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In a groundbreaking study, researchers at the University of California, San Francisco (UCSF) have uncovered a previously unknown function of the human lungs: the production of blood-forming stem cells. This discovery challenges long-held beliefs that blood cell generation occurs exclusively in the bone marrow and could significantly impact the field of stem cell transplants.
A New Source of Life-Saving Stem Cells
Red blood cells, essential for oxygen transport throughout the body, are produced at an astonishing rate of 200 billion per day. For years, scientists believed that the bone marrow was solely responsible for this process. However, new research, published in the journal Blood on February 27, 2025, has revealed that the lungs also serve as a source of hematopoietic stem cells (HSCs), the crucial precursors to blood cells.
The study identified lung-based HSCs capable of generating red blood cells and megakaryocytes—the latter responsible for producing platelets essential for clot formation. This discovery opens the door to alternative stem cell sources that could be used in life-saving transplant therapies.
“For decades, bone marrow transplants have been pivotal in the treatment of blood-related disorders such as leukemia,” said Dr. Mark Looney, senior author of the study and professor of medicine and laboratory medicine at UCSF. “With lung HSCs, we now have a second, potentially valuable reservoir of these precious stem cells.”
From Mice to Humans: Confirming the Findings
The UCSF team first identified lung-based HSCs in mice back in 2017. They observed that nearly 50% of the platelets in a mouse’s circulatory system were produced in the lungs. Intrigued by these findings, researchers set out to determine if the same phenomenon occurred in humans.
To verify their hypothesis, scientists analyzed donated human lung, bone marrow, and blood samples. Their screening efforts revealed that lung tissue contained HSCs that closely resembled those found in the bone marrow. Moreover, the concentration of these cells in lung tissue was comparable to that in bone marrow.
“The lung HSCs weren’t just anomalies; they were consistently present,” explained Dr. Catharina Conrad, postdoctoral scholar and lead author of the paper. “Our next step was to determine whether they could actually generate blood.”
The Potential for New Therapeutic Applications
To further investigate, researchers cultivated lung-derived and bone marrow-derived HSCs in controlled lab conditions. Both types of HSCs successfully developed into blood cells. However, lung HSCs demonstrated a higher capacity for producing red blood cells and platelets, while bone marrow HSCs predominantly generated immune cells.
Additionally, human lung HSCs were able to restore blood production in mice that lacked functional bone marrow. This finding corroborates previous research suggesting that lung and bone marrow HSCs can complement one another by replenishing deficient cell populations.
“We believe these lung HSCs could act as an emergency backup system, responding to the body’s needs by producing specific blood components—whether it be platelets, red blood cells, or immune cells,” Dr. Looney noted.
A Paradigm Shift in Hematopoiesis
To ensure that the lung HSCs were truly residing in lung tissue rather than migrating from bone marrow, researchers examined their precise location within the lung. The cells were found nestled between blood vessels in a structural arrangement similar to that observed in bone marrow.
“This suggests that lung HSCs are not transient cells passing through the bloodstream but are truly residing within the lung environment,” Dr. Conrad stated.
Further analysis of conventional bone marrow transplants revealed an unexpected insight: approximately 20% of the stem cells isolated from donor blood samples carried the unique markers of lung-derived HSCs. This suggests that current “bone marrow transplants” may already include a significant contribution from lung-based stem cells.
Looking Ahead: The Future of Stem Cell Therapy
With this discovery, scientists now face exciting new questions. Could different pools of HSCs serve distinct therapeutic roles? Why do lungs require their own stem cell production?
“Given the lungs’ central role in blood circulation, it’s fascinating to consider their function as a potential emergency reserve for blood cell production,” Dr. Looney said. “This finding opens new possibilities for hematopoietic stem cell transplants, a therapy already widely used for patients with blood disorders.”
Conclusion
The identification of lung-based HSCs marks a major advancement in the understanding of human blood production. If further research confirms the therapeutic viability of these cells, the field of regenerative medicine could witness a transformation, offering new hope to patients requiring stem cell transplants.
Disclaimer: This article is based on preliminary research findings. While promising, further studies and clinical trials are necessary to validate the therapeutic applications of lung-derived hematopoietic stem cells. Patients should consult medical professionals before considering any new treatment options.
