Mycobacterium tuberculosis-Specific T Cell Functional, Memory, and Activation Profiles in QuantiFERON-Reverters Are Consistent With Controlled Infection.

Cheleka A M Mpande,Tessa Lloyd,Boitumelo Mosito,Thomas J Scriba,Francesca Little,Nicole Bilek,Jason R Andrews,Pia Steigler,Elisa Nemes,Constance Schreuder,Morten Ruhwald,Virginie Rozot,Mark Hatherill,Timothy D Reid

doi:10.3389/fimmu.2021.712480

Abstract

Reversion of immune sensitization tests for Mycobacterium tuberculosis (M.tb) infection, such as interferon-gamma release assays or tuberculin skin test, has been reported in multiple studies. We hypothesized that QuantiFERON-TB Gold (QFT) reversion is associated with a decline of M.tb-specific functional T cell responses, and a distinct pattern of T cell and innate responses compared to persistent QFT+ and QFT- individuals. We compared groups of healthy adolescents (n=~30 each), defined by four, 6-monthly QFT tests: reverters (QFT+/+/-/-), non-converters (QFT-/-/-/-) and persistent positives (QFT+/+/+/+). We stimulated peripheral blood mononuclear cells with M.tb antigens (M.tb lysate; CFP-10/ESAT-6 and EspC/EspF/Rv2348 peptide pools) and measured M.tb-specific adaptive T cell memory, activation, and functional profiles; as well as functional innate (monocytes, natural killer cells), donor-unrestricted T cells (DURT: γδ T cells, mucosal-associated invariant T and natural killer T-like cells) and B cells by flow cytometry. Projection to latent space discriminant analysis was applied to determine features that best distinguished between QFT reverters, non-converters and persistent positives. No longitudinal changes in immune responses to M.tb were observed upon QFT reversion. M.tb-specific Th1 responses detected in reverters were of intermediate magnitude, higher than responses in QFT non-converters and lower than responses in persistent positives. About one third of reverters had a robust response to CFP-10/ESAT-6. Among those with measurable responses, lower proportions of TSCM (CD45RA+CCR7+CD27+) and early differentiated (CD45RA-) IFN-γ-TNF+IL-2- M.tb lysate-specific CD4+ cells were observed in reverters compared with non-converters. Conversely, higher proportions of early differentiated and lower proportions of effector (CD45RA-CCR7-) CFP10/ESAT6-specific Th1 cells were observed in reverters compared to persistent-positives. No differences in M.tb-specific innate, DURT or B cell functional responses were observed between the groups. Statistical modelling misclassified the majority of reverters as non-converters more frequently than they were correctly classified as reverters or misclassified as persistent positives. These findings suggest that QFT reversion occurs in a heterogeneous group of individuals with low M.tb-specific T cell responses. In some individuals QFT reversion may result from assay variability, while in others the magnitude and differentiation status of M.tb-specific Th1 cells are consistent with well-controlled M.tb infection.

Highlights

Immunodiagnostics for Mycobacterium tuberculosis (M.tb) infection, such as tuberculin skin tests (TSTs) and IFN-g release assays (IGRAs), were designed and are clinically interpreted based on the premise that detectable M.tb-specific immune responses are indicative of viable M.tb infection, i.e. bacterial persistence
We have recently demonstrated that relative proportions of M.tb lysate-specific IL-2+ and TNF+ stem cell memory (TSCM) and central memory (TCM) cells are higher in IGRA- compared to IGRA+ individuals, suggesting that low or no in vivo M.tb antigen exposure is associated with higher proportions of early differentiated mycobacteria-specific T cell subsets [24]
Too few reverters and nonconverters had a robust IFN-g+ lymphocyte response to CFP-10/ ESAT-6 to be included in this analysis (Supplementary Table 5). tSNE analysis confirmed CD4 T cells as the major source of IFN-g in persistent QFT+ individuals and reversion, while CD4 T cells accounted for

Summary

Introduction

Immunodiagnostics for Mycobacterium tuberculosis (M.tb) infection, such as tuberculin skin tests (TSTs) and IFN-g release assays (IGRAs), were designed and are clinically interpreted based on the premise that detectable M.tb-specific immune responses are indicative of viable M.tb infection, i.e. bacterial persistence. Longitudinal studies have demonstrated the dynamic nature of M.tb-specific immune responses, whereby TSTs and IGRAs revert from a positive to a negative test in some individuals. Guinea pigs that were infected with M.tb (defined by recent TST conversion upon experimental exposure) and reverted to a negative TST had sterile lung lesions indicative of cured infection [3,4,5]. These findings provide evidence that some individuals can spontaneously cure M.tb infection and gave rise to the hypothesis that reversion of immunodiagnostic test results may be associated with M.tb clearance. As IGRA conversion is increasingly used as an outcome in vaccine trials, correctly interpreting reversions will be important to understanding vaccine efficacy

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