Key Role of Effector Memory CD4⁺T Lymphocytes in a Short-Incubation Heparin-Binding Hemagglutinin Gamma Interferon Release Assay for the Detection of Latent Tuberculosis

Abstract

The treatment of latent tuberculosis infection (LTBI) in target populations is one of the current WHO strategies for preventing active tuberculosis (TB) infection and reducing theT he screening and treatment for LTBI in target populations in order to prevent TB and reduce the Mycobacterium tuberculosis reservoir are some of the main strategies of the WHO's Global Plan to Stop TB (http://www.who.int/tb/publications/global _report/en). However, a major obstacle to the instauration and effectiveness of these preventive measures resides in the lack of a gold standard LTBI screening tool.For several decades, the tuberculin skin test (TST) has been the main screening test for LTBI despite its lack of both sensitivity and specificity (1). Subsequently, T-cell-based gamma interferon release assays (IGRAs) in response to antigens encoded in the M. tuberculosis genomic region of difference 1 (RD-1) and RD-11 were developed and commercialized (QuantiFERON-TB Gold In-Tube [QFT-GIT] and T-SPOT.TB tests), with the objective of offering a more powerful diagnostic tool for LTBI. These tests offer a higher specificity than TST particularly in countries with high Mycobacterium bovis BCG vaccination coverage (2). However, recent studies suggest that these short-incubation RD-1-based IGRAs may have suboptimal sensitivities (3, 4).An alternative IGRA in response to the native mycobacterial antigen heparin-binding hemagglutinin (nHBHA-IGRA) that uses a longer incubation time than the commercialized IGRA has been validated in immunocompetent adults in the screening for LTBI (5). This assay not only demonstrates a high sensitivity and specificity for LTBI diagnosis but also a capacity to detect remote M. tuberculosis infections, a substantial advantage over the commercialized IGRAs (5-7).Remote M. tuberculosis infections are generally believed to be identified through central memory T-cell (Tcm) responses detected with long-incubation IGRAs (3, 4). Here, however, we demonstrate that both recent and remote M. tuberculosis infections can be identified through effector memory T-cell (Tem) responses using a short-incubation nHBHA-IGRA, the upgraded assay presented in this study. Our results suggest that the detection of IFN-␥-producing CD4 ϩ Tem in response to nHBHA reflects the persistence of M. tuberculosis antigens and therefore a true state of latency.(These results were presented in part at the European Congress of Immunology, Glasgow, Scotland, 5 to 8 September 2012, and at the MycoClub,

Immunological Signatures Identifying Different Stages of Latent Mycobacterium tuberculosis Infection and Discriminating Latent from Active Tuberculosis in Humans

“…In vitro stimulation of the PBMC with HBHA induced higher frequencies of IFN-γ-containing CD4 + T lymphocytes in infected compared to non-infected subjects ( Figure 2A). The frequencies were slightly lower for TB patients than for LTBI subjects, in agreement with previous results obtained with HBHA-IGRA [12,13]. Higher frequencies of HBHA-induced TNF-α-containing-CD4 + lymphocytes were also noted in infected compared to non-infected subjects (p<0.001 and p<0.01 for LTBI and TB, respectively), whereas no differences between the groups were observed for the HBHA-induced IL-2-containing CD4 + lymphocytes (Figure 2A).…”

“…Dormancy of the bacteria is associated with the expression of latency antigens, such as HBHA. The effector memory phenotype of the HBHA-induced IFN-γ-producing CD4 + T cells reported previously strongly suggests that this immune response reflects the persistence of M. tuberculosis antigens [13]. We rule out that the HBHA-induced immune responses described here in the QFT -LTBI subjects may have resulted from a previous BCG vaccination that was reported in most LTBI subjects included in this study.…”

“…We rule out that the HBHA-induced immune responses described here in the QFT -LTBI subjects may have resulted from a previous BCG vaccination that was reported in most LTBI subjects included in this study. Several previous studies have indicated that HBHA-IGRA results are not influenced by BCG vaccination in infancy in TST + LTBI adult subjects and can therefore be used to detect LTBI subjects regardless of their BCG vaccination status [12,13]. In this study we therefore identified LTBI by TST, using very strict criteria for their classification as LTBI, with a minimum induration size of 15 mm, knowing that more than 10 years after a BCG vaccination, this size is very unlikely the result of a vaccine-induced response only.…”

“…The identification of these different LTBI subgroups is important, as it may help to target preventive therapy only to those subjects that have the highest risk to reactivate their infection [4,5]. We have previously reported that, in contrast to TST and the commercialized IGRA (QuantiFERON-TB Gold In-Tube assay or QFT -GIT and T-SPOT.TB), the IFN-γ response to the mycobacterial latency antigen heparin-binding haemagglutinin (HBHA) provides good discrimination between subjects with LTBI and patients with active TB [12,13]. We have further proposed a risk stratification of subjects with LTBI based on the combination of IFN-γ responses to HBHA and to the Early-Secreted Antigen Target-6 (ESAT-6) [14].…”

Two-Year Follow-up Study of Mycobacterium tuberculosis Antigen-Driven IFN-γ Responses and Macrophage sCD14 Levels After Tuberculosis Contact

“…Currently, the diagnosis of LTBI relies on specific M.tb antigen-driven IFN-c responses measured in IGRA assays and flow cytometry assays of M.tb antigen driven effector T cell responses [5,15]. In our longitudinal study, we assessed IFN-c responses to specific M.tb antigens (ESAT-6, CFP-10, TB7.7) using QFT, in 60 healthy Polish volunteers with recent domestic or long lasting occupational TB contact and those not exposed to infectious TB.…”