Research involving human stem cells may one day help cure conditions such as Parkinson's disease, but experiments that transplant human stem cells into prenatal nonhumans pose serious ethical concerns, according to ethicist Cynthia Cohen.
| Cynthia Cohen of the Kennedy Institute of Ethics at Georgetown University speaks about the ethics of stem cell research. Her talk was part of a lecture series on human rights and the life sciences.
|Photo by Jordan Bender
Her talk, "Of Mice and Humans: Creating Human-Nonhuman Chimeras in Stem Cell Research," was given Nov. 8 in Konover Auditorium.
It was the second in what is planned to be an annual Heinz and Virginia Herrmann Lecture on Human Rights and the Life Sciences.
It was also part of a new program of UConn's Human Rights Institute, focusing on the interaction between scientific advancement and human rights.
Cohen is a senior research fellow at the Kennedy Institute of Ethics at Georgetown University, and a Fellow at the Hastings Center, an independent, nonpartisan, and nonprofit bioethics research institute that explores fundamental and emerging questions in health care, biotechnology, and the environment.
She said scientists have been combining materials from different species of animals for at least half a century. In 1984, she said, scientists fused goat and sheep embryos to create what became known as a geep.
"Their purpose was not to create weird sorts of animals to satisfy idle curiosity, but to study cell migration in the developing embryo," she said.
In 1988, she noted, scientists transplanted whole regions of the quail brain into chick embryos to study cell development in a living system.
For years, scientists have combined human and animal tissue, for instance putting pig hearts into humans to treat serious cardiac problems.
Scientists also have created mice with human immune systems and human skin tissue.
Now, attempts are being made to transplant human stem cells into nonhumans, and that has become controversial.
Obtaining significant information about how stem cells function can't always be accomplished in a lab dish, she said. A living environment is needed.
Scientists can't insert human stem cells into living human beings, she said, because "they just don't know what would happen." Instead, researchers are inserting human stem cells into nonhumans following special animal care guidelines.
Adult bone marrow cells have been inserted into fetal sheep to learn how to repair damaged livers and hearts in human beings, she noted.
In 2001, a research team inserted human neural progenitor cells - stem cells that have begun to differentiate into brain cells - into the forebrains of fetal monkeys. The forebrain is the largest part of the brain.
"[The researchers] found that the human cells spread throughout the monkeys' brains," Cohen said. "The human cells did not take over the monkeys' brains, one of the concerns of critics of such research."
Another research group transplanted human embryonic stem cells into chicken embryos, and they found that the chicks' brains were not "taken over" by the stem cells.
Cohen said that critics were concerned about such experiments because the researchers used human embryonic stems cells.
"Human embryonic stem cells are undifferentiated," she said.
"They have not become specialized cells, but have the potential to differentiate into more specialized cells. And in theory, they could turn into human neuro cells, impact the brain, and be part of the chick as it develops."
Critics were particularly concerned when a Stanford University research team wanted to inject human neural stem cells into mice brains.
"In principle, such regions that were totally human could be extracted from nonhuman research subjects and could be used to reconstruct damaged brain tissue in human beings, for example, people with Parkinson's and Alzheimer's disease," Cohen said.
She noted that even though the researchers said the mice would still be mice, others predicted that such mice would think and act like humans. The research was not carried out.
Cohen has written on ethical issues connected with stem cell research, genetic testing, and reproductive and therapeutic cloning.
A member of the Canadian Stem Cell Oversight Committee, she has served as executive director of the National Advisory Board on Ethics in Reproduction in Washington, D.C., and was chair of the philosophy department at the University of Denver.
Scientists use the word chimera when referring to organisms in which the cells of two different species are found. In ancient mythology, a chimera was a creature that was part lion, part goat, and part snake. Chimeras generally symbolized evil and chaos.
"The species-integrity argument says that species should not be mixed," Cohen said.
"The human dignity argument says there is something distinctive and valuable about humans. Humans have the ability to reason, to make choices, moral evaluations, and speak in a complex language. The notion is that human dignity is eliminated when the cluster of capacities is wiped out."
Cohen suggested that in animal experiments, the number of human stem cells transferred to non-humans should be limited to "as few as necessary to reach reliable scientific conclusions."
She also recommended the host not be too similar to humans, structurally or functionally.