I’ve wondered how the stem cells were being harvested from blood, instead of from bone marrow, and here’s an explanation printed in Science Daily about the work of Professor Michael King. The author did a good job of explaining a complex process. Although I haven’t copied it here, the article also explains one way that cancer spreads.
During inflammation, the vascular wall presents surface selectins that adhere specifically to white blood cells. These selectins cause the white blood cells to roll slowly along the vascular wall, seeking signals that tell them to crawl out of the bloodstream. This is how white blood cells migrate to bacterial infections and tissue injuries. King set out to find a way to duplicate this natural process.
First, he noted that the selectins form bonds with the white blood cells within fractions of a second, then immediately release the cells back into the bloodstream. He also realized that selectin is the adhesive mechanism by which bone marrow stem cells leave the bloodstream and find their way back into bone marrow. This is how bone marrow transplantation works. Finally, he learned that when a cancer cell breaks free of a primary tumor and enters circulation, it flow through the bloodstream to a remote organ, then leaves the bloodstream and forms a secondary tumor. This is how cancer spreads. He put these facts together with one more, very important fact: the selectins grab onto a specific carbohydrate on the surfaces of white blood cells, stem cells, and cancer cells. Associate Professor King decided to capture stem and cancer cells before the selectins release them.
Harvesting Stem Cells
Because bone marrow stem cells stick to selectin surfaces more strongly than other cells, King’s group coated a slender plastic tube with selectin. They then did a series of lab experiments, both in vitro and in vivo using rats, with this selectin-coated tube to filter the bloodstream for stem cells. It worked, and the King Lab discovered that they could attract a large number of cells to the wall of their selectin-coated device, and that 38% of these captured cells were stem cells. King envisioned a system by which doctors could remove stem cells from the bloodstream by flowing the cells through a device, and make a more concentrated mixture containing, say, 20-40 percent stem cells. These stem cells could then be used for tissue engineering or bone marrow transplantation.
This is a non-controversial way of obtaining stem cells that can be differentiated into other, useful cells.