(American Thoracic Society) -- Based on the results of studies with the tissues of two out of three patients, investigators have provided the first evidence of chimerism in the human lung after human stem cell transplantation, according to an article in the first issue for August 2003 of the American Thoracic Society's peer-reviewed journal.

Benjamin T. Suratt, M.D., of the Division of Pulmonary Sciences and Critical Care Medicine, University of Vermont Health Sciences Research Facility, Burlington, along with seven associates, in a report in the American Journal of Respiratory and Critical Care Medicine, found significant rates of epithelial (2.5 to 8 percent) and endothelial (37.5 to 42.3 percent) chimerism in lung tissue samples from two of three patients who had undergone either lung biopsy or autopsy.

"Many of the body's tissues once thought to be only locally regenerative may, in fact, be actively replaced by circulating stem cells after hematopoietic stem cell transplantation," said Dr. Suratt.

He noted that localization of donor-derived cells or chimerism had recently been shown to occur in the cells of mice after either hematopoietic stem cell transplantation or infusion of cultured marrow.

Dr. Suratt said that his team's results suggest that significant chimerism of the human lung may follow hematopoietic stem cell transplantation and that adult human stem cells could potentially play a therapeutic role in treatment of the damaged lung.

According to the authors, donor-derived epithelial and endothelial cells were predominately found in the alveoli, although donor-derived epithelial cells were occasionally found in the bronchial lining. (The bronchioles are the smaller airways with dozens of bubble-shaped, air-filled cavities at their end called alveoli.)

The tissue specimens were obtained from patients at time periods ranging from 50 to 463 days after transplantation.

"Although the small sample size of this study limits definitive conclusions," said Dr. Suratt, "the lack of chimerism in the second patient is of interest. Given the patient's relatively brief engraftment period at the time of biopsy at 50 days, compared with the first patient at 200 days and the third patient at 462 days, this might reflect a requirement for long-term engraftment before circulating stem cells incorporation or differentiation in the lung."

The authors note that given current limitations in the field, detailed analysis of the true incidence and degree of pulmonary chimerism after a transplant, as well as factors that may influence its appearance, must await the development of better techniques and the examination of large numbers of human stem cell transplant recipients.