Granulocyte Macrophage-Colony Stimulating Factor (GM-CSF) Inhalation to Improve Host Defense and Pulmonary Barrier Restoration

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