The study is designed to look at the safety, tolerability and efficacy of 2 different doses of the study drug (CHF6001, a PDE4 inhibitor) in asthmatics, when given by inhalation, once a day for 9 days. The efficacy will be evaluated by measuring the protective effect of CHF 6001 after an allergen challenge.

Inclusion Criteria:

• written informed consent obtained
• Non smoking or ex-smokers from at least 1 year prior to study entry
• Males of females between 18 and 60 years inclusive
• Body Mass Index between 18 and 32 kg/m2
• Ability to be trained about the proper use of the inhalation device and to perform spirometry
• With mild to moderate allergic asthma as defined by the GINA guideline, steroid naive
• Atopy to at least one common aeroallergen
• Positive allergen-induced Early Asthmatic Response and Late Asthmatic Response at screening
• Ability to produce an adequate sputum sample
• Post-menopausal women, women of not childbearing potential or males and females of childbearing potential willing (they or their partner) to use a reliable method of contraception.

Exclusion Criteria:

• Worsening of asthma or respiratory tract infection prior to study entry
• History of life-threatening asthma or hospitalization for asthma prior to the study entry
• Pregnant or lactating women
• History of clinically significant hypotensive episodes or fainting, dizziness or light-headedness
• History or symptoms of clinically relevant neurologic disease
• Symptomatic hay fever
• Unstable concurrent disease that may impact the feasibility of the study
• Use of systemic corticosteroids, nebulised bronchodilator or oral beta2-agonist
• Use of leukotrienes modifiers, roflumilast or cromoglycate
• Use of long acting beta2-agonist or inhaled corticosteroids
• Use of short-acting or long-acting non-sedatives antihistamines
• Use of any other medication for the treatment of allergic asthma other than salbutamol
• Having received an investigational medicinal drug within 30 days prior to study entry
• Blood drawn of at least 250 ml in the previous 45 days
• Ongoing use of tobacco
• Other lung disease
• Recent history of alcohol dependency
• Inability to comply with the study protocol