Optimisation and application of a T-cell antigen-specific activation assay as diagnostic and treatment-monitoring tool for tuberculosis

Background Mycobacteria-specific T-cell activation is a robust biomarker of recent Mycobacterium tuberculosis infection, disease progression and tuberculosis (TB) disease. We evaluated this promising biomarker, termed TB-TASA, as a treatment monitoring tool in the context of a treatment-shortening study. Methods Using a panel of mycobacterial antigens, we observed higher TB-TASA scores in TB patients compared to interferon-γ (IFN-γ) release assay positive (IGRA + ) controls, regardless of mycobacterial antigen specificity, consistent with previous studies. We derived a TB-TASA positivity threshold of 10% HLA-DR + mycobacteria-specific T-cells using a computational analysis pipeline developed with the OpenCyto R package. This threshold was robust across three previously published case-control studies that used different sample types ( i.e. , whole blood or peripheral blood mononuclear cells), varying duration of antigen stimulation and different flow cytometry antibody panels, all of which achieved sensitivity and specificity >90% and >70%, respectively. Results In a prospective randomised clinical trial assessing treatment shortening in TB patients with less severe disease, higher TB-TASA scores were observed at treatment completion in patients who relapsed or failed treatment during follow-up compared to those successfully treated with a receiver operating characteristic area under the curve (ROC AUC) of 0.89 (95% CI 0.69-1), supporting TB-TASA as a treatment monitoring tool. Discussion We demonstrated that TB-TASA could also be reliably measured in capillary blood collected via fingerprick from IGRA + controls and TB patients, achieving an ROC AUC of 0.96 (95% CI 0.9-1) and sensitivity and specificity of 95% and 69%, respectively. Together, these results support the continued development of TB-TASA as a potential tool for diagnosing TB and monitoring treatment responses.