Abstract: The disclosure provides therapies that are useful in the prevention of pulmonary vascular remodeling and treatment of vascular conditions. In particular, the disclosure provides methods of treatment of pulmonary vascular diseases comprising administration of an inhibitor of programmed cell death protein 1 (PD-1) or the corresponding programmed death-ligand 1 (PD-L1). These methods comprise administering to a subject a PD-1 or PD-L1 inhibitor such as a monoclonal antibody. Further provided herein are diagnostic methods for assessing patient sensitivity to therapies. Methods of identifying a subject having a pulmonary hypertension that is sensitive to treatment with a PD-L1 inhibitor or a PD-1 inhibitor are provided. Subjects identified as having a pulmonary hypertension that is sensitive to anti-PD-L1 treatment may be subsequently administered a PD-L1 inhibition treatment.