CHGA and bronchiolitis obliterans syndrome: To confirm whether the relationship between BO cells and OSGs was stronger than the associations with other gland-type cells, we looked across the RNA compositions of cells from other tissues, i.e. gastric gland cells and BO cells that did not express CHGA or MUC2 (to exclude enteroendocrine and goblet cells, respectively; see Methods for thresholding), and oesophageal cells that expressed TFF3 (to exclude squamous cells, Supplementary Fig. 5d-e).