An Auto-luminescent Fluorescent BCG Whole Blood Assay to Enable Evaluation of Paediatric Mycobacterial Responses Using Minimal Blood Volumes

Practical considerations for a TB controlled human infection model (TB-CHIM); the case for TB-CHIM in Africa, a systematic review of the literature and report of 2 workshop discussions in UK and Malawi

Background: Tuberculosis (TB) remains a major challenge in many domains including diagnosis, pathogenesis, prevention, treatment, drug resistance and long-term protection of the public health by vaccination. A controlled human infection model (CHIM) could potentially facilitate breakthroughs in each of these domains but has so far been considered impossible owing to technical and safety concerns. Methods: A systematic review of mycobacterial human challenge studies was carried out to evaluate progress to date, best possible ways forward and challenges to be overcome. We searched MEDLINE (1946 to current) and CINAHL (1984 to current) databases; and Google Scholar to search citations in selected manuscripts. The final search was conducted 3 rd February 2022. Inclusion criteria: adults ≥18 years old; administration of live mycobacteria; and interventional trials or cohort studies with immune and/or microbiological endpoints. Exclusion criteria: animal studies; studies with no primary data; no administration of live mycobacteria; retrospective cohort studies; case-series; and case-reports. Relevant tools (Cochrane Collaboration for RCTs and Newcastle-Ottawa Scale for non-randomised studies) were used to assess risk of bias and present a narrative synthesis of our findings. Results: The search identified 1,388 titles for review; of these 90 were reviewed for inclusion; and 27 were included. Of these, 15 were randomised controlled trials and 12 were prospective cohort studies. We focussed on administration route, challenge agent and dose administered for data extraction. Overall, BCG studies including fluorescent BCG show the most immediate utility, and genetically modified Mycobacteria tuberculosis is the most tantalising prospect of discovery breakthrough. Conclusions: The TB-CHIM development group met in 2019 and 2022 to consider the results of the systematic review, to hear presentations from many of the senior authors whose work had been reviewed and to consider best ways forward. This paper reports both the systematic review and the deliberations. Registration: PROSPERO ( CRD42022302785; 21 January 2022).

Controlled human infection models in COVID-19 and tuberculosis: current progress and future challenges

Controlled Human Infection Models (CHIMs) involve deliberately exposing healthy human volunteers to a known pathogen, to allow the detailed study of disease processes and evaluate methods of treatment and prevention, including next generation vaccines. CHIMs are in development for both tuberculosis (TB) and Covid-19, but challenges remain in their ongoing optimisation and refinement. It would be unethical to deliberately infect humans with virulent Mycobacteria tuberculosis (M.tb), however surrogate models involving other mycobacteria, M.tb Purified Protein Derivative or genetically modified forms of M.tb either exist or are under development. These utilise varying routes of administration, including via aerosol, per bronchoscope or intradermal injection, each with their own advantages and disadvantages. Intranasal CHIMs with SARS-CoV-2 were developed against the backdrop of the evolving Covid-19 pandemic and are currently being utilised to both assess viral kinetics, interrogate the local and systemic immunological responses post exposure, and identify immune correlates of protection. In future it is hoped they can be used to assess new treatments and vaccines. The changing face of the pandemic, including the emergence of new virus variants and increasing levels of vaccination and natural immunity within populations, has provided a unique and complex environment within which to develop a SARS-CoV-2 CHIM. This article will discuss current progress and potential future developments in CHIMs for these two globally significant pathogens.

Practical considerations for a TB controlled human infection model (TB-CHIM); the case for TB-CHIM in Africa, a systematic review of the literature and report of 2 workshop discussions in UK and Malawi

Background: Tuberculosis (TB) remains a major challenge in many domains including diagnosis, pathogenesis, prevention, treatment, drug resistance and long-term protection of the public health by vaccination. A controlled human infection model (CHIM) could potentially facilitate breakthroughs in each of these domains but has so far been considered impossible owing to technical and safety concerns. Methods: A systematic review of mycobacterial human challenge studies was carried out to evaluate progress to date, best possible ways forward and challenges to be overcome. We searched MEDLINE (1946 to current) and CINAHL (1984 to current) databases; and Google Scholar to search citations in selected manuscripts. The final search was conducted 3 rd February 2022. Inclusion criteria: adults ≥18 years old; administration of live mycobacteria; and interventional trials or cohort studies with immune and/or microbiological endpoints. Exclusion criteria: animal studies; studies with no primary data; no administration of live mycobacteria; retrospective cohort studies; case-series; and case-reports. Relevant tools (Cochrane Collaboration for RCTs and Newcastle-Ottawa Scale for non-randomised studies) were used to assess risk of bias and present a narrative synthesis of our findings. Results: The search identified 1,388 titles for review; of these 90 were reviewed for inclusion; and 27 were included. Of these, 15 were randomised controlled trials and 12 were prospective cohort studies. We focussed on administration route, challenge agent and dose administered for data extraction. Overall, BCG studies including fluorescent BCG show the most immediate utility, and genetically modified Mycobacteria tuberculosis is the most tantalising prospect of discovery breakthrough. Conclusions: The TB-CHIM development group met in 2019 and 2022 to consider the results of the systematic review, to hear presentations from many of the senior authors whose work had been reviewed and to consider best ways forward. This paper reports both the systematic review and the deliberations. Registration: PROSPERO ( CRD42022302785; 21 January 2022).

Comparative transcriptomic analysis of whole blood mycobacterial growth assays and tuberculosis patients' blood RNA profiles

In vitro whole blood infection models are used for elucidating the immune response to Mycobacterium tuberculosis (Mtb). They exhibit commonalities but also differences, to the in vivo blood transcriptional response during natural human Mtb disease. Here, we present a description of concordant and discordant components of the immune response in blood, quantified through transcriptional profiling in an in vitro whole blood infection model compared to whole blood from patients with tuberculosis disease. We identified concordantly and discordantly expressed gene modules and performed in silico cell deconvolution. A high degree of concordance of gene expression between both adult and paediatric in vivo-in vitro tuberculosis infection was identified. Concordance in paediatric in vivo vs in vitro comparison is largely characterised by immune suppression, while in adults the comparison is marked by concordant immune activation, particularly that of inflammation, chemokine, and interferon signalling. Discordance between in vitro and in vivo increases over time and is driven by T-cell regulation and monocyte-related gene expression, likely due to apoptotic depletion of monocytes and increasing relative fraction of longer-lived cell types, such as T and B cells. Our approach facilitates a more informed use of the whole blood in vitro model, while also accounting for its limitations.

Innate Immune Responses of Galleria mellonella to Mycobacterium bovis BCG Challenge Identified Using Proteomic and Molecular Approaches

The larvae of the insect Galleria mellonella, have recently been established as a non-mammalian infection model for the Mycobacterium tuberculosis complex (MTBC). To gain further insight into the potential of this model, we applied proteomic (label-free quantification) and transcriptomic (gene expression) approaches to characterise the innate immune response of G. mellonella to infection with Mycobacterium bovis BCG lux over a 168 h time course. Proteomic analysis of the haemolymph from infected larvae revealed distinct changes in the proteome at all time points (4, 48, 168 h). Reverse transcriptase quantitative PCR confirmed induction of five genes (gloverin, cecropin, IMPI, hemolin, and Hdd11), which encoded proteins found to be differentially abundant from the proteomic analysis. However, the trend between gene expression and protein abundance were largely inconsistent (20%). Overall, the data are in agreement with previous phenotypic observations such as haemocyte internalization of mycobacterial bacilli (hemolin/β-actin), formation of granuloma-like structures (Hdd11), and melanization (phenoloxidase activating enzyme 3 and serpins). Furthermore, similarities in immune expression in G. mellonella, mouse, zebrafish and in vitro cell-line models of tuberculosis infection were also identified for the mechanism of phagocytosis (β-actin). Cecropins (antimicrobial peptides), which share the same α-helical motif as a highly potent peptide expressed in humans (h-CAP-18), were induced in G. mellonella in response to infection, giving insight into a potential starting point for novel antimycobacterial agents. We believe that these novel insights into the innate immune response further contribute to the validation of this cost-effective and ethically acceptable insect model to study members of the MTBC.

Protection against mycobacterial infection: A case-control study of mycobacterial immune responses in pairs of Gambian children with discordant infection status despite matched TB exposure

BACKGROUND

Children are particularly susceptible to tuberculosis. However, most children exposed to Mycobacterium tuberculosis are able to control the pathogen without evidence of infection. Correlates of human protective immunity against tuberculosis infection are lacking, and their identification would aid vaccine design.

METHODS

We recruited pairs of asymptomatic children with discordant tuberculin skin test status but the same sleeping proximity to the same adult with sputum smear-positive tuberculosis in a matched case-control study in The Gambia. Participants were classified as either Highly TB-Exposed Uninfected or Highly TB-Exposed Infected children. Serial luminescence measurements using an in vitro functional auto-luminescent Bacillus Calmette-Guérin (BCG) whole blood assay quantified the dynamics of host control of mycobacterial growth. Assay supernatants were analysed with a multiplex cytokine assay to measure associated inflammatory responses.

FINDINGS

29 pairs of matched Highly TB-Exposed Uninfected and Highly TB-Exposed Infected children aged 5 to 15 years old were enroled. Samples from Highly TB-Exposed Uninfected children had higher levels of mycobacterial luminescence at 96 hours than Highly TB-Exposed Infected children. Highly TB-Exposed Uninfected children also produced less BCG-specific interferon-γ than Highly TB-Exposed Infected children at 24 hours and at 96 hours.

INTERPRETATION

Highly TB-Exposed Uninfected children showed less control of mycobacterial growth compared to Highly TB-Exposed Infected children in a functional assay, whilst cytokine responses mirrored infection status.

FUNDING

Clinical Research Training Fellowship funded under UK Medical Research Council/Department for International Development Concordat agreement and part of EDCTP2 programme supported by European Union (MR/K023446/1). Also MRC Program Grants (MR/K007602/1, MR/K011944/1, MC_UP_A900/1122).

Stimulation of Nucleotide Oligomerization Domain and Toll-Like Receptors 2 to Enhance the Effect of Bacillus Calmette Guerin Immunization for Prevention of Mycobacterium Tuberculosis Infection: Protocol for a Series of Preclinical Randomized Controlled Trials

Background

Bacillus calmette guerin (BCG) immunization has been associated with a reduction in Mycobacterium tuberculosis (MTB) infection. BCG immunization has been shown to enhance innate immunity. This effect of BCG can be explained by an enhancing effect on innate immunity.

Objective

This study aimed to test the following hypotheses: (1) BCG immunization can prevent infection with MTB, (2) prevention of infection occurs via stimulation of NOD2 (nucleotide oligomerization domain) and toll-like receptors 2 (TLR2), and (3) the effect of BCG immunization on prevention of infection with MTB can be enhanced by giving stimulators of NOD2 and TLR2.

Methods

To detect the influence of immunization on infection rates, the ultralow dose (ULD) infection model is used. The infection rate of mice vaccinated with BCG and exposed after 6 weeks to ULD of MTB and unvaccinated mice are compared via cultures of lung homogenates and interferon (IFN) gamma release assay. If a reduced infection rate by BCG immunization is confirmed, the experiment is repeated by giving BCG combined simultaneously or in time sequence with the enhancers of innate immunity murabutide or beta-glycan. The influence of murabutide or beta-glycan alone on infection rates is investigated. To quantify the contribution of innate immunity levels of tumor necrosis factor, IFN gamma expression, histone H3 K4me3 trimethylation, and concentrations of monocytes with features of activation of innate immunity as defined by the Ly6Chigh as well as CD11b positive phenotype in immunized versus unimmunized infected and uninfected mice in the various immunization protocols is compared. The experiments will be repeated with prior application of the inhibitors of epigenetic programming of innate immunity histone methyltransferase inhibitor 5’-deoxy-5’-methylthio-adenosine and histone acetyl transferase inhibitor epigallocatechin-3-gallate. The influence of BCG on innate immunity is further corroborated by a prospective observational study in human infants.

Results

Investigations of derivatives of muramyl dipeptide (MDP) to enhance early immunity in the C57BL/6 mouse strain (mice aged 7 weeks) by another group used 300 micrograms per mouse of oil-associated 6-0-mycoloyl-N-acetylmuramyl-L-alanyl-D-isoglutamine (mycol-MDP) 50/50 mixed with Freund’s incomplete adjuvant. Comparison of colony-forming unit (CFU) count in the lungs 3 weeks after aerosol challenge with Mycobacterium bovis of groups (n=5) between groups receiving mycol-MDP in oil emulsion (see above) versus controls (n=5) showed a significantly lower CFU count of 94.5 x106 (SD 22.0) in cases versus controls with 204.0 X 106 (SD 77.6). It is important to note that after elimination of T-cells in this model, a reduction of CFU in lungs of mice treated with mycol-MDP persisted albeit without statistical significance, which was possibly related to the small number of animals used.

Conclusions

Demonstration of a reduction of MTB infection by enhancement of innate immunity could show a new approach to improving vaccine efficacy against this pathogen.

International Registered Report Identifier (IRRID)

PRR1-10.2196/13045