Diabetes characteristics and long-term management needs in diabetic TB patients.

BACKGROUND: Diabetes mellitus (DM) is common among patients with TB. We assessed DM characteristics and long-term needs of DM-TB patients after completing TB treatment.METHODS: Newly diagnosed TB patients with DM were recruited for screening in a randomised clinical trial evaluating a simple algorithm to improve glycaemic control during TB treatment. DM characteristics, lifestyle and medication were compared before and after TB treatment and 6 months later. Risk of cardiovascular disease (CVD), albuminuria and neuropathy were assessed after TB treatment.RESULTS: Of 218 TB-DM patients identified, 170 (78%) were followed up. Half were males, the mean age was 53 years, 26.5% were newly diagnosed DM. High glycated haemoglobin at TB diagnosis (median 11.2%) decreased during TB treatment (to 7.4% with intensified management and 8.4% with standard care), but this effect was lost 6 months later (9.3%). Hypertension and dyslipidemia contributed to a high 10-year CVD risk (32.9% at month 6 and 35.5% at month 12). Neuropathy (33.8%) and albuminuria (61.3%) were common. After TB treatment, few patients used CVD-mitigating drugs.CONCLUSION: DM in TB-DM patients is characterised by poor glycaemic control, high CVD risk, and nephropathy. TB treatment provides opportunities for better DM management, but effort is needed to improve long-term care.

Potential business model for a European vaccine R&D infrastructure and its estimated socio-economic impact.

Background: Research infrastructures are facilities or resources that have proven fundamental for supporting scientific research and innovation. However, they are also known to be very expensive in their establishment, operation and maintenance. As by far the biggest share of these costs is always borne by public funders, there is a strong interest and indeed a necessity to develop alternative business models for such infrastructures that allow them to function in a more sustainable manner that is less dependent on public financing. Methods: In this article, we describe a feasibility study we have undertaken to develop a potentially sustainable business model for a vaccine research and development (R&D) infrastructure. The model we have developed integrates two different types of business models that would provide the infrastructure with two different types of revenue streams which would facilitate its establishment and would be a measure of risk reduction. For the business model we are proposing, we have undertaken an ex ante impact assessment that estimates the expected impact for a vaccine R&D infrastructure based on the proposed models along three different dimensions: health, society and economy. Results: Our impact assessment demonstrates that such a vaccine R&D infrastructure could achieve a very significant socio-economic impact, and so its establishment is therefore considered worthwhile pursuing. Conclusions: The business model we have developed, the impact assessment and the overall process we have followed might also be of interest to other research infrastructure initiatives in the biomedical field.

Antituberculosis BCG vaccination: more reasons for varying innate and adaptive immune responses.

Bacillus Calmette-Guérin (BCG) vaccination induces variable protection against pulmonary tuberculosis (TB), and a more effective TB vaccine is needed. The potential for BCG to provide protection against heterologous infections, by induction of innate immune memory, is increasingly recognized. These nonspecific responses may substantially benefit public health, but are also variable. In this issue of the JCI, Koeken and de Bree et al. report that BCG reduces circulating inflammatory markers in males but not in females, while de Bree and Mouritis et al. describe how diurnal rhythms affect the degree of BCG-induced innate memory. These studies further delineate factors that influence the magnitude of responses to BCG and may be crucial to harnessing its potential benefits.

Circulating levels of GDF15 in patients with myalgic encephalomyelitis/chronic fatigue syndrome.

BACKGROUND: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating condition characterised by fatigue and post-exertional malaise. Its pathogenesis is poorly understood. GDF15 is a circulating protein secreted by cells in response to a variety of stressors. The receptor for GDF15 is expressed in the brain, where its activation results in a range of responses. Among the conditions in which circulating GDF15 levels are highly elevated are mitochondrial disorders, where early skeletal muscle fatigue is a key symptom. We hypothesised that GDF15 may represent a marker of cellular stress in ME/CFS. METHODS: GDF15 was measured in serum from patients with ME/CFS (n = 150; 100 with mild/moderate and 50 with severe symptoms), "healthy volunteers" (n = 150) and a cohort of patients with multiple sclerosis (n = 50). RESULTS: Circulating GDF15 remained stable in a subset of ME/CFS patients when sampled on two occasions ~ 7 months (IQR 6.7-8.8) apart, 720 pg/ml (95% CI 625-816) vs 670 pg/ml (95% CI 598-796), P = 0.5. GDF15 levels were 491 pg/ml in controls (95% CI 429-553), 546 pg/ml (95% CI 478-614) in MS patients, 560 pg/ml (95% CI 502-617) in mild/moderate ME/CFS patients and 602 pg/ml (95% CI 531-674) in severely affected ME/CFS patients. Accounting for potential confounders, severely affected ME/CFS patients had GDF15 concentrations that were significantly increased compared to healthy controls (P = 0.01). GDF15 levels were positively correlated (P = 0.026) with fatigue scores in ME/CFS. CONCLUSIONS: Severe ME/CFS is associated with increased levels of GDF15, a circulating biomarker of cellular stress that appears which stable over several months.

Point of care HbA1c level for diabetes mellitus management and its accuracy among tuberculosis patients: a study in four countries.

BACKGROUND: Diabetes mellitus (DM) is common among tuberculosis (TB) patients and often undiagnosed or poorly controlled. We compared point of care (POC) with laboratory glycated haemoglobin (HbA1c) testing among newly diagnosed TB patients to assess POC test accuracy, safety and acceptability in settings in which immediate access to DM services may be difficult. METHODS: We measured POC and accredited laboratory HbA1c (using high-performance liquid chromatography) in 1942 TB patients aged 18 years recruited from Peru, Romania, Indonesia and South Africa. We calculated overall agreement and individual variation (mean ± 2 standard deviations) stratified by country, age, sex, body mass index (BMI), HbA1c level and comorbidities (anaemia, human immunodeficiency virus [HIV]). We used an error grid approach to identify disagreement that could raise significant concerns. RESULTS: Overall mean POC HbA1c values were modestly higher than laboratory HbA1c levels by 0.1% units (95%CI 0.1-0.2); however, there was a substantial discrepancy for those with severe anaemia (1.1% HbA1c, 95%CI 0.7-1.5). For 89.6% of 1942 patients, both values indicated the same DM status (no DM, HbA1c <6.5%) or had acceptable deviation (relative difference <6%). Individual agreement was variable, with POC values up to 1.8% units higher or 1.6% lower. For a minority, use of POC HbA1c alone could result in error leading to potential overtreatment (n = 40, 2.1%) or undertreatment (n = 1, 0.1%). The remainder had moderate disagreement, which was less likely to influence clinical decisions. CONCLUSION: POC HbA1c is pragmatic and sufficiently accurate to screen for hyperglycaemia and DM risk among TB patients.

Addressing diversity in tuberculosis using multidimensional approaches.

Tuberculosis is a complex disease, which can affect many organs other than the lungs. Initial infection may be cleared without inducing immunological memory, or progress directly to primary disease. Alternatively, the infection may be controlled as latent TB infection, that may progress to active tuberculosis at a later stage. There is now a greater understanding that these infection states are part of a continuum, and studies using PET/CT imaging have shown that individual lung granulomas may respond to infection independently, in an un-synchronized manner. In addition, the Mycobacterium tuberculosis organisms themselves can exist in different states: as nonculturable forms, as 'persisters', as rapidly growing bacteria and a biofilm-forming cording phenotype. The 'omics' approaches of transcriptomics, metabolomics and proteomics can help reveal the mechanisms underlying these different infection states in the host, and identify biosignatures with diagnostic potential, that can predict the development of disease, in 'progressors' as early as 12-18 months before it can be detected clinically, or that can monitor the success of anti-TB therapy. Further insights can be obtained from studies of BCG vaccination and new TB vaccines. For example, epigenetic changes associated with trained immunity and a stronger immune responses following BCG vaccination can be identified. These omics approaches may be particularly valuable when linked to studies of mycobacterial growth inhibition, as a direct read-out of the ability to control mycobacterial growth. The second generation of omics studies is identifying much smaller signatures based on as few as 3 or 4 genes. Thus, narrowing down omics-derived biosignatures to a manageable set of markers now opens the way to field-friendly point of care assays.

Isolation and Potential for Transmission of Mycobacterium bovis at Human-livestock-wildlife Interface of the Serengeti Ecosystem, Northern Tanzania.

Mycobacterium bovis, the causative agent of bovine tuberculosis (bTB), is a multihost pathogen of public health and veterinary importance. We characterized the M. bovis isolated at the human-livestock-wildlife interface of the Serengeti ecosystem to determine the epidemiology and risk of cross-species transmission between interacting hosts species. DNA was extracted from mycobacterial cultures obtained from sputum samples of 472 tuberculosis (TB) suspected patients and tissue samples from 606 livestock and wild animal species. M. bovis isolates were characterized using spoligotyping and Mycobacterial Interspersed Repetitive Units-Variable Tandem Repeats (MIRU-VNTR) on 24 loci. Only 5 M. bovis were isolated from the cultured samples. Spoligotyping results revealed that three M. bovis isolates from two buffaloes (Syncerus caffer) and 1 African civet (Civettictis civetta) belonged to SB0133 spoligotype. The two novel strains (AR1 and AR2) assigned as spoligotype SB2290 and SB2289, respectively, were identified from indigenous cattle (Bos indicus). No M. bovis was detected from patients with clinical signs consistent with TB. Of the 606 animal tissue specimens and sputa of 472 TB-suspected patients 43 (7.09%) and 12 (2.9%), respectively, yielded non-tuberculous mycobacteria (NTM), of which 20 isolates were M. intracellulare. No M. avium was identified. M. bovis isolates from wildlife had 45.2% and 96.8% spoligotype pattern agreement with AR1 and AR2 strains, respectively. This finding indicates that bTB infections in wild animals and cattle were epidemiologically related. Of the 24 MIRU-VNTR loci, QUB 11b showed the highest discrimination among the M. bovis strains. The novel strains obtained in this study have not been previously reported in the area, but no clear evidence for recent cross-species transmission of M. bovis was found between human, livestock and wild animals.

Association of slow recovery of Mycobacterium africanum-infected patients posttreatment with high content of Persister-Like bacilli in pretreatment sputum.

OBJECTIVES/BACKGROUND: Mycobacterium africanum that causes 40% of tuberculosis (TB) in West Africa grows more slowly in culture and has similar transmission capacity compared with Mycobacterium tuberculosis, but M. africanum-exposed contacts progress more slowly to active disease. The presence of lipid body (LB) containing M. tuberculosis complex (MTBC) cells in sputum samples has been associated with mycobacterial transcriptomes indicating slow or no growth and persister-like antibiotic tolerance. Slow-growing bacilli have been found to display a persister-like phenotype with the accumulation of LBs and drug tolerance. Our previous study showed that the body mass index and lung damage resolution on chest X-ray were significantly improved slower in M. africanum-infected patients posttreatment than in M. tuberculosis-infected patients; however, the reason for this remains unclear. Therefore, we hypothesized that these differences could be either due to significant differences in drug resistance between the MTBC lineages or a difference in their content of persisters, as indicated by the percentage of LP-positive bacilli in sputum. METHODS: Sputum isolates collected before treatment from patients with TB were subjected to drug susceptibility testing using the BD BACTEC MGIT 960 SIRE kit. The percentage of acid-fast bacilli (AFB) and LB-positive bacilli in pretreatment sputum was determined by a dual staining procedure using Auramine O and LipidTOX Red neutral lipid stain, respectively, and fluorescence microscopy imaging. RESULTS: Out of the 77 isolates tested, 9 showed resistance to at least one drug and only 2 showed multidrug (rifampicin and isoniazid) resistance among M. tuberculosis-infected patients. The percentage of AFB-positive smears was similar between the two groups (p=0.821), whereas that of LP-positive bacilli was significantly higher (p=0.0059) in M. africanum-infected patients' sputa (n=24) than in M. tuberculosis-infected patients' sputa (n=36). In addition, the bacillary lengths were significantly higher in M. africanum-infected patients' sputa than in M. tuberculosis-infected patients' sputa (p=0.0007). A high frequency of LP-positive bacilli in pretreatment sputum was associated with a poor body mass index and lung damage on chest X-ray improvement following anti-TB treatment in both the groups (r2=0.022; p=0.017). CONCLUSION: The slow clinical recovery of M. africanum-infected patients compared with M. tuberculosis-infected patients posttreatment may be at least partially associated with the persistence of drug-tolerant "fat and lazy" bacilli.

Differential transcriptomic and metabolic profiles of M. africanum- and M. tuberculosis-infected patients after, but not before, drug treatment.

The epidemiology of Mycobacterium tuberculosis (Mtb) and M. africanum (Maf) suggests differences in their virulence, but the host immune profile to better understand the pathogenesis of tuberculosis (TB) have not been studied. We compared the transcriptomic and metabolic profiles between Mtb- and Maf-infected TB cases to identify host biomarkers associated with lineages-specific pathogenesis and response to anti-TB chemotherapy. Venous blood samples from Mtb- and Maf-infected patients obtained before and after anti-TB treatment were analyzed for cell composition, gene expression and metabolic profiles. Prior to treatment, similar transcriptomic profiles were seen in Maf- and Mtb-infected patients. In contrast, post treatment, over 1600 genes related to immune responses and metabolic diseases were differentially expressed between the groups. Notably, the upstream regulator hepatocyte nuclear factor 4-alpha (HNF4α), which regulated 15% of these genes, was markedly enriched. Serum metabolic profiles were similar in both group pre-treatment, but the decline in pro-inflammatory metabolites post treatment were most pronounced in Mtb-infected patients. Together, the differences in both peripheral blood transcriptomic and serum metabolic profiles between Maf- and Mtb-infected patients observed over the treatment period, might be indicative of intrinsic host factors related to susceptibility to TB and/or differential efficacy of the standard anti-TB treatment on the two lineages.

Differential gene expression of activating Fcγ receptor classifies active tuberculosis regardless of human immunodeficiency virus status or ethnicity.

New diagnostics and vaccines for tuberculosis (TB) are urgently needed, but require an understanding of the requirements for protection from/susceptibility to TB. Previous studies have used unbiased approaches to determine gene signatures in single-site populations. The present study utilized a targeted approach, reverse transcriptase multiplex ligation-dependent probe amplification (RT-MLPA), to validate these genes in a multisite study. We analysed ex vivo whole blood RNA from a total of 523 participants across four sub-Saharan countries (Ethiopia, Malawi, South Africa, and The Gambia) with differences in TB and human immunodeficiency virus (HIV) status. We found a number of genes that were expressed at significantly lower levels in participants with active disease than in those with latent TB infection (LTBI), with restoration following successful TB treatment. The most consistent classifier of active disease was FCGR1A (high-affinity IgG Fc receptor 1 (CD64)), which was the only marker expressed at significantly higher levels in participants with active TB than in those with LTBI before treatment regardless of HIV status or genetic background. This is the first study to identify a biomarker for TB that is not affected by HIV status or geo-genetic differences. These data provide valuable clues for understanding TB pathogenesis, and also provide a proof-of-concept for the use of RT-MLPA in rapid and inexpensive validation of unbiased gene expression findings.

The influence of previous exposure to environmental mycobacteria on the interferon-gamma response to bacille Calmette-Guérin vaccination in southern England and northern Malawi.

We report a large study of the effect of BCG vaccination on the in vitro 6-day whole blood interferon-gamma (IFN-gamma) response to antigens from eight species of mycobacteria among schoolchildren in south-eastern England, where bacille Calmette-Guérin (BCG) vaccination is highly protective against pulmonary tuberculosis, and among young adults in northern Malawi, where BCG vaccination is not protective. In the UK children, BCG induced an appreciable increase in IFN-gamma response to antigens from most species of mycobacteria. The degree of change was linked to the relatedness of the species to Mycobacterium bovis BCG, and provides further evidence of the cross-reactivity of mycobacterial species in priming of the immune system. IFN-gamma responses to purified protein derivatives (PPDs) from M. tuberculosis and environmental mycobacteria were more prevalent in the Malawian than the UK group prior to vaccination; BCG vaccination increased the prevalence of responses to these PPDs in the UK group to a level similar to that in Malawi. There was no evidence that the vaccine-induced change in IFN-gamma response was dependent upon the magnitude of the initial response of the individual to environmental mycobacteria in the United Kingdom or in Malawi. These observations should assist the development and interpretation of human clinical trials of new vaccines against M. tuberculosis in areas of both low and high exposure to environmental mycobacteria.

Interferon-gamma responses to ESAT-6 in tuberculosis patients early into and after anti-tuberculosis treatment.

OBJECTIVE: To investigate T-cell responses to ESAT-6 by an interferon-gamma (IFN-gamma) ex vivo enzyme-linked immunospot (ELISpot) assay in tuberculosis (TB) patients early during treatment and in patients who have completed a course of anti-tuberculosis chemotherapy. DESIGN: T-cell responses following overnight stimulation with 6-kD early secretory antigenic target (ESAT-6) antigen were compared to responses obtained using cells cultured with ESAT-6 for 6 days, using an ELISpot assay. RESULTS: In the ex vivo ELISpot assay, the median IFN-gamma responses in TB patients, irrespective of treatment status, were significantly higher than in healthy BCG-vaccinated controls. In the 6-day ELISpot assay, median IFN-gamma responses were significantly higher in TB patients who had completed treatment than in patients early during therapy. There was considerable individual variability in the degree of expansion of ESAT-6 specific T-cells from day 1 to day 6 in both treatment groups. CONCLUSION: Further studies are required to assess which type of assay provides the best indicator of a memory T-cell response and how ESAT-6 specific T-cells relate to protective immunity in TB infection.

Interferon-gamma and skin test responses of schoolchildren in southeast England to purified protein derivatives from Mycobacterium tuberculosis and other species of mycobacteria.

The immune responses of schoolchildren in southeast England to Mycobacterium tuberculosis and other species of mycobacteria were studied prior to vaccination with bacille Calmette-Guérin (BCG). Data are presented for tuberculin (Heaf) skin test and interferon-gamma (IFN-gamma) responses to M. tuberculosis purified protein derivative (PPD), and IFN-gamma responses to PPDs from eight other environmental mycobacteria, measured in 424 schoolchildren (13-15 years of age). Responses to M. tuberculosis PPD were detected in 27% of schoolchildren by in vitro IFN-gamma response and in 20% by the Heaf test. IFN-gamma responses were more prevalent to PPDs from species of mycobacteria other than M. tuberculosis, predominantly those of the MAIS complex and M. marinum (45-60% responders). Heaf test and IFN-gamma responses were associated (P<0.001) for M. tuberculosis, MAIS and M. marinum. These findings have implications for appropriate implementation of vaccination against tuberculosis.

Human T cell responses to peptides of the Mycobacterium leprae 45-kD serine-rich antigen.

In order to identify T cell epitopes within the Mycobacterium leprae 45-kD serine-rich antigen, we analysed responses to overlapping 17-mer peptides encompassing the whole antigen in non-exposed UK controls, Pakistani leprosy patients and tuberculosis patients in both the United Kingdom and Pakistan. This antigen has been described as M. leprae-specific, although it has a hypothetical homologue in M. tuberculosis. Human peripheral blood mononuclear cells were stimulated with peptide for 5 days and IFN-gamma measured in supernatants by ELISA. Some peptides were recognized more frequently by T cells from tuberculoid leprosy patients than those from UK controls, suggesting that such T cell epitopes might have diagnostic potential, while other peptides induced greater responses among UK control subjects. Short-term cell lines confirmed that these assays detected specific T cell recognition of these peptides. However, many tuberculosis patients also recognized these potentially specific peptides suggesting that there could be a true homologue present in M. tuberculosis.

Decreased IFN- gamma and increased IL-4 production by human CD8(+) T cells in response to Mycobacterium tuberculosis in tuberculosis patients.

To investigate the role of MHC class I restricted CD8(+) T cells in host defense to M. tuberculosis, peripheral blood mononuclear cells (PBMC) from healthy BCG-vaccinated donors and untreated pulmonary tuberculosis (TB) patients in The Gambia were stimulated for 6 days with M. bovis BCG or M. tuberculosis and the CD8(+) T cell response analyzed. Intracellular FACS analysis of cytokine production by CD8(+) T cells showed that IFN- gamma and TNF- alpha production were greatly reduced in TB patients compared to healthy controls. IL-4-producing CD8(+) T cells were detected in TB patients, a phenotype absent in controls. Collectively, these data suggest that an alteration in the type 1/type 2 cytokine balance occurs in CD8(+) T cells during clinical tuberculosis, and that this may provide a surrogate marker for disease.

Relationship between IFN-gamma and skin test responsiveness to Mycobacterium tuberculosis PPD in healthy, non-BCG-vaccinated young adults in Northern Malawi.

SETTING: Rural northern Malawi, where vaccination with BCG Glaxo (1077) provides protection against leprosy but not against pulmonary tuberculosis. OBJECTIVE: To evaluate the patterns of responsiveness to purified protein derivative of Mycobacterium tuberculosis (PPD) in terms of delayed type hypersensitivity (DTH) and interferon-gamma (IFN-gamma) production. DESIGN: IFN-gamma was measured in 6 day whole blood cultures diluted 1 in 10, stimulated with PPD RT48, and the results compared to the DTH response to PPD RT23. A total of 633 individuals aged 12 to 28 years, without prior BCG vaccination, were recruited. RESULTS: Overall, 63% of subjects made a positive IFN-gamma response (defined as >62 pg/ml), and 37% gave a DTH induration of >5 mm. A strong correlation between skin test and IFN-gamma responses was observed, although with interesting exceptions: 13/270 individuals with zero DTH showed IFN-gamma responses >500 pg/ml, and 7/53 individuals with >10 mm induration showed IFN-gamma responses < or = 62 pg/ml. The prevalence of skin test responsiveness increased with age, and was higher among older males than females; age-sex patterns were less clear for IFN-gamma production. CONCLUSION: The 6 day IFN-gamma response to PPD correlates well with Mantoux skin test induration. The discordant individuals may represent important subsets in terms of protective immunity and risk of clinical tuberculosis.

Patterns and implications of naturally acquired immune responses to environmental and tuberculous mycobacterial antigens in northern Malawi.

Interferon (IFN)-gamma responsiveness to 12 purified protein derivative (PPD) and new tuberculin antigens from 9 species of mycobacteria was assessed, using a whole blood assay, in 616 young adults living in northern Malawi, where Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccination provides no protection against pulmonary tuberculosis. The prevalence of IFN-gamma responsiveness was highest for PPDs of M. avium, M. intracellulare, and M. scrofulaceum (the MAIS complex). Correlations between responsiveness paralleled genetic relatedness of the mycobacterial species. A randomized, controlled trial was carried out, to assess the increase in IFN-gamma responsiveness to M. tuberculosis PPD that can be attributed to M. bovis BCG vaccination. The BCG-attributable increase in IFN-gamma response to M. tuberculosis PPD was greater for individuals with low initial responsiveness to MAIS antigens than for those with high initial responsiveness. Although not statistically significant, the trend is consistent with the hypothesis that prior exposure to environmental mycobacteria interferes with immune responses to BCG vaccination.

Presence of human T-cell responses to the Mycobacterium leprae 45-kilodalton antigen reflects infection with or exposure to M. leprae.

The ability of the 45-kDa serine-rich Mycobacterium leprae antigen to stimulate peripheral blood mononuclear cell (PBMC) proliferation and gamma interferon (IFN-gamma) production was measured in leprosy patients, household contacts, and healthy controls from areas of endemicity in Mexico. Almost all the tuberculoid leprosy patients gave strong PBMC proliferation responses to the M. leprae 45-kDa antigen (92.8%; n = 14). Responses were lower in lepromatous leprosy patients (60.6%; n = 34), but some responses to the 45-kDa antigen were detected in patients unresponsive to M. leprae sonicate. The proportion of positive responses to the M. leprae 45-kDa antigen was much higher in leprosy contacts (88%; n = 17) than in controls from areas of endemicity (10%; n = 20). None of 15 patients with pulmonary tuberculosis gave a positive proliferation response to the 45-kDa antigen. The 45-kDa antigen induced IFN-gamma secretion similar to that induced by the native Mycobacterium tuberculosis 30/31-kDa antigen in tuberculoid leprosy patients and higher responses than those induced by the other recombinant antigens (M. leprae 10- and 65-kDa antigens, thioredoxin, and thioredoxin reductase); in patients with pulmonary tuberculosis it induced lower IFN-gamma secretion than the other recombinant antigens. These results suggest that the M. leprae 45-kDa antigen is a potent T-cell antigen which is M. leprae specific in these Mexican donors. This antigen may therefore have diagnostic potential as a new skin test reagent or as an antigen in a simple whole-blood cytokine test.

Human CD8+ CTL specific for the mycobacterial major secreted antigen 85A.

The role of CD8(+) CTL in protection against tuberculosis in human disease is unclear. In this study, we stimulated the peripheral blood mononuclear cells of bacillus Calmette-Guérin (BCG)-vaccinated individuals with live Mycobacterium bovis BCG bacilli to establish short-term cell lines and then purified the CD8(+) T cells. A highly sensitive enzyme-linked immunospot (ELISPOT) assay for single cell IFN-gamma release was used to screen CD8(+) T cells with overlapping peptides spanning the mycobacterial major secreted protein, Ag85A. Three peptides consistently induced a high frequency of IFN-gamma responsive CD8(+) T cells, and two HLA-A*0201 binding motifs, P(48-56) and P(242-250), were revealed within the core sequences. CD8(+) T cells responding to the 9-mer epitopes were visualized within fresh blood by ELISPOT using free peptide or by binding of HLA-A*0201 tetrameric complexes. The class I-restricted CD8(+) T cells were potent CTL effector cells that efficiently lysed an HLA-A2-matched monocyte cell line pulsed with peptide as well as autologous macrophages infected with Mycobacterium tuberculosis or recombinant vaccinia virus expressing the whole Ag85A protein. Tetramer assays revealed a 6-fold higher frequency of peptide-specific T cells than IFN-gamma ELISPOT assays, indicating functional heterogeneity within the CD8(+) T cell population. These results demonstrate a previously unrecognized, MHC class I-restricted, CD8(+) CTL response to a major secreted Ag of mycobacteria and supports the use of Ag85A as a candidate vaccine against tuberculosis.