Ontario researchers say they believe they've made a major breakthrough in stem cell research, isolating the key stem cells that can allow for the endless replenishment of human blood.

Scientists have long known that "mother cells" or "fountainhead" blood-producing cells existed; they know they're in bone marrow, which helps the body replenish blood throughout life.

For decades, bone marrow donations have been used to treat people with blood cancers such as leukemia, or rare genetic diseases.

But such transfusions require that patients receive many other elements along with the stem cells in the bone marrow donations -- components that sometimes increase the risk of rejection.

Being able to narrow in on just the key stem cells needed for new blood production has always held out the hope that it could open the door to entirely new ways of treating cancer and other diseases.

Now, researchers at Toronto's University Health Network say they've found these mother stem cells – or hematopoietic stem cells (HSCs) -- that can regenerate all types of blood cells, including red blood cells, lymphocytes and macrophages.

"This discovery means we now have an increasingly detailed road map of the human blood development system including the much sought after stem cell," said principal investigator Dr. John Dick, a Senior Scientist at the McEwen Centre for Regenerative Medicine and the Ontario Cancer Institute.

Decades of painstaking research was required to get to this point.

Dick and his team made the discovery by systematically transplanting human bone marrow and blood extracts into mice without immune systems.

They uncovered the fountainhead cells by scanning for unique proteins on the cells' surface known as biomarkers. They narrowed the field of potential cells that might be HSCs to about 10,000 candidates, all of which possessed a common biomarker.

Through a long trial-and-error process, they then injected each of the cells one by one into the mice, to see which ones allowed the lab animals to begin producing blood and which didn't.

They finally narrowed in on the signature marker, which they've dubbed CD49f. The discovery is detailed in the latest issue of Science.

Now that researcher know to look for the CD49f biomarker, it will be easier to extract genuine HSCs from all other blood stem cells. Dick and his team say stem cells with CD49f are so rare, there is only one for every three million cells in the human body.

The goal is now to find out whether it's possible to safely regenerate a patient's entire blood system from scratch, using just a small population of the CD49f-marked cell.

"Ever since stem-cell science began, scientists have been searching for the elusive mother lode – the single, pure stem cell that could be controlled and expanded in culture prior to transplantation into patients," Dick said in a news release.

"These new findings are a major step to generate sufficient quantities of stem cells to enable greater clinical use and thus move closer to realizing the promise of regenerative medicine for patients."