The Role of Lipid-specific T cells in Mediating Protection Against M. tuberculosis

PROJECT SUMMARY Several lines of evidence from human and animal studies have revealed the critical importance of T cells in conferring protective immunity to Mycobacterium tuberculosis (M.tb). However, we still do not know which M.tb antigens are targeted by the T cells that confer protection. This information is critical to developing new subunit vaccines that are more effective than Mycobacterium bovis bacille Calmette-Guérin (BCG), which is currently the only licensed vaccine for tuberculosis (TB). Classically, T cells are activated by foreign peptide antigens that are bound to highly polymorphic major histocompatibility molecules. Alternatively, mycobacterial cell wall lipids have conclusively been shown to activate human T cells when bound to non-polymorphic CD1 proteins on antigen-presenting cells. The CD1 system mediates protective T-cell responses in mouse models of autoimmunity, cancer, and infectious diseases. However, the lack of an appropriate animal model has impeded research into the importance of CD1-restricted T cells in the pathogenesis of M.tb. Tools to identify CD1- restricted T cells were also unavailable until recently. We have established lipid-loaded CD1 tetramers as tools to study the phenotypes and functions of CD1-restricted T cells in humans and non-human primates. We have also developed and validated a humanized CD1 transgenic (hCD1Tg) mouse model and shown that T-cells specific for mycolic acid, a major constituent of the mycobacterial cell wall, confer protective immunity to M.tb challenge. Finally, we have developed a lipid-based nanoparticle vaccine and shown that it induces durable T cell responses to mycolic acid in hCD1Tg mice. In Aim 1 of this renewal application, we will determine how lipid chain length, alveolar macrophages, and dendritic cells modulate T cell responses induced by nanoparticle vaccination. In Aim 2, we will use lipid-loaded tetramers to define the phenotypes and functions of CD1-restricted T cells in rhesus macaques after intravenous BCG vaccination, which confers sterilizing immunity to M.tb challenge. We will also use quantitative PCR to enumerate CD1-restricted T cells in pulmonary granulomas and correlate this with bacterial burden. In Aim 3, we will determine the role of CD1-restricted T cells in mediating control of M.tb infection in hCD1Tg mice using adoptive transfer of transgenic T cells as well as a BCG prime and nanoparticle boosting vaccine regimen. Finally, we will leverage a tonsil organoid model of human tuberculosis to determine whether human CD1-restricted T cells are activated and express anti-bacterial effector functions after M.tb infection as well as control bacterial replication. By the end of the funding period, we will have defined the role of CD1-restricted in M.tb pathogenesis and provided the rationale for whether lipid-specific T cells should be considered a correlate of protective immunity in ongoing Phase II/III clinical efficacy studies of whole cell mycobacterial vaccines.