Several studies demonstrated the ability of GM-CSF to rescue mice infected with lethal influenza A.18,21,22 Prior human studies reported recombinant human (rhu) GM-CSF as safe and well tolerated with potential benefit in patients with pulmonary conditions including ARDS and autoimmune pulmonary alveolar proteinosis (aPAP).23–27 In sepsis, GM-CSF is known to reverse immunoparalysis with beneficial outcomes.28–30 Additionally, sargramostim (yeast-derived, glycosylated rhu GM-CSF) can be administered directly to the lung by inhalation. Here, CSF2 is linked to acute respiratory distress syndrome.