Latent Tuberculosis Infection Treatment and T-Cell Responses to Mycobacterium tuberculosis–specific Antigens

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Abstract
Rationale: There is currently no available test for monitoring the effect of treatment of latent tuberculosis infection (LTBI) to indicate cure or predict risk of subsequent progression to disease. Objective: We used the T-SPOT.TB assay, which measures T-cell interferon-γ responses to the Mycobacterium tuberculosis–specific peptides early secretory antigenic target 6-kD protein (ESAT-6) and culture filtrate protein 10 (CFP-10), to determine the effect of LTBI treatment on these responses. Methods: A total of 226 tuberculosis contacts with positive T-SPOT.TB results underwent repeat testing on LTBI treatment completion. The majority (96%) received 6 months of isoniazid. The pre- and post-treatment T-SPOT.TB results were analyzed according to the combined and separate responses to ESAT-6 and CFP-10 antigens. Results: The T-SPOT.TB reverted to negative in 85 (37.6%) contacts at treatment completion. Treatment had a significant effect on the response to CFP-10 (p < 0.001; reversion rate, 48.6%), but not on the response to ESAT-6 (p = 0.081; reversion rate, 21.6%). The median number of spot-forming cells (SFCs)/2.5 × 105 peripheral blood mononuclear cells (PBMCs) pre- and post-treatment was 6 versus 4.5 for ESAT-6 (p = 0.116) and 11 versus 4 for CFP-10 (p < 0.001). There was a significant difference between the change (fall) in the pre- and post-treatment responses to CFP-10 (6 SFCs/2.5 × 105 PBMCs) and ESAT-6 (0 SFCs/2.5 × 105 PBMCs; p < 0.001). Significantly different age-related T-cell responses to the two antigens were found. Conclusion: LTBI treatment had a differential effect on T-cell responses to ESAT-6 and CFP-10 as measured by the T-SPOT.TB. The quantitative response to CFP-10 may be a useful LTBI treatment–monitoring tool.

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