To determine if PD-1 is upregulated on Mtb-specific CD8 T cells in the setting of chronic Mtb infection, we measured PD-1 expression on cytokine+ CFP-10/ESAT-6-specific CD8 T cells in individuals with LTBI, and in smear− and smear+ TB patients (Figure 3A). This evidence concerns the gene PDCD1 and tuberculosis.