Monitoring CD27 expression to evaluate Mycobacterium tuberculosis activity in HIV-1 infected individuals in vivo

Abstract

The level of bacterial activity is only poorly defined during asymptomatic Mycobacterium tuberculosis (MTB) infection. The objective was to study the capacity of a new biomarker, the expression of the T cell maturation marker CD27 on MTB-specific CD4 T cells, to identify active tuberculosis (TB) disease in subjects from a MTB and HIV endemic region. The frequency and CD27 expression of circulating MTB-specific CD4 T cells was determined in 96 study participants after stimulation with purified protein derivative (PPD) using intracellular cytokine staining for IFNgamma (IFNγ). Subjects were then stratified by their TB and HIV status. Within PPD responders, a CD27(-) phenotype was associated with active TB in HIV(-) (p = 0.0003) and HIV(+) (p = 0.057) subjects, respectively. In addition, loss of CD27 expression preceded development of active TB in one HIV seroconverter. Interestingly, in contrast to HIV(-) subjects, MTB-specific CD4 T cell populations from HIV(+) TB-asymptomatic subjects were often dominated by CD27(-) cells. These data indicate that down-regulation of CD27 on MTB-specific CD4 T cell could be used as a biomarker of active TB, potentially preceding clinical TB disease. Furthermore, these data are consistent with the hypothesis that late, chronic HIV infection is frequently associated with increased mycobacterial activity in vivo. The analysis of T cell maturation and activation markers might thus be a useful tool to monitor TB disease progression.

Figure 1. Characterization of CD27 expression on PPD-specific CD4 T cells in whole blood.

(A) The cut off for CD27 expression was determined based on the corresponding isotype control for each antibody. Shown is a representative staining for IFNγ-FITC and CD27-PE as well as their corresponding IgG₁ isotype controls that were used to determine the cut off. (B) Gating strategy to identify PPD-specific CD4 T cells and to analyse the CD27 expression on IFNγ-positive CD4 T cells after 6 h of PPD-stimulation during the cross-sectional study. (C) Representative staining for negative and positive controls using PPD diluent and SEB, respectively, for stimulation.

Figure 2. Down regulation of CD27 on PPD-specific CD4 T cells is associated with active Tuberculosis independent of the HIV status and with progression to active TB in a HIV⁺ seroconverter.

(A) Ratio of IFNγ⁺ CD4 T cells that are CD27⁺ divided by those that are CD27⁻ is shown for 4 different groups of PPD responders delineated by TB disease state and by HIV serology. CD4⁺ T cells were analyzed for each sample using a whole blood intracellular cytokine assay. (B) Histogram analysis of CD27 expression on IFNγ⁺ PPD-specific CD4 T cells (blue line) and total CD4 T cells (black line, grey) over a 15 months period in two subjects who became HIV infected. Subject H19 (upper panel) was diagnosed and treated for active TB 15 months after HIV infection. Subject H228 (lower panel) did not develop TB within three years after HIV infection. Longitudinal analysis of CD27 expression for one subject was determined simultaneously by flow cytometry.