This exploratory laboratory only study will assess alterations in immune cells in blood samples that may be responsive to an inflammatory mediator in asthma called IL-33 (Innate lymphoid type 2 cells, basophils and Th2 cells) in response to treatment with ANB020/placebo (a drug that targets IL-33, in the linked clinical trial ANB020-004). The study will involve additional 10ml blood draws on scheduled study visits in the ANB020-004 clinical trial at baseline, 1 week, 5 weeks, 18 weeks (4 visits total). Total number of subjects is 24 at the same 3 participating UK sites as the main linked clinical trial ANB020-004.

Blood samples will be sent on the same day to a flow cytometry laboratory at the NIHR Leicester Biomedical Research Centre (BRC) - Respiratory. A dedicated post doctoral, trained laboratory scientist will analyse the blood samples for the required cell types using a technique called flow cytometry - this technique identifies cell surface and intercellular markers, that together provide a unique cell identity. The experiments will be supervised by a senior research scientist and flow cytometrist Professor Dave Cousins, at the University of Leicester and results of the experiments will be fed back to AnaptysBio (the linked clinical trial Sponsor). Professor Salman Siddiqui at the University of Leicester will oversee the clinical conduct of this laboratory study and act as the Chief Investigator. Professor Siddiqui is also the local site lead Principal Investigator at Leicester for the linked ANB020-004 clinical trial described below.

The linked study (ANB020-004) is a Double-blind Placebo-Controlled Proof of Concept Study to Investigate ANB020 (a drug that targets an inflammatory mediator called IL-33) Activity in Adult Patients with Severe Eosinophilic Asthma. The expected duration of the study is up to 141 days. Screening period of 7-14 days and treatment and follow-up period of 127 days.

Inclusion Criteria: Consenting participant in the ANB020-004 clinical trial (EudraCT 2017-000647-40) -

Exclusion Criteria:1) Unwilling to have four additional blood samples (10 mls per sample) for flow cytometry as part of the flow cytometry biomarker study linked to existing ANB020-004 study. (EudraCT 2017-000647-40)

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Asthma patients taking part in the link study ANB202-004 (EudraCT 2017-000647-40) will be asked to take part in this observational study, in parallel with the main study.