Sputum Transcriptomic Analysis and Clustering Reveals Insight Into Asthma Heterogeneity.

Introduction: Asthma is a heterogenous disease shaped by different inflammatory pathways. The aim is to investigate transcriptomic profiles in asthmatic patients and associate these with inflammation, airway damage and lung function.

Methods: Adult asthma patients attending the outpatient pneumology clinic in our tertiary center, underwent diagnostic sputum induction and upon consent remaining sputum RNA was used for bulk RNA-sequencing (n = 56) coupled with unsupervised clustering. A retrospective analysis of comorbidities was performed. Sputum cytokine mRNA levels were determined via qPCR. Airway damage markers were determined in sputum supernatant RESULTS: Unsupervised clustering subdivided all asthmatic patients in one of three clusters. Cluster 1 contained most of the pauci-granulocytic asthma patients in whom oxidative stress was upregulated and TLR-signalling and several cytokine pathways down-regulated. Cluster 2 had upregulated S100 family signalling pathway genes, was mostly associated to type 2 inflammation with elevated sputum eosinophils, epithelial damage, IL-4 mRNA levels and allergy. Asthma patients in cluster 3 had worse lung function, upregulated inflammatory genes, increased sputum neutrophils and calprotectin levels.

Conclusion: Three different asthma clusters could be identified bridging over the classical type 2/non-type 2 classification.

Clinical trial: ClinicalTrials.gov Identifier: NCT01224938 registered on 19 October 2010.