Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) infections, claims the lives of 2- 3 million people annually. The importance of the development of more efficient drugs and vaccines is reinforced by: the emergence of multi-drug resistant and extreme-drug resistant Mtb strains and secondly, the deadly synergism between the HIV/AIDS epidemic and TB due to reactivation of persisting bacteria.This proposal seeks to test the hypothesis that the capacity of Mtb to inhibit infection-induced apoptosis of macrophages is a major pathway of the bacteria to avoid the host?s innate and adaptive immune response. Furthermore it proposes that the discovery of mycobacterial genes involved in the inhibition of host cell apoptosis will lead to new drug targets for resolving persistent bacterial infections and to new improved attenuated vaccine strains. Presently, the capacity of mycobacteria to inhibit macrophage apoptosis has been linked to bacterial virulence based only on correlative data due to the lack of defined bacterial mutants. The AIM 1 of the proposal targets to fill that gap in our knowledge by identifying several mycobacterial genes important for apoptosis inhibition using a unique ?gain-of-function? genetic screen. The success of this approach has been proven by the identification of one anti-apoptotic gene of Mtb, nuoG, but at least two additional genes remain to be identified. AIM 2 proposes to characterize the molecular mechanisms by which nuoG is able to suppress host cell apoptosis. Finally, in AIM 3 the bacterial mutants are used to address the importance of apoptosis inhibition for the bacterial escape from the host?s innate and acquired immune response in immunodeficient and immunocompetent mice, respectively. In addition, the identified anti-apoptotic gene will be deleted in the currently used TB vaccine strain (BCG) and the effect of the mutation on the vaccine potential will be tested in the mouse model of TB. Altogether, the successful completion of the proposed studies would lead to the identification of new TB drug targets and may result in an improved TB vaccine strain.