Conflict of interest: T. Yanagihara reports grants from Boehringer Ingelheim, outside the submitted work. C. Guignabert reports grants from Acceleron Pharma (Cambridge, MA, USA), a wholly owned subsidiary of Merck & Co., Inc. (Rahway, NJ, USA), Corteria pharmaceutical, and Structure therapeutics (ex ShouTi), outside of submitted work. M.R.J. Kolb reports being site PI for sponsored clinical trials for Roche and Boehringer Ingelheim, grants from Canadian Institute for Health Research, grants and personal fees for advisory board work from Boehringer Ingelheim and Roche Canada, a chief editor allowance from the European Respiratory Society, personal fees for advisory board work from Horizon, Algernon, CSL Behring, DevPro, Bellerophon and BMS, personal fees for adjudication committee work from United Therapeutics, and personal fees for data monitoring committee work from LabCorp, outside the submitted work.