Comparison of Immune Profiles in Chronic Rhinosinusitis Patients After Mepolizumab Treatment

Who May Qualify: 1. Are over the age of 19. 2. Patients with CRSwNP with or without asthma: - Asthma confirmed with a spirometry and assessment on previous history of asthma (a methacholine challenge test and atopy testing to document positive or negative history of asthma will be performed if there is no clinical record). - Presence or absence of nasal polyps. This can be based on formal exam at Baseline Visit or historical assessment. 3. Patients with CRSsNP with asthma: - These patients will not take the study treatment and they will only complete screening and baseline visits. 4. Females of childbearing potential must commit to using an acceptable method of birth control for the duration of the study and they must have a negative urine pregnancy test at each study visit. Who Should NOT Join This Trial: 1. Current or past sinonasal or bronchial tumours 2. Subjects who have been treated with oral antibiotics in the past month prior to surgery. 3. Subjects with known weakened immune system 4. Subjects with known autoimmune conditions (where your immune system attacks your own body) 5. Smoking history; current or former smokers. 6. Prior lung transplants 7. Subjects with parasitic (helmintic) infection 8. Subjects with hypersensitivity; with allergy/intolerance to a monoclonal antibody or biologic 9. Female participants who are pregnant or breastfeeding Always talk to your doctor about whether this trial is right for you.