Detection of <i>M. tuberculosis</i> DNA in TB contacts’ PBMC does not associate with blood RNA signatures for incipient tuberculosis

ABSTRACT Background We have previously reported detection of genomic DNA of Mycobacterium tuberculosis (Mtb) in peripheral blood mononuclear cells (PBMC) of asymptomatic adults with recent household exposure to an index case of infectious pulmonary tuberculosis (TB). It is not known whether this phenomenon indicates quiescent Mtb infection or incipient TB disease. Methods We did a cross-sectional study with a nested prospective component, utilizing blood samples collected from a previously studied cohort of TB contacts recruited in Ethiopia to detect eight different blood RNA signatures for incipient TB. Gene expression analysis was performed on baseline blood samples from 24 HIV-uninfected Mtb DNA-negative individuals, 24 HIV-uninfected Mtb DNA-positive individuals, and 24 HIV-infected Mtb DNA-positive participants. Analysis was also performed on follow-up blood samples of 24 HIV-infected participants following completion of isoniazid preventive therapy (IPT), of whom 17 were classified as ‘responders’ to IPT (Mtb DNA undetectable at follow-up) and 7 were classified as ‘non-responders’ to IPT (Mtb DNA detectable at follow-up). Results Cross-sectional analysis of baseline gene expression data from HIV-uninfected participants revealed no differences in Z-scores between Mtb DNA-positive vs. Mtb DNA-negative participants for any of the eight gene expression signatures investigated. Prospective analyses comparing expression of the same eight signatures in HIV-infected participants before vs. after administration of IPT showed no change in gene expression Z-scores over the course of treatment, either for ‘responders’ or ‘non-responders’ to treatment. Conclusions Lack of any association between detection of Mtb DNA in PBMC of asymptomatic TB contacts and presence of gene expression signatures investigated suggests that detection of this bacillary biomarker is more likely to represent quiescent Mtb infection than incipient TB disease. Funding United Kingdom Medical Research Council (Ref. MR/P024548/1) RESEARCH IN CONTEXT Evidence before this study□ We searched PubMed from database inception to Sept 30, 2023, for studies published in any language evaluating associations between blood RNA signatures for tuberculosis (TB) and biomarkers of Mycobacterium tuberculosis (Mtb) infection using comprehensive terms for “tuberculosis infection”, “latent tuberculosis”, “transcriptional” and “biomarker”. Several reports have described whole blood transcriptional signatures associating with positive Interferon-Gamma Release Assay results in individuals without clinical or radiological evidence of active tuberculosis, but we did not find studies investigating transcriptional correlates of microbial biomarkers of Mtb infection. Added value of this study□ To our knowledge, this is the first study to investigate whether detection of Mtb DNA in blood of individuals with asymptomatic tuberculosis infection associates with blood RNA signatures for incipient tuberculosis. Cross-sectional analysis of samples from HIV-uninfected TB contacts in Ethiopia revealed no differences in any of eight whole blood gene expression signatures compared between Mtb DNA-positive vs. Mtb DNA-negative participants. Prospective analyses comparing expression of the same eight signatures in HIV-infected participants before vs. after administration of isoniazid preventive therapy showed no change in gene expression signatures over the course of treatment. Implications of all the available evidence□ Lack of any association between detection of Mtb DNA in the blood of asymptomatic TB contacts vs. presence of gene expression signatures for incipient TB provides the best available evidence for bona fide latent Mtb infection.