Their skepticism arises from the fact the scientists did not offer conclusive evidence the stem cells were a genetic match to the women who donated the initial cells, as they would have to be if cloning truly occurred.
"I've checked now with four or five (stem cell scientists) and no one believes the results," a stem-cell expert who requested anonymity, told UPI.
Those with whom the stem-cell expert spoke included "two top Korean scientists and a major person in the field in the United States," he said.
"I even have my doubts, too, but you can't say that publicly," the expert commented, noting because the results were published in the highly regarded journal Science, it could be professionally damaging for a scientist to question them.
The anonymous expert said he had no reason to doubt the integrity of the Korean scientists, but it seemed odd that a verification test, which could have have been performed quickly and easily, was not done.
In addition to "eliminating any doubt in anybody's mind," confirming the cloning results "would be an advantage to both the science and the scientists," he said.
"I could well understand why such a scientist would wish to remain anonymous, since the study has been carefully peer reviewed by experienced developmental biologists and has been evaluated favorably by numbers of others,"
Donald Kennedy, Editor-in-Chief of Science, told UPI.
"I think that kind of anonymous criticism is irresponsible," he added.
Kennedy chaired the news briefing on the research at the American Association for the Advancement of Science's annual meeting in Seattle.
Jose Cibelli, a co-author of the study and a professor of animal biotechnology at Michigan State University in East Lansing, was contacted by UPI for comment but had not responded by presstime.
In the study, which appears in Science's Feb. 13 issue, a team of Korean scientists and Cibelli detailed how they injected the nucleus or DNA material from cumulus cells -- which surround the egg during its maturation in the ovary -- from several female volunteers into egg cells from the same volunteers.
Each egg then was stimulated to divide and develop into an embryo, from which the scientists said they were able to obtain embryonic stem cells. Such stem cells are valued because they are capable of generating any tissue in the body and offer the possibility of repairing diseased or damaged tissue.
The scientists, led by chief study author Woo Suk Hwang, of Seoul National University in Korea, reported the stem cells came from the cloned embryos, but they did not conduct DNA tests to prove either the cloned embryos or the stem cells were genetic matches to the donating women.
The skeptical stem-cell researchers said this raises the slim possibility the embryonic stem cells might have come from some other source, such as surplus embryos from an in-vitro fertilization clinic, and not through cloning.
"I can't believe nobody's asked for verification," the anonymous researcher said. "If the Raelians had done this, people would've demanded it." He was referring to a group that has claimed to have cloned several human babies -- and has garnered considerable publicity -- but has never offered any proof.
"I agree with that, but you get brownie points here if you've done it in animals again and again and Cibelli has," Arthur Caplan, director of the Center for Bioethics at the University of Pennsylvania in Philadelphia, told UPI.
A standard test done by an independent third party could resolve any doubt, said Dr. Robert Lanza, a cloning expert and vice president of medical and scientific development at Advanced Cell Technology in Worcester, Mass., a biotech company that seeks to use cloning to generate medical therapies.
The procedure is identical to a parental-identification test. It involves conducting a DNA analysis of the embryonic stem cells and comparing the result with a DNA analysis on a tissue sample from the woman who donated the egg that gave rise to the embryo.
"They either match or they don't," Lanza told UPI. "Adults don't have embryonic stem cells, so if the DNA matches the donor, then you have proof."
Lanza said he believes the results, however, because he knows from experience it is possible to clone a human. His company's researchers made history in 2001 when they became the first to create a cloned human embryo.
Steve Mitchell is UPI's Medical Correspondent. UPI Science & Technology Editor Phil Berardelli, in Seattle, also contributed to this story. E-mail email@example.com