Defining the role of CD8 T cell subsets in tuberculosis in non-human primates
Caylin G. Winchell1,2, Pauline Maiello1, Sarah Nyquist3, Alex Shalek3, Sarah Fortune4, Philana Ling Lin5, JoAnne L. Flynn1
1Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, 2Division of Pulmonary, Allergy and Critical Care Medicine, University of Pittsburgh School of Medicine, 3Institute for Medical Engineering & Science, Massachusetts Institute of Technology, 4Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA, Department of Pediatrics, 5UPMC Children’s Hospital of the University of Pittsburgh.
In 2019, tuberculosis (TB) was the number one cause of death by a single infectious agent with no protective vaccine currently available. Challenges in vaccine development are partially attributed to a deficiency in knowledge regarding specific immune cell contribution to protection. CD8 T cells comprise ~35% of T cells present in a lung granuloma, a lesion of immune cells that is a hallmark of Mycobacterium tuberculosis (Mtb) infection. However, few studies have explored the diversity, function and contribution to protection by CD8 subsets during TB. We investigated the roles of conventional CD8ab T cells and unconventional CD8aa expressing T cells during early Mtb infection. Cynomolgus macaques were CD8-depleted using anti-CD8a or anti-CD8b antibodies prior to and throughout Mtb infection and necropsied at 6 weeks post-infection. Using spectral flow cytometry, we identified multiple CD8 subsets and assessed their functions in granulomas for the first time in NHPs. After CD8a depletion, the repertoire of CD8 subsets was dramatically reduced granulomas. This resulted in functional changes to other immune cell populations, in particular non-CD8 expressing T cells. Using single-cell RNA-sequencing, we validated and expanded upon the functional changes of the immune landscape, focused on the modulation of cytotoxicity observed by flow cytometry. scRNA-seq identified multiple subsets of cytotoxic cell subsets, highlighting an under-appreciated and diverse role of cytotoxicity in early TB disease. These studies provide insight to the functional immune landscape during early events in Mtb granulomas and shed light on the protective potential of CD8 expressing T cells and cytotoxic functions during TB.