As the controversy over federal funding of embryonic stem cell research rages on, legislators and researchers alike are turning their attention toward alternatives to embryonic stem cells.
The search for this alternative has taken on aspects of a Holy Grail-type quest, as finding or devising a cell that would yield the same scientific potential as embryonic stem cells would allow scientists to continue to search for disease treatments and silence opposition on ethical grounds.
Although some possibilities have emerged in recent years, researchers have thus far been unable to find a way to create cells that precisely emulate the behavior and research potential of embryonic stem cells.
Below are a few of the most hopeful methods on the horizon today:
Recently, a team of researchers from the United States and Japan were able to "rewind the clock" on adult mouse skin cells, yielding cells that looked and acted like embryonic stem cells. It has since been proposed that using similar techniques may one day yield human stem cell that could be used in medical research -- a possibility that has been touted by the administration as a promising research alternative.
Some say this work, along with concurrent research on the creation of adult cell clones, represents the most promising step in stem cell research in years.
"This research in fact lowers the level of ethical concern over reprogramming studies," said Dr. Martin Pera of the University of Southern California Keck School of Medicine. "If it is no longer necessary to make embryos or use eggs to create patient or disease-specific stem cell lines, there are few ethical barriers to the work."
Challenges still exist. Tumors developed frequently in mice that were cloned from the altered cells, since the genes that make able to form a number of different tissues also cause cancer later in life. The researchers agreed that the technique would have to be modified before it could be used on human cells.
Also, since mouse cells are very different from human cells, researchers would likely have to start from square one before any human treatment potential could be realized.
In 2003, researchers noted the existence of stem cells in the amniotic fluid -- the watery medium that cushions a baby while it's in the womb. Scientists at the time were hopeful that they would be able to collect these cells and harness their potential to convert themselves into other cells that would provide some of the same research benefits as embryonic stem cells.
Sampling of amniotic fluid is a routine procedure, and harvesting them poses little, if any, danger to an expecting mother and her developing child. Proponents say this technique might allow researchers in countries that don't permit embryonic stem cell research to study cells that have similar potential.
Thus far, researchers have noted, amniotic stem cells have not shown the same potential as their embryonic counterparts.
"While they are fascinating subjects of study in their own right, they are not a substitute for human embryonic stem cells, which allow scientists to address a host of other interesting questions in early human development," said Dr. George Daley, a stem cell researcher at the Harvard Children's Hospital, in a previous statement.