Blood Gene Expression and Immune Cell Subtypes Associated with Chronic Obstructive Pulmonary Disease Exacerbations.

Abstract

<b>Rationale:</b> Acute exacerbations of chronic obstructive pulmonary disease (AE-COPDs) are associated with a significant disease burden. Blood immune phenotyping may improve our understanding of a COPD endotype at increased risk of exacerbations. <b>Objective:</b> To determine the relationship between the transcriptome of circulating leukocytes and COPD exacerbations. <b>Methods:</b> Blood RNA sequencing data (<i>n</i> = 3,618) from the COPDGene (Genetic Epidemiology of COPD) study were analyzed. Blood microarray data (<i>n</i> = 646) from the ECLIPSE (Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints) study were used for validation. We tested the association between blood gene expression and AE-COPDs. We imputed the abundance of leukocyte subtypes and tested their association with prospective AE-COPDs. Flow cytometry was performed on blood in SPIROMICS (Subpopulations and Intermediate Outcomes in COPD Study) (<i>n</i> = 127), and activation markers for T cells were tested for association with prospective AE-COPDs. <b>Measurements and Main Results:</b> Exacerbations were reported 4,030 and 2,368 times during follow-up in COPDGene (5.3 ± 1.7 yr) and ECLIPSE (3 yr), respectively. We identified 890, 675, and 3,217 genes associated with a history of AE-COPDs, persistent exacerbations (at least one exacerbation per year), and prospective exacerbation rate, respectively. In COPDGene, the number of prospective exacerbations in patients with COPD (Global Initiative for Chronic Obstructive Lung Disease stage ⩾2) was negatively associated with circulating CD8⁺ T cells, CD4⁺ T cells, and resting natural killer cells. The negative association with naive CD4⁺ T cells was replicated in ECLIPSE. In the flow-cytometry study, an increase in CTLA4 on CD4⁺ T cells was positively associated with AE-COPDs. <b>Conclusions:</b> Individuals with COPD with lower circulating lymphocyte counts, particularly decreased CD4⁺ T cells, are more susceptible to AE-COPDs, including persistent exacerbations.