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.     

Mycobacterium tuberculosis Specific CD8+ T Cells Rapidly Decline with Antituberculosis Treatment

Rationale

Biomarkers associated with response to therapy in tuberculosis could have broad clinical utility. We postulated that the frequency of Mycobacterium tuberculosis (Mtb) specific CD8⁺ T cells, by virtue of detecting intracellular infection, could be a surrogate marker of response to therapy and would decrease during effective antituberculosis treatment.Objectives: We sought to determine the relationship of Mtb specific CD4⁺ T cells and CD8⁺ T cells with duration of antituberculosis treatment.

Materials and Methods

We performed a prospective cohort study, enrolling between June 2008 and August 2010, of HIV-uninfected Ugandan adults (n = 50) with acid-fast bacillus smear-positive, culture confirmed pulmonary TB at the onset of antituberculosis treatment and the Mtb specific CD4⁺ and CD8⁺ T cell responses to ESAT-6 and CFP-10 were measured by IFN-γ ELISPOT at enrollment, week 8 and 24.

Results

There was a significant difference in the Mtb specific CD8⁺ T response, but not the CD4⁺ T cell response, over 24 weeks of antituberculosis treatment (p<0.0001), with an early difference observed at 8 weeks of therapy (p = 0.023). At 24 weeks, the estimated Mtb specific CD8⁺ T cell response decreased by 58%. In contrast, there was no significant difference in the Mtb specific CD4⁺ T cell during the treatment. The Mtb specific CD4⁺ T cell response, but not the CD8⁺ response, was negatively impacted by the body mass index.

Conclusions

Our data provide evidence that the Mtb specific CD8⁺ T cell response declines with antituberculosis treatment and could be a surrogate marker of response to therapy. Additional research is needed to determine if the Mtb specific CD8⁺ T cell response can detect early treatment failure, relapse, or to predict disease progression.     

Expanded Polyfunctional T Cell Response to Mycobacterial Antigens in TB Disease and Contraction Post-Treatment

Background

T cells producing multiple factors have been shown to be required for protection from disease progression in HIV but we have recently shown this not to be the case in TB. Subjects with active disease had a greater proportion of polyfunctional cells responding to ESAT-6/CFP-10 stimulation than their infected but non-diseased household contacts (HHC). We therefore wanted to assess this profile in subjects who had successfully completed standard TB chemotherapy.

Methods

We performed a cross-sectional study using PBMC from TB cases (pre- and post-treatment) and HHC. Samples were stimulated overnight with TB antigens (ESAT-6/CFP-10 and PPD) and their CD4+ and CD8+ T cells were assessed for production of CD107a, IFN-γ, IL-2 and TNF-α and the complexity of the responses was determined using SPICE and PESTLE software.

Results and Conclusions

We found that an increase in complexity (i.e., production of more than 1 factor simultaneously) of the T cell profile was associated with TB disease and that this was significantly reduced following TB treatment. This implies that T cells are able to respond adequately to TB antigens with active disease (at least initially) but the ability of this response to protect the host from disease progression is hampered, presumably due to immune evasion strategies by the bacteria. These findings have implications for the development of new diagnostics and vaccine strategies.     

ESAT-6 and HspX Improve the Effectiveness of BCG to Induce Human Dendritic Cells-Dependent Th1 and NK Cells Activation

The limited efficacy of the BCG vaccine against tuberculosis is partly due to the missing expression of immunogenic proteins. We analyzed whether the addition to BCG of ESAT-6 and HspX, two Mycobacterium tuberculosis (Mtb) antigens, could enhance its capacity to activate human dendritic cells (DCs). BCG showed a weak ability to induce DC maturation, cytokine release, and CD4⁺ lymphocytes and NK cells activation. The addition of ESAT-6 or HspX alone to BCG-stimulated DC did not improve these processes, whereas their simultaneous addition enhanced BCG-dependent DC maturation and cytokine release, as well as the ability of BCG-treated DCs to stimulate IFN-γ release and CD69 expression by CD4⁺ lymphocytes and NK cells. Addition of TLR2-blocking antibody decreased IL-12 release by BCG-stimulated DCs incubated with ESAT-6 and HspX, as well as IFN-γ secretion by CD4⁺ lymphocytes co-cultured with these cells. Moreover, HspX and ESAT-6 improved the capacity of BCG-treated DCs to induce the expression of memory phenotype marker CD45RO in naïve CD4⁺ T cells. Our results indicate that ESAT-6 and HspX cooperation enables BCG-treated human DCs to induce T lymphocyte and NK cell-mediated immune responses through TLR2-dependent IL-12 secretion. Therefore ESAT-6 and HspX represent good candidates for improving the effectiveness of BCG vaccination.     

Mycobacterium tuberculosis-Specific IL-21+IFN-γ+CD4+ T Cells Are Regulated by IL-12

In the current study of Mycobacterium tuberculosis (MTB)-specific T and B cells, we found that MTB-specific peptides from early secreted antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10) induced the expression of IL-21 predominantly in CD4⁺ T cells. A fraction of IL-21-expressing CD4⁺ T cells simultaneously expressed Th1 cytokines but did not secrete Th2 or Th17 cytokines, suggesting that MTB-specific IL-21-expressing CD4⁺ T cells were different from Th1, Th2 and Th17 subpopulations. The majority of MTB-specific IL-21-expressing CD4⁺ T cells co-expressed IFN-γ and IL-21⁺IFN-γ⁺CD4⁺ T cells exhibited obviously polyfunctionality. In addition, MTB-specific IL-21-expressing CD4⁺ T cells displayed a CD45RO⁺CD62L^lowCCR7^lowCD40L^highICOS^high phenotype. Bcl-6-expression was significantly higher in IL-21-expressing CD4⁺ T cells than IL-21^-CD4⁺ T cells. Moreover, IL-12 could up-regulate MTB-specific IL-21 expression, especially the frequency of IL-21⁺IFN-γ⁺CD4⁺ T cells. Taken together, our results demonstrated that MTB-specific IL-21⁺IFN-γ⁺CD4⁺ T cells from local sites of tuberculosis (TB) infection could be enhanced by IL-12, which have the features of both Tfh and Th1 cells and may have an important role in local immune responses against TB infection.     

Combined Antigen-Specific Interferon-γ and Interleukin-2 Release Assay (FluoroSpot) for the Diagnosis of Mycobacterium tuberculosis Infection

Background

To evaluate interleukin (IL)-2 and interferon (IFN)-γ secreting T-cells in parallel for the differentiation of latent infection with Mycobacterium tuberculosis infection (LTBI) from active tuberculosis.

Methods

Following ex-vivo stimulation of peripheral blood mononuclear cells (PBMC) with M. tuberculosis-specific antigens early secretory antigenic target (ESAT)-6 and culture filtrate protein (CFP)-10, immune responses were assessed by enzyme-linked immunospot IFN-γ release assay (EliSpot-IGRA) and a novel dual cytokine detecting fluorescence-linked immunospot (FluoroSpot) in 18 patients with pulmonary tuberculosis, 10 persons with previously cured tuberculosis, 25 individuals with LTBI and 16 healthy controls.

Results

Correlation of IFN- γ⁺ spot-forming cells in EliSpot-IGRA and FluoroSpot were R² = 0.67 for ESAT-6 and R² = 0.73 for CFP-10. The number of IL-2^- IFN- γ⁺ producing cells was higher in patients with tuberculosis compared with past tuberculosis (CFP-10-induced p = 0.0068) or individuals with LTBI (ESAT-6-induced p = 0.0136). A cutoff value of >16 CFP-10-induced IFN-γ⁺ secreting cells/200.000 PBMC in the EliSpot-IGRA discriminated with highest sensitivity and specificity (89% and 76%, respectively). However, overlap in cytokine responses precludes distinction between the cohorts on an individual basis.

Conclusions

Combined analysis of IFN-γ and IL-2 secretion by antigen specific T-cells does not allow a reliable differentiation between different states of M. tuberculosis infection in clinical practice.     

A Higher Activation Threshold of Memory CD8+ T Cells Has a Fitness Cost That Is Modified by TCR Affinity during Tuberculosis

T cell vaccines against Mycobacterium tuberculosis (Mtb) and other pathogens are based on the principle that memory T cells rapidly generate effector responses upon challenge, leading to pathogen clearance. Despite eliciting a robust memory CD8⁺ T cell response to the immunodominant Mtb antigen TB10.4 (EsxH), we find the increased frequency of TB10.4-specific CD8⁺ T cells conferred by vaccination to be short-lived after Mtb challenge. To compare memory and naïve CD8⁺ T cell function during their response to Mtb, we track their expansions using TB10.4-specific retrogenic CD8⁺ T cells. We find that the primary (naïve) response outnumbers the secondary (memory) response during Mtb challenge, an effect moderated by increased TCR affinity. To determine whether the expansion of polyclonal memory T cells is restrained following Mtb challenge, we used TCRβ deep sequencing to track TB10.4-specific CD8⁺ T cells after vaccination and subsequent challenge in intact mice. Successful memory T cells, defined by their clonal expansion after Mtb challenge, express similar CDR3β sequences suggesting TCR selection by antigen. Thus, both TCR-dependent and -independent factors affect the fitness of memory CD8⁺ responses. The impaired expansion of the majority of memory T cell clonotypes may explain why some TB vaccines have not provided better protection.     

Immune Responses to ESAT-6 and CFP-10 by FASCIA and Multiplex Technology for Diagnosis of M. tuberculosis Infection; IP-10 Is a Promising Marker

Background

There is a need for reliable markers to diagnose active and latent tuberculosis (TB). The interferon gamma release assays (IGRAs) are compared to the tuberculin skin test (TST) more specific, but cannot discriminate between recent or remote TB infection. Here the Flow-cytometric Assay for Specific Cell-mediated Immune-response in Activated whole blood (FASCIA), which quantifies expanded T-lymphoblasts by flow-cytometric analysis after long-term antigen stimulation of whole blood, is combined with cytokine/chemokine analysis in the supernatant by multiplex technology for diagnosis of Mycobacterium tuberculosis (Mtb) infection.

Methods and Findings

Consecutive patients with suspected TB (n = 85), with microbiologically verified active pulmonary TB (n = 33), extra pulmonary TB (n = 21), clinical TB (n = 11), presumed latent TB infection (LTBI) (n = 23), patients negative for TB (n = 8) and 21 healthy controls were studied. Blood samples were analyzed with FASCIA and multiplex technology to determine and correlate proliferative responses and the value of 14 cytokines for diagnosis of Mtb infection: IFN- γ, IL-2, TNF-α, IP-10, IL-12, IL-6, IL-4, IL-5, IL-13, IL-17, MIP-1β, GM-CSF, IFN-α2 and IL-10. Cytokine levels for IFN-γ, IP-10, MIP-1β, IL-2, TNF-α, IL-6, IL-10, IL-13 and GM-CSF were significantly higher after stimulation with the Mtb specific antigens ESAT-6 and CFP-10 in patients with active TB compared to healthy controls (p<0.05) and correlated with proliferative responses. IP-10 was positive in all patients with verified TB, if using a combination of ESAT-6 and CFP-10 and was the only marker significantly more sensitive in detecting active TB then IFN-γ (p = 0.012). Cytokine responses in patients with active TB were more frequent and detected at higher levels than in patients with LTBI.

Conclusions

IP-10 seems to be an important marker for diagnosis of active and latent TB. Patients with active TB and LTBI responded with similar cytokine profiles against TB antigens but proliferative and cytokine responses were generally higher in patients with active TB.     

Expansion of Pathogen-Specific Mono- and Multifunctional Th1 and Th17 Cells in Multi-Focal Tuberculous Lymphadenitis

Background

Th1 and Th17 responses are known to play an important role in immunity to pulmonary tuberculosis (PTB), although little is known about their role in extrapulmonary forms of tuberculosis (TB).

Methods

To identify the role of Th1, Th17, and Th22 cells in multi-focal TB lymphadenitis (TBL), we examined mycobacteria–specific immune responses in the whole blood of individuals with PTB (n = 20) and compared them with those with TBL (n = 25).

Results

Elevated frequencies of CD4⁺ T cells expressing IFN- γ, TNF-α, and IL-2 were present in individuals with TBL compared with those with PTB at baseline and in response to ESAT-6 and CFP-10. Similarly, increased frequencies of CD4⁺ T cells expressing IL-17A, IL-17F, and IFN-γ were also present in individuals with TBL at baseline and following ESAT-6 and CFP-10 stimulation although no significant difference in frequency of Th22 cells was observed. Finally, frequencies of Th1 (but not Th17) cells exhibited a significantly negative correlation with natural regulatory T cell frequencies at baseline.

Conclusions

Multi-focal TB lymphadenitis is therefore characterized by elevated frequencies of Th1 and Th17 cells, indicating that Th1 and Th17 responses in TB disease are probably correlates of disease severity rather than of protective immunity.     

Hierarchy Low CD4+/CD8+ T-Cell Counts and IFN-γ Responses in HIV-1+ Individuals Correlate with Active TB and/or M.tb Co-Infection

Objective

Detailed studies of correlation between HIV-M.tb co-infection and hierarchy declines of CD8+/CD4+ T-cell counts and IFN-γ responses have not been done. We conducted case-control studies to address this issue.

Methods

164 HIV-1-infected individuals comprised of HIV-1⁺ATB, HIV-1⁺LTB and HIV-1⁺TB^- groups were evaluated. Immune phenotyping and complete blood count (CBC) were employed to measure CD4+ and CD8+ T-cell counts; T.SPOT.TB and intracellular cytokine staining (ICS) were utilized to detect ESAT6, CFP10 or PPD-specific IFN-γ responses.

Results

There were significant differences in median CD4+ T-cell counts between HIV-1⁺ATB (164/μL), HIV-1⁺LTB (447/μL) and HIV-1⁺TB^- (329/μL) groups. Hierarchy low CD4+ T-cell counts (<200/μL, 200-500/μL, >500/μL) were correlated significantly with active TB but not M.tb co-infection. Interestingly, hierarchy low CD8+ T-cell counts were not only associated significantly with active TB but also with M.tb co-infection (P<0.001). Immunologically, HIV-1⁺ATB group showed significantly lower numbers of ESAT-6-/CFP-10-specific IFN-γ+ T cells than HIV-1⁺LTB group. Consistently, PPD-specific IFN-γ+CD4+/CD8+ T effector cells in HIV-1⁺ATB group were significantly lower than those in HIV-1⁺LTB group (P<0.001).

Conclusions

Hierarchy low CD8+ T-cell counts and effector function in HIV-1-infected individuals are correlated with both M.tb co-infection and active TB. Hierarchy low CD4+ T-cell counts and Th1 effector function in HIV-1+ individuals are associated with increased frequencies of active TB, but not M.tb co-infection.     

ESAT-6 Targeting to DEC205+ Antigen Presenting Cells Induces Specific-T Cell Responses against ESAT-6 and Reduces Pulmonary Infection with Virulent Mycobacterium tuberculosis

Airways infection with Mycobacterium tuberculosis (Mtb) is contained mostly by T cell responses, however, Mtb has developed evasion mechanisms which affect antigen presenting cell (APC) maturation/recruitment delaying the onset of Ag-specific T cell responses. Hypothetically, bypassing the natural infection routes by delivering antigens directly to APCs may overcome the pathogen’s naturally evolved evasion mechanisms, thus facilitating the induction of protective immune responses. We generated a murine monoclonal fusion antibody (α-DEC-ESAT) to deliver Early Secretory Antigen Target (ESAT)-6 directly to DEC205⁺ APCs and to assess its in vivo effects on protection associated responses (IFN-γ production, in vivo CTL killing, and pulmonary mycobacterial load). Treatment with α-DEC-ESAT alone induced ESAT-6-specific IFN-γ producing CD4⁺ T cells and prime-boost immunization prior to Mtb infection resulted in early influx (d14 post-infection) and increased IFN-γ⁺ production by specific T cells in the lungs, compared to scarce IFN-γ production in control mice. In vivo CTL killing was quantified in relevant tissues upon transferring target cells loaded with mycobacterial antigens. During infection, α-DEC-ESAT-treated mice showed increased target cell killing in the lungs, where histology revealed cellular infiltrate and considerably reduced bacterial burden. Targeting the mycobacterial antigen ESAT-6 to DEC205⁺ APCs before infection expands specific T cell clones responsible for early T cell responses (IFN-γ production and CTL activity) and substantially reduces lung bacterial burden. Delivering mycobacterial antigens directly to APCs provides a unique approach to study in vivo the role of APCs and specific T cell responses to assess their potential anti-mycobacterial functions.     

Whole-blood flow-cytometric analysis of antigen-specific CD4 T-cell cytokine profiles distinguishes active tuberculosis from non-active states

T-cell based IFN-γ release assays do not permit distinction of active tuberculosis (TB) from successfully treated disease or latent M. tuberculosis infection. We postulated that IFN-γ and IL-2 cytokine profiles of antigen-specific T cells measured by flow-cytometry ex vivo might correlate with TB disease activity in vivo. Tuberculin (PPD), ESAT-6 and CFP-10 were used as stimuli to determine antigen-specific cytokine profiles in CD4 T cells from 24 patients with active TB and 28 patients with successfully treated TB using flow-cytometry. Moreover, 25 individuals with immunity consistent with latent M. tuberculosis infection and BCG-vaccination, respectively, were recruited. Although the frequency of cytokine secreting PPD reactive CD4 T cells was higher in patients with active TB compared to patients with treated TB (median 0.81% vs. 0.39% of CD4 T cells, p?=?0.02), the overlap in frequencies precluded distinction between the groups on an individual basis. When assessing cytokine profiles, PPD specific CD4 T cells secreting both IFN-γ and IL-2 predominated in treated TB, latent infection and BCG-vaccination, whilst in active TB the cytokine profile was shifted towards cells secreting IFN-γ only (p<0.0001). Cytokine profiles of ESAT-6 or CFP-10 reactive CD4 T cells did not differ between the groups. Receiver operator characteristics (ROC) analysis revealed that frequencies of PPD specific IFN-γ/IL-2 dual-positive T cells below 56% were an accurate marker for active TB (specificity 100%, sensitivity 70%) enabling effective discrimination from non-active states. In conclusion, a frequency lower than 56% IFN-γ/IL-2 dual positive PPD-specific circulating CD4 T-cells is strongly indicative of active TB.     

Mycobacterium tuberculosis-specific CD4+, IFNgamma+, and TNFalpha+ multifunctional memory T cells coexpress GM-CSF

Multifunctional T cells expressing several cytokines in parallel are thought to play a crucial role in protection against different infections. To characterize T cell cytokine patterns associated with disease and protection in Mycobacterium tuberculosis infection we determined the expression of IFNγ, IL-2, TNFα, and GM-CSF in T cell subpopulations from children with tuberculosis (TB) and healthy latently M. tuberculosis-infected children (LTBI) after short-term in vitro restimulation. We identified CD4⁺ effector memory T cells (T_EM) as the major source of all measured cytokines after antigen-specific restimulation. T_EM from children with TB expressed higher proportions of IFNγ, TNFα, and IL-2 after Mtb restimulation while no differences were detected for GM-CSF between both study groups. GM-CSF secretion strongly depended on antigen-specific stimulation. Analyses of multiple cytokine patterns revealed that the majority of GM-CSF-positive M. tuberculosis-specific memory T cells coexpressed IFNγ and TNFα therefore showing a characteristic feature of multifunctional T cells. We conclude that children with active TB possess higher proportions of IFNγ-, TNFα-, and/or IL-2-positive T_EM than children with LTBI while GM-CSF coexpression reveals a novel subpopulation within CD4⁺ memory T cells not increased in children with active TB.     

Identification of Mycobacterium tuberculosis-specific Th1, Th17 and Th22 cells using the expression of CD40L in tuberculous pleurisy

Important advances have been made in the immunodiagnosis of tuberculosis (TB) based on the detection of Mycobacterium tuberculosis (MTB)-specific T cells. However, the sensitivity and specificity of the immunological approach are relatively low because there are no specific markers for antigen-specific Th cells, and some of the Th cells that do not produce cytokines can be overlooked using this approach. In this study, we found that MTB-specific peptides of ESAT-6/CFP-10 can stimulate the expression of CD40L specifically in CD4(+) T cells but not other cells from pleural fluid cells (PFCs) in patients with tuberculous pleurisy (TBP). CD4(+)CD40L(+) but not CD4(+)CD40L(-) T cells express IFN-γ, IL-2, TNF-α, IL-17 or IL-22 after stimulation with MTB-specific peptides. In addition, CD4(+)CD40L(+) T cells were found to be mostly polyfunctional T cells that simultaneously produce IFN-γ, IL-2 and TNF-α and display an effector or effector memory phenotype (CD45RA(-)CD45RO(+)CCR7(-)CD62L(-)ICOS(-)). To determine the specificity of CD4(+)CD40L(+) T cells, we incubated PFCs with ESTA-6/CFP-10 peptides and sorted live CD4(+)CD40L(+) and CD4(+)CD40L(-) T cells by flow cytometry. We further demonstrated that sorted CD4(+)CD40L(+), but not CD4(+)CD40L(-) fractions, principally produced IFN-γ, IL-2, TNF-α, IL-17 and IL-22 following restimulation with ESTA-6/CFP-10 peptides. Taken together, our data indicate that the expression of CD40L on MTB-specific CD4(+) T cells could be a good marker for the evaluation and isolation of MTB-specific Th cells and might also be useful in the diagnosis of TB.     

Novel recombinant RD2- and RD11-encoded Mycobacterium tuberculosis antigens are potential candidates for diagnosis of tuberculosis infections in BCG-vaccinated individuals

Proteins encoded by region of deletions (RD) of Mycobacterium tuberculosis are useful in development of vaccines and diagnostic reagents. In the present study, six M. tuberculosis genes from RD2 and RD11, rv1978, nrdf1, mpt64, cfp-21, ppe57 and ppe59, were cloned and overexpressed in Escherichia coli. All six purified recombinant proteins could distinguish tuberculosis (TB) patients and latent TB infected subjects (LTBI), or called subclinical TB infection, from BCG-vaccinated healthy controls by T-cell IFN-γ releasing ELISPOT. ELISPOT of Rv1978, NrdF1, Mpt64, CFP-21, Ppe57 and Ppe59 achieved sensitivities of 59%, 60%, 82%, 48%, 59% and 47% respectively in the detection of active TB and specificities of 94%, 90%, 76%, 93%, 100% and 93% respectively in BCG-vaccinated healthy controls. Combination of Ppe57 or NrdF1 with early secreted antigen target 6 (ESAT-6) or 10-kDa culture filtrate protein (CFP-10) in the IFN-γ releasing ESLIPOT assay could increase the sensitivities in detecting active TB, for ESAT-6 from 82.1% to 85.7% or 92.9% (P = 0.5 or 0.03, respectively) and for CFP-10 from 67.9% to 78.6% or 83.9%, respectively (both P < 0.05). The high sensitivities, specificities and promising antigenic combination of NrdF1 and Ppe57 in detection of TB in BCG-vaccinated controls suggest their potential application in TB diagnosis.     

Signal Regulatory Protein α (SIRPα)+ Cells in the Adaptive Response to ESAT-6/CFP-10 Protein of Tuberculous Mycobacteria

Background

Early secretory antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10) are co-secreted proteins of Mycobacterium tuberculosis complex mycobacteria (includes M. bovis, the zoonotic agent of bovine tuberculosis) involved in phagolysosome escape of the bacillus and, potentially, in the efficient induction of granulomas. Upon tuberculosis infection, multi-nucleate giant cells are elicited, likely as a response aimed at containing mycobacteria. In tissue culture models, signal regulatory protein (SIRP)α (also referred to as macrophage fusion receptor or CD172a) is essential for multi-nucleate giant cell formation.

Methodology/Principal Findings

In the present study, ESAT-6/CFP-10 complex and SIRPα interactions were evaluated with samples obtained from calves experimentally infected with M. bovis. Peripheral blood CD172a⁺ (SIRPα-expressing) cells from M. bovis-infected calves proliferated upon in vitro stimulation with ESAT-6/CFP-10 (either as a fusion protein or a peptide cocktail), but not with cells from animals receiving M. bovis strains lacking ESAT-6/CFP-10 (i.e, M. bovis BCG or M. bovis ΔRD1). Sorted CD172a⁺ cells from these cultures had a dendritic cell/macrophage morphology, bound fluorescently-tagged rESAT-6:CFP-10, bound and phagocytosed live M. bovis BCG, and co-expressed CD11c, DEC-205, CD44, MHC II, CD80/86 (a subset also co-expressed CD11b or CD8α). Intradermal administration of rESAT-6:CFP-10 into tuberculous calves elicited a delayed type hypersensitive response consisting of CD11c⁺, CD172a⁺, and CD3⁺ cells, including CD172a-expressing multi-nucleated giant cells.

Conclusions/Significance

These findings demonstrate the ability of ESAT-6/CFP-10 to specifically expand CD172a⁺ cells, bind to CD172a⁺ cells, and induce multi-nucleated giant cells expressing CD172a.     

Monokine induced by interferon gamma and IFN-gamma response to a fusion protein of Mycobacterium tuberculosis ESAT-6 and CFP-10 in Brazilian tuberculosis patients

IFN-gamma responses to Mycobacterium tuberculosis antigens ESAT-6 and CFP-10 have been proposed as specific markers of M. tuberculosis infection. Monokine induced by gamma interferon (MIG/CXCL9) has been shown to be expressed by IFN-gamma stimulated mononuclear cells and to attract activated T-cells through the chemokine receptor CXCR3. Since MIG is induced early in the response to IFN-gamma, measuring MIG may provide an interesting marker to assess downstream IFN-gamma induced responses, in contrast to assays that mainly focus on quantifying production of IFN-gamma per se. We, therefore, investigated MIG and IFN-gamma responses to a fusion protein of ESAT-6 and CFP-10, and compared responses to the conserved mycobacterial antigen 85B (Ag85B) and purified protein derivative (PPD) of M. tuberculosis, in 29 BCG vaccine controls and 24 TB patients. IFN-gamma secreting cells were determined by ELISPOT, and MIG production was measured by ELISA and flow cytometry. Production of MIG in response to ESAT-6/CFP-10, Ag85B and PPD correlated overall with increased numbers of IFN-gamma secreting cells (r=0.55, P<0.0001). A significant increase was noted among patients compared to controls in the secretion of IFN-gamma and MIG following stimulation with ESAT-6/CFP-10 or PPD (P<0.05). Moreover, MIG intracellular expression was higher in TB patients compared to BCG vaccines (P<0.05) in response to ESAT-6/CFP-10 or PPD. We conclude that MIG production correlates significantly with enhanced T-cell IFN-gamma production induced by M. tuberculosis-specific antigens ESAT-6/CFP-10. These results point to MIG as a potential novel biomarker that may be helpful in assessing downstream responses induced by IFN-gamma in TB.     

Potential Role of M. tuberculosis Specific IFN-γ and IL-2 ELISPOT Assays in Discriminating Children with Active or Latent Tuberculosis

Background

Although currently available IGRA have been reported to be promising markers for TB infection, they cannot distinguish active tuberculosis (TB) from latent infection (LTBI).

Objective

Children with LTBI, active TB disease or uninfected were prospectively evaluated by an in-house ELISPOT assay in order to investigate possible immunological markers for a differential diagnosis between LTBI and active TB.

Methods

Children at risk for TB infection prospectively enrolled in our infectious disease unit were evaluated by in-house IFN-γ and IL-2 based ELISPOT assays using a panel of Mycobacterium tuberculosis antigens.

Results

Twenty-nine children were classified as uninfected, 21 as LTBI and 25 as active TB cases (including 5 definite and 20 probable cases). Significantly higher IFN-γ ELISPOT responses were observed in infected vs. uninfected children for ESAT-6 (p<0.0001), CFP-10 (p<0.0001), TB 10.3 (p = 0.003), and AlaDH (p = 0.001), while differences were not significant considering Ag85B (p = 0.063), PstS1 (p = 0.512), and HspX (16 kDa) (p = 0.139). IL-2 ELISPOT assay responses were different for ESAT-6 (p<0.0001), CFP-10 (p<0.0001), TB 10.3 (p<0.0001), HspX (16 kDa) (p<0.0001), PstS1 (p<0.0001) and AlaDH (p = 0.001); but not for Ag85B (p = 0.063). Comparing results between children with LTBI and those with TB disease differences were significant for IFN-γ ELISPOT only for AlaDH antigen (p = 0.021) and for IL-2 ELISPOT assay for AlaDH (p<0.0001) and TB 10.3 antigen (p = 0.043). ROC analyses demonstrated sensitivity of 100% and specificity of 81% of AlaDH-IL-2 ELISPOT assay in discriminating between latent and active TB using a cut off of 12.5 SCF per million PBMCs.

Conclusion

Our data suggest that IL-2 based ELISPOT with AlaDH antigen may be of help in discriminating children with active from those with latent TB.     

Functional capacity of Mycobacterium tuberculosis-specific T cell responses in humans is associated with mycobacterial load

High Ag load in chronic viral infections has been associated with impairment of Ag-specific T cell responses; however, the relationship between Ag load in chronic Mycobacterium tuberculosis infection and functional capacity of M. tuberculosis-specific T cells in humans is not clear. We compared M. tuberculosis-specific T cell-associated cytokine production and proliferative capacity in peripheral blood from adults with progressively higher mycobacterial loads-that is, persons with latent M. tuberculosis infection (LTBI), with smear-negative pulmonary tuberculosis (TB), and smear-positive TB. Patients with smear-positive TB had decreased polyfunctional IFN-γ(+)IL-2(+)TNF-α(+) and IL-2-producing specific CD4 T cells and increased TNF-α single-positive cells, when compared with smear-negative TB and LTBI. TB patients also had increased frequencies of M. tuberculosis-specific CD8 T cells, compared with LTBI. M. tuberculosis-specific CD4 and CD8 T cell proliferative capacity was profoundly impaired in individuals with smear-positive TB, and correlated positively with ex vivo IFN-γ(+)IL-2(+)TNF-α(+) CD4 T cells, and inversely with TNF-α single-positive CD4 T cells. During 6 mo of anti-TB treatment, specific IFN-γ(+)IL-2(+)TNF-α(+) CD4 and CD8 T cells increased, whereas TNF-α and IFN-γ single-positive T cells decreased. These results suggest progressive impairment of M. tuberculosis-specific T cell responses with increasing mycobacterial load and recovery of responses during therapy. Furthermore, these data provide a link between specific cytokine-producing subsets and functional capacity of M. tuberculosis-specific T cells, and between the presence of specific CD8 T cells ex vivo and active TB disease. These data have potentially significant applications for the diagnosis of TB and for the identification of T cell correlates of TB disease progression.     

Interferon gamma response to combinations 38 kDa/CFP-10, 38 kDa/MPT-64, ESAT-6/MPT-64 and ESAT-6/CFP-10, each related to a single recombinant protein of Mycobacterium tuberculosis in individuals from tuberculosis endemic areas

Several antigens of Mycobacterium tuberculosis have been identified and specificity to one or multiple antigens could determine the distinction between protective and pathogenic host reaction. Therefore T cell immune response to combinations 38 kDa/CFP-10, 38 kDa/MPT-64, ESAT-6/MPT-64 and ESAT-6/CFP-10 (each related to a single protein of Mycobacterium tuberculosis) in individuals from tuberculosis endemic areas have been examined. ELISA was used to detect IFN-gamma production in PBMC priming with single proteins and combinations in a panel of 105 individuals: 38 tuberculosis patients (6 untreated and 32 treated) and 67 healthy controls with tuberculin skin test positive or negative (TST). Brazilian TB patients highly recognized ESAT-6 (66%), but combinations improved response in the following order: ESAT-6/MPT-64 (89%) > ESAT-6/CFP-10 (73%) > 38 kDa/CFP-10 (70%), the last combination showing the highest specificity (TST(/) = 42% and TST(-) = 83%). Average IFN-gamma production in TB patients was signifi-cantly higher for 38 kDa/CFP-10 (P = 0.012) and 38 kDa/MPT-64 (P <0.035), when compared to single antigens. None of the combinations was able to discriminate TB patients from TST(+) controls; however, 38 kDa/CFP-10 displayed a borderline significance (P = 0.053). Similar to the ESAT-6/CFP-10 combination, IFN-gamma response to 38 kDa/CFP-10 showed an increased tendency in treated patients, although not signifi-cant (P = 0.16). We demonstrated for the first time that 38 kDa/CFP-10 had prediction sensitivity for TB patients similar to the ESAT-6/CFP-10 combination and also significant response improvement related to the single proteins with more selective reactivity among TST-positive individuals, which could be of potential interest for diagnostic evaluation for tuberculosis infection.