Jewish World Review

New research questions potential of adult stem cells | (KRT) Adult stem cells have been heralded as the wave of the future for cardiovascular care. Believed to repair damaged heart tissue, and create healthy new cells, they have been touted as an ethically correct and safe avenue for future heart therapy.

But two new papers, the first from labs at the University of Washington and Indiana University and another from Stanford University, question their potential - and call researchers to use caution before proceeding further with human trials.

The studies also highlight the limitations of adult stem cells - once again putting the spotlight on the potential of their sister cells: embryonic stem cells.

In back-to-back papers that appeared in Monday's online release of the journal Nature, researchers have shown that - at least in mice - stem cells that were derived from bone marrow and injected into damaged mouse hearts did not build or regenerate new heart tissue.

This contrasts with work done in 2001 by a team from the National Institutes of Health that purported to show that heart tissue could be repaired using adult mouse stem cells.

That earlier work led to a series of human trials in which bone marrow was harvested from a patient's hip, filtered for stem cells, and then re-injected into the patient's damaged heart.

And although the results of these trials were promising, exactly what the stem cells were doing in the human heart - whether they were creating new tissue or doing something else - remained unknown.

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These new studies suggest that "we really don't understand what's going on," said Tim Kamp, a professor of medicine and physiology at the University of Wisconsin-Madison, who was not involved in these studies.

And it should make people cautious about the potential for adverse effects in these trials, he said.

The hoopla over ready-made stem cells for heart care started in 2001, when the NIH paper was released.

And although that paper was based on research using mice, medical experts immediately grasped its potential.

In medical procedures where a patient receives new tissue, or cells - like from bone marrow - the cells are often donated by someone other than the receiver.

Doctors are careful to make sure the receiver and donor match up - because if they don't, the receiver will reject the new cells and destroy them.

Researchers reasoned that if stem cells could be harvested from a patient and then used to treat him - like in the 2001 mouse study - there would be no risk of rejection.

In addition, there wouldn't be any of the ethical baggage that comes with embryonic stem cells.

Unlike human embryonic stem cells, which are harvested from a blastocyst - or several-day-old embryo - adult stem cells come right out of a living, breathing, voluntary adult.

So, with no rejection risk - or ethical considerations dogging them - doctors started performing this experiment on patients.

The problem was, they couldn't say for sure what was happening to their patients' hearts. They believed the stem cells were probably creating, or repairing damaged tissue, just as in the 2001 mouse study - but there was no way of knowing.

Now, the two new studies suggest that adult bone marrow stem cells do not create new heart tissue, said Loren Field, a researcher from Indiana University and co-author of one of the papers.

And because of this, he and his team, as well as the Stanford researchers, are calling for medical prudence and caution in human trials.

"If we are delivering bone marrow to patients with the expectation that it will regenerate the heart, that may not be realistic," said Leora Balsam, a member of the Stanford team.

And although both teams believe the stem cells could be contributing to increased blood flow through the heart by creating or recruiting new blood cells - exactly what you'd expect from a bone marrow cell - the bottom line is, they are not creating new heart tissue, said Field.

Kamp, who has created beating, pulsing heart tissue in a dish by using embryonic stem cells, said studies like these may highlight the differences in potential for adult and embryonic stem cells.

Researchers have repeatedly demonstrated that embryonic stem cells can become just about any kind of cell.

And although he has not yet published similar studies using embryonic stem cells, he is currently working on some.

"We are asking the same questions," and doing the same kind of experiments, he said. And so far, his results have been encouraging.

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© 2004, Milwaukee Journal Sentinel Distributed by Knight Ridder/Tribune Information Services