Tuberculin skin testing or interferon-γ release assays (IGRAs) are used for M. tuberculosis (TB) contact tracing. Whereas IGRAs allow discriminating TB-specific immunity from BCG vaccination responses, they cannot distinguish active (A-TB) from latent (L-TB) or successfully treated (T-TB) infection. We have previously shown that IFN-γ–IL-2 cytokine profiling of PPD specific T-cells may more specifically diagnose active TB. The aim of this study was to combine cytokine profiling with phenotypical analysis of CTLA-4 and CD27 to improve diagnostic accuracy. We performed 6h stimulation with PPD, ESAT-6 and CFP-10 antigens with subsequent flow cytometric analysis of whole blood samples from a total of 58 confirmed A-TB patients, 34 patients with T-TB, 127 individuals with L-TB and 386 with immunity consistent with BCG vaccination or NTM infection. A loss of CD27 on PPD specific T-cells discriminated best between A-TB and T-TB (100% specificity, 83.3% sensitivity AUC=0.93%). Likewise, increased expression of CTLA-4 discriminated with 88.9% specificity and 72.5% sensitivity (AUC=0.84). Combined analysis of CD27 with CTLA-4 but not with IFNγ–IL-2 further increased diagnostic power. Among 25 individuals with L-TB identified in the setting of contact tracing, 48% expressed one or more markers similarly to patients with A-TB, whereas 52% did not show any alterations in T-cell immunity. In conclusion, combined functional and phenotypical analysis of TB specific T-cells might improve immune based diagnosis of active TB, and to-be more specifically predict the risk of progression towards A-TB in the setting of contact tracing.
Dirks et al. (Mon,) studied this question.