WEDNESDAY, March 13, 2002 (HealthDayNews) -- Adult stem cells are running into the same problem that has bedeviled some prominent historians lately: Accusations that they're passing borrowed material off as original.
Adult stem cells, which in theory can become nearly any tissue in the body, have been touted as a possible cure for everything from heart disease to Parkinson's disease. Better still, because they can be derived from mature cell lines, like skin or blood, scientists needn't tread over ethical land mines by destroying embryos to collect them.
However, two new studies in this week's Nature suggest adult stem cells may not be quite so flexible after all. Rather, the researchers say, the tissues they go on to generate may arise from spontaneous fusion with other cells, and not from the stem cells themselves. What's more, the merger creates cells with twice the normal number of chromosomes and thus unknown implications for the people who might receive them.
"This is a cautionary tale," says Dr. Naohiro Terada, a stem cell expert at the University of Florida and lead author of one of the studies.
Terada and his colleagues combined bone marrow cells -- which contain mature stem cells -- with embryonic stem cells from mice engineered to glow green under a microscope. After letting the cells mingle, they treated them with a drug to kill off only the embryonic stem cells, leaving the rest intact.
What they found, Terada says, was that some of the stem cells had apparently fused with the marrow before going on to become other tissues. Despite appearing outwardly normal, genetic tests of those cells showed them to contain twice the normal cadre of chromosomes.
Spontaneous cell fusion is usually quite rare, but Terada says all the cells he and his colleagues tested had sprung from such combinations.
"We did not know some cells could fuse spontaneously, and stay alive. That was a very unexpected result," he says.
And in a second study, researchers in the United Kingdom saw that fusion also occurred when they combined brain cells with embryonic stem cells.
Austin Smith, a stem cell researcher at the University of Edinburgh and a co-author of one of the studies, refused to comment on the work. However, in a statement released Wednesday he said the finding "suggests a need for caution with regard to the therapeutic use of adult tissue stem cells. If they only make other tissues by fusing with existing cells rather than producing new cells, their utility for tissue repair and regenerative medicine will be greatly restricted."
"If nothing else," Smith adds, "our study indicates that calls for a halt to [embryonic stem] cell research are not scientifically justified."
President Bush's stem cell policy rests largely on the premise that adult stem cells are versatile enough to produce ample other tissues.
Terada stressed that both studies were conducted in lab dishes, not humans.
"We do not know yet such spontaneous fusion could really occur in [the] body," he says. As for what might happen if it did?
"We have over 30 years' experience for bone marrow, or blood stem cell, transplantation, and there are no complications known due to cell fusion," such as cancer, he says. "So, in any case, I don't think our story would limit usage of adult stem cells in clinics."
Nor do the findings necessarily apply to all adult stem cells, but rather only those mixed with embryonic stem cells. However, Terada says his group has unpublished evidence that bone marrow cells can fuse spontaneously with other cells, such as the fibroblasts that make up connective tissue.
What To Do
For more on stem cells and what's realistic to expect from them, check out the Batten Support & Research Trust.
You can also try the National Institutes of Health or the Society for Developmental Biology.
