Flow diagram depicting use of bronchial brushings collected from subjects with (red, n=50) and without (gray, n=25) PMLs from the BCCA as part of the BC-LHS for differential gene expression/pathway analysis and for biomarker development. Independent human and mouse bronchial biopsies and biopsy cell cultures were used to validate these findings via mitochondrial enumeration, bioenergetics, and immunohistochemistry (left panel). Biomarker development was conducted by splitting samples from the BC-LHS into a discovery (n=58) and a validation set (Validation 1, n=17) (right panel).. The discovery set was used to create the gene expression-based biomarker to detect the presence of PMLs in the airway field of injury. The biomarker was tested on the BC-LHS validation set and an external validation set (bottom) from RPCI (Validation 2, n=28 matched time point pairs, stable/progressing pairs in yellow and regressing pairs in blue).