Detection of Mycobacterium tuberculosis DNA in CD34 + peripheral blood mononuclear cells of Ugandan adults with latent infection: a cross-sectional and nested prospective study

Application of Droplet Digital PCR to Detection of Mycobacterium tuberculosis and Mycobacterium leprae Infections: A Narrative Review

Tuberculosis (TB) is a chronic infectious disease caused by Mycobacterium tuberculosis (MTB) infection, which has seriously endangered human health for many years. With the emergence of multidrug-resistant and extensively drug-resistant MTB, the prevention and treatment of TB has become a pressing need. Early diagnosis, drug resistance monitoring, and control of disease transmission are critical aspects in the prevention and treatment of TB. However, the currently available diagnostic technologies and drug sensitivity tests are time consuming, and thus, it is difficult to achieve the goal of early diagnosis and detection drug sensitivity, which results in limited control of disease transmission. The development of molecular testing technology has gradually achieved the vision of rapid and accurate diagnosis of TB. Droplet digital PCR (ddPCR) is an excellent nucleic acid quantification method with high sensitivity and no need for a calibration curve. Herein, we review the application of ddPCR in TB diagnosis and drug resistance detection and transmission monitoring.

Mycobacterium tuberculosis-derived circulating cell-free DNA in patients with pulmonary tuberculosis and persons with latent tuberculosis infection

Objectives

The timely diagnosis of pulmonary tuberculosis (PTB) is challenging. Although pathogen-derived circulating cell-free DNA (cfDNA) has been detected in humans, the significance of Mycobacterium tuberculosis (MTB)-cfDNA detection in patients with PTB remains unclear.

Methods

This study enrolled patients with PTB and persons with latent tuberculosis infection (LTBI) as the study and control groups, respectively, from 2018 to 2020. We measured interferon-γ levels and calculated blood monocyte-to-lymphocyte ratio (MLR). We conducted plasma cfDNA extraction, quantitative polymerase chain reaction (qPCR), and droplet digital PCR targeting the IS6110 gene of MTB. We calculated the sensitivity and specificity of using MTB-cfDNA to identify PTB and analyzed the factors associated with PTB diagnosis and MTB-cfDNA positivity.

Results

We enrolled 24 patients with PTB and 57 LTBI controls. The sensitivity of using MTB-cfDNA to identify PTB was 54.2%(13/24) in total and 46.2%(6/13) in smear-negative cases. Two LTBI controls (3.5%) tested positive for MTB-cfDNA, indicating a specificity of 96.5%(55/57). By using MTB-cfDNA positivity and an MLR ≥0.42 to identify PTB, sensitivity increased to 79.2%(19/24). Among patients with PTB, MTB-specific interferon-γ levels were higher in MTB-cfDNA positive participants than in those who tested negative (7.0 ±2.7 vs 2.7±3.0 IU/mL, p<0.001). MTB-cfDNA levels declined after 2 months of anti-tuberculosis therapy (p<0.001).

Conclusion

The sensitivity of using MTB-cfDNA to identify PTB in participants was 54.2%, which increased to 79.2% after incorporating an MLR ≥0.42 into the analysis. MTB-cfDNA positivity was associated with MTB-specific immune response, and MTB-cfDNA levels declined after treatment. The clinical value of MTB-cfDNA in PTB management necessitates further investigation.

Reece S, R. Martineau A, P. Kateete D. Detection of Mycobacterium tuberculosis DNA in CD34 + peripheral blood mononuclear cells of Ugandan adults with latent infection: a cross-sectional and nested prospective study

Background: Tuberculin skin test and interferon gamma release assay (IGRA) show limitations in diagnosing latent tuberculosis infection (LTBI) and poorly predict progression to active tuberculosis. This study will explore detection of Mycobacterium tuberculosis ( M.tb) DNA in CD34 + peripheral blood mononuclear cells (PBMCs) as a biomarker for LTBI and monitoring chemoprophylaxis response. Methods: In a cross-sectional study, 120 household contacts (60 HIV positive and 60 HIV negative) will be recruited. Also, 10 patients with sputum positive pulmonary tuberculosis and 10 visitors from low incidence countries with no history of TB treatment will be recruited as positive and negative controls, respectively. Participants will donate 100 ml (50 ml for TB patients) of blood to isolate PBMCs using density gradient centrifugation. Isolated PBMCs will be separated into CD34 + and CD34 - enriched cellular fractions. DNA from each fraction will be purified, quantified and subjected to droplet digital PCR targeting IS6110 (a M.tb Complex multi-copy gene) and rpoB, a single copy gene. Also, 4 ml of blood will be drawn for IGRA. In a nested prospective study, 60 HIV positive participants will be given 300 mg of Isoniazid Preventive Therapy (IPT) daily for six months, after which they will donate a second 100 ml blood sample that will be processed as described above. Data from the cross-sectional study will be analysed to determine the proportion of individuals in whom M.tb DNA is detectable in CD34 + and CD34 - fractions and number of M.tb genomes present. Data from the prospective study will be analysed to compare the proportion of individuals with detectable M.tb DNA in CD34 + and CD34 - fractions, and median M.tb genome copy number, post vs pre-IPT. Discussion: This study will determine whether detection of M.tb DNA in CD34 + PBMCs holds promise as a biomarker for LTBI and monitoring chemoprophylaxis response.