New University Of Toronto Strategy Will Boost Cord Blood Stem Cells

In a paper published in the October issue of ExperimentalHematology, researchers working in the University of Toronto's StemCell Bioengineering Laboratory have identified an important componentblocking the growth of stem cells. U of T scientists discovered stemcells in 1961, and for about two decades researchers around the worldhave been searching for a way to expand the number of stem cellsharvested from umbilical cord blood, which can be used instead of bonemarrow for transplantation into patients with blood cancers.

"It's been very hard to grow blood stem cells at all," says ProfessorPeter W. Zandstra of the University of Toronto's Institute ofBiomaterials and Biomedical Engineering, and head of the laboratory inwhich the research was conducted. "We've tried to understand how thosecells talk to each other, and by controlling that, trying to get theones we want to grow better."

In any culture, blood stem cells are very rare, Zandstraexplains: typically less than one in 100 cells. "If you want to growthat one cell among the other cells that are more aggressive, you haveto target that cell."

The research team developed a way to remove the non-stem cells --differentiated cells, or "lineage-positive" cells -- to create anenvironment that allows stem cells to grow better. "A mature[lineage-positive] cell expresses markers of differentiated lineages,and a stem cell is typically negative for these markers," Zandstrasays. "So we removed the lineage-positive cells. They secretemolecules, or cytokines, which inhibit growth of stem cells. So, byremoving them, we're making the environment better for stem cells."

Typically, the umbilical cord does not yield a large volume ofstem cells -- perhaps enough to treat a child, but rarely an adult. Thenew research findings may allow new cord-blood stem cells to bedeveloped in the laboratory -- enough to treat adult patients as wellas children. The major use of blood stem cells is for transplantationinto patients with leukemia and other blood-borne cancers.

From their studies in mice, the researchers know that new stemcells obtained through their expansion technology can engraft in bonemarrow and maintain special properties such as the ability to migratein the body.

The researchers have further refined their system by developinga "bioreactor" -- a vessel in which to grow the stem cells in a closedand controlled environment, away from environmental contaminants.

"The hope is that very soon, if the results are the same withthe bioreactor as they were with our experiments to date, we will moveto clinical trials," says Zandstra -- ideally within the next year.