S., 2018. The TLR-4 agonist adjuvant, GLA-SE, improves magnitude and quality of immune responses elicited by the ID93 tuberculosis vaccine: first-in-human trial. npj Vaccines, 3(1), p.34
  • Baldwin, S., Reese, V., Granger, B., Orr, M., Ireton, G., Coler, R. and Reed, S., 2014. The ID93 Tuberculosis Vaccine Candidate Does Not Induce Sensitivity to Purified Protein Derivative. Clinical and Vaccine Immunology, 21(9), pp.1309–1313
  • Lahey, T., Laddy, D., Hill, K., Schaeffer, J., Hogg, A., Keeble, J., Dagg, B., Ho, M., Arbeit, R. and von Reyn, C., 2016. Immunogenicity and Protective Efficacy of the DAR-901 Booster Vaccine in a Murine Model of Tuberculosis. PLOS ONE, 11(12), p.e0168521
  • von Reyn, C., Lahey, T., Arbeit, R., Landry, B., Kailani, L., Adams, L., Haynes, B., Mackenzie, T., Wieland-Alter, W., Connor, R., Tvaroha, S., Hokey, D., Ginsberg, A. and Waddell, R., 2017. Safety and immunogenicity of an inactivated whole cell tuberculosis vaccine booster in adults primed with BCG: A randomized, controlled trial of DAR-901. PLOS ONE, 12(5), p.e0175215
  • Masonou, T., Hokey, D., Lahey, T., Halliday, A., Berrocal-Almanza, L., Wieland-Alter, W., Arbeit, R., Lalvani, A. and von Reyn, C., 2019. CD4+ T cell cytokine responses to the DAR-901 booster vaccine in BCG-primed adults: A randomized, placebo-controlled trial. PLOS ONE, 14(5), p.e0217091
  • Martin, C., Williams, A., Hernandez-Pando, R., Cardona, P., Gormley, E., Bordat, Y., Soto, C., Clark, S., Hatch, G., Aguilar, D., Ausina, V. and Gicquel, B., 2006. The live Mycobacterium tuberculosis phoP mutant strain is more attenuated than BCG and confers protective immunity against tuberculosis in mice and guinea pigs. Vaccine, 24(17), pp.3408–3419
  • Aguilo, N., Uranga, S., Marinova, D., Monzon, M., Badiola, J. and Martin, C., 2016. MTBVAC vaccine is safe, immunogenic and confers protective efficacy against Mycobacterium tuberculosis in newborn mice. Tuberculosis, 96, pp.71–74
  • Tameris, M., Mearns, H., Penn-Nicholson, A., Gregg, Y., Bilek, N., Mabwe, S., Geldenhuys, H., Shenje, J., Luabeya, A., Murillo, I., Doce, J., Aguilo, N., Marinova, D., Puentes, E., Rodríguez, E., Gonzalo-Asensio, J., Fritzell, B., Thole, J., Martin, C., Scriba, T., Hatherill, M., Africa, H., Arendsen, D., Botes, N., Cloete, Y., De Kock, M., Erasmus, M., Jack, L., Kafaar, F., Kalepu, X., Khomba, N., Kruger, S., Leopeng, T., Makhethe, L., Mouton, A., Mulenga, H., Musvosvi, M., Noble, J., Opperman, F., Reid, T., Rossouw, S., Schreuder, C., Smit, E., Steyn, M., Tyambethu, P., Van Rooyen, E. and Veldsman, A., 2019. Live-attenuated Mycobacterium tuberculosis vaccine MTBVAC versus BCG in adults and neonates: a randomised controlled, double-blind dose-escalation trial. The Lancet Respiratory Medicine, 7(9), pp.757–770
  • Tarancón, R., Domínguez-Andrés, J., Uranga, S., Ferreira, A., Groh, L., Domenech, M., González-Camacho, F., Riksen, N., Aguilo, N., Yuste, J., Martín, C. and Netea, M., 2020. New live attenuated tuberculosis vaccine MTBVAC induces trained immunity and confers protection against experimental lethal pneumonia. PLOS Pathogens, 16(4), p.e1008404
  • Roy, A., Tomé, I., Romero, B., Lorente-Leal, V., Infantes-Lorenzo, J., Domínguez, M., Martín, C., Aguiló, N., Puentes, E., Rodríguez, E., de Juan, L., Risalde, M., Gortázar, C., Domínguez, L. and Bezos, J., 2019. Evaluation of the immunogenicity and efficacy of BCG and MTBVAC vaccines using a natural transmission model of tuberculosis. Veterinary Research, 50(1), p.82
  • Verreck, F., Vervenne, R., Kondova, I., van Kralingen, K., Remarque, E., Braskamp, G., van der Werff, N., Kersbergen, A., Ottenhoff, T., Heidt, P., Gilbert, S., Gicquel, B., Hill, A., Martin, C., McShane, H. and Thomas, A., 2009. MVA.85A Boosting of BCG and an Attenuated, phoP Deficient M. tuberculosis Vaccine Both Show Protective Efficacy Against Tuberculosis in Rhesus Macaques. PLoS ONE, 4(4), p.e5264
  • Spertini, F., Audran, R., Chakour, R., Karoui, O., Steiner-Monard, V., Thierry, A., Mayor, C., Rettby, N., Jaton, K., Vallotton, L., Lazor-Blanchet, C., Doce, J., Puentes, E., Marinova, D., Aguilo, N. and Martin, C., 2015. Safety of human immunisation with a live-attenuated Mycobacterium tuberculosis vaccine: a randomised, double-blind, controlled phase I trial. The Lancet Respiratory Medicine, 3(12), pp.953–962
  • Clark, S., Lanni, F., Marinova, D., Rayner, E., Martin, C. and Williams, A., 2017. Revaccination of Guinea Pigs With the Live Attenuated Mycobacterium tuberculosis Vaccine MTBVAC Improves BCG's Protection Against Tuberculosis. The Journal of Infectious Diseases, 216(5), pp.525–533
  • Aguilo, N., Uranga, S., Mata, E., Tarancon, R., Gómez, A., Marinova, D., Otal, I., Monzón, M., Badiola, J., Montenegro, D., Puentes, E., Rodríguez, E., Vervenne, R., Sombroek, C., Verreck, F. and Martín, C., 2020. Respiratory Immunization With a Whole Cell Inactivated Vaccine Induces Functional Mucosal Immunoglobulins Against Tuberculosis in Mice and Non-human Primates. Frontiers in Microbiology, 11, p.1339
  • Saini, V., Raghuvanshi, S., Talwar, G., Ahmed, N., Khurana, J., Hasnain, S., Tyagi, A. and Tyagi, A., 2009. Polyphasic Taxonomic Analysis Establishes Mycobacterium indicus pranii as a Distinct Species. PLoS ONE, 4(7), p.e6263
  • Yadava, A., Suresh, N., Zaheer, S., Talwar, G. and Mukherjee, R., 1991. T-Cell Responses to Fractionated Antigens of Mycobacterium w, a Candidate Anti-Leprosy Vaccine, in Leprosy Patients. Scandinavian Journal of Immunology, 34(1), pp.23–31
  • Singh, Y., Kohli, S., Sowpati, D., Rahman, S., Tyagi, A. and Hasnain, S., 2014. Gene cooption in Mycobacteria and search for virulence attributes: Comparative proteomic analyses of Mycobacterium tuberculosis, Mycobacterium indicus pranii and other mycobacteria. International Journal of Medical Microbiology, 304(5–6), pp.742–748
  • Gupta, A., Geetha, N., Mani, J., Upadhyay, P., Katoch, V., Natrajan, M., Gupta, U. and Bhaskar, S., 2008. Immunogenicity and Protective Efficacy of “Mycobacterium w” against Mycobacterium tuberculosis in Mice Immunized with Live versus Heat-Killed M. w by the Aerosol or Parenteral Route. Infection and Immunity, 77(1), pp.223–231
  • Singh, B., Saqib, M., Gupta, A., Kumar, P. and Bhaskar, S., 2017. Autophagy induction by Mycobacterium indicus pranii promotes Mycobacterium tuberculosis clearance from RAW 264.7 macrophages. PLOS ONE, 12(12), p.e0189606
  • Gupta, A., Saqib, M., Singh, B., Pal, L., Nishikanta, A. and Bhaskar, S., 2019. Mycobacterium indicus pranii Induced Memory T-Cells in Lung Airways Are Sentinels for Improved Protection Against M.tb Infection. Frontiers in Immunology, 10, p.2359
  • Nagpal, P., Kesarwani, A., Sahu, P. and Upadhyay, P., 2019. Aerosol immunization by alginate coated mycobacterium (BCG/MIP) particles provide enhanced immune response and protective efficacy than aerosol of plain mycobacterium against M.tb. H37Rv infection in mice. BMC Infectious Diseases, 19(1), p.568
  • Gupta, A., Ahmad, F., Ahmad, F., Gupta, U., Natarajan, M., Katoch, V. and Bhaskar, S., 2012. Efficacy of Mycobacterium indicus pranii Immunotherapy as an Adjunct to Chemotherapy for Tuberculosis and Underlying Immune Responses in the Lung. PLoS ONE, 7(7), p.e39215
  • Stanford, J., Stanford, C. and Grange, J., 2004. Immunotherapy with mycobacterium vaccae in the treatment of tuberculosis. Frontiers in Bioscience, 9(1), pp.1701–1719
  • Hernandez-Pando, R., Pavon, L., Orozco, E., Rangel, J. and Rook, G., 2000. Interactions between hormone-mediated and vaccine-mediated immunotherapy for pulmonary tuberculosis in BALB/c mice. Immunology, 100(3), pp.391–398
  • Bourinbaiar, A., Batbold, U., Efremenko, Y., Sanjagdorj, M., Butov, D., Damdinpurev, N., Grinishina, E., Mijiddorj, O., Kovolev, M., Baasanjav, K., Butova, T., Prihoda, N., Batbold, O., Yurchenko, L., Tseveendorj, A., Arzhanova, O., Chunt, E., Stepanenko, H., Sokolenko, N., Makeeva, N., Tarakanovskaya, M., Borisova, V., Reid, A., Kalashnikov, V., Nyasulu, P., Prabowo, S., Jirathitikal, V., Bain, A., Stanford, C. and Stanford, J., 2020. Phase III, placebo-controlled, randomized, double-blind trial of tableted, therapeutic TB vaccine (V7) containing heat-killed M. vaccae administered daily for one month. Journal of Clinical Tuberculosis and Other Mycobacterial Diseases, 18, p.100141
  • Dicks, M., Spencer, A., Edwards, N., Wadell, G., Bojang, K., Gilbert, S., Hill, A. and Cottingham, M., 2012. A Novel Chimpanzee Adenovirus Vector with Low Human Seroprevalence: Improved Systems for Vector Derivation and Comparative Immunogenicity. PLoS ONE, 7(7), p.e40385
  • Stylianou, E., Griffiths, K., Poyntz, H., Harrington-Kandt, R., Dicks, M., Stockdale, L., Betts, G. and McShane, H., 2015. Improvement of BCG protective efficacy with a novel chimpanzee adenovirus and a modified vaccinia Ankara virus both expressing Ag85A. Vaccine, 33(48), pp.6800–6808
  • Montoya, J., Solon, J., Cunanan, S., Acosta, L., Bollaerts, A., Moris, P., Janssens, M., Jongert, E., Demoitié, M., Mettens, P., Gatchalian, S., Vinals, C., Cohen, J. and Ofori-Anyinam, O., 2013. A Randomized, Controlled Dose-Finding Phase II Study of the M72/AS01 Candidate Tuberculosis Vaccine in Healthy PPD-Positive Adults. Journal of Clinical Immunology, 33(8), pp.1360–1375
  • Kumarasamy, N., Poongulali, S., Beulah, F., Akite, E., Ayuk, L., Bollaerts, A., Demoitié, M., Jongert, E., Ofori-Anyinam, O. and Van Der Meeren, O., 2018. Long-term safety and immunogenicity of the M72/AS01E candidate tuberculosis vaccine in HIV-positive and -negative Indian adults. Medicine, 97(45), p.e13120
  • Cardona, P., 2006. RUTI: A new chance to shorten the treatment of latent tuberculosis infection. Tuberculosis, 86(3–4), pp.273–289
  • Festjens, N., Bogaert, P., Batni, A., Houthuys, E., Plets, E., Vanderschaeghe, D., Laukens, B., Asselbergh, B., Parthoens, E., De Rycke, R., Willart, M., Jacques, P., Elewaut, D., Brouckaert, P., Lambrecht, B., Huygen, K. and Callewaert, N., 2011. Disruption of the SapM locus in Mycobacterium bovis BCG improves its protective efficacy as a vaccine against M. tuberculosis. EMBO Molecular Medicine, 3(4), pp.222–234
  • Grode, L., Ganoza, C., Brohm, C., Weiner, J., Eisele, B. and Kaufmann, S., 2013. Safety and immunogenicity of the recombinant BCG vaccine VPM1002 in a phase 1 open-label randomized clinical trial. Vaccine, 31(9), pp.1340–1348
  • Nieuwenhuizen, N., Kulkarni, P., Shaligram, U., Cotton, M., Rentsch, C., Eisele, B., Grode, L. and Kaufmann, S., 2017. The Recombinant Bacille Calmette–Guérin Vaccine VPM1002: Ready for Clinical Efficacy Testing. Frontiers in Immunology, 8, p.1147
  • Santosuosso, M., McCormick, S., Zhang, X., Zganiacz, A. and Xing, Z., 2006. Intranasal Boosting with an Adenovirus-Vectored Vaccine Markedly Enhances Protection by Parenteral Mycobacterium bovis BCG Immunization against Pulmonary Tuberculosis. Infection and Immunity, 74(8), pp.4634–4643
  • Abel, B., Tameris, M., Mansoor, N., Gelderbloem, S., Hughes, J., Abrahams, D., Makhethe, L., Erasmus, M., Kock, M., van der Merwe, L., Hawkridge, A., Veldsman, A., Hatherill, M., Schirru, G., Pau, M., Hendriks, J., Weverling, G., Goudsmit, J., Sizemore, D., McClain, J., Goetz, M., Gearhart, J., Mahomed, H., Hussey, G., Sadoff, J. and Hanekom, W., 2010. The Novel Tuberculosis Vaccine, AERAS-402, Induces Robust and Polyfunctional CD4+and CD8+T Cells in Adults. American Journal of Respiratory and Critical Care Medicine, 181(12), pp.1407–1417
  • Skeiky, Y., Dietrich, J., Lasco, T., Stagliano, K., Dheenadhayalan, V., Goetz, M., Cantarero, L., Basaraba, R., Bang, P., Kromann, I., McMclain, J., Sadoff, J. and Andersen, P., 2010. Non-clinical efficacy and safety of HyVac4:IC31 vaccine administered in a BCG prime–boost regimen. Vaccine, 28(4), pp.1084–1093
  • Arbues, A., Aguilo, J., Gonzalo-Asensio, J., Marinova, D., Uranga, S., Puentes, E., Fernandez, C., Parra, A., Cardona, P., Vilaplana, C., Ausina, V., Williams, A., Clark, S., Malaga, W., Guilhot, C., Gicquel, B. and Martin, C., 2013. Construction, characterization and preclinical evaluation of MTBVAC, the first live-attenuated M. tuberculosis-based vaccine to enter clinical trials. Vaccine, 31(42), pp.4867–4873
  • Aguilo, N., Gonzalo-Asensio, J., Alvarez-Arguedas, S., Marinova, D., Gomez, A., Uranga, S., Spallek, R., Singh, M., Audran, R., Spertini, F. and Martin, C., 2017. Reactogenicity to major tuberculosis antigens absent in BCG is linked to improved protection against Mycobacterium tuberculosis. Nature Communications, 8(1), p.16085

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