Abstract

Around 30% of the World’s population is infected with Tuberculosis (TB) which is an infective disease caused by the microorganism Mycobacterium tuberculosis (MTB).  Each year, about 1

% of the population gets infected with MTB. In 2016, almost 1.8 million died from TB. Majority of the individuals have the Latent Tuberculosis (LTBI) and because the MTB infection is controlled by the immune system, there are no symptoms. About 10 % of LTBI progress to active TB (ATB) where the symptoms are weight loss, fever and blood-containing sputum. Tuberculin skin test (TST) and Interferon gamma release assay (IGRA) are the few diagnostic methods with low accuracy used for LTBI. The predictive value is poor for classifying LTBI individuals with high risk of progression to ATB and to separate ATB and LTBI. Therefore, it is important to discover new diagnostics methods for tuberculosis. In order to detect ATB and LTBI in blood, 22 mRNA markers have previously been selected and validated using literature studies and RNA-sequencing study #1 in order to decide which markers are more probable to differentiate between ATB, LTBI and individuals which are non-infected.

From a RNA-sequencing #2, 4 mRNA markers have been evaluated where the aim was to discover potential biomarkers to differentiate between LTBI and ATB infected. The aim of this degree project is to evaluate these 4 mRNA markers that can precisely diagnose LTBI and/or ATB in patients in order to develop a whole-blood assay which will be able to differentiate between LTBI and TB disease. The definitive goal is to develop an assay able to expect the risk in patients with LTBI to progress to ATB.

A target validation study was performed on patients with active or latent tuberculosis, and close contacts of patients with ATB, using blood samples from Karolinska University Hospital, Solna. In order to evaluate the 4 mRNA markers, qPCR analysis was performed. Furthermore, the two most promising markers with highest AUC-values were used in the development of two prototype GeneXpert cartridge assays, where the two prototype cartridge assays were evaluated, including two of the new markers.

Several combinations of markers for separating MTB infected from control, healthy contact groups were identified. For separating active TB from latent TB, particularly good results for marker #24 and marker #26 were found. Due to low mRNA expression, there were many late or missing Ct-values for marker #27 and therefore, it should either be re-designed or excluded from future studies. The two prototype cartridges for MTB antigen stimulated blood, including two of the new promising markers (marker #24 and marker #26) look very promising and will be further optimized in the future.