Evaluation of Volatile Organic Compounds in Mepolizumab Therapy

Inclusion Criteria: * Age ≥ 18 and ≤ 80 years at Visit 1 * Able and willing to provide written informed consent and to comply with the study protocol * Severe asthma confirmed after assessment by an asthma physician, requiring treatment with high dose inhaled corticosteroids (ICS) as per BTS criteria \[≥1000 micrograms fluticasone propionate equivalent\] and ≥ 1 additional drug for asthma \[e.g. long acting beta2 agonist (LABA), leukotriene receptor antagonist (LTRA) such as montelukast, theophylline, long acting muscarinic antagonist (LAMA) such as tiotropium) at screening \[participants may be included with a lower dose of current ICS at the discretion of the investigator if previous high ICS dose had led to side effects\] * Adherent with background asthma medication in the opinion of the local MDT * Assessed and treatment optimized for any significant asthma-related co-morbidities in the opinion of the local MDT * Considered suitable by an asthma specialist for treatment with a monoclonal antibody to block the Interleukin-5 pathway as per local practice, in accordance with NICE TA 431 * a recorded blood eosinophil count ≥0.3 x 109/L within the past year * history of either ≥ 4 asthma exacerbations requiring high dose oral corticosteroids (exacerbations of asthma in the past year will be defined as worsening of asthma symptoms leading to treatment with prednisolone ≥30 mg oral corticosteroids for ≥3 days as defined by the ERS/ATS Task Force) OR * has had continuous oral corticosteroids of at least the equivalent of prednisolone 5 mg per day over the previous 6 months Exclusion Criteria: * Acute exacerbation requiring high dose oral corticosteroids in the 4 weeks prior to Visit 1. Such patients would be re-assessed when 4 weeks clear of the oral corticosteroid course for re-screening. * Long term systemic antibiotic or antifungal therapy * Other clinically significant medical disease (including malignancy or immunodeficiency requiring treatment) or uncontrolled concomitant disease that is likely, in the opinion of the investigator, to require a change in therapy or impact the ability to participate in the study * Active lung disease other than asthma \[Note: Controlled obstructive sleep apnoea (OSA), minor bronchiectasis, asbestos pleural plaques or old (inactive) TB scars are not exclusion criteria\]. Patients where an asthma-COPD overlap is suspected by the investigator are not eligible for inclusion * History of current alcohol, drug, or chemical abuse or past abuse that would impair or risk the subject's full participation in the study, in the opinion of the investigator * Current smoker or smoked in the past 12 month prior to Visit 1 or any history of e-cigarette use * Female patients who are pregnant or lactating or planning a family * Treatment with any of the following prior to Visit 1 or during the study * Any biologic medicine for asthma or an immunomodulating biologic agent for other conditions in the 6 months prior to Visit 1 * An investigational agent within 30 days of Visit 1 (or five half-lives of the investigational agent, whichever is longer). * Administration of live attenuated vaccine 30 days prior to Visit 1. Other types of vaccines are allowed. * Other ongoing immunosuppressive/ immunomodulating therapy \[e.g. methotrexate, ciclosporine, azathioprine\] other than oral corticosteroids for asthma. * Bronchial thermoplasty conducted within 6 months of Visit 1. * Patients with helminth infections must be excluded until the infection has been treated * Known hypersensitivity to Mepolizumab