The importance of an intact Th1 type cellular immune response in protective immunity has been demonstrated in human genetic studies and murine M. tuberculosis challenge experiments2, 3, 4, 5, 6, 8, 9, however, this is the first time a role has been demonstrated for magnitude of vaccine-induced IFN-γ-secreting T cells and reduced TB disease risk in a human immune correlates study11. The gene discussed is IFNG; the disease is tuberculosis.