Different immunization methods lead to altered gut flora and varied responses to Mycobacterium tuberculosis infection in mice.

INTRODUCTION: Vaccination is an essential means for prevention of tuberculosis infection, but the effects of various vaccines on the intestinal flora of mice and their response to Mycobacterium tuberculosis (Mtb) infection remain poorly understood. METHODOLOGY: In this study, two different vaccinations - ESAT6 and ESAT6 + TLR8 agonists - were administered to mice transgenic for human TLR8 to investigate gut microbiota characteristics following vaccination. Gut microbiota was investigated by next generation sequencing in the MiSeq Sequencing System. Adonis analysis was used to evaluate the effect of variables on gut bacterial community stucture. Chao1, Shannon index, and phylogenetic diversity index were used to explore the gut bacterial diversity. RESULTS: The results showed that different vaccines have significant influence on mice intestinal bacteria (adonis analysis, p < 0.01), with gut bacterial diversity within the ESAT6 + TLR8 agonists group being significantly decreased compared to the ESAT6 treatment group (p < 0.01). Following infection with Mtb via tail vein injection, the bacterial community structure within the control versus vaccinated groups altered significantly (adonis analysis, p < 0.01), and the altered changed genera were markedly different between the groups. Following infection, Bifidobacteria differed between the groups, indicated that they play a vital role in the response to infection. CONCLUSIONS: Our results indicated that different vaccines might have distinct influences on intestinal flora, and their role should not be ignored.

New tuberculosis vaccines: advances in clinical development and modelling.

Tuberculosis remains a major source of morbidity and mortality worldwide, with 10 million cases and 1.5 million deaths in 2018. Achieving 'End TB' prevention and care goals by 2035 will likely require a new tuberculosis vaccine. The tuberculosis vaccine development pipeline has seen encouraging progress; however, questions around their population impact and implementation remain. Mathematical modelling investigates these questions to inform vaccine development and deployment strategies. We provide an update on the current vaccine development pipeline, and a systematic literature review of mathematical modelling of the epidemiological impact of new tuberculosis vaccines. Fourteen prophylactic tuberculosis vaccine candidates are currently in clinical trials. Two candidates have shown promise in phase II proof-of-concept efficacy trials: M72/AS01E demonstrated 49.7% (95% CI; 2.1, 74.2) protection against tuberculosis disease, and BCG revaccination demonstrated 45.4% (95% CI; 6.4, 68.1) protection against sustained Mycobacterium tuberculosis infection. Since the last modelling review, new studies have investigated the epidemiological impact of differential vaccine characteristics, age targeting and spatial/risk group targeting. Critical research priorities for M72/AS01E include completing the currently in-design trial, powered to improve the precision of efficacy estimates, include uninfected populations and further assess safety and immunogenicity in HIV-infected people. For BCG revaccination, the priority is completing the ongoing confirmation of efficacy trial. Critical modelling gaps remain on the full value proposition of vaccines, comparisons with other interventions and more realistic implementation strategies. Using carefully designed trials and modelling, we must prepare for success, to ensure that new vaccines will be promptly received by those most in need.

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

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

Systems approaches to correlates of protection and progression to TB disease.

Tuberculosis (TB) is the leading cause of death due to a single infectious disease and an effective vaccine would substantially accelerate global efforts to control TB. An immune correlate of protection (CoP) from TB disease could aid vaccine optimization and licensure. This paper summarises opportunities for identifying CoP and highlights results from correlates of risk studies. Although we don't have CoP, there are ongoing efficacy trials with both disease and infection endpoints which provide opportunities for such an analysis. Transcriptomics has successfully identified robust CoR, with transcripts found in the Type I IFN pathway. Correlates of lower risk include BCG antigen specific IFN-γ and natural killer cells. Collating evidence from multiple studies using a range of systems approaches supports a role for IFN-γ in protection from TB disease. In addition, the cells that express the IFN-γ receptor are also important in protective immunity. Protection is a culmination not only of the amount of IFN-γ produced by T cells and NK cells but by the ability of IFN-γ receptor expressing monocytes to respond to IFN-γ. To better understand IFN-γ as a correlate we need to understand host-factors such as age, sex, co-infection, nutritional status and stress which may alter or impair the ability of cells to respond to IFN-γ. These studies highlight recent advances in our understanding of the immune mechanisms of TB disease risk and show the importance of whole systems approaches to correlates of risk analysis. CoP may be useful tools for specific vaccine products in specific populations, but a well-designed CoR analysis can identify novel immune mechanisms and provide insights critical for the development of new and better TB vaccines.

Immunization strategies against pulmonary tuberculosis: considerations of T cell geography.

Pulmonary tuberculosis (TB) remains a global health concern with an astounding 9 million new cases and 2 million deaths per year. This leading infectious cause of death remains highly prevalent with one third of the world's population latently infected with Mycobacterium tuberculosis (M.tb) despite routine vaccination against TB in endemic areas. The only approved TB vaccine is the Bacille Calmette-Guerin (BCG), which provides protection against childhood miliary tuberculosis and has been administered intradermally in humans for almost a century. While effective in preventing disseminated forms of TB, the BCG has variable efficacy in providing protection against pulmonary TB. Therefore, the BCG has been unable to control the instance of adult pulmonary TB which constitutes the global disease burden. Despite the fact that mechanisms underlying the lack of pulmonary protection provided by the BCG remain poorly understood, it remains the "Gold Standard" for vaccine-mediated protection against M.tb and will continue to be used for the foreseeable future. Therefore, continued effort has been placed on understanding the mechanisms behind the failure of BCG to provide sufficient protection against M.tb in the lung and to design new vaccines to be used in conjunction with the BCG as boost strategies to install protective immunity at the site of infection. Growing evidence supports that the route of immunization dictates the geographical location of TB-reactive T cells, and it is this distribution which predicts the protective outcome of such vaccine-elicited immunity. Such vaccines that are able to localize TB-reactive T cells to the lung and airway mucosa are thought to fill the "immunological gap" in the lung that is required for enhanced protection against M.tb infection. This chapter focuses on the critical importance of T cell geography when designing new immunization strategies against pulmonary TB.

Improved CD4⁺ T cell responses to Mycobacterium tuberculosis in PPD-negative adults by M72/AS01 as compared to the M72/AS02 and Mtb72F/AS02 tuberculosis candidate vaccine formulations: a randomized trial.

BACKGROUND: The Bacille Calmette-Guérin (BCG) tuberculosis (TB) vaccine provides incomplete protection, necessitating development of an effective vaccine against TB disease. The Mtb72F/AS02 candidate vaccine was previously shown to be clinically well tolerated and immunogenic in Purified Protein Derivative (PPD)-negative adults. To improve the stability of Mtb72F, a point mutation was introduced into a putative serine protease site to give the final M72 construct. AS01 is an Adjuvant System that can potentially improve both humoral and cellular immune responses compared to the AS02 Adjuvant System or unadjuvanted vaccine. This study evaluated the safety and immunogenicity in Mtb-naïve adults of vaccines containing 40 µg of the M72 antigen with AS02 or AS01 and compared the results with Mtb72F/AS02 vaccine (40 µg dose), M72 in saline (40 µg dose) and AS01 alone. METHODS: In this Phase I/II observer-blind controlled trial, 110 participants were randomized (4:4:1:1:1) to receive M72/AS01, M72/AS02, Mtb72F/AS02, M72/saline or AS01, following a 0, 1-month schedule. Subjects receiving the adjuvanted M72 vaccines were followed up until 3 years post vaccination. Evaluation of the immune response and safety/reactogenicity was performed. RESULTS: For all vaccines, solicited adverse events (AEs) were predominantly mild to moderate and transient. No vaccine-related serious AEs occurred and no subject withdrew due to an AE. Immune responses induced by Mtb72F and M72 antigens combined with AS02 were similar. M72/AS01 and M72/AS02 induced robust polyfunctional M72-specific CD4(+) T cell and antibody responses persisting at 3 years, with the highest CD4(+) T cell responses found with M72/AS01. CONCLUSION: This first clinical study with M72/AS01 and M72/AS02 showed that both vaccines were clinically well tolerated and induced high magnitude and persistent cell-mediated and humoral immune responses. The Mtb72F/AS02 and M72/AS02 vaccines were comparably immunogenic with significantly higher immune responses compared to the M72/saline control. Of the formulations tested, M72/AS01 demonstrated significantly higher vaccine specific Th1 CD4(+) T cell responses supporting its further clinical evaluation.

Modeling the effects of strain diversity and mechanisms of strain competition on the potential performance of new tuberculosis vaccines.

While bacillus Calmette-Guérin vaccination plays an important role in reducing the morbidity of tuberculosis (TB) infection during childhood, new tuberculosis vaccines are necessary to disrupt the transmission of disease and improve global control of this pathogen. Growing evidence of the presence of meaningful Mycobacterium tuberculosis strain diversity, coupled with the possibility that new vaccines may differentially protect against infection or disease with circulating M. tuberculosis strains, suggest that these vaccines may have complicated effects on disease dynamics. We use a mathematical model to explore the potential effects of strain diversity on the performance of vaccines and find that vaccines offer great promise for improving tuberculosis control, but the expected benefits of mass vaccination will be eroded if strain replacement with M. tuberculosis variants that are not effectively targeted by vaccines occurs. Determining the likelihood of strain replacement will require additional knowledge of the strain specificities of current vaccine candidates, and an improved understanding of the mechanisms of strain interaction, which are responsible for maintaining the diversity of M. tuberculosis within communities.

Bovine TB and the development of new vaccines.

Bovine tuberculosis (bTB) is caused by Mycobacterium bovis. The incidence of bTB is increasing in cattle herds of developed countries that have a wild life reservoir of M. bovis, such as the UK, New Zealand and the USA. The increase in the incidence of bTB is thought to be due, at least in part, to a wildlife reservoir of M. bovis. M. bovis is also capable of infecting humans and on a worldwide basis, M. bovis is thought to account for up to 10% of cases of human TB [Cosivi O, Grange JM, Daborn CJ et al. Zoonotic tuberculosis due to Mycobacterium bovis in developing countries. Emerg Infect Dis 1998;4(1):59-70]. Thus, the increased incidence of bTB, besides being a major economic problem, poses an increased risk to human health. In the UK, the incidence of bTB continues to rise despite the use of the tuberculin test and slaughter control policy, highlighting the need for improved control strategies. Vaccination of cattle, in combination with more specific and sensitive diagnostic tests, is suggested as the most effective strategy for bovine TB control. The only vaccine currently available for human and bovine TB is the live attenuated Bacille Calmette Guerin (BCG). BCG is thought to confer protection through the induction of Th1 responses against mycobacteria. However, protection against TB conferred by BCG is variable and to this date the reasons for the successes and failures of BCG are not clear. Therefore, there is a need to develop vaccines that confer greater and more consistent protection against bTB than that afforded by BCG. Given that BCG is currently the only licensed vaccine against human TB, it is likely that any new vaccine or vaccination strategy will be based around BCG. In this review we discuss immune responses elicited by mycobacteria in cattle and the novel approaches emerging for the control of bovine TB based on our increasing knowledge of protective immune responses.