The six-gene expression signature in whole sampled sputum provides clinically feasible inflammatory phenotyping of asthma

Abstract

Processing of induced sputum is time consuming and requires trained personnel, and consequently the use of induced sputum is limited to few sites globally. The six-gene signature (6GS) is an mRNA-based gene signature that was developed to provide a clinically feasible method for inflammatory phenotyping. In this study, we assessed whether the 6GS would perform similarly in induced sputum sampled using a simplified method, by which induced sputum can be sampled and stored directly for later qPCR analyses, to the conventional method of manual plug selection. Two separate sputum samples were collected from 27 patients with asthma; one processed as a whole sample in an Oragene-RNA RE 100 vial and one processed using manual plug selection. Expression of 6GS was measured in both samples, of which 20 pairs (74%) had enough samples and results of sufficient quality of gene expression for further analyses. We found a significantly higher median RNA concentration in whole sampled sputum and consistently stronger gene expression compared to the plug method. Further, we found the two methods to agree, as 97% of observations were within the limits of agreement, as well as having a good-to-excellent reliability using intraclass correlation. Finally, we found 6GS in the whole sampled sputum to perform equal to or better than the manually selected plugs for discriminating inflammatory phenotypes defined by sputum differential count. In conclusion, whole sampling of induced sputum provides a clinically feasible method for inflammatory phenotyping.