Differential persistence of Th9 vs. Th1 cell phenotypes was confirmed <i>in vivo</i>, and lung tissue qRT-PCR studies demonstrated the absence of IFN-γ responses in Th9-transferred mice, combined with unique expression of the Th9 specific markers IL-9, IL-10 and PU.1.<h4>Discussion</h4>Th9 cells can provide important protection against Mtb infection, and should be targeted with future TB vaccine strategies. The gene discussed is IL9; the disease is tuberculosis.