The purpose of this study is to identify differentially expressed gene transcripts after initiation of mepolizumab in individuals with severe eosinophilic asthma (SEA).

Inclusion Criteria:

• Age ≥ 18 years old.
• Diagnosis of SEA by a health care provider
• History of an absolute eosinophil count ≥ 300/mm^3
• Prescription for mepolizumab provided during course of routine clinical care but mepolizumab not yet started

Exclusion Criteria:

• Age < 18 years old.
• Pregnancy.
• Currently using or have used within 3 months of the initial baseline visit any biologic or immunomodulatory therapy with the exception of #3.
• Currently using or any prior use of rituximab.
• History of upper/lower respiratory tract infection or asthma exacerbation within the previous four weeks of the first baseline visit.
• Any prior history of malignancy, autoimmune disease, or immune deficiency.
• Any other significant medical issue as determined by the principal investigator.

This study will involve twenty adult (≥18yo) individuals with a diagnosis of severe eosinophilic asthma (SEA) who have been prescribed mepolizumab during their course of routine clinical care.

De-identified individual participant data (IPD) underlying the RNA sequencing results reported in this study will be made available upon reasonable request, beginning after publication of the primary results and for up to five years thereafter. Requests may be submitted to the study PI and will be reviewed based on scientific merit, feasibility, and compliance with applicable ethical and regulatory requirements. Data will be shared under a data use agreement, and only de-identified data will be provided to protect participant confidentiality.

from enrollment until end of follow-up, up to 12 weeks