Specific CD4+ T cell phenotypes associate with bacterial control in people who ‘resist’ infection with Mycobacterium tuberculosis

A subset of individuals with a high probability of exposure to M. tuberculosis (M.tb) appears to ‘resist’ established M.tb infection, as demonstrated by serially negative tuberculin skin test (TST) or IFN-γ release assay (IGRA) results. While these ‘resisters’ (RSTR) display IFN-γ-independent T cell responses to the M.tb-specific antigens ESAT-6 and CFP-10, it is currently unknown whether unique T cell functional programs are associated with this clinical outcome. We used multi-modal single-cell RNA, TCR sequencing, multi-parameter flow cytometry, and cytokine analysis in a discovery and validation format to compare the phenotypes and functions of M.tb-specific T cells between RSTRs and matched controls with ‘latent’ M.tb infection (LTBI). M.tb-specific T cells were clonally expanded in both RSTRs and LTBIs, confirming the priming of adaptive immune responses after M.tb exposure. However, M.tb-specific T cells derived from RSTRs showed enrichment of T regulatory as well as Th17-like functional programs compared to LTBIs, which were characterized by Th1*-like effector programs. Th17-like functional programs were also associated with a lack of progression to active TB among South African adolescents with LTBI, as well as bacterial control in published non-human primate studies. Together, these data suggest that ‘resisters’ may successfully control M.tb after exposure and immune priming and establish a set of T cell biomarkers to facilitate further study of this important clinical phenotype.