Although evidence supports the fundamental role of CD4+ T cells and cytokines (such as interferon gamma (IFNγ) (4, 5), tumor necrosis factor alfa (TNFα), interleukins 2 (IL-2) (6–9), and 12 (IL-12) (10, 11)) in TB, there are still no reliable correlates of protection. The gene discussed is IFNG; the disease is tuberculosis.