A new study shows that adult stem cells, a raw, undifferentiated type of cell found in bone marrow, may be as versatile as those from embryos in becoming several types of organ tissue. The findings offer hope the adult cells can someday be used to treat disease. U.S. abortion opponents are sure to welcome the findings because they argue that extracting stem cells from embryos promotes their destruction.
Embryonic stem cells are considered better than the adult version because of their ability to become all cell types in the body and to continually reproduce. They present a huge potential for treating diseases if scientists can learn how to control this differentiation process.
But their use is ethically controversial because embryos are destroyed to extract them, a practice condemned by people who believe life begins at conception.
Adult stem cells show promise as an alternative, but scientists have not been able to demonstrate they are as versatile or long-lived as embryonic ones.
Now, University of Minnesota scientists led by Catherine Verfaillie say they have overcome many of the problems, at least with rat and mice adult stem cells. "You can create cells that grow for long periods of time in the laboratory and so you can create a large number of these stem cells without aging if the conditions are kept correctly," she said.
The researchers report published by the journal Nature that the stem cells they extracted from adult rodents became different cell types with chemical coaxing in lab dishes. The researchers also injected single adult stem cells into mouse embryos and found they can contribute to most, if not all, mouse tissues.
"If we give an infusion to a mouse, we have been able to show that the cells differentiate into cells with characteristics of the organ they end up with," said Ms. Verfaillie. "But we have still to do an enormous number of studies to try to prove that if they end up in the liver, these cells actually function like liver cells and could replace a diseased liver organ."
Ms. Verfaillie believes adult stem cells may eventually be a therapy for diseased organs and genetic or degenerative disorders.
That is the hope of opponents of stem cells derived from embryos.
In support of their views, President Bush last year restricted U.S. government spending for embryonic stem cell research to about 60 stem cell lines from already destroyed embryos. He refused to fund research on stem cells obtained from embryos that had not yet been destroyed. Many scientists have decried the policy as a limit on research.
Without commenting on the political issues, Ms. Verfaillie said embryonic stem cells have value and should be compared to adult stem cells to determine which would be better for treating a specific disease. "We at this point can't really predict. For instance, liver is fairly easily made from bone marrow stem cells, but other cell types are more difficult to make. It doesn't really overlap completely with embryonic stem cells, so there may be particular disease that may one more easily treatable with one cell type versus the other cell type," she said.
Another study published by Nature shows that embryonic stem cells offer better hope than the adult ones for treating the degenerative brain disorder Parkinson's disease. In this disease, deteriorating brain cells fail to produce the chemical dopamine, causing muscle tremor, stiffness, and weakness.
Scientists at the U.S. government's National Institute of Neurological Disorders and Stroke report that mouse embryonic stem cells corrected the problem in rats with a disease that mimics Parkinson's. Study leader Ron McKay said embryonic cells transplanted into the rats became functioning brain cells. "We can see large numbers, tens of thousands of the cells we've put into the brain, survive for long periods, the right kind of neuron connecting with the host brain, which we've measured directly by listening to the electrical activity of the cells," he said. "We can recognize characteristic signatures of these cells, which indicate that they are the cell type we want."
Furthermore, the rats the scientists treated showed signs of improved movement.
The researchers say their results justify the continued study of embryonic stem cells.