Our data indicate that the majority of proliferating Mtb-specific CD4 T cells express PD-1 on day 6 of our proliferation assays, in both LTBI and smear+ TB patients; however, it remains unclear whether the proliferating Mtb-specific CD4 T cell population originates from cells that expressed PD-1 ex vivo, or whether Mtb-specific CD4 T cells with proliferative capacity induced PD-1 expression only transiently during the 6-day antigen stimulation period. This evidence concerns the gene PDCD1 and tuberculosis.