Serial Testing of T-SPOT.TB Assays with Anti-Tuberculosis Therapy in Patients with Extrapulmonay Tuberculosis

ABSTRACT

BACKGROUND: Limited data are available for the clinical utility of serial interferon-gamma producing T-cell response after initiation of treatment in patients with extrapulmonary tuberculosis (TB). We studied the serial TB-specific antigen T-cell responses measured using the T-SPOT.TB assay during the course of therapy. MATERIALS AND METHODS: We prospectively enrolled adult patients who were newly diagnosed with active extrapulmonary TB over a 24-month period. All patients were given standard anti-TB treatment. Blood samples were obtained for T-SPOT.TB at diagnosis, as well as 1-, 3-, 6-, and 12-months after initiating anti-TB therapy. RESULTS: A total of 52 patients with extrapulmonary TB (38 confirmed and 14 probable TB) were included in the final analysis. All patients had clinical and radiologic improvement after treatment and cured. T-SPOT.TB was positive for 90% at diagnosis, 100% at 1-, 3-, and 6-months, and 93% at 12-months after initiation of anti-TB therapy. There was no significant difference in median T-cell response between early secreting antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10) at all time points. Median T-cell response steadily increased up to 6 months and then decreased. CONCLUSIONS: T-SPOT.TB assay remained positive after successful anti-TB treatment in most patients with extrapulmonary TB. Our data suggests that serial T-SPOT.TB has limited clinical utility as a surrogate marker of treatment response in patients with extrapulmonary TB.