Enumeration of T cells specific for RD1-encoded antigens suggests a high prevalence of latent Mycobacterium tuberculosis infection in healthy urban Indians

Cracking the antigenic code of mycobacteria: CFP-10/ESAT-6 tuberculosis skin test and misleading results

There are different tuberculosis diagnostic tools available that detect an antigen-specific immune response. The present study aims to evaluate the potential of cross-reactive responses of a CFP-10 and ESAT-6 antigen-based TB test using bioinformatics tools. The study found that the presence of the sequences coding for the CFP-10 and ESAT-6 antigens in mycobacterial genomes is not associated with their pathogenicity, and not even consistent within a single species among its strains, which can lead to either false positive or false negative test results. The data that was analyzed included genome assemblies of all available mycobacterial strains obtained from the NCBI Genome database, while the standalone BLAST and tblastn programs were utilized to detect the presence of the CFP-10 and ESAT-6 sequences. The findings revealed that a number of non-pathogenic mycobacteria contained the aforementioned sequences, while some pathogenic mycobacteria did not, indicating that a standard tuberculin skin test should be more preferable for detecting various pathogenic mycobacteria compared to antigen-specific tests. In the Mycobacterium tuberculosis complex (MTBC), the proportion of positive strains varied within individual species, indicating a complex relationship. Among non-tuberculous mycobacteria (NTMB), more than half of the analyzed species did not contain these sequences which is consistent with their non-pathogenicity. Further research is necessary to fully comprehend the relationship between MTBC pathogenicity and the CFP-10 and ESAT-6 sequences. This could lead to a conclusion that a standard tuberculin skin test, although non-specific due to the undefined antigen content, may be able to detect various pathogenic mycobacteria in a more reliable manner than antigen-specific tests.

Diagnostic accuracy of the IFN-γ release assay using RD1 immunodominant T-cell antigens for diagnosis of extrapulmonary tuberculosis

The diagnosis of extrapulmonary tuberculosis (EPTB) poses a significant challenge, with controversies surrounding the accuracy of IFN-γ release assays (IGRAs). This study aimed to assess the diagnostic accuracy of RD1 immunodominant T-cell antigens, including ESAT-6, CFP-10, PE35, and PPE68 proteins, for immunodiagnosis of EPTB. Twenty-nine patients with EPTB were enrolled, and recombinant PE35, PPE68, ESAT-6, and CFP-10 proteins were evaluated in a 3-day Whole Blood Assay. IFN-γ levels were measured using a Human IFN-γ ELISA kit, and the QuantiFERON-TB Gold Plus (QFT-Plus) test was performed. Predominantly, the patients were of Afghan (62%, n = 18) and Iranian (38%, n = 11) nationalities. Eighteen individuals tested positive for QFT-Plus, accounting for 62% of the cases. The positivity rate for IGRA, using each distinct recombinant protein (ESAT-6, PPE68, PE35, and CFP-10), was 72% (n = 21) for every protein tested. Specifically, among Afghan patients, the positivity rates for QFT-Plus and IGRA using ESAT-6, PPE68, PE35, and CFP-10 were 66.7%, 83.3%, 83.3%, 77.8%, and 88.9%, respectively. In contrast, among Iranian patients, the positivity rates for the same antigens were 54.5%, 54.5%, 54.5%, 63.6%, and 45.5%, respectively. In conclusion, our study highlights the potential of IGRA testing utilizing various proteins as a valuable diagnostic tool for EPTB. Further research is needed to elucidate the underlying factors contributing to these disparities and to optimize diagnostic strategies for EPTB in diverse populations.

Mycobacterium tuberculosis: immune response, biomarkers, and therapeutic intervention

Although tuberculosis (TB) is an infectious disease, the progression of the disease following Mycobacterium tuberculosis (MTB) infection is closely associated with the host's immune response. In this review, a comprehensive analysis of TB prevention, diagnosis, and treatment was conducted from an immunological perspective. First, we delved into the host's immune response mechanisms against MTB infection as well as the immune evasion mechanisms of the bacteria. Addressing the challenges currently faced in TB diagnosis and treatment, we also emphasized the importance of protein, genetic, and immunological biomarkers, aiming to provide new insights for early and personalized diagnosis and treatment of TB. Building upon this foundation, we further discussed intervention strategies involving chemical and immunological treatments for the increasingly critical issue of drug-resistant TB and other forms of TB. Finally, we summarized TB prevention, diagnosis, and treatment challenges and put forward future perspectives. Overall, these findings provide valuable insights into the immunological aspects of TB and offer new directions toward achieving the WHO's goal of eradicating TB by 2035.

A type VII secretion system in Group B Streptococcus mediates cytotoxicity and virulence

Type VII secretion systems (T7SS) have been identified in Actinobacteria and Firmicutes and have been shown to secrete effector proteins with functions in virulence, host toxicity, and/or interbacterial killing in a few genera. Bioinformatic analysis indicates that isolates of Group B Streptococcus (GBS) encode at least four distinct subtypes of T7SS machinery, three of which encode adjacent putative T7SS effectors with WXG and LXG motifs. However, the function of T7SS in GBS pathogenesis is unknown. Here we assessed the role of the most abundant GBS T7SS subtype during GBS pathogenesis. In a murine model of hematogenous meningitis, mice infected with GBS lacking a functional T7SS or lacking the secreted WXG100 effector EsxA exhibited less mortality, lower bacterial burdens in tissues, and decreased inflammation in the brain compared to mice infected with the parental GBS strain. We further showed that this T7SS induces cytotoxicity in brain endothelium and that EsxA contributes to these cytotoxicity phenotypes in a WXG motif-dependent manner. Finally, we determined that EsxA is a pore-forming protein, thus demonstrating the first role for a non-mycobacterial EsxA homolog in pore formation. This work reveals the importance of a T7SS in host–GBS interactions and has implications for T7SS effector function in other Gram-positive bacteria.

Group B Streptococcus (GBS) is an important human pathogen that is a leading cause of invasive disease in newborns and certain adult populations, including pregnant women, the elderly, and those with diabetes. During pregnancy, asymptomatically colonizing GBS in the female genital tract can be transmitted to the fetus or newborn and can result in neonatal meningitis upon GBS disruption of the blood-brain barrier (BBB). GBS encodes a type VII secretion system (T7SS), which may allow export of proteins and/or toxins that promote BBB disruption; however, the GBS T7SS has not been studied. Here we show that GBS encodes four types of T7SSs and that the most prevalent subtype is important for GBS meningitis progression, possibly by inducing inflammation and cell death in the brain. We also show that a secreted T7SS effector protein, EsxA, contributes to GBS pathogenesis and can form pores in lipid membranes. This is the first demonstration of EsxA-mediated pore-formation in Gram-positive bacteria.

Patterns of T and B cell responses to Mycobacterium tuberculosis membrane-associated antigens and their relationship with disease activity in rheumatoid arthritis patients with latent tuberculosis infection

This study was aimed at exploring whether latent tuberculosis infection (LTBI) contributes to the pathogenesis of immune-mediated inflammatory diseases in a TB endemic setting. We screened 198 rheumatoid arthritis (RA) patients with tuberculin skin test (TST) and studied 61 (median DAS28-ESR = 6.3) who were positive. Whole blood T cell proliferative responses to Mycobacterium tuberculosis (Mtb) membrane (MtM) antigens, including the latency-induced protein alpha crystallin (Acr), were determined by flow cytometry using Ki67 expression as the marker for nuclear proliferation. Serum antibody levels were determined by ELISA. Follow-up investigations (at 3–6, 9–12 and 15–18 months after baseline) were performed in 41 patients who were classified empirically as ‘high’ (HR-T/HR-B) or ‘low’ (LR-T/LR-B) responders based on their dynamic T cell or antibody responses. Significant correlations were seen between baseline T cell responses to MtM and Acr, and between IgG, IgA and IgM antibody responses to MtM. However, no correlation was seen between T and B cell responses. At all time points during the follow-up, T cell responses to both antigens (except for MtM at one point) were significantly higher in HR-T (n = 25) than LR-T (n = 16) patients. Levels of IgA and IgM (but not IgG) antibodies to MtM were also significantly higher in HR-B (n = 13) than LR-B (n = 28) at all time points. Importantly, HR-T patients exhibited significantly higher baseline and follow-up DAS28 scores than LR-T. Ten (of 61) patients had a history of TB and developed RA 6 years (median) after contracting TB. Three new TB cases (1 from TST-positive and 2 from TST-negative groups) emerged during the follow-up. Our results suggest that persistently elevated T cell responses to Mtb antigens may contribute to disease activity in RA.

Factors associated with differential T cell responses to antigens ESAT-6 and CFP-10 in pulmonary tuberculosis patients

The T-SPOT.TB assay detects cellular immune responses to 2 core Mycobacterium tuberculosis antigens, early secreted antigenic target of 6-kDa protein (ESAT-6) and culture filtrate protein-10 (CFP-10). T-SPOT.TB has been recently used for auxiliary diagnosis of active pulmonary tuberculosis (PTB). However, testing can produce inconsistent results due to differential PTB patient immune responses to these antigens, prompting us to identify factors underlying inconsistent results.Data were retrospectively analyzed from 1225 confirmed PTB patients who underwent T-SPOT.TB testing at 5 specialized tuberculosis hospitals in China between December 2012 and November 2015. Numbers of spot-forming cells (SFCs) reflecting T cell responses to ESAT-6 and CFP-10 antigens were recorded then analyzed via multivariable logistic regression to reveal factors underlying discordant T cell responses to these antigens.The agreement rate of 84.98% (82.85%-86.94%) between PTB patient ESAT-6 and CFP-10 responses demonstrated high concordance. Additionally, positivity rates were higher for ESAT-6 than for CFP-10 (84.8% vs 80.7%, P < .001), with ESAT-6 and CFP-10 microwell SFC numbers for each single positive group not differing significantly (P > .99), while spot numbers of the single positive group were lower than numbers for the double positive group (P < .001). Elderly patients (aged ≥66 years) and patients receiving retreatment were most likely to have discordance results.ESAT-6 promoted significantly more positive T-SPOT.TB results than did CFP-10 in PTB patients. Advanced age and retreatment status were correlated with discordant ESAT-6 and CFP-10 results. Assessment of factors underlying discordance may lead to improved PTB diagnosis using T-SPOT.TB.

Immune responses to Mycobacterium tuberculosis membrane-associated antigens including alpha crystallin can potentially discriminate between latent infection and active tuberculosis disease

Changes in expression of membrane antigens may accompany the transition of Mycobacterium tuberculosis (Mtb) from ‘dormant’ to ‘active’ states. We have determined whether antibody and T cell responses to Mtb membrane (MtM)-associated antigens, especially the latency-induced protein alpha crystallin (Acr), can discriminate between latent tuberculosis infection (LTBI) and active TB (ATB) disease. Study subjects comprised a previously described cohort of healthcare workers (HCWs, n = 43) and smear-positive ATB patients (n = 10). HCWs were further categorized as occupational contacts (OC, n = 30), household contacts of TB (HC, n = 8) and cured TB (CTB, n = 5). Levels (ΔOD) of serum antibody isotypes (IgG, IgA and IgM) were determined by ELISA and blood T cell proliferative responses were determined by flow cytometry using Ki67 protein as marker for DNA synthesis. Antibodies to MtM and Acr were predominantly IgG and their levels in HCWs and ATB did not differ significantly. However, HCWs showed a significantly higher level of anti-MtM IgM and a significantly lower level of anti-Acr IgA antibodies than the ATB patients. Also, a larger proportion of HCWs showed a high (>1) ΔOD_Acr/ΔOD_MtM ratio for IgG. HCWs also showed a higher, though not significantly different from ATB, avidity of anti-MtM (IgG) antibodies. A higher proportion of HCWs (35% of OC, 62.5% of HC and 20% of CTB), compared with ATB (10%) showed a positive T cell response to Acr along with significant difference (P <0.05) between HC and ATB. A significant correlation (r = 0.60, P <0.0001) was noted between T cell responses of HCWs towards Acr and MtM (reported earlier by us) and both responses tended to decline with rising exposure to the infection. Even so, positive responses to Acr (38.5%) were significantly lower than to MtM (92%). Neither antibody nor T cell responses to either antigen appeared affected by BCG vaccination or reactivity to tuberculin. Results of the study suggest that the levels of IgM antibodies to MtM, IgA antibodies to Acr and proliferative T cell responses to both the antigens can potentially discriminate between LTBI and active TB disease. They also underscore the necessity of SOPs for antibody assays.

Immune Biomarkers for Diagnosis and Treatment Monitoring of Tuberculosis: Current Developments and Future Prospects

Tuberculosis (TB) treatment monitoring is paramount to clinical decision-making and the host biomarkers appears to play a significant role. The currently available diagnostic technology for TB detection is inadequate. Although GeneXpert detects total DNA present in the sample regardless live or dead bacilli present in clinical samples, all the commercial tests available thus far have low sensitivity. Humoral responses against Mycobacterium tuberculosis (Mtb) antigens are generally low, which precludes the use of serological tests for TB diagnosis, prognosis, and treatment monitoring. Mtb-specific CD4⁺ T cells correlate with Mtb antigen/bacilli burden and hence might serve as good biomarkers for monitoring treatment progress. Omics-based techniques are capable of providing a more holistic picture for disease mechanisms and are more accurate in predicting TB disease outcomes. The current review aims to discuss some of the recent advances on TB biomarkers, particularly host biomarkers that have the potential to diagnose and differentiate active TB and LTBI as well as their use in disease prognosis and treatment monitoring.

Latent tuberculosis infection and associated risk factors among people living with HIV and apparently healthy blood donors at the University of Gondar referral hospital, Northwest Ethiopia

Objective

Immuno-compromised individuals with latent tuberculosis infection (LTBI) are at an increased risk for tuberculosis reactivation compared with the general population. The aim of this study was to determine the prevalence of latent tuberculosis infection among people living with human immunodeficiency virus (PLWH) and apparently healthy blood donors. Human Immunodeficiency Virus positive individuals and for the purpose of comparison apparently healthy blood donors were enrolled. Blood sample was collected and tested for LTBI using QuantiFeron-TB Gold In-Tube assay (QFT-GIT) and CD4+ T cell count was determined by using BD FACS count.

Results

The overall prevalence of LTBI regardless of HIV status was 46%. The prevalence of LTBI among PLWH was 44% and that of blood donors 48%. ART naïve HIV positive patients were three times more likely to have LTBI than patients under ART treatment (P = 0.04). Data also showed statistically significant negative association between previous or current preventive INH therapy and LTBI among HIV positive cases (P = 0.005). The proportion of LTBI was slightly lower among HIV positive individuals than apparently healthy blood donors. Nevertheless, HIV positive individuals should be screened for LTBI and take INH prophylaxis.

Tuberculosis and HIV Coinfection–the Challenge in the Prevention, Detection and Treatment of Tuberculosis

Background:

Tuberculosis (TB) is still a major public health concern world-wide. The increasing global burden of TB is linked to HIV infection. HIV-TB coinfection has also conditioned clinical aspects of the TB. Since the HIV is beginning in the 1980s, the HIV infection poses a significant challenge in global TB control.

Objective:

In this review we focused on the challenges of epidemiological and clinical feature of tuberculosis presented by the HIV coinfection.

Method:

The article consists of a summary of the most important effects presented by the HIV coinfection on epidemiological and clinical feature of tuberculosis. The article analyzes and summary the causes for these challenges.

Results:

The major challenges to strategy of TB control and clinical feature of TB-HIV coinfection are presented in this paper.

Conclusion:

HIV/TB co-infection is synergic, interactive and reciprocal with significant impact. The infection of HIV and Mtb affect each other and the breakdown the immune function in TB/HIV coinfected individual. HIV infection has changed the strategy of TB control, however HIV increases global burden of TB, the reduction in the TB incidence rate is far from sufficient. Atypically clinical manifestations in TB/HIV co-infected patients and increased MDR-TB and XDR-TB contribute to the challenges in the diagnosis and treatment. Increased complexity of managing patients requires expertise in the clinical m knowledge. The focused efforts to control HIV-related TB are of great urgency. These findings will provide insight into the prevention, detection and treatment of tuberculosis and will guide advances towards tuberculosis control.

Synergy between tuberculin skin test and proliferative T cell responses to PPD or cell-membrane antigens of Mycobacterium tuberculosis for detection of latent TB infection in a high disease-burden setting

Tuberculin skin test (TST) is used most widely for the detection of latent tuberculosis infection (LTBI), even though evidences suggest that it could be underreporting the prevalence of LTBI particularly in high disease-burden settings. We have explored whether in vivo (TST) and in vitro (cell-proliferative) T cell responses to PPD can serve as complementary measures. In addition, we also probed whether in vitro T cell response to cell-membrane antigens (Mem) of Mycobacterium tuberculosis (MTB) can serve as a biomarker for LTBI. Study subjects comprised 43 healthcare workers (HCWs), and 9 smear-positive TB patients served as ‘disease control’. To measure proliferative T cell responses, 0.1 ml blood (diluted 1:10) was incubated (5 days) with test or control antigen. Cells were stained with fluorescent antibodies to T cell (CD3+/CD4+/CD8+) surface markers and, after fixation and permeabilization, to nuclear proliferation marker Ki67. Data was acquired on a flow cytometer. HCWs who had an intimate exposure to MTB showed significantly higher TST positivity (85%) than the rest (43%), notwithstanding their BCG vaccination status. The proliferative responses of CD4+ and CD8+ subsets of T cells were comparable. Sixty seven and 100% TST-negative HCWs, respectively, were positive for proliferative T cell response to PPD and MTBMem. Cumulative positivity (TST or in vitro) was 86% with PPD and 100% with MTBMem indicating complementarity of the two responses. As standalone in vitro assay, MTBMem provided a significantly higher positivity (95%) than PPD (67%). T cell responses of TB patients were ‘generally’ depressed, having implications for the development of immunological assays for ‘progressive’ LTBI. Altogether, these results demonstrate that in vivo and in vitro T cell responses to PPD are complementary and in vitro response to MTBMem can be developed as a highly sensitive biomarker for LTBI.

Human Immunology of Tuberculosis

Immunology is a central theme when it comes to tuberculosis (TB). The outcome of human infection with Mycobacterium tuberculosis is dependent on the ability of the immune response to clear or contain the infection. In cases where this fails, the bacterium replicates, disseminates within the host, and elicits a pathologic inflammatory response, and disease ensues. Clinical presentation of TB disease is remarkably heterogeneous, and the disease phenotype is largely dependent on host immune status. Onward transmission of M. tuberculosis to new susceptible hosts is thought to depend on an excessive inflammatory response causing a breakdown of the lung matrix and formation of lung cavities. But this varies in cases of underlying immunological dysfunction: for example, HIV-1 infection is associated with less cavitation, while diabetes mellitus comorbidity is associated with increased cavitation and risk of transmission. In compliance with the central theme of immunology in tuberculosis, we rely on detection of an adaptive immune response, in the form of interferon-gamma release assays or tuberculin skin tests, to diagnose infection with M. tuberculosis. Here we review the immunology of TB in the human host, focusing on cellular and humoral adaptive immunity as well as key features of innate immune responses and the underlying immunological dysfunction which associates with human TB risk factors. Our review is restricted to human immunology, and we highlight distinctions from the immunological dogma originating from animal models of TB, which pervade the field.

Use of the QuantiFERON-TB Gold In-Tube Test in the Diagnosis and Monitoring of Treatment Efficacy in Active Pulmonary Tuberculosis

The value of QuantiFERON in the diagnosis of tuberculosis disease and in the monitoring of the response to anti-tuberculosis treatment is unclear. The aims of this study were to evaluate the accuracy of the QuantiFERON-TB Gold In-Tube (QFT-GIT) test in the diagnosis of tuberculosis and in the monitoring of the response to anti-tuberculosis treatment in patients with active pulmonary tuberculosis (PTB). Between January 2013 and December 2015, 133 cases with active PTB and 133 controls with no mycobacterial infection, matched by age (within 3 years) and by the week that they visited Tainan Chest Hospital, were enrolled in the study. Serial testing by QFT-GIT at baseline and after 2 and 6 months of treatment was performed. At these time points, a comparison of the performance of QFT-GIT with that of sputum culture status among study subjects was conducted. Compared to baseline, 116 (87.2%) cases showed a decreased response, whereas 17 (12.8%) showed persistent or stronger interferon-gamma (IFN-γ) responses at 2 months. PTB patients IFN-γ responses declined significantly from baseline to 2 months (median, 6.32 vs. 4.12; p < 0.005). The sensitivity values of the QFT-GIT test for the detection of pulmonary tuberculosis at cut-off points of 0.35 IU/mL, 0.20 IU/mL, and 0.10 IU/mL were 74.4%, 78.2%, and 80.5%, respectively. The specificity values at cut-off points of 0.35 IU/mL, 0.20 IU/mL, and 0.10 IU/mL were 66.2%, 63.9%, and 57.1%, respectively. Our results support the QFT-GIT assay as a potential tool for diagnosing tuberculosis and for monitoring the efficacy of anti-tuberculosis treatment.

Official American Thoracic Society/Infectious Diseases Society of America/Centers for Disease Control and Prevention Clinical Practice Guidelines: Diagnosis of Tuberculosis in Adults and Children

BACKGROUND

Individuals infected with Mycobacterium tuberculosis (Mtb) may develop symptoms and signs of disease (tuberculosis disease) or may have no clinical evidence of disease (latent tuberculosis infection [LTBI]). Tuberculosis disease is a leading cause of infectious disease morbidity and mortality worldwide, yet many questions related to its diagnosis remain.

METHODS

A task force supported by the American Thoracic Society, Centers for Disease Control and Prevention, and Infectious Diseases Society of America searched, selected, and synthesized relevant evidence. The evidence was then used as the basis for recommendations about the diagnosis of tuberculosis disease and LTBI in adults and children. The recommendations were formulated, written, and graded using the Grading, Recommendations, Assessment, Development and Evaluation (GRADE) approach.

RESULTS

Twenty-three evidence-based recommendations about diagnostic testing for latent tuberculosis infection, pulmonary tuberculosis, and extrapulmonary tuberculosis are provided. Six of the recommendations are strong, whereas the remaining 17 are conditional.

CONCLUSIONS

These guidelines are not intended to impose a standard of care. They provide the basis for rational decisions in the diagnosis of tuberculosis in the context of the existing evidence. No guidelines can take into account all of the often compelling unique individual clinical circumstances.

Differential positive TSPOT assay responses to ESAT-6 and CFP-10 in health care workers

BACKGROUND

The TSPOT.TB (TSPOT) diagnostic test for latent tuberculosis infection is based on a cell-mediated response to the Mycobacteria tuberculosis antigens, ESAT-6 and/or CFP-10, producing an "interferon-gamma footprint". We investigated the within-sample and within-subject variability of positive TSPOT assays due to the individual assay antigens' reactivity.

METHODS

Positive TSPOT assay frequencies due to ESAT-6 or CFP-10 among health care workers (HCWs) at 6-month intervals for 18 months were compared. Differences in result interpretation (positive or negative) for ESAT-6 and CFP10 and potential prognostic factors were investigated.

RESULTS

There were 576 positive results in 8805 TSPOT assays representing 2418 participants. A significant difference was detected in positive TSPOT results due to a positive response to either ESAT-6, CFP-10 or both antigens at baseline through 12 M (p < 0.001), but not for the 18 M follow-up. Gender, ethnicity, occupation, previous positive tuberculin skin test (TST) and study site were significantly associated with specific antigen positivity.

CONCLUSIONS

Among our HCW samples with positive TSPOT assays, CFP-10 induced a larger proportion of positive TSPOT results than ESAT-6. Potential causes for this finding include: BCG vaccinated subpopulations, certain jobs, history of positive TST, U.S. birth, and study site. A high proportion of single-positive specimens may reflect false-positives results.

A Quantitative Analysis of Complexity of Human Pathogen-Specific CD4 T Cell Responses in Healthy M. tuberculosis Infected South Africans

We performed a quantitative analysis of the HLA restriction, antigen and epitope specificity of human pathogen specific responses in healthy individuals infected with M. tuberculosis (Mtb), in a South African cohort as a test case. The results estimate the breadth of T cell responses for the first time in the context of an infection and human population setting. We determined the epitope repertoire of eleven representative Mtb antigens and a large panel of previously defined Mtb epitopes. We estimated that our analytic methods detected 50-75% of the total response in a cohort of 63 individuals. As expected, responses were highly heterogeneous, with responses to a total of 125 epitopes detected. The 66 top epitopes provided 80% coverage of the responses identified in our study. Using a panel of 48 HLA class II-transfected antigen-presenting cells, we determined HLA class II restrictions for 278 epitope/donor recognition events (36% of the total). The majority of epitopes were restricted by multiple HLA alleles, and 380 different epitope/HLA combinations comprised less than 30% of the estimated Mtb-specific response. Our results underline the complexity of human T cell responses at a population level. Efforts to capture and characterize this broad and highly HLA promiscuous Mtb-specific T cell epitope repertoire will require significant peptide multiplexing efforts. We show that a comprehensive "megapool" of Mtb peptides captured a large fraction of the Mtb-specific T cells and can be used to characterize this response.

Novel T-cell assays for the discrimination of active and latent tuberculosis infection: the diagnostic value of PPE family

OBJECTIVE

The diagnosis of active and latent tuberculosis remains a challenge. Although a new approach based on detecting Mycobacterium tuberculosis-specific T-cells has been introduced, it cannot distinguish between latent infection and active disease. The aim of this study was to evaluate the diagnostic potential of interleukin-2 (IL-2) as biomarker after specific antigen stimulation with PE35 and PPE68 for the discrimination of active and latent tuberculosis infection (LTBI).

METHOD

The production of IL-2 was measured in the antigen-stimulated whole-blood supernatants following stimulation with recombinant PE35 and PPE68.

RESULTS

The discrimination performance (assessed by the area under ROC curve) for IL-2 following stimulation with recombinant PE35 and PPE68 between LTBI and patients with active TB were 0.837 [95 % confidence interval (CI) 0.72-0.97] for LTBI diagnosis and 0.75 (95 % CI 0.63-0.89) for active TB diagnosis, respectively. Applying the 6.4 pg/mL cut-off for IL-2 induced by PE35 in the present study population resulted in sensitivity of 78 %, specificity of 83 %, PPV of 83 % and NPV of 78 % for the discrimination of active TB and LTBI. In addition, a sensitivity of 81 %, specificity of 71 %, PPV of 68 and 83 % of NPV was reported based on the 4.4 pg/mL cut-off for IL-2 induced by PPE68.

CONCLUSION

This study confirms IL-2 induced by PE35 and PPE68 as a sensitive and specific biomarker and highlights IL-2 as new promising adjunct markers for discriminating of LTBI and active TB disease.

Tuberculosis Biomarkers: From Diagnosis to Protection

New approaches to control tuberculosis (TB) worldwide are needed. In particular, new tools for diagnosis and new biomarkers are required to evaluate both pathogen and host key elements of the response to infection. Non-sputum based diagnostic tests, biomarkers predictive of adequate responsiveness to treatment, and biomarkers of risk of developing active TB disease are major goals. Here, we review the current state of the field. Although reports on new candidate biomarkers are numerous, validation and independent confirmation are rare. Efforts are needed to reduce the gap between the exploratory up-stream identification of candidate biomarkers, and the validation of biomarkers against clear clinical endpoints in different populations. This will need a major commitment from both scientists and funding bodies.

Adenylate kinase: a novel antigen for immunodiagnosis and subunit vaccine against tuberculosis

Mycobacterium tuberculosis (M.tb)-derived antigens capable of inducing strong cellular and/or humoral responses are potential targets for both immunodiagnosis and vaccine development against tuberculosis (TB). In the present study, we identified adenylate kinase (ADK, Rv0733) as an antigen that induces high cellular and antibody responses in active TB patients. We consequently tested the use of ADK-specific T cells and antibodies as biomarkers for TB diagnosis. The ADK-specific IFN-γ-producing cells detected by ELISPOT assay showed a sensitivity of 85.0 % and specificity of 94.15 % for TB diagnosis while ADK-specific IgG antibody showed a sensitivity of 40.35 % and specificity of 96.43 %. Combining ADK-specific cellular and antibody responses increased the sensitivity to 91.59 % and the specificity to 96.15 %. Immunogenicity and protection against M.tb infection were further tested in a murine model. Immunization with ADK protein elicited strong specific T- and B-cell responses, and provided protection against the virulent H37Rv stain of M.tb resulting in lower bacilli load in the spleens and lungs. More ADK-specific polyfunctional Th1 cells were observed in the lungs when compared to adjuvant-immunized mice. ADK thus may serve as a novel M.tb antigen for TB immunodiagnosis and development of subunit vaccines.

KEY MESSAGES

ADK induces strong immune responses both in humans and mice. ADK-specific IFN-γ production and B-cell responses have high potential for TB diagnosis. ADK immunization provides protection against M.tb infection.

Manipulation of BCG vaccine: a double-edged sword

Mycobacterium bovis Bacillus Calmette-Guérin (BCG), an attenuated vaccine derived from M. bovis, is the only licensed vaccine against tuberculosis (TB). Despite its protection against TB in children, the protective efficacy in pulmonary TB is variable in adolescents and adults. In spite of the current knowledge of molecular biology, immunology and cell biology, infectious diseases such as TB and HIV/AIDS are still challenges for the scientific community. Genetic manipulation facilitates the construction of recombinant BCG (rBCG) vaccine that can be used as a highly immunogenic vaccine against TB with an improved safety profile, but, still, the manipulation of BCG vaccine to improve efficacy should be carefully considered, as it can bring in both favourable and unfavourable effects. The purpose of this review is not to comprehensively review the interaction between microorganisms and host cells in order to use rBCG expressing M. tuberculosis (Mtb) immunodominant antigens that are available in the public domain, but, rather, to also discuss the limitations of rBCG vaccine, expressing heterologous antigens, during manipulation that pave the way for a promising new vaccine approach.

Naturally produced opsonizing antibodies restrict the survival of Mycobacterium tuberculosis in human macrophages by augmenting phagosome maturation

This study investigated the hypothesis that serum antibodies against Mycobacterium tuberculosis present in naturally infected healthy subjects of a tuberculosis (TB) endemic area could create and/or sustain the latent form of infection. All five apparently healthy Indian donors showed high titres of serum antibodies against M. tuberculosis cell membrane antigens, including lipoarabinomannan and alpha crystallin. Uptake and killing of bacilli by the donor macrophages was significantly enhanced following their opsonization with antibody-rich, heat-inactivated autologous sera. However, the capability to opsonize was apparent for antibodies against some and not other antigens. High-content cell imaging of infected macrophages revealed significantly enhanced colocalization of the phagosome maturation marker LAMP-1, though not of calmodulin, with antibody-opsonized compared with unopsonized M. tuberculosis. Key enablers of macrophage microbicidal action--proinflammatory cytokines (IFN-γ and IL-6), phagosome acidification, inducible NO synthase and nitric oxide--were also significantly enhanced following antibody opsonization. Interestingly, heat-killed M. tuberculosis also elevated these mediators to the levels comparable to, if not higher than, opsonized M. tuberculosis. Results of the study support the emerging view that an efficacious vaccine against TB should, apart from targeting cell-mediated immunity, also generate 'protective' antibodies.

Kinetics of Mycobacterium tuberculosis-specific IFN-γ responses and sputum bacillary clearance in HIV-infected adults during treatment of pulmonary tuberculosis

In HIV-uninfected adults with pulmonary tuberculosis (TB), anti-TB treatment is associated with changes in Mycobacterium tuberculosis (Mtb)-specific immune responses, which correlate with sputum bacillary load. It is unclear if this occurs in HIV-infected TB patients. We investigated changes in Mtb-specific immune responses and sputum bacillary clearance during anti-TB treatment in HIV-infected and HIV-uninfected adults with pulmonary TB. Sputum bacillary load was assessed by smear microscopy and culture. Mtb-specific IFN-γ secreting peripheral blood mononuclear cells were enumerated using an ELISPOT assay following stimulation with PPD, ESAT-6 and CFP-10. The baseline frequency of Mtb-specific IFN-γ secreting cells was lower in HIV-infected than HIV-uninfected patients (median PPD 32 vs. 104 Spot Forming Units (SFU), p = 0.05; CFP-10 19 vs. 74 SFU, p = 0.01). ESAT-6-specific IFN-γ secreting cells and sputum bacillary load declined progressively during treatment in both HIV-infected and HIV-uninfected patients. HIV infection did not influence the 2-month sputum culture conversion rate (Odds Ratio 0.89, p = 0.95). These findings suggest that changes in ESAT-6-specific immune responses during anti-TB treatment correspond with changes in sputum bacillary load irrespective of host HIV infection status. The utility of Mtb-specific IFN-γ responses as a proxy measure of treatment response in HIV-infected TB patients warrants further evaluation in other settings.

Costs and Consequences of Using Interferon-γ Release Assays for the Diagnosis of Active Tuberculosis in India

Background

There is growing concern that interferon-γ release assays (IGRAs) are being used off-label for the diagnosis of active tuberculosis (TB) disease in many high-burden settings, including India, where the background prevalence of latent TB infection is high. We analyzed the costs and consequences of using IGRAs for the diagnosis of active TB in India from the perspective of the Indian TB control sector.

Methods and Findings

We constructed a decision analytic model to estimate the incremental cost and effectiveness of IGRAs for the diagnosis of active TB in India. We compared a reference scenario of clinical examination and non-microbiological tests against scenarios in which clinical diagnosis was augmented by the addition of either sputum smear microscopy, IGRA, or Xpert MTB/RIF. We examined costs (in 2013 US dollars) and consequences from the perspective of the Indian healthcare sector. Relative to sputum smear microscopy, use of IGRA for active TB resulted in 23,700 (95% uncertainty range, UR: 3,800 – 38,300) additional true-positive diagnoses, but at the expense of 315,700 (95% UR: 118,300 – 388,400) additional false-positive diagnoses and an incremental cost of US$49.3 million (95% UR: $34.9 – $58.0 million) (2.9 billion Indian Rupees). Relative to Xpert MTB/RIF (including the cost of treatment for drug resistant TB), use of IGRA led to 400 additional TB cases treated (95% UR: [-8,000] – 16,200), 370,600 (95% UR: 252,200 – 441,700) more false-positive diagnoses, 70,400 (95% UR: [-7,900] – 247,200) fewer disability-adjusted life years averted, and US$14.6 million (95%UR: [-$7.2] – $28.7 million) (854 million Indian Rupees) in additional costs.

Conclusion

Using IGRAs for diagnosis of active TB in a setting like India results in tremendous overtreatment of people without TB, and substantial incremental cost with little gain in health. These results support the policies by WHO and Standards for TB Care in India, which discourage the use of IGRAs for the diagnosis of active TB in India and similar settings.

Effect of isoniazid on antigen-specific interferon-γ secretion in latent tuberculosis

Treatment of persons with latent tuberculosis (TB) infection at greatest risk of reactivation is an important component of TB control and elimination strategies. Biomarkers evaluating the effectiveness of treatment of latent TB infection have not yet been identified. This information would enhance control efforts and assist the evaluation of new treatment regimes.

We designed a two-group, two-arm, randomised clinical study of tuberculin skin test-positive participants: 26 with documented contact with TB patients and 34 with non-documented contact. Participants in each group were randomly assigned to the immediate- or deferred-isoniazid treatment arms. Assays of in vitro interferon (IFN)-γ secretion in response to recombinant Rv1737 and overlapping synthetic peptide pools from various groups of immunodominant proteins were performed.

During isoniazid therapy, a significant increase from baseline in the proportion of IFN-γ responders to the 10-kDa culture filtrate protein, Rv2031, Rv0849, Rv1986, Rv2659c, Rv2693c and the recombinant Rv1737 protein was observed (p⩽0.05). The peptide pool of Rv0849 and Rv1737 recombinant proteins induced the highest percentage of IFN-γ responders after isoniazid therapy.

The in vitro IFN-γ responses to these proteins might represent useful markers to evaluate changes associated with treatment of latent TB infection.

Peptide pool of Rv0849 and recombinant protein Rv1737 may be useful to test the efficacy of treatment of latentTBhttp://ow.ly/Catld

Mycobacterial skin and soft tissue infection

Mycobacterial skin and soft tissue infection (SSTI) includes nontuberculous mycobacterial (NTM) infections, tuberculosis (TB), and leprosy. Diagnosis of mycobacterial SSTI can be challenging due to diverse clinical presentation, low yield from cultured specimens, and nonspecific histopathology on tissue biopsy. In addition, immunosuppressed patients may present with atypical or disseminated disease. Despite aggressive medical treatment and often with surgical intervention, results may be suboptimal with poor outcomes. Regimens typically require multiple antibiotics for extended periods of time and are often complicated by medication side effects and drug-drug interactions. Biopsy with culture is the gold standard for diagnosis, but newer molecular diagnostics and proteomics such as matrix-assisted laser desorption ionization-time of flight mass spectrometry have improved diagnosis with increased identification of clinically significant mycobacteria species in clinically relevant time frames. We will review updates in diagnostic tests along with clinical presentation and treatment of mycobacterial SSTI for NTM, TB, and leprosy.

Diagnosis of latent tuberculosis infection before initiation of anti-tumor necrosis factor therapy using both tuberculin skin test and QuantiFERON-TB Gold In Tube assay

BACKGROUND

Reactivation of latent tuberculosis infection (LTBI) is an important complication in patients treated with tumor necrosis factor-alpha (TNF-α) blocking agents. However, the best method for LTBI detection before initiation of anti-TNF therapy remains to be determined.

METHODS

From January 2010 to August 2013, anti-TNF therapy was initiated in 426 patients with immune-mediated inflammatory diseases (IMIDs). Tuberculin skin test (TST) and Quantiferon-TB Gold In Tube (QFT-GIT) assay were performed before starting anti-TNF treatment. LTBI was defined as a positive TST (induration ≥ 10 mm) or as a positive QFT-GIT result. Patients were followed up until December 2013.

RESULTS

The positive TST and QFT-GIT rates were 22.3% (95/426) and 16.0% (68/426), respectively, yielding a total of 27.0% (115/426) of positive LTBI results. LTBI treatment was initiated in 25.1% (107/426) and was completed in 100% (107/107) of patients. During a median 294 days of follow-up, active TB occurred in 1.4% (6/426) of the patients with negative TST and QFT-GIT results at baseline.

CONCLUSION

The either test positive strategy, using both TST and QFT-GIT assay, is acceptable for LTBI screening before commencing anti-TNF therapy in patients with IMIDs.

Characterization of a cross-reactive, immunodominant and HLA-promiscuous epitope of Mycobacterium tuberculosis-specific major antigenic protein PPE68

PPE68 (Rv3873), a major antignic protein encoded by Mycobacteriun tuberculosis-specific genomic region of difference (RD)1, is a strong stimulator of peripheral blood mononuclear cells (PBMCs) obtained from tuberculosis patients and Mycobacterium bovis bacillus Calmette Guerin (BCG)-vaccianted healthy subjects in T helper (Th)1 cell assays, i.e. antigen-induced proliferation and interferon-gamma (IFN-γ) secretion. To confirm the antigen-specific recognition of PPE68 by T cells in IFN-γ assays, antigen-induced human T-cell lines were established from PBMCs of M. Bovis BCG-vaccinated and HLA-heterogeneous healthy subjects and tested with peptide pools of RD1 proteins. The results showed that PPE68 was recognized by antigen-specific T-cell lines from HLA-heteregeneous subjects. To further identify the immunodominant and HLA-promiscuous Th1-1 cell epitopes present in PPE68, 24 synthetic peptides covering the sequence of PPE68 were indivdually analyzed for HLA-DR binding prediction analysis and tested with PBMCs from M. bovis BCG-vaccinated and HLA-heterogeuous healthy subjects in IFN-γ assays. The results identified the peptide P9, i.e. aa 121-VLTATNFFGINTIPIALTEMDYFIR-145, as an immunodominant and HLA-DR promiscuous peptide of PPE68. Furthermore, by using deletion peptides, the immunodominant and HLA-DR promiscuous core sequence was mapped to aa 127-FFGINTIPIA-136. Interestingly, the core sequence is present in several PPE proteins of M. tuberculosis, and conserved in all sequenced strains/species of M. tuberculosis and M. tuberculosis complex, and several other pathogenic mycobacterial species, including M. leprae and M. avium-intracellulalae complex. These results suggest that the peptide aa 121-145 may be exploited as a peptide-based vaccine candidate against tuberculosis and other mycobacterial diseases.

The performance and limitation of T-SPOT.TB for the diagnosis of TB in a high prevalence setting

BACKGROUND

Tuberculosis (TB) diagnosis remains difficulty. The previous reports have shown that the T-SPOT.TB assay may be a more promising diagnostic tool for TB, however, it needs a further study to evaluate the diagnostic value of T-SPOT.TB for the specific populations in a high prevalence setting.

METHODS

In this present study, we conducted stratified and comparable analyses to explore the clinical value and the limitation of T-SPOT.TB assay in TB diagnosis in a high TB prevalence setting, Southern China. A total of 413 subjects including 163 pulmonary TB (PTB), 39 extrapulmonary TB (EPTB), 106 non-TB pulmonary diseases (NTBPDs), 20 medical staff and 85 healthy controls were included in the study.

RESULTS

According to T-SPOT.TB, there had a high incidence of latent TB infection (LTBI) in general population in Southern China, especially in the NTBPDS and medical staff. The T-SPOT.TB had a high performance in the diagnosis of active TB (ATB) in a lower risk of TB infection population such as the general population, however, the T-SPOT.TB for the diagnosis of ATB in the high risk of TB infection populations involving close contacts such as the patients with pulmonary diseases (PD) or medical staff isn't reliable due to the interference by LTBI. Under this condition, the value of rule-out of the assay was seemed to be better than that of rule-in. We believed that the T-SPOT.TB is suitable for screening both the EPTB and the ATB combined with diabetes mellitus (DM). However, we found that the sensitivity of T-SPOT.TB in sputum smear-negative population wasn't as high as that in smear-positive population.

CONCLUSIONS

The T-SPOT.TB testing results should be interpreted with caution combined with subject's characteristics in a high prevalence setting.

IP-10 is an accurate biomarker for the diagnosis of tuberculosis in children

OBJECTIVE

Performance of IFN-γ assays in children is compromised. Therefore, we investigated the utility of IP-10 for the detection of active tuberculosis (TB) and latent tuberculosis infection (LTBI) diagnosis in children; comparing its positivity with QuantiFERON-TB Gold In-Tube (QFN-G-IT) and T-SPOT.TB.

METHODS

We studied 230 children from three groups: active TB, screening (healthy children without known exposure to active TB patient screened at school or by their paediatrician) and contact-tracing studies. IFN-γ release was determined by QFN-G-IT and T-SPOT.TB. IP-10 was detected in QFN-G-IT supernatants by ELISA.

RESULTS

When combining QFN-G-IT and IP-10 assays, positive results improved significantly from 38.3% in QFN-G-IT and 33.9% in IP-10 to 41.3%. Age and type of contact were significant risk factors associated with positive QFN-G-IT and IP-10 results. IP-10 levels after antigen-specific stimulation were significantly higher in comparison to IFN-γ levels. Correlation between the three assays was good (κ = 0.717-0.783).

CONCLUSIONS

IP-10 cytokine is expressed in response to TB specific-antigens used in QFN-G-IT. In conclusion, the use of IFN-γ T-cell based assays in combination with an additional IP-10 assay detection could be useful for diagnosing active TB and LTBI in children.

Antigens for CD4 and CD8 T cells in tuberculosis

Tuberculosis (TB), caused by infection with Mycobacterium tuberculosis (MTB), represents an important cause of morbidity and mortality worldwide for which an improved vaccine and immunodiagnostics are urgently needed. CD4(+) and CD8(+) T cells play an important role in host defense to TB. Definition of the antigens recognized by these T cells is critical for improved understanding of the immunobiology of TB and for development of vaccines and diagnostics. Herein, the antigens and epitopes recognized by classically HLA class I- and II-restricted CD4(+) and CD8(+) T cells in humans infected with MTB are reviewed. Immunodominant antigens and epitopes have been defined using approaches targeting particular TB proteins or classes of proteins and by genome-wide discovery approaches. Antigens and epitopes recognized by classically restricted CD4(+) and CD8(+) T cells show extensive breadth and diversity in MTB-infected humans.

Establishment of a healthy human range for the whole blood "OX40" assay for the detection of antigen-specific CD4+ T cells by flow cytometry

BACKGROUND

Clinical investigation of antigen-specific T cells in potentially immunodeficient patients is an important and often challenging aspect of patient diagnostic work up. Methods for detection of microbial exposure to the T-cell compartment exist but are laborious and time consuming. Recently, a whole blood technique involving flow cytometry and detection of CD25 and OX40 (CD134) expression on the surface of activated CD4+ T cells was shown to be accurate and concordant when compared with more traditional methods of antigen-specific T-cell detection.

METHODS

Whole heparinized blood was collected from healthy donors and set up using the "OX40" assay to detect antigen-specific CD4+ T-cell responses to Varicella Zoster Virus, Epstein-Barr Virus (EBV), Cytomegalovirus, Candida albicans, and Streptococcus pneumoniae.

RESULTS

The "OX40" assay technique was clinically validated for routine use in an NHS clinical immunology laboratory by analysis of incubation length (40-50 h), sample transport time (up to 24 h at room temperature), concordance with serology testing, proliferation and interferon-gamma production. In addition, 63 healthy controls (age range 21-78) were tested for responses to generate a healthy control reference range.

CONCLUSIONS

The OX40 assay, as presented in this report, represents an economical, rapid, robust whole blood technique to detect antigen-specific T cells, which is suitable for clinical immunology diagnostic laboratory use.

Tuberculin skin testing and treatment modulates interferon-gamma release assay results for latent tuberculosis in migrants

Background

Identifying latent tuberculosis infection (LTBI) in people migrating from TB endemic regions to low incidence countries is an important control measure. However, no prospective longitudinal comparisons between diagnostic tests used in such migrant populations are available.

Objectives

To compare commercial interferon (IFN)-gamma release assays (IGRAs) and the tuberculin skin test (TST) for diagnosing LTBI in a migrant population, and the influence of antecedent TST and LTBI treatment on IGRA performance.

Materials and Methods

This cohort study, performed from February to September 2012, assessed longitudinal IGRA and TST responses in Nepalese military recruits recently arrived in the UK. Concomitant T-SPOT.TB, QFT-GIT and TST were performed on day 0, with IGRAs repeated 7 and 200 days later, following treatment for LTBI if necessary.

Results

166 Nepalese recruits were prospectively assessed. At entry, 21 individuals were positive by T-SPOT.TB and 8 individuals by QFT-GIT. There was substantial agreement between TST and T-SPOT.TB positives at baseline (71.4% agreement; κ = 0.62; 95% CI:0.44–0.79), but only moderate concordance between positive IGRAs (38.1% agreement; κ = 0.46; 95% CI:0.25–0.67). When reassessed 7 days following TST, numbers of IGRA-positive individuals changed from 8 to 23 for QFT-GIT (p = 0.0074) and from 21 to 23 for T-SPOT.TB (p = 0.87). This resulted in an increase in IGRA concordance to substantial (64.3% agreement; κ = 0.73; 95% CI:0.58-0.88). Thus, in total on day 0 and day 7 after testing, 29 out of 166 participants (17.5%) provided a positive IGRA and of these 13 were TST negative. Two hundred days after the study commenced and three months after treatment for LTBI was completed by those who were given chemoprophylaxis, 23 and 21 participants were positive by T-SPOT.TB or QFT-GIT respectively. When individual responses were examined longitudinally within this population 35% of the day 7 QFT-GIT-positive, and 19% T-SPOT.TB-positive individuals, were negative by IGRA. When the change in the levels of secreted IFN-γ was examined after chemoprophylaxis the median levels were found to have fallen dramatically by 77.3% from a pre-treatment median concentration of IFN-γ 2.73 IU/ml to a post-treatment median concentration IFN-γ 0.62 (p = 0.0002).

Conclusions

This study suggests differences in the capacity of commercially available IGRAs to identify LTBI in the absence of antecedent TST and that IGRAs, in the time periods examined, may not be the optimal tests to determine the success of chemoprophylaxis for LTBI.

Human CD8+ T cells from TB pleurisy respond to four immunodominant epitopes in Mtb CFP10 restricted by HLA-B alleles

CD8⁺ T cells are essential for host defense to Mycobacterium tuberculosis (Mtb) infection and identification of CD8⁺ T cell epitopes from Mtb is of importance for the development of effective peptide-based diagnostics and vaccines. We previously demonstrated that the secreted 10-KDa culture filtrate protein (CFP10) from Mtb is a potent CD8⁺ T cell antigen but the repertoire and dominance pattern of human CD8 epitopes for CFP10 remained poorly characterized. In the present study, we undertook to define immunodominant CD8 epitopes involved in CFP10 using a panel of CFP10-derived 13–15 amino acid (aa) peptides overlapping by 11 aa. Four peptides in CFP10 were observed to induce significant CD8⁺ T cell responses and we further determined the size of the epitopes involved in each individual peptide tested. Four 9 aa CD8 epitopes were finally identified and deleting a single amino acid from the N or C terminus of either peptide markedly reduced IFN-γ production, suggesting that they are minimum of CD8 epitopes. In the individuals tested, each epitope represented a single immunodominant response in CD8⁺ T cells. The epitope-specific CD8⁺ T cells displayed effector or effector memory phenotypes and could upregulate the expression of CD107a/b upon antigen stimulation. In addition, we found that epitope-specific CD8⁺ T cells shared biased usage of T cell receptor (TCR) variable region of β chain (Vβ) 12, 9, 7.2 or Vβ4 chains. As judged from HLA-typing results and using bioinformatics technology for prediction of MHC binding affinity, we found that the epitope-specific CD8⁺ T cells are all restricted by HLA-B alleles. Our findings suggest that the four epitopes in CFP10 recognized by CD8⁺ T cells might be of importance for the development of Mtb peptide-based vaccines and for improved diagnosis of TB in humans.

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 ofMycobacterium tuberculosisin 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.

Biomarkers of tuberculosis: a research roadmap

Tuberculosis (TB) continues to represent a major public health problem worldwide. Prompt and accurate diagnosis and effective treatment are fundamental to reducing morbidity and mortality and curtailing spread of infection. Furthermore, tackling the large reservoir of latent infection is the cornerstone to TB control in many high income low TB incidence countries. However, our existing toolkit for prevention, diagnosis and treatment remains outdated and inadequate. Here, we discuss the key targets for biomarker research and discovery in TB and recent developments in the field. We focus on host biomarkers, in particular: correlates of vaccine efficacy and sterilizing immunity; biomarkers of latent TB infection, including diagnosis, risk of progression to active TB and response to treatment; and markers of active TB, including diagnosis, response to treatment and risk of relapse. Recent scientific and technological advances have contributed to significant recent progression in biomarker discovery. Although there are clear remaining paucities, continued efforts within scientific, translational and clinical studies are likely to yield a number of clinically useful biomarkers of TB in the foreseeable future.

Childhood TB: when to think of it and what to do when you do

Although childhood tuberculosis has declined dramatically in the UK over the last century, it is now increasing again and globally childhood tuberculosis still accounts for a significant proportion of the tuberculosis disease burden. Children may present with non-specific symptoms, and because of the paucibacillary nature of disease and the difficulty of producing sputum samples, tuberculosis in children is often difficult to diagnose. Apart from the traditional diagnostic methods, like chest X-ray, tuberculin skin testing and mycobacterial staining or culture, new diagnostic strategies have been developed. In particular, immune-based diagnostics, such as interferon-gamma release assays, have now been introduced for clinical use. However these tests do not offer substantial improvements in sensitivity over tuberculin skin testing for the diagnosis of active disease. Further research is needed to develop better diagnostic tests for tuberculosis in children.

Ethnicity-tailored novel set of ESAT-6 peptides for differentiating active and latent tuberculosis

Differentiation between active and latent TB is a diagnostic challenge in TB-endemic regions. The commercially available IFN-γ-release assays are unsuitable for achieving this discrimination. We, therefore, screened ESAT-6 and CFP-10 proteins through population coverage analysis to identify minimal sets of peptides that can discriminate between these two forms of TB in a North Indian population. Comparing the diagnostic performance of a set of 2 ESAT-6 peptides (positions: 16-36; 59-79) to that of the QuantiFERON(®)-TB Gold IT (QFTGIT) assay, we observed significant difference in IFN-γ and TNF-α levels between patients (n = 15) and their age- and sex-matched healthy household contacts (n = 15). While the mean (±SD) IFNγ titer was 241.8 (±219.24) IU/ml for patients, the same in controls was 564.2 (±334.82) IU/ml (p = 0.039). Similarly the TNFα response was significantly higher in patients, compared to controls (796.47 ± 175.21 IU/ml vs. 481.81 ± 378.72 IU/ml; p = 0.047). IL-4 response to these peptides was non- discriminatory between the two groups. The QFTGIT Assay, however, elicited no significant difference in IFN-γ, TNF-α or IL-4 levels. Hence we conclude that IFN-γ or TNF-α response to these ESAT-6 peptides has the potential to differentiate between active and latent TB in our population.

Incidence and outcomes of paradoxical lymph node enlargement after anti-tuberculosis therapy in non-HIV patients

OBJECTIVES

Limited data are available regarding the incidence and outcomes of lymphadenopathy after completing tuberculosis (TB) treatment.

METHODS

We prospectively evaluated the incidence and outcomes of post-treatment lymphadenopathy in 154 patients with newly diagnosed lymph node TB (group 1) and in 12 patients previously treated for TB (group 2). We assessed the rates of microbiological recurrence, clinical recurrence, and post-treatment paradoxical response (PR) (defined as no microbiological recurrence with spontaneous improvement).

RESULTS

Post-treatment lymphadenopathy occurred in 24 (15.6%) patients of group 1 and in 12 patients of group 2. Re-biopsy was performed in 23 of these 36 patients. AFB stain was positive in four (17.4%) cases, and TB-PCR was positive in 11 (47.8%), but all samples were sterile (no microbiological recurrence). Granuloma was present in 12 (52.2%) histological specimens. Thirty-three (91.7%) of the 36 patients with lymphadenopathy improved spontaneously (post-treatment PR) and 3 (8.3%) were improved with retreatment (clinical recurrence). The overall incidence of post-treatment PR in patients with lymph node TB (group 1) was 8.6 per 100 person-years (95% CI, 5.8-12.7).

CONCLUSIONS

Lymphadenopathy after TB treatment was more likely to be associated with post-treatment PR rather than with microbiological recurrence, and it should be monitored until PR resolve.

Preclinical study and phase I clinical safety evaluation of recombinant Mycobacterium tuberculosis ESAT6 protein

BACKGROUND

To investigate the ability of rESAT6 to identify different mycobacteria-sensitized guinea pigs and its safety in preclinical and phase I clinical study.

MATERIAL AND METHODS

Guinea pigs were sensitized with different Mycobacteria. After sensitization, all animals were intradermally injected with rESAT6 and either PPD or PPD-B. At 24 h after the injection, the erythema of the injection sites were measured using a double-blind method. For the preclinical safety study, different doses of rESAT6 and BSA were given 3 times intramuscularly to guinea pigs. On day 14 after the final immunization, the guinea pigs were intravenously injected with the same reagents in the hind legs and the allergic reactions were observed. A single-center, randomized, open phase I clinical trial was employed. The skin test was conducted in 32 healthy volunteers aged 19-65 years with 0.1 µg, 0.5 µg, and 1 µg rESAT6. Physical examination and laboratory tests were performed before and after the skin test and adverse reactions were monitored. The volunteers' local and systemic adverse reactions and adverse events were recorded for 7 days.

RESULTS

Positive PPD or PPD-B skin tests were observed in all Mycobacteria-sensitized guinea pigs; the diameters of erythema were all >10 mm. The rESAT6 protein induced a positive skin test result in the guinea pigs sensitized with MTB, M. bovis, M. africanum and M. kansasii; the diameters of erythema were 14.7±2.0, 9.3±3.8, 18.7±2.4, and 14.8±4.2 mm, respectively. A negative skin test result was detected in BCG-vaccinated and other NTM-sensitized guinea pigs. The rESAT6 caused no allergic symptoms, but many allergic reactions, such as cough, dyspnea, and even death, were observed in the guinea pigs who were administered BSA. During the phase I clinical trial, no adverse reactions were found in the 0.1 µg rESAT6 group, but in the 0.5 µg rESAT6 group 2 volunteers reported pain and 1 reported itching, and in the 1 µg rESAT6 group there was 1 case of pain, 1 case of itching, and 1 case of blister. No other local or systemic adverse reactions or events were reported.

CONCLUSIONS

The rESAT6 can differentiate effectively among MTB infection, BCG vaccination, and NTM infection and is safe in healthy volunteers.

IGRAs--the gateway to T cell based TB diagnosis

Development of Interferon-Gamma Release Assays (IGRAs) and implementation of their use in clinical practice almost 10 years ago has revolutionised diagnosis of latent tuberculosis (TB) infection (LTBI). The commercially available IGRAs, TSPOT.TB (Oxford Immunotech, Oxford, UK) and QuantiFERON Gold In-Tube (Cellestis, Victoria, Australia), allow detection of TB infection with greater specificity and sensitivity than the tuberculin skin test (TST) and are now recommended for diagnosis of LTBI. The TSPOT.TB assay is a simplified enzyme-linked immunospot assay (ELISpot) that enumerates TB-specific T lymphocytes (T cells) secreting interferon-gamma (IFNγ). In comparison, the QuantiFERON Gold In-Tube assay constitutes an enzyme-linked immunosorbent assay (ELISA) to quantify IFNγ released into blood plasma after incubation of whole blood with TB antigens. Release of IFNγ, as a result of antigen stimulation of TB-specific T cells within blood, is indicative of TB infection. Although IGRAs have significant advantages over the TST in diagnosis of latent TB, they have significant limitations. Discovery of new antigens and advances in methodology for measuring cellular immunity have recently paved the way for novel tests that overcome these limitations. By establishing for the first time technological platforms for T cell based diagnosis in diagnostic service laboratories, IGRAs provide a bridgehead to clinical application of T cell based diagnosis in routine practice.

Dynamic QuantiFERON Response in Psoriasis Patients Taking Long-Term Biologic Therapy

Introduction

The risk of active tuberculosis is increased in psoriasis patients receiving biologic drug therapy. The QuantiFERON-TB Gold In-Tube assay (QFT) is used for latent tuberculosis screening in these patients. This study presents a retrospective analysis on repeated QFT assays, investigating the influence of biologic drugs and isoniazid therapy on the outcome of the assay.

Methods

Serial QFTs of 58 psoriasis patients, who received biologic drug therapy, were evaluated at baseline and after 12 months of treatment. Patients were retrospectively divided in four groups according to QFT results at baseline and at follow-up: patients having a QFT reversion (from positive to negative results); patients with a conversion (from negative to positive); patients confirming the baseline results, either positive or negative.

Results

At the end of the 12-months period, 11.1% of patients with a negative QFT result at baseline presented a conversion, showing low interferon (IFN)-gamma values, whereas 6.9% of positive patients presented a QFT reversion. When the test was repeated after 2–3 months without isoniazid chemoprophylaxis, patients with QFT conversion showed negative results. No patient developed active tuberculosis.

Conclusions

In patients undergoing biologic therapy, a positive QFT assay needs to be further confirmed, as false-positive results may occur after long-term therapy. Repeating QFT tests in patients with low IFN-gamma values could reduce the incidence of false-positive latent tuberculosis infection diagnosis, thus preventing unnecessary tuberculosis chemoprophylaxis. In conclusion, a dynamic QFT response is possible in psoriasis patients undergoing biologic therapy.

Memory T cells in latent Mycobacterium tuberculosis infection are directed against three antigenic islands and largely contained in a CXCR3+CCR6+ Th1 subset

An understanding of the immunological footprint of Mycobacterium tuberculosis (MTB) CD4 T cell recognition is still incomplete. Here we report that human Th1 cells specific for MTB are largely contained in a CXCR3⁺CCR6⁺ memory subset and highly focused on three broadly immunodominant antigenic islands, all related to bacterial secretion systems. Our results refute the notion that secreted antigens act as a decoy, since both secreted proteins and proteins comprising the secretion system itself are targeted by a fully functional T cell response. In addition, several novel T cell antigens were identified which can be of potential diagnostic use, or as vaccine antigens. These results underline the power of a truly unbiased, genome-wide, analysis of CD4 MTB recognition based on the combined use of epitope predictions, high throughput ELISPOT, and T cell libraries using PBMCs from individuals latently infected with MTB.

Mycobacterium tuberculosis is one of the most life-threatening pathogens of all time, having infected one-third of the present human population. There is an urgent need for both novel vaccines and diagnostic strategies. Here, we were able to identify the targets most dominantly recognized by latently infected individual that successfully contain infection. These targets are contained in three broadly genomic antigenic islands, all related to bacterial secretion systems and composed by several distinct ORFs. Thus, our results suggest that vaccination with one or few defined antigens will fail to replicate the response associated with natural immunity. Our analysis also pinpoints that the Th1 cells dominating the response are associated with novel and well-defined phenotypic markers, suggesting that the response is molded by unique MTB associated factors. This study demonstrates further that the approach combining peptide binding predictions with modern high throughput techniques is generally applicable to the study of immunity to other complex pathogens. Together, our data provide a new angle in the worldwide fight against M. tuberculosis and could be used for diagnostic or vaccine developments.