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by John C. Martin
August 18, 2005
Doctors examining the role of naturally-produced stem cells in the repair of damaged lungs have concluded that they contribute very little to the repair process.1
The researchers, reporting in the journal Transplantation, say miniscule levels of a certain type of lung stem cell involved in tissue repair were found in the bone marrow of lung transplant recipients.
Stem cells - parent cells of a wide variety of cells in the body - are housed in the bone marrow of adults. They've caught the eye of medical researchers because of their ability to differentiate into functional tissue cells after older cells in the tissue die or are injured. Stem cells can also transform into blood cells, which circulate between bone marrow and the bloodstream.2 These also include stem cells of the lung, which was the focus of this study.
Other research has shown that stem cells circulating in blood are capable of transforming into other types of tissue, including lung tissue,3 explained the study's head investigator, Dani Zander, MD, of the University of Texas Medical School. But this latest study provides evidence of their transformation.
Zander's group examined lung biopsy specimens collected from seven male transplant recipients who had received lungs from female donors, searching for a specialized type of lung-based stem cell involved in lung repair. While the team uncovered small numbers of the male gender version of the stem cells, they were located in only nine of 25 specimens taken from 5 transplant recipients.
This suggested that bone marrow-derived stem cells play a minor role in lung repair after transplantation, but it's hoped they can be leveraged as a therapy of some sort in the future, explained Zander, who is a professor of Pathology and Laboratory Medicine. "It's possible in the future that circulating stem cells could be augmented to play a greater role in lung repair, and people are looking at ways to do that," she said. "We found that the bulk of stem cell contribution to the repair process belongs to those stem cells normally found in the lungs rather than to circulating stem cells."
Why is lung tissue repair necessary after a transplant? Lung transplant recipients are vulnerable to pulmonary injury from infections, potential rejection of the transplanted lung, ischemia (blockage of blood flow in the lungs prior to transplant), and other factors that damage the organ's air sacs, experts say.
The team also found that the numbers of stem cells in the lung tissue were directly related to the extent of tissue injury, suggesting that stem cell migration to the lungs might be stimulated by greater levels of injury in that organ.
It's not exactly known why the male version of the stem cells was found in lungs donated by women, but it's possible that it might have been connected to an earlier pregnancy with a male fetus, Zander said. Still, the relationship between the numbers of stem cells found in the lung tissue and damage from rejection makes that unlikely, she added.
"The lung has received relatively little investigation in this area," said Zander. "It's a challenging organ to study because the air-tissue interfaces make it difficult to separate different cell types."
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
Copyright © 1999-2005 Priority Healthcare Inc.
This article posted September 17, 2005.