CD4 and tuberculosis: Tuberculosis (TB) remains the leading cause of death by infection worldwide with nearly 10 million new cases and about 1.5 million TB-related deaths in 2018.1 CD4 T-cell responses are critical for control of Mycobacterium tuberculosis (Mtb) infection, and HIV-infection-associated CD4 T-cell depletion greatly increases susceptibility to developing TB disease.