It has been previously shown that the BCG-vaccinated adults harbor early-stage-differentiated, low PD-1-expressing antigen-specific effector memory CD4+ T cells while BCG-vaccinated, latent TB infected (LTBI) adults had late-stage-differentiated PD-1+ T cells [78], and the advanced TB patients harbor PD-1+ severely exhausted T cells with compromised IFN-γ production [74], [79]. The gene discussed is PDCD1; the disease is tuberculosis.