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

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.

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.

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.

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.