Mycobacterium tuberculosis-Specific CFP-10/ESAT-6 CD4 and CD8 T-Cell Non-IFN-γ+ Responses Are Common in Young Kenyan Children Despite Low Reported Tuberculosis Exposure.

BACKGROUND

Reduced early-life interferon-γ (IFN-γ) production capacity may limit sensitivity of IFN-γ release assays to detect Mycobacterium tuberculosis (Mtb)-specific responses in young children. Measuring non-IFN-γ cytokine responses may improve detection.

METHODS

Mononuclear cells isolated from peripheral blood from children exposed to HIV but uninfected and children unexposed to HIV in Western Kenya were collected at 6 to 10 weeks, and 12 and 24 months of age. Cells were incubated overnight with Mtb-specific CFP-10/ESAT-6 peptides and Staphylococcus enterotoxin B (positive control). CD4 and CD8 T-cell expression of IFN-γ and IL-2 and TNF cytokines was measured by flow cytometry.

RESULTS

Among 213 children, 28.6% had CFP-10/ESAT-6-specific CD4 and/or CD8 responses through 24 months. No children with Mtb-specific responses had a reported tuberculosis exposure. Mtb-specific non-IFN-γ+ responses (IL-2+ and/or TNF+) were more common than IFN-γ+ responses (26.3% vs 10.3%, P < .001). Non-IFN-γ cytokines alone identified 18.3% of children, compared with 2.4% identified by IFN-γ+ responses alone (P < .001). Prevalence of Mtb-specific responses was similar regardless of HIV exposure (HIV exposed, 31.5%; HIV unexposed, 25.5%, P = .33). At 6 to 10 weeks, children were more likely to have non-IFN-γ+ than IFN-γ+ responses to the positive control (96.3% vs 77.8%, P = .004); by 24 months, all children mounted both IFN-γ+ and non-IFN-γ+ responses.

CONCLUSIONS

Mtb-specific CD4/CD8 responses were common among Kenyan children through 24 months, despite limited reported tuberculosis exposures. Non-IFN-γ+ cytokine expression identified substantially more children than IFN-γ+ alone, suggesting current IFN-γ release assays may miss early-life Mtb-specific responses.