Cloning moves from the lab to Capitol Hill this week as the US Senate considers a bill that would outlaw the procedure for human reproduction but, permit it for research on stem cells.
The bill, the subject of hearings tomorrow before the Senate Judiciary Committee, is competing with another proposal that would ban human-embryo cloning not only for reproduction, but for research as well.
For many opponents of cloning, the ethical debate revolves around theological issues, such as whether life begins at conception. But important scientific questions are also at play, notably whether the medical possibilities of stem cells can be explored without any embryo cloning at all.
A broad range of scientists and scientific organizations, most recently the National Academy of Science, support cloning for research - the approach backed by Sen. Dianne Feinstein (D) of California. Yet, recent discoveries may pave the way for the full cloning ban proposed by Sen. Sam Brownback (R) of Kansas, some scientists say.
"Ethics aside, science is probably telling us that there are a couple of these ways of doing it that aren't worth following," says David Prentice, a professor of life science at Indiana State University. Cloning embryos, he says, is one of them.
Embryonic stem cells, which appear four to five days after an embryo forms, have triggered intense interest as potential therapeutic tools. Scientists believe that if they can master the techniques for steering stem cells down a particular path of development, they could help millions of people diagnosed with a range of diseases or harboring damaged organs. Biologists also say that embryonic stem-cell research is vital to unraveling the mysteries of how humans develop.
Through cloning, researchers say, the tissue generated through embryonic stem cells would match the patient's genetic makeup, reducing the likelihood that the patient's immune system would reject the new tissue.
Dozens of experiments over the past few years have suggested to biomedical scientists that their hopes for stems cells are well founded.
Last week, for example, scientists at Advance Cell Technology in Worcester, Mass., announced that they had used cells from an embryo cloned from an adult cow to grow miniature kidneys. When transplanted back into the adult, they were able to remove toxins from the cow's system, as a normal kidney would.
The team acknowledges that their results, which have not been formally published in a scientific journal, are preliminary.
Yet Dr. Prentice, a stem-cell researcher who objects to cloning human embryos on ethical grounds and advises Senator Brownback on the issue, says several signs indicate that cloning embryos is not the way to realize the potential stems cells hold.
"By one estimate, to treat the 16 million diabetics in the US, you'd need 800 million eggs," he says. In addition, "embryonic stem cells have a nasty habit of taking off on their own bent once in awhile," leading to serious side effects, Prentice continues.
More promising, he says, is work with adult stem cells. Although the work has not yet been formally published, reports emerged late last month that Minnesota's Stem Cell Institute has drawn stem cells from adult bone marrow that appear to match the advantages often touted for embryonic stem cells: They can make any cell type, and they can be maintained in culture essentially forever.
On Friday, researchers at ACT and Wake Forest University's School of Medicine in Winston-Salem, N.C., reported the results of experiments that they suggest could yield a more ethically acceptable form of embryonic stem-cell work. Using eggs from a monkey, the team cloned stem cells by injecting genetic material into the eggs and triggered their development with a set of chemicals designed to match the composition of sperm. This effort, reported in the current issue of the journal Science, is the first time the approach has been used with primates.
But the cells also lack the full complement of genes that results from the normal union of egg and sperm. Thus, it remains unclear whether these cells would form tissue, and if they did, function as well as normal tissue.
These are issues the team will be exploring next, says Kathleen Grant, a professor in the medical school's department of physiology and pharmacology. "It's far too early to say that any one source of stem cells is better than any other," Dr. Grant says.
Adds colleague Kent Vrana, "If we stop in any line and focus on one, and then we find out we're wrong, think of the years of potential therapy that will have been lost."