Researchers Hunt for New Stem Cell Sources
Adult cells may be more useful than previously believed
TUESDAY, July 6, 2004 (HealthDayNews) -- While embryonic stem cell research has been stymied by limited federal funding, researchers continue to look for other cell sources that offer the same promise for treating disease.
To that end, Tufts University researchers now report there may be a previously unrecognized and untapped source of fetal cells in the blood of women who have been pregnant. And researchers from Yale University believe adult stem cells from bone marrow may have more potential than researchers have realized because they discovered that bone marrow cells play a role in the development of the endometrial lining of the uterus every month in women who have undergone marrow transplants.
Results of both studies appear in the July 7 issue of the Journal of the American Medical Association.
"There's a whole political controversy over embryonic stem cells," said one study's author, Dr. Hugh Taylor, of Yale School of Medicine. "The question is, do we need to use embryonic stem cells, or are there other stem cells, like those in bone marrow?"
Taylor added he believes researchers "haven't realized the full potential of the bone marrow," and said there may be many applications for marrow cells.
Likewise, the author of the Tufts study, Dr. Diana Bianchi, said another potential source of stem cells is women who have been pregnant.
"Studies have virtually ignored the role of pregnancy, but women who have been pregnant potentially have cells with therapeutic potential from their fetus," she said.
Stem cells are unspecialized cells that can develop into many different types of specialized cells. Researchers believe these cells may be the key to developing treatment for diseases such as Parkinson's, Alzheimer's, spinal cord injuries, arthritis and many others.
Embryonic stem cells, which are harvested from human embryos, hold the most promise because they are "pluripotent." That means they can develop into many different types of cells. Adult stem cells are considered "multipotent" and aren't believed to be able to transform into as many types of cells as embryonic stem cells.
Research on embryonic stem cells is limited because of President Bush's decision in August 2001 to only allow federal funding for research on stem cells derived from embryos that had already been destroyed. Most researchers depend, at least in part, on federal funding.
Bianchi and her colleagues retrieved cells from the tissue samples of 10 women who had male sons and compared them to tissue samples from 11 women who had never had male offspring. The reason the researchers chose women with male offspring is that it would be easy to detect cells from male offspring because male cells carry the Y chromosome, while female cells do not.
The tissue samples were from the thyroid, cervix, liver, lymph node, intestine, spleen and gallbladder. Skin samples were also collected from 11 women in a control group.
Bianchi said that not only did they find fetal cells present in the mothers' tissue samples, but that the fetal cells had taken on the characteristics of the mother's cells.
For example, she said, "in the thyroid, there were fetal cells that looked and acted like thyroid cells, and we knew they were fetal cells because they had the Y chromosome."
The next step, according to Bianchi, is to figure out how to harvest these cells before they have transformed. And, she said, that's exactly what the Tufts researchers are working on in experiments with mice.
Taylor's study, unlike Bianchi's, focused on adult stem cells.
He tested samples from the endometrium of four women who had received bone marrow transplants. The endometrium is the lining of the uterus that is shed and then regenerates every month to prepare the body for a potential pregnancy.
Up until now, said Taylor, it was believed that a small layer of cells inside the uterus was what prompted that regrowth every month. But, Taylor found cells in the endometrium that matched the bone marrow transplant donors, rather than the recipients.
"Apparently cells from outside [the uterus] can come in and contribute. Bone marrow cells enter and turn into endometrial cells," said Taylor.
He said these findings could explain why some women with the disease endometriosis -- in which endometrial tissue grows outside of the uterus, usually in the abdominal cavity -- sometimes have endometrial cells in faraway places, such as the lung or brain.
"Bone marrow has the ability to regenerate many cell types thought not to be possible," said Taylor. "We're finding more and more that the body has remarkable plasticity, and bone marrow seems to be very rich in cells that have potential to turn into cells of other organ systems."
To learn more about stem cells, visit the National Institutes of Health.