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:
Skin Cell Reprogramming
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.
Amniotic Stem Cells
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.
"It's good that the study is focusing attention on another cell type that should be considered along with other cell types," said Helen Blau, director of the Baxter Laboratory in Genetic Pharmacology at Stanford University. But she added, "They do not constitute a substitute for embryonic stem cells at this time. Much more research would be required to determine that."
Cord Blood Stem Cells
At the time a baby is born, doctors can harvest the blood from the umbilical cord. Frozen and stored, the umbilical cord blood is a rich source of stem cells which can be used to treat as many as 70 different diseases.
Clinical applications thus far have shown that the cells harvested from cord blood do, indeed, have treatment potential. So far, about 6,000 Americans have received cord blood transplants. Most commonly, the cells are used to regenerate the immune systems of patients who have received treatment for leukemia. And some researchers suggest that as the field of applications broadens, this number could grow.
"Since umbilical cord blood, an adult-derived stem cell source, contains multipotential stem cells with functions similar to cells derived from embryonic stem cells, I do not anticipate that if the embryonic stem cell bill is not passed, that this will significantly impede our progress in stem cell therapeutics in human clinical trials," said Dr. Mary Laughlin of Case Western Reserve University.
As with most of the other alternatives, researchers do not believe that cord blood cells hold the same promise as embryonic stem cells.
"There may be technology developed in the future that allow patients and parents to find it useful in a clinical setting, but there is a lot of science needing to be performed before any of this stem cell hype becomes reality," said Bryon Petersen, associate professor of pathology at the University of Florida.
Blastomere Cell Extraction
In this procedure, doctors remove a single cell from an embryo very early in its development. By doing so, they can obtain a relatively undifferentiated cell, ostensibly without harm to the developing fetus.
Proponents of the technique say it offers access to a cell that, while not quite as biologically "flexible" as an embryonic stem cell, still has the potential to transform into a wide variety of cells and tissues.
"For the first time we are able to create life without destroying it," said Dr. Robert Lanza, following the publication of his August 2006 article on the technique published in the journal Nature.
Lanza, vice president of Research and Scientific Development for the Massachusetts-based Advanced Cell Technology, said at the time that he believed the technology would eliminate the current governmental restrictions on stem cell research.
While the technique is designed to preserve the developing embryo, some researchers note that there is still some risk involved.
"The long-term consequences to the child are completely unknown," said Dr. William Hurlbut, consulting professor at the Neuroscience Institute at Stanford University Medical Center. "Something subtle but significant might be changed in the final physical frame or personality of the person born -- like tipping the rocket slightly on the launch pad, a tiny tilt might make some difference in the final destination.
"From a practical perspective I think this may cause some political stir, but I don't think it will be greeted as much of a solution."
Creation of Clones From Adult Cells
Some researchers are looking at ways to create cloned embryos from adult cells and using the resulting embryos for research. To do this, they insert the genetic material of an adult cell into a human egg cell -- a similar technique used years ago to create Dolly, the cloned sheep.
The technique obviates the need for embryos, opting instead for human egg cells. And thanks to new research, scientists can now tap into the enormous pool of fertilized eggs created through IVF procedures, potentially using them to create clone embryos for stem cells.
"There are a half million fertilized eggs created every year in the U.S., and 3-10 percent of those will not develop," said Dr. Kevin Eggan of Harvard University's Stem Cell Institute, lead author of a recent study on the technique.
As with the other possibilities, the cells that are created cannot differentiate into the full range of tissues offered by embryonic stem cells. Researchers also worry that the political implications of these alternative developments could hinder the progress of the study of actual embryonic stem cells.
"It is important to note that the opponents of stem cell research will seize upon these studies as cause to stop funding human [embryonic stem] cell research...that these alternatives obviate the need to use embryos in research," Harvard's Daley said.