Researchers at the University of California - Los Angeles (UCLA) have found that blood stem cells originate and are nurtured in the placenta, a discovery that may allow scientists to mimic the embryonic environment needed to develop blood stem cells in cell culture.
As part of the study, lead researcher Dr. Hanna Mikkola and her colleagues used a unique mouse model, a mouse embryo without a heartbeat.
"Using this model, we identified that the placenta has the potential to make hematopoietic (blood) stem cells with full differentiation ability to create all the major lineages of blood cells," Mikkola said.
"The placenta acts as a sort of kindergarten for these newly made blood stem cells, giving them the first education they need.
"This is the first time we can really say definitively that blood stem cells are generated in the placenta. There's no more speculation," she said.
Though scientists knew that blood stem cells - that later differentiate into all the cells in the blood supply - could be found in the dorsal aorta, they ruled it out as the sole source of such stem cells as very few were found there.
The new study indicates that the first niche for expansion of blood stem cells is the placenta's vascular labyrinth, where oxygen and nutrients are exchanged between the mother and the foetus.
It also shows that the placenta harbours two different microenvironments, one area where blood stem cells originate and another area, the labyrinth, that nurtures them, allowing them to expand in number.
These niches serve different roles and could provide clues to researchers seeking to grow blood stem cells.
Dr. Mikkola, a researcher in the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research and senior author of the study said that development of blood stem cells in cell culture would then allow researchers to grow them for use in treating diseases like leukemia and aplastic anemia.
"If we want to fully harness the potential of embryonic stem cells to treat disease, it's critical for us to learn how to make tissue specific stem cells. We can learn that by studying what happens during embryonic development," she added.
Boffins are currently able to take embryonic stem cells, the cells that can become any tissue type in the body, and make them into cells in the blood supply, such as red and white blood cells and platelets.
However, they can't make blood stem cells that self-new, or make more of themselves, and don't differentiate prematurely when transplanted into patients.
To generate blood stem cells that are safe for use in patients, it is imperative that scientists learn how to generate self-renewing blood stem cells in a more natural way, by providing the correct developmental cues from the environment in which the cells develop.