Evaluation of CD8⁺ response in QuantiFERON-TB Gold Plus as a marker of recent infection

Diagnosis and treatment of latent tuberculosis (TB) infection (LTBI) is essential for the elimination of TB. Preventive therapy could be limited to those with recent TB contact. QuantiFERON-TB Gold Plus (QFT-Plus), a new Interferon-γ release assay, includes a new antigen tube (TB2), which elicits CD4⁺ and CD8⁺ T-cell responses.

The aim of the study was to evaluate CD8⁺ T-cell response as a marker of recent TB infection.

We retrospectively studied 1165 patients who were screened for LTBI. Patients were divided according to history of recent exposure to TB (contact with a confirmed index case in the previous year). CD8⁺ T-cell activity was measured as the difference between QFT-Plus tubes (TB2-TB1) using two cut-offs (>0.35 IU/mL and >0.60 IU/mL).

CD8⁺ T-cell activity was significantly higher in the exposed group for both cut-offs (96 - 13% vs 36 - 5% patients - OR 1.68, 95% CI 1.13-2.52 for >0.35 IU/mL and 77 vs 28 patients - OR 1.72 95% CI 1.10-2.70 for >0.60 IU/mL). CD8⁺ T-cell activity also showed an association with positive sputum smear of the index case and higher exposure time.

CD8⁺ T-cell activity as measured with TB2-TB1 shows a significant association with recent exposure to TB, especially in patients with higher exposure and may prove to be a useful tool in identifying patients with recent LTBI.