The goal of this proposal is to determine whether vaccine-elicited cytotoxic CD4 T cells contribute to the control of Mycobacterium tuberculosis (Mtb) in vivo. Mtb remains a significant global disease, with one-third of the world population infected and approximately 1.5 million deaths annually. Bacillus Calmette-Guerin (BCG) is the only approved vaccine for tuberculosis, but fails to prevent disease and mortality in adults. To develop new and effective vaccines, immune mechanisms of bacterial control need to be defined. Although Mtb-specific CD4 T cell production of IFN-g and TNF are critical for control of infection, they are insufficient to fully control the infection. We have developed a candidate vaccine that elicits CD4 T cells that produce these cytokines and are also capable of directly killing target cells. We propose to test whether this cytolytic activity contributes to control of tb by vaccination. We will determine the effector pathway(s) used by these cytotoxic CD4 T cells to control Mtb including: FasL, perforin, TRAIL and granulysin. Finally we will measure cytotoxic CD4 T cell activity in immunized non-human primates. The results of these studies will determine whether cytotoxic CD4 T cells can contribute to control of Mtb in vivo. [Additionally we will determine whether granulysin- expression, proposed to be a marker of immunity against Mtb, contributes to bacterial control in vivo.]