Characterization of the CD4 and CD8 T-cell response in the QuantiFERON-TB Gold Plus kit

Elisa Petruccioli; Teresa Chiacchio; Ilaria Pepponi; Valentina Vanini; Rocco Urso; Gilda Cuzzi; Lucia Barcellini; Fabrizio Palmieri; Daniela M Cirillo; Giuseppe Ippolito; Delia Goletti

doi:10.1016/j.ijmyco.2016.09.063

Characterization of the CD4 and CD8 T-cell response in the QuantiFERON-TB Gold Plus kit

Int J Mycobacteriol. 2016 Dec:5 Suppl 1:S25-S26. doi: 10.1016/j.ijmyco.2016.09.063. Epub 2016 Nov 11.

Affiliations

¹ Translational Research Unit, Department of Epidemiology and Preclinical Research, National Institute for Infectious Diseases L Spallanzani (INMI), Rome, Italy.
² Emerging Bacterial Pathogens Unit, Division of Immunology and Infectious Diseases IRCCS, San Raffaele Scientific Institute, Milan, Italy.
³ Scientific Direction, National Institute for Infectious Diseases L Spallanzani (INMI), Rome, Italy.
⁴ Translational Research Unit, Department of Epidemiology and Preclinical Research, National Institute for Infectious Diseases L Spallanzani (INMI), Rome, Italy. Electronic address: delia.goletti@inmi.it.

PMID: 28043588
DOI: 10.1016/j.ijmyco.2016.09.063

Abstract

Objective/background: QuantiFERON-TB Gold In-Tube (QFT-GIT, Qiagen, Hilden, Germany) is an interferon-γ (IFN-γ) release assay designed to detect latent tuberculosis infection (LTBI). Although QFT-GIT has several advantages (mainly that it is not affected by the Bacille Calmette-Guérin vaccination), it has a poor sensitivity in immune-compromised individuals as it involves an immune response-based detection. Recently, QuantiFERON-TB Gold Plus (QFT-Plus) assay has been proposed as a new generation of QFT-GIT. QFT-Plus includes two tubes, TB1 and TB2 with Mycobacterium tuberculosis antigens to elicit a specific immune response. TB1 contains peptides derived from the antigens 6kDa early secretory antigenic target (ESAT-6) and 10kDa culture filtrate protein (CFP-10) (TB-7.7, present in QFT-GIT, has been removed), and it is designed to induce a specific CD4 T-cell response. TB2 contains newly designed peptides stimulating IFN-γ production by both CD4 and CD8 T cells. The additional peptides for eliciting CD8 T-cell responses have been included to increase the sensitivity of the test for LTBI detection. The aim of the study was to evaluate specific CD4 and CD8 T-cell responses to the M. tuberculosis antigens contained within the QFT-Plus test by flow cytometry in individuals with active TB and LTBI.

Methods: We enrolled 23 individuals with active TB and 30 individuals with LTBI. QFT-Plus assay and intracellular staining were performed. One million of peripheral blood mononuclear cells in 1ml of complete medium (RPMI 1640) were dispensed in QFT-Plus tubes. Following 16-24h stimulation, antigen-specific T cells were characterized by flow cytometry evaluating CD4, CD8, CD3 markers, and IFN-γ production. For statistical analysis, nonparametric tests were performed.

Results: We found that CD4 T-cell responses were induced by both TB1 and TB2. Differently, the CD8 T-cell response was mainly induced by TB2 and was significantly higher than that induced by TB1 (p=0.01). The frequency of Mtb specific T-cells observed in individuals with active TB was significantly higher than in those with LTBI (p=0.04). Finally, TB2-specific CD8 T-cell responses in individuals with active TB were associated with high radiological severity of lung lesions and microbiological diagnosis (based on M. tuberculosis isolation in sputum culture).

Conclusion: This is the first characterization of CD4 and CD8 T-cell responses to QFT-Plus TB1 and TB2 tubes in individuals with active TB and LTBI enrolled in a low TB-endemic country such as Italy. We demonstrated that the increased sensitivity is a consequence of the ability of TB2 to induce a CD8 T-cell response which is mainly associated with active TB. This assay has the potential to be very useful in conditions of immune depression due to CD4 T-cell impairments.

Keywords: CD4; CD8; IGRA; QUANTIFERON PLUS; Tuberculosis.