Distinct Effector Memory CD4+ T Cell Signatures in Latent Mycobacterium tuberculosis Infection, BCG Vaccination and Clinically Resolved Tuberculosis

Two billion people worldwide are estimated to be latently infected with Mycobacterium tuberculosis (Mtb) and are at risk for developing active tuberculosis since Mtb can reactivate to cause TB disease in immune-compromised hosts. Individuals with latent Mtb infection (LTBI) and BCG-vaccinated individuals who are uninfected with Mtb, harbor antigen-specific memory CD4+ T cells. However, the differences between long-lived memory CD4+ T cells induced by latent Mtb infection (LTBI) versus BCG vaccination are unclear. In this study, we characterized the immune phenotype and functionality of antigen-specific memory CD4+ T cells in healthy BCG-vaccinated individuals who were either infected (LTBI) or uninfected (BCG) with Mtb. Individuals were classified into LTBI and BCG groups based on IFN-γ ELISPOT using cell wall antigens and ESAT-6/CFP-10 peptides. We show that LTBI individuals harbored high frequencies of late-stage differentiated (CD45RA−CD27−) antigen-specific effector memory CD4+ T cells that expressed PD-1. In contrast, BCG individuals had primarily early-stage (CD45RA−CD27+) cells with low PD-1 expression. CD27+ and CD27− as well as PD-1+ and PD-1− antigen-specific subsets were polyfunctional, suggesting that loss of CD27 expression and up-regulation of PD-1 did not compromise their capacity to produce IFN-γ, TNF-α and IL-2. PD-1 was preferentially expressed on CD27− antigen-specific CD4+ T cells, indicating that PD-1 is associated with the stage of differentiation. Using statistical models, we determined that CD27 and PD-1 predicted LTBI versus BCG status in healthy individuals and distinguished LTBI individuals from those who had clinically resolved Mtb infection after anti-tuberculosis treatment. This study shows that CD4+ memory responses induced by latent Mtb infection, BCG vaccination and clinically resolved Mtb infection are immunologically distinct. Our data suggest that differentiation into CD27−PD-1+ subsets in LTBI is driven by Mtb antigenic stimulation in vivo and that CD27 and PD-1 have the potential to improve our ability to evaluate true LTBI status

Reinstating Mycobacterium massiliense and Mycobacterium bolletii as species of the Mycobacterium abscessus complex

International audienceTheMycobacterium abscessus complex is a group of rapidly growing, multiresistant mycobacteria previously divided into three species. Proposal for the union of Mycobacterium bolletii and Mycobacterium massiliense into one subspecies, so-called M. abscessus subsp. massiliense, created much confusion about the routine identification and reporting of M. abscessus clinical isolates for clinicians. Results derived from multigene sequencing unambiguously supported the reinstatement of M. massiliense and M. bolletii as species, culminating in the presence of erm(41)-encoded macrolide resistance in M. bolletii. Present genome-based analysis unambiguously supports the reinstatement of M. massiliense and M. bolletii as species after the average nucleotide identity values of 96.7 % for M. abscessus versus M. bolletii, and 96.4 % for M. abscessus versus M. massiliense, and the 96.6 % identity between M. bolletii and M. massiliense was put into the perspective of a larger, 28-species analysis. Accordingly, DNA-DNA hybridization values predicted by the complete rpoB gene sequencing analysis were between 68.7 and 72.3 % in this complex. These genomic data as well as the phenotypic characteristics prompted us to propose to reinstate the previously known M. massiliense and M. bolletii into two distinct species among the M. abscessus complex

Higher frequencies of PD-1 expression on antigen-specific memory CD4⁺ T cells in LTBI relative to BCG individuals.

<p>(A) A representative plot of CD4⁺ T cells expressing PD-1 upon CW stimulation, displaying the percentage of antigen-specific IFN-γ producing cells. The summary of percentage (B) and MFI (C) of PD-1 expression on antigen-specific memory CD4⁺ T cells in LTBI (n = 18) and BCG (n = 18) groups. Each data point corresponds to a single donor. Polyfunctional cytokine production by memory PD-1⁺ (D) and PD-1⁻ (E) T cells from LTBI. Data are represented as the mean percentage of responding PD-1⁺ or PD-1⁻ T cells that are triple producers (3+), double producers (2+) or single producers (1+) of IFN-γ, TNF-α, and IL-2 and summarized by the pie charts. Each slice of the pie represents the fractions of the total response that consists of PD-1⁺ or PD-1⁻ cells positive for a given function.</p

Cytokines production by effector memory CD4⁺ T cells from LTBI and BCG individuals.

<p>(A) Functional profile of IFN-γ, IL-2 and TNF-α CD4⁺ T cells are shown in representative LTBI and BCG individuals. (B) Polyfunctional cytokine production by memory CD4⁺ T cells from LTBI and BCG. Data are represented as the mean percentage of responding CD4⁺ T cells that are triple producers (3+), double producers (2+) or single producers (1+) of IFN-γ, TNF-α, and IL-2 and summarized by the pie charts. Each slice of the pie represents the fractions of the total response that consists of CD4⁺ T cells positive for a given function.</p