Mycobacterium tuberculosis-specific IL-17 producing T cells distinguish between distinct TB antigens and varies by age
Paul Ogongo1, Jason Limberis1, Devin Columbus1, Jung Hwa Kirschman2, John Altin2 and Joel Ernst1
1Division of Experimental Medicine, University of California San Francisco, 1001 Potrero Avenue, CA 94110
2Pathogen and Microbiome Division, The Translational Genomics Research Institute, 445 N. Fifth Street Phoenix, AZ 85004
The characteristics of M. tuberculosis-antigen specific T cells that provide protection from disease are not fully defined despite CD4 T cells being crucial for control of tuberculosis. We hypothesised that CD4 T cell functional responses to M. tuberculosis may differ according to the antigens they recognize. To test this, we stimulated PBMC from recently-exposed, QFT+ individuals with Mtb lysate followed by single-cell TCR and RNA-seq analysis and found clonotype associated differences in T cell functional responses, suggesting that functional differences might be associated with distinct antigen specificity. Next, we stimulated PBMC (from 24 participants) at recruitment (baseline) with four single antigens: PPE18, PPE46, EsxA, and EspI, and assessed CD4 T cell responses by intracellular cytokine staining for IFNg, TNF-α, IL-17, and GM-CSF. We found that IL-17 responses had the greatest variation, and varied by antigen and by subject: CD4 T cells from 70% of the individuals produced IL-17 in response to PPE46, while 54% produced IL-17 in response to EsxA or EspI, and 45% produced IL-17 in response to PPE18. When stratified by age, QFT results and gender, the frequency of IL-17 and GMCSF specific to PPE18 and EsxA differed by age and was lowest in individuals ≥52 years. In contrast, TNF-α responses showed the least variation:CD4 T cells from ≥70% of individuals expressed TNF-α in response to each of the antigens. The highest frequency of T cell responses was to PPE46 when all cytokines were considered. Clustering analysis of the responses at 6 months show that PPE46 differs from the other antigens by IL-17 and GMCSF specific responses. From these initial results, we hypothesize that variation in T cell responses to distinct antigens will reveal differences that correlate with, and may be responsible for, differences in TB outcomes in humans. We are currently testing this hypothesis in a prospective cohort of recently-exposed, QFT+ household contacts.