The aim is to study the effect of OC000459 on eosinophilic airway inflammation and asthma control in subjects with severe, refractory eosinophilic asthma.

At week 12 subjects not on oral corticosteroids (OCS) will complete the treatment period and return after 4 weeks for final follow up visit. Those subjects who were taking OCS at baseline will continue for a maximum of 12 additional weeks, double blind period during which their current OCS treatment will be titrated down according to their clinical response.

Inclusion Criteria:

• Show evidence of reversible airflow obstruction documented within the previous 12 months or prior to Randomisation.
• Meet the European Respiratory Society/American Thoracic Society (ERS/ATS) criteria for severe asthma at Screening.
• Have documented evidence of eosinophilic airway inflammation during the 12 months prior to Screening.
• Have evidence of eosinophilic airway inflammation at Screening as reflected by an induced sputum eosinophil count of ≥3%.
• Subjects who are taking oral corticosteroids (OCS) must be receiving a 20 mg prednisolone equivalent dose, or less, daily for at least four weeks before the first dose of study drug. The dose of OCS should be unchanged for at least 14 days prior to the Baseline visit.

Exclusion Criteria:

• Treatment with XolairTM or anti-Th2 biologicals within 6 months prior to screening.
• Subjects with clinically significant abnormal serum biochemistry, haematology and urine examination values
• Subjects who have been hospitalised in the last 3 months.
• History of more than 2 episodes of confirmed bacterial lower respiratory tract infection or current lower respiratory tract infection.
• Subjects are current smokers or have a smoking history of >15 pack years.
• Significant comorbidity that in the Investigator's opinion is likely to impact the subject's participation in a 26 week study.
• Presence of a clinically important lung condition other than asthma, malignancy or previous history of cancer in remission for less than 12 months, clinically important liver or kidney disease, uncontrolled clinically significant cardiovascular disease, hypereosinophilic syndromes such as Churg-Strauss Syndrome or eosinophilic oesophagitis.