Patient description: A 39-year-old man came to the clinic with cough and shortness of breath that was not relieved by his inhaler. He had these symptoms for 5 days during the past 2 weeks. He doubled his oral corticosteroids in the past week. He is a chef with a history of asthma for 3 years, suffering from frequent cough, wheezing, and shortness of breath and chest tightness. The symptoms become more bothersome within 1-2 hours of starting work every day and worsen throughout the work week. His symptoms improve within 1-2 hours outside the workplace. Spirometry was performed revealing a forced expiratory volume in the first second (FEV1) of 63% of the predicted. His past medical history is significant for seasonal allergic rhinitis in the summer. He doesn't smoke or use illicit drugs. His family history is significant for asthma in his father and sister. He currently uses inhaled corticosteroid (ICS) and fluticasone 500 mcg/salmeterol 50 mcg, one puff twice daily.

Clinical trial eligibility criteria: eligible ages (years): 18.0-75.0,  Asthma; Eosinophilic Severe Asthma Patients between 18 and 75 years old Patients diagnosed with severe asthma (Chung and al, Eur Respir J 2014), i.e asthma requiring high doses of ICS (>1000 microgram per day of Beclomethasone or equivalent) associated with LABA and/or systemic corticosteroids to be controlled over one year and/or uncontrolled asthma despite the later medications and/or a controlled asthma worsening after decreasing medications Pre-BronchoDilatator (BD) FEV1 <80% of the predicted value at M-1 Documented historical reversibility of FEV1 ≥12% and FEV1 gain ≥ 200 milliliter ACQ-7 score ≥ 1,5 at M-1 and M0 ≥ 3 exacerbations in the 12 months prior to screening visit M-1 Eosinophil blood count ≥ 0,3 G/L at screening visit or in the 12 months prior to the screening visit. If eosinophil blood count is ≥ 0,15 G/L and < 0,3 G/L, an eosinophilic phenotype defined by at least 1 of the following will be required  Patients diagnosed with difficult-to-treat asthma and/or with asthma differential diagnosis that have not yet been excluded (vocal cord dysfunction, gastroesophageal reflux disease, granulomatous eosinophilic vasculitis, obstructive sleep apnea syndrome, hyperventilation syndrome, allergic broncho-pulmonary aspergillosis, Carrington disease, Diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNEC), asthma/ chronic obstructive pulmonary disease (COPD) overlap syndrome) Non-adherent patients to inhaled treatment (ICS + LABA) Active smokers or former smokers exceeding 20 packs year Exacerbation at screening visit M-1 Exacerbation within the past 4 weeks prior to M0, to avoid confounding effects of a short course of systemic corticosteroids that could bias basal molecular signature Active malignancy or malignancy in remission over less than 5 years Active parasitic infection or parasitic infection in the past 24 weeks Hypersensitivity to Benralizumab or to any of the excipients of Fasenra® (histidine, histidine hydrochloride monohydrate, trehalose dihydrate, polysorbate 20) Patients requiring other immunosuppressive and immunomodulator drugs Patients requiring other biotherapy than Benralizumab, with or without French's marketing authorisation in severe asthma