This study will look at the permeability, or 'leakiness' of the airway epithelium (the inner lining of the lung) in asthmatic patients. Increased leakiness of this lining has been shown in asthmatic patients by other studies, not only in the lung but also possibly in the gut, perhaps reflecting a widespread defect. This leakiness may underline the interaction between the environment and a person's genetic make up, and may contribute to why some people get asthma, and how severe it is. Increased leakiness may allow increased exposure to inhaled allergic substances, helping to perpetuate the inflammation in the lungs that is a hallmark of asthma.

Specifically, this study will attempt to modify and reduce this permeability through the use of a substance called 'keratinocyte growth factor', or 'kgf'. KGF is a naturally occuring human protein, which is involved in stimulating the growth of cells lining the layers of the skin and gut, helping to repair damage and maintain their structure. It has been manufactured in a laboratory as the commercial compound 'Palifermin', which has already been used in humans to reduce damage to the lining of the mouth after chemotherapy. The study will see if Palifermin can similarly improve the lining of the lung in asthma patients and improve their symptoms. To date no treatments have been used in this area in asthma, and if successful the study will open up a whole new area of therapy

Inclusion Criteria:

• Age 18 - 60 years, either gender
• Confirmed diagnosis of asthma for > 1 year as defined by BTS guidelines, requiring treatment with high dose inhaled corticosteroids +/- long acting β2 agonists, with persisting symptoms requiring use of short-acting beta agonist therapy >3x/week.
• Never-smoker or ex-smoker, having stopped >1 year ago, with <10 pack year history.
• Subject must understand the procedures of the study and agree to participation in the study by providing written informed consent
• Subject considered fit enough to undergo lung function testing including provocation tests, and bronchoscopy.
• Subject must not be participating in another clinical trial or have done so within the last 12 weeks.

Exclusion Criteria:

• Patients requiring regular maintenance oral steroids for their asthma, or those who are adhering to symbicort SMART single inhaler regime.
• Pregnancy (where pregnancy is defined as the state of a female after conception and until the termination of gestation, confirmed by a positive hCG laboratory test >5mIU/ml), an intention to become pregnant or breast-feeding (lactating).
• Subjects with active lung disease other than asthma
• Significant medical (cardiopulmonary, neurological, renal, endocrine, gastrointestinal, psychiatric, hepatic or haematological)co-morbidity which in the view of the investigator could impact on the interpretation of results or participation in the trial, or which is uncontrolled with standard treatment.
• Current participation in another clinical trial or previous participation within the last 12 weeks.
• Alcohol or active drug abuse.
• Ongoing allergen desensitisation therapy
• Regular use of sedatives, hypnotics, tranquilisers
• Cancer or previous history of cancer
• Inability to understand directions for dosing and study assessment.
• Inability to be contacted in case of emergency.