Enzyme-linked immunospot assay responses to early secretory antigenic target 6, culture filtrate protein 10, and purified protein derivative among children with tuberculosis: implications for diagnosis and monitoring of therapy

Interferon gamma release assays for diagnosis of osteoarticular tuberculosis: A systematic review and meta-analysis

Background

Although the Interferon Gamma Release Assays (IGRA) is often used to identify latent tuberculosis, it also plays a crucial role in diagnosing active extrapulmonary tuberculosis. Some studies have assessed the use of IGRA as a biomarker for osteoarticular tuberculosis (OATB), which is elevated following TB infection. Still, conclusive results about its effectiveness have not been reported.

Method

We searched PubMed, Embase, and Cochran databases. We obtained literature related to the diagnosis of OATB by IGRA, and the retrieval period was from the establishment of the database to June 2021. The bivariate random effect model was used to summarize the sensitivity, specificity, and accuracy of other indicators in diagnosing OATB by IGRA, and the forest plot and receiver operating characteristic (ROC) curve were used for testing.

Results

We included seven studies involving 643 subjects in diagnosing OATB by IGRA. The comprehensive sensitivity and specificity were 0.84 (95% CI, 0.70–0.92) and 0.78 (95% CI, 0.66–0.87), respectively. The area under the curve (AUC) was 0.87.

Conclusion

In blood samples, the diagnostic accuracy of IGRAS is poor in patients with suspected OAT. We conclude that IGRA may not be appropriate for patients with OATB.

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.

The TBAg/PHA ratio in T-SPOT.TB assay has high prospective value in the diagnosis of active tuberculosis: a multicenter study in China

Background

The positive rate of pathogenic examination about tuberculosis is low. It is still difficult to achieve early diagnosis for some TB patients. The value of Interferon-gamma release assays (IGRA) in the diagnosis of active tuberculosis remains controversial. The purpose of this multicenter prospective study was to verify and validate the role of TBAg/PHA ratio (TB-specific antigen to phytohaemagglutinin) of T-SPOT.TB assay in diagnosing ATB.

Methods

We prospectively enrolled 2390 suspected pulmonary tuberculosis patients with positive T-SPOT assay results from three tertiary hospitals.

Results

A total of 1549 ATB (active tuberculosis) patients (including 1091 confirmed and 458 probable ATB) and 724 non-tuberculosis (non-TB) patients with positive T-SPOT results were included. The results of this study showed that ESAT-6 and CFP-10 in the T-SPOT.TB assay were significantly higher in the ATB group compared with the non-TB group, while PHA was lower in the ATB group. Results of ESAT-6, CFP-10 and PHA show a certain diagnostic performance, but moderate sensitivity and specificity. The TBAg/PHA ratio, a further calculation of ESAT-6, CFP-10 and PHA in T-SPOT.TB assay showed improved performance in the diagnosis of active Tuberculosis. If using the threshold value of 0.2004, the specificity and sensitivity of TBAg/PHA ratio in distinguishing ATB from non-TB were 92.3% and 74.4%, PPV was 95.4, PLR was 9.6.

Conclusion

By recalculating the results of T-SPOT.TB Assay, the TBAg/PHA ratio shows high prospect value in the diagnosis of active tuberculosis in high prediction areas.

Value of serum cytokine biomarkers TNF-α, IL-4, sIL-2R and IFN-γ for use in monitoring bacterial load and anti-tuberculosis treatment progress

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Serum cytokine levels may correlate with tuberculosis patient disease status.

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Serum TNF-α level may be a useful biomarker for predicting bacillar burden.

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Serum TNF-α and IFN-γ levels may reliably monitor anti-TB treatment progress.

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Serum IL-4 level had no value while serum IL-2R level value awaits further study.

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Cytokine biomarkers are useful biomarkers in clinical TB patient care settings.

Tuberculosis (TB) patient serum cytokine levels may be predictive of anti-tuberculosis treatment progress. Here, serum levels of cytokines TNF-α, IL-4, sIL-2R and IFN-γ were measured then correlated to clinical TB manifestations, bacterial burden, chest imaging findings and clinical course. Study subjects included 67 newly diagnosed pulmonary TB (PTB) patients with active disease admitted to Beijing Chest Hospital for anti-TB chemotherapeutic treatment. Blood was drawn at 0 months (pre-treatment), 1–2 months (at any time between 1 and 2 month) and after 6 months completion of treatment and serum TNF-α, IL-4, sIL-2R and IFN-γ levels were measured in duplicate using enzyme-linked immunosorbent assays (ELISAs). Correlation analysis was conducted to evaluate sensitivity and specificity of cytokine levels as predictors of disease activity and treatment progress. The results indicated that the pre-treatment serum TNF-α level of the smear-negative group was lower than that of the smear 1+ group, while serum TNF-α after 6 months completion of treatment and IFN-γ levels at 1–2 months and after 6 months completion of treatment were significantly lower, respectively, than at 0 months (before treatment) (P < 0.05). Using a cut-off value of 845 pg/ml, serum TNF-α level was predictive of treatment progress, with a sensitivity of 51%, specificity of 60% and AUC of 0.594 (P = 0.013). Meanwhile, using a cut-off value of 393 pg/ml, serum IFN-γ provided superior monitoring efficacy, with a sensitivity of 60%, specificity of 64% and AUC of 0.651 (P = 0.017). In conclusion, both serum TNF-α and IFN-γ levels might be useful biomarkers for monitoring treatment progress.

Prevalence of culture positive Tuberculosis and utility of a clinical diagnostic tool for the diagnosis of Tuberculosis among HIV Infected Children attending HIV/AIDS Care and Treatment in Dodoma Municipality, Central Tanzania

OBJECTIVE

To evaluate the performance of the modified Keith Edwards TB clinical diagnostic tool among HIV infected children.

METHODS

Cross sectional study of 252 HIV infected children < 15 years old suspected with TB at four HIV/AIDS Care Clinics in Dodoma, Tanzania from November 2018 - March 2019. The modified Keith Edwards TB clinical diagnostic tool was compared to gastric aspirates, lymphnode aspirates or sputum gene x-pert MTB/RIF and TB culture. Sensitivity, specificity, negative and positive predictive value of the clinical tool were determined. Data was analyzed using SPSS version 25.

RESULTS

Out of 252 children evaluated, 13.5% (34/252) had TB using the clinical diagnostic tool and 5.2% (13/252) had culture positive TB. The sensitivity of the clinical tool was 76.9%, specificity of 90%. Culture positive TB predictors were lymphadenopathy (AOR 13.74, 95%CI (3.86 - 48.86) p value < 0.001), weight loss (AOR 3.19,95%CI (1.38 - 7.36) p value 0.007), and difficulty breathing (AOR 7.25, 95%CI (1.54 - 34.16) p value 0.012).

CONCLUSION

The utility of the modified Keith Edwards clinical diagnostic tool for Tuberculosis diagnosis among HIV infected children is limited, calling for further validation. HIV infected children with lymphadenopathy, failure to thrive and difficulty in breathing are at high risk of Tuberculosis.

Positivity rate of interferon-γ release assays for estimating the prevalence of latent tuberculosis infection in renal transplant recipients in Japan

Renal transplant recipients are at increased risk of reactivating latent tuberculosis infection (LTBI) and developing active tuberculosis. QuantiFERON^®-TB Gold Plus (QFT-Plus) has two TB-specific antigens tubes (TB1 and TB2). TB1 elicits CD4 T-cell response, and TB2 elicits both CD4 and CD8 T-cells responses, with expected increased sensitivity. The aim of this study was to estimate the prevalence of LTBI in renal transplant recipients in Japan. We conducted a cross-sectional study by using two interferon-γ release assays (IGRAs), QFT-Plus and T-SPOT^®.TB (TSPOT). One hundred thirty-five recipients were prospectively enrolled. The median age was 49 years (range: 20 to 79). The positivity rates of QFT-Plus and TSPOT were 5.9% (95%CI 3.0-11.3) and 3.7% (95%CI 1.6-8.4), respectively, with no significant difference. The concordance rate was 95.5% (κ coefficient, 0.76). Age of 60 years and higher was related to the higher positivity rate in both QFT-Plus and TSPOT. The positivity rates of TB1 and TB2 were 5.1% (95%CI 2.5-10.2) and 5.9% (95%CI 3.0-11.2), respectively, with no significant difference. The concordance rate was 99.3% (κ coefficient, 0.93). TB2 did not show a higher positivity rate compared with TB1. The estimated prevalence of LTBI by using the both IGRAs was 3.7-5.9% in renal transplant recipients. These results were equivalent to the IGRAs positivity rate in the general Japanese population, even under the condition of immunosuppressive therapy. In consideration of the higher risk of developing active TB from LTBI, we can use both IGRAs as acceptable tools for LTBI diagnosis in renal transplant recipients.

Prospective Comparison of QFT-GIT and T-SPOT.TB Assays for Diagnosis of Active Tuberculosis

T-SPOT.TB and QuantiFERON-TB Gold In-Tube (QFT-GIT) tests, as two commercial blood assays for diagnosing active tuberculosis (ATB), are not yet fully validated. Especially, there are no reports on comparing the efficacy between the two tests in the same population in China. A multicenter, prospective comparison study was undertaken at four hospitals specializing in pulmonary diseases. A total of 746 suspected pulmonary TB were enrolled and categorized, including 185 confirmed TB, 298 probable TB and 263 non-TB. Of 32 patients with indeterminate test results (ITRs), age and underlying disease were associated with the rate of ITRs. Furthermore, the rate of ITRs determined by T-SPOT.TB was lower than QFT-GIT (0.4% vs. 4.3%, P < 0.01). When excluding ITRs, the sensitivities of T-SPOT.TB and QFT-GIT were 85.2% and 84.8%, and specificities of 63.4% and 60.5%, respectively in the diagnosis of ATB. The two assays have an overall agreement of 92.3%, but exhibited a poor linear correlation (r² = 0.086) between the levels of interferon-γ release detected by the different assays. Although having some heterogeneity in detecting interferon-γ release, both the QFT-GIT and T-SPOT.TB demonstrated high concordance in diagnosing ATB. However, neither of them showed suitability in the definitive diagnosis of the disease.

Diagnosis of Tuberculous Meningitis Using a Combination of Peripheral Blood T-SPOT.TB and Cerebrospinal Fluid Interferon-γ Detection Methods

OBJECTIVE

To evaluate the effectiveness of combined peripheral blood T-SPOT.TB and cerebrospinal fluid interferon-γ (cIFN-γ) detection methods in the diagnosis of tuberculous meningitis (TBM).

METHODS

A total of 30 individuals with TBM and 39 control individuals without TBM participated in this study. IFN-γ-secreting T cells were detected by enzyme-linked immunospot (ELISPOT), and cIFN-γ was detected by enzyme-linked immunosorbent assay (ELISA). We collected cerebrospinal fluid from 10 patients in the TBM group on initial visit and at 4 weeks, to observe changes.

RESULTS

The sensitivity and specificity of peripheral-blood T-SPOT.TB testing in the diagnosis of TBM were 70% and 87%, respectively. The area under the ROC curve of cIFN-γ for TBM diagnosis was 0.819, and the corresponding sensitivity and specificity were 83% and 85%, respectively. When T-SPOT.TB and cIFN-γ results were positive, the specificity and positive predictive value of TBM diagnosis reached 100%.

CONCLUSIONS

Combined use of T-SPOT.TB and cIFN-γ could improve the diagnosis efficiency of TBM. Dynamic observation of cIFN-γ is also important in monitoring TBM because the level of this analyte significantly decreases after treatment.

Dynamics of the T cell response to Mycobacterium tuberculosis DosR and Rpf antigens in a Colombian population of household contacts of recently diagnosed pulmonary tuberculosis patients

Immune response to DosR and Rpf antigens from Mycobacterium tuberculosis (Mtb) seems to be important for latency maintenance. Little is known about the dynamics of the immune response to these antigens in an endemic community. Thus, the IFNγ response and cytokine production in response to PPD, Esat6-Cfp10 (E6-C10), DosR and Rpf antigens in healthy HHC of tuberculosis (TB) patients over a 12 (T12) months period (short-term, stLTBI) was investigated. This response was compared with a group of LTBI, who have remained healthy for 5-7 years (long-term, ltLTBI). According to the IFNγ response, two groups of HHCs were identified in stLTBI in response to E6-C10. At T12, E6-C10(+) HHCs displayed a decrease in the IFNγ levels and a generalized decrease in cytokines production. The E6-C10(-) HHC showed an increase in the IFNγ response and cytokine levels. In stLTBI, the responses to E6-C10, DosR, and Rpf may be interpreted as a protective immune response controlling Mtb infection and may be leading to a state of latent infection. Comparing the response of stLTBI and ltLTBI, we observed significant changes in the proportions of CD45RO(+)CD27(+) T cells to specific DosR and Rpf, which may indicate a persistent immune response to Mtb antigens in ltLTBI.

Kinetics of Mycobacterium tuberculosis-specific IFN-γ responses and sputum bacillary clearance in HIV-infected adults during treatment of pulmonary tuberculosis

In HIV-uninfected adults with pulmonary tuberculosis (TB), anti-TB treatment is associated with changes in Mycobacterium tuberculosis (Mtb)-specific immune responses, which correlate with sputum bacillary load. It is unclear if this occurs in HIV-infected TB patients. We investigated changes in Mtb-specific immune responses and sputum bacillary clearance during anti-TB treatment in HIV-infected and HIV-uninfected adults with pulmonary TB. Sputum bacillary load was assessed by smear microscopy and culture. Mtb-specific IFN-γ secreting peripheral blood mononuclear cells were enumerated using an ELISPOT assay following stimulation with PPD, ESAT-6 and CFP-10. The baseline frequency of Mtb-specific IFN-γ secreting cells was lower in HIV-infected than HIV-uninfected patients (median PPD 32 vs. 104 Spot Forming Units (SFU), p = 0.05; CFP-10 19 vs. 74 SFU, p = 0.01). ESAT-6-specific IFN-γ secreting cells and sputum bacillary load declined progressively during treatment in both HIV-infected and HIV-uninfected patients. HIV infection did not influence the 2-month sputum culture conversion rate (Odds Ratio 0.89, p = 0.95). These findings suggest that changes in ESAT-6-specific immune responses during anti-TB treatment correspond with changes in sputum bacillary load irrespective of host HIV infection status. The utility of Mtb-specific IFN-γ responses as a proxy measure of treatment response in HIV-infected TB patients warrants further evaluation in other settings.

The role of interferon gamma release assays in the monitoring of response to anti-tuberculosis treatment in children

Successful control of childhood TB requires early diagnosis, effective chemotherapy and a method of evaluating the response to therapy. Identification of suitable biomarkers that predict the response to anti-TB therapy may allow the duration of treatment to be shortened. The majority of biomarker studies in paediatric TB have focused on the role of T cell-based interferon-gamma (IFN-γ) release assays (IGRAs) in the diagnosis of either latent or active disease. Little has been published on the role of IGRAs in the monitoring response to therapy in children. We reviewed the available literature to ascertain the value of IGRAs in the monitoring of response to anti-TB therapy in children. We explored the results of the few studies that have investigated the role of IGRAs as markers of response to anti-TB treatment in children. We conclude that the role of IGRAs as surrogate markers appears promising. Robust clinical trials are, however, needed to entrench the value of IGRAs as surrogate biomarkers of response to anti-TB therapy in children.

TB-IRIS after initiation of antiretroviral therapy is associated with expansion of preexistent Th1 responses against Mycobacterium tuberculosis antigens

BACKGROUND

The role of T-cell responses against Mycobacterium tuberculosis antigens in tuberculosis-associated immune reconstitution inflammatory syndrome (TB-IRIS) is unclear.

METHODS

Peripheral blood mononuclear cells from 45 HIV patients with treated TB, of whom 12 developed TB-IRIS, were collected at weeks 0, 2, and 6 of antiretroviral therapy (ART). Production of interferon-gamma (IFN-γ) and interleukin-2 by T cells after stimulation with purified protein derivative (PPD) or early secretory antigenic target-6 (ESAT-6) and T-cell expressions of CCR5 and CXCR3 were assessed by flow cytometry. IFN-γ and CXCL10 were assayed by enzyme-linked immunosorbent assay.

RESULTS

TB-IRIS patients had higher proportions of PPD- and ESAT-6-reactive IFN-γ⁺CD4⁺ and CD3⁺CD4⁻ T cells at weeks 0, 2, and 6. IFN-γ levels were also higher in peripheral blood mononuclear cell culture supernatants at all times with PPD but only at weeks 2 and 6 with ESAT-6. There were few differences for interleukin-2. CXCL10 levels in supernatants after PPD and ESAT-6 stimulation were only higher at week 6. CXCR3⁺/CCR5⁺CD4⁺ T cells were higher at week 2, and CCR5⁺CD4⁺ T cells were higher at week 6.

CONCLUSIONS

TB-IRIS is associated with Th1 responses against M. tuberculosis antigens by CD4⁺ and CD3⁺CD4⁻ T cells that are present before ART and amplified afterward. It is unclear if these cause immunopathology or reflect a high pathogen load.

Interferon-γ responses to Mycobacterium tuberculosis Rpf proteins in contact investigation

Mycobacterium tuberculosis Resuscitation-promoting factor proteins (Rpf) induce stronger T-cell responses in latently infected individuals (LTBI) than in pulmonary tuberculosis patients (PTB), but there are scarce data concerning the responses to Rpf among LTBI with different contact levels. We therefore enrolled LTBI individuals infected through household contacts with PTB as well as people with community exposure who were determined to be LTBI through Interferon-γ (IFN-γ) release assays (IGRAs) and TB antibodies test, and we studied interferon-gamma responses to Rv0867c and Rv2389c which demonstrated the highest recognition of all Rpfs. The results demonstrated that LTBI infected through household contacts possessed higher interferon-gamma production and higher frequencies of CD4(+)IFN-γ(+) T-cells to Rv0867c and Rv2389c than did the community exposed individuals. These findings suggest that the interferon-gamma response to Rv0867c and Rv2389c may help to distinguish LTBI caused by different levels of exposure to M. tuberculosis.

Interferon-γ ELISPOT as a biomarker of treatment efficacy in latent tuberculosis infection: a clinical trial

RATIONALE

Biomarkers that can be used to evaluate new interventions against latent tuberculosis infection (LTBI) and predict reactivation TB disease are urgently required.

OBJECTIVES

To evaluate ESAT-6 and CFP-10 (EC) IFN-γ ELISPOT as a biomarker for treatment efficacy in LTBI.

METHODS

This was a randomized, blinded, and placebo-controlled trial of INH in EC ELISPOT and Mantoux test positive participants.

MEASUREMENTS AND MAIN RESULTS

Participants received a 6-month course of 900 mg INH twice weekly or a matching placebo. INH acetylator genotypes were determined and urine tested for INH metabolites to confirm adherence. The proportion of positive responders for CFP-10 and ESAT-6 between treatment arms was compared using mixed effects logistic regression models. A Tweedie (compound Poisson) model was fitted to allow for zero inflation and overdispersion of quantitative response. The proportions of EC ELISPOT-positive subjects reduced over time (P < 0.001) but did not differ by study arm (P = 0.36). Median spot-forming units for ESAT-6 and CFP-10 also declined significantly with time (P < 0.001) but did not differ by study arm (P = 0.74 and 0.71, respectively). There was no evidence of an interaction between acetylator status and INH treatment with respect to ELISPOT results over time.

CONCLUSIONS

In contacts with LTBI, INH therapy plays no role in observed decreases in Mycobacterium tuberculosis antigen-specific T-cell responses over time. IFN-γ ELISPOT is probably not a useful biomarker of treatment efficacy in LTBI. Clinical trial registered with www.clinicaltrials.gov (NCT 00130325).

Utility of interferon-γ release assay results to monitor anti-tubercular treatment in adults and children

BACKGROUND

Interferon-γ release assays (IGRAs), including the commercially available T-SPOT.TB, QuantiFERON-TB Gold (QFT-G), and QuantiFERON-TB Gold In-Tube (QTF-G-IT), enable detection of circulating T lymphocytes responsive to specific Mycobacterium tuberculosis antigens. Studies of the potential role of serial IGRAs for assessment of response to anti-tubercular therapy are accumulating.

OBJECTIVE

The objective of this systematic review was to evaluate the potential clinical utility of serial IGRAs in anti-tubercular therapy.

METHODS

We conducted a literature search of the Cochrane Library and MEDLINE by PubMed, from database inception through October 1, 2011, for serial IGRA results in anti-tubercular therapy, in adults and children, using commercial stardardized assays. All types of articles in the English language were included. Meta-analysis was performed to estimate the pooled percentage of reversion from a positive to a negative IGRA value at 3- to 6-month follow-up.

RESULTS

According to inclusion and exclusion criteria, three T-SPOT.TB-based (n = 319 patients), three QFT-G-based (n = 75 patients), and seven QFT-G-IT-based (n = 558 patients) longitudinal studies were included. The percentage of patients with reversion from a positive to a negative IGRA value ranged from 5.71% to 13.93% for T-SPOT.TB, 5.26% to 71.05% for QFT-G, and 14.28% to 41.89% for QFT-G-IT assays. Meta-analysis estimation of reversion was feasible only for the QFT-G-IT assay, at 30.54% (95% CI, 22.89-38.75). In two pediatric studies, which were QFT-G-IT based (n = 122 children), the reported reversion rates were 14.28% and 20.33%, respectively.

CONCLUSIONS

Because IGRAs require time and cost resources, and reversion from positive to negative IGRA values occurs in a minority of treated patients, monitoring IGRA changes over time seems to have only speculative value in adults. Data in children are poor, but are in line with results reported in adults.

Serial interferon-γ release assay in children with latent tuberculosis infection and children with tuberculosis

BACKGROUND

Interferon-γ (IFN-γ) release assay (IGRA) is used for diagnosis of latent tuberculosis infection (LTBI), and for serial testing of active tuberculosis (TB). The aim of this study was to evaluate the results of IGRA for diagnosis and treatment monitoring of children with LTBI and children with TB. IGRA was performed in BCG vaccinated children before and six months after the beginning of treatment.

METHODS

A total of 59 BCG vaccinated children aged 4-18 years were investigated due to exposure to active TB. The participants were divided into two groups: Group 1, children with LTBI (N = 41), and Group 2, children with TB (N = 18). IGRA (QuantiFERON-TB Gold In-Tube) was performed twice, i.e., before treatment and at the end of prophylaxis and therapy.

RESULTS

There was no significant difference in IFN-γ concentrations between Group 1 and Group 2 subjects either before or after the treatment. Difference between pre-treatment and post-treatment IFN-γ concentrations compared in either Group 1 or Group 2 was not statistically significant. During follow-up, children with LTBI did not develop active TB. In addition, in children with TB, signs and symptoms of TB improved with anti-TB therapy.

CONCLUSION

This study showed that the concentrations of IFN-γ did not differ in children with LTBI and TB either before or at the end of treatment. IGRA may remain positive over a long period of time. It seems that IGRA is not useful for monitoring treatment of children with LTBI and children with TB.

Classic and new diagnostic approaches to childhood tuberculosis

Tuberculosis in childhood differs from the adult clinical form and even has been suggested that it is a different disease due to its differential signs. However, prevention, diagnostics, and therapeutic efforts have been biased toward adult clinical care. Sensibility and specificity of new diagnostic approaches as GeneXpert, electronic nose (E-nose), infrared spectroscopy, accelerated mycobacterial growth induced by magnetism, and flow lateral devices in children populations are needed. Adequate and timely assessment of tuberculosis infection in childhood could diminish epidemiological burden because underdiagnosed pediatric patients can evolve to an active state and have the potential to disseminate the etiological agent Mycobacterium tuberculosis, notably increasing this worldwide public health problem.

T-SPOT.TB assay usage in adults and children

The diagnosis and treatment of TB infection is one of the public health priorities. Until recently, diagnosis of TB infection has been based on the tuberculin skin test (TST). However, this is neither 100% sensitive nor specific for the diagnosis of TB infection owing to its many drawbacks. More recently, T-cell-based IFN-γ release assays (IGRAs) have been developed. In this article, we review the clinical performance of one of the IGRAs, T-SPOT.TB assay, for the diagnosis of TB infection in adults and children. We discuss the principle of the assay, its utility in active TB diseases, latent TB infection and the performance of the test in specialized subgroups of patients, such as immunocompromised individuals. When compared with the TST, the T-SPOT.TB assay has better specificity in bacillus Calmette-Guérin-vaccinated individuals, and data suggest that T-SPOT.TB may be more sensitive than the TST. Data in groups at high risk of progression to disease support the idea that T-SPOT.TB performs better than the TST. In addition, application of T-SPOT.TB by using bodily fluids such as cerebrospinal fluid, bronchoalveolar lavage fluid and pleural fluid may offer new diagnostic approaches in extrapulmonary TB disease. Although IGRAs cannot distinguish active TB disease from latent TB infection, these assays perform better than the TST for the detection of TB infection.

Diagnostic performance of T-SPOT.TB for extrapulmonary tuberculosis according to the site of infection

BACKGROUND

The clinical manifestations of extrapulmonary tuberculosis (E-TB) vary according to site of disease, so we tested the hypothesis that IFN-γ producing T-cell responses also vary in parallel. Therefore we conducted a prospective, blinded, observational study to evaluate the diagnostic performance of blood T-SPOT.TB according to the various sites of E-TB.

METHODS

From April 2008 to August 2010, all patients with suspected E-TB were enrolled at a tertiary hospital in an intermediate TB-burden country. Final diagnosis in patients with suspected E-TB was classified by clinical category.

RESULTS

A total of 368 patients with suspected E-TB were enrolled; 196 (53%) were classified as having TB, including 119 (32%) with confirmed TB, 34 (9%) probable TB, and 43 (12%) possible TB; the remaining 172 (47%) were classified as not having TB. After excluding patients with possible TB, the T-SPOT.TB was more sensitive in patients with chronic forms of E-TB such as lymph node or osteoarticular TB (93%, 95% CI 83%-97%) than in patients with acute forms of E-TB such as TB meningitis or miliary TB (79%, 95% CI 66%-87%, P = 0.03).

CONCLUSIONS

The diagnostic performance of the blood T-SPOT.TB differs among patients with various clinical manifestations of E-TB.

T cell monitoring of chemotherapy in experimental rat tuberculosis

Mycobacterium tuberculosis is the causative agent of a pulmonary epidemic that is estimated to infect one-third of the world's population and that has an increased incidence of multidrug resistance. The evaluation of new chemical entities against M. tuberculosis is hampered by the lack of biological tools to help predict efficacy, from early drug development to clinical trials. As the rat is the animal species of choice in the pharmaceutical industry, we have developed a rat model of acute and chronic phases of M. tuberculosis infection for drug efficacy testing. In this model, we have evaluated the impact of tuberculosis drugs on T cell response using the enzyme-linked immunospot assay methodology. Infected rats treated with isoniazid (INH) or rifampin (RIF) responded to therapy, the potency of which was comparable to that seen in the mouse. Peripheral blood mononuclear cells from infected rats produced gamma interferon (IFN-γ) in response to RD-1 antigens, such as the 6-kDa early secretory antigen target (ESAT-6) and the 10-kDa culture filtrate protein (CFP-10). A decrease in IFN-γ spot-forming cells (SFCs) was consistently observed in response to drug treatment. In both the acute- and chronic-phase models, the T cell response was more sensitive to ESAT-6 than to CFP-10. The SFC count in response to ESAT-6 appears to be an indicator of bacterial killing in the rat. Collectively, our data suggest that the ESAT-6 response could be used as a potential surrogate of drug efficacy in the rat and that such a readout could help shorten drug testing during preclinical development.

IP-10 response to RD1 antigens might be a useful biomarker for monitoring tuberculosis therapy

Background

There is an urgent need of prognosis markers for tuberculosis (TB) to improve treatment strategies. The results of several studies show that the Interferon (IFN)-γ-specific response to the TB antigens of the QuantiFERON TB Gold (QFT-IT antigens) decreases after successful TB therapy. The objective of this study was to evaluate whether there are factors other than IFN-γ [such as IFN-γ inducible protein (IP)-10 which has also been associated with TB] in response to QFT-IT antigens that can be used as biomarkers for monitoring TB treatment.

Methods

In this exploratory study we assessed the changes in IP-10 secretion in response to QFT-IT antigens and RD1 peptides selected by computational analysis in 17 patients with active TB at the time of diagnosis and after 6 months of treatment. The IFN-γ response to QFT-IT antigens and RD1 selected peptides was evaluated as a control. A non-parametric Wilcoxon signed-rank test for paired comparisons was used to compare the continuous variables at the time of diagnosis and at therapy completion. A Chi-square test was used to compare proportions.

Results

We did not observe significant IP-10 changes in whole blood from either NIL or QFT-IT antigen tubes, after 1-day stimulation, between baseline and therapy completion (p = 0.08 and p = 0.7 respectively). Conversely, the level of IP-10 release to RD1 selected peptides was significantly different (p = 0.006). Similar results were obtained when we detected the IFN-γ in response to the QFT-IT antigens (p = 0.06) and RD1 selected peptides (p = 0.0003). The proportion of the IP-10 responders to the QFT-IT antigens did not significantly change between baseline and therapy completion (p = 0.6), whereas it significantly changed in response to RD1 selected peptides (p = 0.002). The proportion of IFN-γ responders between baseline and therapy completion was not significant for QFT-IT antigens (p = 0.2), whereas it was significant for the RD1 selected peptides (p = 0.002), confirming previous observations.

Conclusions

Our preliminary study provides an interesting hypothesis: IP-10 response to RD1 selected peptides (similar to IFN-γ) might be a useful biomarker for monitoring therapy efficacy in patients with active TB. However, further studies in larger cohorts are needed to confirm the consistency of these study results.

Whole blood interferon-γ release assay is a useful tool for the diagnosis of tuberculosis infection particularly among Bacille Calmette Guèrin-vaccinated children

The performance of QuantiFERON-tuberculosis (TB) Gold-In-Tube assay was compared with the tuberculin skin test for the diagnosis of TB among children. It was shown that among non-Bacille Calmette Guèrin immunized children, agreement between tests was excellent both in those with TB disease and in TB contacts. Among Bacille Calmette Guèrin-immunized children, agreement was fair in those with active disease and poor among TB contacts. It is concluded that QuantiFERON-TB Gold-In-Tube compares with the tuberculin skin test in the diagnosis of TB disease and latent tuberculosis infection in TB contacts among children and has enhanced specificity.

Decay kinetics of an interferon gamma release assay with anti-tuberculosis therapy in newly diagnosed tuberculosis cases

Background

Qualitative and quantitative changes in IGRA response offer promise as biomarkers to monitor Tuberculosis (TB) drug therapy, and for the comparison of new interventions. We studied the decay kinetics of TB-specific antigen T-cell responses measured with an in-house ELISPOT assay during the course of therapy.

Methods

Newly diagnosed sputum smear positive TB cases with typical TB chest radiographs were recruited. All patients were given standard anti-TB treatment. Each subject was followed up for 6 months and treatment outcomes were documented. Blood samples were obtained for the ESAT-6 and CFP-10 (EC) ELISPOT at diagnosis, 1-, 2-, 4- and 6-months. Qualitative and quantitative reversion of the ELISPOT results were assessed with McNemar test, conditional logistic regression and mixed-effects hierarchical Poisson models.

Results

A total of 116 cases were recruited and EC ELISPOT was positive for 87% (95 of 109) at recruitment. There was a significant decrease in the proportion of EC ELISPOT positive cases over the treatment period (p<0.001). Most of the reversion occurred between the start and first month of treatment and at completion at 6 months. ESAT-6 had higher median counts compared to CFP-10 at all time points. Counts for each antigen declined significantly with therapy (p<0.001). Reverters had lower median SFUs at the start of treatment compared to non-Reverters for both antigens. Apart from the higher median counts for non-Reverters, no other risk factors for non-reversion were found.

Conclusions

TB treatment induces qualitative and quantitative reversion of a positive in-house IGRA in newly diagnosed cases of active TB disease. As this does not occur reliably in the majority of cured individuals, qualitative and quantitative reversion of an IGRA ELISPOT has limited clinical utility as a surrogate marker of treatment efficacy.

Reversion and conversion of Mycobacterium tuberculosis IFN-gamma ELISpot results during anti-tuberculous treatment in HIV-infected children

Background

Recent interest has focused on the potential use of serial interferon gamma (IFN-γ) release assay (IGRA) measurements to assess the response to anti-tuberculous (TB) treatment. The kinetics of IFN-γ responses to Mycobacterium tuberculosis (MTB) antigens in HIV-infected children during treatment have not however been previously investigated.

Methods

IFN-γ responses to the MTB antigens, ESAT-6, CFP-10 and PPD were measured by an enzyme-linked immunospot assay (IFN-γ ELISpot) at presentation and at one, two and six months after starting anti-tuberculous treatment in HIV-infected children with definite or probable TB. Responses at different time points were compared using a Mann-Whitney U test with paired data analysed using the Wilcoxon signed rank test. A Fisher's exact or Chi-squared test was used to compare proportions when test results were analysed as dichotomous outcomes.

Results

Of 102 children with suspected TB, 22 (21%) had definite TB and 24 (23%) probable TB. At least one follow up IFN-γ ELISpot assay result was available for 31 (67%) of the 46 children. In children with definite or probable TB in whom the IFN-γ ELISpot assay result was positive at presentation, anti-tuberculous treatment was accompanied by a significant decrease in both the magnitude of the IFN-γ response to individual or combined MTB-specific antigens (ESAT-6 median 110 SFCs/10⁶ PBMC (IQR 65-305) at presentation vs. 15 (10-115) at six months, p = 0.04; CFP-10 177 (48-508) vs. 20 (5-165), p = 0.004, ESAT-6 or CFP-10 median 250 SFCs/10⁶ PBMC (IQR 94-508) vs. 25 (10-165), p = 0.004) and in the proportion of children with a positive IFN-γ ELISpot assay (Fisher's exact test: ESAT-6 15/0 vs 5/11, p = 0.0002, CFP-10 22/0 vs 8/17, p = 0.0001, ESAT-6 or CFP-10 22/0 vs. 9/17, p= 0.002). However almost half of the children had a positive IFN-γ ELISpot assay after six months of anti-tuberculous treatment. In addition, there was conversion of the IFN-γ ELISpot assay result during anti-tuberculous therapy in six of 12 children in whom the initial IFN-γ ELISpot assay was negative.

Conclusions

In HIV-infected children with definite or probable TB, anti-tuberculosis treatment is accompanied by a reduction in the magnitude of the IFN-γ ELISpot response to MTB-antigens. However, serial IFN-γ ELISpot measurements appear to have limited clinical utility in assessing a successful response to anti-tuberculous treatment in HIV infected children.

Role of interferon gamma release assay in the diagnosis of Pott disease

OBJECT

Tuberculosis is ubiquitous in its presence and in its myriad manifestations. Despite several advances, it often poses a diagnostic dilemma. The aim of this study was to evaluate the efficacy of the QuantiFERON assay in the diagnosis of Pott disease.

METHODS

In this study, 70 consecutive patients with vertebral collapse underwent a battery of investigations including radiological evaluation (MR imaging and chest and spine radiography), routine blood workup (hemoglobin, total leukocyte count, differential leukocyte count, and erythrocyte sedimentation rate), enzyme-linked immunosorbent assay (ELISA) for tuberculosis, a bone scan and the QuantiFERON assay, perioperative evaluation, and bacteriological studies. The patients were then classified as having tuberculosis on the basis of positive smear or culture, a biopsy consistent with tuberculosis, or a therapeutic response to antituberculosis chemotherapy on follow-up. The efficacy of the investigations, both individually and in combination, were evaluated.

RESULTS

Tuberculosis was diagnosed in 51 patients, and 19 had vertebral collapse that was attributable to other causes. Based on the authors' data, sensitivity of the QuantiFERON assay in the diagnosis of tuberculosis of the spine was 84% and specificity was 95%. In combination with radiological criteria, bone scan, and ELISA, the QuantiFERON assay was predictive of tuberculosis in 90% of cases (46 patients).

CONCLUSIONS

None of the investigative modalities individually are efficacious enough to make a diagnosis of tuberculosis of the spine with such a degree of certainty as to to obviate the need for a tissue diagnosis or bacteriological confirmation. The ELISA, MR imaging of the spine, and bone scanning findings provide a reasonably certain diagnosis in 90% of cases, providing the grounds for starting a safe trial of antituberculous chemotherapy.

Immunologic paradox in the diagnosis of tuberculous meningitis

We report a patient with microbiologically documented tuberculous meningitis showing that the therapeutic paradox, a therapy-induced switch to a neutrophil-predominant situation in the differential cell counts of cerebrospinal fluid specimens, had a correlation with an immunologic paradox, an increased Mycobacterium tuberculosis-specific gamma interferon-producing T-cell response.

Diagnostic performance of an enzyme-linked immunospot assay for interferon-gamma in extrapulmonary tuberculosis varies between different sites of disease

OBJECTIVES

To evaluate diagnostic performance of an enzyme-linked immunospot assay for interferon-gamma (T SPOT-TB) in patients with suspected extrapulmonary tuberculosis (TB).

METHODS

From January 2007 to December 2008, patients with suspected extrapulmonary TB were prospectively enrolled from 2 tertiary care hospitals.

RESULTS

A total of 138 patients with suspected extrapulmonary TB were enrolled; 50 patients had positive culture for Mycobacterium tuberculosis and 39 patients had probable TB. The sites of infection were lymph node (n = 20), pleura (n = 19), bone/joint (n = 15), urinary tract (n = 7), peritoneum (n = 7), meninges (n = 6), disseminated (n = 5), intestine (n = 3), pericardium (n = 2), skin (n = 2), throat (n = 1), neck (n = 1), and genitalia (n = 1). The overall sensitivity and specificity were 79.8% (71/89) and 81.6% (40/49). The sensitivity ranged from 100% for tuberculous meningitis, tuberculous pericarditis, and intestinal TB, 95% for lymphadenitis, to 42.9% for tuberculous peritonitis. The sensitivity of the T SPOT-TB assay was 70.6% in immunocompromised patients and 85.5% in immunocompetent patients (p = 0.09).

CONCLUSIONS

The T SPOT-TB assay can be a useful tool for diagnosing extra-pulmonary TB in immunocompetent and immunocompromised patients, particularly for tuberculous meningitis, pericarditis, lymphadenitis, and intestinal TB.

T-cell interferon-gamma release assays for the rapid immunodiagnosis of tuberculosis: clinical utility in high-burden vs. low-burden settings

PURPOSE OF REVIEW

The utility of T-cell interferon-gamma (IFN-gamma) responses to Mycobacterium tuberculosis specific antigens [interferon-gamma release assays (IGRAs)] in high-burden settings remains unclear and there is growing evidence that IGRA performance varies across high tuberculosis (TB) burden vs. low TB burden settings. Here we review the evidence supporting the utility of IGRAs in specific subgroups and compare their performance in high-burden vs. low-burden settings.

RECENT FINDINGS

Although the IGRA, compared with the tuberculin skin test (TST), has greater specificity in BCG-vaccinated individuals, treatment of latent tuberculosis infection is not a priority in high-burden setting. Nevertheless, in high-burden settings, the TST performs reasonably well and correlates as well, or better, with proxy measures of exposure.

SUMMARY

IGRAs may still be useful in high-burden settings in specific subgroups at high risk of progression, including young children, HIV-infected individuals and healthcare workers, but this requires confirmation. Although the IGRAs cannot distinguish between latent and active TB, their utility as rule-out tests, when combined with smear microscopy or the TST, requires further study. Prospective studies are required in high-burden settings to confirm whether IFN-gamma responses are predictive of high risk of progression to active TB, particularly in HIV-infected individuals.

IFN-gamma release assays in tuberculosis management in selected high-risk populations

Tuberculosis (TB) is the most deadly infectious disease in the world. TB control relies on passive case findings and targeted treatment of latently infected individuals at high risk of disease progression. Tuberculin skin testing (TST) is conventionally used for detection of TB infection. Recently, blood assays measuring the release of IFN-gamma by TB-specific effector memory T cells have been developed to overcome TST limitations. Overall, IFN-gamma release assays are more specific than TST, more sensitive in detecting active TB and correlate better with TB exposure in immune-competent patients, at least in low-burden settings. There are three US FDA-approved assays commercially available: the ELISpot-based assay T-SPOT.TB (Oxford Immunotech, UK) and two ELISA-based formats, QuantiFERON TB Gold (QFT) and QFT-in tube (Cellestis, Australia). Recent international guidelines and consensus statements recommend the use of IFN-gamma release assays at different levels in TB management. However, conclusive evidence-based information targeting populations at high TB risk, including HIV-infected individuals, children and patient candidates for biotherapy with TNF-alpha blockers, are lacking. The aim of this review is to focus our attention on studies addressing the performance of commercial IFN-gamma release assays in clinical management of TB infection in these highly selected settings to provide a more comprehensive picture of the actual scenario and to identify areas to be investigated further.

Detection of tuberculosis in HIV-infected children using an enzyme-linked immunospot assay

OBJECTIVE

To evaluate an enzyme-linked immunospot assay (ELISPOT) for the diagnosis of tuberculosis (TB) in HIV-infected children with suspected TB and to compare the performance of ELISPOT with the tuberculin skin test (TST).

METHODS

Interferon-gamma responses to Mycobacterium tuberculosis-specific antigens were measured by ELISPOT in HIV-infected children with suspected TB. HIV-infected and HIV-uninfected children without TB were taken for comparison.

RESULTS

Results were available for 188 children, of whom 139 (74%) were HIV-infected. Of these, 22 were classified as having definite TB: 24 probable TB, 14 possible TB and 128 not having TB. The median (range) age of patients was 20 (10-54.1) months. Median interferon-gamma responses to early-secreted antigenic target-6 and culture filtrate protein-10 were higher in children with definite or probable TB compared with children without TB (P < 0.002). In HIV-infected children with an interpretable ELISPOT result, the ELISPOT was positive in 14/21 (66%) with definite TB. A significantly higher proportion of HIV-infected children with definite or probable TB had a positive ELISPOT compared with a positive TST [25/39 (64%) vs. 10/34 (29%), P = 0.005]. In contrast to TST, results from ELISPOT were not affected by young age or severe immunosuppression. In HIV-infected children without active TB disease, 27% had a positive ELISPOT, suggesting latent TB infection.

CONCLUSION

ELISPOT is more sensitive than TST for the detection of active TB in HIV-infected children. However, the sensitivity of current ELISPOT assays is not sufficiently high to be used as a rule out test for TB.

Diagnostic usefulness of a T-cell-based assay for extrapulmonary tuberculosis in immunocompromised patients

BACKGROUND

The low reactivity of the tuberculin skin test limits its clinical use in immunocompromised patients with extrapulmonary tuberculosis. A recently developed T-cell-based assay for diagnosing tuberculosis infection gave promising results. However, there were few data on the usefulness of this assay for diagnosing extrapulmonary tuberculosis in immunocompromised patients.

METHODS

All adult patients with suspected extrapulmonary tuberculosis were prospectively enrolled at 2 university-affiliated hospitals over an 18-month period. In addition to the conventional tests for diagnosing extrapulmonary tuberculosis, enzyme-linked immunospot (ELISPOT) assay for the interferon-gamma-producing T-cell response to early secretory antigenic target-6 and culture filtrate protein-10 was performed. The final diagnoses in patients with suspected extrapulmonary tuberculosis were classified by clinical category.

RESULTS

There were 179 patients with suspected extrapulmonary tuberculosis enrolled: 59 (33%) were classified as immunocompromised. Of the 179 patients, 75 (42%) were classified as extrapulmonary tuberculosis, including 56 confirmed tuberculosis plus 19 probable tuberculosis, and 97 (54%) were classified as not tuberculosis. The remaining 7 (4%) had possible tuberculosis and were excluded from the final analysis. The tuberculin skin test (induration size >or=10 mm) was less sensitive in immunocompromised patients (38%; 95% confidence interval [CI], 19%-59%) than in immunocompetent patients (69%; 95% CI, 54%-81%, P=.01). In contrast, the ELISPOT assay retained a high sensitivity: (88%; 95% CI, 68%-97%) in immunocompromised patients compared with 96% (95% CI, 87%-100%) in immunocompetent patients (P=.32).

CONCLUSION

The immunosuppressive condition does not affect the diagnostic sensitivity of the ELISPOT assay for extrapulmonary tuberculosis.

Safety and immunogenicity of a new tuberculosis vaccine, MVA85A, in Mycobacterium tuberculosis-infected individuals

RATIONALE

An effective new tuberculosis (TB) vaccine regimen must be safe in individuals with latent TB infection (LTBI) and is a priority for global health care.

OBJECTIVES

To evaluate the safety and immunogenicity of a leading new TB vaccine, recombinant Modified Vaccinia Ankara expressing Antigen 85A (MVA85A) in individuals with LTBI.

METHODS

An open-label, phase I trial of MVA85A was performed in 12 subjects with LTBI recruited from TB contact clinics in Oxford and London or by poster advertisements in Oxford hospitals. Patients were assessed clinically and had blood samples drawn for immunological analysis over a 52-week period after vaccination with MVA85A. Thoracic computed tomography scans were performed at baseline and at 10 weeks after vaccination. Safety of MVA85A was assessed by clinical, radiological, and inflammatory markers. The immunogenicity of MVA85A was assessed by IFNgamma and IL-2 ELISpot assays and FACS.

MEASUREMENTS AND MAIN RESULTS

MVA85A was safe in subjects with LTBI, with comparable adverse events to previous trials of MVA85A. There were no clinically significant changes in inflammatory markers or thoracic computed tomography scans after vaccination. MVA85A induced a strong antigen-specific IFN-gamma and IL-2 response that was durable for 52 weeks. The magnitude of IFN-gamma response was comparable to previous trials of MVA85A in bacillus Calmette-Guérin-vaccinated individuals. Antigen 85A-specific polyfunctional CD4(+) T cells were detectable prior to vaccination with statistically significant increases in cell numbers after vaccination.

CONCLUSIONS

MVA85A is safe and highly immunogenic in individuals with LTBI. These results will facilitate further trials in TB-endemic areas. Clinical trial registered with www.clinicaltrials.gov (NCT00456183).

Temporal dynamics of interferon gamma responses in children evaluated for tuberculosis

Background

Development of T-cells based-Interferon gamma (IFNγ) assays has offered new possibilities for the diagnosis of latent tuberculosis infection (LTBI) and active disease in adults. Few studies have been performed in children, none in France. With reference to the published data on childhood TB epidemiology in the Paris and Ile de France Region, we considered it important to evaluate the performance of IGRA (QuantiFERON TB Gold In Tube®, QF-TB-IT) in the diagnosis and the follow-up through treatment of LTBI and active TB in a cohort of French children.

Methodology/Principal Findings

131 children were recruited during a prospective and multicentre study (October 2005 and May 2007; Ethical Committee St Louis Hospital, Paris, study number 2005/32). Children were sampled at day 0, 10, 30, 60 (except Healthy Contacts, HC) and 90 for LTBI and HC, and a further day 120, and day 180 for active TB children. Median age was 7.4 years, with 91% of the children BCG vaccinated. LTBI and active TB children undergoing therapy produced significant higher IFNγ values after 10 days of treatment (p = 0.035). In addition, IFNγ values were significantly lower at the end of treatment compared to IFNγ values at day 0, although the number of positive patients was not significantly different between day 0 and end of treatment.

Conclusions/ Significance

By following quantitative IFNγ values in each enrolled child with LTBI or active TB and receiving treatment, we were able to detect an increase in the IFNγ response at day 10 of treatment which might allow the confirmation of a diagnosis. In addition, a decline in IFNγ values during treatment makes it possible for clinicians to monitor the effect of preventive or curative therapy.

Comparison of T-SPOT.TB assay and tuberculin skin test for the evaluation of young children at high risk for tuberculosis in a community setting

OBJECTIVE

We wished to compare the sensitivity of an enzyme-linked immunospot assay (T-SPOT.TB; Oxford Immunotec, Oxford, United Kingdom) and the tuberculin skin test for the detection of tuberculosis infection in very young children being evaluated for active tuberculosis in a rural community setting.

METHODS

Children with a history of exposure to tuberculosis and children presenting to a local clinic or hospital with symptoms suggesting tuberculosis were admitted to a dedicated case verification ward. T-SPOT.TB testing was performed, and children were evaluated with a clinical examination, a tuberculin skin test, chest radiographs, and cultures of induced sputum and gastric lavage specimens. The diagnosis was determined by using a clinical algorithm.

RESULTS

A total of 243 children (median age: 18 months) were recruited, of whom 214 (88%) had interpretable T-SPOT.TB results. Children > or =12 months of age were more likely than younger children to have positive T-SPOT.TB results, whereas tuberculin skin test results were unaffected by age. The sensitivity of the T-SPOT.TB was no better than that of the tuberculin skin test for culture-confirmed tuberculosis (50% and 80%, respectively) and was poorer for the combined group of culture-confirmed and clinically probable tuberculosis (40% and 52%, respectively). For the 50 children clinically categorized as not having tuberculosis, the specificity of both the T-SPOT.TB and the tuberculin skin test was 84%.

CONCLUSIONS

For young children presenting in a community setting after exposure to tuberculosis or with symptoms suggesting tuberculosis, T-SPOT.TB cannot be used to exclude active disease. The sensitivity of this assay may be impaired for very young children.

Type 1 helper T cells and FoxP3-positive T cells in HIV-tuberculosis-associated immune reconstitution inflammatory syndrome

RATIONALE

Tuberculosis-associated immune reconstitution inflammatory syndrome (TB-IRIS) induced by combination antiretroviral therapy (cART) has been attributed to dysregulated expansion of tuberculin PPD-specific IFN-gamma-secreting CD4(+) T cells.

OBJECTIVES

To investigate the role of type 1 helper T cell expansions and regulatory T cells in HIV-TB IRIS.

METHODS

Longitudinal and cross-sectional studies of Mycobacterium tuberculosis-specific IFN-gamma enzyme-linked immunospot responses and flow cytometric analysis of blood cells from a total of 129 adults with HIV-1-associated tuberculosis, 98 of whom were prescribed cART.

MEASUREMENTS AND MAIN RESULTS

In cross-sectional analysis the frequency of IFN-gamma-secreting T cells recognizing early secretory antigenic target (ESAT)-6, alpha-crystallins 1 and 2, and PPD of M. tuberculosis was higher in patients with TB-IRIS than in similar patients treated for both HIV-1 and tuberculosis who did not develop IRIS (non-IRIS; P <or= 0.03). The biggest difference was in the recognition of alpha-crystallin molecules: peptide mapping indicated a polyclonal response. Flow cytometric analysis indicated equal proportions of CD4(+) and CD8(+) cells positive for activation markers HLA-DR and CD71 in both patients with TB-IRIS and non-IRIS patients. The percentage of CD4(+) cells positive for FoxP3 (Forkhead box P3) was low in both groups (TB-IRIS, 5.3 +/- 4.5; non-IRIS, 2.46 +/- 2.46; P = 0.13). Eight weeks of longitudinal analysis of patients with tuberculosis who were starting cART showed dynamic changes in antigen-specific IFN-gamma-secreting T cells in both the TB-IRIS and non-IRIS groups: the only significant trend was an increased response to PPD in the TB-IRIS group (P = 0.041).

CONCLUSIONS

There is an association between helper T-cell type 1 expansions and TB-IRIS, but the occurrence of similar expansions in non-IRIS brings into question whether these are causal. The defect in immune regulation responsible for TB-IRIS remains to be fully elucidated.

Systematic review: T-cell-based assays for the diagnosis of latent tuberculosis infection: an update

BACKGROUND

Interferon-gamma-release assays (IGRAs) are alternatives to the tuberculin skin test (TST). A recent meta-analysis showed that IGRAs have high specificity, even among populations that have received bacille Calmette-Guérin (BCG) vaccination. Sensitivity was suboptimal for TST and IGRAs.

PURPOSE

To incorporate newly reported evidence from 20 studies into an updated meta-analysis on the sensitivity and specificity of IGRAs.

DATA SOURCES

PubMed was searched through 31 March 2008, and citations of all original articles, guidelines, and reviews for studies published in English were reviewed.

STUDY SELECTION

Studies that evaluated QuantiFERON-TB Gold, QuantiFERON-TB Gold In-Tube (both from Cellestis, Victoria, Australia), and T-SPOT.TB (Oxford Immunotec, Oxford, United Kingdom) or its precommercial ELISpot version, when data on the commercial version were lacking. For assessing sensitivity, the study sample had to have microbiologically confirmed active tuberculosis. For assessing specificity, the sample had to comprise healthy, low-risk individuals without known exposure to tuberculosis. Studies with fewer than 10 participants and those that included only immunocompromised participants were excluded.

DATA EXTRACTION

One reviewer abstracted data on participant characteristics, test characteristics, and test performance from 38 studies; these data were double-checked by a second reviewer. The original investigators were contacted for additional information when necessary.

DATA SYNTHESIS

A fixed-effects meta-analysis with correction for overdispersion was done to pool data within prespecified subgroups. The pooled sensitivity was 78% (95% CI, 73% to 82%) for QuantiFERON-TB Gold, 70% (CI, 63% to 78%) for QuantiFERON-TB Gold In-Tube, and 90% (CI, 86% to 93%) for T-SPOT.TB. The pooled specificity for both QuantiFERON tests was 99% among non-BCG-vaccinated participants (CI, 98% to 100%) and 96% (CI, 94% to 98%) among BCG-vaccinated participants. The pooled specificity of T-SPOT.TB (including its precommercial ELISpot version) was 93% (CI, 86% to 100%). Tuberculin skin test results were heterogeneous, but specificity in non-BCG-vaccinated participants was consistently high (97% [CI, 95% to 99%]).

LIMITATIONS

Most studies were small and had limitations, including no gold standard for diagnosing latent tuberculosis and variable TST methods and cutoff values. Data on the specificity of the commercial T-SPOT.TB assay were limited.

CONCLUSION

The IGRAs, especially QuantiFERON-TB Gold and QuantiFERON-TB Gold In-Tube, have excellent specificity that is unaffected by BCG vaccination. Tuberculin skin test specificity is high in non-BCG-vaccinated populations but low and variable in BCG-vaccinated populations. Sensitivity of IGRAs and TST is not consistent across tests and populations, but T-SPOT.TB appears to be more sensitive than both QuantiFERON tests and TST.