In the Double-blind treatment period, eligible subjects will be randomised to treatment for up to 24 weeks with either: 1) inhaled molgramostim (300 µg) once daily, 2) inhaled molgramostim (300 µg) and matching placebo administered intermittently (seven days on and seven days off) or 3) inhaled placebo once daily. During the trial, WLL may be applied as rescue therapy in case of significant clinical worsening. In the Follow-up period, open-label treatment with molgramostim will be provided.