HBHA-Induced Polycytotoxic CD4+ T Lymphocytes Are Associated with the Control of Mycobacterium tuberculosis Infection in Humans.

Heparin-binding hemagglutinin (HBHA), a surface protein of Mycobacterium tuberculosis, is an attractive vaccine candidate and marker of protective immunity against tuberculosis, although the mechanisms underlying this protective immunity are not fully understood. Comparisons of the immune responses of latently M. tuberculosis-infected (LTBI) subjects to those of patients with active tuberculosis (aTB) may help to identify surrogate markers of protection, as LTBI subjects are most often lifelong protected against the disease. HBHA was shown to induce strong Th1 responses and cytotoxic CD8+ responses in LTBI subjects, but additional mechanisms of control of M. tuberculosis infection remain to be identified. In this study, using HBHA-induced blast formation as a readout of specific T lymphocyte activation, we report the presence in M. tuberculosis-infected subjects of HBHA-induced CD4+ T cell blasts that degranulate, as measured by surface capture of CD107a. This suggests the induction by HBHA of a CD4+ T cell subset with cytolytic function, and as nearly half of these cells also contained IFN-γ, they had both Th1 and cytotoxic characteristics. We further identified a CD4+ T lymphocyte subset producing IFN-γ together with a combination of mediators of cytotoxicity, i.e., perforin, granzymes, and granulysin, and we called them polycytotoxic CD4+ T lymphocytes. Interestingly, whereas purified protein derivative induced such cells in both LTBI subjects and patients with aTB, HBHA-specific polycytotoxic CD4+ T lymphocytes were detected in LTBI subjects and not in patients with pulmonary aTB. To our knowledge, we thus identified a new HBHA-induced CD4+ T cell subset that may contribute to the control of M. tuberculosis infection.

Identification of Mycobacterium tuberculosis Infection in Infants and Children With Partial Discrimination Between Active Disease and Asymptomatic Infection.

Background: Improved diagnostic tests are needed for the early identification of Mycobacterium tuberculosis-infected young children exposed to an active TB (aTB) index case. We aimed to compare the diagnostic accuracy of new blood-based tests to that of the tuberculin skin test (TST) for the identification of all infected children and for a potential differentiation between aTB and latent TB infection (LTBI). Methods: 144 children exposed to a patient with aTB were included, and those who met all inclusion criteria (130/144) were classified in three groups based on results from classical investigations: non-infected (NI: n = 69, 53%, median age 10 months), LTBI (n = 28, 22%, median age 96 months), aTB disease (n = 33, 25%, median age 24 months). The first whole blood assay consisted of a 7-days in vitro stimulation of blood with four different mycobacterial antigens (40 µl/condition), followed by flow cytometric measurement of the proportions of blast cells appearing among lymphocytes as a result of their specific activation. Thresholds of positivity were determined by Receiver Operating Characteristic (ROC) curve analysis (results of NI children vs. children with LTBI/aTB) in order to identify infected children in a first stage. Other cut-offs were determined to discriminate subgroups of infected children in a second step (results from children with aTB/LTBI). Analysis of blood monocytes and dendritic cell subsets was performed on 100 µl of blood for 25 of these children as a second test in a pilot study. Results: Combining the results of the blast-induced CD3+ T lymphocytes by Heparin-Binding Haemagglutinin and by Culture Filtrate Protein-10 identified all but one infected children (sensitivity 98.2% and specificity 86.9%, compared to 93.4 and 100% for the TST). Further identification among infected children of those with aTB was best achieved by the results of blast-induced CD8+ T lymphocytes by purified protein derivative (sensitivity for localized aTB: 61.9%, specificity 96.3%), whereas high proportions of blood type 2 myeloid dendritic cells (mDC) were a hallmark of LTBI. Conclusions: New blood-based tests requiring a very small volume allow the accurate identification of M. tuberculosis-infected young children among exposed children and are promising to guide the clinical classification of children with aTB or LTBI.

Age-Stratified T Cell Responses in Children Infected with Mycobacterium tuberculosis.

Tuberculosis (TB) in young children differs from adult TB in that the risk of rapid progression to active TB (aTB) is higher in children than in adults. The reasons for this increased risk are not fully understood. Early differentiation remains difficult between children at risk to develop aTB from those who will remain healthy and develop a latent TB infection (LTBI). Biomarkers to differentiate aTB from LTBI in children, especially in very young children, are urgently needed. To identify M. tuberculosis-specific functional T cell subsets related to clinical manifestations in children, we enrolled 87 children exposed to M. tuberculosis. After standard clinical assessment, the children were classified as aTB, LTBI, or uninfected. Their CD4+ T cell cytokine profiles (IFN-γ, TNF-α, IL-2, IL-17) were analyzed at the single-cell level by flow cytometry after stimulation with three mycobacterial antigens, purified protein derivative (PPD), early-secreted-antigenic target-6 (ESAT-6), or heparin-binding hemagglutinin (HBHA). This approach identified age-related discriminative markers between aTB and LTBI. Whereas among the 3- to 15-year-old children, an excellent discrimination between aTB and LTBI was provided by comparing the ratio between the proportions of ESAT-6-induced IFN-γsingle+ and ESAT-6-induced TNF-αsingle+CD4+ T lymphocytes, this was not the case for children younger than 3 years. By contrast, in this group (<3years), the analysis of HBHA-induced IL-17single+CD4+ T lymphocytes allowed us to identify children with LTBI by the high proportion of this cellular lymphocyte subset, whereas this was not the case for children with aTB. The analysis at the single-cell level of T cell immune responses induced by mycobacterial antigens are, thus, different in infected children younger or older than 3 years of age. HBHA-induced IL-17 production by CD4+ T lymphocytes was associated with protection only in children under 3 years who are at high risk for rapid progression to aTB. This suggests that the HBHA-induced IL-17 production by CD4+ T lymphocytes is a potential new correlate of protection against M. tuberculosis in humans, and that the distinction between children with LTBI and those with aTB is possible based on age-related diagnostic markers.

Identification of pertussis-specific effector memory T cells in preschool children.

Whooping cough remains a problem despite vaccination, and worldwide resurgence of pertussis is evident. Since cellular immunity plays a role in long-term protection against pertussis, we studied pertussis-specific T-cell responses. Around the time of the preschool acellular pertussis (aP) booster dose at 4 years of age, T-cell memory responses were compared in children who were primed during infancy with either a whole-cell pertussis (wP) or an aP vaccine. Peripheral blood mononuclear cells (PBMCs) were isolated and stimulated with pertussis vaccine antigens for 5 days. T cells were characterized by flow-based analysis of carboxyfluorescein succinimidyl ester (CFSE) dilution and CD4, CD3, CD45RA, CCR7, gamma interferon (IFN-γ), and tumor necrosis factor alpha (TNF-α) expression. Before the aP preschool booster vaccination, both the proliferated pertussis toxin (PT)-specific CD4(+) and CD8(+) T-cell fractions (CFSE(dim)) were higher in aP- than in wP-primed children. Post-booster vaccination, more pertussis-specific CD4(+) effector memory cells (CD45RA(-) CCR7(-)) were induced in aP-primed children than in those primed with wP. The booster vaccination did not appear to significantly affect the T-cell memory subsets and functionality in aP-primed or wP-primed children. Although the percentages of Th1 cytokine-producing cells were alike in aP- and wP-primed children pre-booster vaccination, aP-primed children produced more Th1 cytokines due to higher numbers of proliferated pertussis-specific effector memory cells. At present, infant vaccinations with four aP vaccines in the first year of life result in pertussis-specific CD4(+) and CD8(+) effector memory T-cell responses that persist in children until 4 years of age and are higher than those in wP-primed children. The booster at 4 years of age is therefore questionable; this may be postponed to 6 years of age.

Toward Understanding the Essence of Post-Translational Modifications for the Mycobacterium tuberculosis Immunoproteome.

CD4(+) T cells are prominent effector cells in controlling Mycobacterium tuberculosis (Mtb) infection but may also contribute to immunopathology. Studies probing the CD4(+) T cell response from individuals latently infected with Mtb or patients with active tuberculosis using either small or proteome-wide antigen screens so far revealed a multi-antigenic, yet mostly invariable repertoire of immunogenic Mtb proteins. Recent developments in mass spectrometry-based proteomics have highlighted the occurrence of numerous types of post-translational modifications (PTMs) in proteomes of prokaryotes, including Mtb. The well-known PTMs in Mtb are glycosylation, lipidation, or phosphorylation, known regulators of protein function or compartmentalization. Other PTMs include methylation, acetylation, and pupylation, involved in protein stability. While all PTMs add variability to the Mtb proteome, relatively little is understood about their role in the anti-Mtb immune responses. Here, we review Mtb protein PTMs and methods to assess their role in protective immunity against Mtb.