A High Throughput Whole Blood Assay for Analysis of Multiple Antigen-Specific T Cell Responses in Human <i>Mycobacterium tuberculosis</i> Infection

Antigen-specific CD4 and CD8 T cells are important components of the immune response to Mycobacterium tuberculosis , yet little information is currently known regarding how the breadth, specificity, phenotype, and function of M. tuberculosis -specific T cells correlate with M. tuberculosis infection outcome in humans. To facilitate evaluation of human M. tuberculosis -specific T cell responses targeting multiple different Ags, we sought to develop a high throughput and reproducible T cell response spectrum assay requiring low blood sample volumes. We describe here the optimization and standardization of a microtiter plate-based, diluted whole blood stimulation assay utilizing overlapping peptide pools corresponding to a functionally diverse panel of 60 M. tuberculosis Ags. Using IFN-γ production as a readout of Ag specificity, the assay can be conducted using 50 μl of blood per test condition and can be expanded to accommodate additional Ags. We evaluated the intra- and interassay variability, and implemented testing of the assay in diverse cohorts of M. tuberculosis -unexposed healthy adults, foreign-born adults with latent M. tuberculosis infection residing in the United States, and tuberculosis household contacts with latent M. tuberculosis infection in a tuberculosis-endemic setting in Kenya. The M. tuberculosis -specific T cell response spectrum assay further enhances the immunological toolkit available for evaluating M. tuberculosis -specific T cell responses across different states of M. tuberculosis infection, and can be readily implemented in resource-limited settings. Moreover, application of the assay to longitudinal cohorts will facilitate evaluation of treatment- or vaccine-induced changes in the breadth and specificity of Ag-specific T cell responses, as well as identification of M. tuberculosis -specific T cell responses associated with M. tuberculosis infection outcomes.