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Researchers from UC San Francisco have discovered blood stem cells in the lungs, disrupting a decades-old belief that new blood cells were only made in the bone marrow. Conventionally it was thought that hematopoietic stem cells (HSCs) which produce different types of blood cells were mostly found in the bone marrow, a spongy mass found in the middle of large bones like the legs and hips. But the new finding published in the journal Blood shows that these stem cells, capable of producing a variety of cells including red blood cells and platelets which form blood clots and aid in tissue healing, are also found in the lungs.
“For decades, bone marrow transplants have been a lynchpin in the treatment of cancers like leukemia,” said Mark Looney , MD, senior author of the paper and professor of medicine and laboratory medicine at UCSF. “The lung HSCs could prove to be a second and significant reservoir of these precious stem cells," said in a news release from UCSF. Blood stem cells, often extracted from bone marrow have been used for decades as a successful treatment for a variety of diseases including blood cancers such as leukemias, as well as autoimmune diseases.
There is a constant need for new donors, especially individuals from racial and ethnic minorities and the new research suggests that the lungs could be an important new source of these cells for transplants. The research started back in 2017 where the team found HSCs in the lungs of mice which were capable of making red blood cells, as well as white blood cells which help with fighting infections and healing and also cells which produce platelets. The team then looked at donated lung tissue from humans, finding similar HSCs in lung tissue.
The team extracted these cells from lung tissue and grew them in the lab, showing that they were able to produce different types of blood cell, including red blood cells and megakaryocytes, the cells which produce platelets. When these cells were put into immunocompromised mice that had a lack of their own HSCs, the human HSCs were able to produce blood cells in the mice. “We think these HSCs could be a reservoir of hematopoiesis [blood cell production] in a particular organ, in this case the lung, that gets activated whenever the body needs more of any part of the blood, whether it’s platelets, red blood cells or immune cells,” said Looney.
The researchers aren’t exactly sure yet why the HSCs are in the lung, but speculate that their presence could act as a “backup” in case the lungs urgently need more blood cells of a certain type. “The lungs are critical to blood circulation, so it’s tantalizing to see the lung HSCs as an emergency reservoir for red blood cell and platelet production,” said Looney..
