Relationship between inflammatory status and microbial composition in severe asthma and during exacerbation

Background In T2-mediated severe asthma, biologic therapies, such as mepolizumab, are increasingly used to control disease. Current biomarkers can indicate adequate suppression of T2 inflammation, but it is unclear whether they provide information about airway microbial composition. We investigated the relationships between current T2 biomarkers and microbial profiles, characteristics associated with a Proteobacteria(HIGH) microbial profile and the effects of mepolizumab on airway ecology. Methods Microbiota sequencing was performed on sputum samples obtained at stable and exacerbation state from 140 subjects with severe asthma participating in two clinical trials. Inflammatory subgroups were compared on the basis of biomarkers, including FeNO and sputum and blood eosinophils. Proteobacteria(HIGH) subjects were identified by Proteobacteria to Firmicutes ratio >= 0.485. Where paired sputum from stable visits was available, we compared microbial composition at baseline and following >= 12 weeks of mepolizumab. Results Microbial composition was not related to inflammatory subgroup based on sputum or blood eosinophils. FeNO >= 50 ppb when stable and at exacerbation indicated a group with less dispersed microbial profiles characterised by high alpha-diversity and low Proteobacteria. Proteobacteria(HIGH) subjects were neutrophilic and had a longer time from asthma diagnosis than Proteobacteria(LOW) subjects. In those studied, mepolizumab did not alter airway bacterial load or lead to increased Proteobacteria. Conclusion High FeNO could indicate a subgroup of severe asthma less likely to benefit from antimicrobial strategies at exacerbation or in the context of poor control. Where FeNO is <50 ppb, biomarkers of microbial composition are required to identify those likely to respond to microbiome-directed strategies. We found no evidence that mepolizumab alters airway microbial composition.

Automated summary

This study investigated the relationship between T2 biomarkers and airway microbial composition, as well as the effects of mepolizumab on airway ecology. The results showed that high FeNO levels may indicate a subgroup of severe asthma patients less likely to benefit from antimicrobial strategies, while low FeNO levels require biomarkers of microbial composition to identify patients likely to respond to microbiome-directed strategies. Additionally, mepolizumab did not alter airway microbial composition.