This trial evaluates efficacy and safety of inhaled molgramostim (rhGM-CSF) in 45 patients with pneumonia associated acute respiratory distress syndrome (ARDS). A third of the patients will receive 150 mcg inhaled molgramostim, another third 450 mcg and the remaining third will receive inhaled placebo for 3 days. The patients will be followed for 28 days.

Inclusion Criteria:

1. Signed informed consent form by the patient or a legal representative according to local regulations
2. Man or woman 18 to 75 years of age, inclusive
3. Women who have been post-menopausal for more than 1 year or women of childbearing potential period using a highly efficient method of contraception (i.e. a method with less than 1% failure rate such as combined hormonal contraception, progesterone-only hormonal contraception, intrauterine device, intrauterine hormone-releasing system, bilateral tube occlusion, vasectomized partner, sexual abstinence) during dosing and hospitalisation. Women must have a negative serum or urine pregnancy test before the first dose of study medication and must not be lactating.
4. Diagnosis of pneumonia-associated ARDS, where the underlying condition is Community-Acquired Pneumonia (CAP) or Hospital-Acquired Pneumonia (HAP) in patients not on invasive ventilation upon diagnosis of HAP.
5. Diagnosis of ARDS according to the Berlin ARDS definition.
6. Requirement for positive pressure ventilation (non-invasive or via endotracheal tube) for more than 72 hours in total with inspiratory oxygen concentration (FiO2) ≥ 50% (or less when on additional ECMO therapy) not longer than 14 days

Exclusion Criteria:

1. Receiving vasopressors of >100 µg/min
2. History of liver cirrhosis Child Pugh C, chronic hemodialysis (before severe pneumonia/ARDS), lung cancer
3. Malignancy with expected survival time of less than 6 months
4. History of or listing for lung transplantation
5. Highly immunosuppressive therapy or anti-malignant combination chemotherapy within 3 weeks prior to first dose of study drug
6. Any anti-malignant chemotherapy within 24 hours prior to first dose of study drug
7. AIDS or known history of HIV infection
8. Pregnancy
9. Autoimmune thrombocytopenia, myelodysplastic syndromes with > 20% marrow blast cells
10. History or presence of hypersensitivity or idiosyncratic reaction to molgramostim or to related compounds (i.e., Growgen®, Leucomax®, Leukine™, Topleucon™)
11. Participation in another clinical trial within 90 days prior to the first dose of study drug