Researchers at U of T have discovered a new source of stem cells that may have use in bone marrow transplants, and which raise fewer ethical dilemmas than embryonic stem cells.
Stem cells are the focus of intense medical research because they are capable of forming many different kinds of cells. They could be used to regenerate lost or damaged human organs. But although adult humans have stem cells in many different kinds of tissues, such as bone marrow, brain, muscle, and eye tissue, the stem cells are few and far between, and difficult to isolate. The richest sources of human stem cells are embryos and umbilical cord blood, and most feel that it is from these sources that stem cells could be harvested for therapeutic use.
Bone marrow, bone, ligaments, fat, and the tissue holding them together all grow from mesenchymal stem cells. U of T professor John E. Davies and his team at the Institute of Biomaterials and Biomedical Engineering (IBBME) have discovered a new source of these cells, in the jelly-like mass surrounding the blood vessels of the umbilical cord.
Usually this material, called Wharton’s Jelly, is discarded after birth. Samples of umbilical cord blood, on the other hand, are often saved by parents as insurance against future disease or injury because the blood contains stem cells. But only one out of 200 million blood cord cells is a stem cell. In some regions of the jelly, however, one in every 300 cells is a stem cell.
Scientists first suggested that Wharton’s Jelly contained precursor cells in 1991. But it took 14 years for anyone to find a significant source of jelly stem cells because nobody knew precisely where to look, explained Davies.
As the growing umbilical cord itself requires a steady supply of mesenchymal stem cells, Davies reasoned that “the most obvious location for the cells would be [right] around the blood vessels of the cord, from which they would get their nutrient supply. Other investigators have seen the presence of the vessels as a complication, and have thus discarded [the vessels] before recovering the remaining Wharton’s Jelly. The problem with [that] approach is that in disposing of the vessels you also remove the Jelly [located immediately next to the blood vessels]-the very region which we hypothesized would contain the most interesting cells.”
The use of human embryonic stem cells is extremely controversial. “Our cells are not embryonic,” countered Davies. The cells come from the umbilical cord and not the actual body of the embryo. But “embryonic stem cells are totipotent [capable of forming any kind of cell], ours are [merely] multipotent; they can only [form] a restricted number of cell types, rather than all cell types,” said Davies. For this reason, many experts believe that only embryonic stem cells will be useful in medical treatments.
Mick Bhatia, director of the Robarts Research Institute based in London, Ontario, voiced some of the difficulties in to the Senate’s Committee on Social Affairs, Science and Technology, on February 19, 2004.
“One of the difficulties in the use of [adult] stem cells…[is that] there a limited numbers of cells,” he continued. “There has been a lot of work done to try to regrow these cells in large numbers to compensate for this deficiency; however, adult stem cells have limited growth potential. Therefore, you have a problem in terms of being able to get enough cells to transplant.”
But unlike adult stem cells, the cells Davies isolated from the umbilical cord can divide and grow rapidly. When cultured in petri dishes, Davies’ cells divided at twice the rate of adult bone marrow stem cells and slightly faster even than embryonic stem cells.
Davies says these results are very encouraging. “It would be very nice to think that many labs will want to use these cells for both their research and for cell-based therapies,” said Davies. “We have already shipped cells to labs in Germany and England-the results from these labs confirm some of our most important findings. Thus, for those wishing to generate lots of mesenchymal cells, our cells could [be the answer].”
