The IMPALA-2 trial

Why we are conducting the IMPALA-2 clinical trial

Autoimmune pulmonary alveolar proteinosis (aPAP) is a rare lung disease with no approved pharmacologic treatment options. This condition belongs to a family of distinct rare lung diseases collectively referred to as PAP. Autoimmune Pulmonary Alveolar Proteinosis represents about 90% of all patients with PAP.

PAP is characterized by the build-up of surfactant in the alveoli (air sacs) of the lungs. The surfactant consists of proteins and lipids and is an important physiological substance that lines the inside of the alveoli to prevent the lungs from collapsing. The lungs continuously produce new active surfactant. In a healthy lung, the surfactant is cleared by immune cells called alveolar macrophages. However, in lungs of patients with aPAP, the macrophages do not effectively clear the surfactant from the alveoli, leading to gradual accumulation of surfactant in the alveoli. The root cause of aPAP is an autoimmune response against granulocyte-macrophage colony-stimulating factor (GM-CSF), a naturally occurring protein in the body. Pulmonary macrophages need to be stimulated by GM-CSF to function properly, but in aPAP, GM-CSF is neutralized by antibodies against GM-CSF, rendering the macrophages unable to perform their tasks effectively, including the clearance of surfactant from the alveoli.

As a result of the accumulation of surfactant, oxygen transfer in the lungs is reduced and patients start to experience shortness of breath and decreased exercise tolerance as early symptoms. Typically, shortness of breath is first observed upon exertion, but as the disease progresses, shortness of breath can be experienced even when a person is at rest. Patients may experience cough, as well as episodes of fever, especially if secondary lung infection develops. In the long-term, the disease can lead to serious complications, including lung fibrosis and the need for lung transplant.