We have developed a novel lentiviral vector, pseudotyped with the F and HN proteins from Sendai virus (rSIV.F/HN), which produces long-lasting, high efficiency transduction of the respiratory epithelium. Here, we addressed whether this platform technology can secrete sufficient levels of a therapeutic protein into the lung to ameliorate a fatal pulmonary disease, as an exemplar of its translational capability. Pulmonary Alveolar Proteinosis (PAP) results from alveolar GM-CSF insufficiency, resulting in abnormal surfactant homeostasis and consequent ventilatory problems. Lungs of GM-CSF knockout mice were transduced with a single dose of rSIV.F/HN expressing murine (m)GM-CSF (1e5-92e7 TU/mouse); mGM-CSF expression was dose-related and persisted for at least 11 months. PAP disease biomarkers were rapidly and persistently corrected, but we noted a narrow toxicity/efficacy window. rSIV.F/HN may be a useful platform technology to deliver therapeutic proteins for lung diseases requiring long-lasting and stable expression of secreted proteins.