CD27 expression as a new tool to distinguish active tuberculosis from latent infection

Abstract

Background: There is still not reliable tests to distinguish active tuberculosis (TB) from latent TB infection (LTBI) by an immune diagnostic test. QuantiFERON TB Gold (QFT) is used for LTBI diagnosis; however this test does not distinguish between LTBI and active TB. Recently, cytometric studies from high TB endemic countries showed an association of low CD27 level on circulating Mtb-specific CD4 T-cells with active TB. No studies using a similar approach have been conducted in Europe, nor studies have been performed using whole blood. Aim: To validate in a low TB endemic country as Italy, if the modulation of CD27 in whole blood is a tool to discriminate, among QFT-IT-positive patients, active TB from LTBI. Methods: 107 HIV-uninfected QFT-IT-positive subjects were enrolled: 21 active TB; 20 cured TB; 66 LTBI. Whole blood was stimulated with RD1 proteins. Interferon (IFN)γ response was evaluated by cytometry. The data were presented as RATIO of the Median Fluorescence Intensity (MFI) of CD27 + CD4 + T-cells over the MFI of CD27 + IFNγ + CD4 + T-cells. Results: Active TB patients showed higher RATIO to RD1 antigens compared to LTBI (p=0.0005). We performed a ROC analysis to evaluate the potential of CD27 MFI RATIO for TB diagnostics comparing TB and LTBI. We found a significant area under the curve (AUC) (AUC 0.84; 95% CI, 0.68-0.99, p=0.0004) and a cut-off of 3.19 to predict active TB with 61.54% sensitivity (95% CI, 31.58% to 86.14%) and 96.67% specificity (95% CI, 82.78% to 99.92%). Conclusions: This study proposes a cytometric tool based on the modulation of CD27 + CD4 + IFNγ + T-cells in whole blood that may allow to distinguish TB disease from LTBI in a low TB endemic country.