Bone marrow-derived stem-cell repopulation contributes minimally to the in transplanted type II pneumocyte pool human lungs

Background. Lung transplant recipients are vulnerable to immunologic, infectious, ischemic, and toxic pulmonary injuries. The authors investigated whether type 11 pneumocytes in the lungs of cross-gender lung transplant patients show genotypic evidence to support repopulation of the lung by stem cells of bone marrow origin, and whether the degree of repopulation was related to rejection history. Methods. Recut sections were obtained from lung biopsy specimens from seven male recipients of transplanted lungs from female donors. Sequential inummohistochemistry and fluorescence in situ hybridization was performed on each section to evaluate for Y-chromosome-containing type II pneumocytes. Results. Y-chromosome-containing type 11 pneumocytes were found in 9 of 25 biopsy specimens from 5 of 7 gender-mismatched male lung transplant recipients, and accounted for 0% to 0.553% of type 11 pneumocytes. There was no evidence of polyploidy to suggest cell-cell fusion. The number of type II pneumocytes of male karyotype showed a statistically significant relationship to the cumulative number of episodes of acute cellular rejection. Conclusions. Lung transplant recipients develop low levels of pneumocyte repopulation by bone marrow-derived stem cells or their progeny. These cells contribute minimally to the type 11 pneumocyte proliferation that is often present in these patients as a sequela to alveolar injury.