RT Journal Article SR Electronic T1 Primary mesenchymal stem cells in human transplanted lungs are CD90/CD105 perivascularly located tissue-resident cells JF BMJ Open Respiratory Research JO BMJ Open Resp Res FD British Thoracic Society SP e000027 DO 10.1136/bmjresp-2014-000027 VO 1 IS 1 A1 Sara Rolandsson A1 Annika Andersson Sjöland A1 Jan C Brune A1 Hongzhe Li A1 Moustapha Kassem A1 Fredrik Mertens A1 Albert Westergren A1 Leif Eriksson A1 Lennart Hansson A1 Ingrid Skog A1 Leif Bjermer A1 Stefan Scheding A1 Gunilla Westergren-Thorsson YR 2014 UL http://bmjopenrespres.bmj.com/content/1/1/e000027.abstract AB Background Mesenchymal stem cells (MSC) have not only been implicated in the development of lung diseases, but they have also been proposed as a future cell-based therapy for lung diseases. However, the cellular identity of the primary MSC in human lung tissues has not yet been reported. This study therefore aimed to identify and characterise the ‘bona fide’ MSC in human lungs and to investigate if the MSC numbers correlate with the development of bronchiolitis obliterans syndrome in lung-transplanted patients. Methods Primary lung MSC were directly isolated or culture-derived from central and peripheral transbronchial biopsies of lung-transplanted patients and evaluated using a comprehensive panel of in vitro and in vivo assays. Results Primary MSC were enriched in the CD90/CD105 mononuclear cell fraction with mesenchymal progenitor frequencies of up to four colony-forming units, fibroblast/100 cells. In situ staining of lung tissues revealed that CD90/CD105 MSCs were located perivascularly. MSC were tissue-resident and exclusively donor lung-derived even in biopsies obtained from patients as long as 16 years after transplantation. Culture-derived mesenchymal stromal cells showed typical in vitro MSC properties; however, xenotransplantation into non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice showed that lung MSC readily differentiated into adipocytes and stromal tissues, but lacked significant in vivo bone formation. Conclusions These data clearly demonstrate that primary MSC in human lung tissues are not only tissue resident but also tissue-specific. The identification and phenotypic characterisation of primary lung MSC is an important first step in identifying the role of MSC in normal lung physiology and pulmonary diseases.