Defining the role of CD8 T cell subsets in tuberculosis in non-human primates

Abstract Tuberculosis (TB) is the number one cause of death by a single infectious agent with no protective vaccine available. Challenges in vaccine development are partially attributed to a deficiency in knowledge regarding specific immune cells’ contribution to protection. CD8 T cells comprise ~30–40% of T cells in the lung granuloma, an organized collection of immune cells that is a hallmark of Mycobacterium tuberculosis (Mtb) infection. However, few studies have explored the diversity, function and contribution to protection of CD8 subsets during TB. We investigated the roles of conventional CD8αβ T cells and unconventional CD8αα T cells during early Mtb infection. Cynomolgus macaques were CD8-depleted using anti-CD8α or anti-CD8β antibodies prior to and during Mtb infection and necropsied at 6 weeks post-infection. CD8α depleted NHPs (CD8αα and CD8αβ depletion) had higher bacterial burdens, worse pathology and overall poorer disease outcome compared to IgG controls, while CD8β depleted (CD8αβ only depletion) displayed an intermediate phenotype. This provides the first evidence for an important early role for non-conventional CD8 T cells in TB. Using spectral flow cytometry we identified multiple CD8 subsets and assessed their functions in granulomas for the first time in NHPs. After CD8α depletion, the repertoire of CD8 subsets dramatically changed in granulomas. This was associated with functional alterations in other immune cell populations which we validated and expanded upon using single-cell RNA sequencing. These studies provide a functional immune landscape of early events in Mtb granulomas as well as the effects of CD8 depletion, shedding light on the protective potential of CD8 T cell subsets during primary Mtb infection.