An expert panel of stem cell scientists, primatologists, philosophers and lawyers has concluded that experiments implanting, or grafting, human stem cells into non-human primate brains could unintentionally shift the moral ground between humans and other primates. Writing in the July 15 issue of Science, the panel reports its recommendations for minimizing the chances that experiments with human stem cells could change the cognitive and emotional capabilities -- and hence the "moral status" -- of the animals.
"We quickly realized that a fundamental issue was whether such experiments might unintentionally alter the animals' normal cognitive capacity in ways that could cause considerable suffering," says Ruth Faden, Ph.D., M.P.H., director of the Phoebe R. Berman Bioethics Institute at The Johns Hopkins University. Faden, John Gearhart, Ph.D., of Johns Hopkins' Institute for Cell Engineering, and Guy McKhann, M.D., of Hopkins' Zanvyl Krieger Mind/Brain Institute, were co-organizers of the panel.
The panel's deliberations focused on the potential effects of grafting human stem cells into the brains of non-human primates. Gearhart notes that such experiments are already under way and that some people see them as a necessary step toward using human stem cells as treatments to replace or repair brain cells lost in conditions like Parkinson's disease or Lou Gehrig's disease.
"We agreed to disagree about whether non-human primates should be used for invasive biomedical procedures at all, and to focus instead on whether experiments with stem cells and the brain posed any new, unique ethical dilemmas," says Faden.
Although the assembled experts agreed it was unlikely that grafting human stem cells into the brains of non-human primates would alter the animals' abilities in morally relevant ways, they also felt strongly that the risk of doing so is real and too ethically important to ignore.
"Our group struggled with many fundamental questions," says Faden. "Are there cognitive or emotional capacities that are unique to humans in ways that make us worthy of higher moral status? What sets one primate, including us, apart from another primate, cognitively speaking?
"There are biblical injunctions and secular reflection over the course of centuries, but nothing is certain or universally accepted, either scientifically or morally," she adds. "Debate is complicated by uncertainty and uncharted territory in all of our fields of expertise. It quickly became clear how little is known."
"Many of us expected that, once we'd pooled our expertise, we'd be able to say why human cells would not produce significant changes in non-human brains," says Mark Greene, Ph.D., then a Greenwall Fellow at Hopkins and now a professor at the University of Delaware. "But the cell biologists and neurologists couldn't specify limits on what implanted human cells might do, and the primatologists explained that gaps in our knowledge of normal non-human primate abilities make it difficult to detect changes. And there's no philosophical consensus on the moral significance of changes in abilities if we could detect them."
Although unable to rule out the possibility of morally significant changes resulting from implantation of human stem cells into the non-human primate brain, the panel concluded that cognitive and emotional changes are least likely to occur when such work is conducted on healthy adult members of species distantly related to humans, such as macaques, rather than early in the brain development of our closest biological relatives, the chimpanzees and other great apes.