Interpretation of Mycobacterium tuberculosis antigen-specific IFN-γ release assays (T-SPOT.TB) and factors that may modulate test results

A rare case series of HIV-negative patients with early relapsing cervical tuberculosis lymphadenitis

Most patients with early recurrent tuberculous lymphadenitis (RTL) can be overlooked due to the paucibacillary character of Mycobacterium tuberculosis complex (MTBC) causing difficulty in the differential diagnosis. Here, we present three cases with early RTL that occurred after completing pulmonary tuberculosis (TB) therapy with a cure, and that improved by early diagnosis and therapy. A 30-year-old migrant male, HIV-negative patient, who had used immunosuppressive drugs for Crohn's disease presented to the TB outpatient clinic with a new anterior cervical lymph node enlargement. Two months ago, his therapy for pulmonary TB and intra-abdominal tuberculous lymphadenitis (TL) was completed. Real-time polymerase chain reaction (RT-PCR) of purulent fine-needle aspiration (FNA) specimen from the anterior cervical lymphadenopathy (LAP) was detected positive for MTBC. Isoniazid (H) resistance was determined via the Seegene system. The 6 cm anterior cervical LAP regressed to a 1.6 cm LAP at the 4^th month of initial therapy with first-line antitubercular drugs. A 25-year-old female, the HIV-negative patient, was admitted to the TB outpatient clinic with a bulge on the submandibular area 3 months after the cessation of pulmonary multidrug-resistance TB therapy lasting 2 years. She had an index case but no comorbidity. The cytomorphology of FNA biopsy from the submandibular LAP reported granuloma with necrosis. RT-PCR of the purulent FNA specimen was positive for MTBC. H and rifampicin (R) resistances were found via the Seegene system. The right submandibular 2.9 cm LAP improved to a 1.7 cm LAP 6 months after the initiation of second-line antitubercular therapy. A 19-year-old male, the HIV-negative patient, presented to the TB outpatient clinic with a new bulge on the left supraclavicular area 9 months after cessation of pulmonary TB. He had no comorbidity and index case. RT-PCR of the purulent FNA specimen was positive for MTBC. H and R sensitivities were determined via the Seegene system. After the initial therapy with first-line antitubercular drugs for 2 months, the 1.5 cm left supraclavicular LAP improved to a 1.2 cm LAP.

Use of the QuantiFERON-TB Gold In-Tube Test in the Diagnosis and Monitoring of Treatment Efficacy in Active Pulmonary Tuberculosis

The value of QuantiFERON in the diagnosis of tuberculosis disease and in the monitoring of the response to anti-tuberculosis treatment is unclear. The aims of this study were to evaluate the accuracy of the QuantiFERON-TB Gold In-Tube (QFT-GIT) test in the diagnosis of tuberculosis and in the monitoring of the response to anti-tuberculosis treatment in patients with active pulmonary tuberculosis (PTB). Between January 2013 and December 2015, 133 cases with active PTB and 133 controls with no mycobacterial infection, matched by age (within 3 years) and by the week that they visited Tainan Chest Hospital, were enrolled in the study. Serial testing by QFT-GIT at baseline and after 2 and 6 months of treatment was performed. At these time points, a comparison of the performance of QFT-GIT with that of sputum culture status among study subjects was conducted. Compared to baseline, 116 (87.2%) cases showed a decreased response, whereas 17 (12.8%) showed persistent or stronger interferon-gamma (IFN-γ) responses at 2 months. PTB patients IFN-γ responses declined significantly from baseline to 2 months (median, 6.32 vs. 4.12; p < 0.005). The sensitivity values of the QFT-GIT test for the detection of pulmonary tuberculosis at cut-off points of 0.35 IU/mL, 0.20 IU/mL, and 0.10 IU/mL were 74.4%, 78.2%, and 80.5%, respectively. The specificity values at cut-off points of 0.35 IU/mL, 0.20 IU/mL, and 0.10 IU/mL were 66.2%, 63.9%, and 57.1%, respectively. Our results support the QFT-GIT assay as a potential tool for diagnosing tuberculosis and for monitoring the efficacy of anti-tuberculosis treatment.

Bacillus Calmette-Guérin (BCG) Revaccination of Adults with Latent Mycobacterium tuberculosis Infection Induces Long-Lived BCG-Reactive NK Cell Responses

One third of the global population is estimated to be latently infected with Mycobacterium tuberculosis We performed a phase I randomized controlled trial of isoniazid preventive therapy (IPT) before revaccination with bacillus Calmette-Guérin (BCG) in healthy, tuberculin skin test-positive (≥15-mm induration), HIV-negative South African adults. We hypothesized that preclearance of latent bacilli with IPT modulates BCG immunogenicity following revaccination. Frequencies and coexpression of IFN-γ, TNF-α, IL-2, IL-17, and/or IL-22 in CD4 T cells and IFN-γ-expressing CD8 T, γδ T, CD3(+)CD56(+) NKT-like, and NK cells in response to BCG were measured using whole blood intracellular cytokine staining and flow cytometry. We analyzed 72 participants who were revaccinated with BCG after IPT (n = 33) or without prior IPT (n = 39). IPT had little effect on frequencies or cytokine coexpression patterns of M. tuberculosis- or BCG-specific responses. Revaccination transiently boosted BCG-specific Th1 cytokine-expressing CD4, CD8, and γδ T cells. Despite high frequencies of IFN-γ-expressing BCG-reactive CD3(+)CD56(+) NKT-like cells and CD3(-)CD56(dim) and CD3(-)CD56(hi) NK cells at baseline, BCG revaccination boosted these responses, which remained elevated up to 1 y after revaccination. Such BCG-reactive memory NK cells were induced by BCG vaccination in infants, whereas in vitro IFN-γ expression by NK cells upon BCG stimulation was dependent on IL-12 and IL-18. Our data suggest that isoniazid preclearance of M. tuberculosis bacilli has little effect on the magnitude, persistence, or functional attributes of lymphocyte responses boosted by BCG revaccination. Our study highlights the surprising durability of BCG-boosted memory NKT-like and NK cells expressing antimycobacterial effector molecules, which may be novel targets for tuberculosis vaccines.

Kinetics of T-cell-based assays on cerebrospinal fluid and peripheral blood mononuclear cells in patients with tuberculous meningitis

BACKGROUND/AIMS

The goal of this study was to monitor tuberculosis (TB)-specific T-cell responses in cerebrospinal fluid-mononuclear cells (CSF-MCs) and peripheral blood mononuclear cells (PBMCs) in patients with tuberculous meningitis (TBM) over the course of anti-TB therapy.

METHODS

Adult patients (≥ 16 years) with TBM admitted to Asan Medical Center, Seoul, South Korea, were prospectively enrolled between April 2008 and April 2011. Serial blood or CSF samples were collected over the course of the anti-TB therapy, and analyzed using an enzyme-linked immunosorbent spot (ELISPOT) assay.

RESULTS

Serial ELISPOT assays were performed on PBMCs from 17 patients (seven definite, four probable, and six possible TBM) and CSF-MC from nine patients (all definite TBM). The median number of interferon-gamma (IFN-γ)-producing T-cells steadily increased during the first 6 months after commencement of anti-TB therapy in PBMCs. Serial CSF-MC ELISPOT assays revealed significant variability in immune responses during the first 6 weeks of anti-TB therapy, though early increases in CSF-MC ELISPOT results were associated with treatment failure or paradoxical response.

CONCLUSIONS

Serial analysis of PBMCs by ELISPOT during the course of treatment was ineffective for predicting clinical response. However, increases in TB-specific IFN-γ-producing T-cells in CSF-MC during the early phase of anti-TB therapy may be predictive of clinical failure.

Immunogenicity of 60 novel latency-related antigens of Mycobacterium tuberculosis

The aim of our work here was to evaluate the immunogenicity of 60 mycobacterial antigens, some of which have not been previously assessed, notably a novel series of in vivo-expressed Mycobacterium tuberculosis (IVE-TB) antigens. We enrolled 505 subjects and separated them in individuals with and without latent tuberculosis infection (LTBI) vs. patients with active tuberculosis (TB). Following an overnight and 7 days stimulation of whole blood with purified recombinant M. tuberculosis antigens, interferon-γ (IFN-γ) levels were determined by ELISA. Several antigens could statistically significantly differentiate the groups of individuals. We obtained promising antigens from all studied antigen groups [dormancy survival regulon (DosR regulon) encoded antigens; resuscitation-promoting factors (Rpf) antigens; IVE-TB antigens; reactivation associated antigens]. Rv1733, which is a probable conserved transmembrane protein encoded in DosR regulon, turned out to be very immunogenic and able to discriminate between the three defined TB status, thus considered a candidate biomarker. Rv2389 and Rv2435n, belonging to Rpf family and IVE-TB group of antigens, respectively, also stood out as LTBI biomarkers. Although more studies are needed to support our findings, the combined use of these antigens would be an interesting approach to TB immunodiagnosis candidates.

Effect of isoniazid therapy for latent TB infection on QuantiFERON-TB gold in-tube responses in adults with positive tuberculin skin test results in a high TB incidence area: a controlled study

BACKGROUND

T-cell interferon-γ release assays (IGRAs) are used in the diagnosis of Mycobacterium tuberculosis infection and could be useful biomarkers of response to treatment of latent TB infection for clinical trials, infection control units, and TB programs.

METHODS

This investigation was a prospective, controlled substudy of IGRA responses in 82 healthy South African adults with HIV seronegative and positive tuberculin skin test results randomly assigned to treatment with 6 months of daily isoniazid preventive therapy (IPT) or observation before Bacillus Calmette-Guérin revaccination in a clinical trial. QuantiFERON-TB Gold In-Tube (QFT-GIT) assay was used to measure interferon-γ (IFN-γ) response to mycobacterial antigens at baseline and after IPT or observation.

RESULTS

IFN-γ levels declined between baseline and the end of IPT (signed rank test P≤.0001) and between baseline and a similar period of observation without IPT (signed rank test P=.03). The rate of decrease in IFN-γ responses over time did not differ between the groups (Mann-Whitney-Wilcoxon test P=.31). QFT-GIT test results in two subjects (5%) in the IPT group and two subjects (5%) in the observation group reverted from positive to negative during follow-up. No significant difference was found between the groups with respect to baseline positivity or the proportion of patients whose tests reverted to negative.

CONCLUSIONS

IPT had no effect on changes in QFT-GIT readouts during short-term follow-up of adults with positive tuberculin skin tests in a high TB incidence setting. QFT-GIT is unlikely to be a useful biomarker of response to treatment of latent TB infection.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT01119521; URL: www.clinicaltrials.gov.

Incidence and outcomes of paradoxical lymph node enlargement after anti-tuberculosis therapy in non-HIV patients

OBJECTIVES

Limited data are available regarding the incidence and outcomes of lymphadenopathy after completing tuberculosis (TB) treatment.

METHODS

We prospectively evaluated the incidence and outcomes of post-treatment lymphadenopathy in 154 patients with newly diagnosed lymph node TB (group 1) and in 12 patients previously treated for TB (group 2). We assessed the rates of microbiological recurrence, clinical recurrence, and post-treatment paradoxical response (PR) (defined as no microbiological recurrence with spontaneous improvement).

RESULTS

Post-treatment lymphadenopathy occurred in 24 (15.6%) patients of group 1 and in 12 patients of group 2. Re-biopsy was performed in 23 of these 36 patients. AFB stain was positive in four (17.4%) cases, and TB-PCR was positive in 11 (47.8%), but all samples were sterile (no microbiological recurrence). Granuloma was present in 12 (52.2%) histological specimens. Thirty-three (91.7%) of the 36 patients with lymphadenopathy improved spontaneously (post-treatment PR) and 3 (8.3%) were improved with retreatment (clinical recurrence). The overall incidence of post-treatment PR in patients with lymph node TB (group 1) was 8.6 per 100 person-years (95% CI, 5.8-12.7).

CONCLUSIONS

Lymphadenopathy after TB treatment was more likely to be associated with post-treatment PR rather than with microbiological recurrence, and it should be monitored until PR resolve.

Interferon-Gamma Release Assays versus Tuberculin Skin Testing for the Diagnosis of Latent Tuberculosis Infection: An Overview of the Evidence

A profusion of articles have been published on the accuracy and uses of interferon-gamma releasing assays. Here we review the clinical applications, advantages, and limitations of the tuberculin skin test and interferon-gamma release assays and provide an overview of the most recent systematic reviews conducted for different indications for the use of these tests. We conclude that both tests are accurate to detect latent tuberculosis, although interferon-gamma release assays have higher specificity than tuberculin skin testing in BCG-vaccinated populations, particularly if BCG is received after infancy. However, both tests perform poorly to predict risk for progression to active tuberculosis. Interferon-gamma release assays have significant limitations in serial testing because of spontaneous variability and lack of a validated definition of conversion and reversion, making it difficult for clinicians to interpret changes in category (conversions and reversions). So far, the most important clinical evidence, that is, that isoniazid preventive therapy reduces the risk for progression to disease, has been produced only in tuberculin skin test-positive individuals.

Gamma interferon release assay for monitoring of treatment response for active tuberculosis: an explosion in the spaghetti factory

Few studies have correlated the results of interferon (gamma interferon) release assays (IGRAs) with known markers of tuberculosis (TB) treatment response. We report the results of serial QuantiFERON-TB gold in-tube assay (QFT) testing on 149 patients with active tuberculosis and correlate the results with smear and culture conversion. We show that QFT results do not offer much value for treatment monitoring of TB disease.

Evaluation of interferon-gamma release assays for the diagnosis of tuberculosis: an updated meta-analysis

The objective of this investigation was to systematically evaluate the diagnostic accuracy of interferon-gamma release assays (IGRAs) for tuberculosis disease. Both English and Chinese databases were searched for relevant articles through January 2012. We included studies that were restricted to diagnostic applications of IGRAs in patients with active tuberculosis and excluded studies performed in the immune-compromised population. We used Meta-DiSc software to handle the data. We calculated the sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), and 95 % confidence interval (CI) for each study. We also calculated the pooled sensitivity, specificity, PLR, NLR, DOR, and produced forest plots and summary receiver operating characteristic (SROC) curves. A total of 61 papers (73 studies) were eligible for meta-analysis, including 36 published in English and 25 published in the Chinese language. The overall sensitivity, specificity, PLR, NLR, DOR, and 95 % CI of IGRAs were 0.85 (95 % CI: 0.84-0.86), 0.84 (95 % CI: 0.83-0.85), 7.82 (95 % CI: 6.01-10.19), 0.17 (95 % CI: 0.14-0.21), and 59.27 (95 % CI: 40.19-87.42), respectively. For ten studies evaluating T-SPOT.TB in China, the combined sensitivity, specificity, PLR, NLR, DOR, and 95 % CI were 0.88 (95 % CI: 0.86-0.91), 0.89 (95 % CI: 0.86-0.92), 8.86 (95 % CI: 5.42-14.46), 0.13 (95 % CI: 0.10-0.17), and 88.15 (95 % CI: 41.76-186.07), respectively. The SROC area under the curve (AUC) was 0.9548 (95 % CI: 0.9323-0.9773). Though IGRAs showed good sensitivity and specificity for the detection of tuberculosis in this meta-analysis, the decision to use an IGRA should be based on the local prevalence of the disease and the country guidelines, as well as resources and logistical considerations.

Correlation of mycobacterium tuberculosis specific and non-specific quantitative Th1 T-cell responses with bacillary load in a high burden setting

Background

Measures of bacillary load in patients with tuberculosis (TB) may be useful for predicting and monitoring response to treatment. The relationship between quantitative T-cell responses and mycobacterial load remains unclear. We hypothesised that, in a HIV-prevalent high burden setting, the magnitude of mycobacterial antigen-specific and non-specific T-cell IFN-γ responses would correlate with (a) bacterial load and (b) culture conversion in patients undergoing treatment.

Methods

We compared baseline (n = 147), 2 (n = 35) and 6 month (n = 13) purified-protein-derivative (PPD) and RD1-specific (TSPOT.TB and QFT-GIT) blood RD1-specific (TSPOT.TB; QFT-GIT) responses with associates of sputum bacillary load in patients with culture-confirmed TB in Cape Town, South Africa.

Results

IFN-γ responses were not associated with liquid culture time-to-positivity, smear-grade, Xpert MTB/RIF-generated cycle threshold values or the presence of cavities on the chest radiograph in patients with culture-confirmed TB and irrespective of HIV-status. 2-month IGRA conversion rates (positive-to-negative) were negligible [<11% for TSPOT.TB (3/28) and QFT-GIT (1/29)] and lower compared to culture [60% (21/35); p<0.01].

Conclusions

In a high burden HIV-prevalent setting T-cell IFN-γ responses to M. tuberculosis-specific and non-specific antigens do not correlate with bacillary load, including Xpert MTB/RIF-generated C_T values, and are therefore poorly suited for monitoring treatment and prognostication.

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.

Pre-vaccination nasopharyngeal pneumococcal carriage in a Nigerian population: epidemiology and population biology

BACKGROUND

Introduction of pneumococcal vaccines in Nigeria is a priority as part of the Accelerated Vaccine Introduction Initiative (AVI) of the Global Alliance for Vaccines and Immunisation (GAVI). However, country data on the burden of pneumococcal disease (IPD) is limited and coverage by available conjugate vaccines is unknown. This study was carried out to describe the pre vaccination epidemiology and population biology of pneumococcal carriage in Nigeria.

METHODS

This was a cross sectional survey. Nasopharyngeal swabs (NPS) were obtained from a population sample in 14 contiguous peri-urban Nigerian communities. Data on demographic characteristics and risk factor for carriage were obtained from all study participants. Pneumococci isolated from NPS were characterised by serotyping, antimicrobial susceptibility and Multi Locus Sequencing Typing (MLST).

RESULTS

The prevalence of pneumococcal carriage was 52.5%. Carriage was higher in children compared to adults (67.4% vs. 26%), highest (≈90%) in infants aged <9 months and reduced significantly with increasing age (P<0.001). Serotypes 19F (18.6%) and 6A (14.4%) were most predominant. Potential vaccine coverage was 43.8%, 45.0% and 62% for PCV-7, PCV-10 and PCV-13 respectively. There were 16 novel alleles, 72 different sequence types (STs) from the isolates and 3 Sequence Types (280, 310 and 5543) were associated with isolates of more than one serotype indicative of serotype switching. Antimicrobial resistance was high for cotrimoxazole (93%) and tetracycline (84%), a third of isolates had intermediate resistance to penicillin. Young age was the only risk factor significantly associated with carriage.

CONCLUSIONS

Pneumococcal carriage and serotype diversity is highly prevalent in Nigeria especially in infants. Based on the coverage of serotypes in this study, PCV-13 is the obvious choice to reduce disease burden and prevalence of drug resistant pneumococci. However, its use will require careful monitoring. Our findings provide sound baseline data for impact assessment following vaccine introduction in Nigeria.

Effect of chemotherapy on whole-blood cytokine responses to Mycobacterium tuberculosis antigens in a small cohort of patients with pulmonary tuberculosis

The development of genomic and proteomic tools has enabled studies that begin to characterize the molecular targets of an effective host immune response to Mycobacterium tuberculosis, including understanding the specific immune responses associated with tuberculosis (TB) disease progression, disease resolution, and the development of latency. One application of such tools is the development of diagnostic reagents and assays useful as a test of cure. Such a test could be of considerable importance for the evaluation of new therapeutics. We and others have previously described immunodominant proteins of M. tuberculosis, including both vaccine and diagnostic candidates. In the present study, we describe the changes in immune responses to a panel of 71 M. tuberculosis antigens in six patients during the course of therapy. The levels of six cytokines were measured in 24-h whole-blood assays with these antigens, revealing that gamma interferon (IFN-γ), tumor necrosis factor (TNF), and interleukin-10 (IL-10) were differentially regulated in response to a subset of antigens. Therefore, measuring the production of these three cytokines in response to a panel of carefully selected M. tuberculosis proteins during the course of TB therapy might be a promising path toward the development of a test of cure and warrants further validation in larger cohorts of pulmonary TB patients.

Are interferon-γ release assays useful for diagnosing active tuberculosis in a high-burden setting?

Although interferon-γ release assays (IGRAs) are intended for diagnosing latent tuberculosis (TB), we hypothesised that in a high-burden setting: 1) the magnitude of the response when using IGRAs can distinguish active TB from other diagnoses; 2) IGRAs may aid in the diagnosis of smear-negative TB; and 3) IGRAs could be useful as rule-out tests for active TB. We evaluated the accuracy of two IGRAs (QuantiFERON®-TB Gold In-tube (QFT-GIT) and T-SPOT®.TB) in 395 patients (27% HIV-infected) with suspected TB in Cape Town, South Africa. IGRA sensitivity and specificity (95% CI) were 76% (68-83%) and 42% (36-49%) for QFT-GIT and 84% (77-90%) and 47% (40-53%) for T-SPOT®.TB, respectively. Although interferon-γ responses were significantly higher in the TB versus non-TB groups (p<0.0001), varying the cut-offs did not improve discriminatory ability. In culture-negative patients, depending on whether those with clinically diagnosed TB were included or excluded from the analysis, the negative predictive value (NPV) of QFT-GIT, T-SPOT®.TB and chest radiograph in smear-negative patients varied between 85 and 89, 87 and 92, and 98% (for chest radiograph), respectively. Overall accuracy was independent of HIV status and CD4 count. In a high-burden setting, IGRAs alone do not have value as rule-in or -out tests for active TB. In smear-negative patients, chest radiography had better NPV even in HIV-infected patients.

Serial interferon-gamma release assays during treatment of active tuberculosis in young adults

Background

The role of interferon-γ release assay (IGRA) in monitoring responses to anti-tuberculosis (TB) treatment is not clear. We evaluated the results of the QuantiFERON-TB Gold In-tube (QFT-GIT) assay over time during the anti-TB treatment of adults with no underlying disease.

Methods

We enrolled soldiers who were newly diagnosed with active TB and admitted to the central referral military hospital in South Korea between May 1, 2008 and September 30, 2009. For each participant, we preformed QFT-GIT assay before treatment (baseline) and at 1, 3, and 6 months after initiating anti-TB medication.

Results

Of 67 eligible patients, 59 (88.1%) completed the study protocol. All participants were males who were human immunodeficiency virus (HIV)-negative and had no chronic diseases. Their median age was 21 years (range, 20-48). Initially, 57 (96.6%) patients had positive QFT-GIT results, and 53 (89.8%), 42 (71.2%), and 39 (66.1%) had positive QFT-GIT results at 1, 3, and 6 months, respectively. The IFN-γ level at baseline was 5.31 ± 5.34 IU/ml, and the levels at 1, 3, and 6 months were 3.95 ± 4.30, 1.82 ± 2.14, and 1.50 ± 2.12 IU/ml, respectively. All patients had clinical and radiologic improvements after treatment and were cured. A lower IFN-γ level, C-reactive protein ≥ 3 mg/dl, and the presence of fever (≥ 38.3°C) at diagnosis were associated with negative reversion of the QFT-GIT assay.

Conclusion

Although the IFN-γ level measured by QFT-GIT assay decreased after successful anti-TB treatment in most participants, less than half of them exhibited QFT-GIT reversion. Thus, the reversion to negativity of the QFT-GIT assay may not be a good surrogate for treatment response in otherwise healthy young patients with TB.

Rv1985c, a promising novel antigen for diagnosis of tuberculosis infection from BCG-vaccinated controls

BACKGROUND

Antigens encoded in the region of difference (RD) of Mycobacterium tuberculosis constitute a potential source of specific antigens for immunodiagnosis. In the present study, recombinant protein Rv1985c from RD2 was cloned, expressed, purified, immunologically characterized and investigated for its potentially diagnostic value for tuberculosis (TB) infection among BCG-vaccinated individuals.

METHODS

T-cell response to Rv1985c was evaluated by IFN-γ ELISPOT in 56 TB patients, 20 latent TB infection (LTBI) and 30 BCG-vaccinated controls in comparison with the commercial T-SPOT. TB kit. Humoral response was evaluated by ELISA in 117 TB patients, 45 LTBI and 67 BCG-vaccinated controls, including all those who had T-cell assay, in comparison with a commercial IgG kit.

RESULTS

Rv1985c was specifically recognized by cellular and humoral responses from both TB and LTBI groups compared with healthy controls. Rv1985c IgG-ELISA achieved 52% and 62% sensitivity respectively, which outperformed the sensitivity of PATHOZYME-MYCO kit (34%) in detecting active TB (P = 0.011), whereas IFN-γ Rv1985c-ELISPOT achieved 71% and 55% sensitivity in detecting active and LTBI, respectively. Addition of Rv1985c increased sensitivities of ESAT-6, CFP-10 and ESAT-6/CFP-10 combination in detecting TB from 82.1% to 89.2% (P = 0.125), 67.9% to 87.5% (P < 0.001) and 85.7% to 92.9% (P = 0.125), respectively.

CONCLUSIONS

In conclusion, Rv1985c is a novel antigen which can be used to immunologically diagnose TB infection along with other immunodominant antigens among BCG-vaccinated population.

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.

Limited usefulness of QuantiFERON-TB Gold In-Tube for monitoring anti-tuberculosis therapy

The usefulness of IFN-gamma release assays to monitor the efficacy of anti-tuberculosis (TB) treatment is controversial. Sixty patients affected by culture-confirmed pulmonary TB (M = 36; mean age: 39.2 yr; Italians = 28) were serially tested in a low prevalence setting by means of QuantiFERON-TB GOLD In-Tube (QFT-IT) at baseline and after a successful six-month therapy regimen (T6). A sub-group of 40 cases was also tested at 1 and 3 months. Overall, 88.3% of patients scored a QFT-IT positive result at baseline, with the higher proportion of TB-specific IFN-gamma responses in foreign-born patients (p = 0.04). TB-specific responses were highly variable over time, the within-person variability being correlated with baseline IFN-gamma levels (r = 0.731; p < 0.001). Overall, 61.6% of cases still tested QFT-IT positive at the completion of therapy. Average IFN-gamma levels increased over time, being persistently significantly higher in Italian patients than in foreign-born cases both at baseline (p = 0.03) and at T6 (p = 0.02). Reversion mainly occurred in patients (26.6%) with baseline IFN-gamma levels close to the conventional cut-off value. No indeterminate results were recorded at any study time point. In conclusion, QFT-IT adds no significant information to clinicians for treatment monitoring when applied in routine clinical practice in a low prevalence setting. Kinetics of T cell responses upon TB treatment and reversion (and conversion) thresholds need to be addressed. Diversity of IFN-gamma responses among patients of different geographic origin is an issue to be investigated further.

Diagnosis and follow-up of treatment of latent tuberculosis; the utility of the QuantiFERON-TB Gold In-tube assay in outpatients from a tuberculosis low-endemic country

Background

Interferon-gamma (IFN-γ) Release Assays (IGRA) are more specific than the tuberculosis skin test (TST) in the diagnosis of latent tuberculosis (TB) infection (LTBI). We present the performance of the QuantiFERON^®-TB Gold In-tube (QFT-TB) assay as diagnostic test and during follow-up of preventive TB therapy in outpatients from a TB low-endemic country.

Methods

481 persons with suspected TB infection were tested with QFT-TB. Thoracic X-ray and sputum samples were performed and a questionnaire concerning risk factors for TB was filled. Three months of isoniazid and rifampicin were given to patients with LTBI and QFT-TB tests were performed after three and 15 months.

Results

The QFT-TB test was positive in 30.8% (148/481) of the total, in 66.9% (111/166) of persons with origin from a TB endemic country, in 71.4% (20/28) previously treated for TB and in 100% (15/15) of those diagnosed with active TB with no inconclusive results. The QFT-TB test was more frequently positive in those with TST ≥ 15 mm (47.5%) compared to TST 11-14 mm (21.3%) and TST 6-10 mm (10.5%), (p < 0.001). Origin from a TB endemic country (OR 6.82, 95% CI 1.73-26.82), recent stay in a TB endemic country (OR 1.32, 95% CI 1.09-1.59), duration of TB exposure (OR 1.59, 95% CI 1.14-2.22) and previous TB disease (OR 11.60, 95% CI 2.02-66.73) were all independently associated with a positive QFT-TB test. After preventive therapy, 35/40 (87.5%) and 22/26 (84.6%) were still QFT-TB positive after three and 15 months, respectively. IFN-γ responses were comparable at start (mean 6.13 IU/ml ± SD 3.99) and after three months (mean 5.65 IU/ml ± SD 3.66) and 15 months (mean 5.65 IU/ml ± SD 4.14), (p > 0.05).

Conclusion

Only one third of those with suspected TB infection had a positive QFT-TB test. Recent immigration from TB endemic countries and long duration of exposure are risk factors for a positive QFT-TB test and these groups should be targeted through screening. Since most patients remained QFT-TB positive after therapy, the test should not be used to monitor the effect of preventive therapy. Prospective studies are needed in order to determine the usefulness of IGRA tests during therapy.

Evaluation of interferon-gamma release assays in the diagnosis of recent tuberculosis infection in health care workers

BACKGROUND

Health care workers (HCWs) are a group at risk of latent tuberculosis infection (LTBI). The aims of this study were to determine IFN-gamma response by QuantiFERON-TB GOLD In Tube (QFN-G-IT) and T-SPOT.TB in HCWs, comparing the results with tuberculin skin test (TST); and to analyze the capacity of IFN-gamma tests to detect recent versus remote LTBI with a prolonged stimulation test (PST).

METHODOLOGY/PRINCIPAL FINDINGS

A total of 147 HCWs were enrolled; 23 of whom were BCG vaccinated. 95 HCWs (64.6%) had a previous positive TST and were not retested; and 52 HCWs had a previous negative TST or were tested for the first time. When we analysed individuals without previous positive TST, the number of positive results for T-SPOT.TB was 12/52 (23.1%); and for QFN-G-IT, 9/52 (17.3%). The global concordance (kappa) between T-SPOT.TB and QFN-G-IT with TST was 0.754 and 0.929 respectively. Of individuals with previous positive TST, T-SPOT.TB and QFN-G-IT were negative in 51.6% (49/95) and 62.1% (59/95) respectively, decreasing the concordance to 0.321 and 0.288, respectively. In non-BCG vaccinated HCWs with previous positive TST a positive IFN-gamma test was associated with degree of exposure and diameter of TST. PST was performed in 24 HCW with previous positive TST and negative IFN-gamma tests. PST was developed in 3 cell cultures stimulated with medium alone, ESAT-6 and CFP-10, respectively. In the third and sixth day of incubation period, part of the supernatants were replaced with complete medium supplemented with (rIL)-2. On day 9, ELISPOT assay was performed. In 14 samples PST was not valid due to not having enough cells. In 8 cases, the response was negative, and in 2 cases positive, suggesting that these patients were infected with Mycobacterium tuberculosis in some point in the past.

CONCLUSIONS

Both IFN-gamma tests showed a similar number of positive results, and concordance between the tests was excellent. None of the tests was affected by prior BCG vaccination. IFN-gamma tests are a useful tool for detecting recent infection in HCW population.

Usefulness of interferon-gamma release assays for diagnosing TB infection and problems with these assays

The specificity of the tuberculin skin test (TST) in the diagnosis of tuberculosis infection is seriously compromised because of extensive use of the bacille Calmette-Guérin (BCG) vaccination. The interferon-gamma release assay (IGRA), a new diagnostic using Mycobacterium tuberculosis-specific antigens has been introduced in response to these needs. In this review, published findings on the performance of the QuantiFERON-TB (QFT), one of the IGRA formats, are summarized and discussed. In addition to its high specificity, the QFT has considerably high sensitivity, comparable with or superior to that of the TST, if applied to patients with active tuberculosis as a surrogate of latent tuberculosis infection. When applied to patients with immunosuppression, such as aging patients, or those with HIV infection, those with immunosuppressive drug therapies, or those with renal hemodialysis, QFT is shown to be more robust than the TST. As regards the dynamics of QFT responses to chemotherapy, there are many reports showing a decrease in responses during the treatment, which indicates the possibility that QFT could be used as a tool for monitoring the progress of treatment. However, there are discordant reports that warrant further study.

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.

In vivo and in vitro effects of antituberculosis treatment on mycobacterial interferon-gamma T cell response

Background

In recent years, the impact of antituberculous treatment on interferon (IFN)-γ response to Mycobacterium tuberculosis antigens has been widely investigated, but the results have been controversial. The objective of the present study was: i) to evaluate longitudinal changes of IFN-γ response to M. tuberculosis-specific antigens in TB patients during antituberculous treatment by using the QuantiFERON-TB Gold (QFT-G) assay; ii) to compare the differences in T-cell response after a short or prolonged period of stimulation with mycobacterial antigens; iii) to assess the CD4+ and CD8+ T cells with effector/memory and central/memory phenotype; iv) to investigate the direct in vitro effects of antituberculous drugs on the secretion of IFN-γ.

Principal Findings

38 TB patients was evaluated at baseline and at month 2 and 4 of treatment and at month 6 (treatment completion). 27 (71%) patients had a QFT-G reversion (positive to negative) at the end of therapy, while 11 (29%) TB patients remained QFT-G positive at the end of therapy. Among the 11 patients with persistent positive QFT-G results, six had a complete response to the treatment, while the remaining 5 patients did not have a resolution of the disease. All 27 patients who became QFT-G negative had a complete clinical and microbiological recovery of the TB disease. In these patients the release of IFN-γ is absent even after a prolonged 6-day incubation with both ESAT-6 and CFP-10 antigens and the percentage of effector/memory T-cells phenotype was markedly lower than subjects with persistent positive QFT-G results. The in vitro study showed that antituberculous drugs did not exert any inhibitory effect on IFN-γ production within the range of therapeutically achievable concentrations.

Conclusions

The present study suggests that the decrease in the M. tuberculosis-specific T cells responses following successful anti-TB therapy may have a clinical value as a supplemental tool for the monitoring of the efficacy of pharmacologic intervention for active TB. In addition, the antituberculous drugs do not have any direct down-regulatory effect on the specific IFN-γ response.

T-SPOT.TB responses during treatment of pulmonary tuberculosis

Background

Immune responses to Mycobacterium tuberculosis antigens could serve as surrogate markers of treatment response.

Methods

Using the T-SPOT.TB assay and frozen peripheral blood mononuclear cells, we enumerated ESAT-6- and CFP-10-specific IFN-γ-producing T cells over time in pulmonary TB patients receiving directly observed treatment. T cell responses (measured as "spot forming cells" or "SFCs") were assessed prior to treatment and at 16 and 24 weeks of treatment.

Results

58 patients were evaluated, of whom 57 were HIV seronegative. Mean (SD) ESAT-6, CFP-10, and summed RD1 specific SFCs declined from 42.7 (72.7), 41.2 (66.4), and 83.8 (105.7) at baseline to 23.3 (39.4, p = 0.01), 23.2 (29.4, p = 0.18), and 46.5 (59.5, p = 0.02) at completion of 24 weeks of treatment, respectively. Only 10% of individuals with a baseline reactive test reverted to negative at treatment week 24. For the group that was culture positive at completion of 8 weeks of treatment compared to the culture negative group, the incidence rate ratio (IRR) of ESAT-6, CFP-10, and summed RD1 specific SFC counts were, respectively, 2.23 (p = 0.048), 1.51 (p = 0.20), and 1.83 (p = 0.047). Patients with cavitary disease had mean ESAT-6 specific SFC counts that were higher than those without cavitary disease (IRR 2.08, p = 0.034).

Conclusion

IFN-γ-producing RD1-specific T cells, as measured in the T-SPOT.TB assay, may be directly related to bacterial load in patients undergoing treatment for pulmonary TB. However, high inter-subject variability in quantitative results coupled with failure of reversion to negative of qualitative results in most subjects at treatment completion may limit the utility of this assay as a surrogate marker for treatment efficacy.

Use of the T-SPOT.TB Assay to Detect Latent Tuberculosis Infection Among Rheumatic Disease Patients on Immunosuppressive Therapy

Objective.

We evaluated the T-SPOT.TB assay to identify latent tuberculosis infection (LTBI) in patients with rheumatic disease receiving immunosuppressive medication including tumor necrosis factor (TNF) antagonists.

Methods.

A total of 200 patients seen in the Arthritis Center at Brigham and Women’s Hospital were enrolled for study. Most patients were US-born women with rheumatoid arthritis. A medical history was obtained using a questionnaire, whole blood was drawn for the T-SPOT.TB assay, and tuberculin skin testing (TST) was performed.

Results.

Both tests were performed on 179 subjects, who had no history of a positive TST. All subjects had a strong response to the T-SPOT.TB test positive control, and there were no indeterminate results. Among these 179 subjects, 2 had a positive TST and 10 had a positive T-SPOT.TB test. No subject was positive for both tests. Patients with a positive T-SPOT.TB test did not have typical risk factors for LTBI based on clinical evaluation.

Conclusion.

The lack of concordance between the TST and the T-SPOT.TB assay may indicate that the immunoassay is more sensitive, particularly in a patient population taking immunosuppressive medications. It is equally likely that the low prevalence of LTBI in this low-risk population led to an increase in the false-positive rate despite the high sensitivity and specificity of the T-SPOT.TB assay. In the context of our patient population, the T-SPOT.TB assay is likely to be most useful in evaluation of patients with a positive TST, since these patients have a higher pretest probability of having LTBI.

T-cell responses to the Mycobacterium tuberculosis-specific antigens in active tuberculosis patients at the beginning, during, and after antituberculosis treatment

The objectives of the study were to assess the performance of the QuantiFERON-TB Gold In-Tube (QFN-G-IT) and the T-SPOT.TB tests in the immunodiagnosis of active tuberculosis (TB) in adult patients, and to study the T-cell interferon gamma (IFN-gamma) responses during treatment and in patients who have recovered after curative treatment and self-healed TB patients. When only analyzing patients included at the beginning of treatment, the sensitivity was 83.3% for T-SPOT.TB and 69.4% for QFN-G-IT. In contrast, when evaluating patients during treatment, the sensitivity of the T-SPOT.TB and QFN-G-IT decreased to 69.8% and 48.8%, respectively. The response to the specific antigens increased after finishing the treatment compared with the values during the treatment. The T-SPOT.TB was more sensitive in diagnosing active TB than the QFN-G-IT. The IFN-gamma tests could be used as a complementary method in the diagnosis of active TB.

Peripheral blood gamma interferon release assays predict lung responses and Mycobacterium tuberculosis disease outcome in mice

Current diagnostic tests for tuberculosis (TB) are not able to distinguish active disease from latent Mycobacterium tuberculosis infection, nor are they able to quantify the risk of a latently infected person progressing to active TB. There is interest, however, in adapting antigen-specific gamma interferon (IFN-gamma) release assays (IGRAs) to predict disease outcome. In this study, we used the differential susceptibilities of inbred mouse strains to M. tuberculosis infection to evaluate the prognostic capabilities of IGRAs. Using lung and blood cultures, we determined that CBA/J, DBA/2, and C3H/HeJ mice (models of heightened risk of progression to active TB) produced less antigen-specific IFN-gamma in response to M. tuberculosis culture filtrate proteins and early secreted antigenic target-6 than the relatively resistant C57BL/6 mouse strain. Additionally, reduced IFN-gamma secretion in supernatants reflected a reduced frequency of IFN-gamma-responding cells in the lung and blood and not a specific defect in IFN-gamma secretion at the single-cell level. Importantly, detection of antigen-specific IFN-gamma from blood cultures accurately reflected lung responses, indicating that blood can be an appropriate test tissue in humans. Furthermore, reduced antigen-specific IFN-gamma production and low frequencies of IFN-gamma-responding cells from peripheral blood predicted increased risk of TB disease progression across genetically diverse TB disease-susceptible mouse strains, suggesting that similar results may occur in humans. The development of efficacious predictive diagnostic tests for humans would lead to targeted therapy prior to progression to active TB, reducing transmission, incidence, and prevalence rates while maximizing the use of public health resources.