For the first time ever, blood-producing stem cells have been generated in a lab. Two separate teams of researchers have come up with differing ground-breaking methods to generate these important blood-forming cells, paving the way for the development of treatments for a variety of blood diseases and also offering a clear path towards an unlimited supply of lab-made blood for transfusions.

For almost 20 years, scientists have been searching for a way to use human embryonic stem cells to make blood-forming stem cells. While various researchers have discovered methods to get stem cells to grow into other human cell types, the trick to triggering blood stem cell generation has remained elusive.

A team of researchers at the Boston Children's Hospital just published a breakthrough study outlining a new process that has successfully generated blood stem cells in a lab environment and shown these cells to be capable of making several types of human blood cells when put into mice.

"This step opens up an opportunity to take cells from patients with genetic blood disorders, use gene editing to correct their genetic defect, and make functional blood cells," explains Ryohichi Sugimura, the study's first author.

Human induced pluripotent stem cells(Credit: Boston Children's Hospital)

Currently, patients with blood diseases, or those who have had their blood stem cells decimated from chemotherapy, often need bone marrow transplants as healthy blood stem cells are found in the body's bone marrow. But there is great difficulty in finding bone marrow transplant matches, with the probability of a match with a sibling being just one in four, while the chances of finding a match skyrocketing, depending on how rare your type is, to up to one in a million when moving out to the general population.

The Boston team's process starts with human pluripotent stem cells generated from skin cells, and exposes them to chemicals that direct the formation of an embryonic tissue that can lead to blood stem cells. The second step involved the discovery of five proteins that encourages those embryonic cells to transition into blood stem cells.

The team then transplanted those final cells into mice, and weeks later the mice were found to be carrying multiple types of human blood cells, from red blood cell precursors to T and B lymphocytes. This signaled to the researchers that the transplanted cells had functioned exactly as human blood stem cells.

Blood progenitor cells(Credit: Boston Children's Hospital)

The creation of whole blood suitable for transfusions is still some time away, but the team sees a pathway towards the development of lab-made blood that is reliable and free of disease.

"This also gives us the potential to have a limitless supply of blood stem cells and blood by taking cells from universal donors," adds Sugimura. "This could potentially augment the blood supply for patients who need transfusions."

Simultaneously to this remarkable announcement, a separate team of scientists announced a similar achievement in the generation of blood-forming stem cells in a lab, but by using a completely different process.

A team at Weill Cornell Medicine discovered a technique that generates hematopoietic stem cells (HTCs) from the simple vascular endothelial cells that line all blood vessels. HSCs are long-lasting cells that can turn into a variety of blood cells upon maturing.

The researchers discovered that they could take these vascular endothelial cells and engineer them to over-produce certain proteins associated with the functions of blood stem cells. When the reprogrammed HTCs were then transplanted into mice they saw the mice producing a variety of blood cells endowed with the genetic attributes of the original vascular cells.

The Weill Cornell research is an exciting discovery that increases our understanding of how stem cells self-renew in the human body, and both studies offer valuable insights into how our bodies regenerate blood. As well as looking to make unlimited supplies of clean blood in laboratories, this research directs us to new hopes for curing leukemia, correcting genetic defects that cause blood diseases such as sickle-cell anemia, and reducing the random lottery that is trying to find bone marrow transplant matches.

The Boston Children's Hospital team's research was published in the journal Nature, as was the Weill Cornell Medicine team's research.

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