The greatest barrier to development of efficacious vaccines against tuberculosis is the ability of Mycobacterium tuberculosis to persist and to cause progressive infection despite development of an adaptive immune response. While partially-efficacious vaccines may result from optimal selection of antigens, adjuvants, and delivery systems, major progress against tuberculosis will require novel approaches to enhancing resistance, based on overcoming or bypassing the mechanisms used by M. tuberculosis to evade adaptive immune responses. To identify and characterize those mechanisms, we have developed novel tools for use in a mouse model of immunity to M. tuberculosis to discover and characterize mechanisms that limit the efficacy of the adaptive immune response to M. tuberculosis. We have developed a system using a monoclonal antibody that recognizes a specific peptide:MHC II complex and several recombinant strains of M. tuberculosis, to test the hypothesis that M. tuberculosis inhibits MHC II antigen presentation in vivo, and to test the hypothesis that M. tuberculosis transfers antigens to uninfected cells as an immune evasion strategy. We have also developed a system using CD4+ T cells from a unique line of mice with a transgenic T cell antigen receptor specific for M. tuberculosis Ag85B, and have discovered that downregulation of the gene encoding Ag85B during the chronic stage of M. tuberculosis infection is accompanied by diminished in vivo CD4+ T cell responses to Ag85B. Taken together, these results suggest that M. tuberculosis may modulate expression of antigen genes as a means of avoiding recognition and elimination by CD4+ effector T cells. We also developed a method for visualization and localization of M. tuberculosis-infected cells and CD4+ T cells in the lungs, and have found that a minority of M. tuberculosis-infected cells in the lungs are in direct contact with CD4+ T cells, which supports the hypothesis that CD4+ T cells recognize M. tuberculosis-infected cells poorly at the site of infection. In this application, we propose experiments to test the general hypothesis that interactions between M. tuberculosis-infected cells and antigen-specific CD4+ T cells in the lungs are defective, and that this contributes to persistence of the infection. We will test the specific hypothesis that defective interactions between M. tuberculosis-infected cells and CD4+ T cells during chronic infection are due to a combination of: 1) M. tuberculosis inhibition of antigen presentation by infected cells;2) decreased expression of M. tuberculosis antigens during the chronic stage of infection;and 3) transfer of M. tuberculosis antigens from infected cells to neighboring uninfected cells in granulomas, allowing uninfected cells to act as decoys to activate T cells at a distance from infected cells. Our proposed studies will provide unprecedented insight into the mechanisms used by M. tuberculosis to evade elimination by the mammalian adaptive immune response, and will guide future efforts to develop the means to increase human resistance to tuberculosis.
One of the major problems that has prevented development of a successful TB vaccine is that the bacteria that cause TB are not eliminated by normal immune responses. In this project, we will identify and characterize the mechanisms that TB bacteria use to avoid recognition and elimination by immune cells. We expect that understanding these mechanisms will allow us and others to develop novel ways to increase resistance of people to tuberculosis.
|Srivastava, Smita; Ernst, Joel D (2014) Cell-to-cell transfer of M. tuberculosis antigens optimizes CD4 T cell priming. Cell Host Microbe 15:741-52|
|Srivastava, Smita; Ernst, Joel D; Desvignes, Ludovic (2014) Beyond macrophages: the diversity of mononuclear cells in tuberculosis. Immunol Rev 262:179-92|
|Srivastava, Smita; Ernst, Joel D (2013) Cutting edge: Direct recognition of infected cells by CD4 T cells is required for control of intracellular Mycobacterium tuberculosis in vivo. J Immunol 191:1016-20|
|Desvignes, Ludovic P; Ernst, Joel D (2013) Taking sides: interferons in leprosy. Cell Host Microbe 13:377-8|
|Bold, Tyler D; Davis, Daphne C; Penberthy, Kristen K et al. (2012) Impaired fitness of Mycobacterium africanum despite secretion of ESAT-6. J Infect Dis 205:984-90|
|Urdahl, K B; Shafiani, S; Ernst, J D (2011) Initiation and regulation of T-cell responses in tuberculosis. Mucosal Immunol 4:288-93|
|Bold, Tyler D; Banaei, Niaz; Wolf, Andrea J et al. (2011) Suboptimal activation of antigen-specific CD4+ effector cells enables persistence of M. tuberculosis in vivo. PLoS Pathog 7:e1002063|
|Kwan, Candice K; Ernst, Joel D (2011) HIV and tuberculosis: a deadly human syndemic. Clin Microbiol Rev 24:351-76|