Mycobacterium tuberculosis specific CD8(+) T cells rapidly decline with antituberculosis treatment

Abstract

Rationale: Biomarkers associated with response to therapy in tuberculosis could have broad clinical utility. We postulated that the frequency of Mycobacterium tuberculosis (Mtb) specific CD8(+) T cells, by virtue of detecting intracellular infection, could be a surrogate marker of response to therapy and would decrease during effective antituberculosis treatment.

Objectives: We sought to determine the relationship of Mtb specific CD4(+) T cells and CD8(+) T cells with duration of antituberculosis treatment.

Materials and methods: We performed a prospective cohort study, enrolling between June 2008 and August 2010, of HIV-uninfected Ugandan adults (n = 50) with acid-fast bacillus smear-positive, culture confirmed pulmonary TB at the onset of antituberculosis treatment and the Mtb specific CD4(+) and CD8(+) T cell responses to ESAT-6 and CFP-10 were measured by IFN-γ ELISPOT at enrollment, week 8 and 24.

Results: There was a significant difference in the Mtb specific CD8(+) T response, but not the CD4(+) T cell response, over 24 weeks of antituberculosis treatment (p<0.0001), with an early difference observed at 8 weeks of therapy (p = 0.023). At 24 weeks, the estimated Mtb specific CD8(+) T cell response decreased by 58%. In contrast, there was no significant difference in the Mtb specific CD4(+) T cell during the treatment. The Mtb specific CD4(+) T cell response, but not the CD8(+) response, was negatively impacted by the body mass index.

Conclusions: Our data provide evidence that the Mtb specific CD8(+) T cell response declines with antituberculosis treatment and could be a surrogate marker of response to therapy. Additional research is needed to determine if the Mtb specific CD8(+) T cell response can detect early treatment failure, relapse, or to predict disease progression.

Figure 1. Magnitude of Mycobacterium tuberculosis (Mtb) specific T cell responses in smear and culture positive, HIV negative, pulmonary TB patients over time during antituberculosis therapy.

The magnitude of the Mtb specific CD4⁺ T cell response (A) and Mtb specific CD8⁺ T cell response (B) is shown by IFN-γ ELISPOT in response to ESAT-6 and CFP-10 and reported in spot forming units per 250,000 T cells. Evaluable samples (n) analyzed per time point were 49, 48 and 42 for baseline, week 8 and week 24 respectively. A negative binomial mixed model was used to assess the overall change during 24 weeks. Raw data, surrounded by the box demonstrates the distribution of 25–75% of the data, with the whiskers representing the non-outlier data, and the horizontal line depicting the median. Raw data is shown with a triangle, outliers with a circle, and extremes with a star.

Figure 2. Individual profiles of the absolute change in the Mtb specific T cell responses (spot forming units; SFU) from baseline to week 8 and baseline to week 24 in smear and culture positive, HIV negative, pulmonary TB patients during antituberculosis therapy.

The waterfall plots show the absolute change in magnitude (SFU) between the baseline time point to week 8 for the Mtb specific CD4⁺ (A) and CD8⁺ (C) T cell response. The absolute change in magnitude for the baseline time point to week 24 is shown for the Mtb specific CD4⁺ (B) and CD8⁺ (D) T cell response. Black bars represent SFU decreasing from baseline to the respective time point, whereas white bars represent increasing SFU from baseline to the respective time point.

Figure 3. Mycobacterium tuberculosis (Mtb) specific T cell responses at baseline and BMI.

The magnitude of the Mtb specific T cell response by IFN-γ ELISPOT to ESAT-6 and CFP-10, and reported in spot forming units/250,000 T cells, is shown at baseline for the Mtb specific CD4⁺ response (A) and the Mtb specific CD8⁺ response (B) for BMI≤17 (n = 14) and >17 (n = 34). A negative binomial model was used to assess differences in the Mtb specific T cell responses and BMI≤17 and >17. Raw data, shown as a triangle, surrounded by the box demonstrates the distribution of 25–75% of the data, with the whiskers representing the non-outlier data, and the horizontal line depicting the median.

Figure 4. Mycobacterium tuberculosis (Mtb) specific T cell responses during antituberculosis treatment in subjects with baseline malnutrition (BMI≤17).

The subgroup of subjects, who started therapy with a BMI≤17 with baseline and week 24 analyzable ELISPOT data (n = 11) are shown. The magnitude of the Mtb specific T cell response is shown by IFN-γ ELISPOT to ESAT-6 and CFP-10 and reported in spot forming units per 250,000 T cells. Connected lines at baseline and week 24 reflect a individual subject's profile for the Mtb specific CD4⁺ T cell response (A) and the Mtb specific CD8⁺ T cell response (B).

Figure 5. Quantitative cultures and treatment duration.

Quantitative cultures from subjects with smear positive pulmonary TB as shown by the log of colony forming units (CFU) enumerated on 7H10 media at week 0 (n = 35) and week 4 (n = 14). Raw data, shown as a triangle, surrounded by the box demonstrates the distribution of 25–75% of the data, with the whiskers representing the non-outlier data, and the horizontal line depicting the median. The dotted line connects the median points. Wilcoxon signed rank test was performed comparing subjects with week 0 and week 4 (n = 12).