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The Stem Cell Challenge: What hurdles stand between the promise of human stem cell therapies and real treatments in the clinic? (Robert Lanza and Nadia Rosenthal, 5/24/04, Scientific American)

Stem cells raise the prospect of regenerating failing body parts and curing diseases that have so far defied drug-based treatment. Patients are buoyed by reports of the cells' near-miraculous properties, but many of the most publicized scientific studies have subsequently been refuted, and other data have been distorted in debates over the propriety of deriving some of these cells from human embryos.

Provocative and conflicting claims have left the public (and most scientists) confused as to whether stem cell treatments are even medically feasible. If legal and funding restrictions in the U.S. and other countries were lifted immediately, could doctors start treating patients with stem cells the next day? Probably not. Many technical obstacles must be overcome and unanswered questions resolved before stem cells can safely fulfill their promise. [...]

[T]he extraordinary regenerative potential of embryonic stem cells has intensified the search for similar cells that may be involved in normal healing in the adult body.

Skin begins repairing itself immediately after being injured. The human liver can regenerate up to 50 percent of its mass within weeks, just as a salamander regrows a severed tail. Our red blood cells are replaced at a rate of 350 million per minute. We know that prolific stem cells must be at work in such rapidly regenerating tissues. But their very vigor raises questions about why other organs, such as the brain and heart, seem incapable of significant self-repair, especially when purported stem cells have also recently been discovered in those tissues.

The best-known stem cells in the adult body are the hematopoietic stem cells found in bone marrow, which are the source of more than half a dozen kinds of blood cells. Their ability to generate a variety of cell types, at least within a specific tissue family, is why hematopoietic stem cells have been described as multipotent.

There is great hope that similar multipotent stem cells found in other body tissues might be drafted into repairing damage without the need to involve embryos--or better still, that an adult stem cell with more versatility, approaching the pluripotency of embryonic cells, might be discovered.

But scientists are just beginning to investigate whether natural regeneration is somehow blocked in tissues that do not repair themselves easily and, if so, whether unblocking their regenerative capacity will be possible. The very source, as well as the potential of various adult stem cells, is still disputed among researchers. We cannot say for sure whether tissue-specific adult stem cells originate within those tissues or are descendants of circulating hematopoietic stem cells. Nor do we know how far these cells can be pushed to differentiate into functional tissues outside their specific type or whether such transdifferentiation produced in the laboratory could be reproduced in a living organism.

The idea that certain adult stem cells might have greater potential first came from observations following human bone marrow transplants, when donor cells were subsequently found in a wide range of recipients' tissues. These accounts implied that under the right conditions, stem cells from the bone marrow could contribute to virtually any part of the body. (Similar claims have been made for the so-called fetal stem cells found in umbilical cord blood, which resemble hematopoietic stem cells.)

Find a way to use a patient's own cells instead of preying on other persons for them and the controversy will largely disappear.

Posted by Orrin Judd at June 1, 2004 8:25 PM