Abstract
BACKGROUND: Reduced early life IFN-γ production capacity may limit sensitivity of IFN-γ release assays (IGRAs) to detect M. tuberculosis (Mtb)-specific responses in young children. Measurement of non-interferon-γ (IFN-γ) cytokine responses may improve detection of these responses in children. METHODS: PBMCs from HIV-exposed uninfected (cHEU) and HIV-unexposed (cHUU) children in Western Kenya collected between 6-10 weeks, and at 12 and 24 months of age were incubated overnight with Mtb-specific CFP-10/ESAT-6 peptides and staphylococcus enterotoxin B (SEB, positive control). CD4 and CD8 T cell expression of IFN-γ and non-IFN-γ (IL-2, TNF) cytokines was measured by flow cytometry. RESULTS: Among 213 children, 28.6% had CFP-10/ESAT-6 CD4 and/or CD8 responses up to 24 months of age. No children with a positive Mtb-specific response had a reported known TB exposure. More children exhibited Mtb-specific non-IFN-γ+ (IL-2+ and/or TNF+) responses than IFN-γ+ responses (26.3% vs. 10.3%, p<0.001), including 18.3% identified by non-IFN-γ+ responses alone (non-IFN-γ+ alone 18.3% vs. IFN-γ+ alone 2.4%, p <0.001). Proportion of children with Mtb-specific responses were similar regardless of HIV exposure (cHEU 31.5% vs. cHUU 25.5%, p=0.33). At 6-10 weeks of age, children were more likely to have non-IFN-γ+ vs. IFN-γ+ responses to SEB (positive control) (96.3% vs. 77.8%, p=0.004); however, by 24 months of age 100% of children had both IFN-γ+ and non-IFN-γ+ SEB responses. CONCLUSION: Mtb-specific CD4/CD8 responses were common among young Kenyan children up to 24 months of age, despite limited reported TB exposures. Non-IFN-γ+ T cell cytokine expression identified more children than IFN-γ+ who would be potentially missed by commercially available IGRAs.