TFF3 and bronchiolitis obliterans syndrome: Although samples collected via the Cytosponge can be assayed for several biomarkers including methylation [53], multigene next-generation sequencing panels [54], and microRNAs [55] useful for screening and surveillance, the current modus operandi for detecting BO from specimens obtained using this device is immunohistochemical staining of Trefoil Factor Protein 3 (TFF3) which is an indicator of intestinal metaplasia (the histopathological feature of BO).