By contrast, the roles of DPP-4, DPP-9, and DPP-10 are supported mainly by preclinical studies in pulmonary hypertension, acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), pulmonary fibrosis, asthma, non-small cell lung cancer (NSCLC), and nonsteroidal anti-inflammatory drugs (NSAIDs)/aspirin-exacerbated respiratory disease. Here, DPP9 is linked to pulmonary arterial hypertension.