In a study that will further cement this city’s pioneer standing in the field, Toronto scientists have become the first in the world to isolate the stem cell for human blood.
The work out of the University Health Network will greatly increase researchers’ abilities to study the blood-producing cells and will lead to better therapies for treating diseases like leukemia, the study’s authors say.
“We’ve never really had this stem cell in our hands before,” says John Dick, a senior scientist at the hospital’sOntario Cancer Institute.
“And if you haven’t had it in your hands before (you) actually don’t know what makes it tick,” says Dick, the senior study author.
The study was released Thursday by the journal Science.
Blood stem cells have been utilized more successfully than any other variety in the treatment of diseases.
Donated stem cells from matched donors are most often used to replenish the blood-producing bone marrow that is destroyed by chemotherapy in the treatment of leukemia patients.
But those patients, who have their own defective stem cells destroyed to stop their runaway blood production, are currently being transfused with many other marrow elements in addition to the life-saving stem cells, Dick says.
“We’re transplanting a whole (mishmash) of cells and relying on the rare stem cells (in the mix) to actually do the job,” Dick says.
These non-stem cell components, he says, increase the risk of a rejection condition known as graft-versus-host disease, where immune cells lingering in the donated marrow begins to attack the recipient.
“By now going in and fishing out stem cells, we’ll be able to transplant pure populations of cells for transplantation,” Dick says.
The discovery will also allow researchers to study the cells far more closely and seek a technique that will coax them to multiply.
“Even after all these years of study, we don’t know what makes a stem cell tick . . . because we never had one in our hands,” he says. “Now we have almost pure stem cells in a test tube, we can begin to look at their molecular workings.”
The problem with stem cells in therapeutic use is that there are so few of them and those that are there cannot be made to multiply readily in laboratories.
By having actual specimens to study, Dick says, research can now focus on creating a recipe of growth factors and other bio-chemicals that will coax the cells to multiply, greatly expanding the supply for patients who need transplants.
“If we knew how to trick them to get out of their dormancy and to expand to make more stem cells, that would be a big advance,” Dick says. “That would open the window to having a lot more sources of stem cells for people who need it.”
The Toronto team uncovered the fountainhead cells — which account for only one in 3 million blood cells — by scanning for unique proteins on their surface known as markers.
By injecting cells with different markers into mice, which have a compatible system to humans, scientists could see which ones produced blood and which didn’t.
Through more than 20 years of such work, Dick and other scientists had narrowed the field of potential stem cells down to about 10,000 candidates, all of which possessed a common marker.
Through a process of elimination the search was now on for cells that possessed additional markers unique to the stem cell variety.
The new study has identified that signature marker, labelling it CD49f.
“Now, for the first time, we can basically sift through a haystack of a million straws and find that one needle that is the stem cell,” Dick says.
Following in the footprints of James Till and Ernest McCulloch, who discovered their existence at the same institute half a century ago, Dick’s finding is the latest in a subsequent series of groundbreaking stem cell work that originated in this city.