Understanding Asthma Phenotypes, Endotypes, and Mechanisms of Disease

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Abstract

The model of asthma as a single entity has now been replaced by a much more complex biological network of distinct and interrelating inflammatory pathways. The term asthma is now considered an umbrella diagnosis for several diseases with distinct mechanistic pathways (endotypes) and variable clinical presentations (phenotypes). The precise definition of these endotypes is central to asthma management due to inherent therapeutic and prognostic implications. This review presents the molecular mechanisms behind the heterogeneity of airway inflammation in asthmatic patients. Asthma endotypes may be broadly regarded as type 2 (T2) high or T2-low. Several biologic agents have been approved for T2-high asthma, with numerous other therapeutics that are incipient and similarly targeted at specific molecular mechanisms. Collectively, these advances have shifted existing paradigms in the approach to asthma to tailor novel therapies.

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T-helper type 2-driven inflammation defines major subphenotypes of asthma.

Prescott G Woodruff, Barmak Modrek, David F Choy … (2009)

T-helper type 2 (Th2) inflammation, mediated by IL-4, IL-5, and IL-13, is considered the central molecular mechanism underlying asthma, and Th2 cytokines are emerging therapeutic targets. However, clinical studies increasingly suggest that asthma is heterogeneous. To determine whether this clinical heterogeneity reflects heterogeneity in underlying molecular mechanisms related to Th2 inflammation. Using microarray and polymerase chain reaction analyses of airway epithelial brushings from 42 patients with mild-to-moderate asthma and 28 healthy control subjects, we classified subjects with asthma based on high or low expression of IL-13-inducible genes. We then validated this classification and investigated its clinical implications through analyses of cytokine expression in bronchial biopsies, markers of inflammation and remodeling, responsiveness to inhaled corticosteroids, and reproducibility on repeat examination. Gene expression analyses identified two evenly sized and distinct subgroups, "Th2-high" and "Th2-low" asthma (the latter indistinguishable from control subjects). These subgroups differed significantly in expression of IL-5 and IL-13 in bronchial biopsies and in airway hyperresponsiveness, serum IgE, blood and airway eosinophilia, subepithelial fibrosis, and airway mucin gene expression (all P < 0.03). The lung function improvements expected with inhaled corticosteroids were restricted to Th2-high asthma, and Th2 markers were reproducible on repeat evaluation. Asthma can be divided into at least two distinct molecular phenotypes defined by degree of Th2 inflammation. Th2 cytokines are likely to be a relevant therapeutic target in only a subset of patients with asthma. Furthermore, current models do not adequately explain non-Th2-driven asthma, which represents a significant proportion of patients and responds poorly to current therapies.

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Lebrikizumab treatment in adults with asthma.

Jonathan Corren, Robert Lemanske, Nicola Hanania … (2011)

Many patients with asthma have uncontrolled disease despite treatment with inhaled glucocorticoids. One potential cause of the variability in response to treatment is heterogeneity in the role of interleukin-13 expression in the clinical asthma phenotype. We hypothesized that anti-interleukin-13 therapy would benefit patients with asthma who had a pretreatment profile consistent with interleukin-13 activity. We conducted a randomized, double-blind, placebo-controlled study of lebrikizumab, a monoclonal antibody to interleukin-13, in 219 adults who had asthma that was inadequately controlled despite inhaled glucocorticoid therapy. The primary efficacy outcome was the relative change in prebronchodilator forced expiratory volume in 1 second (FEV(1)) from baseline to week 12. Among the secondary outcomes was the rate of asthma exacerbations through 24 weeks. Patient subgroups were prespecified according to baseline type 2 helper T-cell (Th2) status (assessed on the basis of total IgE level and blood eosinophil count) and serum periostin level. At baseline, patients had a mean FEV(1) that was 65% of the predicted value and were taking a mean dose of inhaled glucocorticoids of 580 μg per day; 80% were also taking a long-acting beta-agonist. At week 12, the mean increase in FEV(1) was 5.5 percentage points higher in the lebrikizumab group than in the placebo group (P = 0.02). Among patients in the high-periostin subgroup, the increase from baseline FEV(1) was 8.2 percentage points higher in the lebrikizumab group than in the placebo group (P = 0.03). Among patients in the low-periostin subgroup, the increase from baseline FEV(1) was 1.6 percentage points higher in the lebrikizumab group than in the placebo group (P = 0.61). Musculoskeletal side effects were more common with lebrikizumab than with placebo (13.2% vs. 5.4%, P = 0.045). Lebrikizumab treatment was associated with improved lung function. Patients with high pretreatment levels of serum periostin had greater improvement in lung function with lebrikizumab than did patients with low periostin levels. (Funded by Genentech; ClinicalTrials.gov number, NCT00930163 .).

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Mepolizumab for prednisone-dependent asthma with sputum eosinophilia.

Parameswaran Nair, Marcia M M Pizzichini, Melanie Kjarsgaard … (2009)

Eosinophilic inflammation, which may be a consequence of interleukin-5 action, is a characteristic feature of some forms of asthma. However, in three previous clinical trials involving patients with asthma, blockade of this cytokine did not result in a significant improvement in outcomes. We studied the prednisone-sparing effect of mepolizumab, a monoclonal antibody against interleukin-5, in a rare subgroup of patients who have sputum eosinophilia and airway symptoms despite continued treatment with prednisone. Secondary objectives were to examine its effect on the number of eosinophils in sputum and blood, symptoms, and airflow limitation. In this randomized, double-blind, parallel-group trial involving patients with persistent sputum eosinophilia and symptoms despite prednisone treatment, we assigned 9 patients to receive mepolizumab (administered in five monthly infusions of 750 mg each) and 11 patients to receive placebo. There were 12 asthma exacerbations in 10 patients who received placebo, 9 of whom had sputum eosinophilia at the time of exacerbation. In comparison, only one patient who received mepolizumab had an asthma exacerbation, and this episode was not associated with sputum eosinophilia (P=0.002). Patients who received mepolizumab were able to reduce their prednisone dose by a mean (+/-SD) of 83.8+/-33.4% of their maximum possible dose, as compared with 47.7+/-40.5% in the placebo group (P=0.04). The use of mepolizumab was associated with a significant decrease in the number of sputum and blood eosinophils. Improvements in eosinophil numbers, asthma control, and forced expiratory volume in 1 second were maintained for 8 weeks after the last infusion. There were no serious adverse events. Mepolizumab reduced the number of blood and sputum eosinophils and allowed prednisone sparing in patients who had asthma with sputum eosinophilia despite prednisone treatment. (ClinicalTrials.gov number, NCT00292877.) 2009 Massachusetts Medical Society