Inclusion Criteria:
* Participants must be \>=19 of age at the time of signing the informed consent form.
* Capable of giving signed informed consent.
* Treatment group:
1. Bilateral Chronic Rhinosinusitis with Nasal Polyposis and Asthma
a. Diagnosis consistent with EPOS 2020 b. Endoscopic Nasal Polyps Score (1-8) c. Asthma diagnosis based on: i. Consistent Clinical symptoms (History of wheeze, cough and breathlessness) ii. Reversible airflow obstruction (Spirometry)
2. Eligibility for Mepolizumab therapy (Canada)
3. On waiting list for surgery with planned wait of \>6 months
* Disease control group:
* Bilateral Chronic Rhinosinusitis without Nasal Polyposis, (only for the disease control group) oDiagnosis consistent with EPOS 2020
Healthy controls:
* Participants \>=19 of age and capable of giving signed informed consent
* Participants with no history of sinonasal or lower airway disease
Exclusion Criteria:
* Participants are excluded from the trial if any of the following criteria apply:
1. Women who are pregnant, plan to become pregnant or breastfeed during the trial.
2. Current participation in any other interventional treatment trials.
3. Compliance: is unlikely to comply with trial visits based on investigator judgment.
4. Secondary, or suspected secondary, cause of nasal polyposis:
1. EGPA, positive MPO ANCA or circulating eosinophilia \>10% total leukocytes
2. Known or suspected hereditary ciliary dysmotility (e.g: Cystic fibrosis, childhood-onset nasal polyposis)
3. Diagnosed or suspected malignant or premalignant nasal disease (e.g: Schniderian Papilloma, unilateral nasal polyposis)
4. Fungal rhinosinusitis (CT/Histology), positive Aspergillus skin prick testing and/or positive Aspergillus IgE RAST testing.
5. Aspirin Exacerbated Respiratory Disease/Salicylate allergy
5. Known hypersensitivity or significant allergies to monoclonal antibodies.
6. Malignant neoplasm within 5 years (from screening) excluding basal cell or squamous cell carcinoma of the skin treated with local resection only or carcinoma in situ of the uterine cervix treated locally and without metastatic disease for 3 years.
7. A history of a primary immunodeficiency.
8. Active bleeding disorders, and/or inability to support interruption to anticoagulant or anti-platelet therapies for nasal biopsy.
9. Severe nasal deformity precluding endoscopic assessment/biopsy of postnasal space
10. Severe heart failure (New York Heart Association Class IV) or other severe, uncontrolled cardiac disease.
11. Have a history of a major organ transplant or hematopoietic stem cell/marrow transplant.
12. Have an acute or chronic infection (excluding that related to CRS) requiring management as follows:
* Currently on any treatment for a chronic infection such as pneumocystis, cytomegalovirus, herpes simplex virus, herpes zoster, or atypical mycobacteria
* Hospitalisation solely for treatment of proven infection requiring parenteral (IV or IM) antibiotics (antibacterial, antiviral, antifungal, or anti-parasitic agents) within 60 days of Day 1.
* Proven severe infection requiring outpatient treatment with parenteral (IV or IM) antibiotics (antibacterial, antiviral, antifungal, or anti-parasitic agents) within 60 days of Day 1. Prophylactic anti-infective treatment is allowed.
13. Known positive human immunodeficiency virus (HIV) status.
14. Known positive Hepatitis B (HB) or Hepatitis C status.
15. Have clinical evidence of significant unstable or uncontrolled acute or chronic diseases not related to asthma which, in the opinion of the principal investigator, could confound the results of the trial or put the participant at undue risk.
16. Have a planned surgical procedure, laboratory abnormality, or condition that, in the opinion of the principal investigator, makes the participant unsuitable for the trial.
17. Have received any monoclonal antibody therapy ever.
18. Have received any investigational agent (that is not approved for sale in Canada) within 60 days of Day 1.
19. Have previously undergone sinus surgery or nasal polypectomy
20. Previous immunomodulatory therapy (excluding corticosteroids)
Healthy controls exclusion criteria
1. Have previously undergone sinus surgery or nasal polypectomy
2. Have received any monoclonal antibody therapy (e.g., dupilumab, mepolizumab, omalizumab)
3. Have known hypersensitivity or significant allergies to monoclonal antibodies
4. Have a positive human immunodeficiency virus (HIV), Hepatitis B or Hepatitis C status
5. Have tumors in the nasal cavity
6. Participants currently participating in other clinical trials
7. Have severe, uncontrolled cardiac disease
8. Have a history of a major organ transplant or hematopoietic stem cell/marrow transplant
9. Have an acute or chronic infection that is not related to chronic rhinosinusitis
