Donor-derived type II pneumocytes are rare in the lungs of allogeneic hematopoietic cell transplant recipients.

Lung injury is a common cause of death and disability. Stem cell-related therapies are widely viewed as offering promise for people suffering from various types of pulmonary diseases, and gender-mismatched bone marrow transplant recipients serve as natural populations in which to study the role of bone marrow-derived stem cells in recovery from pulmonary injury. We evaluated the extent of lung repopulation by type II pneumocyte descendents of adult bone marrow-derived stem cells in allogeneic hematopoietic cell transplant recipients. Recut sections were obtained from five lung biopsy specimens and autopsy lung tissues from four female recipients of transplanted mobilized peripheral blood stem cells or bone marrow from male donors. Sequential immunohistochemistry and fluorescence in situ hybridization was performed on each section to evaluate for Y-chromosome-containing type II pneumocytes. A single Y-chromosome-containing type II pneumocyte was found in one lung biopsy from one hematopoietic cell transplant recipient. After adjustment for the effects of incomplete nuclear sampling, this pneumocyte represented 1.75% of all type II pneumocytes in the biopsy sample. There was no evidence of polyploidy to suggest cell-to-cell fusion. No donor-derived type II pneumocytes were found in samples from the other three patients. In conclusion, repopulation by bone marrow-derived stem cells or their progeny occurs at a low frequency in the lungs of hematopoietic cell transplant recipients. Conversely, proliferation by local stem cell populations appears to be more important for recovery from alveolar injury.