Inhaled Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF) in Hereditary Pulmonary Alveolar Proteinosis (PAP)

Inclusion Criteria: * A diagnosis of PAP caused by bi-allelic mutations in CSF2RA or CSF2RB associated with impaired GM-CSF-R-alpha or GM-CSF-R-beta function, respectively, resulting in reduced but non-zero GM-CSF signaling * Able and willing to give written informed consent / assent as necessary * Clinically stable Exclusion Criteria: * Confirmed diagnosis of a disorder of surfactant production caused by bi-allelic mutations in ABCA3, SFTPB, or SFTPC * Confirmed diagnosis of autoimmune PAP caused by a high level of GM-CSF autoantibody * Confirmed diagnosis of secondary PAP caused by an underlying clinical disorder known to be associated with the development of PAP, e.g., inhalation of silica or titanium; myelodysplasia and others * Treatment with any investigational agent in the 3 months prior to enrollment * History of severe allergic or anaphylactic reactions to GM-CSF or other yeast-derived products * History of asthma or other reactive airways disease * Known active, viral, fungal, mycobacterial, or other infection * A serious medical condition which, in the opinion of the investigator or data and safety monitoring committee, would make the patient unsuitable for the study