Clinical evaluation of host transcriptional markers for tuberculosis diagnosis and treatment response monitoring

The World Health Organization (WHO) called for non-sputum-based tests for tuberculosis (TB). This thesis considered the role of host transcriptional markers (HTM) for diagnosis of latent TB infection (LTBI) and active pulmonary TB (ATB) and for ATB treatment monitoring. To measure HTM expression, a multiplex reverse-transcriptase quantitative polymerase chain reaction (RT-qPCR) assay was developed for 17 genes. Participants were recruited in Blantyre, Malawi. Amongst predefined study populations were the following key groups: ATB patients, who expectorated Mycobacterial Growth Indicator Tube (MGIT) culture and Xpert MTB/RIF positive sputum; patients with other respiratory diseases (ORDs) who had negative sputum tests and were not diagnosed with ATB; LTBI patients, who were TB exposed (TBEx) household contacts of ATB patients with a positive Interferon Gamma Release Assay (IGRA); TBExIGRA- participants, who were contacts with a negative IGRA- result; and Healthy Controls (HCs), who were asymptomatic IGRA negative individuals without household TB exposure. Cross-sectional analyses evaluated whether HTM expression profiles could discriminate LTBI from HCs, LTBI from ATB, and ATB from ORDs. Patients receiving ATB treatment were followed for 8 months to compare sputum bacteriology tests (Time to Positivity in MGIT culture and the TB Molecular Bacterial Load Assay [TB-MBLA]) with HTM profiles for treatment monitoring. LTBI was associated with suppression of gene expression compared to HCs. ZNF296 and KLF2 distinguished LTBI from HCs more accurately than other HTM. A proportion of TBExIGRA- negative participants exhibited similar HTM expression patterns to LTBI. ATB was associated with upregulated HTM expression compared to ORDs. CD64 most accurately distinguished ATB from ORDs. HIV co-infection did not affect HTM expression in either LTBI or ATB. HTM expression declined in response to treatment in a manner that mirrored bacteriological measures of treatment response. Blood-based HTM have potential to improve LTBI and ATB diagnosis and monitor ATB treatment response.