Male and female subjects addressed to the Asthma Center, aged ≥12 yrs with severe asthma as defined by ATS/ERS guidelines (≥12months high-dose ICS + additional controller treatments), ≥2 exacerbations (corticosteroid and/or ED visit and/or hospitalization in the previous 12 months), blood eosinophil ≥150 cells/µl at study entrance or ≥300cells/µl historically and a smoking history <2 pack/year.