Evaluation of Mycobacterium tuberculosis derived cell-free DNA using pleural fluid and paired plasma samples for the diagnosis of pleural tuberculosis

Cell-free DNA: a promising biomarker in infectious diseases

Infectious diseases pose serious threats to public health worldwide. Conventional diagnostic methods for infectious diseases often exhibit low sensitivity, invasiveness, and long turnaround times. User-friendly point-of-care tests are urgently needed for early diagnosis, treatment monitoring, and prognostic prediction of infectious diseases. Cell-free DNA (cfDNA), a promising non-invasive biomarker widely used in oncology and pregnancy, has shown great potential in clinical applications for diagnosing infectious diseases. Here, we discuss the most recent cfDNA research on infectious diseases from both the pathogen and host perspectives. We also discuss the technical challenges in this field and propose solutions to overcome them. Additionally, we provide an outlook on the potential of cfDNA as a diagnostic, treatment, and prognostic marker for infectious diseases.

Utility of pleural fluid-derived extracellular vesicles as a source of Mycobacterium tuberculosis antigens MPT51 and MPT64 for pleural TB diagnosis: a proof-of-concept study

Extracellular vesicles (EVs) have recently emerged as a source of microbe-specific biomarkers for disease diagnosis. In the present study, we evaluated the utility of pleural fluid-derived extracellular vesicles (pEVs) as a source of Mycobacterium tuberculosis (M. tb.) antigens for pleural TB (pTB) diagnosis. EVs were isolated from pleural fluid (PF) samples and were characterized by scanning electron microscopy, and immunoblotting by targeting CD63 and LAMP2 markers. Antigen-detection ELISAs were developed for 2 M.tb.-specific antigens, MPT51 and MPT64 in pEVs (pEV-ELISA) and direct PF samples (PF-ELISA), and were evaluated on n = 86 samples in a blinded manner. Cut-off values were calculated by ROC-curve analysis to achieve 90 % (95%CI:73.47-97.89) and 86.67 % (95%CI:69.28-96.24) specificity for MPT51 and MPT64 pEV-ELISA respectively. The sensitivity of pEV-ELISA was 71.43 % (95%CI; 29.04-96.33) for MPT51 antigen and 57.14 % (95%CI; 18.41-90.1) for MPT64 antigen in the 'Definite' pTB group, while in the 'Definite and Probable' pTB group, the sensitivity was 62.86 % (95%CI:44.92-78.53) for MPT51 and 65.71 % (95%CI:47.79-80.87) for MPT64. The performance of PF-ELISA was sub-optimal, with 28.57 % (95%CI:3.67-70.96) and 14.29 % (95%CI:0.36-57.87) sensitivity for MPT51 and MPT64 in 'Definite' pTB group respectively. We conclude that M. tb.-antigens are concentrated in the EV-fraction of PF samples and EVs can be utilized for antigen-detection assays for pTB diagnosis.

Diagnostic Value of Cross-priming Amplification Combined With CRISPR-Cas12b in Detecting Cell-free DNA in Tuberculous Pleural Effusion

Background

Diagnosis of tuberculous pleural effusion (TPE) remains challenging. Studies have shown that detecting cell-free Mycobacterium tuberculosis (cf-TB) DNA in pleural effusion can improve TPE diagnosis. This study aimed to evaluate the diagnostic value of our recently developed TB One-Pot assay, which combines cross-priming amplification with CRISPR-Cas12b, in detecting cf-TB for TPE.

Methods

Pleural effusion samples were collected from inpatients with suspected TPE at Hangzhou Red Cross Hospital. After centrifugation, the precipitate was used for culture, Xpert, and pleural effusion cytologic testing, while the supernatant was used for biochemical and cf-TB assays, including TB One-Pot and the quantitative polymerase chain reaction method (cf-TB-PCR). Assessment of diagnostic performance was based on a comprehensive reference standard.

Results

A total of 115 patients were included: 88 TPE cases (diagnosed per the comprehensive reference standard) and 27 non-TPE cases. The sensitivity of TB One-Pot in detecting pleural cf-TB for diagnosing TPE was 64.8%, with an area under the curve (AUC) of 0.805, significantly superior to culture and Xpert (P < .05). When compared with cf-TB-PCR (sensitivity, 53.4%; AUC, 0.767) and the adenosine deaminase assay (sensitivity, 52.3%; AUC, 0.761), TB One-Pot demonstrated slightly higher sensitivity and AUC, but the differences were not statistically significant (P > .05). The specificity of TB One-Pot was 96.3%, while the specificity of the other tests was 100%, with no statistically significant differences (P > .05).

Conclusions

cf-TB provides direct evidence of the etiology of TPE. TB One-Pot for detecting cf-TB in diagnosing TPE outperforms existing TB laboratory tests and may represent a more effective approach for TPE diagnosis in resource-limited settings.

Tuberculous pleuritis: clinical presentations and diagnostic challenges

PURPOSE OF REVIEW

Tuberculous pleuritis (TBP) is one of the most common types of extrapulmonary tuberculosis. We highlight the latest epidemiology of TBP, the heterogeneity of its presentation and the performance of different diagnostic strategies.

RECENT FINDINGS

There are differential trends in the incidences of TBP worldwide. Its incidence increased in China but decreased in the United States in the past decade. The presentation of TBP is heterogeneous regarding clinical symptoms, radiological findings and pleural fluid analysis results. Conventional microbiological tests have low sensitivities to diagnose TBP. Recent research focused on various diagnostic tools with better yield. The sensitivity of nucleic acid amplification tests (NAAT) in pleural fluid, including the latest generation of PCR and sequencing-based techniques for detecting tuberculosis, remains suboptimal. Various pleural fluid biomarkers have been explored, but there is a lack of consensus on their clinical utility and cutoff levels.

SUMMARY

The heterogeneity of clinical presentation poses obstacles to diagnosing TBP. Further development of diagnostic tools, including more robust NAAT and biomarkers with additional validation, is needed before incorporation into routine clinical practice.