Clinical Testing of Tuberculosis Vaccine Candidates

Bridging the gaps to overcome major hurdles in the development of next-generation tuberculosis vaccines

Although tuberculosis (TB) remains one of the leading causes of death from an infectious disease worldwide, the development of vaccines more effective than bacille Calmette-Guérin (BCG), the only licensed TB vaccine, has progressed slowly even in the context of the tremendous global impact of TB. Most vaccine candidates have been developed to strongly induce interferon-γ (IFN-γ)-producing T-helper type 1 (Th1) cell responses; however, accumulating evidence has suggested that other immune factors are required for optimal protection against Mycobacterium tuberculosis (Mtb) infection. In this review, we briefly describe the five hurdles that must be overcome to develop more effective TB vaccines, including those with various purposes and tested in recent promising clinical trials. In addition, we discuss the current knowledge gaps between preclinical experiments and clinical studies regarding peripheral versus tissue-specific immune responses, different underlying conditions of individuals, and newly emerging immune correlates of protection. Moreover, we propose how recently discovered TB risk or susceptibility factors can be better utilized as novel biomarkers for the evaluation of vaccine-induced protection to suggest more practical ways to develop advanced TB vaccines. Vaccines are the most effective tools for reducing mortality and morbidity from infectious diseases, and more advanced technologies and a greater understanding of host-pathogen interactions will provide feasibility and rationale for novel vaccine design and development.

Particle Dynamics and Bioaerosol Viability of Aerosolized Bacillus Calmette-Guérin Vaccine Using Jet and Vibrating Mesh Clinical Nebulizers

Background: Bacillus Calmette-Guérin (BCG) is a vaccine used to protect against tuberculosis primarily in infants to stop early infection in areas of the world where the disease is endemic. Normally administered as a percutaneous injection, BCG is a live significantly attenuated bacteria that is now being investigated for its potential within an inhalable vaccine formulation. This study investigates the feasibility and performance of two jet and two vibrating mesh nebulizers aerosolizing BCG and the resulting particle characteristics and residual viability of the bacteria postaerosolization. Methods: A jet nebulizer (Collison), outfitted either with a 3- or 6-jet head, was compared with two clinical nebulizers, the vibrating mesh Omron MicroAir and Aerogen Solo devices. Particle characteristics, including aerodynamic particle sizing, was performed on all devices within a common aerosol chamber configuration and comparable BCG innocula concentrations. Integrated aerosol samples were collected for each generator and assayed for bacterial viability using conventional microbiological technique. Results: A batch lot of BCG (Danish) was grown to titer and used in all generator assessments. Aerosol particles within the respirable range were generated from all nebulizers at four different concentrations of BCG. The jet nebulizers produced a uniformly smaller particle size than the vibrating mesh devices, although particle concentrations by mass were similar across all devices tested with the exception of the Aerogen Solo, which resulted in a low concentration of BCG aerosols. Conclusions: The resulting measured viable BCG aerosol concentration fraction produced by each device approximated one another; however, a measurable decrease of efficiency and overall viability reduction in the jet nebulizer was observed in higher BCG inoculum starting concentrations, whereas the vibrating mesh nebulizer returned a remarkably stable viable aerosol fraction irrespective of inoculum concentration.

An Update on Tuberculosis Vaccines

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is a leading cause of mortality and morbidity due to a single infectious agent. Aerosol infection with Mtb can result in a range of responses from elimination, active, incipient, subclinical, and latent Mtb infections (LTBI), depending on the host's immune response and the dose and nature of infecting bacilli. Currently, BCG is the only vaccine approved to prevent TB. Although BCG confers protection against severe forms of childhood TB, its use in adults and those with comorbid conditions, such as HIV infection, is questionable. Novel vaccines, including recombinant BCG (rBCG), were developed to improve BCG's efficacy and use as an alternative to BCG in a vulnerable population. The first-generation rBCG vaccines had different Mtb antigens and were tested as a prime, prime-boost, or immunotherapeutic intervention. The novel vaccines target one or more of the following requirements, namely prevention of infection (POI), prevention of disease (POD), prevention of recurrence (POR), and therapeutic vaccines to treat a TB disease. Several vaccine candidates currently in development are classified into four primary categories: live attenuated whole-cell vaccine, inactivated whole-cell vaccine, adjuvanted protein subunit vaccine, and viral-vectored vaccine. Each vaccine's immunogenicity, safety, and efficacy are tested in preclinical animal models and further validated through various phases of clinical trials. This chapter summarizes the various TB vaccine candidates under different clinical trial stages and promises better protection against TB.

Of tuberculosis and non-tuberculous mycobacterial infections - a comparative analysis of epidemiology, diagnosis and treatment

Pulmonary diseases due to mycobacteria cause significant morbidity and mortality to human health. In addition to tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), recent epidemiological studies have shown the emergence of non-tuberculous mycobacteria (NTM) species in causing lung diseases in humans. Although more than 170 NTM species are present in various environmental niches, only a handful, primarily Mycobacterium avium complex and M. abscessus, have been implicated in pulmonary disease. While TB is transmitted through inhalation of aerosol droplets containing Mtb, generated by patients with symptomatic disease, NTM disease is mostly disseminated through aerosols originated from the environment. However, following inhalation, both Mtb and NTM are phagocytosed by alveolar macrophages in the lungs. Subsequently, various immune cells are recruited from the circulation to the site of infection, which leads to granuloma formation. Although the pathophysiology of TB and NTM diseases share several fundamental cellular and molecular events, the host-susceptibility to Mtb and NTM infections are different. Striking differences also exist in the disease presentation between TB and NTM cases. While NTM disease is primarily associated with bronchiectasis, this condition is rarely a predisposing factor for TB. Similarly, in Human Immunodeficiency Virus (HIV)-infected individuals, NTM disease presents as disseminated, extrapulmonary form rather than as a miliary, pulmonary disease, which is seen in Mtb infection. The diagnostic modalities for TB, including molecular diagnosis and drug-susceptibility testing (DST), are more advanced and possess a higher rate of sensitivity and specificity, compared to the tools available for NTM infections. In general, drug-sensitive TB is effectively treated with a standard multi-drug regimen containing well-defined first- and second-line antibiotics. However, the treatment of drug-resistant TB requires the additional, newer class of antibiotics in combination with or without the first and second-line drugs. In contrast, the NTM species display significant heterogeneity in their susceptibility to standard anti-TB drugs. Thus, the treatment for NTM diseases usually involves the use of macrolides and injectable aminoglycosides. Although well-established international guidelines are available, treatment of NTM disease is mostly empirical and not entirely successful. In general, the treatment duration is much longer for NTM diseases, compared to TB, and resection surgery of affected organ(s) is part of treatment for patients with NTM diseases that do not respond to the antibiotics treatment. Here, we discuss the epidemiology, diagnosis, and treatment modalities available for TB and NTM diseases of humans.

Tuberculosis Vaccine Development: Progress in Clinical Evaluation

Tuberculosis (TB) is the leading killer among all infectious diseases worldwide despite extensive use of the Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccine. A safer and more effective vaccine than BCG is urgently required. More than a dozen TB vaccine candidates are under active evaluation in clinical trials aimed to prevent infection, disease, and recurrence. After decades of extensive research, renewed promise of an effective vaccine against this ancient airborne disease has recently emerged. In two innovative phase 2b vaccine clinical trials, one for the prevention of Mycobacterium tuberculosis infection in healthy adolescents and another for the prevention of TB disease in M. tuberculosis-infected adults, efficacy signals were observed. These breakthroughs, based on the greatly expanded knowledge of the M. tuberculosis infection spectrum, immunology of TB, and vaccine platforms, have reinvigorated the TB vaccine field. Here, we review our current understanding of natural immunity to TB, limitations in BCG immunity that are guiding vaccinologists to design novel TB vaccine candidates and concepts, and the desired attributes of a modern TB vaccine. We provide an overview of the progress of TB vaccine candidates in clinical evaluation, perspectives on the challenges faced by current vaccine concepts, and potential avenues to build on recent successes and accelerate the TB vaccine research-and-development trajectory.

Insights and challenges in tuberculosis vaccine development

Tuberculosis kills more people than any other pathogen and the need for a universally effective vaccine has never been greater. An effective vaccine will be a key tool in achieving the targets set by WHO in the End TB Strategy. Tuberculosis vaccine development is difficult and slow. Substantial progress has been made in research and development of tuberculosis vaccines in the past 20 years, and two clinical trial results from 2018 provide reason for optimism. However, many challenges to the successful licensure and deployment of an effective tuberculosis vaccine remain. The development of new tools for vaccine evaluation might facilitate these processes, and continued collaborative working and sustained funding will be essential.

IFN-γ-independent immune markers of Mycobacterium tuberculosis exposure

Exposure to Mycobacterium tuberculosis (Mtb) results in heterogeneous clinical outcomes including primary progressive tuberculosis and latent Mtb infection (LTBI). Mtb infection is identified using the tuberculin skin test and interferon-γ (IFN-γ) release assay IGRA, and a positive result may prompt chemoprophylaxis to prevent progression to tuberculosis. In the present study, we report on a cohort of Ugandan individuals who were household contacts of patients with TB. These individuals were highly exposed to Mtb but tested negative by IFN-γ release assay and tuberculin skin test, ‘resisting’ development of classic LTBI. We show that ‘resisters’ possess IgM, class-switched IgG antibody responses and non-IFN-γ T cell responses to the Mtb-specific proteins ESAT6 and CFP10, immunologic evidence of exposure to Mtb. Compared to subjects with classic LTBI, ‘resisters’ display enhanced antibody avidity and distinct Mtb-specific IgG Fc profiles. These data reveal a distinctive adaptive immune profile among Mtb-exposed subjects, supporting an expanded definition of the host response to Mtb exposure, with implications for public health and the design of clinical trials.

New immune biomarkers of exposure to tuberculosis may require a rethink of evidence of Mycobacterium tuberculosis infection and control.

SapM mutation to improve the BCG vaccine: Genomic, transcriptomic and preclinical safety characterization

The Mycobacterium bovis Bacille Calmette Guérin (BCG) vaccine shows variable efficacy in protection against adult tuberculosis (TB). Earlier, we have described a BCG mutant vaccine with a transposon insertion in the gene coding for the secreted acid phosphatase SapM, which led to enhanced long-term survival of vaccinated mice challenged with TB infection. To facilitate development of this mutation as part of a future improved live attenuated TB vaccine, we have now characterized the genome and transcriptome of this sapM::Tn mutant versus parental BCG Pasteur. Furthermore, we show that the sapM::Tn mutant had an equal low pathogenicity as WT BCG upon intravenous administration to immunocompromised SCID mice, passing this important safety test. Subsequently, we investigated the clearance of this improved vaccine strain following vaccination and found a more effective innate immune control over the sapM::Tn vaccine bacteria as compared to WT BCG. This leads to a fast contraction of IFNγ producing Th1 and Tc1 cells after sapM::Tn BCG vaccination. These findings corroborate that a live attenuated vaccine that affords improved long-term survival upon TB infection can be obtained by a mutation that further attenuates BCG. These findings suggest that an analysis of the effectiveness of innate immune control of the vaccine bacteria could be instructive also for other live attenuated TB vaccines that are currently under development, and encourage further studies of SapM mutation as a strategy in developing a more protective live attenuated TB vaccine.

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

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

A Systematic Review on Novel Mycobacterium tuberculosis Antigens and Their Discriminatory Potential for the Diagnosis of Latent and Active Tuberculosis

Background: Current immunodiagnostic tests for tuberculosis (TB) are based on the detection of an immune response toward mycobacterial antigens injected into the skin or following an in-vitro simulation in interferon gamma-release assays. Both tests have limited sensitivity and are unable to differentiate between tuberculosis infection (LTBI) and active tuberculosis disease (aTB). To overcome this, the use of novel Mycobacterium tuberculosis (M. tuberculosis) stage-specific antigens for the diagnosis of LTBI and aTB has gained interest in recent years. This review summarizes current evidence on novel antigens used for the immunodiagnosis of tuberculosis and discrimination of LTBI and aTB. In addition, results on measured biomarkers after stimulation with novel M. tuberculosis antigens were also reviewed.

Methods: A systematic literature review was performed in Pubmed, EMBASE and web of science searching articles from 2000 up until December 2017. Only articles reporting studies in humans using novel antigens were included.

Results: Of 1,533 articles screened 34 were included in the final analysis. A wide range of novel antigens expressed during different stages and types of LTBI and aTB have been assessed. M. tuberculosis antigens Rv0081, Rv1733c, Rv1737c, Rv2029c, Rv2031 and Rv2628, all encoded by the dormancy of survival regulon, were among the most widely studied antigens and showed the most promising results. These antigens have been shown to have best potential for differentiating LTBI from aTB. In addition, several studies have shown that the inclusion of cytokines other than IFN-γ can improve sensitivity.

Conclusion: There is limited evidence that the inclusion of novel antigens as well as the measurement of other biomarkers than IFN-γ may improve sensitivity and may lead to a discrimination of LTBI from aTB.

A lipidated bi-epitope vaccine comprising of MHC-I and MHC-II binder peptides elicits protective CD4 T cell and CD8 T cell immunity against Mycobacterium tuberculosis

Background

The clinical trials conducted at Chingleput India suggest that BCG fails to protect against tuberculosis (TB) in TB-endemic population. Recent studies advocate that non-tuberculous mycobacteria and latent Mycobacterium tuberculosis (Mtb) infection interferes in the antigen processing and presentation of BCG in inducing protective immunity against Mtb. Thereby, indicating that any vaccine that require extensive antigen processing may not be efficacious in TB-endemic zones. Recently, we have demonstrated that the vaccine candidate L91, which is composed of lipidated promiscuous MHC-II binder epitope, derived from latency associated Acr1 antigen of Mtb is immunogenic in the murine and Guinea pig models of TB and conferred better protection than BCG against Mtb.

Methods

In this study, we have used a multi-stage based bi-epitope vaccine, namely L4.8, comprising of MHC-I and MHC-II binding peptides of active (TB10.4) and latent (Acr1) stages of Mtb antigens, respectively. These peptides were conjugated to the TLR-2 agonist Pam2Cys.

Results

L4.8 significantly elicited both CD8 T cells and CD4 T cells immunity, as evidenced by increase in the enduring polyfunctional CD8 T cells and CD4 T cells. L4.8 efficiently declined Mtb-burden and protected animals better than BCG and L91, even at the late stage of Mtb infection.

Conclusions

The BCG-L4.8 prime boost strategy imparts a better protection against TB than the BCG alone. This study emphatically denotes that L4.8 can be a promising future vaccine candidate for controlling active and latent TB.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1653-x) contains supplementary material, which is available to authorized users.

Development of tuberculosis vaccines in clinical trials: Current status

Tuberculosis (TB) is an important infectious disease worldwide. Currently, Bacillus Calmette-Guérin (BCG) remains the only TB vaccine licensed for human use. This TB vaccine is effective in protecting children against severe military TB but offers variable protective efficacy in adults. Therefore, new vaccines against TB are needed to overcome this serious disease. At present, around 14 TB vaccine candidates are in different phases of clinical trials. These TB vaccines in clinical evaluation can be classified into two groups including preventive pre- and post-exposure vaccines: subunit vaccines (attenuated viral vectors or adjuvanted fusion proteins), and whole-cell vaccines (genetically attenuated Mycobacterium tuberculosis (M. tb), recombinant BCG, killed M. tb or M. vaccae). Although, over the last two decades a great progress in the search for a more effective TB vaccine has been demonstrated there is still no replacement for the licensed BCG vaccine. This article summarizes the current status of TB vaccine development and identifies crucial gaps of research for the development of an effective TB vaccine in all age groups.

Prevention of M. tuberculosis Infection with H4:IC31 Vaccine or BCG Revaccination

BACKGROUND

Recent Mycobacterium tuberculosis infection confers a predisposition to the development of tuberculosis disease, the leading killer among global infectious diseases. H4:IC31, a candidate subunit vaccine, has shown protection against tuberculosis disease in preclinical models, and observational studies have indicated that primary bacille Calmette-Guérin (BCG) vaccination may offer partial protection against infection.

METHODS

In this phase 2 trial, we randomly assigned 990 adolescents in a high-risk setting who had undergone neonatal BCG vaccination to receive the H4:IC31 vaccine, BCG revaccination, or placebo. All the participants had negative results on testing for M. tuberculosis infection on the QuantiFERON-TB Gold In-tube assay (QFT) and for the human immunodeficiency virus. The primary outcomes were safety and acquisition of M. tuberculosis infection, as defined by initial conversion on QFT that was performed every 6 months during a 2-year period. Secondary outcomes were immunogenicity and sustained QFT conversion to a positive test without reversion to negative status at 3 months and 6 months after conversion. Estimates of vaccine efficacy are based on hazard ratios from Cox regression models and compare each vaccine with placebo.

RESULTS

Both the BCG and H4:IC31 vaccines were immunogenic. QFT conversion occurred in 44 of 308 participants (14.3%) in the H4:IC31 group and in 41 of 312 participants (13.1%) in the BCG group, as compared with 49 of 310 participants (15.8%) in the placebo group; the rate of sustained conversion was 8.1% in the H4:IC31 group and 6.7% in the BCG group, as compared with 11.6% in the placebo group. Neither the H4:IC31 vaccine nor the BCG vaccine prevented initial QFT conversion, with efficacy point estimates of 9.4% (P=0.63) and 20.1% (P=0.29), respectively. However, the BCG vaccine reduced the rate of sustained QFT conversion, with an efficacy of 45.4% (P=0.03); the efficacy of the H4:IC31 vaccine was 30.5% (P=0.16). There were no clinically significant between-group differences in the rates of serious adverse events, although mild-to-moderate injection-site reactions were more common with BCG revaccination.

CONCLUSIONS

In this trial, the rate of sustained QFT conversion, which may reflect sustained M. tuberculosis infection, was reduced by vaccination in a high-transmission setting. This finding may inform clinical development of new vaccine candidates. (Funded by Aeras and others; C-040-404 ClinicalTrials.gov number, NCT02075203 .).

Experimental infection of human volunteers

Controlled human infection (CHI) trials, in which healthy volunteers are experimentally infected, can accelerate the development of novel drugs and vaccines for infectious diseases of global importance. The use of CHI models is expanding from around 60 studies in the 1970s to more than 120 publications in this decade, primarily for influenza, rhinovirus, and malaria. CHI trials have provided landmark data for several registered drugs and vaccines, and have generated unprecedented scientific insights. Because of their invasive nature, CHI studies demand critical ethical review according to established frameworks. CHI-associated serious adverse events are rarely reported. Novel CHI models need standardised safety data from comparable CHI models to facilitate evidence-based risk assessments, as well as funds to produce challenge inoculum according to regulatory requirements. Advances such as the principle of controlled colonisation, the expansion of models to endemic areas, and the use of genetically attenuated strains will further broaden the scope of CHI trials.

Importance of differential identification of Mycobacterium tuberculosis strains for understanding differences in their prevalence, treatment efficacy, and vaccine development

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a serious global health problem in the 21^st century because of its high mortality. Mtb is an extremely successful human-adapted pathogen that displays a multifactorial ability to control the host immune response and to evade killing by drugs, resulting in the breakdown of BCG vaccine-conferred anti-TB immunity and development of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mtb. Although genetic components of the genomes of the Mtb complex strains are highly conserved, showing over 99% similarity to other bacterial genera, recently accumulated evidence suggests that the genetic diversity of the Mtb complex strains has implications for treatment outcomes, development of MDR/XDR Mtb, BCG vaccine efficacy, transmissibility, and epidemiological outbreaks. Thus, new insights into the pathophysiological features of the Mtb complex strains are required for development of novel vaccines and for control of MDR/XDR Mtb infection, eventually leading to refinement of treatment regimens and the health care system. Many studies have focused on the differential identification of Mtb complex strains belonging to different lineages because of differences in their virulence and geographical dominance. In this review, we discuss the impact of differing genetic characteristics among Mtb complex strains on vaccine efficacy, treatment outcome, development of MDR/XDR Mtb strains, and epidemiological outbreaks by focusing on the best-adapted human Mtb lineages. We further explore the rationale for differential identification of Mtb strains for more effective control of TB in clinical and laboratory settings by scrutinizing current diagnostic methods.

Neonatal Immunization: Rationale, Current State, and Future Prospects

Infections take their greatest toll in early life necessitating robust approaches to protect the very young. Here, we review the rationale, current state, and future research directions for one such approach: neonatal immunization. Challenges to neonatal immunization include natural concern about safety as well as a distinct neonatal immune system that is generally polarized against Th1 responses to many stimuli such that some vaccines that are effective in adults are not in newborns. Nevertheless, neonatal immunization could result in high-population penetration as birth is a reliable point of healthcare contact, and offers an opportunity for early protection of the young, including preterm newborns who are deficient in maternal antibodies. Despite distinct immunity and reduced responses to some vaccines, several vaccines have proven safe and effective at birth. While some vaccines such as polysaccharide vaccines have little effectiveness at birth, hepatitis B vaccine can prime at birth and requires multiple doses to achieve protection, whereas the live-attenuated Bacille Calmette-Guérin (BCG), may offer single shot protection, potentially in part via heterologous ("non-specific") beneficial effects. Additional vaccines have been studied at birth including those directed against pertussis, pneumococcus, Haemophilus influenza type B and rotavirus providing important lessons. Current areas of research in neonatal vaccinology include characterization of early life immune ontogeny, heterogeneity in and heterologous effects of BCG vaccine formulations, applying systems biology and systems serology, in vitro platforms that model age-specific human immunity and discovery and development of novel age-specific adjuvantation systems. These approaches may inform, de-risk, and accelerate development of novel vaccines for use in early life. Key stakeholders, including the general public, should be engaged in assessing the opportunities and challenges inherent to neonatal immunization.

Vaccines for Leprosy and Tuberculosis: Opportunities for Shared Research, Development, and Application

Tuberculosis (TB) and leprosy still represent significant public health challenges, especially in low- and lower middle-income countries. Both poverty-related mycobacterial diseases require better tools to improve disease control. For leprosy, there has been an increased emphasis on developing tools for improved detection of infection and early diagnosis of disease. For TB, there has been a similar emphasis on such diagnostic tests, while increased research efforts have also focused on the development of new vaccines. Bacille Calmette–Guérin (BCG), the only available TB vaccine, provides insufficient and inconsistent protection to pulmonary TB in adults. The impact of BCG on leprosy, however, is significant, and the introduction of new TB vaccines that might replace BCG could, therefore, have serious impact also on leprosy. Given the similarities in antigenic makeup between the pathogens Mycobacterium tuberculosis (Mtb) and M. leprae, it is well possible, however, that new TB vaccines could cross-protect against leprosy. New TB subunit vaccines currently evaluated in human phase I and II studies indeed often contain antigens with homologs in M. leprae. In this review, we discuss pre-clinical studies and clinical trials of subunit or whole mycobacterial vaccines for TB and leprosy and reflect on the development of vaccines that could provide protection against both diseases. Furthermore, we provide the first preclinical evidence of such cross-protection by Mtb antigen 85B (Ag85B)-early secretory antigenic target (ESAT6) fusion recombinant proteins in in vivo mouse models of Mtb and M. leprae infection. We propose that preclinical integration and harmonization of TB and leprosy research should be considered and included in global strategies with respect to cross-protective vaccine research and development.

TBVAC2020: Advancing Tuberculosis Vaccines from Discovery to Clinical Development

TBVAC2020 is a research project supported by the Horizon 2020 program of the European Commission (EC). It aims at the discovery and development of novel tuberculosis (TB) vaccines from preclinical research projects to early clinical assessment. The project builds on previous collaborations from 1998 onwards funded through the EC framework programs FP5, FP6, and FP7. It has succeeded in attracting new partners from outstanding laboratories from all over the world, now totaling 40 institutions. Next to the development of novel vaccines, TB biomarker development is also considered an important asset to facilitate rational vaccine selection and development. In addition, TBVAC2020 offers portfolio management that provides selection criteria for entry, gating, and priority settings of novel vaccines at an early developmental stage. The TBVAC2020 consortium coordinated by TBVI facilitates collaboration and early data sharing between partners with the common aim of working toward the development of an effective TB vaccine. Close links with funders and other consortia with shared interests further contribute to this goal.

What We Have Learned and What We Have Missed in Tuberculosis Pathophysiology for a New Vaccine Design: Searching for the "Pink Swan"

This is a call to encourage the search for a new vaccine to stop the progression of Mycobacterium tuberculosis infection to tuberculosis (TB) disease. TB is a highly discreet and stigmatized disease, with a massive impact on human health. It has killed 1.2 billion people in the last 200 years and still kills 1.5 million people per year. Over the last 20 years, the TB vaccine field has experienced spectacular developments, and we have learned about (1) the importance of the Th1 response in controlling infection, mainly against RD1 and Ag85 antigens; (2) the stability of the antigenic repertoire; (3) the dynamics of M. tuberculosis granulomas; or (4) the link between typical and atypical pulmonary TB and the immune status of the host. However, we still do not (1) know how to avoid M. tuberculosis infection and reinfection; (2) understand the major role of the increase in lesion size in progression from infection to disease; (3) the role of interlobular septa in encapsulating pulmonary lesions; or (4) the role of neutrophilic infiltration and an exaggerated inflammatory response in the development of TB disease. These are strong reasons to pursue new, imaginative proposals involving both the antibody response and a balanced, tolerant immune response that averts progression toward TB. So far, the scientific mindset has been quite monolithic and has mainly focused on the stimulation of conventional T cells. But this approach has failed. For that reason, we are seeking unconventional perspectives to find a “pink swan,” a more efficacious and safer vaccine candidate.