Feasibility of commercial interferon-gamma-based methods for the diagnosis of latent Mycobacterium tuberculosis infection in Finland, a country of low incidence and high bacille Calmette-Guérin vaccination coverage

Cytotoxic response persists in subjects treated for tuberculosis decades ago

BACKGROUND

Data exploring the potential use of effector molecules produced by cytotoxic T lymphocytes (CTLs) in the immunodiagnostics of tuberculosis (TB) are scarce. The present study focused a) to gain an insight into the discriminatory power of CTLs in patients with acute pulmonary or extra-pulmonary TB, or latent tuberculosis infection (LTBI); and b) to evaluate the influence of various anti-TB therapeutic schemes on the immunological profiles of residual CTLs.

METHODS

Immunological signatures of antigen-specific CTLs were explored in patients with active pulmonary and extra-pulmonary TB, LTBI and in those treated for TB decades ago by using ELISPOT, intracellular flow cytometry and extracellular CD107a detection.

RESULTS

No difference was seen between active TB, LTBI or any of those treated for TB in the ELISPOT analysis of antigen-specific Granzyme B (GrB), Perforin (Prf) and interferon-gamma (IFN-γ) producing lymphocytes, the FACS analysis of the intracellular expression of IFN-γ, or the surface expression of CD107a degranulation factor of both CD8+ and CD4+ antigen-specific T cell subsets. The effector memory (TEM) phenotype proved predominant in the surface marker profiling both in active TB and LTBI. The proportion of the CD107a degranulation factor proved higher in the central memory (TCM) than in the other cell subsets in all the study groups. Interestingly, functionally and phenotypically similar CTLs profiles were observed in active TB, LTBI and in all the three groups treated for TB.

CONCLUSION

The phenotypic and functional profiling of CTLs has a limited potential in the immunodiagnostics of active TB. Antigen-specific CTLs persist in patients treated for TB decades ago regardless of the efficacy of implemented and completed anti-TB therapy.

Immunosuppression Adversely Affects TST but Not IGRAs in Patients with Psoriasis or Inflammatory Musculoskeletal Diseases

The performance of the interferon gamma release assays (IGRAs) and tuberculin skin test (TST) was reviewed retrospectively in patients with psoriasis, inflammatory musculoskeletal diseases, or miscellaneous inflammatory conditions. The study was carried out over a 22-month period using 109 records of patients with psoriasis (n = 21), musculoskeletal disease (n = 74), or other inflammatory conditions (n = 14). Forty-four (48%) of 109 patients were on immunosuppressive therapy and 38/109 (35%) on systemic glucocorticoid therapy. The agreement between the IGRAs was substantial (κ = 0.71) whilst that between the IGRAs and TST was low (κ = 0.32). Logistic regression models revealed that IGRAs associated with risk factors for latent tuberculosis infection better than TST. TST was influenced by age, BCG vaccination, sex, and glucocorticoid therapy. We found that IGRAs performed equally well with low level of indeterminate results (1-2%). IGRAs were superior to TST because the latter was influenced by BCG-vaccination status and immunosuppressive therapy.

Consistency of Mycobacterium tuberculosis-specific interferon-gamma responses in HIV-1-infected women during pregnancy and postpartum

Background. We determined the consistency of positive interferon-gamma (IFN-γ) release assays (IGRAs) to detect latent TB infection (LTBI) over one-year postpartum in HIV-1-infected women. Methods. Women with positive IGRAs during pregnancy had four 3-monthly postpartum IGRAs. Postpartum change in magnitude of IFN-γ response was determined using linear mixed models. Results. Among 18 women with positive pregnancy IGRA, 15 (83%) had a subsequent positive IGRA; 9 (50%) were always positive, 3 (17%) were always negative, and 6 (33%) fluctuated between positive and negative IGRAs. Women with pregnancy IGRA IFN-γ>8 spot forming cells (SFCs)/well were more likely to have consistent postpartum IGRA response (odds ratio: 10.0; 95% confidence interval (CI): 0.9–117.0). Change in IFN-γ response over postpartum was 10.2 SFCs/well (95% CI: −1.5–21.8 SFCs/well). Conclusion. Pregnancy positive IGRAs were often maintained postpartum with increased consistency in women with higher baseline responses. There were modest increases in magnitude of IGRA responses postpartum.

Interferon-gamma releasing assay versus tuberculin skin testing for latent tuberculosis infection in targeted screening programs for high risk immigrants

BACKGROUND

Recent immigrants from developing countries (<2 years since immigration) are at very high risk of active TB disease due to reactivation of latent infections acquired in the country of origin. In industrialized low-incidence TB countries targeted testing programs for high risk groups could allow the detection of latently infected persons who would likely benefit from a course of preventive treatment. In this study we evaluated the tuberculin skin test (TST) and interferon-gamma enzyme-linked immunosorbent assay (QuantiFERON TB-gold in tube, QFT-IT) strategies for TB infection screening programs in recent immigrants from highly endemic countries.

PATIENTS AND METHODS

This is a prospective cross-sectional study. Paired tests performed in 1,130 immigrants attending an outpatient ward, between 2005 and 2007 for any health problem were evaluated by intention-to-treat (ITT) and per-protocol (PP) analysis for efficiency and efficacy of screening program.

RESULTS

Positive TST and QFT-IT were observed in 36.04 versus 29.82% (ITT) and in 45.27 versus 30.22% (PP) respectively. A higher drop-out rate was observed for TST (20.35 vs. 1.33%) (p < 0.0001). Second level assessment was accepted by half of the TST positive patients. Overall agreement rate between 887 paired tests was fair (k = 0.38). Higher k values were observed for higher TB prevalence rate in the country of origin (k = 0.43), for TST induration diameters >20 mM (k = 0.47), in subjects aged 40-50 years (k = 0.41) and in unvaccinated persons (k = 0.40). In a multiple logistic regression model continent of origin, class of TB prevalence in the country of origin and contacts with TB patients were found to be significantly associated with the probability of TST and QFT-IT positive result. Low education levels were associated only to an increased risk of TST positive results.

CONCLUSIONS

The drawback of the TST screening strategy in recent immigrants from highly endemic countries is due to low sensitivity/specificity of the test and to high drop-out rate with an overall significant lowering in strategy efficacy/efficiency. The higher QFT-IT specificity prevents unnecessary overload of the health care system and, although more expensive, might represent a cost-effective alternative to TST in targeted screening programs directed to high risk populations.

Assessment of Imprecision in gamma interferon release assays for the detection of exposure to Mycobacterium tuberculosis

New gamma interferon (IFN-gamma) release assays (IGRAs) to detect an exposure to Mycobacterium tuberculosis have recently been launched. The majority of the studies in temperate-climate countries agree that these methods have superior specificity and equal or even superior sensitivity over tuberculin skin tests (TSTs) in the diagnosis of latent tuberculosis (TB) infection (LTBI). However, reproducibility data of IGRAs are virtually missing. We assessed within-run, between-run, and total imprecision of two commercial IGRAs by testing samples from subjects with a stable state of TB infection or treated pulmonary TB, a sample from a healthy volunteer, and internal quality control samples. We calculated coefficients of variance (CV%s) to describe assays variability and compared the obtained results to the reported CV%s for other commercial immunodiagnostic methods. We illustrate an example of assay variability near the cutoff zone to demonstrate the necessity of a gray zone. Due to the strict adherence to the standard operation procedures (SOP) adopted in our laboratory, the total imprecision of enzyme-linked immunospot (ELISPOT)- and enzyme immunoassay (EIA)-based IGRAs was at a maximum CV% of 37.8% for the samples with moderate and high reactivities. Imprecision of testing samples with very low reactivity levels or nonreactive samples may, however, exceed 100%. In conclusion, despite multiple steps of the method performance, the analytical imprecision of IGRAs, which in our study design included also between-lot variability and had a component of normal biological variation, was well in accordance with the reported imprecisions of other manual immunodiagnostic tests. The recognition of the variability around the cutoff point advocates the use of a gray zone to avoid ambiguous result interpretations.

T-cell-based diagnosis of tuberculosis infection in children in Lithuania: a country of high incidence despite a high coverage with bacille Calmette-Guerin vaccination

Background

Lithuania is a country with a high incidence of tuberculosis (TB), despite a high coverage with bacille Calmette-Guerin (BCG) vaccination. Until now the only method used to detect latent TB infection was the tuberculin skin test (TST). However, TST may have a cross reactivity to the BCG vaccine and to environmental mycobacteria. The aim of this study was to conduct assessments of the diagnostic accuracy of the T-cell based test (T SPOT TB) for TB in children who had previously been BCG vaccinated and compare these with the results of the TST.

Methods

Between January 2005 and February 2007, children with bacteriologically confirmed TB, children having contacts with a case of infectious pulmonary TB and children without any known risk for TB were tested with both the TST and T SPOT TB.

Results

The TST and T SPOT TB tests were positive for all patients in the „culture-confirmed TB“ group. Whereas, in the „high risk for TB“ group, the TST was positive for 60%, but the T SPOT TB test, only for 17.8%. Meanwhile the results for the „low risk for TB“ group were 65.4% and 9.6%, respectively. A correlation between the TST and T SPOT TB was obtained in the "culture-confirmed TB" group where the TST ≥15 mm (r = 0.35, p < 0.001).

Conclusion

The T-cell based method is more objective than the TST for identifying latent TB infection in children who had been previously BCG vaccinated. This method could be useful in countries like Lithuania where there is a high incidence of TB despite a high coverage with BCG vaccination. It may also help to avoid unnecessary chemoprophylaxis when TST reactions are false-positive.

IGRA tests perform similarly to TST but cause no adverse reactions: pediatric experience in Finland

Background

Two commercial interferon gamma release assays (IGRAs) (QuantiFERON^®-TB Gold in Tube and T SPOT^®-TB) to detect a contact with M. tuberculosis have recently become available. The majority of studies agree that the sensitivity and specificity of these methods are superior to the Tuberculin Skin Tests (TSTs) in detecting an exposure to bacteria in latently infected individuals and in clinical tuberculosis. However, the data in children remains limited.

Findings

Consecutively collected samples from children (n = 99) representing age range from zero to 18 years were analyzed in a retrospective non-blinded study. The two IGRAs were modified and adapted to the needs of Finland, a country of a low tuberculosis incidence. For 27 children, both tests were performed simultaneously and compared with the TST and clinician's diagnosis. The sensitivity, specificity, and accuracy of both IGRAs was determined. QuantiFERON TB Gold and T SPOT-TB performed (respectively) as follows: sensitivities 0.92 (95% confidence interval, CI, 0.67–0.99) and 0.85 (0.64–0.95); specificities 0.91 (0.77–0.97) and 1.00 (0.93–1.00); accuracies 0.91 (0.80–0.97) and 0.96 (0.88–0.99). This compares favorably to the TST whose known figures are 0.90, 0.95, and 0.95, respectively. The agreement between the IGRAs was high, k = 0.89. Finally, both methods agreed well with the TST, k = 0.86 for TST/QuantiFERON-TB Gold and k = 0.76 for TST/T SPOT-TB.

Conclusion

The sensitivity and specificity of IGRA methods compares well with the TST without the inconveniences and complications associated with TST, including exaggerated delayed type hypersensitivity reactions. These properties place them as acceptable substitutes for TST.