Dried blood spot IP-10 as a biomarker of tuberculosis severity and treatment responses: results from a phase IIb trial of adjunctive acetylsalicylic acid and ibuprofen

Background: Host-directed therapies may improve tuberculosis (TB) outcomes by modulating immune responses and attenuating hyperinflammation, yet accessible biomarkers remain limited. We hypothesized that interferon-γ-inducible protein 10 (IP-10/CXCL10) measured in dried blood spot (DBS), a low-threshold and field-adapted sampling method, has potential as a biomarker for treatment response in pulmonary TB. Accordingly, we assessed IP-10 levels in patients receiving adjunctive acetylsalicylic acid (ASA) or ibuprofen (IBU) alongside TB standard therapy. Methods: IP-10 levels were quantified longitudinally in DBS from 120 pulmonary TB patients enrolled in the SMA-TB clinical trial (NCT04575519) at two sites in South Africa. Samples collected at baseline, week 2, week 8, and week 24 were analyzed by the enzyme-linked immunosorbent assay (ELISA). Associations with disease severity and treatment response were assessed, and the predictive value of IP-10 for microbiological, clinical, and radiological outcomes was evaluated. Results: IP-10 levels correlated with TB disease severity, with higher concentrations observed in patients with elevated clinical and radiological scores and positive sputum acid-fast-bacilli staining. This association was reflected in treatment response, as patients with good clinical outcomes exhibited an earlier decline in IP-10 (week 8, p=0.0005), whereas those with poor outcomes showed a delayed decline (week 24, p<0.0001). Overall, IP-10 levels decreased during treatment irrespective of intervention or HIV status, with no significant differences between treatment arms at week 24. Notably, IP-10 levels at week 2 predicted rapid sputum culture conversion in the IBU arm, as well as in HIV-negative patients in the ASA arm (AUC: ASA 0.79; IBU 0.76). Conclusion: IP-10 levels measured in DBS are associated with disease severity and treatment response and may serve as a biomarker for therapy monitoring and early prediction of microbiological outcomes in TB, irrespective of adjunctive host-directed therapies. These findings require validation in larger patient cohorts before the method can be implemented in clinical practice.