 M. tuberculosis infects a third of the worlds population, and TB is the leading cause of morbidity and mortality due to a single infectious agent. However, only 5 to 10 of M. tuberculosis-infected subjects without an underlying immunodeficiency develop disease during their lifetimes. Therefore protective immunity is induced in the majority of subjects. Understanding correlates of protection against M. tuberculosis in humans is needed to better direct efforts in the development of antituberculosis vaccines. 