Researchers in Oregon say they have cracked the "primate barrier," reporting yesterday that they had cloned monkey embryos and extracted stem cells - an advance other scientists said offered the strongest proof yet that the same feat can eventually be carried out with human cells.
"This demonstrates convincingly that embryonic stem cells can be produced from primates . . . and this means it should be feasible in humans," said George Daley, president of the International Society for Stem Cell Research and a stem cell scientist at Children's Hospital Boston. "There has never been a good reason to doubt that primate [cloning] could work, and this settles the issue."
The groundbreaking work was quickly damned by opponents of the controversial process, which involves destruction of laboratory-created, early-stage embryos after harvesting them of stem cells.
In research published online by the journal Nature, scientists reported that the new clones were used to create batches of embryonic stem cells forged from monkey skin cells and unfertilized eggs.
Because monkeys are so similar to humans, the research at Oregon Health & Science University appears to mark a significant breakthrough toward creating human embryonic stem cells that are genetically matched to a particular patient. That feat has for years been the holy grail of medical researchers because the cells can replicate and produce the more specialized cells that comprise the blood, tissue, and organs.
Actual cloning of human embryos remains some time off because of ethical and technical hurdles. But scientists are pushing relentlessly toward that day.
"I am quite sure it will work in humans," Shoukhrat Mitalipov, who led the Oregon team, told reporters in a telephone briefing.
He said stem cell research holds "great promise for treating a variety of diseases, including Parkinson's, multiple sclerosis, diabetes, cardiac disease, and spinal cord injuries."
The work involved extracting the nuclei from skin cells of a 9-year-old rhesus macaque and infusing them into unfertilized monkey eggs from which the DNA had been removed. It took 304 eggs from 14 monkeys to produce just two stem cell lines - illustrating just how tricky the process remains - but Mitalipov said he is confident that practice will eventually make scientists proficient.
"It's inefficient, for now, but we are fine-tuning," said Mitalipov. He said tests showed that the stem cells produced were "pluripotent," able to transform themselves into any other body cell. The Oregon researchers coaxed the monkey stem cells into forming heart and nerve cells, for example.
Ian Wilmut, the Scottish scientist who oversaw the team that in 1997 was the first to clone a sheep, named Dolly, described the Oregon research as "the first convincing evidence that nuclear reprogramming is feasible in primates," including humans.
A team led by South Korean scientist Hwang Woo-suk claimed in 2004 and 2005 to have obtained stem cells from cloned human embryos, but the two papers, published in the American journal Science, turned out to be fraudulent. That experience caused the Britain-based Nature to take the unusual precaution of asking a separate team of scientists to verify the work of Mitalipov and his colleagues at the Oregon university's National Primate Research Center before publishing their findings.
The Oregon paper was released ahead of its scheduled publication in the Nov. 22 Nature because the research was receiving wide media attention based on rumor and sketchy information from a presentation the scientists made at an Australian conference.
Most research on human embryonic stem cells is opposed by the Bush administration and some religious conservatives on the grounds that it involves making and then destroying an embryo that holds the potential to become a human being. Proponents of the process argue that such embryonic clones would never be more than blobs of undifferentiated cells in a laboratory petri dish.
Human embryonic stem cells are believed to hold tremendous potential for curing disease. Scientists currently work with such cells obtained from fertilized embryos that would otherwise be discarded by fertility clinics, but these have limited value for therapies because they are not genetically matched to patients.
Despite the monkey advance, research into cloned human embryonic stem cells remains critically hampered by a shortage of donated eggs. The availability of human eggs would facilitate planned studies at Harvard University and other top centers that have vowed to press ahead despite a federal ban on funding for stem cell research involving human embryos.
Critics of human embryonic stem cell research, however, were quick to assail the monkey studies.
"The risk lies in applying the technique to humans," said the Rev. Thomas Berg, head of the Westchester Institute, a Roman Catholic think tank. "Such a pursuit, if successful, would be one of humanity's darkest endeavors."
The process Mitalipov and his colleagues used to obtain stem cells had previously succeeded only in experiments involving mice.
Other animals have been cloned, of course, but extracting embryonic stem cells from some complex species has proved extremely difficult - and similar obstacles are likely to face researchers when, and if, human embryos are cloned.
The next and probably even more controversial step in the Oregon research will be to transplant the embryos into female monkeys and create actual cloned creatures.
"We have the goal of producing live monkeys using the somatic cell nuclear transfer technique," Mitalipov said.
"We hope the techniques will be useful for other labs that are working with human eggs."
Colin Nickerson can be reached at nickerson@globe.com.
