Tuberculosis antigen-specific immune responses can be detected using enzyme-linked immunospot technology in human immunodeficiency virus (HIV)-1 patients with advanced disease

Enhanced diagnosis of HIV-1-associated tuberculosis by relating T-SPOT.TB and CD4 counts

The sensitivity of the tuberculin skin test is impaired in HIV-1-infected persons. Enzyme-linked immunospot-based detection of immune sensitisation may be less affected. Furthermore, the quantitative response can be related to the CD4 count, potentially improving specificity for active disease. The T-SPOT.TB assay was performed on HIV-1-infected participants, 85 with active tuberculosis (TB) and 81 healthy patients (non-TB). The ratio of the sum of the 6-kDa early secretory antigenic target and culture filtrate protein 10 response to the CD4 count (spot-forming cell (SFC)/CD4) was calculated. Using the manufacturer's guidelines, active TB was diagnosed with 76% sensitivity and 53% specificity. Using an SFC/CD4 ratio of 0.12, sensitivity (80%) and specificity (62%) improved. The quantitative T-cell response increased with increasing smear-positivity in the active TB group (p = 0.0008). In the non-TB group, the proportion of persons scored positive by T-SPOT.TB assay was lower in the group with a CD4 count of <200 cells·mm(-3) (p = 0.029). The ratio of the summed T-cell response to CD4 count improved the diagnostic accuracy of the T-SPOT.TB assay in HIV-1-infected persons, and a ratio of SFC/CD4 of >0.12 should prompt investigation for active disease. A strong association between the degree of sputum positivity and T-SPOT.TB score was found. The sensitivity of the T-SPOT.TB assay in active disease may be less impaired by advanced immunosuppression.

A decade of infliximab: The Austrian evidence based consensus on the safe use of infliximab in inflammatory bowel disease

Infliximab (IFX) has tremendously enriched the therapy of inflammatory bowel diseases (IBD) and other immune mediated diseases. Although the efficacy of IFX was undoubtedly proven during the last decade numerous publications have also caused various safety concerns. To summarize the immense information concerning adverse events and safety issues the Austrian Society of Gastroenterology and Hepatology launched this evidence based consensus on the safe use of IFX which covers the following topics: infusion reactions and immunogenicity, skin reactions, opportunistic infections (including tuberculosis), non-opportunistic infections (bacterial and viral), vaccination, neurological complications, hepatotoxicity, congestive heart failure, haematological side effects, intestinal strictures, stenosis and bowel obstruction (SSO), concomitant medication, malignancy and lymphoma, IFX in the elderly and the young, mortality, fertility, pregnancy and breast feeding. To make the vast amount of information practicable for routine application the consensus was finally condensed into a checklist for a safe use of IFX which consists of two parts: issues to be addressed prior to anti-TNF therapy and issues to be addressed during maintenance. Both parts are further divided into obligatory and facultative items.

Negative and positive predictive value of a whole-blood interferon-γ release assay for developing active tuberculosis: an update

RATIONALE

only limited data are available on the predictive value of interferon-γ release assays for progression from latent tuberculosis infection to active tuberculosis (TB).

OBJECTIVES

to build on our initial study comparing the QuantiFERON-TB Gold in-tube assay (QFT) with the tuberculin skin test (TST) in close contacts of patients with TB and evaluating progression to active TB for up to 4 years.

METHODS

a cohort of close contacts of smear-positive index cases established between May 2005 and April 2008 was tested with QFT and TST. Through April 2010, progressors to active TB were consecutively recorded.

MEASUREMENTS AND MAIN RESULTS

of the 1,414 contacts (141 children), 1,033 were still resident in Hamburg at the end of the study period, and results of both tests were available for 954. QFT, but not TST, results were associated with exposure time (P < 0.0001). For QFT, 198 of 954 (20.8%) were positive; 63.3% (604) were TST positive at greater than 5 mm and 25.4% at greater than 10 mm. Nine hundred and three contacts refused chemoprevention and 19 developed active TB. All 19 (100%) had been QFT positive with a progression rate of 12.9% (19 of 147) over the observation period. Corresponding values for the TST were significantly lower: 89.5% (17 of 19) and 3.1% (17 of 555) at greater than 5 mm, and 52.6% (10 of 19) and 4.8% (10 of 207) at greater than 10 mm, respectively. The progression rate of 28.6% (6 of 21) for QFT-positive children was significantly higher than 10.3% (13 of 126) for adults (P = 0.03).

CONCLUSIONS

results suggest that QFT is more reliable than the TST for identifying those who will soon progress to active TB, especially in children.

Interpreting tuberculin skin tests in a population with a high prevalence of HIV, tuberculosis, and nonspecific tuberculin sensitivity

Understanding the epidemiology and clinical course of tuberculosis is hampered by the absence of a perfect test for latent tuberculosis infection. The tuberculin skin test (TST) is widely used but suffers poor specificity in those receiving the bacille Calmette-Guérin vaccine and poor sensitivity in individuals with human immunodeficiency virus (HIV) infections. TST responses for a target population in Harare, Zimbabwe (HIV prevalence, 21%), recruited in 2005–2006, were interpreted by using a separate calibration population in Harare, for which interferon-gamma release assays (enzyme-linked immunosorbent spot (ELISpot)) results were also known. Statistical fitting of the responses in the calibration population allowed computation of the probability that an individual in the target population with a given TST and HIV result would have tested ELISpot positive. From this, estimates of the prevalence of tuberculosis infection, and optimal TST cutpoints to minimize misdiagnosis, were computed for different assumptions about ELISpot performance. Different assumptions about the sensitivity and specificity of ELISpot gave a 40%–57% prevalence of tuberculosis infection in the target population (including HIV-infected individuals) and optimal TST cutpoints typically in the 10 mm–20 mm range. However, the optimal cutpoint for HIV-infected individuals was consistently 0 mm. This calibration method may provide a valuable tool for interpreting TST results in other populations.

Role of interferon-gamma release assays in the diagnosis of pulmonary tuberculosis in patients with advanced HIV infection

Background

T-cell interferon-gamma release assays (IGRAs) may have a role in the diagnosis of active tuberculosis when evaluating patients for whom standard microbiology has limited sensitivity. Our objective was to examine the accuracy of a commercial IGRA for diagnosis of active tuberculosis in HIV-infected persons.

Methods

We enrolled HIV-infected patients admitted to Mulago Hospital in Kampala, Uganda with cough ≥ 2 weeks. All patients underwent standard medical evaluation. We collected peripheral blood specimens at enrollment and performed a commercial, ELISPOT-based IGRA according to the manufacturer's recommendations. IGRA sensitivity and specificity were determined using mycobacterial culture results as the reference standard.

Results

Overall, 236 patients were enrolled. The median CD4+ T-lymphocyte count was 49 cells/μl and 126 (53%) patients were diagnosed with active pulmonary tuberculosis. IGRAs were not performed in 24 (10%) patients due to insufficient mononuclear cell counts. In the remaining 212 patients, results were indeterminate in 54 (25%). IGRAs were positive in 95 of 158 (60%) patients with interpretable results. The proportion of positive test results was similar across CD4+ count strata. IGRA sensitivity was 73% and specificity 54%. IGRA results did not meaningfully alter the probability of active tuberculosis in patients with negative sputum smears.

Conclusions

An ELISPOT-based IGRA detected a high prevalence of latent tuberculosis infection in a hospitalized population of tuberculosis suspects with advanced HIV/AIDS but had limited utility for diagnosis of active tuberculosis in a high prevalence setting. Further research is needed to identify stronger and more specific immune responses in patients with active tuberculosis.

Impact of peripheral lymphocyte count on the sensitivity of 2 IFN-gamma release assays, QFT-G and ELISPOT, in patients with pulmonary tuberculosis

OBJECTIVE

This study evaluated the effect of peripheral lymphocyte count on 2 interferon-gamma release assays [QuantiFERON TB-Gold (QFT-G) and enzyme-linked immunospot (ELISPOT)] and their sensitivity in patients with pulmonary tuberculosis, including HIV-negative immunocompromised patients.

PATIENTS AND METHODS

Two hundred thirty patients with microbiologically confirmed active pulmonary tuberculosis were subjected to the tests. Lymphocyte counts were analyzed simultaneously.

RESULTS

Overall sensitivity was 74% (159/215; 95% CI, 68-80%) for QFT-G and 92% (198/215; 89-96%) for ELISPOT (p<0.0001). In patients with peripheral lymphocyte counts of > or =1000/microL, sensitivity was high for both QFT-G (88%, 111/126; 82-94%) and ELISPOT (97%, 122/126; 94-100%). However, the sensitivity decreased significantly with decreasing peripheral lymphocyte count for both QFT-G (test for trend p<0.0001) and ELISPOT (test for trend p=0.007). When lymphocyte counts were <500/microL, the sensitivity was 81% (25/31; 66-96%) for ELISPOT, but only 39% (12/31; 21-57%) for QFT-G.

CONCLUSION

Both QFT-G and ELISPOT are sensitive methods for detecting active pulmonary tuberculosis, but their sensitivity partly depends on peripheral lymphocyte counts. At low lymphocyte count conditions, ELISPOT is superior to QFT-G for detecting tuberculosis, irrespective of age, gender, and nutrition.

A 100 year update on diagnosis of tuberculosis infection

BACKGROUND

Diagnosis and treatment of latent tuberculosis infection (LTBI) is a cornerstone of tuberculosis (TB) control in the developed world. In the last century, the tuberculin skin test (TST) was the only means of diagnosing LTBI. ELISpot and whole-blood ELISA, collectively known as interferon-gamma release assays (IGRAs), are promising new tools.

AREAS OF AGREEMENT

IGRAs are more specific than TST for diagnosis of LTBI as they are not confounded by previous bacille Calmette-Guerin (BCG) vaccination. Assessing IGRA sensitivity in the absence of a gold standard for LTBI is challenging. Studies have therefore used surrogate markers such as active TB and correlation with degree of TB exposure in contact investigations. These studies suggest that sensitivity of ELISpot is higher than TST while whole-blood ELISA has similar sensitivity to TST. Recent longitudinal studies demonstrating the prognostic power of these tests for development of active TB provide definitive evidence that positive IGRA results reflect infection with dormant yet viable bacilli.

AREAS OF CONTROVERSY

Is the prognostic power of IGRAs greater than the TST? What are the false-negative rates in immunocompromised individuals with LTBI at high risk of progressing to active TB?

GROWING POINTS

IGRAs have been incorporated into national guidelines, although their optimal deployment in diagnostic algorithms is evolving. The health economic benefits of utilizing IGRAs are increasingly recognized, partly because their high specificity avoids unnecessary chemoprophylaxis in BCG-vaccinated persons with false-positive TST results.

AREAS TIMELY FOR DEVELOPING RESEARCH

Current IGRAs are being improved and next-generation tests, with improved sensitivity, could enable the reliable exclusion of LTBI in immunocompromised individuals.

Evidence-based comparison of commercial interferon-gamma release assays for detecting active TB: a metaanalysis

Test accuracy of interferon-gamma release assays (IGRAs) for diagnosing TB differs when using older or precommercial tools and inconsistent diagnostic criteria. This metaanalysis critically appraises studies investigating sensitivity and specificity of the commercial T-Spot.TB and the QuantiFERON-TB Gold In-Tube Assay (QFT-IT) among definitely confirmed TB cases. We searched Medline, EMBASE, and Cochrane bibliographies of relevant articles. Sensitivities, specificities, and indeterminate rates were pooled using a fixed effect model. Sensitivity of the tuberculin skin test (TST) was evaluated in the context of IGRA studies. In addition, the rates of indeterminates of both IGRAs were assessed. The pooled sensitivity of TST was 70% (95% CI, 0.67-0.72) compared with 81% (95% CI, 0.78-0.83) for the QFT-IT and 88% (95% CI, 0.85-0.90) for the T-Spot.TB. Sensitivity increased to 84% (95%CI, 0.81-0.87) and 89% (95% CI, 0.86-0.91) for the QFT-IT and T-Spot.TB, respectively, when restricted to performance in developed countries. In contrast, specificity of the QFT-IT was 99% (95% CI, 0.98-1.00) vs 86% for the T-Spot.TB (95% CI, 0.81-0.90). The pooled rate of indeterminate results was low, 2.1% (95% CI, 0.02-0.023) for the QFT-IT and 3.8% (95% CI, 0.035-0.042) for the T-Spot.TB, increasing to 4.4% (95% CI, 0.039-0.05) and 6.1% (95% CI, 0.052-0.071), respectively, among immunosuppressed hosts. The newest commercial IGRAs are superior, in comparison with the TST, for detecting confirmed active TB disease, especially when performed in developed countries.

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.

[ELISPOT response to Mycobacterium tuberculosis antigens for diagnosing and monitoring tuberculosis patient therapy]

BACKGROUND

Using the ELISPOT assay, a promising immunological tool for detecting Mycobacterium tuberculosis (MTB) antigen-specific response, we monitored the clinical course of patients with tuberculosis (TB).

METHODS

Blood samples were obtained from 35 patients with TB and healthy controls, numbering 52 age-matched control subjects and 43 university students. Nine of those with TB were examined twice before and after anti-tuberculosis treatment. The frequency of IFN-gamma secreting cells was determined using the ELISPOT assay in peripheral mononuclear cells (PBMC) stimulated with purified protein derivative (PPD), early secretory antigenic target 6 (ESAT-6), and culture filtrate protein 10 (CFP-10).

RESULTS

The frequency of PPD secreting cells correlated significantly with tuberculin skin test (TST) magnitude in BCG-vaccinated individuals. Significant responses to either ESAT-6 or CFP-10 were found in 94% of those with TB. The frequency of IFN-gamma secreting cells decreased when negative sputum tests were confirmed by successful tuberculosis treatment.

CONCLUSIONS

The ELISPOT assay detecting MTB-specific immune response is promising both in diagnosing MTB and monitoring responsiveness to tuberculosis therapy.

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.

New diagnostic methods for tuberculosis

PURPOSE OF REVIEW

During the last decade, laboratory tests for the detection of Mycobacterium tuberculosis (Mtb) have improved dramatically. Improvements in the ability to detect latent infection with Mtb, disease associated with Mtb, and strains resistant to commonly used antibiotics are reviewed.

RECENT FINDINGS

Advances in the detection of Mtb include light-emitting diode fluorescence microscopy, nucleic acid amplification of Mtb and drug-resistant strains, and more rapid liquid culture with adjunct drug susceptibility testing. In the detection of latent tuberculosis infection, interferon [gamma] release assays offer improved accuracy over the tuberculin skin test.

SUMMARY

The past 10 years have seen the most rapid growth in new diagnostics for Mtb in over a century. Although these tests offer improvements in the ability to detect Mtb, drug-resistant isolates, and those with latent tuberculosis infection, these improvements are counter-balanced by the need to deploy these tests in areas where Mtb burden is highest.

Lymphocyte proliferation to mycobacterial antigens is detectable across a spectrum of HIV-associated tuberculosis

Background

Identifying novel TB diagnostics is a major public health priority. We explored the diagnostic characteristics of antimycobacterial lymphocyte proliferation assays (LPA) in HIV-infected subjects with latent or active TB.

Methods

HIV-infected subjects with bacille Calmette Guérin (BCG) scars and CD4 counts ≥ 200 cells/mm³ entering a TB booster vaccine trial in Tanzania had baseline in vivo and in vitro immune tests performed: tuberculin skin tests (TST), LPA and five day assays of interferon gamma (IFN-γ) release. Assay antigens were early secreted antigenic target 6 (ESAT-6), antigen 85 (Ag85), and Mycobacterium tuberculosis whole cell lysate (WCL). Subjects were screened for active TB at enrollment by history, exam, sputum smear and culture. We compared antimycobacterial immune responses between subjects with and without latent or active TB at enrollment.

Results

Among 1885 subjects screened, 635 had latent TB and 13 had active TB. Subjects with latent TB were more likely than subjects without TB to have LPA responses to ESAT-6 (13.2% vs. 5.5%, P < 0.0001), Ag85 (18.7% vs. 3.1%, P < 0.0001), and WCL (45.7% vs. 17.1%, P < 0.0001). Subjects with active TB also were more likely than those without active TB to have detectable LPA responses to ESAT-6 (38.5% vs. 8.1%, P = 0.0001), Ag85 (46.2% vs. 8.5%, P < 0.0001), and WCL (61.5% vs. 27.0%, P = 0.0053). In subjects with a positive TST, LPA responses to ESAT-6, Ag85 and WCL were more common during active TB (p < 0.0001 for all tests). In diagnosing active TB, in vivo and in vitro tests of mycobacterial immune responses had sensitivity and specificity as follows: TST 84.6% and 65.5%, ESAT-6 LPA 38.5% and 92.0%, Ag85 LPA 46.2% and 91.5%, and WCL LPA 61.5% and 73.0%. Detectable LPA responses were more common in patients with higher CD4 counts, and higher HIV viral loads.

Conclusion

Lymphoproliferative responses to mycobacteria are detectable during HIV-associated active TB, and are less sensitive but more specific than TST.

Trial registration

ClinicalTrials.gov Identifier NCT00052195.

Paediatric tuberculosis

Tuberculosis continues to cause an unacceptably high toll of disease and death among children worldwide, particularly in the wake of the HIV epidemic. Increased international travel and immigration have led to a rise in childhood tuberculosis rates even in traditionally low burden, industrialised settings, and threaten to promote the emergence and spread of multidrug-resistant strains. Whereas intense scientific and clinical research efforts into novel diagnostic, therapeutic, and preventive interventions have focused on tuberculosis in adults, childhood tuberculosis has been relatively neglected. However, children are particularly vulnerable to severe disease and death following infection, and those with latent infection become the reservoir for future transmission following disease reactivation in adulthood, fuelling future epidemics. Further research into the epidemiology, immune mechanisms, diagnosis, treatment, and prevention of childhood tuberculosis is urgently needed. Advances in our understanding of tuberculosis in children would provide insights and opportunities to enhance efforts to control this disease.

Diagnosing latent tuberculosis infection in the HIV era

Tuberculin skin testing (TST) and Interferon-gamma (IFNγ)release assays (IGRAs) are presently the only available assays for the detection of Mycobacterium tuberculosis infected individuals. IGRAs might progressively replace TST, as numerous published reports establish their higher specificity and similar sensitivity when tested in BCG vaccinated, immunocompetent individuals or in populations who may have been in contact with atypical mycobacteria. However, few published reports have commented on their role in TB diagnosis in immunocompromised individuals (HIV, immunosuppressive therapy, cancer…). It is the purpose of this report to review IGRAs published studies in HIV individuals in endemic and non endemic area for tuberculosis (TB). IGRAs were tested in the presence or absence of active TB but correlated to duration of exposure. In newly diagnosed active TB, IGRAs demonstrated a similar sensitivity to TST. In TB non infected individuals, TST and IGRAs also gave similar values when categorization of individuals was correlated to the risk of infection. A higher number of positive IGRAs was observed in individuals from TB endemic areas, in similar proportions to immunocompetent individuals. Comparison between the two IGRAs: QuantiFERON-TB Gold^® (QF-TB, Cellestis, Australia) and T-SPOT-TB^® (Oxford Immunotec, UK), and against TST, in the same HIV population demonstrates a higher sensitivity of T-SPOT-TB and TST than QF-TB. Indeterminate results, which correspond to the absence of a positive T-cell IFNγ response towards phytohemaglutinin (PHA), is a key point when comparing both IGRAs. This PHA control is indicative of the level of immunosuppression observed in the tested individual. QF-TB seems to present, in HIV populations, more indeterminate results than T-SPOT-TB. The calibration and/or concentration of PBMC on nitrocellulose membrane for the T-SPOT-TB, as compared to a whole blood assay, might explain this difference, with less indeterminate results with the T-SPOT-TB assay. Neither assay is able to differentiate active TB from latent TB infection (LTBI). Several laboratories have tried new antigenic epitopes to solve this issue. It is of importance that these studies need to be repeated on a larger scale by others to validate their results. Two blood assays might add information characterising the evolution from LTBI to active TB: either by losing protective immunity, as demonstrated by the whole blood killing assay, or by evaluating the kinetics of the antibodies synthesized against M. tuberculosis specific antigens. In conclusion, longitudinal studies are still needed to validate IGRAs and other assays and to define their respective predictive values.