By contrast with human viral infections in which upregulation of PD-1 has been widely reported on virus-specific CD8 T cells, we found that expression of PD-1 on Mtb-specific CD8 T cells is similar across individuals with LTBI, smear− TB and smear+ TB, consistent with a previous report that expression of PD-1 on Mtb-specific CD8 T cells is not significantly different between individuals with LTBI and active TB disease (53). This evidence concerns the gene PDCD1 and viral infectious disease.