Postdoctoral Fellow UCSF San Francisco, California, United States
Disclosure(s):
Zachary P. Howard, PhD: No financial relationships to disclose
Introduction/Rationale: Tuberculosis (TB) is a major threat to global health, with >1 million deaths/year. Optimal TB vaccine design is hampered by gaps in understanding the mechanisms and limitations of TB immunity. CD4 T cells are essential for TB immunity but do not reliably eliminate the pathogen. Therefore, it is critical to identify factors that promote and restrict T cell interactions and functions in vivo.
Methods: The 'uLIPSTIC' (Universal Labelling Immune Partnerships by SorTagging Intercellular Contacts) system enables labelling of cells that interact with a cell of interest by transferring a biotin tag, for identification and characterization by flow cytometry or single cell sequencing. We adapted uLIPSTIC to identify cells that interact with Mtb-specific CD4 T cells in the lungs. We generated C7 TCR transgenic mice that produce ‘donor’ CD4 T cells that label interacting ‘acceptor’ cells after T cell adoptive transfer.
Results: During the peak of T cell responses to Mtb at 28 days post-infection, we found that CD11b+CD11c+ monocyte-derived lung macrophages (MDMs) are the most frequently T cell-interacting cells: 54% of this cell population were biotin+. Of the Mtb-infected MDMs, 23% were biotin+ while 54% of the Mtb-uninfected (bystander) MDMs were biotin+.
Conclusion: This suggests that T cell recognition of Mtb-infected cells is impaired and that most Mtb-specific CD4 T cell interactions are futile, since prior work has established that direct cognate interactions between CD4 T cells and Mtb-infected cells are essential for optimal control of infection. Single cell RNA sequencing is ongoing to further characterize the population of cells that are interacting with Mtb-specific CD4 T cells. The results generated by experiments with the Mtb-adapted uLIPSTIC system will identify determinants associated with T cell mediated immune control of Mtb infection and inform host-directed therapies and ongoing vaccine development.
