An estimated one third of the world's population is latently infected with Mycobacterium tuberculosis (Mtb), and HIV infection significantly increases the risk of developing TB, making HIV/TB co-infection a serious health threat. Conventional peptide antigen-specific CD4+ and CD8+ T cell responses play important roles in adaptive immunity to Mtb and are being targeted by various vaccination strategies. However, the in vivo role of lipid antigen-specific CD1-restricted T cell responses in TB immunity remains largely unknown despite an indication of anti-TB potential in small animal models. We have found that Mtb lipid antigen-specific T cell cytokine and cytotoxic responses can be detected in uninfected macaques suggesting that these immune responses may play important roles in early defense against Mtb. Furthermore, we observed significantly higher Mtb lipid- specific responses in cynomolgus macaques in comparison to rhesus macaques. Utilizing the BCG model of mycobacterial exposure in cynomolgus macaques that display more potent innate Mtb lipid antigen-specific responses, we aim to define the role of CD1-restricted immune responses in TB immunity. Our previous data also indicate a decline in peripheral blood Mtb lipid antigen-specific responses of SIV-infected macaques. Thus we propose that SIV infection induces perturbations in the host CD1-restricted immune responses that contribute to increased risk of TB in co-infection.
The specific aims of this proposal are focused on the understanding of the in vivo role of CD1-restricted immune responses in protection against TB and the impact of SIV infection on their anti-mycobacterial effector functions. In the first aim, the phenotypic and functional characteristics of systemic and mucosal mycobacterial lipid-specific T cells will be examined longitudinally in BCG-inoculated macaques to determine anti-mycobacterial effector functions and relationship with adaptive immune responses. The anti-mycobacterial effector functions will be investigated by evaluation of in vitro cytokine responses to lipid antigen-stimulation, cytotoxicity towards autologous Mtb-infected monocytes, and activation of CD1-expressing antigen presenting cells. In the second aim, in order to understand their role in SIV-induced reactivation of TB, the study will determine the impact of SIV infection on these effector functions in blood and lungs of BCG-vaccinated macaques. These studies are relevant because they focus on understanding novel mechanisms of mycobacterial immunity in the nonhuman primate model of TB and HIV. The results will provide valuable insights into the immune mechanisms of protection against TB, and how lentiviral infection impairs these mechanisms, and will open new avenues to explore specific lipid-based modes of intervention in TB.
The identification of novel immune cells that participate in the early immune response to mycobacterial exposure will aid the development of better TB vaccines or therapeutic strategies targeting these T cells. This project aims to investigate the protective functions of lipid antigen-specific immune cells responding to BCG exposure in the presence or absence of SIV co-infection and will thus improve the current understanding of HIV-induced increase in the risk of TB.
