Kerry A. Millington

Dynamic relationship between IFN-gamma and IL-2 profile of Mycobacterium tuberculosis-specific T cells and antigen load

Distinct IFN-γ and IL-2 profiles of Ag-specific CD4+ T cells have recently been associated with different clinical disease states and Ag loads in viral infections. We assessed the kinetics and functional profile of Mycobacterium tuberculosis Ag-specific T cells secreting IFN-γ and IL-2 in 23 patients with untreated active tuberculosis when bacterial and Ag loads are high and after curative treatment, when Ag load is reduced. The frequencies of M. tuberculosis Ag-specific IFN-γ-secreting T cells declined during 28 mo of follow-up with an average percentage decline of 5.8% per year (p = 0.005), while the frequencies of Ag-specific IL-2-secreting T cells increased during treatment (p = 0.02). These contrasting dynamics for the two cytokines led to a progressive convergence of the frequencies of IFN-γ- and IL-2-secreting cells over 28 mo. Simultaneous measurement of IFN-γ and IL-2 secretion at the single-cell level revealed a codominance of IFN-γ-only secreting and IFN-γ/IL-2 dual secreting CD4+ T cells in active disease that shifted to dominance of IFN-γ/IL-2-secreting CD4+ T cells and newly detectable IL-2-only secreting CD4+ T cells during and after treatment. These distinct T cell functional signatures before and after treatment suggest a novel immunological marker of mycobacterial load and clinical status in tuberculosis that now requires validation in larger prospective studies.

Screening for tuberculosis infection prior to initiation of anti-TNF therapy

T-cell interferon-gamma release assays (IGRAs) are more specific and probably more sensitive than the tuberculin skin test (TST) for the diagnosis of latent tuberculosis infection (LTBI). Patients with immune-mediated inflammatory diseases (IMID) and suspected LTBI who are candidates for anti-TNF therapy are at a significant risk of TB reactivation yet are prone to false-negative TST results because they are already on immunosuppressive medications. The role of these new blood tests in this patient population is therefore of considerable interest but is currently unclear. The limited published evidence-base shows that agreement between IGRA and TST results is poor in patients with IMID compared to patients without IMID, due to lower proportions of TST-positive results in patients with IMID. Discordant TST-positive, IGRA-negative results are associated with prior BCG vaccination and discordant TST-negative, IGRA-positive results are associated with steroid therapy. Notably, positive IGRA results are more closely associated with the presence of risk factors for LTBI than TST. The percentage of indeterminate IGRAs can be up to 12%. IGRA results in patients already taking anti-TNF agents currently remain uninterpretable. Given the clinical imperative to prevent reactivation of TB in patients starting anti-TNF therapy, screening algorithms should maximise diagnostic sensitivity for detection of LTBI. Therefore, a positive result to either an IGRA or TST, in addition to currently recommended clinical screening for risk factors for LTBI, should prompt consideration of preventive treatment of LTBI in this population.

Enumeration of functional T-cell subsets by fluorescence-immunospot defines signatures of pathogen burden in tuberculosis.

Background IFN-γ and IL-2 cytokine-profiles define three functional T-cell subsets which may correlate with pathogen load in chronic intracellular infections. We therefore investigated the feasibility of the immunospot platform to rapidly enumerate T-cell subsets by single-cell IFN-γ/IL-2 cytokine-profiling and establish whether immunospot-based T-cell signatures distinguish different clinical stages of human tuberculosis infection. Methods We used fluorophore-labelled anti-IFN-γ and anti-IL-2 antibodies with digital overlay of spatially-mapped colour-filtered images to enumerate dual and single cytokine-secreting M. tuberculosis antigen-specific T-cells in tuberculosis patients and in latent tuberculosis infection (LTBI). We validated results against established measures of cytokine-secreting T-cells. Results Fluorescence-immunospot correlated closely with single-cytokine enzyme-linked-immunospot for IFN-γ-secreting T-cells and IL-2-secreting T-cells and flow-cytometry-based detection of dual IFN-γ/IL-2-secreting T-cells. The untreated tuberculosis signature was dominated by IFN-γ-only-secreting T-cells which shifted consistently in longitudinally-followed patients during treatment to a signature dominated by dual IFN-γ/IL-2-secreting T-cells in treated patients. The LTBI signature differed from active tuberculosis, with higher proportions of IL-2-only and IFN-γ/IL-2-secreting T-cells and lower proportions of IFN-γ-only-secreting T-cells. Conclusions Fluorescence-immunospot is a quantitative, accurate measure of functional T-cell subsets; identification of cytokine-signatures of pathogen burden, distinct clinical stages of M. tuberculosis infection and long-term immune containment suggests application for treatment monitoring and vaccine evaluation.

T Cells and Tuberculosis: Beyond Interferon-γ

The cytokine interferon-y (IFN-y) plays a pivotal role in protective immunity against intracellular pathogens. Specifically, in Mycobacterium tuberculosis (MTB) infection, IFN-y is an important mediator of macrophage activation [ 1 ] . Mice deficient in the gene for IFN-y are susceptible to fatal tuberculosis (TB) [1, 2], and humans deficient in either the gene for IFN-y or the IFN-y receptor show enhanced susceptibility to mycobacterial infections [3]. Measurement of the IFN-y response to MTB infection has been exploited in research and in clinics, to evaluate and develop new tools for the prevention, diagnosis, and treatment of infection. For example, the development of standardized quantitative ex vivo assays of T cell function, along with the discovery of antigens that are highly specific for MTB, led us [4, 5] and other investigators [6] to develop new diagnostic tools for the detection of MTB infection. These T cell IFN-y release

Mycobacterium tuberculosis-specific cellular immune profiles suggest bacillary persistence decades after spontaneous cure in untreated tuberculosis

Individuals with self-healed tuberculosis from the preantibiotic era offer a unique insight into the natural history of and protective immunity to tuberculosis. In 27 such persons whose tuberculosis self-healed >50 years earlier, circulating Mycobacterium tuberculosis antigen-specific interferon γ (IFN-γ)- and interleukin 2 (IL-2)-secreting T cells were detected ex vivo in 16 and 19 individuals, respectively. The M. tuberculosis-specific T cell cytokine profile was dominated by effector memory T cells that secrete both IFN-γ and IL-2 and included T cells that secrete only IFN-γ or IL-2, suggesting persistence of antigen secreted by viable bacilli. Of 10 individuals with no M. tuberculosis antigen-specific IFN-γ-secreting T cells detectable ex vivo, 7 had evidence of central memory T cells, consistent with clearance of infection.

A Molecular Assay for Sensitive Detection of Pathogen- Specific T-Cells

Here we describe the development and validation of a highly sensitive assay of antigen-specific IFN-γ production using real time quantitative PCR (qPCR) for two reporters - monokine-induced by IFN-γ (MIG) and the IFN-γ inducible protein-10 (IP10). We developed and validated the assay and applied it to the detection of CMV, HIV and Mycobacterium tuberculosis (MTB) specific responses, in a cohort of HIV co-infected patients. We compared the sensitivity of this assay to that of the ex vivo RD1 (ESAT-6 and CFP-10)-specific IFN-γ Elispot assay. We observed a clear quantitative correlation between the two assays (P<0.001). Our assay proved to be a sensitive assay for the detection of MTB-specific T cells, could be performed on whole blood samples of fingerprick (50 uL) volumes, and was not affected by HIV-mediated immunosuppression. This assay platform is potentially of utility in diagnosis of infection in this and other clinical settings.

Use of T Cell-Based Diagnosis of Tuberculosis Infection to Optimize Interpretation of Tuberculin Skin Testing for Child Tuberculosis Contacts

BACKGROUNDnTreatment of recent tuberculosis infection in children aged <2 years is essential, because of high risk of progression to disease, but diagnosis is hindered by the inaccuracy of the tuberculin skin test (TST). More-accurate T cell-based tests of infection could enhance diagnosis by optimizing interpretation of the TST results.nnnMETHODSnA total of 979 child tuberculosis contacts in Istanbul underwent the TST and enzyme-linked immunospot assay. Using enzyme-linked immunospot test results as a reference standard, we assessed the effect of age and bacille Calmette-Guérin (BCG) vaccination on the sensitivity and specificity of the TST, and we computed the optimal TST cutoff points, using receiver operating characteristic curves.nnnRESULTSnWith a TST cutoff point of >or=10 mm, the sensitivity of the TST was 66% for children aged <2 years, which was lower than that for older children (P= .006). Specificity was 75% for BCG-vaccinated children, compared with 92% for unvaccinated children (P= .001). Optimal cutoff points improved TST specificity for children with 1 BCG scar, with little loss of sensitivity. Despite the use of optimal cutoff points, TST sensitivity remained <70% for children aged <2 years, specificity remained <87% for BCG-vaccinated children aged >or=2 years, and overall accuracy was low for children with >1 BCG scar.nnnCONCLUSIONSnNegative results of the TST cannot exclude tuberculosis infection for child tuberculosis contacts aged <2 years, which supports the use of preventive therapy regardless of the TST results for this age group. In children aged >or=2 years, the accuracy of the TST can be improved by adjustment of cutoff points for BCG-vaccinated children but remains poor for children with >1 BCG scar. This methodology can define optimal TST cutoff points for diagnosis of tuberculosis infection tailored to target populations.

Novel M tuberculosis Antigen-Specific T-Cells Are Early Markers of Infection and Disease Progression

Background Mycobacterium tuberculosis Region-of-Difference-1 gene products present opportunities for specific diagnosis of M. tuberculosis infection, yet immune responses to only two gene-products, Early Secretory Antigenic Target-6 (ESAT-6) and Culture Filtrate Protein-10 (CFP-10), have been comprehensively investigated. Methods T-cell responses to Rv3873, Rv3878 and Rv3879c were quantified by IFN-γ-enzyme-linked-immunospot (ELISpot) in 846 children with recent household tuberculosis exposure and correlated with kinetics of tuberculin skin test (TST) and ESAT-6/CFP-10-ELISpot conversion over six months and clinical outcome over two years. Results Responses to Rv3873, Rv3878, and Rv3879c were present in 20–25% of contacts at enrolment. Rv3873 and Rv3879c responses were associated with and preceded TST conversion (Pu200a=u200a0.02 and Pu200a=u200a0.04 respectively), identifying these antigens as early targets of cell-mediated immunity following M. tuberculosis exposure. Responses to Rv3873 were additionally associated with subsequent ESAT-6/CFP-10-ELISpot conversion (Pu200a=u200a0.04). Responses to Rv3873 and Rv3878 predicted progression to active disease (adjusted incidence rate ratio [95% CI] 3.06 [1.05,8.95; Pu200a=u200a0.04], and 3.32 [1.14,9.71; Pu200a=u200a0.03], respectively). Presence of a BCG-vaccination scar was associated with a 67% (Pu200a=u200a0.03) relative risk reduction for progression to active tuberculosis. Conclusions These RD1-derived antigens are early targets of cellular immunity following tuberculosis exposure and T-cells specific for these antigens predict progression to active tuberculosis suggesting diagnostic and prognostic utility.

Diagnosis of occult tuberculosis in hematological malignancy by enumeration of antigen-specific T cells.

Diagnosis of occult tuberculosis in hematological malignancy by enumeration of antigen-specific T cells