Preliminary evaluation of a new prototype interferon-gamma release assay for the detection of Mycobacterium tuberculosis-specific T-cell responses in patients with tuberculosis

Screening for tuberculosis infections (TBI) using the tuberculin skin test or interferon-gamma release assays (IGRA) is crucial in controlling the global TB burden. This study evaluates the performance of a new IGRA for the detection of T-cell responses against Mycobacterium tuberculosis. Blood samples from 34 adults with tuberculosis disease (TB) and from 30 children with TB, TBI or without TB were analyzed using the prototype Quan-T-Cell TB (EUROIMMUN). The pediatric samples were additionally measured using the established QuantiFERON-TB Gold Plus assay (Qiagen). Clinical performance and inter-assay concordance were analyzed. The prototype Quan-T-Cell TB yielded positivity rates of 88.2% and 100% in adults with TB and children with TBI, respectively, at a specificity of 93.8%. Comparison between the two IGRAs showed positive, negative and overall agreement rates of 100%, 93.8% and 96.3%, respectively, with a kappa score of 0.924 indicating almost perfect agreement. Our study shows promising results of the new prototype Quan-T-Cell TB, as reflected by high concordance with the final diagnosis in adults and children and performance comparable to that of the QuantiFERON IGRA. In individual cases, the data suggest that the prototype Quan-T-Cell TB may be even more consistent with TBI-related clinical findings. Unlike the QuantiFERON assay, the Quan-T-Cell TB has a predefined borderline range, which is advantageous as it may help to differentiate non-specific variation near the cut-off, and fewer sample tubes are required per analysis. The new Quan-T-Cell TB may therefore be a good alternative to the established QuantiFERON IGRA for TBI screening. Further assay optimization is underway, including evaluation studies based on larger patient and control cohorts.