Detection of M. tuberculosis DNA in CD34-Positive Peripheral Blood Mononuclear Cells of Asymptomatic TB Contacts

Background: Haematopoietic stem cells expressing the CD34 surface marker have been posited as a niche for M. tuberculosis complex (MTBC) bacilli during latent tuberculosis infection (LTBI). Methods: We conducted a cross-sectional study in Ethiopia to determine whether MTBC DNA was detectable in peripheral blood mononuclear cells (PBMC) isolated from 100 ml blood taken from 197 asymptomatic adults with a history of recent household TB contact and/or HIV infection, using digital polymerase chain reaction (dPCR). A nested prospective study was conducted in a sub-set of 43 HIV-infected individuals to evaluate whether administration of isoniazid preventive therapy (IPT) was effective in clearing MTBC DNA from PBMC. Results: MTBC DNA was detected in PBMC of 156/197 participants (79.2%; 95% CI 73.5% to 84.9%). Where present, it was found more frequently in CD34-positive vs. CD34-negative PBMC (154/155 [99.4%] vs. 46/155 [29.7%], P<0.001). Prevalence of dPCR-detected MTBC DNA did not differ between QuantiFERON-negative vs. QuantiFERON-positive participants (77/99 [77.8%] vs. 79/98 [80.6%], P=0.73), but it was higher in HIV-infected vs. HIV-uninfected participants (67/75 [89.3%] vs. 89/122 [73.0%], P=0.006). By contrast, the proportion of QuantiFERON-positive participants was lower in HIV-infected vs. HIV-uninfected participants (25/75 [33.3%] vs. 73/122 [59.8%], P<0.001). Administration of IPT reduced prevalence of dPCR-detected MTBC DNA from 41/43 (95.3%) at baseline to 23/43 (53.5%) post-treatment (P<0.001), but it did not influence prevalence of QuantiFERON-positivity (17/43 [39.5%] at baseline vs. 13/43 [30.2%] post-treatment; P=0.13). Conclusions: We report a novel molecular microbiological biomarker of LTBI with properties that are distinct from those of a commercial interferon-gamma release assay. Our findings implicate the bone marrow as a niche for M. tuberculosis in latently infected individuals. Detection of MTBC DNA in PBMC has potential applications in the diagnosis of LTBI, in monitoring response to chemoprophylaxis and as an outcome measure in clinical trials of interventions to prevent or treat LTBI. Funding Statement: This work was supported by a grant from the United Kingdom Medical Research Council (Reference Number MR/P024548/1, to ARM). SF and STR acknowledge support from the Cambridge NIMR BRC antibiotic resistance theme. JM acknowledges support from the DELTAS Africa Initiative (ref DEL-15-011, via THRiVE-2). JFH, GJ and DMO’S acknowledge support from the UK government Department for Business, Energy & Industrial Strategy (BEIS). Declaration of Interests: STR has a pending patent that is relevant to the work. All other authors have no competing interests to declare. Ethics Approval Statement: The study was approved by the Ethiopian National Research Ethics Review Committee, Addis Ababa, Ethiopia (ref 310/253/2017). Written informed consent was obtained from all participants.