1 From the Division of Pulmonary Allergy and Critical Care Medicine, Center for Clinical Epidemiology and Biostatistics, Lung Biology Institute at the University of Pennsylvania Perelman School of Medicine, Philadelphia (J.D.C.); the Department of Thoracic Surgery, University Hospitals Leuven, and the Laboratory of Respiratory Diseases and Thoracic Surgery, Department of Chronic Diseases and Metabolism, KU Leuven University - both in Leuven, Belgium (D.V.R.); and the Department of Transplantation and Regenerative Medicine, Newcastle University Translational and Clinical Research Institute, Newcastle University, Newcastle upon Tyne, United Kingdom (A.J.F.).