The aim of the study is to evaluate, comparatively to a placebo, the activity of oral AB1010, administered at three dose levels during 4 months to patients with severe persistent corticosteroid dependent asthma, assessed on :

• the decrease in corticosteroid therapy
• the asthma control improvement (symptomatic scores, rescue medication intake, respiratory function)
• the pharmacokinetic profile of AB1010
• clinical and biological safety parameters

This is a double-blind, placebo-controlled, randomized, parallel-groups, multicenter study of daily oral AB1010 at doses 3, 4.5 and 6 mg/kg/day.

The study treatment is administered for 16 weeks:

• the first 4 weeks are a run-in period during which corticosteroids remain stable;
• during the following 8 weeks, corticosteroids are decreased every week until weaning or an exacerbation occurs;
• the last 4 weeks are a stabilization period. Patients have to perform a visit every 2 weeks during run-in, then every week for the following 3 months.

Inclusion Criteria:

• Known severe persistent corticosteroid dependent asthma (WHO/NHLBI workshop definition).
• Disease duration > 1 year.
• Stable disease with no exacerbation episode for at least one month before inclusion.
• Daily treated with 10 to 50 mg of equivalent prednisolone, with stable dosage since at least 3 months.
• Known reversibility of bronchial obstruction, defined as an enhancement of FEV1 ≥ 12%, 10 minutes after salbutamol administration, or 14 days after systemic treatment with 1 mg/kg/day of equivalent prednisolone.

Exclusion Criteria:

• Asthmatic patients still exposed to allergens or to triggering factors influencing asthma control.
• History of infection requiring hospitalization or treatment with antibiotics within 2 weeks of screening.