Several studies have demonstrated that CD4 T cells that secrete only IFN-γ have a limited capacity to develop into memory cells (18, 28) but that the proportion of multifunctional Th1 cells (characterized by their simultaneous secretion of multiple cytokines [IFN-γ, IL-2, and TNF-α; (18, 27–29)] positively correlates with protection against various cancers and infectious diseases, including leishmaniasis (29, 30) and tuberculosis (31, 32). The gene discussed is IFNG; the disease is leishmaniasis.