Age-Stratified T Cell Responses in Children Infected with Mycobacterium tuberculosis

A Review Of Host-Specific Diagnostic And Surrogate Biomarkers In Children With Pulmonary Tuberculosis

BACKGROUND

Tuberculosis (TB) is one of the most common causes of mortality globally with a steady rise in paediatric cases in the past decade. Laboratory methods of diagnosing TB and monitoring response to treatment have limitations. Current research focuses on interrogating host- and/or pathogen-specific biomarkers to address this problem.

METHODS

We reviewed the literature on host-specific biomarkers in TB to determine their value in diagnosis and treatment response in TB infected and HIV/TB co-infected children on anti-tuberculosis treatment.

RESULTS AND CONCLUSION

While no single host-specific biomarker has been identified for diagnosis or treatment responses in children, several studies suggest predictive biosignatures for disease activity. Alarmingly, current data on host-specific biomarkers for diagnosing and assessing anti-tuberculosis treatment in TB/HIV co-infected children is inadequate. Various factors affecting host-specific biomarker responses should be considered in interpreting findings and designing future studies within specific clinical settings.

Evolving role of chest radiographs for diagnosis of pediatric pulmonary tuberculosis

Chest radiographs (CXR) have played an important and evolving role in diagnosis, classification and management of pediatric pulmonary tuberculosis (TB). During the pre-chemotherapy era, CXR aided in determining infectiousness, mainly to guide isolation practices, by detecting calcified and non-calcified lymphadenopathy. The availability of TB chemotherapy from the mid-1900s increased the urgency to find accurate diagnostic tools for what had become a treatable disease. Chest radiographs provided the mainstay of diagnosis in children, despite high inter-reader variability limiting its accuracy. The development of cross-sectional imaging modalities, such as computed tomography, provided more accurate intra-thoracic lymph node assessment, but these modalities have major availability, cost and radiation exposure disadvantages. As a consequence, CXR remains the most widely used modality for childhood  pulmonary TB diagnosis, given its relatively low cost and accessibility. Publication of the revised 2022 World Health Organization Consolidated TB guidelines added practical value to CXR interpretation in children, by allowing the selection of children for shorter TB treatment using radiological signs of severity of disease, that have high reliability. This article provides a review of the historical journey and evolving role of CXR in pediatric pulmonary TB.

Performance of adenosine deaminase in detecting paediatric pleural tuberculosis: a systematic review and meta-analysis

BACKGROUND

Paediatric pleural tuberculosis (TB) is a paucibacillary disease, which increases the difficulty of examination. We aimed to assess the performance of pleural fluid adenosine deaminase (ADA) in the detection of paediatric pleural TB.

METHODS

PubMed, Web of Science Core Collection, Embase and Cochrane Library databases were searched up to 20 December 2021. We used the bivariate and hierarchical summary receiver operating characteristic models to compute pooled estimates for the overall diagnostic accuracy parameters of ADA for diagnosing paediatric pleural TB.

RESULTS

Eight studies, including 290 pleural fluid samples, met the inclusion criteria. The pooled sensitivity of ADA was 0.85 (95% CI: 0.78-0.90, I²: 55.63% < 75%) for detecting patients with paediatric pleural TB. A total of 262 pleural fluid samples from four studies were included to differentiate patients with paediatric pleural TB from controls. At a unified cut-off value of 40 U/L, the pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio and area under the summary receiver operating characteristic curve of ADA were 0.89, 0.58, 2.09, 0.20, 10.48 and 0.89, respectively.

CONCLUSIONS

At a cut-off value of 40 U/L, the overall performance of ADA was good for detecting paediatric pleural TB, with relatively high sensitivity and low specificity. Key messageAccurate identification of paediatric pleural TB will help eliminate TB in children. At a cut-off value of 40 U/L, the overall performance of ADA was good for detecting paediatric pleural TB, with relatively high sensitivity and low specificity.

Immuno-Diagnosis of Active Tuberculosis by a Combination of Cytokines/Chemokines Induced by Two Stage-Specific Mycobacterial Antigens: A Pilot Study in a Low TB Incidence Country

Active tuberculosis (aTB) remains a major killer from infectious disease, partially due to delayed diagnosis and hence treatment. Classical microbiological methods are slow and lack sensitivity, molecular techniques are costly and often unavailable. Moreover, available immuno-diagnostic tests lack sensitivity and do not differentiate between aTB and latent TB infection (LTBI). Here, we evaluated the performance of the combined measurement of different chemokines/cytokines induced by two different stage-specific mycobacterial antigens, Early-secreted-antigenic target-6 (ESAT-6) and Heparin-binding-haemagglutinin (HBHA), after a short in vitro incubation of either peripheral blood mononuclear cells (PBMC) or whole blood (WB). Blood samples were collected from a training cohort comprising 22 aTB patients, 22 LTBI subjects and 17 non-infected controls. The concentrations of 13 cytokines were measured in the supernatants. Random forest analysis identified the best markers to differentiate M. tuberculosis-infected from non-infected subjects, and the most appropriate markers to differentiate aTB from LTBI. Logistic regression defined predictive abilities of selected combinations of cytokines, first on the training and then on a validation cohort (17 aTB, 27 LTBI, 25 controls). Combining HBHA- and ESAT-6-induced IFN-γ concentrations produced by PBMC was optimal to differentiate infected from non-infected individuals in the training cohort (100% correct classification), but 2/16 (13%) patients with aTB were misclassified in the validation cohort. ESAT-6-induced-IP-10 combined with HBHA-induced-IFN-γ concentrations was selected to differentiate aTB from LTBI, and correctly classified 82%/77% of infected subjects as aTB or LTBI in the training/validation cohorts, respectively. Results obtained on WB also selected ESAT-6- and HBHA-induced IFN-γ concentrations to provided discrimination between infected and non-infected subjects (89%/90% correct classification in the training/validation cohorts). Further identification of aTB patients among infected subjects was best achieved by combining ESAT-6-induced IP-10 with HBHA-induced IL-2 and GM-CSF. Among infected subjects, 90%/93% of the aTB patients were correctly identified in the training/validation cohorts. We therefore propose a two steps strategy performed on 1 mL WB for a rapid identification of patients with aTB. After elimination of most non-infected subjects by combining ESAT-6 and HBHA-induced IFN-γ, the combination of IP-10, IL-2 and GM-CSF released by either ESAT-6 or HBHA correctly identifies most patients with aTB.

The Magnitude of Interferon Gamma Release Assay Responses in Children With Household Tuberculosis Contact Is Associated With Tuberculosis Exposure and Disease Status

BACKGROUND

The clinical utility of the magnitude of interferon gamma (IFNγ) in response to mycobacterial antigens is unknown. We assessed the association between quantitative IFNγ response and degree of Mycobacterium tuberculosis exposure, infection and tuberculosis (TB) disease status in children.

METHODS

We completed cross-sectional analysis of children (≤15 years) exposed to an adult with bacteriologically confirmed TB, 2007-2012 in Cape Town, South Africa. IFNγ values were reported as concentrations and spot forming units for the QuantiFERON-TB Gold In-Tube (QFT-GIT) and T-SPOT.TB, respectively. Random-effects linear regression was used to investigate the relation between the M. tuberculosis contact score, clinical phenotype (TB diseased, infected, uninfected) and IFNγ▪response as outcome, adjusted for relevant covariates.

RESULTS

We analyzed data from 669 children (median age, 63 months; interquartile range, 33-108 months). A 1-unit increase in M. tuberculosis contact score was associated with an increase of IFNγ 0.60 international unit/mL (95% confidence interval [CI], 0.44-0.76 international unit/mL), and IFNγ spot forming unit 2 counts (95% CI, 1-3). IFNγ response was significantly lower among children with M. tuberculosis infection compared with children with TB disease (β = -1.42; 95% CI, -2.80 to -0.03) for the QFT-GIT, but not for the T-SPOT.TB. This association was strongest among children 2-5 years (β = -2.35 years; 95% CI, -4.28 to -0.42 years) and absent if <2 years.

CONCLUSIONS

The magnitude of IFNγ response correlated with the degree of recent M. tuberculosis exposure, measured by QFT-GIT and T-SPOT.TB, and was correlated with clinically relevant TB phenotypes using the QFT-GIT. IFNγ values are not only useful in estimating the risk of M. tuberculosis infection but may also support the diagnosis of TB disease in children.

DISCUSSION

The magnitude of IFNγ response correlated with the degree of recent M. tuberculosis exposure, measured by QFT-GIT and T-SPOT.TB, and was correlated with clinically relevant TB phenotypes using the QFT-GIT. IFNγ values are not only useful in estimating the risk of M. tuberculosis infection but may also support the diagnosis of TB disease in children.

Screening tests for active pulmonary tuberculosis in children

BACKGROUND

Globally, children under 15 years represent approximately 12% of new tuberculosis cases, but 16% of the estimated 1.4 million deaths. This higher share of mortality highlights the urgent need to develop strategies to improve case detection in this age group and identify children without tuberculosis disease who should be considered for tuberculosis preventive treatment. One such strategy is systematic screening for tuberculosis in high-risk groups.

OBJECTIVES

To estimate the sensitivity and specificity of the presence of one or more tuberculosis symptoms, or symptom combinations; chest radiography (CXR); Xpert MTB/RIF; Xpert Ultra; and combinations of these as screening tests for detecting active pulmonary childhood tuberculosis in the following groups. - Tuberculosis contacts, including household contacts, school contacts, and other close contacts of a person with infectious tuberculosis. - Children living with HIV. - Children with pneumonia. - Other risk groups (e.g. children with a history of previous tuberculosis, malnourished children). - Children in the general population in high tuberculosis burden settings.

SEARCH METHODS

We searched six databases, including the Cochrane Central Register of Controlled Trials, MEDLINE, and Embase, on 14 February 2020 without language restrictions and contacted researchers in the field.

SELECTION CRITERIA

Cross-sectional and cohort studies where at least 75% of children were aged under 15 years. Studies were eligible if conducted for screening rather than diagnosing tuberculosis. Reference standards were microbiological (MRS) and composite reference standard (CRS), which may incorporate symptoms and CXR.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed study quality using QUADAS-2. We consolidated symptom screens across included studies into groups that used similar combinations of symptoms as follows: one or more of cough, fever, or poor weight gain and one or more of cough, fever, or decreased playfulness. For combination of symptoms, a positive screen was the presence of one or more than one symptom. We used a bivariate model to estimate pooled sensitivity and specificity with 95% confidence intervals (CIs) and performed analyses separately by reference standard. We assessed certainty of evidence using GRADE.

MAIN RESULTS

Nineteen studies assessed the following screens: one symptom (15 studies, 10,097 participants); combinations of symptoms (12 studies, 29,889 participants); CXR (10 studies, 7146 participants); and Xpert MTB/RIF (2 studies, 787 participants). Several studies assessed more than one screening test. No studies assessed Xpert Ultra. For 16 studies (84%), risk of bias for the reference standard domain was unclear owing to concern about incorporation bias. Across other quality domains, risk of bias was generally low. Symptom screen (verified by CRS) One or more of cough, fever, or poor weight gain in tuberculosis contacts (4 studies, tuberculosis prevalence 2% to 13%): pooled sensitivity was 89% (95% CI 52% to 98%; 113 participants; low-certainty evidence) and pooled specificity was 69% (95% CI 51% to 83%; 2582 participants; low-certainty evidence). Of 1000 children where 50 have pulmonary tuberculosis, 339 would be screen-positive, of whom 294 (87%) would not have pulmonary tuberculosis (false positives); 661 would be screen-negative, of whom five (1%) would have pulmonary tuberculosis (false negatives). One or more of cough, fever, or decreased playfulness in children aged under five years, inpatient or outpatient (3 studies, tuberculosis prevalence 3% to 13%): sensitivity ranged from 64% to 76% (106 participants; moderate-certainty evidence) and specificity from 37% to 77% (2339 participants; low-certainty evidence). Of 1000 children where 50 have pulmonary tuberculosis, 251 to 636 would be screen-positive, of whom 219 to 598 (87% to 94%) would not have pulmonary tuberculosis; 364 to 749 would be screen-negative, of whom 12 to 18 (2% to 3%) would have pulmonary tuberculosis. One or more of cough, fever, poor weight gain, or tuberculosis close contact (World Health Organization four-symptom screen) in children living with HIV, outpatient (2 studies, tuberculosis prevalence 3% and 8%): pooled sensitivity was 61% (95% CI 58% to 64%; 1219 screens; moderate-certainty evidence) and pooled specificity was 94% (95% CI 86% to 98%; 201,916 screens; low-certainty evidence). Of 1000 symptom screens where 50 of the screens are on children with pulmonary tuberculosis, 88 would be screen-positive, of which 57 (65%) would be on children who do not have pulmonary tuberculosis; 912 would be screen-negative, of which 19 (2%) would be on children who have pulmonary tuberculosis. CXR (verified by CRS) CXR with any abnormality in tuberculosis contacts (8 studies, tuberculosis prevalence 2% to 25%): pooled sensitivity was 87% (95% CI 75% to 93%; 232 participants; low-certainty evidence) and pooled specificity was 99% (95% CI 68% to 100%; 3281 participants; low-certainty evidence). Of 1000 children, where 50 have pulmonary tuberculosis, 63 would be screen-positive, of whom 19 (30%) would not have pulmonary tuberculosis; 937 would be screen-negative, of whom 6 (1%) would have pulmonary tuberculosis. Xpert MTB/RIF (verified by MRS) Xpert MTB/RIF, inpatient or outpatient (2 studies, tuberculosis prevalence 1% and 4%): sensitivity was 43% and 100% (16 participants; very low-certainty evidence) and specificity was 99% and 100% (771 participants; moderate-certainty evidence). Of 1000 children, where 50 have pulmonary tuberculosis, 31 to 69 would be Xpert MTB/RIF-positive, of whom 9 to 19 (28% to 29%) would not have pulmonary tuberculosis; 969 to 931 would be Xpert MTB/RIF-negative, of whom 0 to 28 (0% to 3%) would have tuberculosis. Studies often assessed more symptoms than those included in the index test and symptom definitions varied. These differences complicated data aggregation and may have influenced accuracy estimates. Both symptoms and CXR formed part of the CRS (incorporation bias), which may have led to overestimation of sensitivity and specificity.

AUTHORS' CONCLUSIONS

We found that in children who are tuberculosis contacts or living with HIV, screening tests using symptoms or CXR may be useful, but our review is limited by design issues with the index test and incorporation bias in the reference standard. For Xpert MTB/RIF, we found insufficient evidence regarding screening accuracy. Prospective evaluations of screening tests for tuberculosis in children will help clarify their use. In the meantime, screening strategies need to be pragmatic to address the persistent gaps in prevention and case detection that exist in resource-limited settings.

Specific Host Signatures for the Detection of Tuberculosis Infection in Children in a Low TB Incidence Country

Diagnosis of tuberculosis (TB) in children remains challenging due to unspecific clinical presentation and low bacillary load. In low TB incidence countries, most cases are diagnosed by a contact screening strategy after exposure to an index TB case. Due to the severity of TB in young children, the priority is to determine whether a child is infected or not, whereas differential diagnosis between active TB (aTB) and latent TB constitutes a second step. In Belgium, a low TB incidence country, we prospectively included 47 children with a defined M. tuberculosis infection status (12 children with aTB, 18 with latent TB, and 17 uninfected) (exploratory cohort), and determined the optimal combinations of cytokines secreted by their peripheral blood mononuclear cells in response to a 5-days in vitro stimulation with four different mycobacterial antigens, in an attempt to classify the children according to their infectious status. Correct identification of all infected children was obtained by several combinations of two purified protein derivative (PPD)-induced cytokines (IFN-γ and either GM-CSF, MIP-1α, sCD40L or TNF-α), or by combining PPD-induced IFN-γ with culture-filtrate protein-10 (CFP-10)-induced TNF-α. Alternatively, combining CFP-10-induced TNF-α and IP-10 with heparin-binding haemagglutinin (HBHA)-induced-IFN-γ was more effective in testing recently BCG-vaccinated children or those suspected to be infected with non-tuberculous mycobacteria, providing a correct classification of 97% of the M. tuberculosis-infected children. This combination also correctly classified 98% of the children from a validation cohort comprising 40 M. tuberculosis infected children and 20 non-infected children. Further differentiation between aTB and children with latent TB was more difficult. Combining ESAT-6-induced MIP1-α and IP-10, CFP-10-induced MIG, and HBHA-induced MIG provided a correct classification of 77% of the children from the exploratory cohort but only of 57.5% of those from the validation cohort. We conclude that combining the measurement of 2–4 cytokines induced by three different mycobacterial antigens allows an excellent identification of M. tuberculosis-infected children, whereas differentiating children with aTB from those with latent TB remains far from perfect.

Immunological Aspects of Diagnosis and Management of Childhood Tuberculosis

The diagnosis of tuberculosis (TB) in children is difficult because of the low sensitivity and specificity of traditional microbiology techniques in this age group. Whereas in adults the culture of Mycobacterium tuberculosis (M. tuberculosis), the gold standard test, detects 80% of positive cases, it only detects around 30-40% of cases in children. The new methods based on the immune response to M. tuberculosis infection could be affected by many factors. It is necessary to evaluate the medical record, clinical features, presence of drug-resistant M. tuberculosis strains, comorbidities, and BCG vaccination history for the diagnosis in children. There is no ideal biomarker for all TB cases in children. A new strategy based on personalized diagnosis could be used to evaluate specific molecules produced by the host immune response and make therapeutic decisions in each child, thereby changing standard immunological signatures to personalized signatures in TB. In this way, immune diagnosis, prognosis, and the use of potential immunomodulators as adjunct TB treatments will meet personalized treatment.

Cell-Mediated Immune Responses to in vivo-Expressed and Stage-Specific Mycobacterium tuberculosis Antigens in Latent and Active Tuberculosis Across Different Age Groups

A quarter of the global human population is estimated to be latently infected by Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). TB remains the global leading cause of death by a single pathogen and ranks among the top-10 causes of overall global mortality. Current immunodiagnostic tests cannot discriminate between latent, active and past TB, nor predict progression of latent infection to active disease. The only registered TB vaccine, Bacillus Calmette-Guérin (BCG), does not adequately prevent pulmonary TB in adolescents and adults, thus permitting continued TB-transmission. Several Mtb proteins, mostly discovered through IFN-γ centered approaches, have been proposed as targets for new TB-diagnostic tests or -vaccines. Recently, however, we identified novel Mtb antigens capable of eliciting multiple cytokines, including antigens that did not induce IFN-γ but several other cytokines. These antigens had been selected based on high Mtb gene-expression in the lung in vivo, and have been termed in vivo expressed (IVE-TB) antigens. Here, we extend and validate our previous findings in an independent Southern European cohort, consisting of adults and adolescents with either LTBI or TB. Our results confirm that responses to IVE-TB antigens, and also DosR-regulon and Rpf stage-specific Mtb antigens are marked by multiple cytokines, including strong responses, such as for TNF-α, in the absence of detectable IFN-γ production. Except for TNF-α, the magnitude of those responses were significantly higher in LTBI subjects. Additional unbiased analyses of high dimensional flow-cytometry data revealed that TNF-α+ cells responding to Mtb antigens comprised 17 highly heterogeneous cell types. Among these 17 TNF-α+ cells clusters identified, those with CD8+TEMRA or CD8+CD4+ phenotypes, defined by the expression of multiple intracellular markers, were the most prominent in adult LTBI, while CD14+ TNF-α+ myeloid-like clusters were mostly abundant in adolescent LTBI. Our findings, although limited to a small cohort, stress the importance of assessing broader immune responses than IFN-γ alone in Mtb antigen discovery as well as the importance of screening individuals of different age groups. In addition, our results provide proof of concept showing how unbiased multidimensional multiparametric cell subset analysis can identify unanticipated blood cell subsets that could play a role in the immune response against Mtb.

Human Immunodeficiency Virus Infection Impairs Th1 and Th17 Mycobacterium tuberculosis-Specific T-Cell Responses

Background

Human immunodeficiency virus (HIV)-infected individuals have a higher risk of developing active tuberculosis (TB) than HIV-uninfected individuals, but the mechanisms underpinning this are unclear. We hypothesized that depletion of specific components of Mycobacterium tuberculosis (Mtb)-specific CD4+ and CD8+ T-cell responses contributed to this increased risk.

Methods

Mtb-specific T-cell responses in 147 HIV-infected and 44 HIV-uninfected control subjects in a TB-endemic setting in Bloemfontein, South Africa, were evaluated. Using a whole-blood flow cytometry assay, we measured expression of interferon gamma, tumor necrosis factor alpha, interleukin 2, and interleukin 17 in CD4+ and CD8+ T cells in response to Mtb antigens (PPD, ESAT-6/CFP-10 [EC], and DosR regulon-encoded α-crystallin [Rv2031c]).

Results

Fewer HIV-infected individuals had detectable CD4+ and CD8+ T-cell responses to PPD and Rv2031c than HIV-uninfected subjects. Mtb-specific T cells showed distinct patterns of cytokine expression comprising both Th1 (CD4 and CD8) and Th17 (CD4) cytokines, the latter at highest frequency for Rv2031c. Th17 antigen-specific responses to all antigens tested were specifically impaired in HIV-infected individuals.

Conclusions

HIV-associated impairment of CD4+ and CD8+Mtb-specific T-cell responses is antigen specific, particularly impacting responses to PPD and Rv2031c. Preferential depletion of Th17 cytokine-expressing CD4+ T cells suggests this T-cell subset may be key to TB susceptibility in HIV-infected individuals.

Mycobacterium tuberculosis-specific cytokine biomarkers for the diagnosis of childhood TB in a TB-endemic setting

The tuberculin skin test and interferon-gamma release assays have limitations in diagnosing tuberculosis (TB), particularly in children. This study investigated the performance of candidate M. tuberculosis-specific cytokine biomarkers for TB in children in a TB-endemic setting. A total of 237 children with a household contact with smear-positive pulmonary TB were recruited. Importantly, a group of children with illnesses other than TB (sick controls) was included to assess specificity. Median IFN-ɣ, IL-1ra, IL-2, IL-13, IP-10, MIP-1β and TNF-α responses were significantly higher in children with active TB and latent TB infection (LTBI) than in both healthy and sick control children. Three of these cytokines - IL-2, IL-13 and IP-10 - showed better performance characteristics than IFN-ɣ, with IL-2 achieving positive and negative predictive values of 97.7% and 90.7%, respectively. Furthermore, IL-1ra and TNF-α responses differed significantly between active TB and LTBI cases, suggesting that they may be stage-specific biomarkers. Our data indicate that incorporating these biomarkers into future blood-based TB assays could result in substantial performance gains.

Epidemiology and disease burden of tuberculosis in south of Tunisia over a 22-year period: Current trends and future projections

BACKGROUND

Tuberculosis (TB) is a public health problem worldwide. Characterizing its trends over time is a useful tool for decision-makers to assess the efficiency of TB control programs. We aimed to give an update on the current chronological trends of TB in Southern Tunisia from 1995 to 2016 and to estimate future trajectories of TB epidemic by 2030.

METHODS

We retrospectively collected data of all notified TB new cases by the Center of Tuberculosis Control between 1995 and 2016 in South of Tunisia. Joinpoint Regression Analysis was performed to analyze chronological trends and annual percentage changes (APC) were estimated.

RESULTS

In the past 22 years, a total of 2771 cases of TB were notified in Southern Tunisia. The annual incidence rate of TB was 13.91/100,000 population/year. There was a rise in all forms of TB incidence (APC = 1.63) and in extrapulmonary tuberculosis (EPTB) (APC = 2.04). The incidence of TB increased in children and adult females between 1995 and 2016 (APC = 4.48 and 2.37, respectively). The annual number of TB declined in urban districts between 2004 and 2016 (APC = -2.85). Lymph node TB cases increased (APC = 4.58), while annual number of urogenital TB decreased between 1995 and 2016 (APC = -3.38). Projected incidence rates would increase to 18.13 and 11.8/100,000 population in 2030 for global TB and EPTB, respectively.

CONCLUSIONS

Our study highlighted a rise in all forms of TB and among high-risk groups, notably children, females and lymph node TB patients in the last two decades and up to the next one.

Identification of Mycobacterium tuberculosis Infection in Infants and Children With Partial Discrimination Between Active Disease and Asymptomatic Infection

Background: Improved diagnostic tests are needed for the early identification of Mycobacterium tuberculosis-infected young children exposed to an active TB (aTB) index case. We aimed to compare the diagnostic accuracy of new blood-based tests to that of the tuberculin skin test (TST) for the identification of all infected children and for a potential differentiation between aTB and latent TB infection (LTBI). Methods: 144 children exposed to a patient with aTB were included, and those who met all inclusion criteria (130/144) were classified in three groups based on results from classical investigations: non-infected (NI: n = 69, 53%, median age 10 months), LTBI (n = 28, 22%, median age 96 months), aTB disease (n = 33, 25%, median age 24 months). The first whole blood assay consisted of a 7-days in vitro stimulation of blood with four different mycobacterial antigens (40 μl/condition), followed by flow cytometric measurement of the proportions of blast cells appearing among lymphocytes as a result of their specific activation. Thresholds of positivity were determined by Receiver Operating Characteristic (ROC) curve analysis (results of NI children vs. children with LTBI/aTB) in order to identify infected children in a first stage. Other cut-offs were determined to discriminate subgroups of infected children in a second step (results from children with aTB/LTBI). Analysis of blood monocytes and dendritic cell subsets was performed on 100 μl of blood for 25 of these children as a second test in a pilot study. Results: Combining the results of the blast-induced CD3⁺ T lymphocytes by Heparin-Binding Haemagglutinin and by Culture Filtrate Protein-10 identified all but one infected children (sensitivity 98.2% and specificity 86.9%, compared to 93.4 and 100% for the TST). Further identification among infected children of those with aTB was best achieved by the results of blast-induced CD8⁺ T lymphocytes by purified protein derivative (sensitivity for localized aTB: 61.9%, specificity 96.3%), whereas high proportions of blood type 2 myeloid dendritic cells (mDC) were a hallmark of LTBI. Conclusions: New blood-based tests requiring a very small volume allow the accurate identification of M. tuberculosis-infected young children among exposed children and are promising to guide the clinical classification of children with aTB or LTBI.

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.

Update on trends in childhood tuberculosis

PURPOSE OF REVIEW

Although tuberculosis (TB) causes much morbidity and mortality in children, diagnosis and treatment remain challenging. Recently, children have gained increasing attention in research and clinical trials driving improved contact management, case identification and treatment of both drug-susceptible and drug-resistant TB. This review highlights some recent advances.

RECENT FINDINGS

The tuberculin skin test is the most widely used test to distinguish Mycobacterium tuberculosis (M. tuberculosis) infection from active TB, however, using M. tuberculosis-specific, antigenic stimulation of CD4 and CD8 cells appear more effective. The use of Xpert MTB/RIF to identify M. tuberculosis in clinical samples, together with novel sampling methods have in part, overcome the difficulty of sampling and increased case identification capacity. Advances in treating both drug-susceptible and drug-resistant childhood TB show promise in being more paediatric friendly and improving adherence. Dosing strategies for drug-sensitive TB have improved with dispersible fixed drug combinations now available. In the treatment and prevention of drug-resistant TB, however, research involving the use of newer and more effective drugs currently recommended for adults, are still ongoing in children.

SUMMARY

The World Health Organization aims to end the TB epidemic by 2035 whereas the United Nations' Sustainable Developmental Goals sets this ambitious target for 2030. Therefore, adequate funding and implementing effective national TB programs must be prioritized, particularly in high-burden, low-income settings.